[AR] Re: danger (was Re: MSR reactors.)
- From: <anthony@xxxxxxxxxxx>
- To: <arocket@xxxxxxxxxxxxx>
- Date: Sat, 13 Jul 2019 22:13:35 -0400
From a Stack Exchange citation;
"Second, there was no one single mission before (13) which pogo was a
serious problem, and after which it wasn't. Pogo occurred in the Saturn V
all the way up to Apollo 17. But during the program engineers took a series
of steps to make pogo less of a problem for each successive mission. But
there was often a delay because engineers needed time to analyze the results
from a Saturn V flight, and in most cases the next Saturn V was already
"stacked" in the assembly building and couldn't be easily modified."
Anthony J. Cesaroni
President/CEO
Cesaroni Technology/Cesaroni Aerospace
http://www.cesaronitech.com/
(941) 360-3100 x101 Sarasota
(905) 887-2370 x222 Toronto
-----Original Message-----
From: arocket-bounce@xxxxxxxxxxxxx <arocket-bounce@xxxxxxxxxxxxx> On Behalf
Of Henry Spencer
Sent: Saturday, July 13, 2019 8:27 PM
To: Arocket List <arocket@xxxxxxxxxxxxx>
Subject: [AR] danger (was Re: MSR reactors.)
On Sat, 13 Jul 2019, William Claybaugh wrote:
Apollo was estimated at the time as having a one in five probability
of loss of crew.
The actual flight history argues -- somewhat weakly -- that the risk for a
lunar flight was about one in ten.
There were 9 such flights (Apollos 8, 10, and 11-17), one of which (13) was
a failure. While no crews were lost, the Apollo 13 oxygen-tank burst came
*extremely* close to being fatal; it would have been fatal had it happened
on the trip home, or had any of several other factors been a little worse.
Moreover, the same flight (!) came very close to a catastrophic launch
failure due to the pump-amplified second-stage center-engine Pogo (which is
not well known because the tank burst overshadowed it and MSFC
understandably kept a low profile about it -- 13's Flight Evaluation Report
has a whole chapter about it, but with such bland matter-of-fact wording
that you have to read and understand the numbers to realize what a close
call it was). There were a few other lesser incidents on other flights that
were a bit worrisome.
That adds up to maybe 1 in 9, which you might as well call "about one in
ten" because there's room to argue about the addition, and the sample size
is too small to be very precise anyway. (If one case turning out
differently would greatly change your estimate, then your estimate can't be
very precise.) It would be a bit surprising if the real odds were as bad as
one in five or as good as one in twenty, but there isn't enough data to
reject such a suggestion very convincingly. There *is* enough to inspire
real doubt that the official crew-survival spec (99%) was met.
A decade ago the then Constellation architecture for earth-Moon human
transport came in at about one in ten.
The initial flight of the Space Shuttle was retrospectively estimated
at one in four; the last flight at one in 63.
Plausible numbers.
However, a caution: all this is not saying that human spaceflight is
*inherently* very dangerous. It's saying that human spaceflight done the
traditional way is inherently very dangerous. Which isn't too surprising,
given that all of those crews were (or would have been) flying on what
should be considered *early test flights* of complex new vehicles, all also
involving major hardware that was flying for the very first time.
We *know* how to do much better. Nobody puts valuable payloads, or crews
other than test pilots, on the first flight of a new aircraft design *or*
the first flight of a new production article of an established design.
Proper flight-test programs for new designs involve hundreds of flights, not
two or three, including systematic envelope expansion and tests of
contingency cases like engine failure, and every single new production
vehicle is test-flown before it's used.
Doing the equivalent for spaceflight should be possible. It would require
vehicles that are designed rather differently, and development programs that
are designed and run very differently. (Notably, the ability to fly some
semblance of a proper flight-test program, at an affordable cost in a
reasonable time, needs to be a non-negotiable design requirement. This does
preclude (a) major expendable components and (b) vehicles that have to be
essentially rebuilt after every flight.)
"Spaceflight is difficult -- today. It is expensive -- today. And the
level of risk remains high -- today. But it need not remain so forever.
We must resist the idea that space is inherently difficult, expensive, and
risky. Aviation once seemed so, too. Today, aviation is efficient and
safe. Space can get there -- if we accept that it can improve, and realize
that it will require hard work, investment, and experimentation."
-- Joseph C. Anselmo (AW&ST Editor-In-Chief), 3/10 Nov. 2014 issue.
Henry
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