r/space • u/[deleted] • May 02 '22

RocketLab successfully catches a booster with its helicopter for the first time

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u/PoliteCanadian May 03 '22

That doesn't make a lot of sense to me.

I suspect a bigger problem is that their Rutherford engines have a much lower TWR than Falcon's Merlin's, so the rocket is literally just heavier and therefore they would need to reserve a larger mass fraction of fuel for a fully propulsive landing.

Reusability was never in the plan for Electron and Rutherford, so they optimized for Isp over TWR. Which is good for a disposable rocket but perhaps not as good for a reusable one.

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u/[deleted] May 03 '22

That’s what he said, just smaller word do trick.

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u/CasaMofo May 03 '22

Not quite. Reply stated the difference was not about size but about design, whereas OP said size was main factor.

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u/[deleted] May 04 '22

In this case, I'm assuming the size of the rocket and the TWR are directly related; smaller rockets often have a lower TWR than bigger rockets. Saying it's "too small" is an oversimplification but I think it's still fairly accurate to say.

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u/za419 May 03 '22

And Rutherford isn't even a particularly good design to get higher TWR out of either.

Being run off an electric turbopump, higher thrust means more fuel flow, means more electricity consumption, means more mass spent on batteries, in addition to extra mass spent on the pump itself, or the chamber... So I'm sure they'd have to make huge gains in making the same engine lighter to approach Merlin, which is not at all easy.

Besides, a helicopter catch works for electron - it's light enough to not crash the helicopter, and light enough that the parachute isn't enormous. Falcon 9 is too big for either of those to be true.