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EDIT: Please note the following items:

The Mission Requirements for claiming the Grand or Second Place Prize include the following:

  • Landing – A team must land its craft on the surface of the Moon after providing advance notice of its launch and intended landing site to XPRIZE.

  • Mobility – After landing, a team must move its craft a distance of at least five hundred meters below, on, or above the lunar surface along an interesting path in a deliberate manner. The distance can be a straight line or may be a series of waypoints approved by the Judging Panel.

As in some games of pool, you have to indicate your intended landing area ahead of time. Your actual landing site should be close, and allow for an acceptable course of travel for your rover. If you are driving a lunarized Sand Flea maybe the second part is relatively easy. Otherwise, you don't want to end up at the bottom of a hole or wedged in a crevasse.

As I've said here there's no GPS on the moon. I am presuming the Lunar X Prize landers will start would have started from an established lunar orbit (where they can get could have gotten their bearing and wait for a final "Go" from Earth). This gives them time to receive any of various potential beacon and telemetry signals from Earth, and data from their cameras (e.g. Earth, Moon, Sun, Stars...)

But once descent has started, I am not sure which of these are would have been still helpful, during attitude, and especially propulsive maneuvers.

I don't want to know about any competitive secrets, or "special sauce" that that various teams are were counting on, but from a general perspective, what navigational information is likely to have been useful for these small, limited budget, limited development, limited previous experience lunar landing craft?

If the Moon were a smooth sphere with a painted pattern on it, a nice landing might be done with some nice cameras. But the Moon has substantial topography - would they need to be ready to do a "Neil Armstrong" and look around for what looks like a good place to land? Or could they use a "rover-friendly" region map and have precise enough navigational data to put themselves down within a few meters or tens of meters of an absolute spot?

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    $\begingroup$ Even a modest modern computer could generate a decent 3D representation of the terrain from a camera on the way down. A stereo pair of cameras would be even better, but I suspect that even a cyclopean lander could identify a safely flat spot for a landing. $\endgroup$
    – Russell Borogove
    Jan 27, 2017 at 19:18
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    $\begingroup$ It's also worth noting that Surveyor I landed safely on the moon with no particular ability to choose a landing site -- it preceded the Lunar Orbiter missions which provided photographs of potential landing sites for later Surveyors and Apollo. Even the later Surveyors had uncertainty ellipses measured in kilometers; those that made it to the surface all landed more or less safely. $\endgroup$
    – Russell Borogove
    Jan 27, 2017 at 19:40
  • $\begingroup$ @RussellBorogove I'm quite sure you are right about the hardware capability, but how hard would it be to develop it in a hurry, on a shoestring budget, with reliability to the extent you'd bet your X-prize on it working? Are they really going to do this as you've described? $\endgroup$
    – uhoh
    Jan 27, 2017 at 19:42
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    $\begingroup$ @RussellBorogove It would take more than two days just to build a model of the Moon's surface, and learn to light it properly. Shadows are often nearly black on the moon - terrain is quite varied, there's cliffs, giant boulders, I think you are underestimating the task of putting together a package that a descending spacecraft would need at only two days. $\endgroup$
    – uhoh
    Jan 27, 2017 at 19:59
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    $\begingroup$ There are software packages available to generate representative images that a visual based navigation module could be trained on, e.g. star-dundee.com/products/… $\endgroup$
    – djr
    Jan 27, 2017 at 22:23

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