Propellant depot and rocket size

[DSS_jgarzik]

Eric Anderson @ Planetary Resources was recently discussing propellant depots.  My curiosity was piqued.

Let us assume a simple design where hypergolic upper stages are "parked" in high LEO, waiting for a payload.

1) What is the smallest "parked" upper stage that would be required to take a 1kg 1U cubesat payload from high LEO to Mars orbit?  (feel free to pick any existing LV, orbital velocity, etc.)  Must make trip in under 48 months or so.

2) What space-tested methods exist for payload transfer, such as transferring a cubesat (or P-POD) from an LV to the "parked" upper stage, besides (a) human hands or (b) human-controlled robotic arm?  Free-floating, automated capture and docking systems seem still under heavy R&D.

Thanks!

[jabe]

i like this concept..microsats to Mars using ionic fluid engine

http://actu.epfl.ch/news/getting-to-the-moon-on-drops-of-fuel/

http://lmts.epfl.ch/microthrust

jb