# Tag: re-entry

## Desktop Project Part 23: What are the odds of a satellite re-entering over water?

By Phil Plait | April 17, 2012 2:00 pm

[I’m approaching the Desktop Project endgame here; I’m almost out of pictures to post. I’ve done this every day for weeks, and my computer desktop is almost clean! Of course, more stuff keeps coming in, so I could do this forever. But that would be cheating. Sweet, sweet cheating.]

I’ve got something different for you today. Over the past few weeks I’ve posted an illustration, and a couple of dozen pictures, but no graphs! That’ll change now, and I think this particular set of plots is nifty.

Whenever a big satellite is about to re-enter Earth’s atmosphere — like UARS, or ROSAT, or Phobos-Grunt — the media freak out. You start seeing numbers being thrown about of the odds of getting hit by a chunk of flaming debris, and I get lots of panicked email and tweets. Then I have to point out to people that the Earth has a lot of real estate for a satellite to come down on, and of that, 3/4 is water. And most of that is Pacific Ocean. So really, the most likely scenario is a re-entry into the Pacific, or some other ocean, and that’s that.

But is that really true? After all, satellites can have different orbits, inclined with respect to the Earth’s equator. So the odds of getting dumped in the ocean might be different for a satellite that’s over the equator versus one in a polar orbit (that is, orbits almost completely in a north/south direction).

Happily, orbital debris specialist Mark Matney did the math! In a paper published in the Orbital Debris Quarterly Newsletter (bet you didn’t know that existed!) he calculated those odds. He created two graphs for the paper, and both are really cool if you’re a graph nerd like I am.
Here’s the first one:

That plot shows the fraction of the total area of the Earth covered by land versus latitude. It’s easy to read: at 0° latitude — the equator — the amount of land is 23%. In other words, if you flew a plane around the world at the equator, you’d be over land 23% of the time.

CATEGORIZED UNDER: Cool stuff, DeathfromtheSkies!, Space

## Phobos-Grunt to come down today

By Phil Plait | January 15, 2012 6:45 am

[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.

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CATEGORIZED UNDER: Space

## Cool picture of Expedition 29 on its way home

By Phil Plait | December 30, 2011 7:00 am

When Expedition 29 astronauts Mike Fossum, Sergei Volkov, and Satoshi Furukawa returned to Earth from the ISS on November 21, Dan Burbank stayed aboard the station and got this dramatic picture of them coming home:

[Click to deorbitenate.]

See it? The returning Soyuz capsule itself is the bright dot in the center of the picture, and you can see the trail of plasma behind it, pointing almost straight down. It’s almost lost against the city lights below it.

I couldn’t find this picture on NASA’s Gateway to Astronaut Photography, unfortunately, but a little sleuthing gleans some info anyway. Read More

CATEGORIZED UNDER: NASA, Pretty pictures, Space

## Video of the Progress re-entry!

By Phil Plait | November 3, 2011 1:30 pm

Last week I posted a picture of the fiery re-entry of a Progress re-supply ship as seen by Mike Fossum on board the space station. It was one of several pictures he took, and via Universe Today is a video of the descent of the spacecraft!

Holy wow! You can see the trail of plasma starting to blow off the main spacecraft just as the video begins, and if you look carefully you can see bigger chunks of material falling off the main body — just like in the big picture I posted earlier (seen below).

While this may seem like a waste of a spacecraft, in fact this serves a very useful purpose: it gets rid of trash and other cast-offs by the astronauts on the International Space Station. By collecting it and getting rid of it all at once they don’t have to worry about creating more space debris which is a hazard to other satellites, or even the ISS itself — a very real concern.

Moreover, Progresses are not re-usable, so there’s no sense in trying to land them again. Also, it takes less fuel to slow a Progress spacecraft enough to let it burn up in our atmosphere than it would to slow it down enough to land it safely anyway. That means even more savings in getting payloads to space.

So all in all it makes sense to simply use them as a way to keep the ISS tidy. It may be a bit ignominious, but wow, what a way to go!

