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SYFY WIRE Bad Astronomy

Phobos-Grunt to come down today

By Phil Plait

[Update 2 (18:40 UTC): According to the US Strategic Command, Phobos-Grunt re-entered over the Pacific ocean, not far west of Chile. This is unconfirmed, but STRATCOM is usually quite reliable. As I write this, I'm pretty sure the spacecraft is down, and hopefully we'll know more about where it came down in the next few hours.]

[Update 1 (15:50 UTC): The predicted re-entry time is now around 17:20 UTC or so, but still not exact (Eastern US time is UTC - 5 hours, so 12:20 in the afternoon). The Russian space agency Roscomos has created a map of the predicted final orbit:

That's over more land than I would've expected, but still lots of water. And remember, even if it falls over land the odds of it hitting anyone are incredibly low. Follow PhG_Reentry and me on Twitter for constant updates.]

I've been referring to Phobos-Grunt as "the doomed Russian space probe". Today, that name gets verified: it's due to re-enter Earth's atmosphere today, sometime around 18:30 UTC (plus/minus 3 hours), though the exact time is still unsure.

Emily Lakdawalla at The Planetary Society has an excellent blog post with lots of details on what we know. Basically, the third stage on the rocket failed to ignite, stranding the spacecraft in Earth orbit. The air is thin up there, but still exerts a small force, dragging the spacecraft's orbit lower and lower. In the past few months it's been dropping, and sometime today it will get low enough that the Earth's air will consume it.

Since there are too many variables in the re-entry, it's impossible to know when it will come down with any real accuracy until right before the actual event. And since it's moving at about 8 km/sec (5 miles/sec), being wrong by five minutes in time means a difference of 2500 km in distance. That's half the width of the US, so that's why it's not known where it will come down. Since the Earth is mostly water, the chances are it'll drop into the Pacific, but that's just statistics. We don't know for sure.

If you want constant (and somewhat technical) updates, follow PhG_Reentry on Twitter. As we get more info, I'll update this post, as well as tweet about it and post on Google+ too.

Related posts:

- Doomed Russian Mars probe seen from the ground
- ESA writes off Phobos-Grunt
- Phobos-Grunt scheduled to launch at 20:16 UT
- Final: ROSAT came down in the Bay of Bengal
- UARS official re-entry⦠and up next: ROSAT

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