A long-serving Earth observation satellite has succumb to a fiery demise via an uncontrolled destructive re-entry on Tuesday. The Tropical Rainfall Measuring Mission (TRMM) spacecraft – a joint mission of NASA and JAXA – re-entered Earth’s atmosphere at 03:55 am UTC, according to the US Strategic Command’s Joint Functional Component Command for Space.
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The destructive End Of Mission (EOM) events concluded the lifetime of a spacecraft that surpassed all expectations.
The spacecraft had a design lifetime of three years but soldiered on for a total of 17 years, providing a wealth of valuable scientific data since its launch in November 1997 on a Japanese H-II rocket.
The joint mission between NASA and JAXA studied rainfall for weather and climate research before the mission finally came to an end on April 15, 2015.
Work in this field has since been taken up by more powerful spacecraft, such as the Global Precipitation Measurement constellation.
TRMM carried five instruments, with a package consisting of three sensor rainfall suite (PR, TMI, VIRS) and two related instruments (LIS and CERES).
“The TRMM dataset became the space standard for measuring precipitation, and led to research that improved our understanding of tropical cyclone structure and evolution, convective system properties, lightning-storm relationships, climate and weather modeling, and human impacts on rainfall,” noted NASA in an epitaph to the spacecraft.
“The data also supported operational applications such as flood and drought monitoring and weather forecasting.”
The spacecraft fate was known well in advance, with the US Space Surveillance Network, operated by the Department of Defense US Strategic Command’s Joint Space Operations Center (JSpOC), closely monitoring TRMM’s descent from orbit.
Predicting an uncontrolled re-entry requires a large amount of refining, as seen with the recent demise of the Russian Progress M-27M spacecraft. Officials closed in on the expected area the TRMM spacecraft, but were still unable to provide an accurate entry point with just hours remaining.
“Although the exact location of the re-entry cannot be predicted, TRMM’s orbit only brings it over the tropics between 35 degrees North latitude and 35 degrees South latitude. Europe, Russia and most of North America and Japan are outside of the potential re-entry area,” added NASA.
An expected Entry time of around midnight proved to be three hours wide of the margin, with confirmation of the spacecraft’s entry noted at 03:55am UTC, in an entry corridor over the South Indian ocean.
NASA’s Orbital Debris Program Office estimated 12 components of the TRMM spacecraft could survive reentry. The chance that one of these pieces would strike someone is approximately 1 in 4,200, which is a relatively low chance.
Of the spacecraft’s total mass (about 5,800 lbs.), 96 percent would not reach Earth. The pieces of TRMM expected to survive re-entry are made of titanium or stainless steel – with no toxic materials involved.
The last NASA spacecraft to re-enter was the Upper Atmosphere Research Satellite (UARS) in September 2011. UARS was a much larger satellite than TRMM and NASA received no reports of surviving debris.
NASA takes the risks involved very seriously, as seen via a study conducted in 2011 where a NASA team held a Special Safety Topic review into the hazards posed by space hardware fragmentation during re-entry, with the aim to apply mitigation to any potential risks from hardware breaking up and surviving entry – in turn threatening human life on the ground.
“As we progress forward with future programs, we should keep in mind that in systems engineering the definition of a System Life Cycle includes not just deployment and operation but also retirement and disposal,” a presentation from the meeting (available on L2) noted.
Several examples of hardware entering and surviving the extreme heat and aerodynamic stresses – which usually destroys returning hardware – are cited, starting with Apollo 13’s Lunar Module in April 1970.
“The Aquarius LEM re-entered Earth’s atmosphere after having served as a lifeboat for the Apollo 13 crew. Mounted on the LEM descent stage, was a SNAP-27 (System For Nuclear Auxiliary Power) RTG (Radioisotope Thermoelectric Generator) which contained 8.3 lbs (3.9 kg) of Plutonium-238,” added the presentation.
“Re-entry was at 122 km above the South Pacific Ocean near the Fiji Islands. High and low altitude atmospheric sampling in the area indicated there was no release of plutonium, so the graphite fuel cask is assumed to have survived re-entry and now resides on the bottom of the Tonga Trench in 6 to 9 km of water.”
“COSMOS – A Soviet surveillance satellite that used a nuclear reactor for power (~50 kg of Uranium-235). By design, at the end of the satellite’s life, the reactor was supposed to separate and be boosted to a high parking orbit.
“COSMOS-954’s reactor failed to separate and when it re-entered, pieces of the satellite fell over a sparsely populated section of the North West Territories in Canada. 12 large pieces were recovered. Some were highly radioactive (less than 1 percent of the fuel was recovered).”
The presentation also notes that in 1983, COSMOS-1402 landed in the Indian Ocean, while in 1988, COSMOS-1900 landed in the Atlantic Ocean.
