There are many things that probably should be said about the latest Mars landing. I see it as a great achievement in development of technology, it creates new possibilities for both research, and development of even more complex equipment for space exploration, but at the moment one question bothers me:
The whole crane thing was supposed to soften the landing, so rover will not be subjected to rapid deceleration that would happen when a more conventional platform touches the ground. I guess, it's possible that a crane supported by nothing but rockets is more stable while in flight than a landing platform when it touches the ground over a pillow of gas from the same rockets, so there may be less acceleration in the end.
But on NASA TV it was clearly visible that when the whole thing entered the atmosphere, acceleration was more than 10g, therefore each and every component of the rover and its carrier, was supposed to tolerate many minutes of such acceleration. So if the platform can guarantee less than 10g when it touches the ground, it can safely land without any complicated mechanisms, with rover on top, just like it was done for decades with smaller but just as fragile devices.
So traditional solution has top mount for rover, low-altitude altimeter, rocket engines designed to exploit ground effect while immediately over the ground, but no crane, no procedure for keeping platform extremely stable for the whole time while rover is lowered by the crane then getting the platform away from the rover, and no weird direction of the nozzles to keep gas away from the rover. For me, that sounds clearly superior.
I really can't understand what was the reason for choosing the crane. Anyone has any idea?