The Intelsat 603 satellite during a 1992 shuttle repair mission. That satellite is based on a bus similar to one that an unnamed government agency, perhaps the NRO, is offering to NASA.

WASHINGTON — NASA is soliciting concepts for payloads that could fly on a mysterious satellite it is in discussions to inherit from another government agency.

NASA issued a request for information (RFI) Feb. 15 for a proposed spacecraft called the NASA Science/Technology Platform Satellite, or NSTP-Sat. The RFI was the first time NASA had publicly discussed such a mission.

The RFI, issued by NASA's science mission directorate, solicits ideas for payloads, including remote sensing instruments and technology demonstrations, which could fly on the spacecraft. The RFI offered few details about the proposed mission, noting NSTP-Sat could fly "to low Earth orbit, geostationary equatorial orbit, medium Earth orbit, Earth-Moon L1, or lunar orbit in the 2021 timeframe."

The RFI, which remains open until March 17, seeks ideas for how this spacecraft could be used to meet NASA's science and technology development goals. The RFI states that NASA will use the responses to determine "whether there are science opportunities for new uses of this spacecraft" and "whether a solicitation for proposals is warranted to enable such opportunities." [Satellite Quiz: What's Up There?]

The RFI offered few details about the spacecraft itself. "The NSTP-Sat is a spacecraft platform that has become available to NASA as excess Government property through an interagency agreement," it stated. It added the spacecraft was a "Boeing GEO spinner bus" that could launch on an EELV-class rocket or as a secondary payload on a Space Launch System mission.

NASA and other organizations involved with NSTP-Sat have been reticent to provide additional details about how NASA gained access to the satellite bus. Alan Zide, a program executive in NASA's heliophysics division and the point of contact listed in the RFI, did not respond to email messages with questions about the satellite.

A diagram of the satellite bus being offered to NASA from the NASA RFI issued in February. (Image credit: NASA)

NASA spokesman Dwayne Brown said March 1 that NASA is in discussions with the U.S. Air Force to obtain the bus. "NASA and the U.S. Air Force (USAF) are in discussions concerning the transfer of a satellite bus that the USAF has determined does not meet current or projected Air Force mission requirements," he said.

U.S. Air Force spokeswoman Capt. AnnMarie Annicelli said March 2 she was not familiar with the satellite and was looking into it, but has not provided any additional information. When asked who the original customer was for this Boeing-built satellite, Addrian Brooks, a spokesman for Boeing Network and Space Systems, said March 2 that the company was "unable to disclose this information."

Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics who specializes in space history, notes the dimensions for the satellite provided in the RFI are consistent with two versions of satellites built by Hughes Space and Communications. One, the HS-389, was used for the Intelsat 6 series of satellites, while the HS-393 was sold to other commercial customers. Those satellites were built and launched in the late 1980s and early 1990s. Boeing acquired Hughes Space and Communications in 2000.

The National Reconnaissance Office (NRO), he noted, is thought to have used the same bus for a series of data relay satellites operating under the code name QUASAR, also known as the Satellite Data System (SDS). Four such satellites launched from 1989 through 1996.

Spin-stabilized satellites have fallen out of favor, having been replaced by three-axis stabilized satellites. The last Boeing-built commercial spin-stabilized satellite, a Boeing 376 spacecraft called e-BIRD, launched in 2003.

McDowell said a later generation of QUASAR satellites, launched from 1998 to as recently as 2014, were also assumed to be three-axis stabilized. However, he noted there’s little known about this series of satellites, leaving open the possibility it also used the same bus as the earlier spacecraft.

"It's possible that some other NRO program also used this bus, but QUASAR/SDS is definitely the most likely," he said in a March 3 email.

If the satellite in question is indeed from the NRO, it would not be the first time NASA inherited spare hardware from that intelligence agency. In 2012, NASA announced it was taking possession of two 2.4-meter mirror assemblies from the NRO. The mirrors were reportedly built for NRO's Future Imagery Architecture program, and became surplus when the NRO cancelled the optical portion of that program in the mid-2000s.

NASA, after taking possession of the mirrors, solicited ideas from the scientific community on how to use what it called Astrophysics Focused Telescope Assets. NASA decided to use one of the mirrors for the Wide Field Infrared Survey Telescope (WFIRST), which originally planned to build a much smaller mirror. WFIRST is planned for launch in the mid-2020s.

Phillip Swarts contributed to this story.

This story was provided by SpaceNews, dedicated to covering all aspects of the space industry.