dave.taht at gmail.com
Tue Mar 13 14:06:56 EDT 2018
On Tue, Mar 13, 2018 at 10:49 AM, <valdis.kletnieks at vt.edu> wrote:
> 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).
"U.S. space agency NASA estimated that the satellite collision created
approximately 1,000 pieces of debris larger than 10 centimeters (4
inches), in addition to many smaller ones"
Can you run the probability of a hit for two objects 10 centimeters in
size in the 2009 orbital conflict vs, say, 2 meters, with a margin of
measurement error of 500 meters?
> 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.
I am painfully aware of this. On of my big fears in the SDI 80s was
that someone would deploy pebbles in a reverse or polar GEO orbit,
rigged to explode in a war extending to space. It could render GEO
useless in a matter of weeks. The technique (I can't remember the
codename) is so obvious (and so essentially MAD), that I've long
assumed every spacefaring nation had one or more stealthy sats rigged
that way on the drawing boards at some point or another.
> 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.
It was a sat from the early 90s. The collision took place in 2009.
I remember (early 00s) how n-body sims took weeks, nowadays that's
thoroughly parallized on gpus.
> And NASA has an in-progress experiment to measure how often the really
> small stuff hits:
thx for the pointer!
> 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.
Yes we should worry about creating sea lanes for
CEO, TekLibre, LLC
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