Hydrazine is a chemical compound made up of hydrogen and nitrogen. It is used as a fuel for rockets and also as a component in certain medications and pesticides. Full definition
Controllers used hydrazine fuel in the thrusters to keep SOHO pointed in the right direction, but they were using quite a bit of it — 15 pounds (7 kilograms) a week, on average. (space.com)
There is evidence that these tanks susvive reentry — Columbia's hydrazine tanks did. (dotearth.blogs.nytimes.com)
Kepler was launched with 3 gallons (12 kilograms) of hydrazine in its fuel tank. (space.com)