Mobile redundancy

Orbital Express has demonstrated a number of interesting techniques of great long-term importance, such as the automated refueling of spacecraft. (Here is the biggest long-term reason why automated and on-orbit assembly and refueling are important). But the mission also demonstrated the feasibility of an idea that is probably also of great but nearer-term importance, which I call mobile redundancy. The idea is that if one has a constellation of standard satellites, redundancy can be provided with mobile spare parts rather than by building on-board redunancy into each satellite as is done now. This could result in a large overall savings in weight launched per year of useful satellite lifetime.