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I thought that was crazy at first but the Orion capsule uses proven reentry tech. SpaceX hasn't landed Starship successfully yet and hasn't proven their reentry

I thought that was crazy at first but the Orion capsule uses proven reentry tech. SpaceX hasn't landed Starship successfully yet and hasn't proven their reentry strategy, and coming back from the moon will be harder because they'll be coming in faster. I can't blame NASA for not committing their astronauts to it yet. But yeah, I think SpaceX will prove it all works and then NASA has the option to change the plan. In the meantime, officially keeping SLS keeps Congress happy.

wmf 6y ago
Starship can come back from the moon to LEO then the crew transfers into a Crew Dragon and lands.
- cwkoss 6y ago
  Yeah, once you have a large ship out of earths gravity well, would be a waste to land it back on earth. Heck, even if it breaks, park it in a stable orbit so the next generation can salvage it for parts as needed.
  - m4rtink 6y ago
    PSA: Most orbits around Moon are not long term stable due to underground mass concentrations.
    - cwkoss 6y ago
      Neat! If you park a satellite at moon geosychronous orbit how unstable is it? Would it be lost in the order of months or decades? Does that also effect the Lagrange points for the moon? Do human currently have anything parked at earth moon lagrange points?
      - perl4ever 6y ago
        There appears to be no such thing. "the radius for a selenostationary orbit is much farther than the Hill radius, meaning that no stable orbit can be achieved as it would be too much perturbed by the Earth and/or the Sun" "all of the Lagrangian points of the Earth-Moon system are stationary relative to the Moon surface" ...but then it is explained that stationary doesn't mean stable. Links: https://astronomy.stackexchange.com/questions/20499/is-it-possible-to-achieve-a-stable-lunarstationary-orbit-around-the-moon https://astronomy.stackexchange.com/questions/20499/is-it-po... https://en.wikipedia.org/wiki/Hill_sphere https://en.wikipedia.org/wiki/Hill_sphere
- jccooper 6y ago
  It would need lunar or high elliptic refueling to do that. Which is possible, but more complicated.
  - deleted 6y ago
    [deleted]
- simonh 6y ago
  The Lunar Starship has enough dV to land on the moon and return to orbit, about 3.44 km/s but boosting from the moon to Earth and braking into Low Earth Orbit actually takes more dV than that, about 3.94 km/s. Unless they build in extra 0.5 km/s capacity or about an extra 20%, it flat out won't be able to do it.
  - wmf 6y ago
    Here's where I got the idea and some different calculations: https://caseyhandmer.wordpress.com/2021/03/26/lunar-starship-and-unnecessary-operational-complexity/ https://caseyhandmer.wordpress.com/2021/03/26/lunar-starship...
    - simonh 6y ago
      The diagrams say "Crew transfer in LEO or direct entry of Starship" as if they're interchangeable options, but these are not equivalent. Returning from the Moon and braking into LEO takes just as much dV as transferring from LEO up to Lunar orbit. Per the diagram that's 3.94 km/s as I said. Conversely landing on the moon and returning to Lunar orbit takes 1.72 km/s twice, which is again consistent with my numbers if we assume the payload mass is constant. That may not be the case of course but any cargo taken from the Lunar surface to Lunar orbit will also need to be brought back to Earth somehow.
ArPDent 6y ago
currently the lunar version of Starship is not designed to land back on earth - it lacks both the TPS and aero surfaces required for entry & landing.
deleted 6y ago
[deleted]
mlindner 6y ago
The Lunar Starship requires a functioning Starship capable of reentering in order to refuel the Lunar Starship before it heads to the moon (and it will need to eventually travel back to the Earth for refueling after some number of uses).
- m4rtink 6y ago
  I don't think the lunar Starship is ever intended for returning to the Earth after it's launched - it has no flaps and no heat shield. It will either be discarded after use or refueled and reused fully in space.
  - avhon1 6y ago
    Lunar Starship won't be (intentionally, excepting emergencies or retirement) returning to Earth's Surface, but the plan might involve it returning closer to Earth for refueling.

wmf 6y ago

Starship can come back from the moon to LEO then the crew transfers into a Crew Dragon and lands.

cwkoss 6y ago
Yeah, once you have a large ship out of earths gravity well, would be a waste to land it back on earth. Heck, even if it breaks, park it in a stable orbit so the next generation can salvage it for parts as needed.
- m4rtink 6y ago
  PSA: Most orbits around Moon are not long term stable due to underground mass concentrations.
  - cwkoss 6y ago
    Neat! If you park a satellite at moon geosychronous orbit how unstable is it? Would it be lost in the order of months or decades? Does that also effect the Lagrange points for the moon? Do human currently have anything parked at earth moon lagrange points?
    - perl4ever 6y ago
      There appears to be no such thing. "the radius for a selenostationary orbit is much farther than the Hill radius, meaning that no stable orbit can be achieved as it would be too much perturbed by the Earth and/or the Sun" "all of the Lagrangian points of the Earth-Moon system are stationary relative to the Moon surface" ...but then it is explained that stationary doesn't mean stable. Links: https://astronomy.stackexchange.com/questions/20499/is-it-possible-to-achieve-a-stable-lunarstationary-orbit-around-the-moon https://astronomy.stackexchange.com/questions/20499/is-it-po... https://en.wikipedia.org/wiki/Hill_sphere https://en.wikipedia.org/wiki/Hill_sphere
jccooper 6y ago
It would need lunar or high elliptic refueling to do that. Which is possible, but more complicated.
- deleted 6y ago
  [deleted]
simonh 6y ago
The Lunar Starship has enough dV to land on the moon and return to orbit, about 3.44 km/s but boosting from the moon to Earth and braking into Low Earth Orbit actually takes more dV than that, about 3.94 km/s. Unless they build in extra 0.5 km/s capacity or about an extra 20%, it flat out won't be able to do it.
- wmf 6y ago
  Here's where I got the idea and some different calculations: https://caseyhandmer.wordpress.com/2021/03/26/lunar-starship-and-unnecessary-operational-complexity/ https://caseyhandmer.wordpress.com/2021/03/26/lunar-starship...
  - simonh 6y ago
    The diagrams say "Crew transfer in LEO or direct entry of Starship" as if they're interchangeable options, but these are not equivalent. Returning from the Moon and braking into LEO takes just as much dV as transferring from LEO up to Lunar orbit. Per the diagram that's 3.94 km/s as I said. Conversely landing on the moon and returning to Lunar orbit takes 1.72 km/s twice, which is again consistent with my numbers if we assume the payload mass is constant. That may not be the case of course but any cargo taken from the Lunar surface to Lunar orbit will also need to be brought back to Earth somehow.

ArPDent 6y ago

currently the lunar version of Starship is not designed to land back on earth - it lacks both the TPS and aero surfaces required for entry & landing.

deleted 6y ago

[deleted]

mlindner 6y ago

The Lunar Starship requires a functioning Starship capable of reentering in order to refuel the Lunar Starship before it heads to the moon (and it will need to eventually travel back to the Earth for refueling after some number of uses).

m4rtink 6y ago
I don't think the lunar Starship is ever intended for returning to the Earth after it's launched - it has no flaps and no heat shield. It will either be discarded after use or refueled and reused fully in space.
- avhon1 6y ago
  Lunar Starship won't be (intentionally, excepting emergencies or retirement) returning to Earth's Surface, but the plan might involve it returning closer to Earth for refueling.