Okay, I know there have been a lot of threads on this before, but none recently.What about staging an exploration mission from the ISS?It could be that most of the mission hardware (like a lander or a MTV) is sitting out at a lagrange point, but not necessarily.The idea is that you transfer from the station to, say, an Orion spacecraft with an enlarged service module which can act like an EDS (an idea I think I heard OV-106 mention recently).The EDS could be launched fully fueled or could be launched partly empty and refueled in orbit, like how Zvezda and Zarya are currently refueled. The EDS would probably be attached to the Orion capsule, not launched separately.This means that man-rating the HLV (as well as a crew tower, LAS, etc, etc) is unnecessary (even an HLV would not be strictly unnecessary in this scenario... but lets not go there).What about it?
Unlike in terrestrial systems, where strain and wear cause failure rate to be a linear function of time, spacecraft failure rates diminish over time. This relationship, a Weibull distribution, is shown in Figure B.1, where the average number of failures reported annually for a given spacecraft decreases.