Semper Fly: Marines in Space

In addition to quicker prelaunch procedures, the program needs durable, reusable heat shields in place of the space shuttle´s fragile ceramic tiles, which require 60 days´ preparation. And whereas two stages are a given, which combination of stages is best depends on who you ask. Even with a hypersonic Falcon first-stage craft, â€there are several different approaches†to propulsion, says scientist James Pittman of the NASA Langley Research Center in Hampton, Virginia. â€The use of rockets to boost the vehicle to hypersonic speed is one approach. [Or] you could look at an air-breathing solution from takeoff to hypersonic speed to landing.â€

Lockheed´s Rattlrs program may provide key breakthroughs. This $100-million initiative is targeted at creating hypersonic missiles for the Navy, using new alloys, composites and ceramics to allow the engines to withstand extreme heat. The resulting high-speed turbine will eventually appear in RLVs, according to Lockheed´s Craig Johnston. â€The turbine-based combined cycle offers probably the greatest promise,†he says, â€because it allows you to operate in the low-speed regime much the same way that current aircraft operate.â€

There are other hurdles. Dwayne Day, a space analyst, notes that SpaceShipOne is the only successful RLV so far. But, he says, its payload is limited: â€If you want to carry a lot of armed combat troops and their equipment, you need a much bigger ship.†Another critic cites the huge challenge of heavily laden long-range spaceflight-something SpaceShipOne doesn´t even come close to accomplishing. â€I don´t think you could carry even zero payload and do the [Sustain] mission,†says Preston Carter, a researcher at Lawrence Livermore National Laboratory. â€It´s beyond normal propulsion and normal structures.â€

Taylor Dinerman, a space analyst for Space Review, says that Sustain is feasible, given enough time for R&D. The key, he believes, is to pursue the programs that might feed into a transport-and then have the financial support from Congress to push the project through. But once the technological and financial hurdles are overcome, there´s still one that would remain. â€Probably the most difficult challenge would be extracting the personnel,†Wassink confesses-that is, bringing them home safely at mission´s end.