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CATEGORIZED UNDER: Cool stuff, NASA, Pretty pictures

## UARS official re-entry… and up next: ROSAT

By Phil Plait | September 27, 2011 11:51 am

NASA has released the final update on the UARS bird that burned up in re-entry last week: it came down in the Pacific, west of the US.

The Earth’s atmosphere is not a lid over us, but gets thinner with height, so it’s hard to define exactly what it means to say that the satellite burned up at such-and-such a spot. However, at 04:01 UTC on September 24th, the satellite’s motion became dominated by the Earth’s atmosphere, and for all intents and purposes that can be called the point where it came back in… or at least, where it started. The forward motion of the satellite took the pieces along a track 500 – 1300 km (300 to 800 miles) long, which is still safely out in the ocean.

Thus ends the UARS tale.

… but we’re not quite done yet. The venerable German astronomical satellite ROSAT is due to come back down in about a month or so. Smaller than UARS — a little over 2 tons, as opposed to over 6 — ROSAT will probably have more pieces survive the ride down because its mirrors had to be shielded from heat to operate. That means the odds of it hitting someone will be slightly higher than from UARS, about 1 in 2000. Bear in mind that’s still really small odds! The chance of a specific individual getting hit are still something like only 1 in 14 trillion.

ROSAT is an X-ray satellite, designed to study high-energy radiation from astronomical sources. Years ago, I looked briefly at ROSAT data of a supernova remnant while putting together an educational activity about exploding stars. I don’t feel the same connection to the satellite as I do to, say, Hubble, but still, it’s a little sad to see it come down. However, it did provide years of outstanding service to the astronomical community, and gathered a vast amount of data about the high-energy Universe around us.

Image credits: NASA; German Aerospace Center (DLR)

CATEGORIZED UNDER: NASA, Space

## UARS down over the Pacific ocean

By Phil Plait | September 24, 2011 9:02 am

NASA has confirmed that the Upper Atmosphere Research Satellites, UARS, burned up over the Pacific Ocean last night, September 24, between 03:23 and 04:09 a.m. UTC (11:23 p.m. and 12:09 Eastern US time). I have no other reliable information on it, but I expect we’ll get more updates soon. There were lots of reports last night of it falling over Canada, but those were mistakes or hoaxes. Apparently some people were fooled by meteors, Chinese lanterns, and possibly even the planet Jupiter. That’s happened before.

If I find photos or such I’ll try to post them, but I’ve heard no reports of witnesses, and I’ll be away this afternoon for my TEDxBoulder talk, so if any pictures turn up I may not be able to get to them. I imagine SpaceWeather will post any if they crop up.

Thus ends that saga. If you’re curious, you can read about the history of the UARS and what we learned from its 15 year mission to investigate our planet’s atmosphere.

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CATEGORIZED UNDER: NASA, Space

## UARS update 5: new predicted re-entry tonight at 05:10 UTC +/- 2 hrs

By Phil Plait | September 23, 2011 8:35 pm

The Center for Orbital and Reentry Debris Studies has updated their predicted re-entry time for NASA’s UARS satellite. It is now 9/24 (tonight!) at 05:10 UTC (01:10 Eastern US time), which puts it over the southern Indian ocean:

See Related posts below for information and background. Note the uncertainty is once again smaller, at +/- 2 hours!

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CATEGORIZED UNDER: Cool stuff, NASA, Space

## UARS update 3: new predicted re-entry tonight at 03:16 UTC +/- 5 hrs

By Phil Plait | September 23, 2011 11:07 am

[UPDATE to the update (22:00 UTC): a new prediction just came out: tonight, September 23/24, at 04:04 UTC (midnight Eastern US time). The uncertainty is down to +/- 3 hours, and the location is the middle of the Pacific. Clicking the links below to CORDS or the image itself will take you to the most current prediction.]

