WetEV wrote: ↑
Fri May 07, 2021 10:51 am
frontrangeleaf wrote: ↑
Fri May 07, 2021 10:15 am
But fully reusable TSTO (2-stage to orbit) super-heavy-scale launch vehicles will change the economics and practical possibilities by several orders of magnitude. That's no small potatoes either.
Sounds just like the Space Shuttle. Which had better engines than the Raptor.
Uh, no. Not even remotely close. Better how?
The RS-25 is a dual fuel-rich staged combustion engine running hydrolox. It is nominally reusable, but more accurately refurbishable. Every engine is torn down and rebuilt after every flight.
Raptor is a full-flow gas-gas staged combustion design running methalox capable of extracting a much higher percentage of available energy from the prop load on board than RS-25 ever will. Main combustion chamber pressures on the RS-25 don't begin to approach what Raptor runs. Higher MCC drives thrust and specific impulse. No full-flow gas-gas design has ever progressed to flight testing, ever, in the history of the world. The design has only ever been attempted 3 times. To claim that the RS-25 was somehow the "better" engine is to ignore the fundamental differences in them.
And let's not even get into cost. The latest contract has new RS-25s for a cool $146M per copy. This is being bandied about as "cheaper" somehow. That's a bald-faced lie. Sorry. Not cheaper. Not by any rational standard. More like triple the old cost. The worst kind of political pork.
The only advantage the RS-25 has over Raptor is in specific impulse, which is entirely a matter of the fuel it burns. RS-25 was a fine engine - in the 70's. Today it's been surpassed. I would argue there are Russian designs that also better the RS-25 as well. We conceded world leadership in liquid rocket engine design to the Russians for decades. Until Raptor. Merlin also holds some impressive new world records of its own, namely around thrust to weight ratio, previously held by the Russians.
As to the space shuttle, as we all know, it was no where near fully reusable. Certainly not compatible with fast turnaround. Starship is being built to be fully reusable, and with heretofore unheard of short turnaround times. Days, not weeks, not months. Care to compare useful payloads?
You can't be serious. Starship doesn't "sound" anything like Space Shuttle. We retired Space Shuttle a decade ago and for good reason. Belongs to history now.
Edit: See JLV's post above for the numbers. Didn't have that handy.