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Phobos-Grunt probe begins entering the Earth’s atmosfere


Stranded Phobos-Grunt probe, one of the largest objects to re-enter the atmosphere in decade, begins entering the Earth’s atmosphere. It will probably begin its descent on Sunday evening. By the latest estimate Phobos-Grunt could enter the atmosphere over Argentina and have its fragments splashed down in the Atlantic Ocean. According to Roscosmos latest estimate, the craft should splash down at 8:22 pm (16:22 GMT) about 1,000 miles (1,600 kilometres) due south of Buenos Aires – close to Falkland Islands. The previous Roscosmos estimate was that craft  would come down between the northwestern shores of Madagascar and the east coast of AfricaOne of the first estimates was that would splash down into the Indian Ocean near Java.

Following the favourable outcomes of the UARS and ROSAT re-entries in the past year, the entire world is awaiting the re-entry of the Russian Mars probe Phobos-Grunt. Around the world, research and aerospace organisations are working to provide a precise re-entry forecast. Russian officials still aren’t sure what caused the failure, though they recently raised the possibility that some sort of sabotage may be responsible.

For those who are not familiar with Phobos-Grunt recent history AGI made a great video that explains the situation. Watch it below!

You may download an interactive simulation of the PHOBOS-GRUNT reentry scenario, which uses the free AGI Viewersoftware to allow you to explore the latest reentry prediction in more detail.

PHOBOS-GRUNT Reentry Interactive Simulation

Atmospheric conditions and the diminishing altitude of the vessel’s orbit, as well as solar activity, influenced the change in the time and location of the landing. A major cause of orbital decay for satellites in low Earth orbit is the drag of Earth’s atmosphere. Note that during solar maximum the Earth’s atmosphere causes significant drag up to a hundred kilometers higher than during solar minimum. Once Phobos-Grunt probes reaches the height of 120 km (75 miles) above the Earth’s surface it will have only around 30 minutes left before re-entry (less than one third of an orbit).

Estimating the location of orbital decay is impossible until several orbits prior to entry. Phobos-Grunt is orbiting Earth with an inclination of 51.4 degrees, so all areas 51 degrees north and south of the equator are possbile entry zones. Predictions will become more accurate over the final two hours before its final destruction.

Uncontroled re-entry

Re-entry is generally accepted as commencing from orbit around at around 80km altitude. At this point the acceleration due to drag becomes appreciable (greater than 0.1G) thus causing further irreversible loss of altitude and increase in drag. At peak deceleration extreme heating, due to friction, and drag forces can destroy the objects integrity and disintegrate part or all of the object. This continues to around 45km altitude when the remaining objects have slowed and deceleration forces decrease. Remaining objects continue a ballistic trajectory, impacting the earths surface.

Usually 10-40% of the mass of the reentering object is likely to reach the surface of the Earth. On average, about one catalogued object re-enters per day. Due to the Earth’s surface being primarily water, most objects that survive reentry land in one of the world’s oceans. In 1978, Cosmos 954 reentered uncontrolled and crashed near Great Slave Lake in the Northwest Territories of Canada. Cosmos 954 was nuclear powered and left radioactive debris near its impact site.  In 1979, Skylab reentered uncontrolled, spreading debris across the Australian Outback, damaging several buildings and killing a cow. The re-entry was a major media event largely due to the Cosmos 954 incident, but not viewed as much as a potential disaster since it did not carry nuclear fuel.

Phobos-Grunt dangerous load

Phobos-Grunt probe is loaded with enough toxic fuel to take it to the Mars moon Phobos. A total of about 11,150 Kilograms of  Hydrazine and Dinitrogen Tetroxide propellants (which boil at 113 degrees Celsius) were inside the vehicle’s tanks at liftoff. The Phobos-Grunt contains a tiny quantity of the radioactive metal Cobalt-57 in one of its instruments, but Roscosmos said it poses no threat of radioactive contamination. The Russian expert predict that only 20 or 30 segments weighing no more than 200 kg could survive the fiery re-entry and actually hit the Earth’s surface. The chief NASA scientist on orbital space debris meanwhile dismissed the threat posed by the craft’s toxic fuel. NASA reported on its website that the craft’s fuel tanks are made of aluminium, which has a lower melting point than commonly used titanium, and that significantly reduces the chances of the propellant reaching the surface of the Earth. Also taking into account that all propellants explode upon reentry, around 475 to 950 kg of Phobos-Grunt debris could reach the ground. Other experts warn that part of the fuel might have frozen in the cold of space and could survive the reentry, posing a strong threat if it spills over populated areas. (Such fears prompted the United States to shoot down its USA-193 spy satellite with a Navy missile in 2008.)

Chinese Yinghuo 1 Satellite  is travelling “0n board” Phobos-Grunt craft. The satellite weighs 113kg. Its mission was to study magnetic field of Mars, observing martian dust and measure ionosphere occultation. China has not released detailed technical information on any toxic or dangerous satellite components. The mission is China’s first of this kind and is considered a test flight. More information on Yinghuo 1 can be found here.

Entry capsule that was specially designed to bring soil from Phobos back to Earth is one component that will survive re-entry and impact the ground. LIFE biomodule is loaded with  7.5 kg of bacterias, fungus 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. Phobos-Grunt carry representatives of all three domains of life: bacteria, eukaryota, and archaea. Most have been flown in near-Earth space on short missions.  All have been studied extensively, most having their genomes sequenced. Most are “extremophiles”: organisms resistant to one or more environmental factors such as radiation, high salt concentration, heat, etc.  10 individual organisms in 30 self-contained samples. In addition, one native soil sample will be flown in its own self contained capsule. Find more about on board organisms.

Other organizations and observers tracking Phobos-Grunt have their own estimates, some of which roughly agree with Roscosmos’ predictions and some of which have the probe crashing later, perhaps early Monday morning (Jan. 16).

Re-Entry Predictions:
Spaceflight101: January 15, 2012 – 16:34 UTC +/- 06 Hours
Harro Zimmer: January 15, 2012 – 17:05 UTC +/- 03 Hours
Ted Molczan: January 15, 2012 – 21:36 UTC +/- 10 Hours
Aerospace Corp.: January 15, 2012 – 17:52 UTC +/- 14 Hours
Official Russian Prediction: January 15, 2012


Phobos-Grunt re-entry – A quick guide for skywatchers

>>>Observe Phobos-Grunt!<<<

Featured image credit: AGI

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