In November 2011, the Russian space agency launched the much-anticipated Mars probe called Phobos-Grunt (which means "Phobos dirt" or "ground"), which would go to the Red Planet, soft-land a probe on the tiny moon Phobos, and return a sample of the surface to Earth. Unfortunately, the booster that would take it from Earth orbit into a Mars-intercept trajectory failed to fire, stranding the spacecraft in low-Earth orbit. Atmospheric drag has doomed the mission; it will most likely burn up sometime in the next two weeks.
Phobos-Grunt is visible to the naked eye as a bright star if it happens to pass overhead. Astronomer Thierry Legault, an expert in nabbing incredible images of objects in orbit (and no stranger to this blog!), traveled to Nice, France to observe it, and (as usual) got great video of it:
You can actually see detail in the probe; he provided a helpful picture to make it more clear:
The solar panels and other parts are pretty obvious.
Like UARS and ROSAT last year, Phobos-Grunt is making an uncontrolled re-entry, and it’s not entirely clear where it will fall. Odds are it’ll be over water, since the majority of Earth’s surface is ocean. The predictions I’m seeing look like it’ll be on or around January 15th. The actual location of re-entry won’t be known pretty much until the moment it comes down; it’s moving at several kilometers every second, so being off by a few minutes in the time means being off by thousands of kilometers in the location! There are a lot of variables involved too, including the orientation of the satellite (which changes the drag it feels from the atmosphere), solar activity (a solar storm can make the atmosphere puff up, speeding up the date of the spacecraft’s demise), and so on. I’ll write more information as I hear it.
In the meantime, you can check to see if Phobos-Grunt will pass over your location and you can see it; I suggest using Heavens-Above.com.
Image and video credit: Thierry Legault, used by permission. Slight edit of image done by The Bad Astronomer to compress it horizontally.
The German space center DLR is reporting that ROSAT — an astronomical satellite launched in 1990 — re-entered the Earth’s atmosphere just after 01:50 UTC last Sunday, October 23, burning up over the waters of the Bay of Bengal, to the southwest of Thailand. This was during the day, which is why there were no reports of it coming in, and no reports of debris hitting the ground. There are no reports of anyone getting hit, either, of course.
I was thinking about why it’s so hard to know exactly where and when a satellite comes down. New Scientist has a short, to-the-point article about it. In a nutshell, low-Earth orbit satellites like ROSAT are a few hundred kilometers above the Earth’s surface, circling every 1.5 hours or so. The Earth’s atmosphere doesn’t just stop if you go high enough; it thins out slowly, and even at 300 km there is still some air, though incredibly tenuous. However, over days, months, and years, a satellite moving through it feels a drag, feels air resistance. This drops its orbit, putting it into thicker air, which slows it faster, dropping it more… this process is very slow at first, but at some point increases rapidly, and the satellites drops into air thick enough that, at its high speed, causes it to burn up. I’ll note it’s mostly due to gas compression, not friction, that heats the satellite up.
And that’s why it’s so hard to know in advance where these things will come down. Read More
[UPDATE 3: ROSAT fell at 01:50 UTC last night (9:50 p.m. Eastern US time), +/- 7 minutes. The track over the Earth during that time is shown here. The center of the track is the most likely re-entry time, and stretches for seven minutes in both directions (the yellow pins mark five minute intervals). It probably fell over the Indian Ocean, though the track stretches into southern China. There are still no reports of debris sightings. Picture courtesy ROSAT_Reentry and Google Earth.]
[UPDATE 2: (03:30 UT) It's official. According to the DLR website, ROSAT de-orbited between 1:45 and 2:15 UTC. It's not known precisely where itfell; no confirmed reports of pieces have been seen yet. During that period of time, ROSAT was traveling across the Indian Ocean and China. Spaceflight 101 has some maps showing the location.]
[UPDATE: Reports are saying ROSAT may re-enter as soon as 01:00 UT (9:00 p.m. Eastern US time), though more likely a bit later. Follow ROSAT_reentry on Twitter for the up-to-the-minute news.]
We’re less than a day away from ROSAT’s final plunge into Earth’s atmosphere. Even this close to its last moments, it’s difficult to know just where it will drop down; it’s orbiting the Earth at 8 km/sec (5 miles/sec), so if predictions are off by just a couple of minutes that translates to a nearly 1000 km (600 miles) in position! And the models are still uncertain by a few hours.
|A meteor burning up in our atmosphere; this is
NOT actually ROSAT but just meant
to give you an idea of what it will look like.
As it stands, right now as I write this the nominal time of re-entry is sometime on October 23 between 06:00 and 13:00 UT (02:00 – 09:00 Eastern US time). The uncertainty means we still are not sure just where on Earth it will come down.
Yesterday, I was on NPR’s Science Friday show talking about ROSAT. Also on was Mark Matney, an Orbital Debris Specialist with NASA, and we talked about what happens when a satellite re-enters. That link goes to the show page, or you can grab the MP3 file directly. You can get a lot of the basic info there. Still, if you prefer old fashioned reading…
ROSAT is an astronomical satellite, designed to observe high-energy X-rays from space. Launched in 1990, it has a mass of about 2.5 tons, much less than the UARS satellite which came down in September. It was shut down in 1999 after some of its hardware failed; during the decade it was operational it provided astronomers with vast amounts of data about supernovae, black holes, neutron stars, and other cool cosmic objects. It’s been in low-Earth orbit ever since. Over time, the very tiny drag it has experienced due to passing through the very thin upper atmosphere of our planet has dropped it into an ever-lower orbit, and now, after several years, it’s about to re-enter for real.
I actually kinda half-expected this would happen: the fantastic "amateur" astronomer Thierry Legault was able to observe and get video of the astronomical satellite ROSAT as it’s making its final orbits around the Earth:
He also observed it on October 16th, but I think the video above from late September shows it better.
To show you how good this is, I took an image he provided of stills from his video and added a drawing of the satellite below them:
Amazingly, in Thierry’s images you can clearly see the boom extending from the satellite’s main body (at the bottom of the photos, and off to the left in the drawing). That boom holds a magnetometer (to measure the Earth’s magnetic field) and an antenna used to communicate with Earth. From what I can tell, the boom is about 4.4 meters (14.4 feet) in length. In that September image, ROSAT was over 450 km (270 miles) away from Thierry when he took it!
Last month, after the UARS satellite burned up over the Pacific, I mentioned that the German Astronomical satellite ROSAT will be burning up soon as well. It’s looking that will happen next week, with some models pointing to October 23rd. The exact time and even the date are still a bit uncertain, because it’s impossible to perfectly model the incredibly complex interaction between the satellite and the very thin atmosphere hundreds of kilometer up.
Emily Lakdawalla at The Planetary Society Blog has a nice write up of this, as does Dan Vergano at USA Today (featuring a quote by me, of all people, from that post last month). I imagine Space Weather will have info too as it comes out.
There’s a ROSAT Twitter stream with fairly up-to-date information as well. I’ll be paying attention to that carefully.
Just to be clear, I’ll state that even though more pieces of this satellite will survive re-entry than UARS did, the odds of anyone getting hit by a piece are still many thousands to one against, and of any particular person getting hit (meaning you) are trillions to one against. So while I don’t want satellites to fall from the sky every day, I’m not too concerned over this one.
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)