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Heads Up! The sky is falling!

  1. Jan 27, 2008 #1

    Astronuc

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    Well part of it.

    Disabled spy satellite threatens Earth
    http://news.yahoo.com/s/ap/20080127/ap_on_go_ot/dead_satellite
    BobG, what's up? Or down as the case may be.

    Interesting to see if this has any impact on the launch of Atlantis.
     
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  3. Jan 27, 2008 #2

    BobG

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    A deorbiting satellite won't have any impact on a Shuttle launch. This sort of thing happens all the time. The only newsworthy thing is that the satellite is bigger than usual (plus the fact that the satellite never worked properly, but that's newsworthy to a very small crowd).

    A few hundred objects a year re-enter the atmosphere (http://www.aero.org/capabilities/cords/chart1.html). The spikes correspond to solar max, which tends to expand the atmosphere and clean up debris in low orbits. You had about 111,000 kg of space debris return to Earth in 2003. http://www.aero.org/capabilities/cords/reentry-stats.html

    Large objects that have re-entered the atmosphere: http://www.reentrynews.com/largeobject.html

    Hopefully, something like this (http://orbitaldebris.jsc.nasa.gov/reentry/reentry.html) doesn't land on your house.

    Lowering the amount of debris in space is reaching a pretty high priority, hence the latest solar max not producing much of a spike. There's an effort to reduce the amount of debris created by each launch (explosive bolts, springs, bands that are expelled when the satellite unfolds from the launch vehicle, etc), reduce the amount of time rocket bodies stay in orbit, and intentionally deorbit low orbiting satellites at the end of their life.

    Since this satellite has never functioned properly, they can't intentionally deorbit it, so it will come down more or less at some random spot (probably in an ocean since oceans cover most of the Earth).

    Satellites in extremely high orbits (geosynchronous communication satellites, for example) don't come back down. They're pushed out into a higher orbit to make room for their replacement - at least ideally. The geos that die unexpectedly tend to sweep across the geo belt periodically causing headaches for operators of the functional satellites.

    The uncontrolled re-entry of space stations (Salyut 7 and Skylab) were embarrassing for the country that owned them. Skylab re-entered because the Shuttle program fell behind and we had no manned launch program to span the gap. Salyut 7 re-entered because the USSR space program had serious budget problems during the break-up of the Soviet Union.
     
    Last edited: Jan 27, 2008
  4. Feb 14, 2008 #3

    BobG

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    Hmm. This sounds as if the decision came from Bush, himself - Pentagon to shoot down broken spy satellite

    You toss something in the air and it suddenly occurs to you it's going to fall back down to the ground? Simple, just shoot it down. Then it will, uh, :uhh:, well :redface:... it will fall back down to the ground.

    At least most of it. If I blow it up, then at least portions of it will become space debris that will orbit the Earth until .... well, :uhh:, until they fall down to the ground. Unless we get lucky and a piece or two hit another satellite - surely that will keep at least one or two pieces up for quite a while, right?
     
    Last edited: Feb 14, 2008
  5. Feb 14, 2008 #4

    mgb_phys

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    The fuel tank in the above link isn't so bad, it's relatively light so reaches a low velocity.
    The problem with a deorbiting keyhole/hubble type satelite is that the mirror is likely to reach the ground intact - so you get hit by a 1ton block of glass at high speed rather than a shower of smaller debris.

    Where it hits depends on the orbit - you normally put photo-recon sats in a polar orbit so they get lots of passes accross the width of a certain large country that covers quite a lot of the northern hemisphere - in which case it is likely to hit the pacific.
    This is also lets you keep the solar panels constantly in sunlight and lets you take pictures at dawn/dusk when shadows give you good height information.

    But since it didn't make orbit it could still be in an east-west orbit which means it is most likely to land in the certain large country. Hence the sudden concern to destroy it.

