## Thursday, August 13, 2009

### Space Junk - how much is too much?

Can math answer just one simple question? How much is too much?

"How much is too much?" generated 295 million responses in .23 seconds on Google.
• How much drinking (alcohol or caffeine or water) is too much?
• How much exercise (running or training) is too much?
• How much homework is too much?
• How much junk in orbit around Earth is too much?
Math can help you make decisions. Let's look at that space junk question.

1. Define the terms.
Space junk is stuff we have sent into space from Earth
. Space junk is a nice catchy title. It means man-made objects larger than 4 inches in diameter that are orbiting earth. We could also say "Orbital Debris" if we want to be more precise.

2. Can we establish a baseline for the activity or situation?
Yes. There was no space junk at all before October 1957 when Sputnik went into orbit.

3. Can we get reliable information on the subject?
We probably can - at the
NASA Orbital Debris Office.

4. What is the current state of affairs?
We are still sending stuff up into orbit, collisions and explosions are breaking it into smaller pieces, and some pieces are falling back to Earth. Most burn up and a few hit the ground. The population has increased from 0 in 1957 to 9000 in 2000 to 13,000 in 2009.

5. What does the trend look like (change from base state to current state, over time)?
We could draw a chart - try it at home.
OR
We can say "At this rate within 50 years there will be millions of pieces of space junk"
.
OR
"There are 80 trillion cubic acres of space and only a few pieces of junk. It will take a million years to fill it up."

6. Now what should we do about space junk?
"We ought to start sending Earth junk up too."
OR
"We should stop sending up satellites. We should bring it back. We should send it further out. We could charge people to blow all the big stuff into tiny bits (it would be fun), etc."

Can we answer "How much Space Junk is too much?" and "What should we do about it?" No, not yet. We need a lot more information. And some consensus.

This decision-making approach is reasonable when there is a clean starting point, it all happens up in space and we are not personally or emotionally involved.

It's much harder when the question is "How much homework is too much?"