Posted on 02/01/2003 2:41:25 PM PST by theFIRMbss
Ah, such a simpler era...
250K lines of code probably wouldn't make a decent spreadsheet program these days.
1. Suppose we did the odds of death from the shuttle after the first 50 shuttle flights. 1 failure out of 50 = 2%. If we did it after 100 flights, sure, it would be 1%, but we already have the second failure after only 13 flights into the second 100-flight cohort, so the shuttle better fly the next 87 missions without fatality or that percentage goes back up. Since it has been about 80 flights between crashes, that may or may not happen.
2. We could calculate it based on persons who have died as a percentage of those who have flown. This, in fact, might be the most useful statistic. Since Yuri Gagarin in 1961, approximately 400 different humans have attempted to fly into space. At least 17 died (I say "at least" because there are suspicions of unreported Cosmonaut deaths). 17 out of 400 is about 4%. That percentage would be higher if it were just US astronauts, btw. I saw an astronaut quote this figure on tv today, so it is not something I pulled out of the air but rather the kind of figure real-life prospective astronauts think about, however slightly, when signing that release.
3. We could look at the average time between major catastrophes. The three years are 1967, 1986 and 2003. A nineteen-year interval followed by a seventeen-year interval. While there were a lot more flights in the latter period, we also were much more technologically sophisticated and had learned from a lot of mistakes. That suggests that the odds of dieing as a function of time are staying about the same or even increasing.
My opinion from the facts is that boarding a government spacecraft for a spaceflight has a statistically significant death rate in the low single digits, around 2% and maybe higher. As long as the technologically obsolete Space Shuttle keeps flying, I doubt those odds will go down much no matter how many lessons NASA learns from each crash. I would make sure my life insurance were fully funded before boarding one of those ageing deathtraps.
One thing to look at
will be the thirteen "fixes."
Bugs feed on kludges...
Yes, well, remember
one of the big arguments
for a big OS
integrated to
a graphic interface was
that all the shared code
would allow user
programs to get much smaller!
(If we all used FORTH...)
As if you understood a word. These were SSME (main ENGINE) problems. Just FYI, the engines are TURNED OFF during descent.
Oy.
--Boris
Hey, take a chill pill.
Just about every system
has been fiddled with
since the Challenger.
All those "fiddles" could add up
to lots of strange bugs.
And they probably
burn the main engine to slow
their orbit and start
re-entry. (Save your
oys and the duh FYI's
for people who care.)
They do not. There is a separate propulsion system called the OMS (Orbital Maneuvering System) which does the retro burn. It is as different from the SSME as a snail is from a lion.
--Boris
"The OMS engines burn monomethyl hydrazine fuel (CH3NHNH2) and nitrogen tetroxide oxidizer (N2O4). Interestingly, when these two substances come in contact, they ignite and burn automatically (i.e., no spark required) in the absence of oxygen. The fuel and oxidizer are kept in separate tanks, each pressurized by helium. The helium is used to push the fluids through the fuel lines (i.e., no mechanical pump required). In each fuel line, there are two spring-loaded solenoid valves that close the lines. Pressurized nitrogen gas, from a small tank located near the engine, is used to open the valves and allow the fuel and oxidizer to flow into the combustion chamber of the engine. When the engines are shut off, the nitrogen goes from the valves into the fuel lines momentarily to flush the lines of any remaining fuel and oxidizer; this purge of the line prevents any unwanted explosions. During a single flight, there is enough nitrogen to open the valves and purge the lines 10 times!"-----------------------------------------------------------------------------------
There you go! You see--
it's nicer to be helpful
than a smart aleck...
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