    Because the orbit of any satelite is quite easy to work out from the launch site a couple of sightings they are quite easy to spot http://mysite.wanadoo-members.co.uk/satcom_transits/193bw.jpg

    If you want to spot it yourself the USAF provides this useful identification chart
    https://freeinternetpress.com/mirrors/usaf/airforce-id-chart.jpg
     
    Last edited: Feb 14, 2008
  6. Feb 14, 2008 #5

    BobG

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    :rofl::rofl::rofl:

    Actually, the entire spacecraft will break up as it enters the atmosphere. The likelihood of pieces surviving re-entry depend on their shape and the material they're made out of. I don't know the construction of this satellite, but spherical titanium fuel tanks are a popular option for satellites and the most likely part to survive re-entry. A large mirror would be unlikely to survive.

    Blowing the satellite up with a missile will break up the satellite almost as effectively as the atmosphere will. Any objects likely to survive re-entry would also the be the pieces most likely to be propelled away from the explosion intact. The pieces might be propelled into a new orbit that take longer to decay. The pieces might be propelled into a new orbit that intersects the Earth's atmosphere, resulting in the pieces reentering sooner. I don't think there's any net gain.

    At best, you spread the debris shower over a longer period of time. At worst, you create more space debris for at least a short period of time, increasing the chances of colliding with an operational satellite.

    And, of course, all of the pieces from the missile will also re-enter the atmosphere.

    If the satellite's a low altitude, polar orbiting satellite, then it was launched directly into its final orbit, so it would be in a polar orbit no matter what. High altitude satellites are launched into a parking orbit and later maneuvered into their final inclination.
     
  7. Feb 14, 2008 #6

    D H

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    It's a bit of a misnomer to call the planned activity "shooting it down", since (a) the satellite is already on the way down, and (b) the explosion won't make it magically deorbit. The explosion won't change the momentum of the pieces by much. So ... I'll simply call the planned activity "blowing it up".

    Blowing this satellite up accomplishes at least four ends:
    • It will nearly eliminate the likelihood of hazardous chemicals (i.e. hydrazine) from reaching the ground.
    • It will most likely render sensitive avionics and sensors useless if the pieces fall into the wrong hands.
    • It will drastically reduce the likelihood of anything reaching the ground. Debris from a satellite is most likely to hit the ground if the satellite remains intact through at least part of the entry. If the satellite finally breaks up in the dense lower atmosphere the fragments will quickly slow down and fall. An upper atmosphere breakup means the fragments are subject to very intense heating as air drag is roughly inversely proportional to fragment size.
    • Last but certainly not least, it gives the military a chance to play with their ASAT toys.
     
  8. Feb 14, 2008 #7

    mgb_phys

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    I think lots of sensitive circuitry in very heavily sheilded boxes is the surving bit they worried about.
    One of the major concerns about Hubble was the damage the mirror would do on re-entry. It was predicted to survive rather well since all the instrumentation around the back of it would make a good heat shield. Obviously it wouldn't be in good shape when it hit the ground but it might be in one piece.

    Given the StarWars/ASAT technology tests upto now the safest thing to do would probably be to paint a big red target on your roof - it pretty much guarantees it will miss you!
     
  9. Feb 14, 2008 #8
    US plans to shoot down a spy satellite

    http://news.yahoo.com/s/ap/20080214/ap_on_go_ca_st_pe/dead_satellite


    Is this a response to last year's Chinese weather satellite shoot down? We had this capability since the '80s. Why now? I thought we had a treaty with the Russians outlawing just that.
     
  10. Feb 14, 2008 #9

    turbo

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    Right now, that object is just one big inanimate piece of hardware, and its trajectory is known. If they manage to break it up into lots of little pieces, that's one thing, but if they don't get a clean hit and it breaks up into just a few massive pieces, those pieces will have brand-new trajectories that could very well endanger other satellites. Most of the Earth is uninhabited and/or covered with ocean, so why not let it come down in one piece?
     
