WASHINGTON — NASA is taking preliminary steps toward buying replacements for the constellation of Tracking and Data Relay Satellites (TDRS) it relies on to communicate with the space shuttle and nearly two dozen other spacecraft in low Earth orbit.

NASA’s Goddard Space Flight Center issued a request for information Nov. 2 seeking input from companies interested in building two replacement satellites, dubbed TDRS-K and TDRS-L, that would be launched respectively in 2011 and 2012. Options under the contract NASA intends to award by the end of 2007 would cover two additional satellites, TDRS-M and TDRS-N, that would be launched in 2015 and 2016 respectively.

Robert Spearing, NASA deputy associate administrator for space communications, said all nine TDRS satellites the U.S. space agency has launched since the start of the space shuttle program are still in orbit, though many are showing their age.

The oldest TDRS, he said, is in a state of semi-retirement, used only to support the U.S. National Science Foundation’s Antarctic research operations. The other two TDRS satellites NASA launched in the 1980s are still in service, but are both one failure away from retirement. Spearing said NASA does not expect them to last beyond another two or three years.

The TDRS constellation currently includes two spare satellites, one of which, Spearing said, will be pressed into duty in 2007.

Spearing said NASA needs to have at least seven TDRS spacecraft in service to meet its current and projected demand.

Space Shuttle Challenger launched the first satellite, TDRS- A, in 1983, and was carrying TDRS- B on Jan. 28, 1986, when it was destroyed on launch. The two newest TDRS satellites were launched in 2002 on Atlas 2 rockets.

About 20 spacecraft, including the shuttle and the international space station, depend on TDRS for tracking and data relay support, according to Spearing. The system also supports commercial launches and will be used by Ares 1 and the Orion Crew Exploration Vehicle in the coming years.

The U.S. Defense Department is also a heavy user of TDRS services.

TDRS is the responsibility of NASA’s Space Operations Mission Directorate, the $6.2-billion-a-year enterprise that funds the space shuttle and international space station programs.

Operating and maintaining the TDRS system costs NASA roughly $100 million a year. The Defense Department, however, reimburses NASA for about three-quarters of that annual tab, Spearing said.

NASA’s 2007 budget request, currently awaiting the approval of Congress, includes no money for buying new TDRS satellites.

Spearing said NASA has asked the White House to include TDRS money in the 2008 budget request, which is due to be submitted to Congress in February.

If the TDRS money is included in the request, Spearing said, NASA would expect to issue a formal request for proposals in late winter or early spring and award a contract by the end of the year.

The coming TDRS competition would be the first since 1995 when Boeing Satellite Systems beat incumbent TRW Space and Electronics — now Northrop Grumman Space Technology, Redondo Beach, Calif. — to win a $485 million delivery-on-orbit contract for TDRS-H, TDRS-I and TDRS-J.

Boeing plans to compete for the upcoming TDRS contract.

“Given that we built the last three, we would be highly interested in any TDRS work we can obtain,” said Diana Ball, a spokeswoman for Seal Beach, Calif.-based Boeing Space and Intelligence Systems, which encompasses Boeing’s satellite business.

Denver-based Lockheed Martin Space Systems also plans to pursue the TDRS contract.

“At this point, we do intend to pursue the TDRS opportunity as a prime contractor and will leverage our proven experience in building advanced satellite communications systems for both government and commercial customers worldwide,” Lockheed Martin spokesman Steven Tatum wrote in a Nov. 20 e-mail.

Northrop Grumman Space Technology was less explicit about its intentions. “We responded to the RFI,” Northrop Grumman spokesman Bob Bishop said.

NASA initially refused to take possession of the first Boeing-built satellite, TDRS-H, because it had been launched with a faulty phased array antenna. The satellite otherwise worked fine, Spearing said, but did not deliver on the promised signal strength improvement over the original TDRS satellites. NASA ultimately accepted the satellite after Boeing agreed to refund the agency $35 million.

Boeing also had a problem with TDRS-I, which launched in March 2002. The satellite spent a few months short of its intended orbit while Boeing engineers devised a solution to a malfunction that had trapped half the satellite’s fuel in an unpressurized tank. Spearing said the only lasting impact was late arrival to its desired orbit. “But it went into storage, so it really didn’t matter.”

According to the NASA request for information, the agency wants the new TDRS satellites built to last at least 11 years. One notable change from the last TDRS procurement is that this time NASA is making the inclusion of a Ka-band frequency a firm requirement instead of just an option.

The document also notes that timely delivery of the replenishment satellites is critical.

“In order to ensure sufficient flight assets are available to support the user community, it is critical to the TDRS Program that TDRS-K and TDRS-L launch in 2011 and 2012,” the document says. “To this end, NASA may consider financial incentives for enhanced performance, early deliver, on-orbit life, etc.”

Spearing would not say what NASA expects to spend for the new TDRS satellites. The last three cost collectively about $800 million to build and launch. But, he noted, satellites and launches have not gotten any cheaper since the 1995 TDRS buy.

“That particular contract was signed back in the heyday of the construction of commercial communications satellites. The agency got a very good deal. I doubt we would see that good of deal in the future.”

Brian Berger is editor in chief of SpaceNews.com and the SpaceNews magazine. He joined SpaceNews.com in 1998, spending his first decade with the publication covering NASA. His reporting on the 2003 Space Shuttle Columbia accident was...