So I had an idea. A very simple electric rocket engine exists that gives both high thrust and high ISP. It’s the MPD thruster. I’ve read that 15k ISP, at about 50% efficiency, is possible with hydrogen propellant.
The catch is you need enormous amounts of electricity, on the order of gigawatts, to drive one of these thrusters. Also, the lightest designs use sacrificial electrodes that will erode during thruster firing and limit your burn duration.
So, if you had an interplanetary mother-ship, something with the capability to explore all the planets on a single mission and carry crew onboard, you’d need something else as a main engine. A fusion exhaust engine or something. But for the lander…
You’d mount the rectenna on the top of the lander and use a larger phase array antenna on the mothership to focus a microwave beam on the lander. The lander would basically look like a big disk with a mesh of rectenna elements, and the MPD engines and propellant tanks and crew module and so forth would all hang off the bottom, with the mass distributed to give it a low center of gravity and a wide base.
How many watts per kilogram could you reasonably receive with the rectenna? With that information, I could work out what ISP you could throttle your MPD thrusters to, and what your payload ratio and fuel consumption would end up being for a landing on Luna or Ganymede or one of the other high gravity vacuum moons in the Solar System.