Re:SpaceX is now building a Raptor engine a day, NASA says
by jvanderbot on Wednesday November 02, 2022 @12:56PM
(#33439010)
The bigger rockets use many engines, and for NASA applications, may not be coming home. So, deep space / Mars will be littered with raptors in 20 years, I bet.
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Re:SpaceX is now building a Raptor engine a day, NASA says
by adgjlsfhk1 on Wednesday November 02, 2022 @01:16PM
(#33439435)
I doubt it. Raptor isn't a great deep space engine. It's ISP is a good bit lower than hyrdalox engines.
Re:SpaceX is now building a Raptor engine a day, NASA says
by Me1000 on Wednesday November 02, 2022 @01:36PM
(#33439814)
ISP is like fuel milage, and the economics change drastically when there's infrastructure in place. Having an abundant source of propellant near a celestial body with a much smaller gravity well (Mars) could easily change the economics and practicality of which fuels make sense for different missions.
Put another way, we might one day look at Starship as a big rig semi truck (though the ISP of Raptor is actually really good while a big rig's is very much not). The fuel efficiency isn't really that important.
I think (or hope at least) we're far away from being able to really see how much space access is going to change if Starship actually pulls off what they're trying.
Re:SpaceX is now building a Raptor engine a day, NASA says
by adgjlsfhk1 on Wednesday November 02, 2022 @02:17PM
(#33440498)
The big difference between ISP and millage is that ISP has exponential effects.
Re:SpaceX is now building a Raptor engine a day, NASA says
by bryanlarsen on Wednesday November 02, 2022 @01:23PM
(#33439557)
Hydralox is worst of both worlds. To get out of gravity well thrust/weight is key, and Raptor is king at that. In deep space ISP is key, and ion thrusters are way more efficient than hydrolox at that. People don't realize that SpaceX is perhaps the world's largest manufacturer of ion thrusters since they use them on Starlink.
Re:SpaceX is now building a Raptor engine a day, NASA says
by avmich on Wednesday November 02, 2022 @01:42PM
(#33439913)
Storage time is also important, and it's likely easier to store long term (Earth-Mars flight time is months) mid-cryogenic LOX and liquid methane rather than deep-cryogenic LH2.
Re:SpaceX is now building a Raptor engine a day, NASA says
by adgjlsfhk1 on Wednesday November 02, 2022 @01:49PM
(#33440037)
"To get out of gravity well thrust/weight is key" this isn't really true. TWR matters a lot for the first stage, but by the seccond stage, higher ISP and lower TWR is worth it as long as thrust is reasonable. ion thrusters are great for light unmanned probes but anything heavy needs higher thrust and hydralox is key for that. Ion propulsion is also pretty much worthless past jupiter since you can't get enough electricity.
Re:SpaceX is now building a Raptor engine a day, NASA says
by bryanlarsen on Wednesday November 02, 2022 @02:15PM
(#33440462)
Past Jupiter hydrolox is unusable because of boil-off issues. The best option past Jupiter is nuclear electric, aka ion propulsion.
If you need both thrust & efficiency, a large number of ion thrusters is often a good option.
Re:SpaceX is now building a Raptor engine a day, NASA says
by jvanderbot on Wednesday November 02, 2022 @03:57PM
(#33442055)
Yes, but the economy of scale makes it much better than alternatives for now. (Cost wise).