While NASA’s shuttle fleet faces retirement and a gap before a new spaceship debuts, the stage is set for private firms hoping to offer commercial cargo and crew services to the international space station (ISS).

Six contenders — from a field of more than 20 hopefuls — have weathered NASA’s round of culling for the Commercial Orbital Transportation Services (COTS) effort, with the first awards slated to be announced in August, according to some competitors. NASA plans to spend about $500 million on the COTS effort over the next five years, the agency has said.

Among the teams that reportedly made the cut are:

– Andrews Space, a Seattle-based firm, has been cited by industry sources as a finalist, though company officials would not comment on the matter aside from stating they have received a response from NASA on their proposal.

– Oklahoma City-based Rocketplane Kistler, a cooperative effort between Rocketplane Limited and Kistler Aerospace, which is developing a payload launch and cargo-ferrying vehicle around its K-1 rocket.

– SpaceDev of Poway, Calif., which previously announced plans for a spaceplane dubbed Dream Chaser.

– El Segundo, Calif.-based Space Exploration Technologies (SpaceX), which is developing its Dragon capsule system and Falcon 9 rocket for cargo and manned spaceflights.

– Spacehab of Houston, where designs for the Apex 400, the largest in a trio of spacecraft, are under way to resupply the ISS.

– Transformational Space Corp. (t/Space), Reston, Va., which has le d a group of firms pursuing a crewed transfer vehicle for NASA use, also has been cited by experts as a COTS finalist.

While some COTS contenders have spoken openly of their selection as finalists, others — such as Andrews Space and t/Space — remain reticent since the competition is still under way.

According to SpaceDev, the COTS competition comprises four different arenas: a pressurized vehicle to ferry cargo to and from the ISS; a pressurized variant that disposes of the spacecraft; unpressurized cargo to the station and disposal; and crew transportation.

Two other teams — Lockheed Martin and the joint Northrop Grumman-Boeing group — are competing in a separate race to build NASA’s post-shuttle crewed spacecraft, the Crew Exploration Vehicle.

And the finalists are…

At the heart of Rocketplane Kistler’s COTS entry is the K-1 rocket, a two-stage booster with reusable components and an orbital stage designed to carry deployable satellites or other payloads as well as a cargo container for the ISS.

Published specifications call for a 37-meter rocket capable of launching payloads of nearly 5,000 kilograms into low Earth orbit, though Rocketplane Kistler officials said their effort has moved beyond that specified on Kistler’s Web site. Other details indicate target launch sites from the Nevada Test Site outside Las Vegas and Woomera, Australia.

“It gives the reader … a very good sense of how the vehicle operates and is appropriately out of phase with our development,” Bob Seto, Rocketplane’s vice president of engineering systems and analysis, said of the earlier documentation. “The actual development is ahead, but it gives you the sense of where we were and probably where we’re going.”

Out from under wraps

Meanwhile SpaceX, led by entrepreneur Elon Musk, unveiled plans for its reusable Dragon space capsule earlier this year.

Musk said his firm is tackling the development of the heavy-lift Falcon 9 booster — while fine-tuning its Falcon 1 rocket at the same time — to support the 3.3-meter wide Dragon spacecraft.

“There are some things I didn’t talk about, that we’re keeping closer to the vest, that will be of benefit to NASA,” Musk said in a telephone interview, reiterating that human spaceflight was always on the SpaceX docket. “Really, the major goal in the long run is human space transportation, that’s the reason for the founding of the company.”

SpaceX had kept its Dragon project under wraps while publicly moving ahead with its unmanned Falcon 1 effort since 2004, but the company reported that a prototype flight crew capsule already had been built. While the prototype lacks a reaction control system or re-entry heat shield, a life-support system for the vehicle already has been tested.

The spacecraft is intended not to dock itself at the ISS, but use a laser-guided system to maneuver near the station to be grappled with the outpost’s robotic arm. The capsule then can be mated manually, as NASA’s shuttle-carried cargo modules are, to deliver supplies or new crew members.

