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Eh. Apollo 12 landed within 200 meters of Surveyor 3 with 1960s-era technology and after manually evading a bunch of boulders. These days, SpaceX can land a boo

by dlgeek 6y ago

Eh. Apollo 12 landed within 200 meters of Surveyor 3 with 1960s-era technology and after manually evading a bunch of boulders. These days, SpaceX can land a booster on a ship in the middle of the ocean after a hypersonic return. I think they could manage a precision landing on the moon.

brnt 6y ago
Planning to land in a designated area is easy. Ruling out any deviations is a challenge. SpaceX knows booster landing on earth, but that may not be the the same on the moon. Moreover, it can afford to lose a booster every know and then here, but there it can't. It can be done, but can it be guaranteed?
- rbanffy 6y ago
  > but that may not be the the same on the moon True. No wind or waves, everything standing perfectly still. I'd say it's much easier.
  - detritus 6y ago
    Principal negative as I can imagine it is the constitution of the regolith. I remember reading that one of the concerns about the original lunar programs was how soft and deep the regolith might be at the landing site - if it's loose and silty and 6' deep, then that's going to get tricky. Sure, we have much better radar and composition maps of the lunar surface these days, but it strikes me that it's still not as 100% as landing on a barge's [presumably] metal surface or concrete and Cape Canaveral.
    - rbanffy 6y ago
      The tiny landing legs (more like landing pinkies) of Starship concern me a lot, but whatever would be going to land with this approach would have reasonably robust landing legs with feet that can handle soft surface. I'm more worried about sandblasting the surroundings.
      - detritus 6y ago
        Aye, that's it! The huge and wonderful mass of a Starship plonking down three spindle-thin legs onto and into luna incognita. I'm sure smarter people than I have thought about this, but it was a thought that struck me when I saw the mockups in the NASA lunar bid vid a wee while back.
        rbanffy 6y ago
        Well... At least it's more than 3. Still, by then the ship should be somewhat top-heavy and those six landing pinkies do not inspire much trust. OTOH, the people designing this are smarter than we are and much more experienced than me in rocket design, so they may know one or two things I don't.
m4rtink 6y ago
The thing is that if you are landing a two stage rocket (or a rocket with enough delta-v for ascent) you can abort the landing back to orbit (unless you are crazy enouh to do direct ascent from earth without entering lunar orbit). Apollo basically had a switch + sensor based tigers to start an automatic segvence that shuts down and drops the first stage, starts the seconds stage and flies it back to lunar orbit. If you don't have an ascent stage or enough delta-v, you have to land, potentially many kilometers of course or even crash if something goes very wrong.
- rbanffy 6y ago
  That's a very good point. A lander without an ascent module can't abort to space. Once you do your deorbit burn, you will land no matter what. That's a good reason to have multiple supply/equipment depots on the surface before you even land the ascent vehicles. Walk up to the nearest one, then drive the rest of the way. Also that's one good reason to have spare ascent craft (or supply depots) parked on low lunar orbit that could be directed to pick up any stranded astronauts. A last option is a LESS-like lifeboat assembled from lander components. Surface to orbit on a convertible has some appeal.
  - m4rtink 6y ago
    >A last option is a LESS-like lifeboat assembled from lander components. Surface to orbit on a convertible has some appeal. Already considered in Apollo days: https://en.wikipedia.org/wiki/Lunar_escape_systems https://en.wikipedia.org/wiki/Lunar_escape_systems A very simple "rocket chair" using residual fuel from the LEM. There were also variants for regular use during exploration using only leftover propellant from the descent stage. Flown manually all the way to lunar orbit due to guidance computer being to heavy back then: "Guidance in typical LESS designs was simple: an 'eight-ball' to show spacecraft attitude, a clock to show time since liftoff, and a planned pitch program. The Apollo Guidance Computer used as an autopilot for the CSM and LM had a mass of around a hundred pounds and consumed a significant amount of power, so computer controlled flight was out of the question. This would be one of the few cases where an astronaut flew a rocket manually all the way to orbit, and with far less instrumentation than normal."
rbanffy 6y ago
I remember reading somewhere the astronauts noted Surveyor 3 looked sandblasted, presumably because of the LM's ejecta. That's why the ascent vehicle should probably not be the first thing to land and, perhaps, should be located not too close to the crew landing spot.

