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See other posts from February 2009

Headshot of Emily Lakdawalla

Two Earth-orbiting satellites collide

Posted by Emily Lakdawalla

2009/02/11 09:51 CST

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This is a big deal. It doesn't have any immediate ramifications for space science, but it's still a big deal. Two spacecraft -- one of them a functioning Iridium communications satellite, part of their satellite phone network, and the other one a defunct Russian spacecraft -- smashed into each other in Earth orbit. According to the Associated Press story, the loss of the Iridium satellite is actually causing "brief, occasional outages in its service," though the company does have eight spare satellites on orbit (compared to 65 active satellites in its constellation), and will be able to move one of those into position within a month. The Reuters story has a little more detail on the crash: it happened at an altitude of 780 kilometers, and created more than 500 bits of debris larger than 10 centimeters across.

At least Iridium has spares, though I'm sure the company's accountants are feeling the pain. What if the collision had involved an irreplaceable machine like a science satellite? NASA does watch the cloud of Earth-orbiting satellites and trackable debris very carefully, and makes use of the thrusters on its various satellites to prevent these kinds of collisions. (I'm actually very curious why Iridium didn't manage to do the same in this case. So is my boss.) But the collision of two complete satellites, for the first time in history, has created a huge, and expanding, cloud of debris. Some of that debris is large enough to be tracked and avoided, and none of it is orbiting low enough to represent an immediate threat to any of the human spaceflight. But there will be hundreds or thousands of much smaller bits, pieces too small to be tracked, that'll be flying around and posing a threat to other machines at the same altitude. The AP story says that "the risk of damage from Tuesday's collision is greater for the Hubble Space Telescope and Earth-observing satellites." Great.

One thing is sure: although this was a rare and low-probability event, so rare that it's never happened before, it is in all likelihood a harbinger of more orbital disasters to come. Now, we can no longer say that two satellites have never collided in orbit. When will the first unique, irreplaceable satellite (or, worse, shuttle or station) have a catastrophic encounter with a piece of orbital debris?

I feel like I should close this blog entry with a suggestion for a way forward, a way to prevent such a tragedy from ever happening, but honestly, I'm not sure what to suggest. It seems like international cooperation will be necessary in any solution. But I don't think I've ever heard anyone suggest anything that would effectively remove hazards from orbit -- only that different space agencies need to have open enough communication that all foreseeable and preventable collisions can be prevented, and that there need to be treaties preventing littering in space.

 

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