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Doesn't it just make you mad?

  1. Oct 25, 2007 #1
    Well I don't have very much knowledge on this topic, but doesn't it just irritate you that NASA never even bothered to fix the hole in the Space Shuttle Endeavour when it went up a few months ago? Please correct me if I'm wrong about this. But you figure that after what happened to Columbia, thats what they would do when that situation happened. :confused:
     
    Last edited: Oct 25, 2007
  2. jcsd
  3. Oct 25, 2007 #2
  4. Oct 25, 2007 #3

    mgb_phys

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    Ice hitting the tiles isn't really a problem - it only happened once and so that was just a statistical freak, all the other times that it didn't crash prove that it's safe. Similair 'manager logic' can be applied to proving that icebergs are not a statisticaly significant threat to ships called Titanic.

    The problem with the shuttle is the rather brittle nature of any advanced technology. Because it is difficult to get into space the shuttle is only just capable of doing it if everything works - so pretty much anything failing is a disaster. Compared to aircraft which regularly take off with a list of problems (snags) but still manage to fly safely because they are over engineered.
     
  5. Oct 25, 2007 #4
    Generally the shuttle team has to weigh a variety of "risks" to the shuttle and crew before deciding what to do with damaged tiles. The shuttle tiles have been damaged on many occasions, but only rarely has that damage posed a significant and life threatening problem. Most of the small cracks and holes in the tiles are not "mission threatening". Even more relevant is the fact that adding material into the hole poses the threat of that patch material dislodging during reentry and causing more tile damage than they started with. The NASA team (and flight team) have to weigh a variety of factors before they decide to attempt to "patch" the system in flight.

    Our ability to "patch" things up in space is still pretty limited by the way. A major amount of tile damage would probably result in the shuttle having to dock with the space station while the folks on the ground decide what they want to do. Smaller cracks and nicks are often not "messed with" in flight because they are small, or they occur in areas that don't receive as much heat during the reentry process. Columbia was a special case scenario, where the damage was severe (more severe than they realized), and it took place is a very vulnerable area of the tiles, an area that receives a lot of heat buildup during reentry, and an area that has to open up to allow for the wheels to come down. Because patch materials can come loose, it's sometimes much safer to leave the crack alone, than to attempt to patch it up in space. It's definitely a "judgment call" type of process. You can be sure that NASA is highly sensitive to this issue now, and they run through a variety of computer simulation scenarios before they decide what to do with damaged tiles.
     
  6. Oct 25, 2007 #5
    Oooh okay I understand now. Thanks! :)
     
  7. Oct 25, 2007 #6

    mgb_phys

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    What would you do with a broken shuttle? After you dock with the ISS and book a flight back with the Russians, you have a shuttle stuck to the ISS.

    Even assuming it isn't a problem sitting there and doesn't add enough drag to compromise the ISS. The space station is due to be dumped in a few years.
    The shuttle is a fairly solid lump of metal and is designed to survive re-entry.
    Would you open the cargo doors and deliberately try and re-entrer it upside down so it would break up, or install demolition charges to break it inot smaller pieces that would re-enter safely, or would you have enough control to aim it at the middle of the pacific (hopefully missing Hawaii) ?
     
  8. Oct 25, 2007 #7
    I thought the re-entry process was entirely controlled by computer so they couldn't NASA fly the unmanned shuttle back? If it blew up nobody would get hurt and if it didn't they could reexamine it to find out what went wrong where.
     
  9. Oct 25, 2007 #8

    mgb_phys

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    I didn't know if they can do the full orbit - landing automatically ( which of course begs the question of why crew it in the first place!)

    The danger is that if you know it's going to blow up and you are flying it over the whole of the USA to land it then you risk hitting a lawyer.
     
  10. Oct 25, 2007 #9
    I'm unsure if they can do the entire orbit (I would imagine so, as computers should theoretically be more accurate than humans) but I remember reading in Richard Feynman's autobiography detailing his accounts with the Challenger disaster that NASA had computers doing taking care of all landing details. I could, of course, be remembering incorrectly.

    As for your second part...well you win. Excellent point. :)
     
  11. Oct 25, 2007 #10

    russ_watters

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    They can do an entire shuttle flight without a crew. Why have a crew? Why have a shuttle if you don't want to send people up?

