The first Russian interplanetary mission in 15 years, called Phobos-Grunt (or “Phobos-Ground” or “Phobos-Soil”) because it was destined for the Mars moon Phobos and it contained soil experiments, is now almost certain to be stuck in low Earth orbit until it reenters within the month. The difference between this reentry and the other 2 large satellite reentries this year, NASA’s 6-ton UARS and the German 2.4 ton ROSAT, is that this vehicle was meant for a very lengthy journey away from the Earth. As such, it’s radioactive power supply was of no concern, but that’s changed now that it will be dispersed in our atmosphere. Of more concern to this Grunt is the 10 tons of deep-space storable propellants on board.
That’s right. Ten tons. That propellant is divided between fuel and oxidizer. Unfortunately, the oxidizer is not harmless liquid oxygen, which cannot be used for long missions. This more stable oxidizer, nitrogen tetroxide, is a highly corrosive acid and a very toxic chemical. The fuel, unsymmetrical dimethylhydrazine, is unfortunately one of the most toxic carcinogens known to man. But people exposed to it rarely have time to die from cancer. Exposure to even a drop or small amount of vapor means very quick and certain death.
Let me be clear. There are ten tons of these substances neatly packed aboard this spacecraft. I’m fairly sure that no object has ever reentered the Earth’s atmosphere before with this enormous quantity of storable propellant onboard. Therefore, no one can predict whether it will all vaporize before it hits the ground. Even the residue left on surviving pieces will be exceedingly dangerous if anyone comes in contact with it. Let us hope for a nice mid-ocean breakup.