The future of NASA’s Tropical Rainfall Measuring Mission (TRMM) — whether it will be turned off this year — is expected to be decided in the month ahead. NASA announced at the start of hurricane season last year that it planned to turn off TRMM to save fuel for an eventual deorbit burn designed to drop the satellite into an uninhabited stretch of the Pacific Ocean. NASA also said it needed to save the $4 million a year it costs to keep the satellite in service.

Pushback from the science community and some members of Congress prompted NASA to keep operating the research satellite, which has proven useful to storm trackers, through the 2004 hurricane season. Early this year, NASA again extended TRMM operations, this time until June 15.

The $650 million environmental satellite is almost eight years old but has no major problems save one: it is fast approaching the point where continued operations will make a controlled re-entry impossible.

According to NASA’s calculations, TRMM must have at least 138 kilograms of propellant on board to perform a series of deorbit burns designed to drop the satellite into the ocean. Every time TRMM fires its thrusters to maintain a stable position in orbit, it consumes propellant. TRMM is expected to reach the 138-kilogram fuel threshold in August.

Proponents of keeping TRMM in service, however, want NASA to forget about a controlled ocean disposal and instead allow the satellite to re-enter the atmosphere on its own many years from now. TRMM, these proponents believe, is in good enough shape to remain in service at least until the first of the proposed Global Precipitation Measurement satellites are launched around 2010.

While operating TRMM beyond this August would require NASA to waive its own safety requirements, TRMM supporters point out that NASA’s top safety official, Bryan O’Connor, reviewed the TRMM disposal plan in 2002 and concluded that the added risks of an uncontrolled re-entry were minor and “appear to be reasonable” when weighed against the public safety benefit of improved storm analysis and tracking.

NASA Goddard Space Flight Center Director Edward Weiler cited the O’Connor memorandum when he wrote NASA Headquarters in March in support of waiving TRMM’s controlled re-entry requirement and keeping the satellite in service beyond this summer, provided the mission passes muster with a senior review team looking at the costs and benefits of extending TRMM and several other Earth science missions that have lasted longer than planned.

NASA spokeswoman Erica Hupp said NASA will decide what to do about TRMM once the senior review is completed in mid-June.

“We plan to make a decision based on its recommendations and the outcome of our discussion with” the National Oceanic and Atmospheric Administration (NOAA).

NOAA, however, has decided not to take over ownership of TRMM.

NOAA Administrator Conrad Lautenbacher told reporters in mid-April that his agency would not be assuming responsibility for the satellite, even though NOAA has started using TRMM observations to improve hurricane and typhoon tracking.

Al Diaz, NASA associate administrator for science, informed NASA Administrator Mike Griffin around the same time that NOAA was not interested in taking over the satellite. Diaz also informed Griffin that he would not be seeking a waiver to the TRMM controlled re-entry requirement and would be terminating TRMM science operations this summer in preparation for an eventual deorbit burn.

Under that plan, NASA would allow TRMM’s orbit to naturally decay over two years before firing the thrusters to drop the spacecraft in the ocean.