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

Comments (43)

  1. Alex

    By the way, “safely out in the ocean” is a little misleading. There are a lot of islands in that ocean, and people do live there. The re-entry point was about 30-40 miles from American Samoa. I realize that the islands are miniscule compared to the size of the Pacific and the risk statistics still apply, but as a former Peace Corps volunteer in the area I feel responsible for reminding Americans of its existence! (disclaimer: I work with UARS in a very tiny way but my comment is not officially sanctioned)

  2. John Baxter

    Is ROSAT another one that it picking its own time, or is it being guided in?

    There’s an advantage to the UARS method: no one can make a silly but dangerous mistake. (I’m sensitive to that, as mother was doing math and physics at JPL during–and long before–Mariner time. But I’m pretty sure the minus sign confusion wasn’t hers.)

  3. It’s not even 2012 yet, but things are already starting to fall out of the skies! Run for your lives! Someone should have warned us about all of this death from the skies stuff!

  4. Jeffrey

    I actually went outside at 3:50 pm that day to see if I could see UARS from Christchurch, New Zealand. But it was only about 10 degrees above the horizon according to Heavens-Above so I didn’t look hard. Would have tried harder if I’d known it was very close to re-entry.

  5. Keith Bowden

    Does this mean I’m going to have to calm my Facebook friends again and explain why it can’t be easily pinpointed? Yeesh. :)

  6. Wzrd1

    There are 17 items coming in before ROSAT. Some of it is debris, others are dead birds.
    At least, per Space-Track.

  7. Gonçalo Aguiar

    I remember that the probability of UARS hitting anyone was 1 in 3200. If we had something like thousands of satellites coming down in the next decades, then could I assume that someone would be to most likely be hit by one?

  8. Chief

    Does this mean that if we wait long enough the skies above us will clear out of all the junk.

    I assume that there are still plans on deorbiting the hubble when its life is up. hopefully in more than 10 years from now. Be kinda neat to push it to a higher orbit so it can remain as a reminder of what the 1st great scope in space is.

  9. andy

    Does this mean that if we wait long enough the skies above us will clear out of all the junk.

    Last I heard we’ve reached the initial stages of Kessler syndrome: there are enough satellites up there that the rate of production of debris from collisions exceeds the rate at which material is being removed by atmospheric drag.

  10. Don Shipman

    Wow way to Copy TheWeatherSpace.com on the ROSAT story. Bravo

  11. alfaniner

    High odds are “1 in 14 trillion”. Low (small) odds, i.e., much more likely, are “1 in 2000″. I know that’s what you said, but I don’t think it’s what you meant. (fyi, I had to look it up myself!) :)

    My impression is that you meant to say, “Bear in mind that’s still really high odds!”? (i.e. quite unlikely)? It could be read either way.

  12. kevbo

    @ 7. Gonçalo Aguiar:

    Lots on lots and lots of satellites WILL come down in the next few decades. Most of them are small enough that they won’t survive re-entry, however. And I think you are not quite understanding the ’1 in 3200′ statistic that UARS presented.

    Once again, that meant that there was a 1 in 3200 chance that some surviving piece of UARS would hit anyone at all on the planet, not that there was a 1 in 3200 chance that any given person on earth would be hit.

    If the latter was the case, then with something like 7 billion people on earth, if every single one of them had a 1:3200 chance of being hit, then we would have expected to see:

    1/3200 X 7,000,000,000 people hit by a piece. That’s 2,187,500 people! Obviously, this cannot be right, as there wasn’t enough metal in UARS to hit that many people!