by dlgeek 6y ago

brnt 6y ago

Planning to land in a designated area is easy. Ruling out any deviations is a challenge. SpaceX knows booster landing on earth, but that may not be the the same on the moon. Moreover, it can afford to lose a booster every know and then here, but there it can't. It can be done, but can it be guaranteed?

rbanffy 6y ago
> but that may not be the the same on the moon True. No wind or waves, everything standing perfectly still. I'd say it's much easier.
- detritus 6y ago
  Principal negative as I can imagine it is the constitution of the regolith. I remember reading that one of the concerns about the original lunar programs was how soft and deep the regolith might be at the landing site - if it's loose and silty and 6' deep, then that's going to get tricky. Sure, we have much better radar and composition maps of the lunar surface these days, but it strikes me that it's still not as 100% as landing on a barge's [presumably] metal surface or concrete and Cape Canaveral.
  - rbanffy 6y ago
    The tiny landing legs (more like landing pinkies) of Starship concern me a lot, but whatever would be going to land with this approach would have reasonably robust landing legs with feet that can handle soft surface. I'm more worried about sandblasting the surroundings.
    - detritus 6y ago
      Aye, that's it! The huge and wonderful mass of a Starship plonking down three spindle-thin legs onto and into luna incognita. I'm sure smarter people than I have thought about this, but it was a thought that struck me when I saw the mockups in the NASA lunar bid vid a wee while back.
      - rbanffy 6y ago
        Well... At least it's more than 3. Still, by then the ship should be somewhat top-heavy and those six landing pinkies do not inspire much trust. OTOH, the people designing this are smarter than we are and much more experienced than me in rocket design, so they may know one or two things I don't.

m4rtink 6y ago

The thing is that if you are landing a two stage rocket (or a rocket with enough delta-v for ascent) you can abort the landing back to orbit (unless you are crazy enouh to do direct ascent from earth without entering lunar orbit). Apollo basically had a switch + sensor based tigers to start an automatic segvence that shuts down and drops the first stage, starts the seconds stage and flies it back to lunar orbit. If you don't have an ascent stage or enough delta-v, you have to land, potentially many kilometers of course or even crash if something goes very wrong.

rbanffy 6y ago
That's a very good point. A lander without an ascent module can't abort to space. Once you do your deorbit burn, you will land no matter what. That's a good reason to have multiple supply/equipment depots on the surface before you even land the ascent vehicles. Walk up to the nearest one, then drive the rest of the way. Also that's one good reason to have spare ascent craft (or supply depots) parked on low lunar orbit that could be directed to pick up any stranded astronauts. A last option is a LESS-like lifeboat assembled from lander components. Surface to orbit on a convertible has some appeal.
- m4rtink 6y ago
  >A last option is a LESS-like lifeboat assembled from lander components. Surface to orbit on a convertible has some appeal. Already considered in Apollo days: https://en.wikipedia.org/wiki/Lunar_escape_systems https://en.wikipedia.org/wiki/Lunar_escape_systems A very simple "rocket chair" using residual fuel from the LEM. There were also variants for regular use during exploration using only leftover propellant from the descent stage. Flown manually all the way to lunar orbit due to guidance computer being to heavy back then: "Guidance in typical LESS designs was simple: an 'eight-ball' to show spacecraft attitude, a clock to show time since liftoff, and a planned pitch program. The Apollo Guidance Computer used as an autopilot for the CSM and LM had a mass of around a hundred pounds and consumed a significant amount of power, so computer controlled flight was out of the question. This would be one of the few cases where an astronaut flew a rocket manually all the way to orbit, and with far less instrumentation than normal."

rbanffy 6y ago

I remember reading somewhere the astronauts noted Surveyor 3 looked sandblasted, presumably because of the LM's ejecta. That's why the ascent vehicle should probably not be the first thing to land and, perhaps, should be located not too close to the crew landing spot.