[AR] Re: [AR] Re: “Transitioning space propulsion to a nitrous-based industry standard”
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Tue, 4 Apr 2023 17:46:38 -0400 (EDT)
On Tue, 4 Apr 2023, Norman Yarvin wrote:
...The industry has moved away from hypergolics for launch,
but not for precise orbital maneuvering, likely because it's a big
advantage to be able to just release a blip of fuel and oxidizer and
know they will combust immediately: no having to wait for a torch
igniter to fire up.
For precise orbital maneuvering, there's no reason why you need anything
more than a torch igniter! At least one of the innumerable proposals for
a nontoxic-propellants Shuttle RCS/OMS system envisioned eliminating the
RCS vernier thrusters in favor of igniter-only operation of the main RCS
thrusters.
Setting that aside, bear in mind that torch igniters don't necessarily
have to add a lot of complexity or delay. The Apollo SM/LM RCS engines
used a "preigniter" scheme, with the plumbing arranged so that propellant
flow through the main valves reached the preigniter chamber first, so it
would light (hypergolically) and pressurize the main chamber before flow
reached the main injector, minimizing (hypergolic) ignition delays there.
You could presumably do the same thing with a spark-ignited torch, so it
would still need the spark system but wouldn't have its own valves etc.
(That does lose one advantage of separate valves: verifying torch
ignition before committing to main-chamber flow, so the control system can
abort startup if the igniter malfunctions.)
Henry
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