This is a post for manned space geeks, arising from questions in comments earlier. As I note there:

We’re going to be stuck with both CBM and NDS for a long time. The latter is much more flexible, (e.g., allowing docking to an unmanned facility), but the former will stick around for its ability to transfer large objects.

Note that Dragon can’t serve as a lifeboat currently, because it has to have someone in the station, with power, to unberth from the CBM, even though it’s functionally capable of doing so with a rudimentary life support system. One of the key changes for commercial crew will be adoption of the NDS. One more reason that we should be accelerating that capability, because a Dragon lifeboat would allow the addition of another crew member, doubling or maybe even quadrupling the science that could be performed at the station.

I discuss this issue in the book:

To get back to the bizarre (at least that’s how it would appear to a Martian) behavior with respect to ISS, what is it worth? Of what value is it to have people aboard? We have spent about a hundred billion dollars on it over almost three decades. We are continuing to spend two or three billion a year on it, depending on how one keeps the books. For that, if the purpose is research, we are getting about one person-year of such (simply maintaining the facility takes a sufficient amount of available crew time that on average, only one person is doing actual research at any given time). That would imply that we think that a person-year of orbital research is worth two or three gigabucks.

What is the constraint on crew size? For now, not volume, though the life support system may be near its limits (the US segment can supposedly support four, and the Russian segment three) – I don’t know how many ultimately it could handle, but we know that there is currently not a larger crew because of NASA’s lifeboat requirement, and there has to be a Soyuz (which can return three) for each three people on the station. If what they were doing was really important, they’d do what they do at Scott-Amundsen, and live without. After all, as suggested earlier, just adding two researchers would immediately triple the productivity of the facility. In fact, because the ISS has recently been unable to average more than twenty-seven hours per week1, adding one person for a forty-hour week would increase it by two and a half times, and adding a second would increase it by a factor of four. If what we’re getting from the ISS in terms of research is really worth three billion a year, then quadrupling it would be, at least in theory, a huge value.

That’s not to say that they couldn’t be continuing to improve the safety, and develop a larger life boat eventually (the Dragon is probably very close to being able to serve as one now, since it doesn’t need a launch abort system for that role – only a new mating adaptor that allows it to dock to or depart from an unmanned or unpowered station), but their unwillingness to risk crew now is indicative of how unimportant whatever science being done on the station really is.

I should note that last week, the station did manage a record seventy-one hours, but I don’t think they’ll be able to keep that up with current crew size.