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CHAPTER 19: THE SPACE SHUTTLE

John F. Graham, 1995
Photos courtesy NASA

When NASA first sent men into space in the 1960s, they put the men into tight cocoons tailor made for each astronaut and blasted him into orbit aboard an operational ICBM. These capsules returned to Earth in a blazing descent as the Earth's atmosphere totally destroyed the blunt heat shield in order to keep the astronaut alive. Today the Russian Soyuz does exactly the same thing; it goes into orbit where it remains attached to its MIR space station until it's time to return to Earth. Then the spacecraft returns to Earth through a fiery reentry as the heatshield is burned off.

One big fact remains about the Russian and the Early American space program; every part of the vehicle was finally discarded, never to be used again, with the exception of the human cargo. The Russians have made a great number of Soyuz capsules not only for spacecraft, but also for resupply ships as well. Additionally, they have made numerous SL-4 Soyuz rockets using the Henry Ford techniques where mass production actually makes a product cheaper. The Americans have opted out of the Henry Ford techniques and have built a ship which is ostensibly reuseable, the Space Shuttle.

THE SPACE SHUTTLE

The space shuttle represents America's initial try at making a reuseable spacecraft. The shuttle is unique in that it launches vertically as a rocket and returns to Earth horizontally like an airplane as it lands on a concrete runway, is recycled, and launched on another mission. Also recycled are the solid rocket boosters (SRBs) and the space shuttle's main engines (SSMEs). The only part of the rocket totally discarded is the $30 million external tank (ET).

Although the shuttle is currently a "shuttle to nowhere" because it has no real destination in space a number of tasks can be performed aboard it. The astronauts can launch other satellites using several different launch techniques, they can study the effects of space travel upon the human body, they can retrieve and repair other satellites such as the Hubble Space Telescope, they can conduct experiments in materials processing, or they can study the Earth. In the next five years the astronauts will us e the space shuttle to help build the international space station and the true exploration of space can begin.

The shuttle is really the most complicated vehicle ever to orbit the Earth and it is the most expensive. The number of missions, originally predicted to be more than fifty a year, quickly fell to about eight while the operational and development costs rose as quickly as the vehicle leaving the launch pad. These costs are often even more expensive than the expendable launch vehicles (ELVs) that the space shuttle was supposed to supplant as the main road to space. Because of the soaring costs, NASA has limited space shuttle flights to only those missions needing a human presence or which require an exceptional heavy lift vehicle.

The space shuttle consists of millions of complicated parts all of which must be working in order for the vehicle to reach space and to return safely to Earth. These million parts of working machinery can be grouped for simplicity sake into four main parts: the orbiter, the space shuttle main engines, the solid rocket boosters, and the external tank. These are the parts of the vehicle seen when the space shuttle is launched.

The delta winged orbiter is the working part of the space shuttle that carries the crew and resembles an airplane. It is similar in size to a Boeing 727 or a McDonnell Douglas DC-9. Size is really the only similarity between these comparisons because the astronauts occupy only a small area in the front of the craft. A typical orbiter is 112 feet long 56 feet high and 78 feet wide from wingtip to wingtip. Limited for flight only into LEO with a typical altitude of 185 miles, the orbiter has gone as high as 200 miles to place the Hubble Space Telescope into its orbit. The orbiter contains the crew cabin, the payload bay, the SSMEs and the Orbital Maneuvering System (OMS) engines used to change orbits once the vehicle is in space. The orbiter is designed to carry from two to eight crewmembers on a ten to fourteen day mission. Most of the space on the orbiter is for the payload which can weigh up to 51,600 pounds.

Rockwell International Corporation constructed six orbiters. Each one had a code number of OV attached to it as well as its name to designate the vehicle. Each orbiter is named for a famous American/British sailing ship of exploration. The larger number indicated the newer vehicle. Challenger (OV-99) was supposed to be the original test vehicle, but during construction, NASA decided to make this orbiter into an operational spacecraft. The Enterprise (OV-101) became the test vehicle to determine the aerodynamic and handling qualities of the orbiter during drop tests from a NASA Boeing 747. The Enterprise never flew into space and was used strictly for testing and static displays.

The first shuttle to launch into space was the Columbia (OV-102) under the command of astronauts John Young and Robert Crippen. Ironically, it launched on the 20th anniversary of Yuri Gagarin's first space flight April 12, 1981. The next shuttle was the Challenger launched on April 4, 1983. The Discovery (OV-103) made its maiden flight on August 30, 1984 and the Atlantis (OV-104) first flew in 1985. Following the Challenger tragedy in 1986 Congress appropriated money for the Endeavor (OV-105) which launched on May 7, 1992.

NASA designed the shuttle to carry large payloads into space; it can carry 51,800 pounds into a 28 inclination orbit and 37,800 into a 57 inclination orbit. The orbiter's payload bay measures 60 feet long, 17 feet wide, and 13 feet deep. It was designed to carry payloads as large as the Hubble Space Telescope which fills the entire orbiter payload bay. The payload bay is protected by two large doors during ascent and descent. For on orbit operations these doors must be open to provide coo ling for the orbiter. If the doors cannot open the orbiter must return to Earth within eight hours.

Another vital portion of the orbiter are the SSMEs. which provides the thrust necessary for the orbiter to achieve orbit. These three engines, located on the rear of the orbiter, burn a propellant of liquid hydrogen (LH2) and liquid oxygen (LOX). This mixture is also called cryogenic fuel because the temperature approaches -460F. During operation a single LH2 turbo pump transfers its fluid to the engine at 45,300 gallons per minute or the same amount of liquid as in an Olympic swimming pool.

Each SSME is rated at 375,000 pounds of thrust for sea level operations. These engines can be throttled from as low as 65% of rated thrust up to 109%. This differs from previous liquid engines that were either off or delivered 100% rated thrust. These SSMEs are the most complicated and dangerous parts of the shuttle; without their 100% thrust on all of these engines the shuttle cannot attain orbit, and every part of these engines must work perfectly. After operation the SSMEs are usually removed from the orbiter, inspected and then put into a rotation for inclusion in a future shuttle flight. The orbiter is normally fitted with new SSMEs prior to its next flight. In July 1994 the Endeavor was prevented from liftoff by computer when it detected an overheat in one of the SSMEs. To launch this vehicle in September NASA technicians had to remove and replace the SSMEs, a rather lengthy and tedious process.

If the orbiter had its own propellant storage tanks it would be a huge craft with extremely complicated aerodynamic flight capabilities. For this reason, all of the orbiter's ascent fuel is stored in a huge external tank (ET) attached piggy back to the orbiter. The ET has a length of 154 feet and a diameter of 28 feet. The ET contains two tanks: a top tank containing 143,100 gallons of LOX and a bottom tank containing 383,100 gallons of LH2. Even though there is a greater volume of LH2 it actually weighs one quarter of the LOX because oxygen is sixteen times heavier than hydrogen. The oxygen tank is put above the hydrogen tank to keep a relatively stable center of gravity as the fuel is used during flight. A 17 inch pipe carries LOX from its tank' s base, out the area between tanks also known as the intertank, down the side of the LH2 tank and out the bottom of the ET into the orbiter. Another 17 inch pipe goes from the LH2 tank out the bottom of the ET into the orbiter. Both of these pipes attach to the orbiter's bottom side near the main engines at a position called the disconnect.

The cryogenic propellant presents a unique problem because of its boiling points of around -200. To keep the boil off at an acceptable level prior to flight the ET is covered with a thin layer of burnt orange foam called polyisocyanurate; this material keeps ice from forming on the ET. On the first shuttle launches the ET was painted white to provide further aerodynamic protection as well as a matching paint scheme for the entire shuttle transportation system (STS). This was stopped because the weight penalty of several thousand pounds of paint was better used on payloads.

The ET is the only portion of the STS completely discarded after use. There have been several proposals to boost the ET into orbit and use its space for such things as laboratories, telescopes, and space stations, but NASA has not agreed to any proposal and following its use, the $30 million ET goes crashing into either the Indian or the Pacific Oceans.

The mass of the orbiter, its payload, the ET, and its propellant is about 1.9 million pounds. This amount of mass needs a thrust of greater than 1.9 million pounds to accelerate it into orbit. The SSMEs, rated at 375,000 pounds of thrust each, can only provide 1.125 million pounds of thrust which is not enough to lift the structure off the launch pad. Because of this two solid rocket boosters (SRBs) must augment the SSME thrust to get the STS off the pad and accelerate it into orbit.

The SRBs are the largest solid rockets ever designed. They are 149 feet high and 12 feet in diameter. and produce 2.65 million pounds of thrust each at liftoff. Each SRB consists of four segments of solid propellant vertically stacked with a nose cone o n top. This nose cone contains the propellant igniter, electronic devices which interrelate with the orbiter, and parachutes for recovery at sea. A nozzle, located at the booster's base has a 7 gimbaling capability to steer the STS during ascent.

