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With current technologies, are there practical limits on the number of times a rocket engine can be restarted while still remaining in orbit? Given sufficient fuel, could an engine be designed today that could do 1000 short orbital burns? What about 100 burns, each lasting no more than two minutes or so?

For my purposes, you can exclude engines that de-orbit and then go back up. I am only interested in high-thrust rockets, be they conventional, hybrid or other types; I am thinking about something that could reasonably move major tonnage.

I would also be interested in current record-holding designs in terms of how many times they have successfully refired on a single mission. A reasonable analysis of what subsystem would likely fail first would also be appreciated.

Jerard Puckett
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  • Might be worth looking into attitude thrusters as those designs may be scalable and they can be used many thousands of times. – ThePlanMan Feb 02 '15 at 10:01
  • @FraserOfSmeg AFAIK, most of those designs are too inefficient to be seriously considered for propulsion, no matter what the size. – Jerard Puckett Feb 02 '15 at 13:29
  • what makes you think attitude thrusters are inefficient? – ThePlanMan Feb 02 '15 at 18:20
  • Cold gas jets? . . .If other types could work, let me know. – Jerard Puckett Feb 02 '15 at 18:27
  • Hydrogen peroxide monopropellant? – DJohnM Feb 02 '15 at 18:51
  • @User58220 No monopropellant can compete with bipropellants. I don't want to sacrifice too much in terms of amount of propellant required. – Jerard Puckett Feb 02 '15 at 18:57
  • Check this out: http://www.moog.com/literature/Space_Defense/ISP/Bipropellant_Thrusters_Rev_0913.pdf – ThePlanMan Feb 03 '15 at 02:33
  • @FraserOfSmeg impressive specific impulses on those. I wonder if pressure fed can be truly scaled up to compete with turbopumps in terms of thrust. – Jerard Puckett Feb 03 '15 at 06:09
  • @FraserOfSmeg this morning I'm seeing a couple pressure fed designs, e.g. AJ-10 & Kestrel. – Jerard Puckett Feb 03 '15 at 13:32
  • @NathanTuggy that question is not an exact duplicate, I was thinking of a scenario that wound require many many restarts on the same mission. Russell Borogrove's answer applies, certainly, but I'd still like to know the record for number of high-thrust engine restarts – Jerard Puckett Mar 01 '16 at 02:59
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    Regarding restart records on real missions, RL-10 has done at least 7 starts (hydrolox); Apollo 9 SPS likewise 7 (hypergolic). I think most of the Apollos fired SPS 5-7 times including midcourse corrections. (google Apollo _ timeline for details). – Russell Borogove Mar 01 '16 at 03:10
  • Air Force wanted to test a Titan IIIC transtage (AJ-10 engine, hypergolic) through 10 burns on one mission in late '65 (lofting a few satellites into different orbits with the first few, then just showing off), but the launch failed and I don't know if they tried a 10-burn test again. Titan IIICs did put 8 satellites up on one launch, presumably needing a lot of burns to do so, on three separate occasions in '66, '67, and 1968. – Russell Borogove Mar 01 '16 at 03:34

1 Answers1

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For the purposes of your question, I will subdivide rocket engine designs into two categories, and some sub-categories

  1. Designs using hypergolic propellants
  2. Designs using non-hypergolic propellants
    1. Designs using a torch igniter or something similar
    2. Designs using non-reusable ignition mechanisms (e.g. hypergolic slugs, solid fuel igniters, probably others I haven't thought of)

Designs of type 1 can be restarted any number of times. Hypergolic propellants ignite on contact with each other, meaning no separate ignition mechanism is necessary. For this reason you see them used in Reaction Control Systems (RCS) on the space shuttle, SpaceX's Dragon, and other vehicles

Designs of type 2.1 can also be restarted any number of times, theoretically, but they rely on an ignition mechanism that has moving parts (i.e. valves) that can fail, so the upper limit on the number of times it can restart would depend on the reliability of the mechanical components.

Designs of type 2.2 can only be restarted a fixed number of times, in some cases they can't be restarted at all. Designs using hypergolic 'slugs' place a 'slug' of hypergolic propellant in front of the 'normal' propellant, so that the slugs ignite and provide the heat to ignite the rest of the propellant. Here, you're limited to the number of slugs you take with you. This will typically be a single-digit number. I believe this is the method SpaceX uses for their upper stage engines when they need to deliver satellites to higher orbits. And as Rikki-Tikki-Tavi pointed out, other engines use solid fuel mechanisms to ignite their fuel, and in that case you're limited to the number of solid fuel igniters you bring with you.

Nickolai
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    @Nickolai Hypergolic (your #1) would still have moving parts (valves), just fewer than other designs. – Anthony X Feb 02 '15 at 19:20
  • What's a torch igniter? How about electrical igniters (effectively, spark plugs) -- no moving parts, no consumables other than electricity. – Russell Borogove Mar 01 '16 at 03:16
  • A torch igniter, if I recall correctly, uses smaller quantities of the fuel and oxidizer and ignites them with something like a spark plug to create a larger flame that has enough heat to ignite the propellants going into the main combustion chamber. @AnthonyX correctly points out that even hypergolic designs are limited by their valve reliability and such things. Torch igniters will need more valve since there's more propellant lines, so presumably they're less reliable, but I suppose it eventually comes down to how you engineer the system, i.e. what parts you choose, etc. – Nickolai May 19 '16 at 15:04