Break the problem into parts. Design a system to get sample canisters into martian orbit. Design a Martian orbital system to catch the canisters and send them towards earth. Design an earth orbital system to intercept the canisters. Design a system to get the canisters from Earth orbit to the surface.

Each of these systems will be separate structures with different goals. Each one will be technically difficult and require new methods but each smaller piece will be easier to solve than the problem as a whole.

After R-ing TFA, this is pretty much their plan.