Alternators

[NathanKell]

How should alternators be handled? Were (are) the avionics and the payload always battery powered, or did (do) pump-fed engines hook into the main circuits with their generators? I would guess with pressure-fed engines (which lack generators to run the pumps) no alternator should be simulated, but for pump-fed engines...?

[Felger]

You know, I have no idea if alternators on engines is even realistic. I'm inclined to think it's not, since the added weight would hurt engine performance, along with the wire weight and whatnot to transport the electricity.

But on the other hand, it'd add a redundant source of power for the avionics during launch, ensuring that as long as the engine was firing they'd have power.

Historically speaking, is it realistic?

[NathanKell]

Apologies for being unclear. I don't think engines include alternators. However, my understanding is that pump-fed engines usually use an electrical generator to power their pumps, and thus I wonder whether that generator is hooked into the stack's circuits.

[Felger]

I'm not sure. I can ask some coworkers who used to work shuttle ascent shifts if shuttle used fuel cells or an alternator from the RS-25s on the way to orbit. My guess is the ~7-10 minutes of fuel cell power is not worth the extra mass of hooking the avionics up to the alternator. But that's just my guess.

[NathanKell]

Yeah. My thinking was if the alternator is already there (to power the pumps) then it's just a question of wiring. Thanks!

[RedAV8R]

From what I can tell besides actual sensors and what not that are obviously connected to the brains of a launch vehicle the actual power is also supplied from that vehicle or stage, not the engine. That I know of pump fed engines do not have an electrical generator to power pumps. If anything they would have a starter motor, fed by battery power, to start the pump initially until it could be ignited. Really, it's not so much different than an aircraft. Battery power starts a starter/generator, which spins the compressor and/or turbine, which when fuel is introduced and ignited, creates a self-sustaining reaction as long as fuel continues to flow. Now obviously this is where things differ, in that an aircraft starter/generator changes function from starter to generator to resupply the aircraft. From what I can tell, the RS-25 had it's engine controllers on the engine, they were hooked up to the vehicle through it's own bus. Likely again powered by the vehicle not the engine. But what do I know. No Holiday Inn Express for me last night.

In conclusion I recommend that rocket engines do NOT have a generator, however air breathing engines do.

Perhaps we need to make a 'standards' policy file for configs for others to read and conform to?

[NathanKell]

That makes sense to me, on both counts. :)

[kiwivogel]

SSME engine controllers were powered by the shuttle's fuel cells. With 2 redundant controllers per engine on separate busses (and backup switchover capabilities).

[stratochief66]

@NathanKell close?