Formerly the Deep Space Gateway and now the Lunar Orbital Gateway or LOPG station, is planned for Expedition 1 aka the maiden launch of the SLS. After reading several specifications, to avoid the "gravity well" of earth the station will remain on a cislunar orbit. Some sources say that the station will be equipped with electric propulsion systems to adjust orbits, around the earth and the moon.

What is a cislunar orbit, and with this sort of orbit, could the station also orbit the earth with minor burns, and how would this work for rendezvous and docking?


Cislunar space is a large area:

The region outside Earth's atmosphere and extending out to just beyond the Moon's orbit, including the Lagrangian points, is sometimes referred to as cis-lunar space.

Earth orbits, Moon orbits and orbits around both (like Apollo 13's free return trajectory) can all be called cislunar orbits.

LOP-G would use a halo orbit:

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Such orbits, which make close passes by the moon and loop far out, have the advantage of being near the moon, but always keep a station within the line of sight of flight controllers on Earth, as well as in sunlight for solar arrays.

  • $\begingroup$ For these elliptical orbits, how will rendezvous and docking occur for refueling and crew transportation etc? $\endgroup$ – Matt Smallwood Apr 7 '18 at 11:38
  • $\begingroup$ I personally wouldn't consider geosynchronous satellites to be operating in cislunar space. $\endgroup$ – David Hammen Apr 7 '18 at 13:43
  • $\begingroup$ @MattSmallwood, I wonder that in a similar way as two-body problem rendezvous... with a well characterisation of the periods for the surrounding halo orbits close to the target one, typical phasing strategies can still be applied $\endgroup$ – Julio Apr 7 '18 at 14:42
  • $\begingroup$ @Julio Surely the ship would have to match the elliptical orbit to match the relative velocity to properly rendezvous and dock? Of course this would be very expensive fuel wise... $\endgroup$ – Matt Smallwood Apr 8 '18 at 19:17
  • $\begingroup$ Yes, that's the condition for rendezvous to happen. As a matter of fact, reaching the orbit with the current launchers is one of the drivers to choose that particular place, see: Why is a near rectilinear halo orbit proposed for LOP-G (formerly known as Deep Space Gateway?. Anyway, close rendezvous operations are typically just a small fraction of the total mission fuel cost. $\endgroup$ – Julio Apr 10 '18 at 10:21

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