    The correct way to look at it (as Phil and others have done) is to say that IF there are 7 billion people on earth (of which I am one of), AND if there is a 1:3200 chance of the satellite hitting ANYONE AT ALL, then the chances of ME is:

    Odds = (chance of satellite hitting someone on earth) X (that person being me)
    = 1/3,200 X 1/7,000,000,000
    = 1/22,400,000,000,000

    That’s a big number. Big like, if you were to play PowerBall every day (odds of winning being 195,249,054), and a UARS-sized satellite came down every day, you’d probably win 114,725 times before getting hit by a satellite…

    (this is not an endorsement of PowerBall as an investment strategy)

  13. Jake

    Will we see an increase in the frequency of falling satellites in the coming years. Because we’ve littered the earth with ton’s of metal in the last 50 years that some of the suff is starting to fall down now?

  14. Bigfoot

    Since ROSAT is explicitly claimed to be a astronomical satellite, many confused individuals are likely worried that their horoscopes are in danger of malfunctioning. Thus it is time to reflect on the difference between astronomy and astrology once again.

    The key difference that I want to point out to both astronomers and horoscope observers, of course, is that man-made astrological satellites never, ever fall out of the sky! I can only conclude that those astrologers could teach their astronomers a thing or two about falling satellite bombardment prevention — it appears that astronomers dismiss astrological advice at their own peril.

    Perhaps a simple horoscope check before the next satellite launch is all that is needed — I mean, shouldn’t they check where the sun and moon and planets and stars are before they fling multi-million dollar hunks at them at astromical (whoops, I meant astrological) speeds? Makes sense!

  15. Jens Randrup

    The space debris will keep hitting the Earth. Always with a 1-in-several-thousand probability of hitting a person. But with the amount of space debris coming down, the time when its even-odds of someone getting hit, is fast approaching. In my view, only a global organization setting global limits and standards for “burnability” or “waste disposal” will keep our skies and ourselves relatively safe.

  16. Molly

    This blog is having too much influence on my subconscious. The other night I had a dream that a satellite crashed right by me in a field and caught fire.

  17. DigitalAxis

    Aw, ROSAT? I’m still using ROSAT All-Sky Survey data (mostly because GALEX isn’t all sky just yet). I know ROSAT went off-line in like 1999, but it’s still sad.

  18. DrFlimmer

    Good German Quality coming down. That means it will stay intact until it hits the ground. :-D

    @ #16 Molly

    The other night I had a dream that a satellite crashed right by me in a field and caught fire.

    Are you sure, this was a dream? Was there probably a blue police box standing near by? :-D

  19. mechbill2112

    So, Hubble weighs 26,000 lbs with no prop system and a decaying orbit. Depending on solar cycles, the predicted re-entry was as early as 2021. 17% would survive such that the odds of hitting someone are 1:250. NASA requirements for needing a controlled re-entry were less than 1:10,000. There was a design for a propulsion unit many years ago (before STS-125), but I don’t think anyone is executing on it.

  20. Chris S

    Can anyone comment on how exactly they go about confirming re-entry in places where there doesn’t seem to be anything there? Are there particular effects of re-entry that allow eventual finding of satellite records that show it’s passage?

  21. K

    Come ON, Germany!
    NASA failed me repeatedly. No jet packs. No flying cars. No space hotels. AND THEY COULDN’T target my stupid house with a falling satellite!
    Come on! I need the insurance money! Hit my friggin’ house! If nothing else, maybe I can at least get it rented this year if I can drum up the media attention.

  22. MadScientist

    “… will probably have more pieces survive the ride down because its mirrors had to be shielded from heat to operate”

    Now why would the shielding mean more parts surviving? The shields are meant to keep radiation off the mirrors, not to survive re-entry, so unless the shields are a refractory material I don’t see what it has to do with surviving the plunge.

  23. http://spiff.rit.edu/classes/phys240/lectures/other_views/rosat_mirrors.gif
    http://www.mpe.mpg.de/xray/research/gallery/calendar/Kal2003/cover.php

    ROSAT’s mirrors are 0.89 tonne of gilded Zerodur (no sweat to 850 C, softens around 1000 C). It will be orbit to ground impact intact, you betcha.

