The Complete Book of Spaceflight: From Apollo 1 to Zero Gravity

from the rest of the Shuttle. About 225 seconds after
separation, at an altitude of 4,800 m, the nose cap of
each SRB is ejected and a pilot parachute is deployed.
This serves to pull out the 16.5-m-diameter drogue
parachute, which orients and stabilizes the descent of
each SRB to a tail-first attitude ready for deployment of
the main parachutes. At an altitude of 1,800 m, the
three 41-m-diameter main parachutes open to slow
each SRB to water impact at about 25 m/s. The SRBs
splash down in the Atlantic about 225 km from the
launch site. Retrieval ships locate each SRB by homing
in on radio beacon signals transmitted from each
booster and by flashing lights activated on each SRB.
Once on location, recovery crews plug the SRB nozzles,
empty the motors of water, and tow the rockets
back to a receiving and processing site on Cape
Canaveral. After inspection, the SRBs are disassembled,
washed with fresh, deionized water to limit saltwater
corrosion, and refurbished ready to fly again.
Length: 45.5 m
Diameter: 3.7 m
Mass (per SRB): 585,000 kg (with fuel); 85,000 kg
(empty)
Thrust (per SRB): 14.7 million N
Space Shuttle Main Engines (SSMEs)
The most advanced liquid-fueled rocket engines ever
built. Each SSME generates enough thrust to maintain
the flight of 2.5 Boeing 747 jumbo jets and is
designed for 7.5 hours of operation over an average
lifespan of 55 starts. Each Orbiter has three SSMEs
mounted on its aft fuselage in a triangular pattern.
The Main Engines burn a combination of liquid oxygen
and liquid hydrogen fed from the ET and employ
a staged combustion cycle, in which the fuels are first
partially burned at high pressure and low temperature,
then burned completely at high pressure and high
temperature. This allows the SSMEs to produce
thrust more efficiently than other rocket engines.
space station
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return hoped to conduct long-term research onboard the
Russian station until it could build its own. But these
efforts ended with the collapse of East-West detente in
1979. Better progress was made on other fronts, and in
space station 401
SSME thrust can be varied from 65% to 109% of
rated power at increments of 1%. Rated power is
100% thrust, or 1,670,000 N per each SSME at sea
level. A thrust value of 104%, known as full power, is
typically used as the Shuttle ascends, although, in an
emergency, each SSME may be throttled up to 109%
power. All three SSMEs receive identical and simultaneous
throttle commands, which usually come from
general purpose computers aboard the Orbiter. The
firing of the three SSMEs begins at launch minus 6.6
seconds, at which time general-purpose computers
aboard the Orbiter command a staggered start of each
SSME. The first to fire is Main Engine number three
(right), followed by number two (left) and number
one (center) at intervals of 120 milliseconds. If all
three SSMEs do not reach at least 90% thrust over the
next 3 seconds, a main engine cutoff (MECO) command
is issued automatically, followed by cutoff of all
three SSMEs. If all SSMEs are performing normally,
the Shuttle can be launched. The SSMEs achieve full
power at launch, but they are throttled back at about
launch plus 26 seconds to protect the Shuttle from
aerodynamic stress and excessive heating. They are
throttled up to full power again at about launch plus
60 seconds, and typically they continue to produce
full power for about 8.5 minutes until shortly before
the Shuttle enters orbit. During ascent, each SSME
may be gimbaled plus or minus 10.5° in pitch and
yaw to help steer the Shuttle. At about launch plus 7
minutes 40 seconds the SSMEs are throttled back to
avoid subjecting the Shuttle and crew to gravitational
forces over 3g. At about 10 seconds before main
engine cutoff, a MECO sequence begins. About 3
seconds later, the SSMEs are commanded to begin
throttling back at intervals of 10% thrust per second
until they reach a thrust of 65% of rated power, called
minimum power. This power is maintained for just
under 7 seconds, then the SSMEs shut down.
Length: 4.3 m
Diameter: 2.3 m
1973 Europe agreed to supply NASA with Spacelab
modules—mini-labs that would ride in the Shuttle’s
payload bay. When the Shuttle flew for the first time
in 1981, a permanently manned space station was
once again touted as the next logical step for the United
States in space. Budgetary, programmatic, and political