WASHINGTON — NASA has agreed to monitor the progress of three more private firms that aim to field new space transportation systems that could carry cargo and/or astronauts to the international space station.

The U.S. space agency announced June 18 that it had signed separate non-reimbursable Space Act Agreements with Constellation Services International (CSI), SpaceDev and Spacehab pledging to provide each of the three with up-to-date technical requirements and specifications for crew and cargo flights to the international space station. Similar agreements were announced in February with Reston, Va.-based Transformational Space Corp. and Chicago-based PlanetSpace Inc.

“This is a significant development,” Scott Horowitz, NASA associate administrator for exploration systems said in a statement. “First there were two, and now there are a total of five private companies cooperating with NASA by dedicating entirely private funding to help establish a robust commercial space transportation industry.”

CSI, SpaceDev and Spacehab all submitted proposals in early 2006 for some of the $500 million NASA plans to spend under the Commercial Orbital Transportation Services (COTS) demonstration program subsiding new space station resupply services. The COTS awards ultimately went to Oklahoma City-based Rocketplane Kistler and El Segundo, Calif.-based Space Exploration Technologies (SpaceX), but SpaceDev, Spacehab and Transformational Space were among the six finalists.

Unlike Rocketplane Kistler’s and SpaceX’s COTS awards, this year’s crop of Space Act Agreements include no financial support. However, NASA has agreed to share information that will help the companies monitor their progress as they seek to develop vehicles that could ferry cargo and crews to the space station.

“It provides a legal mechanism for NASA to give unfunded support and technical assistance. They can provide technical assistance without giving us any money. That is useful,” CSI President Charles Miller said in a telephone interview. “It is also a statement of confidence in the fundamentals of our cargo system.”

CSI’s proposed solution to NASA’s space station cargo needs entails launching a Russian-built cargo container atop a U.S. rocket, such as the Atlas 5. Once in orbit, the cargo container would be retrieved by an unmanned Russian Progress cargo spacecraft already docked to the international space station. The Progress then would transport CSI’s container to the space station to unload its supplies.

The beauty of CSI’s approach, Miller said, is that “99 percent” of the hardware needed for LEO Express already has flown in space. Miller said CSI could be ready to conduct its first demonstration flight by November 2008 provided work on the spacecraft resumes soon. CSI’s development activities are on hold until the company finds a new source of funding.

“We are in a holding pattern. Our next real task is to sign up either customers or investors to advance the development,” Miller said.

CSI has raised and spent roughly $5 million to date, about $3 million of which came from a NASA study contract awarded in 2002 that has since expired. With investors on standby waiting for CSI to sign up a customer for its systems, Miller said he and CSI’s other principals have been doing consulting to bring in revenue.

Spacehab, which did not disclose details about its proposed cargo system, said in a press release that the Houston-based company’s “technical approach utilizes existing flight-proven hardware, significantly reducing technical risk and development costs.”

Spacehab spokeswoman Eva-Marie deCardenas said June 19 that the company’s current concept is different than the Atlas-5 launched Apex system it proposed last year under COTS. She said Spacehab would be “releasing more information on the maturing design shortly.”

Mark Sirangelo, SpaceDev chairman and chief executive, said the Poway, Calif.-based company has continued development of the Dreamchaser crew-and-cargo vehicle with private financing since NASA passed on its COTS proposal last year. Recognizing that NASA was not entirely comfortable with the all-hybrid engine launch vehicle it proposed, Sirangelo said SpaceDev is looking at other launch alternatives, including Atlas 5 and the same five-segment solid-rocket booster Alliant TechSystems is developing for NASA’s Ares 1 crew launch vehicle.

SpaceDev founder Jim Benson, who left the company last year to found Benson Space Co., said the Space Act Agreement is a positive development for SpaceDev.

“Even though this agreement is currently unfunded, such an agreement is a prerequisite to getting funding, which may or may not happen, depending on many constantly changing factors, including the performance of current COTS awardees,” he said.

NASA’s current COTS awardees are required to meet periodic technical, programmatic and financial milestones in order to continue receiving government financial assistance.

Rocketplane Kistler, NASA disclosed June 13, missed its May financial milestone. But the U.S. space agency intends to continue subsidizing Kistler’s development of the K-1 reusable launcher for now. “[Rocketplane Kistler] has made progress in developing its capability and NASA is hopeful the company can complete this milestone with some schedule adjustments,” NASA spokeswoman Beth Dickey said in a statement.

NASA has said it intends to let companies beyond Rocketplane Kistler and SpaceX submit proposals when NASA solicits bids for actual space station resupply services down the road. NASA Administrator Mike Griffin said as recently as March that the agency would solicit such bids in 2009, but Dickey told Space News June 18 that the procurement plan for what the agency is calling COTS Phase 2 still is under consideration.

“NASA has begun preliminary planning efforts associated with COTS Phase 2 procurement. The Commercial Crew and Cargo Program Office and the COTS project have not developed a procurement schedule yet,” Dickey said.