The third example shown related to the US station Skylab, which had originally hoped for an orbital reboost from an early space shuttle mission, prior to an eventful re-entry in July of 1979, which resulted in large pieces of hardware surviving.
“Increased solar activity, along with shuttle delays prevented any possibility of a reboost of the 90.6 ton space station. JSC (Johnson Space Center) controllers commanded Skylab into a tumble, hoping this would increase the amount of disintegration upon re-entry.
“Large chunks of debris were spread over a 100 mile long strip of land near Perth, Australia.”
The Russian’s own space station also suffered the fate of re-entry, as MIR saw its life ended in 2001. However, while pieces of the station survived, all the hardware followed a pre-planned disposal corridor over the southern Pacific Ocean.
“Entry was East of Australia, over the southern Pacific Ocean. Approximately 1,500 pieces of debris weighing 50 tons may have survived, including pieces as heavy as a small car.”
Other examples include an incident during Columbia’s STS-75 mission, when the Tethered Satellite System (TSS) was to be deployed to a distance of 12 miles to place the TSS into the rarefied electrically charged layer of the atmosphere known as the ionosphere.
As described in Chris Gebhardt’s overview of Columbia’s service and missions, it was hoped that the TSS would generate high voltage and electrical currents as it moved through the ionosphere and across the magnetic field lines of Earth.
Deployment of the TSS proved successful at first. But just before the TSS reached full deployment, the tether snapped and the TSS was lost. It remained in orbit for several weeks before finally re-entering Earth’s atmosphere.
“During the STS-75 mission, with the TSS at 19.6 km (of a planned 20 km deployment), the tether broke due to a break down in insulation, short and subsequent melting of the cable,” added the presentation.
“At this point the 518 kg TSS became a free-flying satellite (trailing a very long tail). While the satellite and tether did not pose a hazard to the ground, there was pre-flight concern that should the tether break, it could pose a re-contact risk to the orbiter.
Her loss resulted in additional work on computer models related to the mitigation of public risk for spacecraft debris.
“In the vicinity that debris fell, there are an average of 85 inhabitants per square mile. In the aftermath of the accident, NASA pursued the development of computer tools to predict the survivability of spacecraft debris during re-entry to help assess public risk. Entry paths were modified to mitigate the risk posed by the over flight of densely populated areas.”
The final example cited was USA-193 – also known as NRO launch 21 – was a military spy satellite launched on December 14, 2006 – the first launch of the then newly formed United Launch Alliance (ULA), via a Delta II launch vehicle.
Unfortunately, the satellite malfunctioned shortly after deployment,and was intentionally destroyed 14 months later on February 21, 2008, by a modified SM-3 missile fired from the warship USS Lake Erie, stationed west of Hawaii.
“Shortly after launch, all communication with a 5000 lbs, classified, US experimental radar reconnaissance satellite, was lost. The decision was made to destroy the satellite to prevent larger pieces from reaching the ground,” the presentation noted.
“The primary reported concern was contamination should the onboard hydrazine tank survive to the ground. A secondary concern was the classified nature of any hardware that did make it to the ground.
“A SM-3 missile was fired from the USS Lake Erie in the Pacific Ocean. The impact caused the satellite to break into more than 80 pieces, which at its orbital altitude (150 miles) , was expected to have a short lifetime (24-48 hours for most debris, with some not entering for 40 days).”
As NASA aim to control debris both in space and from surviving entry, the presentation noted that the International Space Station (ISS) has provided additional insights – from the standpoint of what they jettison from the orbital outpost.
“As the ISS program progressed, it became apparent that there needed to exist a standard policy for the jettison of hardware. Reasons for jettison could include: Safety issue for return (contamination, material properties, etc.). On-orbit stowage return manifest. EVA timeline savings. Hardware is designed to be jettison (ex. micro-sat).
As noted in flight rules (FR B4-104) for jettisoning hardware, “Whenever possible, hardware will be jettisoned from the ISS in a retrograde direction.”
This allows controllers on the ground to analyze the expected relative motion and ensure the jettisoned item cannot pose a collision hazard to the ISS. USSTRATCOM are notified by NASA – and if available, a state vector is provided.
According to the Special Safety Topic meeting’s findings, the key to providing additional mitigation against risks to the public will be found via improving computer models on how hardware is expected to disintegrate during entry.
“Improving re-entry fragmentation models can help ensure that planned (or contingency) disposal of on orbit hardware does not pose a hazard to the public. For first entry of new program (unproven) hardware, tracking and interception help to ensure a safe trajectory and provide confirmation of the above models.”
On the whole, no risks are associated with re-entering vehicles, given the tight pre-planned disposal corridors. The mitigation – however – will provide a safety net for those vehicles which may suffer an issue and an uncontrolled re-entry, such as the incident with the Progress M-27M.
(Images: Via the cited presentation – available on L2, plus ESA and NASA TV.)
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