[freeopinion]

> Anything that requires significant energy

So instead of sending a rover with 4x or 10x energy, the answer is a mission that requires enough energy to launch the samples all the way back to Earth? This makes me smile.

I do agree though. We can expend 1000x the energy of the return trip once the samples are back on earth. And we also have the luxury of unlimited time to invent new tests and new tech to apply to whatever is left of the samples.

[jerf]

"So instead of sending a rover with 4x or 10x energy"

The rocket equation is a real jerk. You're likely thinking "that sounds linearly harder" when you should be thinking it's exponentially harder.

[marcosdumay]

At that point, adding weight to the rover or to the return system is an equivalent cost.

[jerf]

No, rover is easier; return system has to fly all of its mass back to Earth, rover never leaves Mars.

In which case you might be asking what the advantage of a return system is in the first place, the answer being for much the same reason that we have "stages" of rockets. The return system gets a fresh exponential curve to work with. If you tried to ship both at once it would be a nightmare. Plus there are all the advantages of shipping things back, regardless of what the rocket equation says. Science via a rover is great but it just can't match numerous full laboratories with humans in them.

The part that disappoints me a bit is that I still don't see us launching fuel into space for space refueling very often. Rocket equation bites no matter what you do, but launching a Falcon fuel of nothing but fuel (to the extent possible) shrinks the solar system a lot. It's still pretty big after that, but it's a different place, even with conventional chemical rockets. I hope we'll see it soon. I'm not sure it'll be quite as simple as "SpaceX will have a Mars Starship there before the mission can get there", but there is a real prospect of making it so space missions takes weeks instead of years if we can get space refueling figured out. A lot of other things come into reach as well, like satellite reclamation.