I don't recall hearing about this when it happened. There's much more info in the article. A lot of satellites serve us in ways we take for granted and may be unaware of.

And I wonder how hard it would be for a country to intentionally crash a satellite and then plead: "Oooops!"


http://www.reuters.com/article/rbssTechMediaTelecomNews/idUSN0351968920091103

Pentagon eyes crash analysis on 1,300 satellites

Tue Nov 3, 2009 6:09pm EST

The U.S. Air Force began upgrading its ability to predict possible collisions in space after a dead Russian military communications satellite and a commercial U.S. satellite owned by Iridium collided on Feb. 10.

The crash, which was not predicted by the U.S. military or private tracking groups, underscored the vulnerability of U.S. satellites, which are used for a huge array of military and civilian purposes.

Chilton said the Air Force was tracking more than 20,000 satellites, spent rocket stages and other objects in space, up from just 14,000 a few years ago.

But he said that was just what U.S. could "see" and there were estimates that the actual number was much greater, posing a potential threat to satellites on orbit.

Firstly space is big...
And satellites tend to all be going in roughly the same direction (you get a boost from the rotation rate of the earth if you launch west-east).

Low earth orbit (Shuttle+ISS) is the busiest, with lots of spent booster rockets and most of th emanuouverable satelites. But the drag from the upper reaches of the atmosphere will soon de-orbit any small pieces of junk like the residue of a collision or a dropped toolkit ;-)

Mid orbit (GPS, Iridium) is the worst, there are lots of satellites all going in different full earth coverage orbits and often not steerable. So far it's been lucky. It was a little better when the military (USA+USSR) where the main users since they tended to have a more robust attitude to safety and disposing of old satellites, now there are a lot more commercial lunches in this area it's getting bad. It's hard to convince shareholders to pay another few $10M and delay their service for extra safety systems or testing.

Geostationary (communications and TV) is going to get bad. Although there is a lot more space (in space) this far out there are only a few places you want to put satelites, over USA, Europe, Japan+Korea etc. They don't normally move but have small positioning thrusters to stop them drifting into each other. So far they have all been successfully put in parking orbits at the end of their life but an explosion in one of these congested spots would be a real pain. Any debris is going to stay there pretty much for ever.

I remember reading about the Iridium impact and I thought it seemed strange. I know that the US tracks thousands and thousands of bits of orbital debris. How could the collision of two satellites be a surprise to them?

I was listening to some aerospace guy on the radio a few months back. He was mentioning that we've entered a new era of hazardous space debris. Before, stuff that fell off boosters and such would create a finite amount of debris that needed to be tracked. But we've gotten to the point where there is enough junk out there that they occasionally collide with other junk, thereby creating a lot MORE debris which is harder to track since they are now much smaller pieces. The problem is only going to get worse over time as more chunks collide with other chunks.

I'm not sure how long it would take for gravity to pull these very small bits of debris out of orbit, if at all.

The orbits drift slightly due to the predictable effects of the Earth, Sun and moon and the random effect of traces of atmosphere.
There was a close approach prediction but you have to make a business decision for each approach warning. If you use up propellant to move out of the way then you reduce the life of the satellite and reduce service if you needed to have a craft in that particular orbit. Whether they should have moved it is something their lawyers will be arguing with the insurers lawyers.
Of course there is the also the "it's never happened before so don't worry" effect.


That's a worry as more satellites are launched, especially at the mid orbits of Iridium and GPS. Where any debris takes a long time to decay.


It's not gravity as such that pulls them down - it's the braking effects of the atmosphere. The height of the atmosphere mostly depends on the sun's activity and the last solar cycle was a lot less active then usual which meant the atmosphere was lower and there was less drag in low earth orbit. This has been great for the ISS and Hubble but means that junk hasn't been cleaned out as quickly.

Earlier thread on subject. Beware the Kessler Syndrome!

-Blast

I ran across this article while trying to find out how many objects are being tracked these days (still haven't found a number for that).

What's interesting is that only two recent events have apparently contributed 40% of the total orbital debris, according to this article. One is the Iridium incident. The other is from when the Chinese destroyed one of their old satellites with an anti-satellite missile in 2007. (But didn't we also shoot down one of our own retired satellites some time later in response? That should be one of the top "polluters," too, you'd think, right?)

We shot ours down as it was tumbling from orbit and about to crash into the Earth (no space derbis left behind). The story was we did it to vaporize it's toxic fuel but most likely it was to show off our capabilities.

And now for the really paranoid thought for the day: do any anti-Western countries have the ability to throw a bunch of nuts and bolts high enough into space to knock out satellites?

-Blast

An Anti Satellite active denial system launched against the Navstar or any loe Satellite network would just need 1 small launcher no bigger than the Black Arrow Rocket, which could deliver 100 kg of 2 mm stainless steel ball bearings with a mass of 1.5 grams (approx 45,000 objects all with differing orbits). Now if these bullets were traveling in the opposite direction to the satellites orbital direction the kinetic energy of the 2mm ball bearing with respect to the satellite would be around 0.5*0.0015*(15645^2)= 190KJ or about 10 times the energy of a .50 cal BMG round exiting the end of a gun barrel.

Those 45,000 2 mm ball bearing would be very difficult to track individually using ground based RADAR and would make it extremely difficult to operate satellites at the altitudes the ball bearings were released. It would take just a few days to weeks before Kessler Syndrome became a reality.

It's not as effective as you would think.
Even if you dispersed a large number of pellets with an explosive charge they would still be in a relatively small cloud traveling in a single orbit - you rely on your target crossing this orbit at right angles to have a reasonable chance of hitting them.

That was the problem with Iridium collision - the Iridium satellites are in a polar orbit (to give a full Earth coverage) the Russian Kosmos was in a nearly equatorial orbit - so every orbit their paths cross (although normally well apart).

The main source of pellets in LEO is from the upper stages of large solid rocket boosters (eg Delta + Ariane) they contain aluminium to control the burn rate. As the motor runs it spits out little balls of molten Al in a trail behind it. In low orbits these decay fairly quickly. The shuttle SRB don't reach orbit.

The Chinese weapons test was particularly annoying because they used a satellite in a mid orbit where it will take a couple of hundred years for the debris to decay. The US test was deliberately done at a very low altitude and any debris would have de-orbited in a year.

I figured there was a name for that.... after reading the article that was the first thing that came to mind!