Because this solid rocket is larger than any built previously, each SRB is made in segments. This allows better control of making a uniform mixture of propellant. This propellant contains by weight, 16% aluminum powder fuel, 70% ammonium perchlorate oxidizer, 12 % polybutadiene acrylic acid acrylonitrile which is a binding agent, 2% epoxy used for curing, and iron oxide to help control the burning rate. The mixture of these materials looks like a dense viscous plaster which is poured into a mold where it is dried (cured) for several days resulting in a material that looks and feels like a rubber eraser or hard putty. Each booster weighs 1.3 million pounds which is easily lifted from the pad by its 2.65 million pounds of thrust. The residual thrust lifts the orbiter and the ET as well.

When assembled the complete STS consists of the orbiter with its SSMEs, the ET, and two SRBs. This configuration is 184 feet tall, 79 feet wide from either side, and weighs 4.4 million pounds. When the launch finally occurs 6.425 million pounds of thrust lift the entire ship into the air very quickly because of the excess power; these launches occur only at the Kennedy Space Center.

The Kennedy Space Center (KSC) is a NASA facility co-located with the Cape Canaveral Air Force Station. There is frequent reference to Cape Kennedy in the media, but it is no longer officially called by that name. KSC is based in the middle of a wildlife preserve on Florida's Atlantic coastline. The space shuttle begins its journey into space from this location.

Each space shuttle flight requires years of mission planning and months of getting the shuttle prepared or processed to go into orbit. After an orbiter arrives at KSC either piggy back on a 747 or from space it is towed into the orbiter processing facility (OPF). This three building complex with a height of 100 feet can house three orbiters simultaneously. Each high bay serves as a hanger and maintenance bay for its particular orbiter.

Once inside the high bay the orbiter is jacked up off its landing gear and is surrounded by platforms and scaffolds which allow access to every portion of the vehicle. Large cranes are used to remove previous payloads and to provide support to any heavy equipment which may be used for orbiter processing. In this area engineers inspect every system on the orbiter and repair or replace items failing the rigorous exam. This process takes from four to six weeks

Every one of the 32,000 heat tiles must be inspected and replaced if they are damaged or missing. These tiles are specifically made for their position on the orbiter. Their damage or loss could possibly mean the loss of thermal protection for the orbiter and its precious human cargo upon reentry of the Earth's atmosphere.

The SSMEs and their respective fuel pumps must be removed, inspected, and refurbished. The engineers may install the same engines, new engines, or previously refurbished engines. While this activity continues, electricians inspect every circuit and rep air them if needed. They also verify computer operation along with communications, guidance, and navigation systems. At the end of all this activity, the orbiter is lowered on to a mover, gear up and locked, and towed to the vehicle assembly building (V AB).

The VAB stands 525 feet high and is the world's largest building in volume under a single roof. Here the orbiter is attached to the external tank and the SRBs which have been undergoing their own processing activities prior to their admittance into the VAB.

Each SRB arrives at KSC in four separate segments from its plant in Utah by train. These segments have been flown about six months previously, recovered from the ocean, sent to Utah by train, filled with new propellant, and returned to KSC. Upon arrival here they immediately go into the VAB to be mated with an orbiter and ET. The SRB arrival is typically six months before launch.

The new external tanks (ET) are manufactured in New Orleans, LA and shipped to KSC via barge. Each new mission requires a new ET because they crash into the Indian or Pacific Oceans. Upon arrival, the ET goes immediately into the VAB to be attached to the SRBs and orbiter.

The assembly of the STS takes place on the side of the VAB nearest to the ocean where two shuttles can be assembled simultaneously. The process of integrating the major shuttle parts is called stacking and takes about four to six weeks. This process takes place on the mobile launch platform (MLP) which is two stories tall, weighs eight million pounds, and rests on four support posts.

Stacking begins with transferring the bottom segments of the SRBs to the several support posts on the MLP. The posts hold the segment upright slightly above the platform's base. Technicians transfer the second segments of the SRBs and stack them on the irrespective boosters. Stacking continues until all four segments are placed in position by means of giant cranes to carefully join each SRB segment. The boundary between each segment is called a field joint which requires a complete seal to keep the hot propellant gases from burning through the joints. These seals are called O-rings which are similar to washers in home plumbing. These three rings line the inner side of the metal casing segment to seal each joint. A lot of time is spent aligning the four segments of each SRBs because this was the cause for the Challenger accident in 1986.

The next step in the integration process is joining the ET to the SRBs. A giant crane suspends the ET in mid air while technicians bolt the SRBs to the tank. These major portions of the vehicle must be precisely mated and so this process takes several days. After this integration, several sets of platforms and scaffolds are set up around the semi-completed stack in order to permit easy access to the it.

Next, the orbiter is hoisted by two metal slings and rotated from the horizontal to the vertical. To miss the series of platforms built around the half-finished stack, the crane lifts the orbiter over 300 feet into the air and slides it down into a slot next to the ET. The orbiter is attached to the ET and after its mating is secured the crane takes away the slings. In the final launch configuration the orbiter is attached to the ET and the ET is attached to the SRBs which rest on the MLP support post s.

At this point the STS is ready to be transported to one of the two shuttle launch pads, Launch Complex 39-A or 39-B. This is accomplished by a flatbed vehicle called the crawler which weighs six million pounds, is 131 feet long, 114 feet wide, and one story tall. It has two huge metallic tracks similar to armored tank treads located at each corner of the vehicle to serve as wheels. This monstrous machine drives into the VAB and under the MLP. Hydraulic jacks lift the crawler's top platform until it pushes the bottom of the MLP above the support posts. Once clear of these posts the operators drive the crawler out of the VAB with the MLP containing the STS stack on top.

The process of driving the crawler with the STS out of the VAB to the launch pad is called the roll out. A gravel road called the crawlway goes from the VAB to the pad. This road is about 40 feet wide and has another similar sized lane separated by a 5 0 foot grass median. The crawler takes six hours to travel the 3.4 mile distance from the VAB to the launch pad. At the launch pad the crawler places the MLP on a base of support posts similar to those in the VAB. Its job done, the crawler departs the pad and journeys back to the VAB for its next trip.

Launch Complexes 39-A and 39-B are identical in appearance; each has the shape of an octagon and occupies about 165 acres. The cement pad sits in the middle of the complex and is surrounded by a huge field of grass which acts as a baffle and buffer between the STS engines and the propellant storage tanks. The STS sits next to the launch tower called the fixed service structure (FSS). The FSS has twelve decks which allow technicians to work on all parts of the STS from the ground to the top of the ET. Several steel walkways called access arms stretch from the FSS to the STS. From the FSS' seventh deck is the crew access arm (CAA) which allows technicians and astronauts to enter the orbiter crew cabin.

At the top of the ET is the oxygen vent access arm on the ninth and tenth decks of the FSS. On top of the ET is a little cap which keeps out the rain and warms the ET. This heating minimizes the buildup of ice crystals on the STS which could damage the structure during liftoff and flight.

The STS is ready to launch when it approaches its planned launch window which includes all mission objectives and safety criteria. Most of these launch windows are several hours and some are measured in minutes. The rendezvous and docking of STS-71 wit h the MIR had a launch window of seven minutes. The countdown before the launch window must be planned to include the thousands of checklist items necessary to launch the STS correctly with the minimum of danger to the crew, the vehicle, and the launch complex.

Countdown terminology is used to provide a rough guideline for accomplishing the mandatory checklist items prior to launch. The phrase T-minus denotes the time remaining in the countdown. Liftoff occurs at T minus zero, but there are a frequent number of delays called holds that are used to fix malfunctions on the pad, in the controlling agencies, or on the rocket range. Holds also are used for weather problems and for final checks before the launch controller proceeds to the next major phase in the countdown. These are called preplanned holds and allow engineers, technicians, crewmembers, and controllers to catch up on any unfinished checklist procedures which may not have been accomplished. A key factor is arriving at the exact launch time within the specified launch window.

The heart of shuttle launch operations is the launch control center (LCC) under the direction of the Launch Director. The countdown normally begins at T-43 hours or about 72 hours with preplanned holds from the start of the launch window. Crew supplies are loaded and drinking water is tested during the first thirteen hours of the countdown. At T-27 hours the countdown reaches its first preplanned hold allowing all technicians time to clear the FSS for cryogenic fuel cell loading. Cryogenic fuel includes liquid hydrogen and oxygen that mixes to produce electricity to run the orbiter's electronic systems. Drinking water is a by-product of this process. At this time the cryogenics begin to flow.

At T-19 hours another preplanned hold occurs permitting extra cryogenic fuel to be loaded aboard if it is needed for a long duration mission such as a spacelab. This fuel is loaded aboard a pallet called the extended duration orbiter pallet (EDO). After the cryogenic loading is completed, the pad engineers activate the orbiter's navigation and flight control equipment. Also at this time the pad technicians prepare the orbiter for astronaut boarding. If there is a spacelab aboard which requires life science experiments, these are loaded at this time to ensure the tadpoles, the bees, the mice, or other life science passengers which cannot survive the several weeks in the cargo bay remain alive. Some mid-deck crew cabin life science experiments are loaded as late as T-12 hours.

At T-11 the countdown enters another preplanned hold as engineers activate the three inertial measuring units (IMUs). These are navigation and attitude equipment that tell the ship's computers the craft's location. One operational IMU is mandatory for landing. At T-9 hours the orbiter's fuel cells activate and at T-8 hours the pad is cleared for a three mile radius. At T- 6 hours and 45 minutes the IMUs go from standby to active modes. At T-6 hours another preplanned hold occurs as pad engineers complete preparation to load the liquid hydrogen (LH2) and the liquid oxygen (LOX). The launch director checks the weather to insure that the ET can begin fueling.

