NASA SOLICITS PROPULSION PROPOSALS: NASA Calls On Industry, Academia For In-Space Propulsion Innovations. Well, this is potential good news for Mars exploration -- anything that gets us there faster, cheaper, and with larger useful payloads is an especially welcome innovation when it comes to human missions and settlement.

"It's not our intent to develop flight hardware geared exclusively to one-shot missions," Johnson said. "Instead, we are working to develop cost-effective propulsion technologies that will support multiple missions, enabling us to send spacecraft on longer, more useful voyages -- and in many cases to destinations that were previously unreachable using traditional propulsion systems."

Even with robotic missions, this sort of thing makes a whole lot of sense. Designing and building one-off or two-off probes from scratch each time provides a whole lot of aerospace jobs, sure, and it allows one to incorporate new technologies and lessons learned from previous missions. But on the other hand, it drives up the cost of each mission dramatically, and stretches out the gap between missions, the engineering and testing requiring more time to perform and budget limitations neccessarily restricting the frequency of expensive missions.

The development of a standard propulsion and power bus for deep space use would make a lot of sense, particularly if it is a modular system that can be "dialed" up or down as suits the particular mission. To some extent, this has already been attempted in the commercial satellite field (though there is still a lot of customer-driven customization of designs such as A2100), and in some of NASA's earlier probes (the Voyager structural bus was the same as for the Pioneers sent to the outer planets, as I recall, but I can't find a link to prove it). Certainly, some mission-specific customization would need to be done, but if the "chassis" design is mostly standardized, it should dramatically reduce the cost and lead-time for a given mission.