The Orbital Propellant Transfer Vehicle (OPTV) is an important vehicle in order to achieve the reuse portion of reuse and commonality.
In the past, NASA had envisioned a propellant depot in Earth orbit (Image A).
 |
| Image A; a 1970s era Liquid Hydrogen Fuel Depot in Earth orbit |
Our vision is slightly different in that we need LO2 as well as LH2. So a propellant depot in orbit is not feasible.
Instead, our plan is to refill a propellant module (OPTV) and bring it up to orbit. Once emptied, the OPTV returns to Earth for refurbish, refill, and relaunch.
::