Re: Shuttle Safe as an Automobile?
- From: "Jorge R. Frank" <jrfrank@xxxxxxxxxxx>
- Date: 27 Apr 2005 05:12:11 GMT
"Ray S" <rjs41@xxxxxxxxxxxxx> wrote in
news:Gexbe.7154$J12.5327@xxxxxxxxxxxxxxxxxxxxxxxxxx:
> So much for launch risk. What about the risk associated with the
> entire shuttle flight regime (launch, orbit, reentry/landing)? In 1997
> the National Research Council was tasked to estimate the risk to the
> shuttle from orbital debris and meteoroids. In doing this work, the
> NRC considered the entire flight regime and came up with the
> following:
>
> Without meteoroid and orbital debris
> Ascent Reentry Debris Total
> Median 1/248 1/350 na 1/145
> Mean 1/219 1/326 na 1/131
>
> With meteoroid and orbital debris
> Ascent Reentry Debris Total
> Median 1/248 1/350 1/200 1/84
> Mean 1/219 1/326 1/200 1/79
>
> NRC used 1/200 as the failure frequency associated with orbital debris
> and meteoroids, a supposedly "worst case" value obtained from NASA,
> DOD and industry experts. I don't know if there have been more recent
> updates for this number and I don't whether NASA really agrees with it
> today. Regardless, the NRC was pretty disturbed by the relatively high
> failure frequency (1/84, median) that fell out of this calculation and
> tried to light a fire under NASA to pay more attention to meteoroid
> and orbital debris risk.
Which to some extent, NASA did. Prior to 1997, NASA chose shuttle free-
flight attitudes that optimized comm, thermal, and payload constraints.
That usually resulted in a payload bay-to-Earth, wing to the velocity
vector attitude. After 1997, NASA switched to a free-flight attitude that
minimizes the debris risk (bay to Earth, tail to velocity). NASA also
installed a payload bay radiator bypass so that a debris strike on a
radiator would not result in the loss of the associated Freon coolant loop.
Regarding updates, if anything NASA now believes the debris risk to be
worse than what the NRC determined, especially given NASA's new
understanding of just how vulnerable the RCC is. NASA is taking further
measures such as "flipping" the shuttle-ISS docked attitude. Previously,
the shuttle flew in front, belly to velocity. Now, the better-shielded
station will fly in front to shadow the orbiter from debris.
> I assume that the CAIB will make NASA do other things to
> mitigate this particular risk (inspecting the TPS via milsats, using
> the ISS arms and cameras for closeup TPS inspection, etc).
Unless the milsats are an order of magnitude better than what's suggested
in the open literature, they won't be able to detect RCC damage down to the
critical threshold. The CAIB mostly addressed ascent debris, and
recommended (R6.4-1) that NASA perform a TPS inspection as early as
possible in each mission. That would not necessarily detect orbital debris
damage sustained later in the flight.
--
JRF
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- References:
- Shuttle Safe as an Automobile?
- From: Nomen Nescio
- Re: Shuttle Safe as an Automobile?
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- Shuttle Safe as an Automobile?
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