5 ms·

But NASA cares about delta v most. Although that would make Mars closer. So perhaps closest approach is thought to be what laymen mean by closest.

eunoia 8y ago
For the fellow curious, here’s a solar system delta-v chart [1]. [1]https://goo.gl/images/83YdXE https://goo.gl/images/83YdXE
- isostatic 8y ago
  Is Venus really 27km/s to get to a 400km orbit? I'd have expected a number nearer Earth's
  - danw1979 8y ago
    Atmospheric density ? or maybe that the “low orbit” distance given for Venus is 400km vs 250km for Earth.
    - pdonis 8y ago
      > maybe that the “low orbit” distance given for Venus is 400km vs 250km for Earth No, that won't make much of a difference: the gain is basically just the gain in potential energy for the extra 150 km, which is equivalent to only a few tens of meters per second delta-v.
  - BenMorganIO 8y ago
    Is that escape velocity or how fast it goes around the sun? I know it's days are exceptionally slow.
  - pdonis 8y ago
    I think that delta v includes an extra allowance for the extremely thick atmosphere as compared to Earth's. The delta-v for Earth is given as 9 km/s, which is actually greater than orbital velocity at 250 km altitude; the difference is the extra delta-v you have to allow for atmospheric drag. Venus' atmosphere would give a lot more drag.
    - seszett 8y ago
      On the other hand, the atmosphere of Venus could also been seen as a help since you could "just" float or fly to a great altitude instead of departing from the ground. The ground is pretty much impossible to reach anyway, and not as interesting as the atmosphere about 50 km up, where temperature and pressure are about the same as on Earth and where breathable air is buoyant.
      - pdonis 8y ago
        > the atmosphere of Venus could also been seen as a help since you could "just" float or fly to a great altitude instead of departing from the ground Yes, but I don't think the numbers given in the chart consider such possibilities. I think they're for a standard rocket blasting off from the surface and having to account for atmospheric drag when determining how much delta-v is required to reach orbit.
- tokai 8y ago
  > Do not use for actual mission planing Darn it, I have just finished my burns.
  - skunkworker 8y ago
    Don't leave Jeb stranded on Duna.
- ian0 8y ago
  Really interesting! The expanded image was 404ing for me, I found this slightly different one for anyone interested: https://i.imgur.com/WGOy3qT.png https://i.imgur.com/WGOy3qT.png
- baxtr 8y ago
  Awesome! Things like that are the reason we can't stop reading HN. There are way too many interesting pieces popping up. I just need to be careful not to spend the entire day here.
- diggernet 8y ago
  That image looks like it would be a great game board for some sort of strategy game.

eunoia 8y ago

For the fellow curious, here’s a solar system delta-v chart [1]. [1]https://goo.gl/images/83YdXE https://goo.gl/images/83YdXE

isostatic 8y ago
Is Venus really 27km/s to get to a 400km orbit? I'd have expected a number nearer Earth's
- danw1979 8y ago
  Atmospheric density ? or maybe that the “low orbit” distance given for Venus is 400km vs 250km for Earth.
  - pdonis 8y ago
    > maybe that the “low orbit” distance given for Venus is 400km vs 250km for Earth No, that won't make much of a difference: the gain is basically just the gain in potential energy for the extra 150 km, which is equivalent to only a few tens of meters per second delta-v.
- BenMorganIO 8y ago
  Is that escape velocity or how fast it goes around the sun? I know it's days are exceptionally slow.
- pdonis 8y ago
  I think that delta v includes an extra allowance for the extremely thick atmosphere as compared to Earth's. The delta-v for Earth is given as 9 km/s, which is actually greater than orbital velocity at 250 km altitude; the difference is the extra delta-v you have to allow for atmospheric drag. Venus' atmosphere would give a lot more drag.
  - seszett 8y ago
    On the other hand, the atmosphere of Venus could also been seen as a help since you could "just" float or fly to a great altitude instead of departing from the ground. The ground is pretty much impossible to reach anyway, and not as interesting as the atmosphere about 50 km up, where temperature and pressure are about the same as on Earth and where breathable air is buoyant.
    - pdonis 8y ago
      > the atmosphere of Venus could also been seen as a help since you could "just" float or fly to a great altitude instead of departing from the ground Yes, but I don't think the numbers given in the chart consider such possibilities. I think they're for a standard rocket blasting off from the surface and having to account for atmospheric drag when determining how much delta-v is required to reach orbit.
tokai 8y ago
> Do not use for actual mission planing Darn it, I have just finished my burns.
- skunkworker 8y ago
  Don't leave Jeb stranded on Duna.
ian0 8y ago
Really interesting! The expanded image was 404ing for me, I found this slightly different one for anyone interested: https://i.imgur.com/WGOy3qT.png https://i.imgur.com/WGOy3qT.png
baxtr 8y ago
Awesome! Things like that are the reason we can't stop reading HN. There are way too many interesting pieces popping up. I just need to be careful not to spend the entire day here.
diggernet 8y ago
That image looks like it would be a great game board for some sort of strategy game.