Graham Warwick/WASHINGTON DC
NASA will brief the US Administration by the end of September on its proposal to spend $1.2 billion over five years to prepare for a "low risk" competition to select a next-generation space transporter by 2005.
The agency is to present its plans to the US Office of Management and Budget by 1 October. These will lay out the technology demonstrations, starting in 2001 and funded jointly with industry, which are required to ensure that there will be competing reusable launch vehicles (RLVs) available to choose from by 2005, when NASA expects to select the replacement for the Space Shuttle.
Contractor teams briefed NASA on progress with the latest phase of space transportation architecture studies earlier in September. Phase III, to be completed by December, broadens the scope of the studies to look at a wider range of missions, says Dan Mulville, NASA's chief engineer. "We want to look beyond just servicing the ISS [International Space Station]."
Missions being considered range from assembling, servicing and retrieving spacecraft in low earth orbit, to carrying crews to high earth orbit to rendezvous with exploration vehicles.
Phase III has an "increased focus" on safety, Mulville says, with NASA aiming for an ascent loss-of-vehicle risk of one in 1,000, and a loss-of-crew risk of one in 10,000. The comparable risk for the Shuttle is one in 400, a figure which is expected to improve with planned safety and reliability upgrades, he says.
NASA had planned to select a new space transportation architecture by the end of next year, "but we don't know enough", Mulville says. The delay is a blow to Lockheed Martin, which has built its business case for commercial development of the VentureStar single-stage-to-orbit RLV around NASA's original requirements.
Although the VentureStar is still in the running, other second- and third-generation RLVs and Shuttle-derived vehicles are being evaluated, Mulville says. Another option which has emerged mates a reusable crew/cargo transfer vehicle (CCTV) with an expendable launch vehicle.
Phase III is establishing requirements for the CCTV, which could provide an early complement or alternative to the Shuttle to ensure guaranteed access to the ISS. The vehicle could be a small "space taxi" to service the ISS, or a larger "mini-shuttle" capable of taking crews and payloads to higher orbits.
In Phase II, contractors looked at a crew transfer vehicle (CTV), evolved from the crew rescue vehicle (CRV) that NASA plans for the ISS. Mulville says that this led to concerns that the CTV design would be constrained unduly by the requirement that it, like the CRV, fit inside the Shuttle.
"We took a step back, so as not to constrain the design," he says. "We will address the CRV requirement while providing the opportunity for growth to the CTV, but without constraining it to be the CTV."
NASA has earmarked $1 billion of the ISS budget to develop and acquire four CRVs based on the in-house X-38 design. Development of a CTV, meanwhile, is expected to cost $2.5 billion, to take longer and to be largely commercially funded, Mulville says.
The new CCTV approach is seen as a way of injecting competition into the CRV programme while providing a transition path to the eventual CTV, he says.
Source: Flight International