As the countdown resumes at T-6 hours the pipes carrying the cryogenic propellants are chilled down to minimize the amount of cryogenics which will boil off prior to launch. The fueling takes place until about the T-3 hour point. At this time a preplanned two hour hold takes place to verify that no ice has built up on the ET. If ice has built up the hold is extended an extra two hours to allow melting because ice can easily damage the orbiter during launch.

During the T-3 hour hold the astronauts are awakened and given a physical exam. Following this, they eat breakfast and put on orange Crew Altitude Protection Suits (CAPS) to protect them should depressurization occur in the ascent, descent, or in the event the crew must perform an emergency egress from the orbiter on the launch pad. These suits are similar to those worn by SR-71 crewmembers. It is fire-retardant to 88F and provides some protection from g forces. A backpack attached to the suit contains oxygen, an inflatable raft, a survival kit, and a parachute. At T-2 hours and 55 minutes the astronauts leave the Operations and checkout building, enter a van, and take a 20 minute ride to the launch pad.

Upon arrival at the pad the astronauts ride an elevator to the seventh deck where clean room technicians help them into the orbiter and strap each crewmember into position. Once this is accomplished the staff seals the hatch and drives back to the VAB t o watch the launch. The astronauts are alone on the shuttle at this time.

For the next two hours the launch team in the LCC monitors the weather, the pressure in the ET, and sensors around the STS which would indicate a fuel or oxidizer leak. Inside the orbiter the commander and the pilot check communications, calibrate the IMUs with launch pad coordinates, and prepare the primary flight control systems for launch. While the crew is accomplishing these checks, an astronaut in a shuttle training airplane is flying around the shuttle runway determining that the weather is good enough for an emergency shuttle landing if it is needed.

At T-20 minutes another ten minute preplanned hold allowing the launch director to brief his launch team. When the countdown resumes the orbiter's primary and secondary computers go from standby to active. At T-9 minutes the countdown enters its last preplanned hold. The launch director uses this time to poll the launch control team on the STS' readiness to launch. The roll call of each major shuttle launch system is answered with either a "go" or a "no go". This poll continues until every technician is "go" for launch.

Also during this time the weather is examined critically. All clouds above the launch pad must be at an altitude of 8000 feet or greater. The cloud cover cannot exceed 50% of the sky to allow the astronauts a clear view of the runway in the event an in tact abort forces them to return to the launch site's runway. Another weather factor is the low altitude wind. Because the SRBs only gimbal 7 their steering is limited in the event of a strong gust which may easily blow the shuttle off course. A further weather constraint is the existence of lightning or cumulo-nimbus clouds capable of producing lightning within 50 miles of the launch pad. If there is bad weather the launch director may hold the count until only nine minutes remain in the launch window.

When the countdown resumes it is controlled by the automatic ground launch sequencer. At T-7 minutes 30 seconds the CAA retracts from the orbiter. It can attach itself back on the orbiter in less than 20 seconds in the event of an emergency. At T-6 minutes the three auxiliary power units (APUs) begin to warm up. The APUs provide power to the hydraulic motors that provide the force to gimbal the main engines for their steering during launch. The APUs are on-line by T-5 minutes. If the launch director is informed of had weather at this point he/she may hold the count to re-evaluate the weather. If the weather is bad the launch director may cancel or scrub the mission. In this event the astronauts leave the orbiter and the engineers defuel the ET. A soft count is started to alleviate having to go to the T-43 position. Normally it starts at T-24 hours. If the launch is scrubbed the second day the launch attempt has to wait for the fourth day because too much of the cryogenic fuel has boiled off from the launch pad storage tanks; it takes an entire day for fuel trucks to replenish the storage tanks.

However, if all goes well at T-5 minutes the countdown continues unabated. At T-4 minutes and 30 seconds the orbiter switches from external launch pad power to internal fuel cell power. At about T-3 minutes and 30 seconds the computer tests the main engine gimbaling capability and warms up the hydraulic system by placing the SSMEs in various positions. At T-3 minutes the SSMEs are gimbaled into their launch position. By T-2 minutes the LH2 tank and the LOX tank reach the proper pressure required for launch. At T-1 minute and 57 seconds the oxygen vent service arm is retracted; this takes about thirty seconds. At T-31 seconds, the automatic ground launch sequencer transfers the countdown control over to the orbiter's onboard computers; at this time t he orbiter controls its own countdown and launch. The orbiter's computers are checking and rechecking all systems and sensors thousands of times each second; they can find an abnormality and halt the countdown by initiating a Redundant Set Launch Sequence r (RSLS) abort faster than any human action. This abort typically takes place from six minutes prior to main engine start to SRB ignition. This abort cancels the flight for the day and if the SSMEs were started they would have to be replaced. This is t he most common abort of the space program. Once the SRBs ignite there is no more RSLS abort; the astronauts have to ride out the SRB burn.

At T-11 seconds, a water tower near the pad provides water to pipes that empty into the flame trench below the MLP. This water reduces the noise from the SSMEs and the SRBs to keep this acoustic force from reflecting off the pad and damaging the shuttle . The sound waves strike water which causes them to lose energy and prevent damage to the STS.

THE NOMINAL LAUNCH

At T-8 seconds sparks begin to appear beneath the SSMEs; this is not ignition, but rather a device to burn excess hydrogen which escapes through the SSMEs' nozzles when LH2 begins to flow. At T-6.6 seconds the computers command the SSMEs to start. The first engine starts at T-6.6 seconds, the second at T-6.48 seconds and the third at T-6.36 seconds. The sudden force of the SSMEs starting tilts the entire stack toward the ET by about three feet and recoils back into its original position. By staggering the SSMEs starts by 0.12 seconds spacing the overall force on the entire structure and thus the tilt is reduced. The exhaust flows through an opening in the MLP into the flame pit where it vaporizes the water. All the while the computer is analyzing each engine verifying that each SSME is up to at least 90% of its rating. If one of the engines is not up to this rating, the computer shuts all engines down. If all is well, the computer simultaneously commands the igniters in the SRBs to shoot a 148 foot flame the length of the rocket to ignite its propellant. At T-0 seconds the computer commands the explosive bolts on the MLP to activate and the shuttle lifts off the pad. Once the solid rockets ignite, they operate until all of their propellant is done burning; the shuttle is on its way.

The shuttle takes three seconds to clear the top of the service tower. Once the tower is passed the control of the shuttle flight goes from KSC to Johnson Space Center (JSC) in Houston, Texas.

Shortly after clearing the launch tower the shuttle initiates its roll program. This means that the stack rotates around the vertical axis to place the entire vehicle on the correct launch heading (Azimuth) for its correct orbital inclination. Most of t he shuttle launches from KSC have an azimuth of 090 which means they are launched due East. This gives the shuttle an inclination of 28.5. If the shuttle is launched at its upward azimuth of 038, directly to the Northeast, it will have its greatest inclination of 57. At the same time as the roll program initiation, the solid rocket boosters gimbal accomplishing the pitch initiation program so that the launch goes from the vertical to an attitude slightly off the vertical. This maneuver allows the Earth's gravity to slowly pitch the space shuttle over until it is flying eastward in the horizontal direction rather than straight upward. In this configuration, the orbiter payload bay faces the Earth while the ET is above it.

Fifty seconds into the flight the shuttle is at an altitude of 5.7 miles or about 35,000 feet. At this time it passes through the sound barrier and the combination of the vehicle velocity and the density of the atmosphere maximizes the amount of force o n the shuttle from the pressure of the air around it. This force is called maximum dynamic pressure or in NASA jargon "Max Q." To minimize the chance of damage due to aerodynamic forces the onboard computer reduces the SSMEs thrust rating from 100% to 6 7%. The SRBs are designed so that at 55 seconds into their burn the thrust is reduced, by changing the shape of the grain, after ten seconds the shape has burned out and the SRBs begin to increase thrust further. After passing Max Q the atmosphere thins out extremely quickly thus reducing the chance for aerodynamic damage. At about 70 seconds the computers resume the SSMEs thrust rating from 67% back to full power which is about 109% thrust rating. The command to resume full power with which everyone who watched the Challenger accident is very familiar is "Go with throttle up."

At two minutes into the launch both SRBs begin to burn out at an altitude of 29 miles and a range of 23.7 miles East of the Cape. At two minutes and four seconds into the launch the explosive bolts which hold the SRBs to the ET explode and tiny rockets at the top of each SRB push the still thrusting boosters away from the rest of the shuttle. After the boosters burn completely out, they fall into the Atlantic Ocean beneath large parachutes where they are recovered by two NASA ships, Liberty and Freedom. These ships tow each booster back to KSC where the process for the launch of these boosters starts all over again. The thrust from the SRBs is very violent with large vibrations; once they are jettisoned and the main engines continue to burn the ride is very smooth. At this time the shuttle's angle of climb is now 30 from the vertical and its velocity is four times the speed of sound, Mach 4, or 2880 miles per hour.

