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Comment by akamaka | Hacker News Reader

I don’t usually post a middlebrow dismissal, but using an electric compressor is a fairly obvious idea which often gets discussed and immediately dismissed, so there’s not much interesting here until they reveal more of their design.

Typical discussion: https://aviation.stackexchange.com/questions/90862/are-there...

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OP engine's goal is "as the first stage of an orbital launch vehicle. [...] get payloads to orbit dramatically cheaper than all-rocket systems".

The discussion you linked discards electric compressors because of loss of 20% efficiency due to conversions, but for normal air travel.

Twitter thread mentions a combined efficiency of >95% thanks to cryocooling from fuel.

I didn’t see much discussion on potential efficiency gains in that thread.

A launcher would aim for higher altitudes than an airplane, so the question of maintaining efficiency the whole way becomes much more important.

I suspect this kind of engine would need something like a single-use aluminium air battery to make sense though. You could get really high energy density that way. Power density might be a challenge though.

I would assume they just use a generator on the shaft? This would be dramatically more weight-efficient than any kind of batteries.

Scott Manley in the X thread said "So, is the turbine section driving a generator to make electricity to power the compressor" and Ian Brooke replied "Exactly that. ... The key insight is to use electric motors to drive a compressor. That way we can make it spin at any speed, allowing it to "adapt" to it's airspeed and combustion cycle."

I remember reading somewhere that electric compressor stages are apparently getting used to reduce input lag on automotive turbo chargers.

> lectric compressor stages are apparently getting used to reduce input lag on automotive turbo chargers

Yup, E-Turbo [1].

[1] https://www.motortrend.com/how-to/e-turbo-electric-assist-tu...

In F1 they also recover energy and charge battery or help power the electric motor (as explained in the article)

Until the new engine rules when it will be removed because it was deemed to expensive, complex and the technology didn't translate to road cars enough for them to justify the R&D.

Which is a shame because it's the most fun part of the F1 engines to me.

And the only thing that would justify this kind of global waste.

Even that’s not interesting. It’s just an electric version of an antilag system, first developed in the 80s.

Rockets were first developed 1,000 years ago. Nothing is interesting, by your reasoning.

The liquid fuel rocket motor was only invented 98 years ago (https://www.nasa.gov/history/95-years-ago-goddards-first-liq...)

Though borderline possible, it is very hard for solid fuel rockets to make it to orbit, and they have horrible payload to total mass ratios. It all has to do with the specific impulse of the fuels, no solid fuel provides as much as hydrogen/oxygen.

It's not so much just the Isp -- rockets can easily get to orbit on LOX/RP-1; LOX-LH2 is not needed -- but also dry mass of the stage. Basically the entire solid rocket motor is a thrust chamber, and must be strong enough to withstand that pressure. In a pump fed liquid propellant rocket, this is not the case: the tanks need only withstand a pressure high enough to avoid cavitation in the pumps.

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