4 ms·

> By that metric Venus is the closest at 640 m/s from Earth intercept to Venus intercept By the way, I think there is a typo on that delta-v map. I doubt low V

> By that metric Venus is the closest at 640 m/s from Earth intercept to Venus intercept By the way, I think there is a typo on that delta-v map. I doubt low Venus orbit to Venus is 27km/s, vs 9.4 for the earth, when Venus gravity is just 90% that of Earth.

mnw21cam 3y ago
Depends on whether you take atmospheric drag into account. If you do, then you'll be fighting Venus' thick atmosphere all the way up, and that 27km/s figure could well be accurate. I don't like it when delta-v maps include atmospheric drag, because the numbers depend on how aerodynamic your rocket is, in contrast to the other manoeuvres where the amount of delta-v doesn't depend on the type of rocket you have at all.
- TeMPOraL 3y ago
  Here is the OG source of those numbers: https://old.reddit.com/r/space/comments/1ktjfi/deltav_map_of_the_solar_system/ https://old.reddit.com/r/space/comments/1ktjfi/deltav_map_of.... Skimming the thread, they made "assumptions" for cases like taking off from bodies with atmosphere. Here is more on how they came up with the number for Venus, including some actual math: https://old.reddit.com/r/space/comments/1ktjfi/deltav_map_of_the_solar_system/cbsq64k/ https://old.reddit.com/r/space/comments/1ktjfi/deltav_map_of.... The OG image mentions that there are assumptions being made. The image linked by GP is a derivative work, improving on and crediting the work of /u/CuriousMetaphor, however it omits some of the caveats in the legend.
- vikingerik 3y ago
  As other replies are saying, that does include the atmospheric drag. But that number wouldn't actually happen with rocket thrust. You'd never actually do that, launch a rocket from the surface of Venus - you'd first take advantage of the atmosphere to do aerodynamic flight, first carry the rocket to much higher altitude with an airplane and then ignite it from there.
  - ooboe 3y ago
    Didn't work out so well for Branson.
    - mnw21cam 3y ago
      It would be much more of an advantage on Venus than it is on Earth.
    - mlyle 3y ago
      Worked just fine for Orbital/ATK Pegasus.
- MayeulC 3y ago
  Thank you for pointing this out. > I don't like it when delta-v maps include atmospheric drag Yes, I find it quite unintuitive, especially as the map is now asymmetric: if you take into account drag on liftoff, you would also take into account aerobraking for reentry. It means that the map can't really be used for body-to-body calculations, as it assumes "rocket liftoff" for the low orbit<->surface transition. Ideally, atmospheric parameters should be specified some other way on the map, or it could branch to show both liftoff and reentry costs on each body (and possibly delta-v due only to gravity).
  - mlyle 3y ago
    It's just the first segment on the trip. Reentry delta-V isn't really well-posed. The delta V that would enter orbit, or even less, with a somewhat different angle reenters. So the "reentry delta V" might very possibly be negative, in that you could go Earth LEO to body surface with less velocity change. > possibly delta-v due only to gravity) Now, that's more useful to have around.
Symmetry 3y ago
The numbers for reaching LEO include typical atmospheric drag losses. That's only a km/s or so on Earth but on Venus with it's very thick atmosphere the losses are much higher.
- mr_toad 3y ago
  From the surface? It’s unlikely that anything would every launch from the surface of Venus.
  - jjk166 3y ago
    Probably more likely than a launch from the surface of Jupiter.
  - mlyle 3y ago
    It's not only unlikely, it's unpossible. If you're using chemical propulsion, you're not going to get much more than 20km/sec even with a whole lot of stages.
    - Symmetry 3y ago
      You'd certainly need something beyond a chemical rocket but there are options. At that density a turborocket[1] would certainly be worth the extra mass but I think still wouldn't be enough of an advantage. In the realm of roughly existing technology, a nuclear ramjet[2] could get you to the upper reaches of the atmosphere and give you a nice little initial boost as well to your speed. And in the realm of SF, a nuclear saltwater rocket[3] would still be easily capable of making it out of Venus in one stage. [1]https://en.wikipedia.org/wiki/Air_turborocket https://en.wikipedia.org/wiki/Air_turborocket [2]https://en.wikipedia.org/wiki/Project_Pluto https://en.wikipedia.org/wiki/Project_Pluto [3]https://en.wikipedia.org/wiki/Nuclear_salt-water_rocket https://en.wikipedia.org/wiki/Nuclear_salt-water_rocket
      - mlyle 3y ago
        > At that density a turborocket[1] would certainly be worth the extra mass but I think still wouldn't be enough of an advantage. How's a turborocket work without free oxygen gas in the atmosphere? I mean, maybe fluorine, but I doubt you come out ahead that way. Density effects, though, make balloon-launched rockets, etc, conceivable.

mnw21cam 3y ago

Depends on whether you take atmospheric drag into account. If you do, then you'll be fighting Venus' thick atmosphere all the way up, and that 27km/s figure could well be accurate. I don't like it when delta-v maps include atmospheric drag, because the numbers depend on how aerodynamic your rocket is, in contrast to the other manoeuvres where the amount of delta-v doesn't depend on the type of rocket you have at all.

