Phobos-Grunt Likely to Reenter January 14-16 EST

Predicting when Earth-orbiting objects will reenter the atmosphere is a tricky business, but at the moment, January 14-16 Eastern Standard Time (EST) is likely to be the window when Russia’s Phobos-Grunt spacecraft will meet its end.

Phobos-Grunt (Phobos-soil) was intended to return to Earth a sample of the Martian moon Phobos as well as drop off a small Chinese satellite to orbit Mars.   It successfully reached Earth orbit on November 8, 2011 EST, but its upper stage never fired to send it on its way to Mars.  The reason for the failure remains a mystery.

The European Space Agency (ESA) assisted Russia in trying to contact the probe and succeeded initially.  After two communications sessions, however, the probe went silent and has not been heard from again.

As evidenced by two high-profile satellite reentries last fall — NASA’s UARS satellite and ESA’s ROSAT — reentering satellites are exposed to unpredictable natural forces such as sunspot activity that make forecasting when and where they will fall an extremely inexact science.   On the Space-Track.org website, the U.S. Joint Space Operations Center (JPSpOC) shows “15Jan12 0239Z-16Jan12 0739Z” as the predicted reentry time.  Z is for “Zulu” or Greenwich Mean Time (GMT), which is five hours ahead of Eastern Standard Time.   Thus, the prediction would be in the 29 hour window between 9:39 pm January 14 and 2:39 am January 16 EST.

Russian news source RIA Novosti is reporting that January 15 (Moscow Time) plus or minus four days is the likely reentry window.  Russia’s Itar-Tass news agency says January 14-16, with January 15 at 13:18 Moscow Time (5:18 am EST) as the “focal point” of the window.

The spacecraft is in an orbit inclined 51.4 degrees to the equator, meaning that its orbit traces a path between 51.4 degrees north and 51.4 degrees south latitude.  Debris could fall anywhere in that range, which is most of the populated areas of the world.  However, since approximately 70 percent of the Earth’s surface is covered with water, the danger to inhabited areas is limited, but not inconsequential.