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Why it scrubbed: NASA engineers troubleshoot Endeavour ‘s electrical problems

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shuttle Endeavour on the launch padKENNEDY SPACE CENTER—When NASA scrubbed the shuttle Endeavour‘s final launch here on Friday, engineers said there was a best-case and a worst-case scenario. Well, guess what: it was the worst case. The trouble began when an electric heater for the hydraulics system failed to turn on. When engineers opened the hatch into the left aft engine compartment (arrowed in photo), they found the problem lay not in a faulty thermostat (best case: it would have been fixed in a matter of minutes) but in an electrical subpanel called the load control assembly (worst: it takes days to replace and retest). "The power’s not getting out to the heaters," said Mike Moses, the launch integration manager.

NASA hasn’t set a new launch date yet, except to say it won’t be until May 8; even if the repair goes well, the Air Force has May 6 reserved for a rocket launch of its own. The Endeavour astronauts have flown back to Houston, although they remain in medical quarantine (which basically just means no contact with young children or anyone sniffly) at NASA’s Johnson Space Center. Support crews from other NASA centers have gone back home, too, and the press corps is dispersing. I got a parking spot in the first row this morning, and the press-conference room—which was standing-room-only on Friday—was only half full this afternoon.

Engineers are in the process of draining fluids from the ship and powering it down. They plan to pull out the glitchy load control assembly on Monday and install a new one Tuesday. It is a box about the size of a microwave oven, weighing 40 to 50 pounds, packed with switches and fuses. It feeds power into nine separate systems, not just the hydraulics but also life support and the main engines. All those systems will have to be retested with the new box in place—a process that takes a full two days. Although a failure of the box would not have shut down those systems, since there are backup power lines, NASA policy is to fly the shuttle only when everything, both primary and backup, is good to go.

In the scheme of things, the loss of a load control assembly is not a major problem. Electronics do fail. Much the same thing happened to the shuttle Discovery during preparations for takeoff in July 1995. To be sure, engineers need to take apart the box to make sure it was indeed to blame. If not, they’ll clearly need to do more detective work. "How the failure occurred, we just don’t know yet," said shuttle launch manager Mike Leinbach. This is one reason NASA has not set a new launch date—the better to let engineers stay focused on the problem at hand, rather than add the extra stress of a countdown.

If the delay goes beyond May 8, the shuttle may run into a scheduling conflict with the undocking of a Russian Soyuz spacecraft from the space station, and the final shuttle launch—of Atlantis in late June—may have to be pushed back.

Image: Courtesy of Ken Kremer





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  1. 1. SigmaEyes 1:24 am 05/2/2011

    FIRST!!

    I have never understood how NASA got the Apollo missions through the radiation belt, and why no other nation on Earth has been able to do it.

    I always assumed the shuttles and space station would be used to ferry parts to assemble a craft in orbit, so that heavy shielding would protect the humans going to the Moon or Mars or an asteroid.

    Since that is not going to happen, perhaps some nuclear supporter will explain the levels of radiation in the radiation belt, and the amount of shielding that would be required (lead?).

    I still wonder why the Apollo crews did not cook in passing through it twice (and in some cases more often), and why each one didn’t live a short life, ended by cancer.

    Personally, I think NASA deserves a lot of continued funding, and that we should not jump into privatization of space just now. But NASA is becoming increasingly irrelevant as the DoD has been doing far more launches per year for many, many years.

    I’d like to see an updated replacement shuttle program, and a space craft built in orbit, but automation seems to be the current mode of exploration, and manufacturing in orbit has not panned out into any commercially viable option; which of course leaves orbital tourism.

    But what about the promises for colonization and extra-terrestrial self sustainable ecosystems? I am so sorry to see the shuttle program end while military budgets grow. It kind of shows what kind of people we have become. Explorers and achievers somehow became warmongers and attackers. But hey, when the North American continent was discovered, we wrongly did the same transformation. I just hope the learning curve has shortened considerably.

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  2. 2. mudphud 6:34 am 05/2/2011

    The Apollo missions travelled only through the edge of the Van Allen belt (it’s a gradient, the edge is much less intense than the center). All radiation is not the same, and the type of particles they were shielding against were blocked for the most part by the fibrous insulation of the capsules. The astronauts got higher than normal doses of radiation, but not life shortening doses.

    As far as other nations not attempting a similar program, I don’t think the issue is radiation. The Apollo program was estimated to cost $170 billion in 2009 dollars, and that’s not the cost to stay there. That’s a lot of money to be the second nation on the moon.

    Link to this
  3. 3. jack.123 6:50 pm 05/2/2011

    Much study went into creating the correct flight paths,to minimise the radiation.There was also a lot shielding in all the right places,remember all the gold.Even today when you look at satellites you still see lots of gold shielding.

    Link to this
  4. 4. SigmaEyes 3:41 pm 05/4/2011

    Thank you for that information. I had spent some time on the NASA website looking for some rational explanation a few years ago. I even began a year long online chat with a Fla NASA engineer who got shockingly offended at the mere question.

    While I would like a little more specifics, yours is the first rational explanation I have heard that seems it could be feasible. If you could point me to any solid sites that have info on the subject, I would be glad to investigate a little further.

    Link to this
  5. 5. DanSchultz 4:24 am 05/6/2011

    The Apollo missions passed through the Van Allen belts very quickly, in only a few hours. While you wouldn’t want to live there, you can pass through the belts if you don’t stay too long.

    Radiation from solar flares was a much bigger concern. NASA kept a constant lookout for solar flares while the astronauts were on or near the moon so that they could lift off from the surface and get back to the command module with its heavier walls. The lunar module had very thin walls that provided little radiation shielding.

    The gold foil that you see on space vehicles is a very thin layer of gold that reflects infrared radiation to keep the spacecraft from overheating. It provides no protection against ionizing radiation or particles. There is more gold in your wedding ring than there is on a spacecraft’s thermal blanket.

    Link to this
  6. 6. DanSchultz 4:24 am 05/6/2011

    The Apollo missions passed through the Van Allen belts very quickly, in only a few hours. While you wouldn’t want to live there, you can pass through the belts if you don’t stay too long.

    Radiation from solar flares was a much bigger concern. NASA kept a constant lookout for solar flares while the astronauts were on or near the moon so that they could lift off from the surface and get back to the command module with its heavier walls. The lunar module had very thin walls that provided little radiation shielding.

    The gold foil that you see on space vehicles is a very thin layer of gold that reflects infrared radiation to keep the spacecraft from overheating. It provides no protection against ionizing radiation or particles. There is more gold in your wedding ring than there is on a spacecraft’s thermal blanket.

    Link to this

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