At four minutes and thirty seconds into the launch the space shuttle is no longer able to return to KSC if it had an engine problem or other major emergency. During the next two minutes the shuttle climbs from the "negative RTLS" altitude of 64 miles to 75 miles and gains a horizontal velocity of 5000 miles per hour. Also during this time the shuttle goes from 30 off the vertical to 90 off the vertical. The orbiter is now in the "heads down" position, the astronauts' heads are pointing directly to the ground. By six minutes after launch the shuttle has a horizontal velocity of 12,400 miles per hour. This is not enough velocity to go into orbit so for the next two minutes the shuttle begins a shallow descent back toward the Earth. During t his maneuver the shuttle loses from three to ten miles in altitude, but it picks up a horizontal velocity of 17,500 miles per hour. This maneuver is called "lofting" to minimize the use of propellant because the procedure is more efficient to overshoot t he target altitude and descend back than to gradually achieve orbital altitude and velocity simultaneously. The SSMEs provide the acceleration rather than the slight descent.

Because the ET has used most of its propellant at this time the mass of the shuttle is much less and it accelerates quickly. This raises the acceleration within the orbiter to 3g's or three times the Earth's acceleration due to gravity. To keep the flight tolerable, the SSMEs are throttled back until the orbiter's computers shut down the engines at eight minutes and thirty seconds into flight. This is called main engine cutoff or MECO and the orbiter is inserted into a small elliptical orbit with a perigee of 62 miles and an apogee of 180 miles. Twenty seconds after MECO the explosive bolts holding the ET to the orbiter activate and the two large bodies are separated. Two small thrusters on the ET cause it to start to tumble and it eventually burns into the Indian Ocean.

The orbiter continues to climb toward apogee its astronauts now experiencing zero g, freefall, or weightlessness. At 45 minutes after launch the orbiter reaches apogee and two thrusters located in the blisters at the left and right of the craft's vertical stabilizer begin to fire to raise the shuttle's orbit. This rocket system is called the orbital maneuvering system (OMS) and it increases the spacecraft's velocity by 150 miles per hour. The rocket burn is called the OMS-2 burn and it circularizes the shuttle's orbit at about 185 miles above the Earth's surface. Without this rocket burn the orbiter would return to the MECO point and eventually the shuttle would have to land due to atmospheric drag with its ensuing frictional heating. After the OMS- 2 burn the astronauts unstrap and go to work.

LAUNCH EMERGENCY PROCEDURES

Abort profiles deal with launch emergencies which occur during ascent. The two types of aborts are the intact and the contingency aborts. An intact abort is a plan to return the orbiter to a preplanned landing site while the contingency abort is used if an intact abort procedure is no longer possible. In the event of a contingency abort the astronauts attempt to land the orbiter wherever they can and if a safe landing is impossible, the crewmembers bail out of the stricken craft and use their parachutes. The contingency abort was examined thoroughly after the Challenger accident and was thought to be survivable. Both of these abort modes assume the orbiter remains in a functioning or flyable condition; the Challenger accident was a catastrophic failure which falls into a non- survivable category.

There are four basic intact shuttle abort modes. They are based upon time of flight of emergency occurrence, energy available, and location of the orbiter. The intact abort mode cannot be initiated until after the SRBs have separated from the rest of t he shuttle. The earliest intact abort is the return to launch site (RTLS). If a main engine fails in the first four minutes of flight the orbiter will not reach orbit and the crew must return the shuttle back to KSC. After the SRBs separate the two remaining SSMEs continue to operate to burn as much of the remaining ET propellant as possible. With as little of the fuel remaining in the ET as possible the shuttle executes a powered pitch around maneuver (PPA) where the orbiter and the ET rotate 180_ 6; so that the craft is headed back to KSC. The orbiter is now on top of the ET at this time and the remaining SSMEs are still operating. When the fuel runs out and MECO occurs the ET can be jettisoned safely. It cannot be done so until all of the fuel from the ET has been used because the propellant sloshing around in the ET may cause it to collide with the orbiter. Once the ET has separated the orbiter glides to landing at KSC. This maneuver has never been tried; the aerodynamics involved in rotating a vehicle as large as the orbiter with the ET attached while the SSMEs are still operating could be prohibitive. The RTLS cannot be used after four minutes and thirty seconds into the flight.

If a shuttle main engine fails between 4 minutes 30 seconds and six minutes after launch, the orbiter has enough energy to fly across the Atlantic and land in Morocco, Senegal, Gambia, or Spain depending upon the mission's planned inclination. This is called a Trans Atlantic Landing (TAL). After initiating the TAL the orbiter continues to climb using up all the ET fuel by the operating SSMEs until reaching MECO. The velocity and altitude at this time are far below those required to achieve orbit. The entire vehicle is rolled so the orbiter is on top of the ET and the big tank is jettisoned. The orbiter then lands at the appropriate airfield. The TAL is considered safer than the RTLS and if there is a choice at the four minute mark, the NASA controllers and the astronauts would probably choose the TAL. The TAL is possible at five minutes and thirty seconds into the launch even if two SSMEs are lost.

Six minutes after launch the third option or abort once around (AOA) becomes feasible if one SSME fails. After the ET's propellant burns out and MECO occurs there is enough velocity to achieve a very low orbit through the Earth's upper atmosphere. These orbits decay extremely rapidly, but permit the orbiter to land in California. The astronauts activate the OMS thrusters to sustain a temporary orbit prior to attempting a landing. At seven minutes into the launch the AOA is feasible even if two SSMEs fail.

The final option, abort to orbit (ATO), occurs at six minutes and thirty seconds after launch if one SSME fails. When the ET runs out of propellant and MECO occurs the velocity required for orbit falls short of that required to orbit normally. In this case the velocity differential is so small that it can be compensated by OMS thruster burns. ATO is possible after seven minutes into the flight if two SSMEs fail. In this case the remaining operable SSME is throttled up to 109% at seven minutes or 104% at seven minutes thirty seconds into the flight to achieve ATO.

Of these four intact abort mode only the ATO has been used; the other modes are practiced constantly by the astronauts in the simulators, but have not been necessary in actual flight. Extreme emergencies such as three SSME failure, ruptured ET, or malfunctioning SRB may not be survivable because the SRBs and the ET must be jettisoned before the astronauts can bring the orbiter back to Earth. After Challenger many people conjectured about jettisoning the orbiter away from a malfunctioning stack; the experts say that the survivability factor in such an attempt is little or none.

THE SPACE MISSION

Once the astronauts reach orbit, have unstrapped, and are experiencing weightlessness for the first time they have several very important tasks to accomplish; the most important of these is opening the payload bay doors. The payload bay doors serve two purposes: first, they expose the entire bay and all of its contents to the vacuum of space; second, the inner lining of the payload doors serves as heat radiators and cool the orbiter by removing the excess heat caused by electrical equipment and life sup port systems operations. If the doors cannot be opened the mission must abort within eight hours of entering space because the heat saturation of the orbiter starts to cause equipment breakdown.

After the doors are opened the astronauts transform the crew cabin from the ascent into the orbital operations mode. This is done by removing the seats needed for the mission and payload specialists. The seat removal gives the astronauts more room to work in a cramped space. The flight deck is the upper portion of the crew cabin. It contains the controls necessary to fly the orbiter during ascent, on orbit, and landing. The front of the flight deck contains the controls and instruments required for the two pilots to operate the shuttle. Large cockpit windows permit the crewmembers views outside of the orbiter. On the wall directly behind the cockpit is the payload bay control system. It contains the controls necessary to operate systems in the payload bay and it has large windows to view the payload bay and the outside when the bay doors are open.

The bottom section of the crew cabin is called the mid deck. It contains area for food storage, sleeping quarters, hygiene, and airlock access into the payload bay. During flight the crew access hatch located on the mid deck remains sealed. An interdeck hatch allows astronaut movement between the flight and mid decks.

The crew cabin remains pressurized through all flight phases and its atmosphere is controlled to resemble that of Earth at sea level. The astronauts wear bulky pressure suits for ascent and descent, but once they are in orbit they operate in a shirt-sleeve environment, wearing ordinary clothing.

LIFE IN SPACE

The orbiter has a pressure in the crew cabin of 14.7 psi with 80% nitrogen and 20% oxygen. The crew members wear ordinary clothing. Fans circulate the air throughout the crew cabin; the air passes through filters which are changed regularly. These filters contain activated charcoal to remove the cabin odors and lithium hydroxide to remove carbon dioxide. Excess moisture is removed leaving air far cleaner than that on Earth.

The mid deck contains a galley including special serving trays that hold different food containers in place in microgravity. The galley also contains a convection oven to heat the food packages before they are placed in the food containers.

If there is no galley loaded the astronauts eat the same meals heated in a food warmer. The orbiter does not normally carry a refrigerator, but if one is needed for biomedical experiments the astronauts can carry ice cream and steak.

About half of the shuttle's foods and beverages are dehydrated for weight and storage considerations. Water for rehydration is readily available due to the shuttle's fuel cells providing an ample supply of water, a by-product of generating electricity. Some foods are thermostabilized; they are heat-sterilized and put into containers. Cookies and nuts are available in ready-to-eat forms.

