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NASA is optimizing for different capabilities than SpaceX. With SpaceX's Starship every launch will require them leaving fuel for landing. Every gram of fuel yo

NASA is optimizing for different capabilities than SpaceX. With SpaceX's Starship every launch will require them leaving fuel for landing. Every gram of fuel you don't burn is less velocity you impart on your vehicle. To get to the Moon a Starship will require two launches. A manned vehicle and a fuel tanker. They have to dock in Earth orbit, refuel, then the manned vehicle transfers to a Lunar injection orbit. It's very likely a Starship will need a tanker waiting on the Moon to refuel a lander for the return trip and landing back on Earth. Starship hasn't even flown let alone demonstrated in-orbit refueling. SpaceX hasn't even demonstrated that in the small scale with Dragon capsules. It's a hard problem with a lot of unknowns. SLS can launch the manned element directly into a Lunar injection orbit. It doesn't require any refueling to get anywhere. It also doesn't need a fuel tank at the destination to allow a lander to return home. In order to do that the launch stages don't save any fuel for landing. It's "more expensive" to use expendable stages but all of their energy is used for their payload and none is saved for landing (and landing safety margin). Overall SLS is mass optimized rather than cost optimized. The NASA way involves a lot fewer moving parts and <unproven technology goes here>.

bryanlarsen 4y ago
Starship has twice the thrust of SLS. It could do everything SLS or Saturn 5 can. It just chooses not to because it chooses to be fully reusable. If you stuck a third stage, Orion and an Apollo CM style lander on top of Starship you could do everything in a single launch Saturn 5 style. That's something SLS can't do because Orion is much heavier than Apollo was. But Starship could. It'd have to run expendable. The difference is that Starship is getting $3B from NASA vs the $40B that SLS got. NASA could get a single launch moon mission using Starship, but they'd have to pay SpaceX more than $3B to get it. > SLS can launch the manned element directly into a Lunar injection orbit. It doesn't require any refueling to get anywhere. It also doesn't need a fuel tank at the destination to allow a lander to return home. SLS doesn't carry the lander nor the fuel for the lander. So yes, it does need something else to get the lander's fuel to the destination.

bryanlarsen 4y ago

Starship has twice the thrust of SLS. It could do everything SLS or Saturn 5 can. It just chooses not to because it chooses to be fully reusable. If you stuck a third stage, Orion and an Apollo CM style lander on top of Starship you could do everything in a single launch Saturn 5 style. That's something SLS can't do because Orion is much heavier than Apollo was. But Starship could. It'd have to run expendable. The difference is that Starship is getting $3B from NASA vs the $40B that SLS got. NASA could get a single launch moon mission using Starship, but they'd have to pay SpaceX more than $3B to get it. > SLS can launch the manned element directly into a Lunar injection orbit. It doesn't require any refueling to get anywhere. It also doesn't need a fuel tank at the destination to allow a lander to return home. SLS doesn't carry the lander nor the fuel for the lander. So yes, it does need something else to get the lander's fuel to the destination.