Let's say the Earth got knocked a bit silly in the distant past and somehow space-loving life evolved on this planet. They roll around on an Earth with an axial tilt of 98°. How much harder is it for this species to go visit the moon (which was unaffected). What about rest of the planets?

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    $\begingroup$ I think the influence of the moon is pretty good at keeping Earth's axial tilt under control. Lots of interesting tidal interaction there. You're also going to have issues evolving complex terrestrial life on a world like that. Might be mostly aquatic, making spacefaring awkward. $\endgroup$ Feb 6, 2020 at 11:04
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    $\begingroup$ 98° is by coincidence similar to the inclination of a sun-synchronous orbit on Earth. Hence, the difference is more or less exactly the same as the difference between an equatorial and a polar orbit. $\endgroup$
    – asdfex
    Feb 6, 2020 at 18:08
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    $\begingroup$ I removed your hypothetical tag. Please take some time to review Should I create a new tag?. Also, see this meta post where we have ruled that we do not want a hypothetical tag. $\endgroup$
    – called2voyage
    Mar 4, 2020 at 16:04

1 Answer 1


For a Moon mission, the difference is very small.

Even if one makes no attempt at picking launch sites other than the equator, or don't use any inclined orbit, the resulting lunar transfer orbit isn't all that bad:

A apogee velocity of 190 m/s tangential to lunar orbit, instead of parallel to lunar orbit increases lunar orbital injection (and escape) cost by 70 m/s. That's the easiest burn of the whole mission getting 10% more expensive.

For comparison, this is about the same delta-v advantage one gives up launching from Cape Canaveral instead of the equator, which means that our hypothetical Uranus-Earth moon mission has pretty much the exact same delta-v budget by launching from the equator.

For an interplanetary mission, there is no difference.

When entering a planet from solar orbit, one can pick any target orbital inclination by picking which side of the planet one enters from before making the breaking burn.

Since orbits are time reversible, this also means one can launch a spacecraft into the ecliptic plane from any LEO inclination at equal cost. Interplanetary spacecraft already do this all the time, and this would be no different on Uranus-Earth.

  • $\begingroup$ Add something about thermal management. Spacecraft launched into the easiest equatorial orbits would spend much more time in the sunlight $\endgroup$
    – Innovine
    Jul 10, 2021 at 9:32
  • $\begingroup$ @Innovine The question asks about Moon and planetary missions, and those spend almost all their time in sunlight anyway. $\endgroup$ Jul 10, 2021 at 9:33

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