A menu in orbit contains 70 food items and 20 beverages; astronauts can vary their choices every four days. A typical breakfast menu includes orange juice, peaches, scrambled eggs, sausage, and a sweet roll. Lunch might be mushroom soup, a ham and cheese sandwich, stewed tomatoes and bananas. Shrimp cocktail, beefsteak, broccoli au gratin, strawberries and pudding make up a typical evening meal. These menus provide about 3000 calories per person per day because astronauts working in space were found to need as many calories in space as they do on Earth.

Sanitation in space is more important in the shuttle than on Earth. The populations of some microbes were found to increase extraordinarily in microgravity which means infectious disease could run rampant on the shuttle or a space station.

The eating equipment, dining area, toilet and sleeping facilities are regularly cleaned to prevent the spread of microorganisms. Because there is no washing machine on board, trousers are changed weekly, and socks, shirts, and underwear are changed ever y two days. The dirty clothes are sealed in plastic bags as is garbage and other trash. The dirty dishes are put into plastic bags while the utensils and food trays are wiped clean with wet wipes.

A toilet which operates similar to the ones on Earth provides a steady stream of air carrying the wastes to a special container or into plastic bags which are sealed. Some of the waste is returned to Earth for laboratory analysis to determine how a body functions in microgravity including what type of minerals the body may lose in unusual amounts.

Shuttle travelers only take sponge baths in space because of the hazard of floating water droplets. The water comes from a temperature varying water gun and is squeezed into an airflow system which carries the dirty water into the orbiter's waste collection tank.

Male astronauts found that by using standard shaving cream and a razor, shaving is a possibility without losing the various whiskers in electronic equipment.

Sleeping is accomplished in seats, sleeping bags, bunks, or on the walls. The astronauts have slept in any position in microgravity, vertical or horizontal. Bunkbed kits were available after the STS-9 mission. Each bunk is available with an individual light, communications station, fan, sound suppression blanket, and sheets with microgravity restraints. These bunks even have pillows.

A GOOD ATTITUDE

After the payload bay doors are open and the astronauts have settled into their orbital mission mode they must control the orbiter's position to keep the correct instruments pointing either toward space, the Earth or shielded from the Sun. To control the vehicle orientation the astronauts must execute attitude control.

Attitude control describes the process needed to control the orbiter's orientation or the way it points. The shuttle pilot changes the shuttle's attitude by adjusting its pitch, roll, or yaw. Roll occurs when the orbiter rotates around its longitudinal axis, an imaginary line that runs from the nose to the tail of the spacecraft. Pitch occurs when the craft rotates around its transverse axis, an imaginary line running from wingtip to wingtip. Yaw occurs when the spacecraft rotates around its vertical axis, an imaginary line running from the top of the payload bay directly to its bottom. In zero g a rotating object will spin around its center of mass.

Attitude is controlled by the reaction control system (RCS) a series of small rockets which burn the hypergolic fuels of hydrazine and nitrogen tetroxide. One RCS pod in the shuttle's nose and two RCS pods in the tail contain different rocket nozzles that thrust up, down, left, and right. Once an RCS thruster is activated and a movement starts an equal and opposite RCS thruster must be activated to stop the motion; Newton's third law is paramount in zero g. To rotate the shuttle, thrusters on both sides of the craft's center of mass must be activated; to stop the rotation two opposite thrusters must be employed. A force on only one side of the orbiter will cause it to translate and rotate. Rotation will not change a vehicle's orbit, but translation will accomplish it.

During the orbital portion of the mission the astronauts frequently change the shuttle's orbit to rescue satellites, to deploy satellites, or to reenter the Earth's atmosphere. These orbital changes are accomplished by the OMS engines located in the shuttle's tail section because the SSMEs have no fuel once the ET has been jettisoned. Each OMS engine develops 6000 pounds of thrust and uses a hypergolic fuel of monomethyl hydrazine and nitrogen tetroxide. There is comparatively little fuel on board the OMS, enough to accomplish a total of one 1000 feet per second orbital change. Within these changes must be the OMS-2 burn to put the shuttle into its initial orbit, all mission orbital changes, and the reentry burn to return back to Earth.

Both OMS engines point in the opposite direction as the orbiter's nose. When these engines are activated they thrust the vehicle in the same direction as the orbiter's nose points. The shuttle pilots must first position the shuttle via the RCS before activating the OMS to insure the correct direction for thrust applications. The orbiter must point in its direction of travel for a posigrade thrust to raise the orbit and opposite its direction of travel for a retrograde thrust to lower the orbit. The OMS engines point 15 below the orbiter's longitudinal axis and they can also gimbal to provide steering.

LAUNCHING SATELLITES

On most missions the shuttle carries satellites for deployment; the method of deployment depends upon the satellite's mission. There are generally four methods of satellite deployment; one major method for low Earth orbit (LEO) and three for geosynchronous orbits (GEO). Since the amount of fuel in the OMS limits the orbiter to LEO, spacecraft going to GEO must have an upper stage, a small rocket to provide thrust for the satellite to reach the required altitude of 22,300 miles above Earth.

The first and most common upper stage used for satellite deployment to GEO is the payload assist module or PAM. This upper stage is simply a propellant tank attached to a rocket nozzle. The top of the propellant tank connects to the satellite by means of a device called a mating ring. Another rocket called an apogee kick motor (AKM) is usually imbedded in the satellite. It looks like a smaller version of the PAM and is attached to the mating ring.

The PAM and the satellite form a vertical stack with the satellite at the top and the PAM's nozzle at the bottom. The stack stands upright inside a protective white shroud at the rear of the payload bay. The shroud looks like a pair of jaws; when close d, it protects the satellite from the solar intensity and when open, it allows the entire satellite to be launched. An orbiter can carry three satellites and three PAMs in three separate shrouds for one mission.

Before deployment a device which resembles a record turntable begins to spin the PAM stack within its protective shroud. The turntable is called the spin table. The satellite is spun to achieve attitude control by spin stabilization. This helps to point the satellite into the correct direction in space without using attitude control thrusters. About 45 minutes or approximately one-half orbit before the PAM's scheduled ignition an astronaut mission specialist opens the payload shroud, insures the PAM is spinning at its correct rpm, and then flips a switch that uncoils several springs beneath the PAM. The resulting force ejects the spinning satellite from its shroud container.

Following the PAM deployment the astronauts maneuver the orbiter away from the satellite to insure safety from the rocket firing. The astronauts position the shuttle into a higher, slower orbit about six miles behind and above the PAM. This position al so minimizes contact with the aluminum oxide particles emitted by the PAM's exhaust.

The PAM ignites and burns for about 85 seconds placing it into a highly elliptical orbit with its apogee at GEO. When the satellite reaches GEO its apogee kick motor (AKM) fires to circularize the orbit in GEO. The AKM remains with the satellite to pre vent polluting the GEO orbit with more orbital debris. The technicians on the ground then begin satellite checkout and operations while the astronauts resume their other orbital duties.

A second GEO satellite deployment is used for spacecraft weighing more than the PAM's boost capability. These spacecraft are typically bound for interplanetary flight or are huge GEO satellites that accomplish everything from communications relay, such as the Tracking and Data Relay Satellite (TDRS), to early warning, the Defense Support Program Satellites (DSP). These large spacecraft use a large upper stage called the Inertial Upper Stage (IUS). The IUS has two stages: the first places the spacecraft into a GEO transfer orbit and the second performs the AKM function. Spacecraft which use the IUS usually fill the orbiter's payload . Since the IUS itself is 17 feet long this size dictates a launch in a method very different from the PAM.

When the astronaut mission specialists are given a go decision for deployment, the flight crew activates ordnance that separates the IUS and spacecraft umbilical cables. The crew commands an electromechanical tilt actuator which raises the tilt table to a 59 deployment position. Compressed springs jettison the IUS and spacecraft from the orbiter at a very gentle rate of 5 inches per second. The IUS and its spacecraft are always deployed in the shadow of the orbiter or in Earth eclipse. At 19 minutes after deployment the astronauts maneuver to gain separation distance and at 45 minutes after deployment the bottom of the orbiter is oriented toward the IUS to protect the orbiter's windows from the IUS plume. The first stage burns for 145 seconds executing a GEO transfer orbit and upon reaching GEO the second stage burns for 103 seconds placing the craft into its GEO slot.

The third method for releasing a satellite requiring an upper stage burn is called the "frisbee" method. This is used when a PAM stack exceeds the 13 foot diameter limit of the payload bay, but the spacecraft is too small to employ the IUS method of deployment. In this case the PAM and its satellite sit in a shroud where the top of the stack faces the front of the payload bay. At the time of deployment a mechanical device spins the stack to gain spin stabilization and then gently ejects it away from the shroud like a frisbee being thrown. The upper stage ignition occurs about 45 minutes later in a method exactly like the previous upright PAM deployments.

Most of the LEO spacecraft are launched by the robotic arm which is the fourth method of satellite deployment. The robot arm is officially called the remote manipulator system (RMS). A Canadian company, Spar Aerospace, manufactured the arm and it was installed aboard all the orbiters except the Enterprise . The astronauts can use the arm from inside the orbiter's crew cabin to grasp and move payloads or astronauts around the payload bay and to deploy satellites.

