ROSAT's final hours

By Phil Plait | October 22, 2011 10:30 am

[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.

Most of the satellite pieces are fragile and will burn up as they slam into the Earth’s atmosphere. About 30 more durable pieces are expected to survive re-entry and make it all the way down to the ground. The thing is, one of those pieces will be the mirrors, which are heavy. ROSAT’s mirror assembly was designed to withstand a lot of heat (otherwise thermal stress — flexing under temperature changes — would have messed up its ability to see astronomical objects), which means that it will be able to stay intact as ROSAT comes down. The total weight of the mirror assembly is about 1600 kg — well over 1.5 tons. That’s a big chunk of material.

The good news here, as it is with every time space junk returns to Earth, is that our planet is big. 500 million square kilometers (almost 200 million square miles) is a lot of real estate, and the pieces coming down are small. Most of the Earth’s surface is water, and most of the land is unoccupied. That’s why the odds of anyone getting hit are so small; about 1 in 2000. And that’s for anyone getting hit! The odds of you specifically getting hit are more like trillions to one.

Think of it this way. I have a deck a cards, and you pick one at random. What are the odds of you picking the ace of spades? 1 in 52.

Now let me get 52 people and do the same thing until the cards are gone. What are the odds someone picked the ace of spades? 100%. But your odds of getting it are still small.

So the odds of any particular person getting hit by ROSAT are incredibly small, and there’s not much to worry about. In fact, on Science Friday, Mark said that stuff from space burns up over the Earth pretty much every day! Yet you never hear about anyone getting creamed by a fuel tank or an errant wrench. So there you go.

As the time gets closer I’ll post important updates as I hear them. For current news on the situation, I suggest following ROSAT_reentry on Twitter, who has constant updates on the predicted re-entry time, as well as plots and pictures of what’s going on.

CATEGORIZED UNDER: Piece of mind, Space

Comments (49)

Links to this Post

  1. Heads up! The sky is falling again | Doubtful Newsblog | October 22, 2011
  1. Infinite123Lifer

    Ah com’ on, reading is ol’ fashioned? :-) I am not even old and I am getting old.

  2. I’ve discovered that when I start explaining odds and statistics to people, only about 1 in 10 will have a clue what I’m on about.

  3. Chris

    Don’t you have an idea where it won’t hit the earth?

    Actually your statistics made me think of this

  4. Shatners Basoon

    How did you get a photo of it burning up on re-entry when it hasn’t even happened yet. This site is soooo fake!

  5. A lot of times numbers just go in one and out the other even though I have a strong math background. But when I actually think about some of this stuff it always amazes me.

    5 miles per second is obviously slow in terms of things moving through space but in practical terms on Earth it means I’m at work in under five seconds instead of one hour. Obviously I’d wear decent goggles to protect my eyes from the dust in the air. At those speeds you can’t be too careful. The hair is a lost cause though – either high speed wind hair or hat hair.

  6. Miles B.

    “…odds of anyone getting hit are so small; about 1 in 2000.”

    That’s ridiculous. Let’s use your 200M sq.mi. size, and say the dying bird flies over 70% of that area, or 140M sq,mi.

    Now let’s say there are 7 billion people, all standing in that 70%, and they each take up three square feet. That’s about 755 square miles of humanity.

    That makes the odds of any person getting hit more like 1 in 185676.4

  7. Geoff

    North of 53 degrees north and south of 53 degrees south Chris.

    Best guesses seem to be around 0800Z on the 23rd, about fourteen hours from now.
    That would put it around Khakassia in Easter Europe, heading east over Mongolia, China, part of North Korea and then Japan.
    Doesn’t mean it will come down there, the 14 hours is when reentry is likely to begin as I understand it, and the debris path will be somewhere along the line of the orbit, with some scattering as it gets into denser atmosphere as I understand it. With any sort of luck it will drop in the East Sea, the Sea of Japan or the Pacific.
    I am not an astronomer or expert on orbital decay, so I could be out by anything up to half an orbit.

  8. Geoff

    Um, Shat Bassoon, if you read the little squiggles under the picture, you’d see that it says it is a meteor burning up and not ROSAT (which is clearly still in orbit)
    You might want to pause before you post, it can save you from serious foot in mouth disease.

  9. Infinite123Lifer

    @ Shatners Basoon:

    Try some ol’ fashion reading. I think it is you who is sooooo fake.

