How to Mail a Package (From Space)

Randall Munroe’s new book, How To: Absurd Scientific Advice for Common Real-World Problems, just came out and Wired has a lengthy excerpt: How to Mail a Package (From Space).

Getting an object down to Earth from the International Space Station is easy: you can just toss it out the door and wait. Eventually, it will fall to Earth.

There’s a very small amount of atmosphere at the ISS’s altitude. It’s not much, but it’s enough to produce a tiny but measurable amount of drag. This drag sooner or later causes objects to slow down, fall into a lower and lower orbit, and eventually hit the atmosphere and (usually) burn up. The ISS also feels this drag; it uses thrusters to compensate, periodically boosting itself up into a higher orbit to make up for lost altitude. If it didn’t, its orbit would gradually decay until it fell back to Earth.

This shipping method has two big problems: First, your package will burn up in the atmosphere before it ever reaches the ground. And second, if it does survive, you’ll have no way to know where it will land. To deliver your package, you’ll have to solve both these problems.

Fun fact: a piece of paper drifting down from orbit might move slowly enough not to burn up on reentry.

• books
• how to
• Randall Munroe
• science
• space