Bowing to political pressure, NASA once again is considering flying a high-priority greenhouse gas sensor on a satellite dedicated to that mission.

In the summer of 2003, at the conclusion of an international Earth Observation Summit hosted by the U.S. State Department, NASA announced that it would be accelerating the development of an aerosol polarimeter sensor and launching it on a dedicated satellite in 2007.

The sensor was already under development for the next generation of military and civilian polar-orbiting weather satellites slated to launch around the end of the decade, but NASA officials said at the time that the new mission, dubbed Glory, would speed the introduction of the new observation capability by at least a couple of years.

Glory also was supposed to be equipped with a second instrument, the Total Irradiance Monitor, that would continue the observations being made by another NASA science satellite launched earlier that year, the Solar Radiation and Climate experiment, or SORCE. Together the two instruments were meant to improve the scientific understanding of whether human activities or natural climate variability are more to blame for global warming.

Since announcing the Glory mission in the summer of 2003, NASA’s science budget has come under increased pressure from the mounting costs of preparing the space shuttle fleet for a return to flight and new space exploration-driven priorities, which include building a new vehicle to return astronauts to the Moon by 2020.

NASA announced in February that it was canceling the Glory climate-monitoring satellite mission but would continue development of the spacecraft’s main instrument, the Aerosol Polarimetric Sensor, with the intent of finding some way short of building and launching a dedicated satellite to fly the instrument.

Practically speaking NASA’s decision meant the climate observations it identified as a high priority less than two years ago would have to wait at least until the launch of the first spacecraft in the National Polar-orbiting Operational Environmental Satellite System (NPOESS) officially slated for late 2009, although widely expected to slip to 2011 or later.

Scrapping the Glory mission and adding another science instrument to NPOESS did not sit well with some lawmakers in the U.S. House of Representatives and Senate. Since late last year, at least five lawmakers have written NASA urging it to proceed with the Glory mission, including House Science Committee Chairman Sherwood Boehlert (R-N.Y.) and Rep. Frank Wolf (R-Va.), the chairman of the House Appropriations science, state, justice and commerce subcommittee. Wolf’s Northern Virginia congressional district is home to Orbital Sciences Corp., the Dulles, Va.-based company that would build and launch the dedicated Glory satellite.

Sens. George Allen and John Warner, both Virginia Republicans, also have sent letters to NASA in support of Glory, as has Sen. Barbara Mikulski, a Maryland Democrat who would like to see the Greenbelt-based Goddard Space Flight Center proceed with the climate-monitoring mission.

NASA has yet to execute an about face on Glory, but the agency’s associate administrator for science, Al Diaz, told the House Science Committee during an April 28 Earth science hearing that work would continue at Orbital Sciences on the Glory spacecraft bus — a leftover from the long-canceled Vegetation Canopy Lidar mission — for the time being.

Mike Luther, director of the mission and systems management division within NASA’s Science Mission Directorate and the agency’s primary liaison to the NPOESS program, said in a May 5 interview that NASA expects to decide in June whether to proceed with Glory as a standalone mission or proceed with plans to launch the aerosol instrument on NPOESS.

Luther did not mention the political pressure NASA is under to finish and launch Glory, but said that NASA was keeping the Glory option open while it evaluates technical and timing considerations involved in flying the aerosol polarimeter on NPOESS.

A recent National Research Council report, “Earth Science and Applications from Space: Urgent Needs and Opportunities to Serve the Nation,” questioned the feasibility of relying on NPOESS to host instruments from a small but growing number of canceled or scaled back NASA science missions, and called on the space agency to commission an independent review before canceling the Glory mission.

A congressional aide following the Glory program said NASA’s February decision to cancel the mission was driven by budget pressures, pure and simple. The mission is expected to cost about $190 million, including launch on a Pegasus or Minotaur rocket. The aide said that while there are certainly parochial reasons for lawmakers to pressure NASA to proceed with the Glory mission, there are also sound scientific reasons.

Scientists would like to see Glory on orbit by 2008 – early enough to overlap with the SORCE mission and in time to observe Solar Minimum, an extreme in the sun’s 11-year activity cycle. The congressional aide said Glory, as envisioned, would help shed light on how much global warming is attributable to human factors such as pollution and natural climate variability caused by the sun.

“This is one of the largest uncertainties of climate change and these measurements were supposed to be a priority for informing rationale decisions for climate policy,” the congressional aide said. “NASA itself said this is a priority for climate change research. The only reason they are punting is because, like everything else having to do with science, something had to get squeezed.”

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