  10. Infinite123Lifer

    @ Elwood Herring:

    Could you explain what you are talking about when you say “1 in 10”

  11. Pete Jackson

    Right out of the Tweety Bird’s mouth:

    “Sat 22 Oct 18:00UT #ROSAT orbit 87.79 minutes 161.4 x 167.3 km Position 30.6S,51.9E alt=167.2km Unlit ~Re-entry ~13h”

    The final plunge will start around 128 km, when the satellite will start glowing.

  12. SkyGazer

    “Mark said that stuff from space burns up over the Earth pretty much every day! Yet you never hear about anyone getting creamed by a fuel tank or an errant wrench. So there you go.”

    But the odds are getting better every day.

  13. Pete Jackson

    “Sat 22 Oct 20:00UT #ROSAT orbit 87.75 minutes 159.2 x 164.9 km Position 6.2S,170.1E alt=164.9km Lit ~Re-entry ~11h”

    The altitude refers to the height above the ground; perigee and apogee refer to the Earth’s equatorial radius. So the densest atmosphere in the orbit is when the satellite is near the equator because of the Earth’s equatorial bulge. I had never really realized that before.

  14. Mike Empyema

    The re-entry survivable fraction is 1.6 metric tonnes. The Wolter I x-ray telescope is four massive nested hollow paraboloids summing to 785 kg of gold-plated Zerodur ultra-low thermal expansion glass-ceramic. Zerodur-K20 is long-term stable to 850 C. Standard Zerodur softens at 600 C. Re-entry is not nearly a long enough time interval to heat the bulk. It is coming down as a lump at no less than terminal velocity in air, some 200 mph for its mass and shape.

    Canada is in the target reticle. Check eBay on Monday.

  15. Pete Jackson

    The reentry has been advanced. Not much more than 3 hours away!

    “Sat 22 Oct 22:00UT #ROSAT orbit 87.68 minutes 156.7 x 162.1 km Position 40.8N,76.3W alt=167.8km Lit ~Re-entry 3+ hours”

  16. Robert

    Wait a minute, odds of 1 in 2000 sound pretty dangerous to me. Considering we have hundreds (thousands?) of satellites up there, if they all come down in the same manner as ROSAT, the odds that at some point in time, someone will get hit by a satellite are rather high!

  17. michael kearney

    Hi Someone:

    I am writing to ask advice from any subscriber who knows, to explain to me what I need to do to sign up for the daily BadAstronomy email. I have been a regular receiver of Phil’s wisdom for years but for some reason beyond my understanding I stopped receiving the emails about two weeks ago. Have no idea why. I am kind of stunned about social networks etc, don’t use FB, don’t Tweet, don’t blog, don’t use them, I just want to receive the daily emailing again. How do I get back on the list or whatever?


    Michael in Labrador

  18. Blargh

    @ 16. Robert

    Wait a minute, odds of 1 in 2000 sound pretty dangerous to me. Considering we have hundreds (thousands?) of satellites up there, if they all come down in the same manner as ROSAT, the odds that at some point in time, someone will get hit by a satellite are rather high!

    A thousand reentries at a 1 in 2000 probability of hitting someone – which is quite high and shouldn’t apply to today’s launches (according to the talk!) – still only gets the probability up to 40%. And if rocket scientists follow the same kind of guidelines that other disciplines use when human health is involved, the estimates are probably on the pessimistic side.

    We’ve had artificial satellites for 54 years, and so far nobody’s died from one of them falling back to Earth. That’s a pretty darned good track record.

  19. Pete Jackson

    “Sat 22 Oct 23:00UT #ROSAT orbit 87.65 minutes 155.4 x 160.5 km Position 9.3N,136.1E alt=161.0km Lit ~Re-entry 2+ hours”

  20. Ganzy

    A thought just occured to me: In the event of ROSAT crashing into the household of a devoutly religious family and killing one or more of the occupants therein, would those remaining family members perceive the random chance of such a catastrophic event as God’s will?

    I’d be sincerely interested in an answer from someone who believes in a God.

    If it was my house that got hit and someone had been killed I’d be extremely emotionally pissed, but ultimately, accepting of the situation for the chance event that it was not because an over-arching intelligence deemed it so.


  21. April Gardner

    The real time map shows it over USA.: 7:41PM EST. Heading for Brazil…It is without question that math permits for more that a “questimate”. Solar maximum is burning up the satellites. The NASA news conference at the beginning of May began with an informal discussion of how the satellites are already “bumping” into their “neighbors”. This is just going to get worse. Maximum has been adjusted, and the “radio flux” we are hearing on our car radios and the unseasonal heat we occasionally experience are all indicators of maximum. More satellites are going to fail and fall.

