TIM FURNISS / LONDON
Improvements will enable more flights while more further initiatives are planned
The first upgraded Block 2 Space Shuttle Main Engine (SSME) is set to fly on the STS 104 Atlantis mission (ISS) to the International Space Station from the Kennedy Space Center, Florida, on 12 July.
The improved-reliability Block 2 engine carries a replacement high pressure liquid hydrogen turbo- pump, made by Pratt & Whitney and featuring a cast housing without welds, an integral shaft/disc with thin wall blades and ceramic bearings. The upgrades are designed to increase the engine's turbo- pump-derived strength, allowing more flights between overhauls.
"We believe we have more than doubled the reliability of the engine" with the new components, says George Hopson, manager of the SSME office at NASA's Marshall Space Flight Center, Alabama. But the new engine adds 135kg (300lb) to the orbiter's weight.
The other two SSMEs on the mission will be standard Block 2A models. These were introduced in 1998 and use a combustion chamber with a larger throat, lowering the engine's operating pressures and temperatures.
The first upgrade to the original SSMEs which powered the STS 1 Columbia in April 1981 was introduced in 1995. That upgrade, Block 1, used a redesigned high pressure liquid oxygen turbopump with silicon nitride ball bearings, a two-duct engine power head and a single-coil heat exchanger.
The SSMEs have successfully operated during 102 launches. The STS 51L Challenger was destroyed in 1986, while in 1985 one SSME shut down on STS 51F Challenger during launch, forcing an abort to orbit. There have been five launch pad aborts, after one engine failed to meet ignition criteria.
Meanwhile, Goodrich is to develop a new wheel for the Space Shuttle main landing gear, which hits the runway at about 225kt (415km/h). NASA wants the tyres redesigned to accommodate an increased landing speed of 250kt and a 17% heavier landing weight, up from 64,410kg (141,800lb) to a maximum of 77,550kg.
This is aimed at improving the safety margin in the event of an emergency return to Earth after a launch or mission abort when the orbiter is carrying a full payload, including cargo and consumables. The tyres will be delivered in 2004.
Space Shuttle orbiters will be using White Sands Space Harbor, New Mexico, as the prime back-up landing site from 1 September to 29 November while repairs are made to one of the runways at Edwards AFB, California, the usual base when a landing at KSC is not possible. Meanwhile, as STS 104 is prepared for launch from pad 39B at KSC, Discovery STS 105 has been rolled out to pad 39A for its 5 August launch to exchange crews and deliver cargo to the ISS. The launch may be delayed to 9 August.Source: Flight International