The RMS includes an upper arm, a lower arm, and a grasper on the end of the apparatus. Various joints in the RMS allow it to move much like the human arm with a shoulder, an elbow, and a wrist. The upper joint allows the arm to move up, down, left, and right. while the elbow joint enables the arm to move towards the upper arm and away from the upper arm to its full extension of 50 feet.

A wrist joint connects the lower arm to the grasper which acts like a fingerless hand. This joint allows the grasper to roll, pitch, and yaw like the human hand. The similarities end at this point with the grasper being totally unlike a human hand. The grasper has no fingers to grasp anything; it has a hollow cylinder end design to grasp satellites and objects by forming a wire triangular snare over the object. Why no fingers? The RMS is 1970s technology and as of yet robotics has not solved the problems of constructing light weight, dexterous, and strong fingers needed for efficient space operations.

The RMS is totally controlled in the crew cabin at the rear of the flight deck through windows facing the payload bay. Two control sticks manually control the arm and the ship's computer can move the arm into a predetermined orientation and location in space. Television cameras on the arm's wrist and elbow provide the astronauts with additional visual coverage of the RMS' operations. A typical operational RMS satellite deployment was the Long Duration Exposure Facility (LDEF) launched by the Challenge r in 1984. A more recent deployment using the RMS was the Hubble Space Telescope capture and repairs in December 1993. Astronauts often attach themselves to foot stirrups in the arm in order to accomplish required tasks during their space walks or extra vehicular activity (EVA). The arm can lift the astronauts to place them at a precise point to work on the Hubble Space Telescope, for example, or help capture an errant Intelsat Communications Satellite. Training to use the arm takes many long hours in t he simulator; the astronaut must know every intricate maneuver that can be performed with it.

SPACE WALKING OR EXTRAVEHICULAR ACTIVITY (EVA)

EVAs are mandatory if astronauts are to repair broken satellites, retrieve derelict satellites, and refuel satellites to give them increased lifetimes. In the next decade astronauts will need all of their past EVA lessons and experience to help construct the new International Space Station.

Most of the current EVAs take place in the shuttle's payload bay. To keep from depressurizing the crew cabin, a small cylindrical room with two hatches, one leading to the crew cabin and another leading to the payload bay, is used as an airlock. The EV A astronauts enter the airlock, don their space suits, secure the crew cabin hatch, depressurize the airlock, and then open the payload bay hatch leading into space. The EVA space suits have enough oxygen and self-contained power for eight hours of operation.

Because outer space has such a harsh environment the astronauts have to be protected by their space suits or extravehicular mobility units (EMUs). Survivability and mobility are two important factors for consideration in designing an EMU.

The first space suits were pressure suits worn by pilots going to high altitudes. When these suits were pressurized, the pilots found that they were not as mobile as they would like to be. The Mercury astronauts wore a US Navy pressure suit as a backup to the cabin pressurization. In the Gemini Program, the astronauts needed flexibility including arm and leg mobility to accomplish their space walk missions. The Apollo astronauts needed a spacesuit with which they could walk down a ladder, walk on the rough terrain of the Moon, and flexible enough to bend down and pick up experiments. These suits had to be low weight, increasingly mobile, and rugged enough to withstand the Lunar dust. These suits evolved into the space shuttle's EMU.

The space shuttle's EMU is modular and it has two basic sizes, one for large astronauts, 69 inches tall and greater, and one for small astronauts, less than 69 inches tall. Built by the Hamilton Standard Corporation it can withstand temperature extremes from +350F to -250F. The EMU is the world's smallest spacecraft with a human aboard; it must provide a survivable environment which protects its occupant from solar radiation, harsh temperatures, and possible space debris or micrometeoroid p articles.

The first part of a space suit is the liquid cooling ventilator garment. It looks like long underwear, but the similarity ends there. This garment is filled with over 300 feet of plastic tubes that circulate water around the astronaut's body. The firs t item the astronaut dons is the lower torso which includes equipment from the waist down and the boots. It includes nine laminated layers. The first layer is the pressure vessel that maintains the astronaut's body pressure at 4.3 pounds per square inch. The subsequent two layers are protection for the pressure vessel. The following five layers form protection against solar thermal effects while the last, outside layer is teflon to protect the astronaut against fire, provide insulation against the temperature, and secures the suit from abrasion.

The connecting part to the lower body torso is the upper body torso, a hard fiberglass shell. This shell or hard upper body torso is the building block for the rest of the suit because all of the remaining equipment attaches to it including the primary life support system, the lower body torso, the helmet, and gloves. The arm assemblies contain ball bearings in the shoulder and elbow joints to insure movement of those limbs while the wrist ball bearings allow the hands to move in all directions. The fingers are kept very flexible and inside the gloves are a molded bladder.

A display control module connects to the front of the upper body torso. This device contains the controls to operate the suit's life support system and communications links.

The primary life support system is a pack attached to the back of the upper body torso. It provides the thermal and environmental control for the suit. This battery powered, stand-alone package provides 100% oxygen at 4.3 psi and includes a temperature control that varies the flow of cold water through the plastic pipes. A contamination control removes the exhaled carbon dioxide by means of a cartridge in the back pack. Humidity from exhaled breath and from sweat is eliminated by air flow preventing the helmet from fogging and keeping the EMU's environment free from unwanted water.

The astronaut's helmet provides thermal and radiation protection and communications capability by means of a communications assembly consisting of two microphones and a headset. The helmet also has three shields and one gold visor to protect the astronaut's eyes from the Sun's glare.

Also included in the EMU are a urine collection device and a drink bag. An umbilical line can be used if necessary for EVAs, but it is used mostly for pre and post-mission servicing.

The EMU takes about 15 minutes to don while the astronaut is in the airlock. The lower body torso and the hard body upper torso attach by quick disconnect fitting as does the liquid garment. The upper body torso is already joined to the life support back pack. The communications head gear goes on next and then the astronaut puts on the gloves. The last item donned is the helmet which also has a quick disconnect device. The EMU has a total weight of 258 pounds and it is good for up to 7.5 hours of operation.

Once in the payload bay, the astronauts attach themselves by means of a tether to the handrails along the sides of the payload bay. This keeps the astronauts from floating out of the payload bay and permits them free access to the bay's contents. When the orbiter flies over the night side of the Earth the payload bay is illuminated by three floodlights.

The astronauts used a manned maneuvering unit (MMU), a large device which looks like an easy chair with rockets, for traveling away from the shuttle to capture satellites or perform other maintenance tasks. The MMU weighed 340 pounds and contained 24 nitrogen thrusters providing roll, pitch, and yaw for a trip of about 600 feet away from the orbiter. The two flight versions of the MMU had been flown a total of nine times by six astronauts resulting in ten hours of operation. Plans for the MMU include d inspections of the underside of the orbiter, satellite servicing, astronaut rescue, and space station assembly. Challenger ended any further use of the MMU because of its low fuel capacity and the safety concerns of the post-Challenger era. Most of t he ambitious tasks for the MMU have been accomplished by other means, but astronaut rescue during an EVA was still unresolved until 1994.

In September 1994 astronauts tested a new device for EVAs called the simplified aid for EVA rescue (SAFER). Like the MMU the SAFER has 24 nitrogen jets with a control device on the front of the unit. Unlike the MMU, the SAFER is simply a backpack weighing 83 pounds and carries 3 pounds of nitrogen. It can move an astronaut up to 10 feet per second if all thrusters are fired at their maximum duration of one minute. The SAFER also contains an automatic attitude hold system which will stop a continuous rotation and stabilize the astronaut in the event of a multiaxis tumbling accident. It will be an astronaut life vest when working at places on the space station which could preclude rescue if the astronaut drifted too far away from a shuttle or an arm .

The most dramatic EVAs are those which require satellite capture and repair. Some satellites such as the Hubble Space Telescope (HST) need constant preventive maintenance scheduled to keep it flying. In December of 1993 the astronauts rendezvoused with the HST, captured it with the RMS and led it into the payload bay where four astronauts in two teams of two repaired the vehicle. They accomplished such activities as removing and replacing the solar panels, removing and replacing the HST's wide angle cameras, and installing a device to correct the HST's faulty optics. Additionally, the astronauts installed new computers and new attitude control devices called magnetometers. This mission was the most successful EVA in history as it definitely proved that humans can perform huge repair jobs in space.

One of the most important missions on the shuttle is performing space research. This is not as dramatic as capturing a satellite during an EVA, but it is very important for the future of spaceflight and life on Earth. There is very little room in the crew cabin to permit any real research and for that reason the European Space Agency (ESA) built a laboratory which fits in the payload bay of the shuttle. This laboratory, Spacelab, has provided opportunities for scientists from the U.S., Europe, and Japan to accomplish many experiments in microgravity.

The spacelab is a cylindrical module about 18 feet long and 13 feet in diameter with a pressurized tunnel leading from the crew cabin to the module. The tunnel traverses the area where the airlock is normally located. Technicians remove the airlock prior to spacelab flights and install the Spacelab. As an astronaut enters the Spacelab he/she notices six racks on either side of the lab containing experiments. The NASA engineers custom build each rack to meet the specific scientific goals of each Spacelab mission. After the racks are used, the engineers break them down and use the parts to build racks for the next Spacelab mission.