  22. Pete Jackson

    “Sun 23 Oct 0:00UT #ROSAT orbit 87.63 minutes 153.9 x 159.0 km Position 51.4S,4.9E alt=168.1km Unlit ~Re-entry 1+? hours”

    It was seen from Florida about 7:30 ET (2330 UT) and should pass over the US again before 0100 UT, and again around 0225 UT if it has survived.

  23. April Gardner

    I made a mistake in my prior comment: The correct NASA conference that referenced the update in Solar Maximum and the satellite situation was in the beginning of September.

  24. Pete Jackson

    @20Ganzy: Although getting a direct hit on your house is a very unlikely event, the reentry of ROSAT has been widely predicted and the orbital tracks are known. So it should be considered as a consequence of the known laws of physics even though there are uncertainties in exactly when and where it would happen. In theory, an observer in an aircraft could have seen the object falling through the sky just before it hit your house.

    On the other hand, getting hit by lightning, although much more common seems to be a much more random event when it happens because nobody could predict the exact moment and place of a lightning bolt until it actually occurs. So one could imagine God moving individual ions around to make a discharge more easily than that He would interfere with a large object like ROSAT.

  25. April Gardner

    If a satellite landed on my house, and I survived, I would blame man for not warning me. If I were struck by lightning it would be God’s decision not to warn me. If I knew a satellite were to land on someone’s home, and I decided not to warn them then it would be God’s decision to handle that situation…I think that is where we get, “What goes around comes around.” Astrophysicists know who to inform to evacuate, if there is a danger from an impact by an NEO/PHA/Statellite. They have a choice. Anyway, so much for philosophy.

  26. Pete Jackson

    “Sun 23 Oct 1:00UT #ROSAT orbit 87.59 minutes 152.3 x 157.1 km Position 27.2N,104.4W alt=157.8km Lit Re-entry window”

    No sightings from US or Mexico

  27. John Sandlin

    I went out to watch for it. But I think the tree’s on my horizon obscured the view so that I missed it. Was supposed to pass between 19:55 and 19:59, with peak altitude (alt-az bearing) at 19:58. Central time, that is. I didn’t see anything. Another satellite flew over at about 20:00 at zenith north to south.

    Observing from my driveway in San Antonio.


  28. Pete Jackson

    “Sun 23 Oct 1:45UT #ROSAT orbit 87.37 minutes 141.0 x 143.7 km Position 20.3S,70.8E alt=144.4km Lit Re-entry window”

    Dramatic drop in altitude; looks like it may come down in China

  29. Pete Jackson

    “Sun 23 Oct 2:00UT #ROSAT orbit 87.31 minutes 139.6 x 141.9 km Position 28.1N,106.9E alt=146.2km Lit Re-entry window”

    Myanmar or China

  30. Messier Tidy Upper

    @ ^ Pete Jackson : Hmm .. wonder what the implications might be if ROSAT fell right on the Communist party HQ in Beijing? 😉

    If this unguided satellite took out the totalitarian Chinese leadership or the Burmese Junta dictators then it’d almost be enough to convince this agnostic that there is a God after all! 😉

    Of course, the odds are exceptionally remote of that & I still think ROSAT will most likely fall in the ocean or maybe now the Gobi or other Chinese / Manchurian / Xinjiang(~ite? ~ese? ~ian?) desert.

    Still, if you prefer old fashioned reading…

    I do prefer the old-fashioned reading indeed. I also appreciate reading it here & seeing what your thoughts on this are BA – thanks. :-)

  31. John Sandlin

    The implication to me would be someone was steering.


  32. John Sandlin

    For those without twitter:
    ROSAT_Reentry ROSAT Reentry
    RT @DLR_en: Today, 23 October 2011, between 1:45 UTC and 2:15 UTC #ROSAT has re-entered Earth’s atmosphere.

    It’s come down.


  33. Geoff

    Never assign to malice that which is adequately explained by stupidity.

    They turned off the satellite years ago. No communication (no control either, IIRC it had flywheels for attituded adjustment and nothing more) so it was never ‘steerable’. I consider anything that big that will have that much mass survive reentry is potentially a hazard. Looks like this time no one would have copped it, but given the amount of junk up there, some of it sizeable, that will make uncontrolled reentries over time, statistically, sooner or later a piece is going to hit someone or something.

