Phobos-Grunt: “Re-entry is now imminent”

The BBC’s spaceman, Jonathan Amos, reports on the imminent re-entry of the 13-tonne failed Russian Mars probe, Phobos-Grunt.  Included in that 13-tonnes are more than 10 tonnes of fuel which is expected to explode when the aluminium storage tanks rupture during re-entry.  From the BBC report

The Russian space agency says little of the probe will survive to the surface.

It calculates no more than 200kg in maybe 20-30 fragments.

Precisely where on the Earth’s surface – and when – this material could impact is impossible to say, however. There are huge uncertainties in forecasting the final moments of a re-entry.

“The major uncertainty for prediction is the atmospheric density the spacecraft encounters in orbit, but it’s also due to the orientation of the vehicle as it comes in,” explained Prof Richard Crowther, the UK Space Agency’s chief engineer.

“It can very quickly tumble and if pieces break off – that all changes the trajectory and where debris might impact.”

Spaceflight 101 has more specific details on the predicted re-entry later today.  And they also have more details on the re-entry process.

One component that will survive re-entry and impact the ground is the Entry capsule that was specially designed to bring soil from Phobos back to Earth. Also inside the 7.5-Kilogram Capsule are bacteria, fungi and other microorganisms. All organisms that are part of the LIFE Experiment are not harmful to humans. It is expected that the entry module will make it to Earth’s surface as intended after being separated from the vehicle during the destructive entry process.

No other items that will likely survive Re-Entry have been noted, however it is known that about 20% to 40% of a re-entering satellite’s components reach Earth. Taking under consideration that Russian Spacecraft are usually built in a more robust fashion than other vehicles – for example US Satellites, the possibility of components other than the re-entry module surviving the Environment during amtospheric entry increases.

Also taking into account that all Propellants explode upon Re-Entry, around 475 to 950 Kilograms of Phobos-Grunt Debris could reach the ground.

Phobos-Grunt is carrying a small amount of radioactive Cobalt-57 Isotopes as part of a Spectrometer Instrument that was supposed to analyze samples on Phobos. Experts do not expect that any radiation could survive Re-Entry and cause problems on Earth. Russian Officials have admitted that 20 to 30 individual pieces weighing no more than 200 Kilograms are expected to reach the ground.

The big unknown is the Chinese Yinghuo 1 Spacecraft that hoped to hitch a ride to Mars on-board Phobos-Grunt. China has not released detailed technical information on any toxic or dangerous satellite components. More information on Yinghuo 1 can be found here.

Let’s be careful out there…

Update  Looks like it came down somewhere over the South Pacific, always the most likely target…  From the updated BBC report

The spacecraft’s last orbit took it over Japan, and the Solomon Islands, and to the east of Australia and New Zealand. Conflicting reports then had the final re-entry point across a great swathe of the Southern Ocean. Certainly, it seems Phobos-Grunt was down and destroyed before it could have passed over Chile.

The Russian space agency (Roscosmos) had estimated that no more than 200kg of the original 13-tonne launch mass of Phobos-Grunt would survive the destructive forces of a dive to Earth.

“According to information from mission control of the space forces, the fragments of Phobos-Grunt should have fallen into the Pacific Ocean at 1745 GMT,” space forces spokesman Alexei Zolotukhin told the Interfax news agency.

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