After America will have returned to the Moon, why won't NASA make a Venus flyby mission with the Orion/SLS before going on to manned flights to Mars?

They are planning crewed missions to Venus (HAVOC) but for the distant future; it seems they want to go to Mars first. It would be much better to test interplanetary travel with the Orion spacecraft to the nearest planet first.

The countless advantages include:

  • proximity to planet Earth
  • you can abort the journey and return to Earth much easier than during a Mars flight
  • the proximity means a faster communication with Houston
  • a not as long journey as to planet Mars in preparation for Mars missions
  • testing human conditions in interplanetary flight (especially psychology and radiation)
  • and a preparation to the already-mentioned HAVOC missions into the Venerean atmosphere

So what do you think, why won't they test the Orion/SLS and the human conditions during a Venus flight first?

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – called2voyage
    May 13, 2019 at 14:27
  • $\begingroup$ Another psychological advantage would be that the crew would always look at the sunny side of the Earth ! $\endgroup$
    – Cornelis
    Aug 20, 2019 at 11:13

2 Answers 2


A Venus flyby does little to nothing towards the stated goal: a manned landing on Mars.

  1. because you get a lot closer to the Sun than on a Mars mission, you need to modify the spacecraft to reject all that extra heat. There goes the commonality in the spacecraft.

  2. A flight time of 5 months vs. 6 months (one way) for a Mars mission is not a significant difference. The difference in mission duration is bigger (1 year vs 20 months). But if all you want is a long-duration test of the spacecraft systems, just stick the spacecraft in a high Earth orbit (above the Van Allen belts), preferably a sun-synchronous one to get permanent sunlight.

  3. Flight parameters for Mars missions are well understood, a Venus mission is not needed for this.

  4. Flyby missions in general won't be popular because you spend months waiting for a very brief flyby - and everything you can do on a flyby is amenable to automation so you might as well have sent an unmanned spacecraft instead.

  • $\begingroup$ Point 2 is error because a manned Mars mission has a duration of 2 Earth years, you have to include the return and the stay on Mars too. $\endgroup$
    – User31481
    May 11, 2019 at 17:49
  • $\begingroup$ During such a long interplanetary mission, which but is not as long as a Mars mission and it is abortable, one could especially test the psychological conditions of the crew during interplanetary flight. And they could do many things worthy to science unmanned spacecraft can't. $\endgroup$
    – User31481
    May 11, 2019 at 17:51
  • 3
    $\begingroup$ @User31481 Pleas elaborate what technique results in a venus mission being more abortable then a mars mission? I see very little support in orbital mechanics for this claim of yours. $\endgroup$
    – Polygnome
    May 11, 2019 at 20:31
  • 1
    $\begingroup$ Re point 4 - a highly reasonable basis for a manned Mars flyby would be to allow near live control of robotic rovers/landers prepping a future manned landing site with delays in seconds rather than minutes. This does not apply if there is no surface rovers to control or manned landing to prep for. $\endgroup$ May 11, 2019 at 23:42
  • 2
    $\begingroup$ @GremlinWranger You'd get a few days of such close control out of a 20 month mission. $\endgroup$ May 12, 2019 at 10:56

A supplementary answer, since comments have got very long. This paper explores options for doing both. For some departure times, there are trajectories which launch from Earth with a manageable 5 or so km/s delta-V on top of what is needed to escape from Earth orbit and then fly by both Mars and Venus without further propulsion (except for trajectory corrections) and return to Earth in around 18-20 months, with a survivable reentry velocity.

The arguments against manned flyby missions still apply though -- that there isn't time to do anything useful during the flyby.


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