1. Stratospheric Soot 2. Rocket Propellants
3. Martian Madness 4. Helium
5. Re-entry Debris 6. Suborbital Debris
7. Plutonium in Space 8. Cosmos 1818
9. Re-useable Rockets 10. Space Tourism
11. Launch Accidents 12. Ozone Depletion
13. Overview Effect 14. HAPS
15. Sustainable Space 16. Our Long Future

Re-entry Debris

Everything that goes into orbit will eventually fall out of orbit and re-enter the Earth's atmosphere. Given that space craft move so fast, re-entering the Earth's atmosphere is a very brutal event. Travelling at over 20,000 km per hour, satellites and old rocket bodies, farings, interstages and other space junk, burns up in the mesosphere, the middle atmosphere, about 70km up.

Example Reentry

On October 30, 2014, the second stage of a Delta II rocket burnt up in the atmosphere. Shown below is what the rocket looked like before launch. The rocket was actually launched in January, 1996. So for 18 years, this junk had been circulating the Earth. It is propelled by a single AJ-10-118K rocket engine, fueled by Aerozine 50 (a hyrdazine blend) and dinitrogen tetroxide and has a mass (without fuel) of about 950 kilograms.

Let us hope that the space junk burning up in the atmosphere is not a significant sustainability issue as the sky will be raining space junk for decades to come.

Throwing out the garbage on the International Space Station

In August, 2014, a Cygnus cargo ship was packed with 1,300 kg of trash from the International Space Station and burnt up in the atmosphere.