Gemini maneuvering thrusters

On the Gemini ships, what did they use for OAMS and RCS thruster fuel?
I think the Mercury spacecraft used hydrogen peroxide across a silver
screen in the combustion chamber. Did they go to hydrazine with
Gemini?

In article ,
Bill wrote:
On the Gemini ships, what did they use for OAMS and RCS thruster fuel?

N2O4/MMH, like the Apollo CM and SM. That propellant combination was just
becoming prominent then.

I think the Mercury spacecraft used hydrogen peroxide across a silver
screen in the combustion chamber.

Correct; *that* approach was just on its way out at the time. The
Gemini bipropellant thrusters had considerably better performance, and
originally looked like they would cause fewer hassles. (It's not clear
that they really did...)
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

Henry Spencer wrote:

In article ,
Bill wrote:


On the Gemini ships, what did they use for OAMS and RCS thruster fuel?



N2O4/MMH, like the Apollo CM and SM. That propellant combination was just
becoming prominent then.


It's surprising how long it took the Soviets to settle on it also; the
first generation Soyuz was still using hydrogen peroxide for all of its
RCS jets, and although they now use hypergolics for the service module
RCS, they still use hydrogen peroxide for the descent module RCS.
(Vostok and Voskhod used compressed nitrogen for RCS).



Correct; *that* approach was just on its way out at the time. The
Gemini bipropellant thrusters had considerably better performance, and
originally looked like they would cause fewer hassles. (It's not clear
that they really did...)



Did anyone take a crack at hydrazine monopropellant RCS for a manned
spacecraft?

Pat

On Sun, 26 Jun 2005 22:03:31 -0500, Pat Flannery
wrote:

Did anyone take a crack at hydrazine monopropellant RCS for a manned
spacecraft?

....Salvage One ran on monohydrozine.

OM

--

"No ******* ever won a war by dying for | http://www.io.com/~o_m
his country. He won it by making the other | Sergeant-At-Arms
poor dumb ******* die for his country." | Human O-Ring Society

- General George S. Patton, Jr

On Sun, 26 Jun 2005 23:02:50 GMT, (Henry Spencer)
wrote:

Correct; *that* approach was just on its way out at the time. The
Gemini bipropellant thrusters had considerably better performance, and
originally looked like they would cause fewer hassles. (It's not clear
that they really did...)

....Well, at least for *one* flight it didn't :-)

OM

--

"No ******* ever won a war by dying for | http://www.io.com/~o_m
his country. He won it by making the other | Sergeant-At-Arms
poor dumb ******* die for his country." | Human O-Ring Society

- General George S. Patton, Jr

In article ,
Pat Flannery wrote:
Did anyone take a crack at hydrazine monopropellant RCS for a manned
spacecraft?

Not that I'm aware of... although I don't remember what X-38 was going
to use.

For big vehicles, people tend to be attracted to biprop systems for lower
fuel mass. And most of the little vehicles were designed back before good
hydrazine catalysts were developed.

(Monoprop hydrazine didn't get popular until the mid-60s, when the first
hydrazine catalysts which *didn't* need preheating were found. Preheating
was marginally acceptable for major burns -- for example, Mariner 4's
midcourse-correction system threw in a squirt of N2O4, running briefly as
a biprop to get its catalyst hot -- but was utterly impractical for RCS
systems, which need to fire frequently and on short notice.)
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

(Henry Spencer) wrote in
:

In article ,
Pat Flannery wrote:
Did anyone take a crack at hydrazine monopropellant RCS for
a manned spacecraft?

Not that I'm aware of... although I don't remember what
X-38 was going to use.

For big vehicles, people tend to be attracted to biprop
systems for lower fuel mass. And most of the little
vehicles were designed back before good hydrazine catalysts
were developed.

(Monoprop hydrazine didn't get popular until the mid-60s,
when the first hydrazine catalysts which *didn't* need
preheating were found. Preheating was marginally
acceptable for major burns -- for example, Mariner 4's
midcourse-correction system threw in a squirt of N2O4,
running briefly as a biprop to get its catalyst hot -- but
was utterly impractical for RCS systems, which need to fire
frequently and on short notice.)

I noticed LockMart's CEV proposal used nitrous oxide as a
monoprop; I'm curious about the Isp and the possible catalyst.
Seem like the performance would be somewhat low, despite
the advantages of low toxicity, easier handling and simpler
system overall. I don't recall nitrous being used this way
before; is it something new?

--Damon

In article ,
OM om@our_blessed_lady_mary_of_the_holy_NASA_researc h_facility.org wrote:
Gemini bipropellant thrusters had considerably better performance, and
originally looked like they would cause fewer hassles. (It's not clear
that they really did...)

...Well, at least for *one* flight it didn't :-)

More true than you probably realized. :-)

One of the little headaches of N2O4/varioushydrazines thrusters, not
appreciated early on, 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.

And *that* is why Gemini mission rules called for immediate descent, to
the first available splashdown area, after any firing of the reentry RCS:
because the reentry-RCS valves couldn't be guaranteed leakproof after
first use, you had to descend while you were still reasonably assured of
a functioning RCS.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

OM om@our_blessed_lady_mary_of_the_holy_NASA_researc h_facility.org
wrote:

On Sun, 26 Jun 2005 23:02:50 GMT, (Henry Spencer)
wrote:

Correct; *that* approach was just on its way out at the time. The
Gemini bipropellant thrusters had considerably better performance, and
originally looked like they would cause fewer hassles. (It's not clear
that they really did...)

...Well, at least for *one* flight it didn't :-)

The hassles were related to wiring, they could have happened
regardless of the propellant(s) used.

D.
--
Touch-twice life. Eat. Drink. Laugh.

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

On 2005-06-27, Henry Spencer wrote:

And *that* is why Gemini mission rules called for immediate descent, to
the first available splashdown area, after any firing of the reentry RCS:
because the reentry-RCS valves couldn't be guaranteed leakproof after
first use, you had to descend while you were still reasonably assured of
a functioning RCS.

Ah ha! I had always wondered about why such a strict rule, when youd think
if they had 95-100% of RCS fuel, surely that would have been within margins
to get home.

Thanks for the education (yet again) Henry


Iain