Re: NASA HONORS LEGENDARY ASTRONAUT VANCE BRAND



Jorge R. Frank wrote:

So that's about a six-to-one safety ratio in favor of the Russians, based on total flight man-hours.



Yes. And if you think that metric is remotely relevant to actual risk, you're a fucking moron. No ifs, ands, or buts about it.



When you stated that total man-hours in space was completely irrelevant to the safety of the two programs, I knew full well what I would find if I looked up total flight man-hours- as I know your debating style, and also know that you work for NASA in the capacity of Shuttle crew trainer: http://edspace.nasa.gov/text/astromeet/dayinlife/bmorgan2.html so that you have a vested interest in putting the Shuttle program in as good of a light as possible, if for no other reason than keeping bread on the dinner table.
Say, if I join Earth Crew do I get a cool armband like the members of Night Watch did in Babylon 5? ;-)
I promise to report anyone I catch saying anything antishuttle: http://www1.edspace.nasa.gov/text/earthcrew/
Just because you're paranoid doesn't mean that there really isn't someone out to get you, and just because Brad Guth is insane doesn't mean that there really isn't a NASA mole lurking about in the newsgroup....and one that uses four letter words at that. :-D
As you say, the most dangerous times for any space mission are during ascent and reentry, if for no other reason than the energies and stresses that the vehicle experiences as it accelerates to, and decelerates from, orbital velocity.
But orbital flight time itself is certainly not risk free, as a study of the Russian space station program will certainly show.
As far as statistics go, each of our programs have lost two spacecraft and their crews over the years and have had a number of close calls.
How precisely you can work out statistics you can even vaguely rely on for machinery as complex as the Shuttle, Soyuz, Apollo, Salyut, Skylab, Mir, and the ISS, much less the earlier manned programs where we both just cutting our teeth in the realm of spaceflight is completely beyond me. There are far too many variables and possible failure modes to ever get anything more than the roughest of guesstimations about what the actual safety factor is.
Even statistical risk modeling for individual aspects of the Shuttle has proven very difficult:
http://www.newscientist.com/article.ns?id=dn6943 not to mention the overall system
NASA had wonderful and very precise risk factors worked out for the Shuttle, then changed them completely after the loss of the Challenger, and again after the loss of the Columbia (what I really found amusing was the precision of these calculated risk factors; it wasn't some rough number like "about one in 400" but more like "one in 383" which gave the illusion that they really could be that precise in their calculations, and that that would be a usable number) When your estimates change as wildly as they did after the Challenger accident, you have to start asking yourself if what they are based on has any relevant connection with the real world.
This problem was addressed in the Gehman report: http://hubblesite.org/newscenter/newsdesk/future/gehman.html
They based the actual safety factor of the Shuttle on its loss rate:

"It was one of CAIB's goals to help national policy makers understand the risks of Shuttle flights by putting space flight as we presently conduct it into context. We as a nation need to understand, as best we can, the amount of risk we accept while accomplishing our goals of space exploration. In Chapter Five, we quote the 1989 Office of Technology Assessment.

'Shuttle reliability is uncertain, but has been estimated to range between 97 and 99 per cent. If the Shuttle reliability is 98 percent, there would be a 50-50 chance of losing an Orbiter with 34 flights … The probability of maintaining at least three Orbiters in the Shuttle fleet declines to less than 50 percent after flight 113.'
(STS-107, the ill fated Columbia flight, was the 113 th Shuttle mission.)

And we quote the 1990 Augustine Commission Report:

'And although it is a subject that meets with reluctance to open discussion, and has therefore too often been relegated to silence, the statistical evidence indicates that we are likely to lose another Space Shuttle in the next several years … probably before the planned Space Station is completely established in orbit.'

To put these very accurate predictions into today's context, we should use figures we know are accurate. We have flown 111 out of 113 Space Shuttle missions safely, for a 98.23 percent reliability rate. The chance that we will be able to fly 25 future missions using this reliability figure without a loss is 64 percent. The more missions we fly, the more that 64 percent number goes down. It is my opinion that implementing all the Return to Flight recommendations made by the CAIB raises the reliability number somewhat, although no one knows for sure what it is. A reliability number more like 99 percent seems reasonable to me, giving a 78 percent chance we will fly the 25 missions without loss. Once again, more missions cause that 78 percent number to go down. Flying one more mission, 26 in all, reduces the probability of series success by about one percentage point.

The bottom line: Shuttle flights are dangerous and we should fly the minimum number necessary. Almost all the risk is concentrated in the front and back of the mission, where one goes on orbit makes little difference."

That last remark is interesting, but certainly given the duration of a average Shuttle flight, the total risk involved in on-orbit time isn't terribly great compared to the risks encountered during ascent and descent.
In the case of a permanently manned space station, that could be a whole different matter. Risk on any given flight day is very low, but there are 365 flight days in a year, and if one waits around long enough, something fatal is bound to occur, be it tomorrow or 30 years down the road.
That's why I thought it relevant to compare the total flight hours of the US and Russian programs.
By far the vast majority of the risk is associated with the events that occur on a individual space mission during its ascent and descent, but there is risk involved in just being in an environment as hostile as space for any length of time, and that should be factored into the equation also.
The Russians have shown a very lackadaisical attitude toward flight safety over the years, but they have the advantage of having a spacecraft that is as tough as Soyuz...it can start reentry going backwards, catch fire on the pad, slide down mountainsides, bob around in a frozen lake, get dragged across the ground by its parachutes, suffer loss of its landing rockets, and make a ballistic rather than lifting reentry (on several occasions) and still have its crew survive, if somewhat the worse for wear, and possibly minus a few teeth.
We on the other hand have a far superior safety ethos- but a extremely fragile and complex space vehicle that will destroy itself if it gets used even slightly out of spec, and has no method of crew escape if something goes wrong other than telling them to jump out the side hatch like on a C-47.

They have the AK-47 of spacecraft; it's heavy, it's crude, it isn't that accurate....and you can dip it in mud and it will not only fire but clean out its workings a it does.
We have the M-16; it's lightweight, it's sophisticated, it's precise...and you have to keep it very clean or the damn thing will jam on you just when you need it most.
It's no coincidence that the Russians have such effective ejection seats on their fighters and a very effective escape system on their Soyuz- given their approach to things they no full well that they are going to get the opportunity to use them. ;-)

That ol' fucking moron:
Pat
.

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