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
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
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 28º inclination orbit and 37,800 into a 57º 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 -460ºF. 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
The cryogenic propellant presents a unique problem because of its boiling
points of around -200º. 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
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 7º 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
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
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
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 88ºF 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"
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
7º 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
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 090º
which means they are launched due East. This gives the shuttle an inclination of
28.5º. If the shuttle is launched at its upward azimuth of 038º, directly to
the Northeast, it will have its greatest inclination of 57º. 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
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 30º 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 30º off the vertical to 90º 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
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
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
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
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
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
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
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
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 15º below the orbiter's
longitudinal axis and they can also gimbal to provide steering.
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 59º 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
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 +350ºF to -250ºF. 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
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
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
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
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.
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 30º 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 1300ºF 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 1200ºF. 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 2300ºF
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 700ºF.
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 22º 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 22º to 1.5º. 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
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.
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
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
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
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 90º 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
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 20º 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
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
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
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
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