4 ms·

- Lower gravity - 2x distance to Earth compared to Venus - No magnetosphere - Thinner atmosphere = you boil at room temperature

mathsmath 2y ago
Lower gravity isn’t necessarily a con. It’s great for rockets!
- fastball 2y ago
  It's definitely a con for human habitation. Our physiology evolved in 1g and without that many of our bodily processes behave poorly over extended timeframes.
  - skissane 2y ago
    We don’t actually know what the long-term health consequences of Martian or lunar gravity are. We know the long-term health consequences of microgravity (as in LEO) are significantly negative. But, we lack data on long-term health effects of Martian or lunar gravity. Pessimistically, humans really need close to 1g, and anything significantly less causes serious problems-lunar isn’t going to be much better than microgravity. Optimistically, humans just need “some gravity”, and while close to zero is harmful, lunar or Martian isn’t. The way things are going, we are likely to find out in the next 10-20 years, at least for the lunar case. If lunar gravity avoids most of the negative health effects of microgravity, Martian gravity will too. If it doesn’t there is still the chance that Martian gravity might be “just enough” even if lunar gravity isn’t
  - mathsmath 2y ago
    Long term yes, but people still go to the ISS in 0g. I was just pointing out that some things that are bad for humans actually make the rocketry problem for returning easier for this bullet point.
pwatsonwailes 2y ago
The second point isn't accurate. You're thinking they're all static, rather than orbiting. There's times when each is closer than the other.
- stoperaticless 2y ago
  I assume we use distance as proxy for “how hard is to get there” (time and energy needed). Actual momentary distance is a bit tangential, because you never move in a straight line.
  - Dylan16807 2y ago
    From low Earth orbit, transfer orbits to Venus and Mars take 3.5 and 3.6 km/s of thrust respectively. According to https://en.wikipedia.org/wiki/Hohmann_transfer_orbit https://en.wikipedia.org/wiki/Hohmann_transfer_orbit
    - pwatsonwailes 2y ago
      The problem with a Hohmann transfer orbit is that you rely on launch windows. You can only do it when the two planets are in a straight line from the sun (or more accurately, and the same equivalent points in each of their orbits at the same time). This is a pain as Earth-Mars launch windows only come along every two years. If you want to launch without that issue, you're then into the world of using more delta-v, which is catastrophically expensive, unless you've got some form of propulsion for your craft beyond what we've got now. So yes, but with caveats. Obviously, there's a giant pile of detail beyond this in terms of the calculations for trading off time of flight vs distance between bodies, vs delta-v to accelerate towards the body, and then accelerate away from it to slow your descent into an orbital trajectory, but that's more depth than I'm going into for a quick HN comment.
      - Dylan16807 2y ago
        If you're jamming the throttle then the difference between Venus and Mars is also not very much.

mathsmath 2y ago

Lower gravity isn’t necessarily a con. It’s great for rockets!

fastball 2y ago
It's definitely a con for human habitation. Our physiology evolved in 1g and without that many of our bodily processes behave poorly over extended timeframes.
- skissane 2y ago
  We don’t actually know what the long-term health consequences of Martian or lunar gravity are. We know the long-term health consequences of microgravity (as in LEO) are significantly negative. But, we lack data on long-term health effects of Martian or lunar gravity. Pessimistically, humans really need close to 1g, and anything significantly less causes serious problems-lunar isn’t going to be much better than microgravity. Optimistically, humans just need “some gravity”, and while close to zero is harmful, lunar or Martian isn’t. The way things are going, we are likely to find out in the next 10-20 years, at least for the lunar case. If lunar gravity avoids most of the negative health effects of microgravity, Martian gravity will too. If it doesn’t there is still the chance that Martian gravity might be “just enough” even if lunar gravity isn’t
- mathsmath 2y ago
  Long term yes, but people still go to the ISS in 0g. I was just pointing out that some things that are bad for humans actually make the rocketry problem for returning easier for this bullet point.

pwatsonwailes 2y ago

The second point isn't accurate. You're thinking they're all static, rather than orbiting. There's times when each is closer than the other.

stoperaticless 2y ago
I assume we use distance as proxy for “how hard is to get there” (time and energy needed). Actual momentary distance is a bit tangential, because you never move in a straight line.
- Dylan16807 2y ago
  From low Earth orbit, transfer orbits to Venus and Mars take 3.5 and 3.6 km/s of thrust respectively. According to https://en.wikipedia.org/wiki/Hohmann_transfer_orbit https://en.wikipedia.org/wiki/Hohmann_transfer_orbit
  - pwatsonwailes 2y ago
    The problem with a Hohmann transfer orbit is that you rely on launch windows. You can only do it when the two planets are in a straight line from the sun (or more accurately, and the same equivalent points in each of their orbits at the same time). This is a pain as Earth-Mars launch windows only come along every two years. If you want to launch without that issue, you're then into the world of using more delta-v, which is catastrophically expensive, unless you've got some form of propulsion for your craft beyond what we've got now. So yes, but with caveats. Obviously, there's a giant pile of detail beyond this in terms of the calculations for trading off time of flight vs distance between bodies, vs delta-v to accelerate towards the body, and then accelerate away from it to slow your descent into an orbital trajectory, but that's more depth than I'm going into for a quick HN comment.
    - Dylan16807 2y ago
      If you're jamming the throttle then the difference between Venus and Mars is also not very much.