    Might be time to think about the proposals to reuse satellite components in orbit (must be a lot of useful stuff floating about in dead sats up there – much of it potentially reusable – the recent concept of reusing comsat antennas is an example). If there were to be a redesign of large sats, so that they could potentially be either serviced (most comsats are decommissioned when their attitude control fuel is exhausted) or readily taken apart. Radio equipment, computer equipment, solar panels etc. etc. are all potentially reusable and are already in orbit (the most expensive value adding there is). This would mean a rethinking of the whole ‘disposable’ design of large satellites, but it might be worth it. Hubble has had several servicing visits when the shuttle was operational, so it’s doable, at least in LEO.

    Geosync is probably better left to telepresence, but if we can get rovers on Mars that last for years, a ‘Servicing Satellite’ for want of a better description, with telepresence capability might well be viable. It would need to be large, with large stores of fuel for itself to visit its ‘clients’ and replenishment propellants for on orbit sats – perhaps it too could be serviced/refuelled by a ‘resupply’ craft along the lines of the Progress system. If the various commercial entities ever get something like the shuttle operational, and ISTR there are at least two in work, perhaps we need to include recovery at end of life in the costings for big stuff like Hubble. Send the bird up to fetch it home at end of life instead of letting it fall down when its ready and hoping it doesn’t hit something or someone.

    Note: I think it was a mistake to retire the shuttle airframes – they should have been rebuilt with contemporary computers and technology – probably increased the payload dramatically given the mass difference in modern electronics v the 80’s stuff in the shuttle alone. Expensive? Yes, but after the Soyuz debacle and talk of demanning the ISS as a consequence, I can’t help but think the timing was bad at best. The damage issue from the ET needs to be solved, -properly this time- the previous bandaid solutions were far from perfect, but the shuttle concept is sound, it simply needs developing beyond the minimalist approach.

    Commercial space seems to have taken this concept on board and in the long term, commercialisation may well be just the thing necessary to get us beyond the disposable booster concept that NASA is so in love with. The waste here is dramatic. The need for a heavy lift booster fell by the wayside for decades, they can’t rebuild Saturn V, which was a man rated heavy lift booster, as the plans and much of the tooling etc is long gone. Shortsighted, at a minimum, the capacity to produce it should have been preserved, they now have to reinvent a wheel that worked very well many years ago and could doubtless be improved drastically with modern electronics instead of the 60s equivalents. But the airframe, tankage and motors were well proven, sound designs, now they are starting again and dependent on the Russians in the interim.

    Ok, that’s my 2c worth (which is probably all its worth – I’m not exactly an expert on these things and I have probably neglected key issues that prevent it, but hey, I’m just an interested observer).

  34. On the lighter side – click my name for one possible scenario for when sputnik ROSAT falls from the skies. 😉

    @28. John Sandlin : “The implication to me would be someone was steering.”

    Yeah, well, we’d certainly suspect that too.

    @29. John Sandlin : “For those without twitter: It’s come down.”

    Thanks for that – do we know where? :-)

    @30. Geoff : “Might be time to think about the proposals to reuse satellite components in orbit ..”

    Seconded. Vaguely recall seeing an article somewhere recently suggesting a plan for doing that too.

    Note: I think it was a mistake to retire the shuttle airframes – they should have been rebuilt with contemporary computers and technology – probably increased the payload dramatically given the mass difference in modern electronics v the 80′s stuff in the shuttle alone.

    Seconding that idea too. We should, I think have built a few more Shuttles – and Mark II and Mark III Space Shuttle versions that were different and better than what we had. The Spacxe Shuttles should have been the first of a long series of such vehicles getting ever better and more capable in my view rather than just a one – or five – off spacecraft set we had. (Yeah, Russia’s Buran copy followed the Shuttle plan too but only once. A few others, eg. X-37, have flown or been proposed but are not exactly the same thing and not enough.) :-(

  35. Pete Jackson

    It’s odd that there were no sightings (reported so far) from the USA, Mexico, or South America on that last pass before it went through the southern hemisphere towards China. Maybe we’ll hear later.

  36. Chris
  37. Pete Jackson

    “Estimated Decay was 2011-10-23 01:50:00 GMT ± 7 minutes as @ 2011-10-23 03:41 GMT”

    That puts it in the Indian Ocean south of the Bay of Bengal, but the error range could still include parts of Myanmar, Thailand, Laos, Vietnam and China.

