Space Shuttle replacement may become clearer in November - but space agency may wait for third-generation craft

A NASA review in November will narrow potential candidates for a proposed second-generation reusable launch vehicle (RLV) to two or three choices, the agency announced on 30 April. But the agency has already decided that there will be no ambitious single-stage-to-orbit concepts with air-breathing engines. The new two-stage-to-orbit vehicle will have traditional rocket propulsion, says NASA.

Final selection of an architecture and the start of government-funded full-scale development is planned for 2006, aiming for a first flight in 2012. NASA is not yet committed to proceeding with a second-generation vehicle, however, and may decide to keep the Space Shuttle flying until 2020. The Shuttle has already received several upgrades, including improved main engines, a lighter-weight external tank, glass cockpit and a more reliable thermal protection system. A programme is underway to include replacements to the auxiliary power units and improved navigation and communications systems.

The decision to keep the Shuttle flying will not be made before 2006. If it decides to do so, NASA is expected to focus on a third-generation air-breathing RLV to succeed the Shuttle after 2020.

NASA's Space Launch Initiative (SLI) reached a milestone on 30 April when the project's initial architecture technology review selected a narrower field of 15 potential candidates for the second-generation RLV from three industry teams led by Boeing, Lockheed Martin and Orbital Sciences/Northrop Grumman.

The chief driver in the review was the propulsion system as this has a longer lead time. "Among the outcomes is a focus on kerosene-fuelled main engines," says Dennis Smith, SLI programme manager at NASA's Marshall Space Flight Center in Huntsville, Alabama.

All-kerosene, all-hydrogen powerplants and a combination of kerosene and hydrogen engines are being considered.

Dependable reusable rocket engines and long-life lightweight integrated airframes, along with crew escape systems, are among the priorities, each having an effect on the programme's goals of increased safety and reliability and reduced cost.

Vertical and horizontal take-off systems are being considered, with fly-back first stages capable of automatic landings. The objective is to reduce the cost to orbit from $4,500/kg for the Shuttle to $455/kg and reduce the risk of a catastrophic failure from 1 in 500 to 1 in 10,000.

Ejection seats and flyaway crew modules are being considered, but it is likely that the new vehicle will not be piloted. Cargo and crew will be carried separately. The second generation RLV could carry a crew transfer vehicle, which NASA is studying as a replacement for the cancelled crew return vehicle, or lifeboat, for the International Space Station.

The objective of the SLI is "not just designing a launch vehicle", says Smith. "We're designing a complete system," including an Earth-to-orbit reusable launch vehicle, upper stages and on-orbit transfer vehicles, together with mission planning, ground and flight operations and ground and in-orbit infrastructure.


Source: Flight International