SpaceX is now building a Raptor engine a day, NASA says

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.

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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.

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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.

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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.

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