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In electric pump fed rocket engines, propellants are pumped by two electric motors. So there is just one combustion chamber and that is the main combustion chamber. I guess electric pumps are fairly reusable. What's about reusability other parts of engine (not including batteries)?

This question is related to reusability of engine only not about the rocket or retrieving it or other economical factors.

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    $\begingroup$ IIRC Rocket Lab doesn't plan to reuse their rockets in the future so we can be quite sure that the engines are not designed to be reused often but Rocket Lab likes to test a lot so I'd guess that they design the engines to last some additional test runs if needed. Therefore I'd guess they might be good for a second or third run especially the lower stage engines which operate at the same conditions as the upper stage variant but only for a fraction of the time. I suggest asking Peter Beck on twitter. He's not Musk in terms of twitter usage but he seems to respond if asked. [citation needed] $\endgroup$
    – Christoph
    Commented Apr 25, 2019 at 8:41
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    $\begingroup$ A related but illuminating question might be, what happens to rocket engines like a Rutherford that would prevent their reuse? Of course it can be reused, unless there are reasons that it can't. But I can only vaguely wave my hands around and say coating, eroding, and fatigue. $\endgroup$
    – Greg
    Commented Apr 25, 2019 at 18:26
  • $\begingroup$ If the rocket first stage crashed to the water, the electric motors might be too unreliable for reuse due to corrosion caused by salt water and mechanical shock of the hard landing. $\endgroup$
    – Uwe
    Commented Apr 29, 2019 at 15:16
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    $\begingroup$ @Christoph: that was true at the time of your comment, but as of a few months later: rocketlabusa.com/news/updates/… $\endgroup$
    – Christopher James Huff
    Commented Jan 25, 2020 at 13:31

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Reusability depends on several factors:

  1. suitability of the propellant: it's easier to reuse a rocket engine if the insides don't get gunked up. RP-1/LOX engines are known to leave combustion products as deposits here and there (source: loose comments made here and there by SpaceX). In an engine without combustion-driven pumps this would be less of an issue.

  2. margins built into the design. This holds in general for all rocket engines. If your engine is worn out after a single mission, it's not very reusable. Pyrotechnics (to control valves) make reuse harder. etc.

  3. the use of single-use items in the design, for instance ablative coatings that are gone after 1 mission.

(and this is not an exhaustive list)

The problem is that the kind of detail needed to judge 2-3 usually isn't made public. Without knowing these design details, it's difficult to impossible for an outsider to estimate how reusable an engine is.

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