Two-Step Crew Vehicle Option Under Study for Space Station

Frank Morring, Jr. / Washington

Top NASA managers are considering a two-step option for flying humans to orbit that would give International Space Station crews a U.S.- built lifeboat for emergency return to Earth as early as 2009 and two-way trans- port with the same basic vehicle a few years later.

An early version of the crew transfer/return vehicle (CTRV) would be delivered to the ISS by a space shuttle or heavy lift Atlas V or Delta IV expendable rocket and left there for use in emergencies. Later, when a next-generation reusable launch vehicle (RLV) is ready, the CTRV would function as the crew transfer portion of the system, riding its two stages to orbit and returning alone.

The option was one of three basic ideas briefed to Administrator Sean O'Keefe by the agency's Space Launch Initiative (SLI), which is running an elaborate series of architecture and technology studies on how to replace the space shuttle with a cheaper, safer vehicle. O'Keefe had ordered the SLI office to see if there was a way to apply the human transport portion of its work to the ISS, which is relying on Russian-built Soyuz capsules for crew rescue while NASA struggles to correct a big funding shortfall in its human spaceflight accounts (AW&ST May 20, p.46).

"There has been one briefing to the administrator on the preliminary results of what we were referring to as the CTRV study, which was what are all the different options for a crew transfer vehicle that could also function as a crew return vehicle, to see if there's a multiuse function rather than building one to do one job and building another vehicle to do another job," said David C. Leestma, the former astronaut who is now project manager for the human spaceflight portion of the SLI at Johnson Space Center, Tex.

Leestma said other options briefed to O'Keefe included sticking to the original SLI schedule and outfitting one transfer vehicle for ISS crew rescue, and building a dedicated "down-only" rescue vehicle like the X-38 that O'Keefe has already terminated. The former option could pro- duce a station crew vehicle by about 2012, while the much simpler vehicle that would be developed under the latter option could be ready by the end of2008. The Bush administration has frozen the size of the ISS crew at the three who can fit into a single Soyuz capsule, limiting the amount of scientific research that can be conducted on the station. For the CTRV study, the basic requirement was a vehicle that could carry three crewmembers to orbit and return to Earth with four on board.

However, the study also examined options for accommodating larger crews.

"If you're going to be able to carry four of them down, you might want to carry four up," said Leestma. "We did look at that. And in some of the designs, at least the preliminary work that we did, there's a break between four and five, and if you can carry five up you can carry seven up. There's really no difference in the weight of the structure, but there is a break between four and five, and that's because you've got to add another row of seats."

Another issue for an accelerated CTRV designed to ride a new RLV would be how to get it to the space station for rescue duty before the RLV is ready. A larger vehicle probably would be too heavy for an expendable launch vehicle (ELV), but the shape of the vehicle itself raises engineering issues beyond the ability of the ELV to lift it.

"One of the trades that we haven't looked at totally but is an issue is do you top-mount or side-mount this thing," Leestma said. "Top-mounting a winged vehicle, launching on an ELV, doesn't come for free. It's easy to draw a picture of a winged vehicle on top of an ELV, but aerodynamically that is a very difficult task because ELVs take axial loads, but a winged vehicle could put a bending moment into it, and they don't take bending moments very well."

Although the CTRV concept involves using the same basic vehicle for transfer and rescue, the different requirements would mean different equipment inside the aerodynamic body. NASA has already decided to separate crew and cargo in its SLI architecture, with robotic arms and other cargo-handling equipment riding in the cargo vehicle and the crew vehicle serving essentially as transportation for humans. But a rescue vehicle would remain docked at the space station, and would have to be able to accommodate an injured or ill crewmember.

"On the inside, the outfitting would be a little bit different than a vehicle that brings people up and down," Leestma said. "You'd have to maybe do some redundancy and reliability things on the systems inside so it could remain on board as a crew rescue vehicle."

Leestma stressed that the delivery dates for the different options are only tentative. While the two-step option could be ready as early as 2009, he said, it also might not be available for ISS return until 2012 or later. A lot will depend on decisions taken at NASA headquarters and the White House as the administration wrestles with upgrading an inadequate NASA financial management system, using the new system to get a handle on future station costs and trying to meet the needs of NASA's international partners on ISS and the scientists who want to do research in its microgravity environment.

The SLI program has a major systems requirements review by the end of the year, and to keep on that schedule it needs to get such "level one" requirements as crew size and duration in orbit from head- quarters by the end of the summer.