TeMPOraL 3y ago
Here is the OG source of those numbers: https://old.reddit.com/r/space/comments/1ktjfi/deltav_map_of_the_solar_system/ https://old.reddit.com/r/space/comments/1ktjfi/deltav_map_of.... Skimming the thread, they made "assumptions" for cases like taking off from bodies with atmosphere. Here is more on how they came up with the number for Venus, including some actual math: https://old.reddit.com/r/space/comments/1ktjfi/deltav_map_of_the_solar_system/cbsq64k/ https://old.reddit.com/r/space/comments/1ktjfi/deltav_map_of.... The OG image mentions that there are assumptions being made. The image linked by GP is a derivative work, improving on and crediting the work of /u/CuriousMetaphor, however it omits some of the caveats in the legend.
vikingerik 3y ago
As other replies are saying, that does include the atmospheric drag. But that number wouldn't actually happen with rocket thrust. You'd never actually do that, launch a rocket from the surface of Venus - you'd first take advantage of the atmosphere to do aerodynamic flight, first carry the rocket to much higher altitude with an airplane and then ignite it from there.
- ooboe 3y ago
  Didn't work out so well for Branson.
  - mnw21cam 3y ago
    It would be much more of an advantage on Venus than it is on Earth.
  - mlyle 3y ago
    Worked just fine for Orbital/ATK Pegasus.
MayeulC 3y ago
Thank you for pointing this out. > I don't like it when delta-v maps include atmospheric drag Yes, I find it quite unintuitive, especially as the map is now asymmetric: if you take into account drag on liftoff, you would also take into account aerobraking for reentry. It means that the map can't really be used for body-to-body calculations, as it assumes "rocket liftoff" for the low orbit<->surface transition. Ideally, atmospheric parameters should be specified some other way on the map, or it could branch to show both liftoff and reentry costs on each body (and possibly delta-v due only to gravity).
- mlyle 3y ago
  It's just the first segment on the trip. Reentry delta-V isn't really well-posed. The delta V that would enter orbit, or even less, with a somewhat different angle reenters. So the "reentry delta V" might very possibly be negative, in that you could go Earth LEO to body surface with less velocity change. > possibly delta-v due only to gravity) Now, that's more useful to have around.

Symmetry 3y ago

The numbers for reaching LEO include typical atmospheric drag losses. That's only a km/s or so on Earth but on Venus with it's very thick atmosphere the losses are much higher.

mr_toad 3y ago
From the surface? It’s unlikely that anything would every launch from the surface of Venus.
- jjk166 3y ago
  Probably more likely than a launch from the surface of Jupiter.
- mlyle 3y ago
  It's not only unlikely, it's unpossible. If you're using chemical propulsion, you're not going to get much more than 20km/sec even with a whole lot of stages.
  - Symmetry 3y ago
    You'd certainly need something beyond a chemical rocket but there are options. At that density a turborocket[1] would certainly be worth the extra mass but I think still wouldn't be enough of an advantage. In the realm of roughly existing technology, a nuclear ramjet[2] could get you to the upper reaches of the atmosphere and give you a nice little initial boost as well to your speed. And in the realm of SF, a nuclear saltwater rocket[3] would still be easily capable of making it out of Venus in one stage. [1]https://en.wikipedia.org/wiki/Air_turborocket https://en.wikipedia.org/wiki/Air_turborocket [2]https://en.wikipedia.org/wiki/Project_Pluto https://en.wikipedia.org/wiki/Project_Pluto [3]https://en.wikipedia.org/wiki/Nuclear_salt-water_rocket https://en.wikipedia.org/wiki/Nuclear_salt-water_rocket
    - mlyle 3y ago
      > At that density a turborocket[1] would certainly be worth the extra mass but I think still wouldn't be enough of an advantage. How's a turborocket work without free oxygen gas in the atmosphere? I mean, maybe fluorine, but I doubt you come out ahead that way. Density effects, though, make balloon-launched rockets, etc, conceivable.