[ben_w]

That's why I phrased it that way.

Most internal combustion engine cars have a lead acid battery to start it up and run the spark plugs (or preheat the glow plugs if diesel). They don't get called "hybrid" or "battery powered" because the batteries aren't the propulsive power themselves.

This is akin to that: the batteries run the pumps, they're not the propulsive system itself.

Ion drives can be run off battery, but you can't launch with those.

[DarmokJalad1701]

Unlike a car battery though, these batteries provide a not-insignificant part of the energy that is generated by the engine. Each Rutherford engine generates around 37 mega-watts of power at sea-level (24900 N and 3.05 km/s exhaust velocity, Power = 1/2 * Thrust * v_e) and there are nine in the first stage. The first stage battery provides around one megawatt [1].

That's about 0.3% of all energy generated by the engines, which is significantly more than what a spark plug does in an ICE.

[1] https://theaeroblog.com/the-rutherford-rocket-engine-the-fir...

This is the closest we have to electric power directly powering the ascent of a rocket from Earth.

Something like a HyperCurie engine (which is also electric pump-fed), could probably lift off from a planetary body like the moon. When they used it in orbit, they actually had to wait for the batteries to charge up from solar panels between each engine burn.

[ben_w]

> not-insignificant

> 0.3%

> the closest we have

I don't understand why you're trying to paint the battery as a significant contribution here.

Like a car battery, although it's neat that they consider it as part of the engineering, it's none of the actual thrust unless it explodes.

[DarmokJalad1701]

It is about 1 megawatt (1341 HP) of the power pushing the rocket into the sky (directly translated into exhaust velocity and therefore thrust). That would be like a spark plug generating 1 HP in a 300 HP engine (Which would exhaust the typical car battery in about 1 second if it could even push that much power out).

It is all semantics anyway.

[DarmokJalad1701]

Correction: It won't drain in a second. But my point is the same. We don't really have 1 HP spark plugs out there :)

[ben_w]

Rough estimates I've seen say the starter motor is about that, though. (Not that I can tell real pages from GenAI ad content farms, I'm not a petrolhead).

I'd agree "it's all semantics", but yours are confusing me :P

(And for energy content, like for like is comparing the size of the fuel tank with the capacity of the battery, but cars aren't 90% fuel by weight).