Tuesday, July 26, 2005

Return To Space, Take Two.

The official countdown has begun for the Space Shuttle Discovery's scheduled 10:39 EDT launch this Tuesday morning. You can watch the launch live over the web at NASA TV and at Foxnews.com.

You will probably hear a lot of coverage about NASA's "shooting from the hip", or "going for broke" by launching an impaired shuttle. As your humble aerospace engineer, I can assure you (in a geek-like fashion) that this is not the case.

There is a fuel gauge in the huge orange gas tank (external tank) which signals to the three main shuttle engines when the external tank is out of gas (just like in your car). Proper operation of the fuel gauge is essential for a safe flight. (Please stop me if I get too geeky... too late!) Anyways, because it is so important, you (or I ) would need two identical fuel gauges for safety reasons. That would give you (or me) a "Safety Factor" of two. Got that? You have double, or two times what you would need for a regular flight. To put it in perspective, the aviation industry uses a safety factor of 1.1 for airplane design, or alternatively, 10% safety margin on all designs. Ok, so now NASA has double redundancy. But double safety wasn't enough. NASA required three fuel sensors to be used up until 1986 - a safety factor of 3, or 200% safety margin. After the Challenger disaster, NASA bumped up the requirement to have four sensors. So now each Shuttle flight has a safety factor of four, or four times the amount of sensors necessary for a safe flight (one).

NASA scrubbed the launch two weeks ago because one of these four redundant sensors was acting weirdly. They still had (and have) three perfectly normal sensors ready to do the job of which on one is necessary to do. NASA is unsure of how the fourth one will behave as the problem only crops up in the final hours of a fully fueled, real shuttle launch attempt.

NASA has three working sensors. They only need one to work. Remember that when the news stations gasp at NASA's cavalier attitude at launching astronauts and aging billion dollar hardware. Remember that when those stations preen at the "New" NASA - the new gunslingin' gung-ho wild-west gotta-get-to-space NASA. The astronauts' safety is not appreciably affected in any real way by choosing to launch today.

So NASA has a choice to make this morning - do we keep a decades' old extra safety factor which has no real bearing on the safety of the astronauts? Or do we "resort" to a safety factor of three (still very safe) in order to launch this Return To Space flight, and get back into the history books. I, personally, would choose the latter.

Update: For more, see Rand Simberg's Transterrestrial Musings.

Update: All Systems Go. Weather is good. Soichi Noguchi was having some fun getting into Discovery. Heh.

Update: T-3 minutes.
10:13 a.m. - A pair of WB-57 spacecraft are flying off the coast to provide images of the Discovery ascent that have never been seen before.

Update: SUCCESS!! Space Shuttle Discovery launch successful.

Update: It was successful, but not perfect. Transterrestrial Musings has the update on some foam coming off, whith no damage, though. [P.S., for all your space blogging needs, Transterrestrial Musings will take good care of you.]

Update: Welcome Transterrestrial readers. Feel free to check out my main page, or my most recent space post: Status of the Space Shuttle.


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