The Spacelab also contains systems called pallets that mount on the floor of the payload bay directly behind the laboratory module. A pallet provides a platform on which to mount experiments that need to be exposed directly to the vacuum of space. High resolution cameras pointed at Earth or telescopes looking directly into space are examples of experiments based on the pallets.

The Spacelab is unique in that it is the only laboratory where scientists can study physical phenomena in microgravity. They can use space experiments to determine what effect gravity has in affecting physical processes in physics, chemistry, engineering and biology. To accomplish all the various experiments the Spacelab missions are divided into several different series.

Spacelab life sciences (SLS) series notes the effects of microgravity on physiological processes and studies possible solutions to such problems as calcium loss, space motion sickness, surgical techniques, red and white blood cell production, and the effects of spaceflight on the heart. Two SLS missions have flown as of this date with three more planned through the year 2000.

The US Microgravity Laboratory (USML) series investigates chemical and physical processes in microgravity. Crystal growth, fluid flow, bubble action, fluid surface tension, thin film manufacture, and flame and combustion mechanics are just a few of the experiments accomplished in the USML series. NASA wants to fly at least two of these missions.

The ASTRO series studies the stars and the universe from the shuttle. Ultraviolet, X-ray, and Gamma ray experiments are vital because these phenomena cannot be seen from the ground due to the Earth's protective atmosphere. By studying the energy output from stars, quasars, pulsars, and possible black holes scientists can understand our universe and what may eventually happen to the Earth and the Sun. NASA plans two ASTRO flights.

The atmospheric laboratory for applications and science (ATLAS) series are used to study the Earth's climate, global change, global warming, and ozone depletion. ATLAS includes studies on atmospheric temperature, pressure, chemical composition, moisture , and solar radiation. Nine more ATLAS missions are planned between now and 2001.

NASA also sponsors three other Spacelab series for international cooperation. This effort, called the international microgravity laboratory (IML), focuses on materials processing and life science. Scientists from 18 different countries have sponsored experiments for this effort which is paving the way for cooperation envisioned on the International Space Station. There are plans for several more IML flights.

Spacelab is performing another task as well; it is the basis for the experimental laboratories that will be established on the International Space Station. These labs will be based on the flight experiences of Spacelab. The U.S. Laboratory, ESA Columbus module, and the Japanese Experimental Module will all incorporate the lessons learned from the vital space shuttle missions.

SPACEHAB

The Spacehab module increases the living and working space in the shuttle. This module is similar to the Spacelab in that it is installed in the shuttle payload bay and doubles the amount of space provided by the shuttle's living quarters, but without m any of the racks needed for experiments. Spacehab has been extremely useful for the Mir rendezvous and docking flights because the docking mechanism is attached to the Spacehab allowing travel between the Mir and space shuttle after the docking is complete.

DEORBITING THE SHUTTLE

To return to Earth the astronauts must perform a number of checklist items including cleaning up the crew cabin, reinstalling the mission and payload specialist seats, powering down scientific experiments or the Spacelab, and closing the payload bay door s. If the doors fail to close an astronaut must perform an EVA to remove four shear pins that allow the doors to be manually closed; the orbiter cannot reenter with the payload bay doors open. Next the astronauts don the pressure suits which they wore during ascent to prevent loss of oxygen and pressure during descent and to accomplish the contingency abort if it becomes necessary.

After the astronauts are suited and seated, the shuttle commander orients the shuttle using the RCS so that the OMS engines are pointing in the direction of the orbiter motion. An OMS burn performed in this position slows down the orbiter so that its new perigee point is about 6 miles or 36,000 feet above the Earth's surface. Another RCS maneuver points the nose forward and sets up a space-atmosphere interface attitude of about 30 nose up. This insures that the thermal energy is concentrated on t he heat tiles. From a point halfway around the world the shuttle begins its entry.

The orbiter enters the Earth's atmosphere as it travels toward its new perigee point. A spacecraft normally increases velocity as it travels from apogee to perigee, but the drag induced by the Earth's atmosphere begins to slow down the shuttle. This decrease in speed causes the orbiter to increase its descent rate as the perigee point changes due to the spacecraft slow down. The pilots continue to orient the spacecraft using the RCS so that its bottom surface faces down with the nose facing forward.

About 30 minutes after the deorbit burn the shuttle begins to penetrate the Earth's atmosphere in earnest. Tremendous heat builds up on the orbiter's underside until it reaches a maximum at 20 minutes before landing. Thermal protection of the spacecraft is vital to human survival; this protection depends upon 32,000 silica glass tiles. These tiles vary from a measurement of six inches by six inches to eight by eight inches. They range in thickness from one-half an inch to 3.5 inches and are the consistency of chalk. Twenty thousand of these tiles are called high temperature reusable surface insulation (HRSI) and cover the areas most likely to encounter intense heat such as the bottom of the orbiter and its nose. These tiles are painted black and resist temperatures up to 1300F by radiating 90% of the heat back into the Earth's atmosphere. Low temperature reusable surface insulation tiles are painted white and resist temperatures up to 1200F. These tiles cover the upper side of the or biter's wing and the sides closest to the nose.

Because of the intense heat generated on the orbiter's nose and leading edges of the wings, reinforced carbon-carbon with a temperature resistance of 2300F is used to cover these surfaces. The rest of the orbiter including the top of the wings and the payload bay only encounter mild heat effects so they are covered with a thin layer of white insulation called flexible reusable surface insulation (FRSI) which protects up to 700F.

The reentry heat also causes another phenomenon called ionized communications blackout. The energy causing the heating strips away the electrons from the nitrogen and oxygen molecules causing positive ions which ensheath the sides and bottom of the orbiter thus causing loss of communications from 25 minutes before landing until 12 minutes before landing.

During the last 16 minutes before landing the orbiter performs four S-turn maneuvers to slow it down. Each of these turns removes energy from the vehicle very much like that experienced by a giant slalom skier. At this time the flight control systems such as the elevons and the rudder have sufficient air pressure to accomplish the maneuvers and the RCS is turned off. The last S-turn is performed five minutes prior to landing while the orbiter's speed is still MACH 2. At 5 minutes before landing the shuttle is at 83,000 feet. Its target is a 15,000 foot runway which looks like a skinny postage stamp at this altitude. At 86 seconds prior to landing the orbiter is at 425 miles per hour and at 13,000 feet; at this point the autoland sequence begins. Approaching the runway from this altitude, the shuttle has a 22 glide slope and a rate of descent approaching 22,000 feet per minute. The average airliner uses three degrees and a rate of descent of 700 feet per minute. At 17 seconds prior to touch down the glideslope is changed from 22 to 1.5. At 14 seconds prior to touchdown the landing gear is lowered and then touchdown occurs at 215 miles per hour. When all three gear are firmly on the runway a small drag chute is released to slow the orbiter further and expend less energy on the wheel brakes. The orbiter rolls to a stop and then a convoy comes out to safe the craft. The major fact to remember is that this entire landing sequence is done without any power and the astronauts are f lying nothing more than a large glider.

The recovery convoy tests the vapor level from the hydrazine used in the RCS; if hydrazine, hydrogen or ammonia are detected a huge fan is used to blow away the hazard. The purge equipment then purges the orbiter's lines of any residual hydrogen and oxygen and sets up an airflow through the payload bay to remove any lethal gas buildups. Once the area is determined to be safe from lethal gas the crew is taken off the shuttle after a brief medical examination. The orbiter is safed for towing and is take n to the OPF for the next flight or to a waiting Boeing 747 for a trip to KSC from Edwards Air Force Base depending upon the landing site.

SO, YOU WANT TO BE AN ASTRONAUT?

The requirements to become an astronaut depend upon the jobs that need to be performed. The people selected will have to drive themselves hard to earn a position to fly, work on board the shuttle and also construct the new International Space Station.

To respond to these needs NASA continually accepts applications for the Astronaut Candidate Program. NASA selects candidates as needed, normally about every two years, for the pilot and mission specialist categories. Both civilian and military personnel may apply for the program; the civilians can apply at any time while the military must be nominated by their parent service, the Army, Navy, Air Force, Marines, or the Coast Guard.

NASA developed this selection process to choose the best candidates possible to become astronauts. The pilot and mission specialists need at least a bachelor's degree from an accredited institution in engineering, biological science, physical science, o r mathematics. Three years of professional experience must follow the degree. An advanced degree is desirable and may be used as a substitute for any or all of the professional experience. A Masters Degree is the equivalent of one year's experience while a Doctoral Degree is equivalent to three years of experience.

Additionally, to become a pilot the candidate must have at least 1000 hours of pilot-in-command time of a jet aircraft. Test pilot experience is really desirable. A pilot must pass a NASA Class I space physical which is similar to an FAA Class I physic al except that distance visual acuity must be 20/50 or better uncorrected, correctable to 20/20 in each eye. A pilot also has a height restriction between 64 and 76 inches.

The mission specialists must pass a NASA Class II space physical which is essentially an FAA Class II flight physical with the visual acuity of 20/100 correctable to 20/20 in each eye.

If an individual meets these standards she/he can obtain an application package by writing to Astronaut Selection Office, Mail Code AHX, Johnson Space Center, Houston, TX 77058.

