And now for a little change of venue. With the obvious exception of “mini-moons” (TCOs and TCFs) asteroid targets are in heliocentric orbits, and often at ranges measured in AUs. Round-trip light time is a few minutes, and it’s unrealistic to expect a human operator to, as they say, ‘joystick it’ from the ground. We have, in our favor, that the gravity of small bodies is, itself, a small number. Accelerations are mild, “landings” are more like dockings, and the notion of a probe ‘crashing’ to the surface is a mental image that doesn’t correspond to the real world. After all, Beresheet crashed, Vikram crashed, Luna-25 crashed, and Hakuto-R crashed. But Hayabusa bounced; NEAR Shoemaker “landed” without even having legs, or a real descent engine. Hayabusa2 then put down multiple sub-spacecraft onto Ryugu.
Still, let’s not bounce our expensive spacecraft. How so? We give our probes something that passes for ‘sight,’ and something that passes for ‘smarts.’ In the October issue (vol. 43, #11) of International Journal of Robotics Research:
Dor, M. Driver, T. Getzandanner, K. et al. 2024 AstroSLAM: Autonomous monocular navigation in the vicinity of a celestial small body- Theory and Experiments 02783649241234367
There was a previous navigation algorithm, SLAM (Simultaneous Localization and Mapping). Dor et al. now adapt it to small bodies, adapting the name to AstroSLAM. This work is ongoing because it is cross-applicable to missile and drone guidance, other spacecraft, underwater bots, to an extent ground vehicles and ships, etc. However, in its application to asteroid ‘landings’, the stakes are low, as given above, and the consequences, mild (as Hayabusa demonstrated). In this application, the target (a given asteroid) is moving; for a given mission, the orbit of that asteroid has already been determined. (How else did the spacecraft get to that point?) The motion of that asteroid (or comet), then, is known to at least a reasonable degree. In other words, the body had some ‘lane’ we can assume, and is unlikely to leave its lane at any given moment, even if it might take some lane position that hasn’t been Unlike self-driving cars, however, other (road) users do not simply appear from ‘nowhere’. Nor can an asteroid make a sudden turn (though comets experience “nongravitational force”- jetting- and can drift ‘out of lane’ on a sufficiently long timescale).
Asteroids are accessible targets, in some cases more accessible than Earth’s natural satellite. Asteroid landings are demonstrated, and demonstrated to be just fine.