[AR] Re: [UK OFFICIAL] Moon Express - HTP/kero
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Mon, 17 Jul 2017 12:29:25 -0400 (EDT)
On Mon, 17 Jul 2017, John Dom wrote:
I count on what I have time for read and I have not read about HP is
going to be re-introduced as for RCS...
As Alex has just posted, ESA is now looking seriously at doing just that,
for Vega upgrades and other applications.
and certainly not as a main propellant.
X-37 was originally going to have HTP/kerosene main propulsion, although
it appears that they switched to NTO/hydrazine, perhaps to support longer
flight times.
Or have you read there were problems with Gemini or Apollo or Shuttle
manoeuvring thrusters?
Uh, it's a matter of record that there *are* a number of issues with those
thrusters. In particular, flight preparations and (for reusable systems)
maintenance are very manpower-intensive, and have considerable impact on
other work because they are hazardous operations and often require
stopping all other work in the vicinity. The shuttle folks repeatedly
looked hard at switching to HTP/kerosene or LOX/alcohol, but the necessary
development funding was never available.
Another issue is that they are prone to small valve leaks in the N2O4 side
after the first firing. The reason is that any trace of water in the N2O4
plumbing gives nitric acid, which tends to dissolve bits of the metal
plumbing, forming metal nitrates... and those tend to crystallize out in
random places downstream. Essentially, there's now a bit of grit in the
liquid, and that can easily prevent a valve from closing completely. If
the valves are closed (and leak-checked) with the plumbing empty, and it's
then filled, you're okay as long as it's just sitting there inactive...
but the first time you open those valves, they just might fail to seal
cleanly on closing again. This is why, when Gemini 8 had to use its
reentry RCS system to deal with a hardware failure in its main RCS, they
had to cancel the rest of the mission and do immediate descent to the
first available recovery area -- they had to do retrofire while they were
still reasonably assured of a functioning RCS for it. Modern valve
designs try to allow for this, but the solutions aren't perfect.
Neither do I remember surreptitiously evaporating LOX being used in any
deep space missions.
Depends on how "deep" you're talking about. The Altair lunar lander of
the Constellation program had LOX/LH2 descent propulsion. And the Russian
LOX/kerosene Blok D upper stage, used for many years as the Proton fourth
stage, was originally designed for their manned lunar program -- it would
do multiple burns, including lunar-orbit insertion and most of the braking
burn for the lander, after several days of coasting to the Moon.
Peroxide *still* has the same catalyst misery and auto-decomposition
losses.
Catalysts are a headache, for sure, but there are straightforward
solutions -- not free of development effort, but with success reasonably
assured -- if you're willing to use 85% HTP rather than pushing for 100%.
Decomposition losses are negligible with proper materials choices -- it's
the pressure buildup that's a nuisance.
If a catalyst pack goes off unexpectedly you are dead in the water (in
space).
As with any other type of engine failure. The answer is, have more than
one engine. (Note that Cassini's NTO/MMH main propulsion system included
a complete spare engine, and would have switched to it automatically if
there had been signs of trouble during Saturn-orbit insertion.)
Also, I am still waiting for that mysterious video showing "direct"
combustion of HTP and kero. The 20th year already and counting. A religion?
People have pointed you to video of Robert Compton's tests, and to
discussion of ignition options in sources like "Ignition!", and you simply
refuse to believe it. Yes, you clearly have some religion there...
Henry
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