21st Century Space Shuttle
Lighter Fuel Tank
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.
Return to Flight
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.
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.
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.
Shuttle Main Engines
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.