3 ms·

Still going to have margins of error with both the measurements and the corrections, right? If those margins are higher than what the Moon forgives…

rbanffy 3y ago
Fully autonomous landing in unknown surfaces is still pretty difficult. Still, the Moon should be more forgiving than the Earth - no wind, lower gravity...
- m4rtink 3y ago
  No atmosphere - need to brake all of the velocity difference with engines & can't use aerodynamic surfaces or parachutes. On a body with atmosphere you can essentially just drop a payload up to some maximum size with a proper heat shield and a parashute and it will end up (somewhere) on the surface in one piece. On an atmosphere less body you essentially need to run precisely controlled flight all the way to touchdown. Everything has tradeoffs. :-P
  - messe 3y ago
    A thin atmosphere like mars can make it worse. The actual amount of braking you get is a bit unpredictable, and the size of the aerodynamic surfaces you need to make a significant impact can use up quite a bit of your mass budget (example: despite the size of the Perseverance/Curiosity parachutes, they still needed a sky-crane for final touchdown).
    - m4rtink 3y ago
      Indeed, Mars is a bit of an annoying edge case here. Still the atmosphere really helps in other regards, such as for orbit circulation for probes via aerobraking. And can be used for aerocapture in the future as well. Given the Mars gravity I still wonder if no atmosphere would still make it worse vs the thin that it has.
  - rbanffy 3y ago
    > need to brake all of the velocity difference with engines Engines are well understood. With enough propellant one can gently hover down at 1 cm/s from 1km. No atmosphere also means few surprises.
- krisoft 3y ago
  But also, here on earth you go to your backyard and try your landing as many times as you want. While with the moon you have simulations and models of various fidelity.
- csunbird 3y ago
  A celestial body with an atmosphere: Very easy to land but incredibly hard to take off from. A celestial body with no atmosphere: Extremely easy to take off from, but very hard to actually land.

rbanffy 3y ago

Fully autonomous landing in unknown surfaces is still pretty difficult. Still, the Moon should be more forgiving than the Earth - no wind, lower gravity...

m4rtink 3y ago
No atmosphere - need to brake all of the velocity difference with engines & can't use aerodynamic surfaces or parachutes. On a body with atmosphere you can essentially just drop a payload up to some maximum size with a proper heat shield and a parashute and it will end up (somewhere) on the surface in one piece. On an atmosphere less body you essentially need to run precisely controlled flight all the way to touchdown. Everything has tradeoffs. :-P
- messe 3y ago
  A thin atmosphere like mars can make it worse. The actual amount of braking you get is a bit unpredictable, and the size of the aerodynamic surfaces you need to make a significant impact can use up quite a bit of your mass budget (example: despite the size of the Perseverance/Curiosity parachutes, they still needed a sky-crane for final touchdown).
  - m4rtink 3y ago
    Indeed, Mars is a bit of an annoying edge case here. Still the atmosphere really helps in other regards, such as for orbit circulation for probes via aerobraking. And can be used for aerocapture in the future as well. Given the Mars gravity I still wonder if no atmosphere would still make it worse vs the thin that it has.
- rbanffy 3y ago
  > need to brake all of the velocity difference with engines Engines are well understood. With enough propellant one can gently hover down at 1 cm/s from 1km. No atmosphere also means few surprises.
krisoft 3y ago
But also, here on earth you go to your backyard and try your landing as many times as you want. While with the moon you have simulations and models of various fidelity.
csunbird 3y ago
A celestial body with an atmosphere: Very easy to land but incredibly hard to take off from. A celestial body with no atmosphere: Extremely easy to take off from, but very hard to actually land.