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From: kent@vf.jsc.nasa.gov
Newsgroups: sci.space.shuttle
Subject: Re: After Endeavour, what then?
Message-ID: <1991May13.170952.1@vf.jsc.nasa.gov>
Date: 13 May 91 23:09:52 GMT
References: <346.281f448d@mwk.uucp> <1991May7.212707.5380@aio.jsc.nasa.gov> <1991May8.092605.1@vf.jsc.nasa.gov> <1991May9.034143.16916@agate.berkeley.edu>
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In article <1991May9.034143.16916@agate.berkeley.edu>, fcrary@headcrash.Berkeley.EDU (Frank Crary) writes:

>>Now if all the Orbiters are still around after 82 flights each is another 
>>question entirely.
> 
> The 100 flight lifetime of an orbiter assumed an impossible reliability of
> 99.97%. The shuttle has demonstrated a 97.5% reliability (39 / 40 ).
> At this rate, there is only a 0.065% (e.g. 1543:1 against) chance of the
> shuttle fleet flying 290 missions without loosing an orbiter. In fact,
> at 97.5% reliability, 3 more flights in 1991 and 12/year in 1992 and later,
> there is only a 8.2% chance that all four orbiters will survive to see the
> year 2000. Also, there is a 35% chance that one of the 17 space station
> construction flights will result in an accident.
> 
> I find it hard to see the shuttle still in use after 2010 (at the latest).
> 
> 					Frank Crary
> 					UC Berkeley

The true reliability of the shuttle is unknown.  As you say is has demostrated
39/40.  But, the shuttle vehicles are designed for to last 100 flights.

The only think I see in your calculations is:

You state the odds of all four vehicles surviving.  What is the odds of one
vehicle surviving 80 flights?

-- 

Mike Kent -  	Lockheed Engineering and Sciences Company at NASA JSC
		2400 NASA Rd One, Houston, TX 77058 (713) 483-3791
		KENT@vf.jsc.nasa.gov