  24. #13 Jake:
    No, we won’t. “Some of the stuff” is not “starting to fall down now”; it has been falling down for decades! Many satellites, which are launched into low orbits ( around 100 miles ), have lifetimes of only a few months before their orbits decay. If they are only intended to operate for a short time, then this doesn’t matter, so they are simply allowed to decay and reenter.
    Satellites have been reentering the atmosphere since the start of the Space Age; it happens many times every year. But most of them are too small for any parts to survive reentry. UARS made the news simply because it was a pretty big satellite.

  25. DigitalAxis

    @16 and @18:

    Or, was it a spaceship with a baby inside?

  26. Joseph G

    I know the 1-in-2000 figure applies to anyone, not any individual, but that STILL seems really freakin’ high to me. Are we sure it’s not a 1 in 2000 chance that it’ll fall within x meters of a structure/vehicle, or something?
    According to teh Google, for each person on Earth, there are over 75,100 square meters of surface area. Assuming a person occupies about a square meter, wouldn’t that make the odds of hitting someone about one in 75,000 (leaving out the issue of multi-story apartment buildings and underground workplaces)?

    EDIT: I just realized that the inclination of ROSAT’s orbit is such that it won’t come down above a certain latitude, and of course the population of the Earth seems to be concentrated in equatorial areas. But still, I can’t imagine those odds getting higher then maybe one in 30,000. That’s still a far cry from the quoted number.

    /Disclaimer: I suck at math. If someone sees where I’m screwing up, please tell me

  27. Joseph G

    @22MadScientist: Depends what the shielding material is. For instance, tungsten is quite dense (70% denser than lead), and generally makes a very good radiation shield, but unlike lead, it has an extremely high melting point and is quite hard. Tungsten has even been suggested as a material for orbit-to-ground kinetic weapons.

  28. Joseph G

    @14 Bigfoot: Since ROSAT is explicitly claimed to be a astronomical satellite, many confused individuals are likely worried that their horoscopes are in danger of malfunctioning. Thus it is time to reflect on the difference between astronomy and astrology once again.

    The key difference that I want to point out to both astronomers and horoscope observers, of course, is that man-made astrological satellites never, ever fall out of the sky! I can only conclude that those astrologers could teach their astronomers a thing or two about falling satellite bombardment prevention — it appears that astronomers dismiss astrological advice at their own peril.

    Perhaps a simple horoscope check before the next satellite launch is all that is needed — I mean, shouldn’t they check where the sun and moon and planets and stars are before they fling multi-million dollar hunks at them at astromical (whoops, I meant astrological) speeds? Makes sense!

    Shoot, if astrology really works, then I can only surmise that satellites, being many orders of magnitude closer to us then the outer planets, have at least as great an effect on our lives. Why aren’t they launching satellites into strategically placed orbits that negate the “negative” traits of various planets and reinforce the “positives”? They could make everyone focused, creative, happy, loved, lucky, intelligent, and wealthy, all the time! :-P

    I’m going to get to work raising money to launch a Gemini Ultra Sex Life-sat ;)

  29. MadScientist

    @UncleAl #23: I suspected the problem would be the mirrors (large mirrors would easily survive reentry), but that has nothing to do with the shielding – unless for some reason the shielding needed to be something very bulky and which would survive reentry, but that still has little to do with the shielding contributing to the survival of other parts; for example, a typical thermal blanket would do its job nicely in space, but it isn’t protecting anything on reentry.

  30. DigitalAxis

    @28: Joseph G

    That’s brilliant! Stupid, but also brilliant. Mind if I put a few instruments on the Gemini Ultra Sex Life Sat? You just worry about the money, launch costs and large enough solar panels (for the sex machine, of course.)

  31. Tribeca Mike

    The Indian Ocean takes up 21% of the world’s salt water, so it shouldn’t be surprising UARS splashed down there.

  32. Joseph G

    @DigitalAxis: Hmm. The solar panels will need to be big enough to generate a surplus of power for said sex machine. Insufficient power means that it may not be fully capable of getting “on the scene”. We’ll also need a heavy-lift vehicle big enough to get up, get on up.

