I was thinking for quite a while about sending this question to Maria Zuber's e-mail address (she was the principal investigator of the GRAIL mission to map the Moon's gravity field), but then I thought that it may not be appropriate. Also, asking her whether she or her collegues have considered this idea. She has been involved on the Clementine mission to the Moon, MESSENGER mission to Mercury, and MAGIC proposal to Callisto, all of which have included gravity mapping and laser altimeter investigations.

My question is simply whether we have the technical ability to perform a similar mission on a much more distant body.

Or, in other words, whether this mission has only succeeded thanks to the fact that it happened on the Moon, where; precise tracking, higher data volumes return, signal delay etc... are greatly facilitated by the shorter distance.

The key to its high sensibility is how well they managed to keep the two spacecraft flying in formation, and how precisely they managed to track the deviations caused by gravity anomalies. By the end of the mission they even managed to orbit at commercial airliner height.

  • $\begingroup$ this doesn't fully answer the question because it doesn't explain why, but on this video at minute 54:13, youtube.com/watch?v=WcPithqyJ20 Maria says, "We are never gonna have a set of datasets like we have here for the moon for this other planets, we've got good data sets, but nowhere near as good..." $\endgroup$
    – we'll see
    Oct 6, 2021 at 9:11
  • $\begingroup$ Related question: space.stackexchange.com/questions/2058/… $\endgroup$
    – Dan Hanson
    Nov 5, 2022 at 1:27

1 Answer 1


I can't provide a definitive answer, but I think the main limiting factor, beyond mere physical matters like getting the spacecraft there or having it be able to transmit data at a useful rate for accomplishing the same thing as on the Moon, is indeed the speed of light itself.

Anything that requires manual control of the spacecraft (such as keeping them flying in formation, or executing precise orbital maneuvers) is inherently much harder when the data you are getting from the spacecraft is a few minutes old AND the instructions you send to it will also be a few minutes old by the time the spacecraft receives it.

Missions to Mars, especially those which required landing something intact on the surface (which, arguably, might not be as complex as keeping two spacecraft in precise formation), have all had to deal with this, usually via obviating the need for manual intervention for at least that bit of the flight. Hypothetically, automating most of the data-collection phase of the flight could maybe fix this aspect, but precise tracking and measurements are likely to remain a problem.

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    $\begingroup$ Welcome to Space! I don't think there was any time-sensitive exchange of data with nor commands from the ground during GRAIL's data-taking phases. There were occasional trajectory correction maneuvers but they probably happened on the scale of weeks, not minutes. What was important was the reception of beacon-like signals from Grail at Earth and the Doppler shifts of those signals, but those can be simply recorded and analyzed later. $\endgroup$
    – uhoh
    Oct 10, 2021 at 0:01
  • $\begingroup$ Yes, if you are farther, then it's more challenging to receive large dumps of recorded data, but that may turn out to be manageable. directory.eoportal.org/web/eoportal/satellite-missions/content/… $\endgroup$
    – uhoh
    Oct 10, 2021 at 0:01
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    $\begingroup$ Yes, loss of bandwidth with distance is something I was aware of, but my main concern was delay and not transmission of data (New Horizons shows that this is feasible even at distances as far as Pluto); but if there is no time-sensitive exchange of data or instructions, then obviously this isn't a disqualifying issue. The other issues I had in mind you already mention. and, taken individually, all of them can/have been achieved (precise tracking? think of Hayabusa2). $\endgroup$
    – AlexJ
    Oct 10, 2021 at 1:44

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