The
21st Century Space Shuttle
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History
 A
Lighter Fuel Tank
April
1983, STS-6
A redesigned
Lightweight External Tank — 4,536 kilograms (10,000 pounds) lighter
than the original design — flew on STS-6 in 1983, increasing the
shuttle’s cargo capacity by the same amount. In 1998, a Super Lightweight
External Tank flew on STS-91, further reducing the tank’s weight
by 3,402 kilograms (7,500 pounds) and again increasing the shuttle’s
cargo capacity by the same amount. The new super lightweight tank
is manufactured from a Lockheed-Martin-developed aluminum-lithium
alloy that is not only lighter, but also is 30 percent stronger
than the previous tank design.
The
Return to Flight
September
1988, STS-26
When Discovery
returned the shuttle fleet to space following the Challenger accident,
more than 200 safety improvements and modifications were ushered
in. The improvements included a major redesign of the solid rockets,
the addition of a crew escape and bailout system, stronger landing
gear, more powerful flight control computers, updated inertial navigation
equipment and several updated avionics units.
Endeavour's
Maiden Voyage
May
1992, STS-49
Endeavour’s
first flight in 1992 marked the debut of many shuttle improvements,
including a drag chute to assist braking during landing, improved
nosewheel steering, lighter and more reliable hydraulic power units
and updates to a variety of avionics equipment.
 Extended
Duration Flights
June
1992, STS-50
Columbia was the first shuttle to be modified to allow long-duration
flights, and flew the first such mission in 1992. The modifications
included an improved toilet, a regenerative system to remove carbon
dioxide from the air, connections for a pallet of additional hydrogen
and oxygen tanks to be mounted in the cargo bay and extra stowage
room in the crew cabin.
 Space
Shuttle Main Engines
July
1995, STS-70
The shuttle
main engines have had three major redesigns that have more than
tripled estimates of their safety. With its first flight in 1995,
the first redesign, called the Block I engine, included design changes
to strengthen the oxygen turbopump and engine powerhead. The second
overhaul, called the Block IIA engine, included a larger throat
to the main combustion chamber and first flew on STS-89 in January
1998. The third redesign, called the Block II engine, includes a
stronger fuel turbopump and will fly for the first time in 2000.
A fourth major overhaul is now planned to fly by 2005. Called the
Block III engine, it will include further improvements to the combustion
chamber and a simplified nozzle design.
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