Re: Man-Rating Atlas V


lou@xxxxxxxxxxx wrote:

But I don't think NASA is that much more talented
than everyone else who has tried this.


NASA isn't more talented. They do, however have different incentives.
NASA management gets raked over the coals every time they lose a manned
launch. A 2% failure rate is viewed as a shameful failure. The same
rate on a Delta II has management clapping themselves on the back for
how reliable they are.

2% is actually a fairly respectable performance for a large, complex
vehicle design with very little direct heritage and a lot less flights
than say, Soyuz. The SDV cargo vehicle should probably be able to beat
that reliability record, given that it will be a more evolutionary
vehicle than the shuttle. The stick, being simpler, should be able to
do rather better than that.



The Atlas agument seems much more solid. The've actually launched it,
so they have some concrete evidence they did not miss anything big.
And in some cases, for some portions, they've launched it in
higher-stress configurations, so they have some proof that the margins
are there. This is not true for the shuttle, for example, where there
might be some part with a safety margin that is 1.001, which is just
waiting to fail on the next flight.

Overall, if you apply any realistic factor for 'unexpected' failures,
the better expendables are likely safer alternatives. Of course this
is hard to quantify - if you *could* quantify it, they would not be
unexpected.

Lou Scheffer

Atlas V hasn't flown nearly enough flights to say whether it has a
reliability of 2% or 5%. And the version they'd use to launch the CEV
hasn't flown at all. Estimates of its reliability are also educated
guessework.

Will McLean

.

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