The uncontrolled tumble of Phobos-Grunt into Earth's atmosphere is being eyed as a possible way to sharpen computer tools to more accurately calculate re-entry predictions.
Russia’s troubled Phobos-Grunt probe, stuck in the wrong orbit for more than a month, appears to be headed for a fiery and uncontrolled fall back to Earth early next month.
Tracking experts are predicting that Phobos-Grunt will re-enter Earth's atmosphere on Jan. 9, 2012, but at present, the forecast includes an uncertainty of plus or minus 5 1/2 days. Some analysts are even suggesting that the spacecraft could see its demise as early as Jan. 1 or 2.
Meanwhile, the uncontrolled tumble of Phobos-Grunt into Earth's atmosphere is being eyed as a possible way to sharpen computer tools to more accurately calculate re-entry predictions.
That option would fall under the Inter-Agency Space Debris Coordination Committee. The IADC is an intergovernmental agency that coordinates research related to orbital debris in space, as well as man-made objects that re-enter the atmosphere.
"IADC is considering to adopt Phobos-Grunt as an IADC re-entry test object," said Heiner Klinkrad, ESA’s senior space debris expert and head of the European Space Operations Center’s Space Debris Office in Darmstadt, Germany. "A final decision, in accordance with IADC’s terms of reference, still needs to be taken," he told SPACE.com.
Since 1998, the IADC has performed re-entry prediction tests. Data-sharing between countries has helped hone skills to more precisely calculate the re-entries of spacecraft, rocket stages and even discarded hardware from the International Space Station.
Over the years, a number of targets have been used for IADC re-entry campaigns.
If Phobos-Grunt is a new target, it will be the third tracking campaign in 12 months — a record for the IADC. This year the agency monitored the uncontrolled re-entry of NASA’s defunct Upper Atmosphere Research Satellite on Sept. 24, followed by the downfall of Germany’s dead Roentgen Satellite (ROSAT) on Oct. 23.
The Phobos-Grunt spacecraft tips the scale at nearly 14 tons. The probe is full of several tons of propellant — a hefty load of toxic hydrazine and nitrogen tetroxide fuel. This propellant, which would have sent Phobos-Grunt toward Mars, was left unused after a malfunction with the probe's engines stranded it in Earth orbit instead.
Phobos-Grunt was designed to land on Phobos, one of two moons circling the Red Planet. The ambitious mission was slated to gather rock and soil samples from Phobos and return them to Earth in 2014.
But after being boosted into space on Nov. 8 (Nov. 9 in Moscow), the craft failed to send itself toward Mars. Russian, European and U.S. space network antennas were mobilized in hopes of salvaging the marooned probe, but flight controllers have struggled to regain control of Phobos-Grunt.
These rescue attempts now seem to be solely the responsibility of the Russians as they continue to try to communicate with Phobos-Grunt.
In a Dec. 8 open letter to Phobos-Grunt colleagues, Lev Zelenyi, director of the Space Research Institute in Moscow and chairman of the Russian Academy of Sciences’ Solar System Exploration Board, said:
"Lavochkin Association specialists will continue their attempts to establish connection with the spacecraft and send commands until the very end of its existence. We are working nevertheless on the issue of reentry and probability of where and which fragments may hit the ground (if any.)"
Debris analysts in the U.S. point to Russian statements that the propellant tanks onboard Phobos-Grunt are made of aluminum, not heat-resistant titanium. As such, any propellant — frozen or unfrozen — should "burn up" or dissipate during the re-entry process.
But according to comments from Viktor Khartov, the head and chief designer of NPO Lavochkin, the Russian aerospace company that designed and manufactured Phobos-Grunt, components of the spacecraft are expected to reach the Earth’s surface — including the probe’s sample-return capsule.
The nose cone-shaped hardware was designed to transport specimens of Phobos to Earth, and it was built to speed through Earth’s atmosphere and make a crash- landing at a recovery site, without a parachute.
Lessons from ROSAT
Still to be seen is how Russian space officials plan to advise the public regarding the death throes of Phobos-Grunt and what leftovers might reach Earth’s surface.
"After ROSAT came down over the Indian Ocean … there was widespread relief," said Johann-Dietrich Wörner, chairman of the executive board of the German Aerospace Center, which is headquartered in Bonn.
In a recent blog entry, Wörner noted that ROSAT carried an X-ray telescope with heat-resistant components. This encouraged the view that larger parts could survive re-entry, he said, and might pose a risk to people and objects on the ground.
Wörner added that he personally drew a number of lessons from the conclusion of the ROSAT mission:
"It seems unlikely that Phobos-Grunt will somehow be rescued at this point," said T.S. Kelso, a senior research astrodynamicist for the Colorado Springs-based Center for Space Standards & Innovation, a research arm of Analytical Graphics Inc.
"The last efforts were tied to a period where the orbit [of Phobos-Grunt] would have the spacecraft in sunlight throughout its orbit, raising hopes that it might have the power necessary to establish communications," Kelso told SPACE.com. "But given the large dishes they've used in this effort and the lack of communications, we're left to await yet another re-entry."
"I hate to say it, but we're already working the 'death' watch here," he said. "The bottom line is that there is very little chance of anything reaching the ground and even if it did, it would likely do so over some ocean."
Risk to the public?
So, with the prospect of a third large spacecraft falling to Earth within the span of about four months, should the public be concerned?
"People should not panic. Space debris is re-entering all the time, including fairly large rocket bodies," said Michael Listner, a space law attorney based in New Hampshire. "However, the public should not be completely dismissive of the threat that space debris poses, either."
Listner observed that ROSAT, for example, fell just short of the Asian continent and landed in the Bay of Bengal. He also recalled the incident in 1978 involving the former Soviet Union's nuclear-energized Cosmos 954 that hurtled into a wilderness area of Canada. [Worst Space Debris Events of All Time]
The clean-up operation from that fall was a coordinated event between the United States and Canada, with an estimated recovery of about 0.1 percent of Cosmos 954's power source.
"If that spacecraft had completed just a couple of more orbits it may have landed in the continental United States," Listner said. "There was also the incident with [NASA’s] Skylab where debris from the falling space station fell onto the Australian town of Esperance."
What we don't know
"One of the uncertainties surrounding Phobos-Grunt is the lack of hard technical information about the spacecraft," Listner said. "If Roscosmos provided hard data about the construction of the spacecraft, including the construction of the propellant tanks, it might allay concerns about the danger the spacecraft poses."
There is some question about the Chinese orbiter Yinghou 1 — a hitchhiking payload attached to Phobos-Grunt. There is little, if any, technical data about its construction and composition, including any potentially hazardous materials that might survive re-entry, Listner said.
"There is a lot of talk about international cooperation, and, in fact, the U.S. Strategic Command’s Joint Space Operations Center is providing Roscosmos with orbital information via a transparency and confidence-building measure signed by the United States and the Russian federation specifically for the purpose of providing such information for space situational awareness," Listner said.
The signed measure was a result of discussions that arose following the collision of a U.S. satellite and Russian satellite in February 2009, Listner said.
"It would stand to reason that a situation such as the Phobos-Grunt re-entry would call for further transparency between the nations involved, including technical data/assurances relating to the spacecraft," Listner concluded.
Leonard David has been reporting on the space industry for more than five decades. He is a winner of this year's National Space Club Press Award and a past editor-in-chief of the National Space Society's Ad Astra and Space World magazines. He has written for SPACE.com since 1999.