This artist rendering shows the TRMM satellite orbiting over a hurricane's eyewall.
Image Credit: NASA

On Monday June 15, 2015, at 11:55 p.m. EDT, an Earth-observing satellite, has ended its long-lasting mission with a fiery re-entry into the atmosphere over the South Indian Ocean. However, the Tropical Rainfall Measuring Mission (TRMM) spacecraft hasn’t completely disintegrated and NASA’s Orbital Debris Program Office estimates that even 12 components of the satellite survived the re-entry and fell to Earth.

But should we worry that some of the spacecraft’s pieces would hit someone on the ground? NASA becalms the public, issuing statement in which the agency calculates that the risk of

anyone in the world being injured by TRMM debris is approximately 1 in  4200. NASA, after conferring with the U.S. Government and some foreign space agencies even limited the risk to less than 1 in 10,000. That is a relatively very low chance.

The objects that probably fell to Earth include, for example: two propellant tanks, a nitrogen pressurant tank and four Reaction Wheel Assembly flywheels. Surviving objects are metallic (titanium alloys), and are not toxic. Total mass of the pieces expected to survive is about 247 lbs. (112 kg).

“Any sightings of suspected TRMM debris should be reported to local authorities. Debris could have sharp edges and should not be touched or handled, in the unlikely event someone were to find TRMM fragments,” NASA warned.

It’s worth adding that since the beginning of the space age, there has been no confirmed report of an injury resulting from reentering space objects.

The last NASA spacecraft to re-enter Earth’s atmosphere was the Upper Atmosphere Research Satellite (UARS) in September 2011. More recently, on May 8, 2015, the Russian Progress M-27M cargo craft re-entered over the Pacific Ocean, as a result of the problems encountered shortly after the launch.

TRMM, jointly built by NASA and the Japan Aerospace Exploration Agency (JAXA), was launched in 1997 to study rainfall for weather and climate research. However, the satellite exceeded all the expectations, operating for 17 years.

In 2001, the mission was given extensions until 2005, when residual propellant would reach the minimum required for controlled reentry from 400 km altitude.

After considerable analysis and review, TRMM was relieved of the controlled reentry requirement to prolong its mission until the Global Precipitation Measurement (GPM) spacecraft could be launched (then predicted to be 2010, actually launched in February 2014). Rationale was that TRMM, through its hurricane tracking and other capabilities, had the potential to save lives, out-weighing the risk of human casualty from uncontrolled reentry.

NASA ceased station-keeping maneuvers of TRMM near the end of the spacecraft’s fuel supply in July 2014. The instruments on the satellite were finally turned off on Apr. 8, 2015 and the spacecraft began to slowly descend from its orbit.

TRMM has provided critical precipitation measurements in the tropical and subtropical regions of our planet. It has delivered crucial information to tropical cyclone forecasting, numerical weather prediction, and precipitation climatologies, among many other topics, as well as a wide array of societal applications.

NASA said that the TRMM dataset will continue to be used for research to improve global weather and climate models. “The data meet exacting standards for data preservation, so that future scientists will be able to use the data. The dataset also is being processed to make up one continuous climate data record with the follow-on GPM, also a joint project between the U.S. and Japan,” the agency noted.

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