    Just a couple of clarification, though - foam hits the space shuttle on virtually every flight and ususally damages tiles. The shuttle used to even lose tiles due to vibrations on launch (not sure if it still does). As much press as it got, the damage to the Endeavour was not newsworthy. It was a minor gouge that iirc did not even penetrate the tile - it wasn't a hole.

    Also, docking with the space station is not generally an option unless you are launched with the intent (into an orbit with the right altitude and inclination) of docking with the space station. It takes an enormous amount of energy to reshape an orbit - it can be a significant fraction of the energy it took to get to orbit in the first place.
     
  12. Oct 26, 2007 #11
    Personally, I'd be inclined to fix it. If I still can't be sure it's safe I'd put it on autopilot and let it land by it's own instruments. If it survives, great! If not, at least I tried, and no humans need lose their lives in the attempt to save the shuttle. :)
     
    Last edited: Oct 26, 2007
  13. Oct 26, 2007 #12
    Oh, I see you beat me to it. :) I like the way you think. :)
     
  14. Oct 27, 2007 #13

    Chronos

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    Risk is inherent to all shuttle missions. Managing risk is a relatively new phenomenon. I have no problem with the assessment on Endeavor. The risk was very low. In the past, risk was a design, not managed factor. That, as NASA learned the hard way, was a dangerous approach.
     
    Last edited: Oct 27, 2007
  15. Nov 5, 2007 #14
    I am in fun speculation mode here :smile:

    Depending on how severe the damage, and how much fuel available, there are some (uncomfortable) calculated strategies for getting a shuttle home in a unconventional re-entry posture. Nobody would want to test them. I tried some quick 'n dirty numbers to see if an extended engine driven slowdown, with the inevitable quite fast drop towards the atmosphere could blunt some of the need to use the atmosphere as a friction brake.

    Not that my very school standard calculations should go too far here, but the ideal would be slowing from about 17,000 mph to about 1000 mph, matching the ground below, and just waft down on parachutes. There is not a need to use as much fuel as it took to get up there, but even so, its too much.

    More dangerous is the drop to a hot re-entry before there is time to slow down to a safe one.
    We just have to accept that space travel is a marginal, very risky thing, and there are economics to making it work. There are only 14 (maybe 13) shuttle missions left, I think. I also think that whatever replaces it will still need to have re-entry insulation. :smile:
     
  16. Nov 6, 2007 #15

    Garth

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    Would it not take the same amount of fuel to stop the Shuttle going at ~ 17,000 mph as it took to get to that speed in the first place?

    Garth
     
  17. Nov 6, 2007 #16

    EL

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    Actually not, since the Shuttle has burned some fuel (that is, decreased its mass) on the way up. The effect should be calculable with a rocket equation.
     
  18. Nov 6, 2007 #17

    Garth

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    But I wasn't including the ride up to orbital height, just orbital speed. :wink:

    Garth
     
  19. Nov 6, 2007 #18

    mgb_phys

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    I thought all flight had to be capable of reaching the ISS in case of an emergency - that's why the shuttle can't be used to launch most satelites anymore ?
     
  20. Nov 6, 2007 #19
    Of course - normally it takes the same burn, (while facing the other way) to get back to any speed you had originally. In the case of the shuttle, the orbital speed was aquired differently. As EL mentioned, the rocket equation applies. NASA do not expend that huge mass of fuel, mostly used up in lifting the remains of itself, without the payoff being a 17,000 mph orbit of shuttle tonnage. Astronauts notice the increasing forces on their bodies as the vehicle gets lighter.

    Once up there, it is true that less is needed to accelerate, but there is very little left. You cannot just choose to head off here or there as takes your fancy (Star Wars style :smile: ). The slightest extra burn, say to catch up to ISS for docking, or fix Hubble or whatever, immediately increases altitude also, and you miss the target. I think it takes a calculated wasteful over-speed plus braking and dropdown to arrive. So instead, you plan the path to leave out the extras.

    That fuel, and the machinery to lift it! Pumps! Think of pumping empty an Olympic swimming pool in about 4 to 5 minutes! I am sure someone here knows how many $K per kilogram it takes to get stuff up there. Whatever it is, I am sure it precludes extra-orbital touring.
     
  21. Nov 6, 2007 #20

    EL

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    Ok, I admit I did not read all previous posts (and I still havn't), so maybe my reply was just bla bla (or wasn't it?). Sorry in that case.
     
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