  38. Jason

    It is 7:08 local time here in Houston, Texas and I just saw something big streak across the sky. Looked exactly like the pic Phil has posted with this post. It was in the west only lasted a second or two. Part of the satellite or just a coincidence? Thoughts?

  39. So, the germans called this one the V3 or V4? (too soon?)

  40. Messier Tidy Upper

    @39. Jason : Sounds like it was probably a meteor. A nice bright one. :-)

    Also a coincidence and unconnected to ROSAT which was falling a long way from Texas.

    @38. Pete Jackson & #37. Chris : Thanks. :-)

  41. Messier Tidy Upper

    BBC world news online has this :

    report saying ROSAT probably ended up in the Indian ocean.

    But as one great old European satellite falls another rises :

    also via BBC online. Meanwhile NASA is also preparing for a new satellite launch :

    for the NPP. (National Polar-orbiting Operational Environmental Satellite System Preparatory Project.) This one“.. heralds a new era of climate change science and weather forecasting..” and is due to be launched on Oct. 28th between 5:48 a.m. & 5:57 a.m. EDT.

  42. StockC

    @Ganzy (#21):

    Yes, a deeply religious person would perceive getting killed by collision with a satellite as God’s will, just as surviving every daily commute to and from work without a collision is God’s will. Check out Jewish liturgy for the holidays of Rosh Hashonah and Yom Kippur. On God knows when, where, and how you will die.

  43. Blargh

    But as one great old European satellite falls another rises :

    Unfortunately, for those of us who live where we have to pay for it. Galileo is pure pork.

    The security/availability argument went out the window they moment they bowed to pressure and changed the frequency to allow jamming. And if the US should suddenly reimplement selective availability on Navstar, there’s always GLONASS.

    The accuracy argument is likewise bollocks: the 10 meters cited in the article is fine for any realtime civilian navigation use. If you need more than that, you can use RGPS and the like to achieve centimeter accuracy. Or just use GLONASS signals as well. Oh, and the operative word in “a position fixed by the publicly available GPS signal might have an error of about 10m” is publicly. The vaunted high accuracy of Galileo? That you have to cough up cold, hard cash for.

    TL;DR: Galileo is a constellation of white elephants in orbit.

  44. Chris Winter

    “How did you get a photo of it burning up on re-entry when it hasn’t even happened yet. This site is soooo fake!”

    Perhaps by using the endochronistic properties of resublimated thiotimoline. <G>

    (NB: Some here may need their sarcasm detectors tuned up…)

  45. Chris Winter

    What strikes me about that picture of Earth is how strongly the ranges of mountains at top center suggest an enormous impact crater.

    I know: If that’s what it was, we’d have figured it out by now. I surmise the convective currents in magma converge on the North Magnetic Pole, which is what drags the continental plates “upward” to produce a roughly circular collision pattern.

  46. TomH

    The chances of a falling satellite killing or injuring anyone are astronomically low; however, every time this happens, NASA (or in this case ESA) gets loads of bad PR. They could have saved themselves loads of grief by including a small, solid-fuel retrorocket in the satellite design. That would allow the satellite to be de-orbited safely into the drink when its useful life ended. That would also help reduce the orbital debris problem.

    As for reusing satellite material in orbit: fuggedaboutit! At least until we have a really reusable spacecraft.

  47. Messier Tidy Upper

    @45. Chris Winter :

    [@4. Shatners Basoon – ed.] “How did you get a photo of it burning up on re-entry when it hasn’t even happened yet. This site is soooo fake!”
    Perhaps by using the endochronistic properties of resublimated thiotimoline.

    LOL. Great Asimovian reference there! :-)

    PS. Shatners Basoon clearly didn’t read the caption below the photo as (#9.) Infinite123Lifer has already observed.

  48. Ian Straton

    @46 Chris Winter,
    You surmise incorrectly. That chain of mountains is the Himalaya (and associated ranges including, but not limited to, the Hindu Kush, the Karakoram and the Tian Shan), the “crater floor” is the Tibetan Plateau.

    The mountains are in fact a impact feature, but rather than a meteoric origin the impact was that of India moving north into Asia, a movement which is ongoing today. Look up Plate tectonics online for more details.

    For reference the magnetic pole is in Canada which is basically on the opposite side of the globe. The earths magnetic field does not influence the convection of magma in the mantle which is what drives plate tectonics.


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