  33. Wzrd1

    @Joseph G, #32, should that rocket look like the one that carried Flesh Gordon when it was hit by the ray?
    Boy, did *I* give away my age with that one…

    As for astrology, I’ll stick with MY astrologer, Phil. For, he can inform me of the ONLY star of significance to my life, Sol. And he can inform me of events that are of import to the only planet of great interest and any impact on my life, Earth. And he can inform me of the movings and doings of the many stars, which do not impact my life, but teach us new things at an astonishing frequency. :)

  34. jack21222

    So you’re saying ROSAT is going to ROAST?

  35. Sir Chaos

    I see it´s autumn again… the satellites have started falling…

  36. Jess Tauber

    Re 31. Yeah, blame the Indian Ocean, Mike. Don’t consider the hit it took from the tsunami a few years back. Give it a little slack. Sheesh! :-)

  37. dr_cy_coe

    Pedantism on: “a little over 2 tons, as opposed to over 6″

    UARS was 5668 kg, so 5.67 tons (metric) or 6.25 tons (US).
    ROSAT is 2,400 (wiki), so 2.40 tons (metric) or 2.65 tons (US).

    If the quote concerns US tons, then ‘a little over 2′ doesn’t compare to ‘over 6′ as it suggests that .65 is less than .25.
    If the quote concerns metric tons, then ‘a little over 2′ applies, but ‘over 6′ should be ‘over 5′.

  38. @ 20. Chris S:
    Unless they had some temporary tracking facility in Polynesia (e.g. a tracking ship), they did not have direct groundbased detection capability at the reported re-entry location. ESA station Awarua in New Zealand would already have lost it 3:56 UT, AFSCN Kaena (Hawaii) station would have first been able to pick it up at 4:07 UT. Kwajalein was too far west. This creates an 11-minute gap (3:56 – 4:07) in which the reentry time sits.
    This is one reason why I think space-based observations (DSP and/or SBIRS early warning satellites) were perhaps involved, but not publicly acknowledged because they come from classified DoD satellite programs. The early warning satellites DSP F20, DSP F16 and SBIRS Geo-1 would have had coverage of the reentry location from space.

  39. @ myself #38 above:
    Someone pointed out to me that the ESA station in New Zealand is a telemetry station only, not a true radar/optical tracking facility. As UARS was no longer sending telemetry, this makes it unlikely that Awarua played any role in the last UARS detections, leaving an even bigger gap untill no-show over Hawaii.

  40. vince charles

    15. Jens Randrup Said:
    September 27th, 2011 at 1:49 pm

    “In my view, only a global organization setting global limits and standards for “burnability” or “waste disposal” will keep our skies and ourselves relatively safe.”

    Oddly enough, the organization appears to be the FCC. After Orbital Sciences Corp. inadvertently led to the HAPS explosion, the fines from the FCC, and the threat of being denied licenses to transmit from comsats, led manufacturers to take the issue seriously. They started minding their hardware and procedures.

  41. vince charles

    19. mechbill2112 Said:
    September 27th, 2011 at 2:53 pm

    “So, Hubble weighs 26,000 lbs with no prop system and a decaying orbit… There was a design for a propulsion unit many years ago (before STS-125), but I don’t think anyone is executing on it.”

    The docking/thrusting interface is now on the back of Hubble, left after the last servicing mission. That’s half the battle. Let’s assume the bird isn’t tumbling with any significant speed. Getting a thruster module onto a purpose-built capture interface was a problem solved by XSS-11, DART, Orbital Express, etc… to say nothing of Soyuz/ATV. Of course, if Hubble starts tumbling, lotsa luck.

  42. Pepijn

    I don’t agree that odds of 1 in 3200 or 1 in 2000 of someone being hit are small odds. Not when it would almost certainly mean the death of that person.

    I find it quite staggering how nonchalant NASA, etc. are about this risk, and how cavalier they apparently were with human lives when they designed these things without a good way of bringing them down safely…

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