Musk said engine tests of the Falcon 9 flight engines could occur this December, with the first launch to follow about one year later.

“There’re actually three Falcon 9 flights on schedule for 2008, with the NASA flights to follow on top of that,” Musk said, adding that some uncertainty is built into that plan. “We’d have a three-flight demonstration ending with a flight to the international space station.”

Partners and competitors

SpaceX has reportedly partnered with several companies for its Dragon project, including fellow COTS competitor Spacehab. But that partnership has not prevented Spacehab from casting its own entry into the commercial space transportation ring.

Last summer, Spacehab — which has been a staple provider of components for NASA’s shuttle system — announced plans to develop a family of spacecraft dubbed Apex to cater to the microsatellite and hefty payload needs of customers. The firm plans to move ahead with the project, COTS or no COTS.

“Spacehab is committed to the Apex program as a whole,” Kimberly Campbell, Spacehab’s vice president of corporate marketing, said in a telephone interview. “Our goal is to provide continuous low-cost access to space.”

The largest in the Apex arsenal, the 400 series, is Spacehab’s bid for NASA’s COTS contest.

Designed to launch atop an Atlas 5 or Delta 4 rocket, the spacecraft could haul payloads of up to 12,300 kilograms into orbit, Spacehab has said. A modified version equipped with a re-entry system to return cargo or material to Earth — a valuable asset for ISS experiments — is expected to orbit 8,600 kilograms, Spacehab officials said.

Spacehab’s Apex 400 series tops the spacecraft family’s payload charts, with specification calling for loads up to 12,300 kilograms for one-way flights and 8,600 kilograms for returnable flights.

“It’s about providing an end-to-end service,” Spacehab’s Apex program manager Jim Baker said of the Apex 400’s multiple booster plan. “If we’re tied to one specific launch vehicle, then if that launch vehicle has issues or problems, or is down, then our business is impacted.”

Orbital dreams

SpaceDev officials have said in the past that they hoped their Dream Chaser vehicle would prove a strong candidate for ISS resupply and crew rotation flights, though whether the vehicle will be modified for NASA’s COTS program is unclear.

Initially unveiled as an evolution of the NASA’s X-34 vehicle design, SpaceDev later opted for a blunt-nosed spacecraft to carry passengers or crew on suborbital or orbital treks. The spacecraft is expected to launch vertically atop a stack of hybrid rocket engines and make runway landings upon its return to Earth. It is small enough — with wings folded — to fit in the payload bay of a NASA shuttle.

“Our employees, project team members and subcontractors are thrilled to have been chosen as a finalist,” SpaceDev chief Mark Sirangelo said in a statement on NASA’s COTS program.

Past statements have said the spacecraft could haul a limited crew and 1 ton of cargo into Earth orbit.

Keeping the lid on

An Andrews Space representative would not comment on the firm’s COTS effort, and t/Space officials did not return phone messages. But projects by both companies hint at what their bids may entail.

Andrews Space recently won a U.S. Air Force contract to define architectures for a flexible hybrid launch vehicle capable of sending payloads ranging from 907 kilograms to 27,215 kilograms into various orbits within a 48-hour period.

Published statements on the firm’s Web site indicate that Andrews Space has developed a “family of vehicles that are capable of addressing existing and emerging commercial and government markets.” The firm also studied design requirements for a shuttle alternative vehicle to deliver and return cargo to the ISS under a past NASA-sponsored project.

“Under the contract, Andrews evaluated for recovering cargo as well as transporting up to 48,700 kilograms of cargo per year,” the firm states on its Web site.

Meanwhile, t/Space has been pursuing an air-launched spacecraft to be lofted by a ramped-up version of its QuickReach 2 booster. The firm has said it could build a commercial crew transport by 2008, well before NASA’s intended shuttle retirement date, given the funds.

Whoever wins out in NASA’s COTS competition, there is no shortage of ideas for orbital spacecraft.

“I’m very pragmatic as far as what gets us to affordable space transportation and have no particular predilection towards private or government funding,” SpaceX’s Musk said. “I just want it to happen.”

Comments: tmalik@space.com