[Cerowrt-devel] spacebee

valdis.kletnieks at vt.edu valdis.kletnieks at vt.edu
Tue Mar 13 13:49:25 EDT 2018

On Tue, 13 Mar 2018 09:52:53 -0700, Dave Taht said:

> Spacebee - Having a payload 1/4th the size of a cubesat *work* and be
> useable! is a major advance. And is 1/4th the space junk. Worrying
> about something smaller than baseball hitting anything strikes me as
> control freakery at the FCC.

For the purposes of this example, we'll assume that a large bolt sized piece of
space debris is about the same size as a 50 caliber sniper round. That leaves
the rifle going about 4,000 feet per second.

A piece of space debris can hit at anywhere from almost zero to twice the
orbital speed, depending on relative orbit angles (the 2009 Iridium incident
they hit at almost exactly 90 degrees, so 17000 mph times sqrt(2)).

For that configuration, they collided at around 25,000 feet per second.  And
kinetic energy is 0.5 * m v ^2.  So that bolt ends up whacking you with about
40 times the force of a 50 caliber round.  That's gonna mess up your day unless
you have some serious armor - which is the last thing anything in orbit has
due to the cost of launching per pound (even the ISS is only armored enough
to stop something up to 1.5cm or so).

If you want to use a baseball as the example, find the video of Randy Johnson
pegging a stray pigeon.  And his baseball was going around 100mph.  Apply "one
half em vee squared" and we get 17000^2 / 100^2 - or a baseball in orbit
has 28,900 times the kinetic energy.

The Iridium constellation of 66 satellites already has to deal with some 400
incidents *per week* where known space junk passes within 5km.  And in most
cases, the exact orbitals for at least one of the bodies aren't exactly known -
in the 2009 incident, they had been predicted to miss by 500 meters.

And NASA has an in-progress experiment to measure how often the really
small stuff hits:


Sure, the chances of any given piece of debris hitting something is pretty low.
But you get enough crap in orbit, the cumulative risk over time starts getting
into territories that make your risk management team start drinking heavily.

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