Florin:
In designing an escape system one can not rely on the rocket(s) shutting
down. That is nice to have, but the escape system has to get the crew away
even if the launch vehicle fails to shut down its motors. Thus in the
practical design of an LES there is no difference between solid and liquid
failures in terms of the LES performance requirements.
We should also observe that the kind of partial failures that sometimes
allow liquid rockets to reach the wrong orbit are probably flight ruled out
when an LES is present: nobody wants to explain to a failure investigation
why they left the crew on a vehicle that was known to be failing. Thus the
flight rules will activate the LES as soon as a hole in the cooling jacket
(to name a common liquid engine failure that sometimes gets to orbit
anyway) is detected.
Bill
On Thu, Feb 8, 2018 at 10:39 AM Florin Mingireanu <
florin.mingireanu82@xxxxxxxxx> wrote:
Henry,
Hence, my note with SF- at least for now.
I am aware of simplicity and I can say that I am a big fan of KISS - Keep
It Simple Stupid.
However, making it smart does not mean that you increase the chance of
failure (depends on how you design it); also making it smart does not
necessarily mean that you unnecessarily make it complex. I can envision
some escape scenarios where not doing anything could be the best thing that
one could do- at least for a while!
My answer was along the lines that even in case of a solid rocket motor
failing and accelerating roughly along the same line one could still use an
efficient escape system by imparting side kick.
The entire discussion started from the observation that a solid rocket
motor cannot easily be shut down while a liquid could be easily shut down;
hence, the escape system could be easier to be implemented on a liquid
architecture.
I am not entirely convinced of this observation and, hence, my message.
Florin
On Thu, Feb 8, 2018 at 7:28 PM, Henry Spencer <hspencer@xxxxxxxxxxxxx>
wrote:
On Thu, 8 Feb 2018, Florin Mingireanu wrote:
One could even think of an active system that "tracks" the remainder of
the rocket and modulates the extraction accordingly. If it seems SF... it
is SF until someone actually does it :-)
Whether it's possible and whether it's desirable are two separate issues.
:-) There is usually a strong preference for making emergency equipment,
like escape systems, *simple*. That's partly to make them reliable, partly
to minimize the possibility of subtle bugs (since they don't get tested
much in normal operation), and partly to make them less dependent on case
analyses that never manage to cover 100% of the cases.
Smart systems are a two-edged sword. Rockets and spacecraft have died
because smart fault recovery was faced with a weird unexpected situation,
and picked the wrong response. Stupid fault recovery that always does one
thing, rather than trying to make clever choices, is usually preferable.
Henry