Orion is returning to Earth with a marked orbital inclination compared to its Lunar Distant Retrograde Orbit (DRO).

Orbital inclination changes require a great deal of delta-v, and Orion is on a tight delta-v budget. In-plane orbital changes are made most economically at periapsis but orbital plane inclination changes are most economical at apoapsis

The published mission descriptions mention major burns during the return trajectory at the Distant Retrograde Orbit Departure (DROD) and the Return Powered Flyby (RPF). I cannot find reference to a plane change as part of either of these. I assume it was done as part of the DROD? What is the angle between the DRO and the return transit?

enter image description here

Red rectangle is plane of DRO

Blue rectangle is plane of return transit

Green rectangle is the plane of the transit between DROD and RPF

The purple line is Orion’s return transit:

  1. in DRO
  2. at braking and presumed plane change DROD burn
  3. at RPF (presumed in-plane only)
  4. trajectory South of the DRO plane
  5. Earth arrival over the South Pacific Ocean

1 Answer 1


You just have to aim at a different part of the moon for your gravity-assist fly-by. For instance, if you flew by the moon over its North pole, it would perturb your Earth-return trajectory to the South of the lunar orbital plane. It seems that this is exactly what they did. This doesn't require any major burns, just directional manoeuvres.

I suspect that this directional manouevre is blobby mcblobby's DPC, but that post is above my head, "like a horse trough to a pig" as they say in Hungary.

  • $\begingroup$ "aim at a different part of the moon" is, by definition, an inclination change. The DRO is roughly Lunar equatorial. To fly over the Lunar North pole would require a 90* change in orbital plane. $\endgroup$
    – Woody
    Dec 6, 2022 at 21:56
  • $\begingroup$ @Woody: OK, step back to the trans-lunar insertion burn: you aim at the South pole of the moon, so that on the way back, you end up flying over the North pole. The details are irrelevant -- the principle is that it takes only a minuscule course change on the way out to produce a major course change on the way back. $\endgroup$
    – TonyK
    Dec 6, 2022 at 22:20
  • $\begingroup$ TonyK ... The DRO plane change is a 2 body problem. The translunar insertion burn is a 3-body problem. You are correct about sensitivity to initial conditions in a 3-body problem. But it does not apply to 2 body problems. Once Orion leaves the Lunar Sphere of Influence, we are back to 3-body. $\endgroup$
    – Woody
    Dec 6, 2022 at 22:34

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