CubeSats to Phobos?

Suggesting that there are ways to travel to other planets that don't require nuclear powered spacecraft, NASA's Innovative Advanced Concepts Program at JPL has sketched out a mission that would send a pair of CubeSats to Phobos for a sample return mission. As envisioned, the two-unit CubeSat would use solar sails to gently raise the craft to an orbit that would then transition to a Lagrange Point to minimize the energy needed for interplantary flight. The outline also includes a unique proposal for landing on the Martian moon:
[T]he two CubeSats will skim the surface of Phobos from a hyperbolic orbit. As the lander CubeSat approaches the surface, its motion relative to the surface is stopped by the action of a preset spring which pushes apart the two CubeSats. It is on the surface with very little relative motion, so it has 'landed.' A robotic scoop might be used to collect a surface sample, but even a sticky surface could do so.
If the two CubeSats remain connected by a tether, when the tether pulls tight both CubeSats will pull free of Phobos' gravitation. The CubeSats then navigate back to the Interplanetary Transit Network, and enter an appropriate zero-energy trajectory ...