The Center for Orbital and Reentry Debris Studies has updated their predicted re-entry time for NASA’s UARS satellite. It is now 9/24 (tonight!) at 03:16 UTC, which puts it over the Sahara:

Note that again this is later than the last estimate. As the satellite has gotten lower, aerodynamic drag — the wind blowing on it, tenuous as it is — has changed its orientation, creating less drag, slowing the descent.

Please note that the time is still uncertain, though now it’s only +/- 5 hours. Still, that’s a wide swath of Earth in that range, so we’re still not sure where it’ll burn up.

Check the Related posts links below for more info on the satellite, why it’s coming down, and how to read that map. Again, the danger from this is pretty minimal. You may note that the three predictions we’ve had have put re-entry over the ocean or otherwise largely uninhabited areas, and that’s not a coincidence: most of the Earth is like that! That’s why the odds of someone getting hit are so low.

I’m sure we’ll get another update or two in the next few hours, so stay tuned. You can also check the CORDS site for updates, and the NASA page as well.

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CATEGORIZED UNDER: Cool stuff, NASA, Space

## UARS update 2: new predicted re-entry at 00:58 UTC

By Phil Plait | September 22, 2011 9:07 pm

The Center for Orbital and Reentry Debris Studies has updated their predicted re-entry time for NASA’s UARS satellite. It is now three hours later than before: 9/24 at 00:58 UTC, which puts it in the middle of the south Pacific:

Mind you, the uncertainty on this is still +/- 7 hours, so we’re a long way from knowing just where it will come down.

For more details, please read this earlier post (and you might as well read this one as well for the background info).

## NASA satellite due to burn up some time in the next few days

By Phil Plait | September 21, 2011 6:27 am

[UPDATE: Alan Boyle at Cosmic Log is reporting that the satellite will definitely come down on Friday, though NASA is not sure yet exactly when and where.]

[UPDATE 2: Emily Lakdawalla at The Planetary Society blog has lots of detailed info now.]

By now you’ve probably heard that NASA’s Upper Atmospheric Research Satellite (UARS, pronounced YOO-arz, though in my head it’s always "You arse!") will burn up in our atmosphere some time between Thursday and Saturday. The satellite was decommissioned in 2005 and they used the remaining fuel to lower the orbit. It’s been slowly getting lower since then, but recently reached the part of our air where it slows and drops dramatically. As you can see from this plot (click to embiggen), it’s dropped from about 375 km to 200 in just the last few months, and down it’ll come later this week.

No one knows where or when it will hit, since the final flight path will depend on changing atmospheric conditions, orientation of the satellite, and so on. Most of the 6 ton satellite will burn up, but some two dozen or so pieces are expected to survive re-entry.

Speaking of which: I’m seeing some concern over people getting hit by this thing. The odds of that are extremely low. It’s possible — NASA rates the odds at about 1 in 3200 — but highly unlikely. Mind you, those are the odds of anyone getting hit by debris. The odds of a specific person, say me, getting hit are far lower — if I’m doing this math correctly, you’d multiply that number by the population of the Earth, nearly seven billion people. So the odds of me (or you, or pick someone) specifically getting hit are about 1 in 20 trillion. Pretty long odds.

In the meantime, on September, 15th, "amateur" astronomer Thierry Legault was able to capture video of the satellite while it passed over his location:

Cool, eh? You can see the rotation; it’s tumbling, apparently. Out of power, it can’t keep the correct attitude, and over time something has caused it to spin. Maybe it was a collision, or maybe it’s from other subtle but persistent forces over the years (solar wind, light pressure, drag through our tenuous upper atmosphere, slow fuel leak, what have you). Here are some stills from Thierry’s video to make that more clear:

Pretty cool. So stay tuned. I’ll update with more info when I get it; we’ll know the re-entry time and location much better as the week progresses. <a href="I’ll be tweeting about it as well as soon as I find anything out.

Credits: Orbit plot: Jonathan McDowell; UARS images: Thierry LeGault.

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CATEGORIZED UNDER: NASA, Space
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