    Last edited: Feb 14, 2008
  11. Feb 14, 2008 #10

    mgb_phys

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    Because of what that one piece might contain.
    The satelite's small size and odd orbit suggest that it wasn't a standard photo-recon, the rumours are that it was a test bed for a range of radar and imaging systems - so it might have some very interesting technology on board.
    Most of the uninhabited Earth is in Russia / China (and Canada!) and it isn't impossible to recover stuff from the ocean if you watched where it landed.

    The tricky bit of shooting it down is that if you shoot it down while it is still in orbit with an ICBM like the Chinese did you create lots of debris. If you wait until it starts deorbiting you have to shoot from near where it is landing, which means a ship.
    The trouble is that if it looks like it is coming in over Russia/China and you shoot a medium range interceptor at it, from just off their coastline - where does space stop and their restricted air space start ?

    The we are doing it because we are concerend about the rocket fuel is pure spin. Hydrazine isn't terribly nice but it's not going to have much left after it burns up in the atmosphere.
     
  12. Feb 14, 2008 #11

    Ivan Seeking

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    Me thinks this is a show for China.
     
  13. Feb 14, 2008 #12

    russ_watters

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    Perhaps it is about China, but also we now have new capabilities that we want to test: A test of this sort would be more a demonstration for North Korea than China.
     
  14. Feb 14, 2008 #13
    I wouldn't be surprised if that satellite is more than just observation equipment. It would explain the need to blow it up before it gets down here.
     
  15. Feb 14, 2008 #14

    Ivan Seeking

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    Considering that China just shot down a satellite and Korea can't get a missile off the ground, I don't see where Korea comes into this.
     
  16. Feb 14, 2008 #15

    russ_watters

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    It is to be shot down by our new Navy-based ABM system. "Hey Kim - look what we can do!"
     
  17. Feb 14, 2008 #16

    RonL

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    Where's Captain Kirk when you need him????:rolleyes:
     
  18. Feb 15, 2008 #17
    i was thinking this too, its a great opportunity for that type thing anyway. imo blowing the satellite up with a nuke would be by far the coolest option. why go small when you can go big when it comes to explosions in space is all im saying.
     
  19. Feb 15, 2008 #18
    The Raetheon standard missile 3 will be used. They are manufactured here in Tucson so we have a lot of local interest. The satellite was launced in 06 and never maintained proper orbit. The local buzz is that there may be some high tech equipment that may survive the trip through the atmosphere if all 5000 lbs came down in one piece.

    Personally I don't think that the hydrazine would survive the heat of re-entry.

    http://www.azstarnet.com/news/225242.php
     
  20. Feb 16, 2008 #19

    BobG

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    Here's James Oberg's take on it: Heading off a toxic iceberg from space
    The fuel tanks aren't completely hollow. Since the fuel is 'weightless' and can slosh around during satellite maneuvers, fuel tanks have a series of vanes and baffles inside. I don't know how much structural integrity they give the tanks, but frozen hydrazine will give it a lot more, at least until the heat of reentry melts it.

    The fuel tanks (or similar spherical tanks) are the most likely part of the spacecraft to survive reentry by far - Summary of Recovered Reentry Debris . In 1997, a piece of debris struck a woman in Oklahoma. Once in a while, the pieces land in a city. Pieces of Salyut 7, a very large Soviet space station, pelted the town of Capitan Bermudez, Argentina in 1991 (a relative term since debris fields are large and only a few pieces actually landed in the city).

    It's not that the idea is unfeasible. It's that it's a lot of money and effort to reduce a snowball's chance in hell to a snowball's chance in an even hotter place in hell. On it's own merits, it's like declaring war on the environment because lightning kills people.

    Obviously, there's ulterior motives. Shooting the missile is more important than reducing the risk of hydrazine.
     
  21. Feb 17, 2008 #20

    Ivan Seeking

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    So remember kids: We were given a very technical and logical explanation for this by the Government, but in all likelihood it is complete nonsense.

    I think this is the second shot in the new cold war with China.
     
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