The applicants who meet the basic qualifications are evaluated by various subject panels during a week-long process of interviews, physical exams, and orientation. The final selection is based upon personal interviews. Astronaut candidates are expected to be team players and highly skilled generalists with just enough individuality and self-reliance to be effective crewmembers.

Once a candidate is selected she/he become astronaut candidates and are assigned to Johnson Space Center for a one year training and evaluation period. During this time candidates are assigned specific technical or scientific duties and they participate in an astronaut training program designed to prepare them for formal astronaut training for specific flights.

Final selection for an astronaut is based on completion of the one- year training program. A civilian selected as an astronaut is expected to remain at NASA for at least five years; a military person remains for a specific tour of duty usually three to five years. Salaries are based on the Federal Government's General Service pay scales for GS-11 through GS-14. These scales are based upon academic achievements and experience.

CREW POSITIONS

COMMANDER/PILOT ASTRONAUTS: The commander and the pilot are both pilot astronauts. The commander has responsibility for the entire orbiter, crew, mission, and most importantly, safety of flight. The pilot assists the commander in operating the vehicle and may assist in using the RMS to deploy and retrieve satellites.

MISSION SPECIALIST: These astronauts work with the commander and pilot and are responsible for crew activity planning, experiment and payload operations, and consumables use. They are trained in the details of orbiter on-board systems, operational characteristics, mission requirements, and supporting systems needed to conduct assigned mission objectives. Mission Specialists also perform EVAs and are responsible for payload operation.

PAYLOAD SPECIALISTS: These are persons other than NASA astronauts who have specialized on-board duties which are uniquely described by a payload sponsor. These people must still have the required education and physical skills even though they are not p art of the NASA Astronaut Candidate Program.

ASTRONAUT BASIC TRAINING

Astronaut candidates attend classes at Johnson Space Center. They study subjects such as basic science, technology, mathematics, Earth resources, meteorology, guidance and navigation, astronomy, physics, and computer science. They also receive training in parachuting, land and sea survival, space suit use, and hand tool operation. Candidates also train in altitude chambers to prepare them for use of pressure suits and emergency situations.

Additionally, astronaut candidates are exposed to microgravity by means of a modified KC-135 jet aircraft which can produce 30 seconds of weightlessness during dives from 34,000 to 24,000. This sequence is repeated up to 40 times each day.

Pilot astronauts must become proficient and maintain it in the T-38 aircraft by flying about 15 hours per month. During this time they practice orbiter landings.

FORMAL TRAINING

Once an astronaut candidate has been accepted into the corps he/she begins a systems training program by reading about the various orbiter functions. The next step in training is to become familiar with the single systems trainer to learn each system an d subsystem using mission checklists. The astronaut learns about normal operations and practices coping with malfunctions.

The astronauts then begin training in the shuttle mission simulators (SMS) which provides mission training in all phases of the mission including prelaunch, ascent, orbit operations, deorbit, and landing. Included is training on payload operation, payload deployment, retrieval, maneuvers, and rendezvous. There are two SMS's , a fixed base and a motion based to train the astronauts.

The fixed base crew station is used for specific mission/payload training. This is the only trainer with complete forward and aft consoles, including a full RMS simulator. Digital image generation provides visuals for out-of-window scenes of Earth, stars, payloads, and the runway. Using the fixed base simulator missions can be simulated from launch to landing.

The motion based simulator is a six degree system which allows the flight deck to be rotated 90 to simulate launch and ascent. This is used to train commanders and pilots in mission phases of launch, ascent, descent, and landing.

The astronauts train with generic training software until they are assigned a mission 10 months before the flight. Their mission specific software is developed 11 weeks prior to launch. During the 11 weeks prior to launch the crew practices with the f light controllers in the Mission Control Center to learn to work as a team working out problems and practicing normal operating procedures. The SMS and the MCC are linked by computer in a manner similar to the orbiter and MCC during actual flight. Astronauts undergo about 300 hours of SMS training.

Other training takes place as well. For example, the weightless environment training facility (WET-F) is used to train astronauts for EVAs. The WET-F is a large water tank which contains a mockup of the orbiter's payload bay and various payloads. The astronauts wear their space suits made neutrally buoyant to simulate weightlessness and to practice working in this environment.

Several scaled mockups are used to train the astronauts for various tasks. A full-scale orbiter mockup also helps to train the astronauts in meal preparation, equipment storage, trash management, camera use, and experiment familiarization. The trainer is also employed for emergency egress training after shuttle landings. Astronauts use the crew compartment trainer to simulate on-orbit living procedures, emergency pad egress, and bailout procedures. The manipulator development facility is a full-scale mockup of the payload bay with a full scale hydraulically operated RMS. Mission specialists use this apparatus to practice deploying and retrieving satellites.

The pilots also experience other training for the most critical part of the mission after launch, the landing. They receive intensive instructions in orbiter approach and landing procedures by flying the shuttle training aircraft (STA) a Gulfstream II business jet modified to fly like the orbiter during approach and landing. Because the orbiter makes an approach at 20 and over 200 miles per hour, the STA approaches with its engines reversed and main landing gear down to duplicate the orbiter's unique glide characteristics. Pilots receive about 50 hours of STA training which is equivalent to 300 shuttle approaches and landings.

While all training is in progress the astronauts also keep themselves updated on the status of the spacecraft and payloads. They study the latest flight rules and attend mission technical meetings. Additionally, they participate in shuttle test and checkout procedures at KSC

By the time of mission launch day the astronauts find that the flight has far less problems than they practiced. The simulation accuracies are authentic; astronauts claim that only the noise and vibrations are missing from the simulations; the training accurately duplicates the flight.

After landing from the mission the astronauts continue debriefing for several days recounting their experience to help future crews and to add to the data base of space flight knowledge. This is the reason the men and women have become astronauts; to push back the mysteries of the new frontier and to go where no one has before.

THE FUTURE OF THE SPACE SHUTTLE

Several questions come to mind when one discusses the space shuttle. Should the space shuttle remain as the U.S.'s primary method of launching astronauts into orbit? Should the shuttle be privatized or should NASA remain as the primary manager of the program? Will the Space Shuttle Program survive another Challenger accident?

With today's set of fiscal constraints, it seems unlikely that a replacement for the current space shuttle system will appear anytime in the near future. NASA would be better off if it invested in a new design to place the astronauts into orbit especially to ferry new crews to the space station. The shuttle is 'everything to everybody' approach is less attractive than the alternative of placing two or three specialized vehicles each capable of doing a specific mission. This approach will cost money, but it is much more flexible, safer, and has decreased operations costs.

The current space shuttle is too large and cumbersome for a simple ferry activity. Instead, a smaller transfer capsule capable of carrying a dozen crewmembers should be developed. This capsule could be placed into orbit with conventional expendable launchers much like the current Soyuz vehicle does for the Russians. This capsule could either be the ballistic pe of the Apollo days or a lifting body like the old USAF Dynosoar Program. This capsule would be easier to handle, cost less per flight, and offer better abort options than the space shuttle.

For larger payloads, an unmanned cargo carrier such as the Space Shuttle C would be an economical alternative to the current space shuttle design. The space shuttle stack would remain the same except a cargo pod would be in place of the orbiter. The space shuttle main engines (SSMEs) would be packaged inside a recoverable container. Just by deleting the orbiter's delta wings alone would allow a greater payload launch weight and increase launch flexibility due to the wind restrictions imposed by the RT LS abort scenario and the wind shear restriction requirements.

If the space shuttle's capability to return large payloads from orbit is still required, the current orbiter could be modified to suit this requirement. The orbiter should be designed with a more autonomous capability and carrying crews only when absolutely necessary. At the same time, several safety changes should be made. Designers should make and install a survivable escape system. The SRBs should be replaced by the more complicated, but safer liquid fueled boosters with throttling capability. Th e SSMEs should be moved to the base of the External Tank and the entire structure be allowed to return for refurbishment to Earth. Designers should also install two deployable turbofan engines for the landing phase and the hypergolic fuel in the OMS should be replaced with LOX and LH2. Space shuttle avionics should be updated with the most modern equipment for increased safety.

Because the space shuttle system is so complex it is difficult to imagine the system being turned over to a private contractor. Because of the addition of humans to the cargo, the space shuttle is very different from the expendable rockets. The space shuttle also has only recently passed its 60th flight. As a comparison, the X-15 had almost 200 flights and it was always deemed a test vehicle. The costs involved in turning the program over to a private company really means that the contractor would be subsidized by the government until the shuttle was on a ground to make a profit. This would not happen with old technology.

Space flight is a high risk business and despite all the safety precautions and hard work there will probably be another fatal accident. If an accident occurred, NASA would have to make do with three orbiters because Congress would never fund another orbiter as it did following Challenger. American citizens would probably accept the accident if it were not as blatant as the Challenger and that the crew had a reasonable chance to escape. Most emphatically the accident must not be caused by something previously known by NASA engineers and contractors to be potentially life threatening and for which there is an engineering solution. The sad part of the Challenger accident was not so much that it happened, but that NASA and Morton Thiokol knew that the accident could happen and they did nothing to stop the launch or fix the problem. People are willing to accept the possibility of death in a high risk venture if the cause is something previously undiscovered by scientists and engineers,; they are less willing to accept it if somebody didn't accomplish a safety task to save time or money.