Space

Is There An ISS Expert In The House?

20 Comments

Ignoring the lifeboat issue, what is the real crew capacity of the system, and what would it take to expand it (e.g, ECLSS)? How many could it comfortably support? What are the fundamental limits? I assume that power is not one of them, and hab volume could still be expanded.

[Update late afternoon]

OK, maybe I haven’t phrased the question properly. My question is not about requirements, but about design. That is, if I wanted to expand crew far beyond that currently designed for, and (once again) ignoring the lifeboat issue, what are the constraints? Dennis implies that it is power (presumably because, admittedly, that would probably be the hardest thing to expand much, absent a nuke in LEO). But if we wanted to (say) triple it, would that be possible, and what would we have to do, and what would be the first things to upgrade, and what would it cost?

20 thoughts on “Is There An ISS Expert In The House?”

  1. See http://forum.nasaspaceflight.com/index.php?topic=21450.0 and the NTRS links mentioned there.

    The International Space Station (ISS) crew complement has increased in size from 3 to 6 crew members. In order to support this increase in crew on ISS, the United States on-orbit Segment (USOS) has been outfitted with a suite of regenerative Environmental Control and Life Support (ECLS) hardware including an Oxygen Generation System (OGS), Waste and Hygiene Compartment (WHC), and a Water Recovery System (WRS). The WRS includes the Urine Processor Assembly (UPA) and the Water Processor Assembly (WPA). With this additional life support hardware, the ISS has achieved full redundancy in its on-orbit life support system between the t OS and Russian Segment (RS). The additional redundancy created by the Regenerative ECLS hardware creates the opportunity for independent support capabilities between segments, and for the first time since the start of ISS, the necessity to revise Life Support strategy agreements. Independent operating strategies coupled with the loss of the Space Shuttle supply and return capabilities in 2010 offer new and unique challenges. This paper will discuss the evolution of the ISS Life Support hardware strategy in support of 6-Crew on ISS, as well as the continued work that is necessary to ensure the support of crew and ISS Program objectives through the life of station.

  3. I’m not an expert, I just remembered that a lot of technical detail was mentioned in the NTRS article. That might be enough to figure out the limitations. I recall concluding that there was capacity for short duration enlarged crews.

  4. Power is a constraint, depending on how much is dedicated to experiments. The orbit average power is about 37 kw.

    I am sure that if a commercial entity came on board that they could buy oxygen candles from the Russians.

  5. The “Fully redundant” line implies to me that they could manage 12. Not as safely, obviously. But it seems to say “Even with one plant off we can keep the six breathing.”

  6. I didn’t read the NTRS article yet, and I’m certainly no expert, but it might be interesting to look at contingency plans for various missions.

    At the end of March 2009, there were ten aboard the ISS (with the Shuttle docked) and the three more were en route via Soyuz. http://www.space.com/missionlaunches/090327-sts119-space-population.html

    I wonder if there were contingency plans for that mission for a damaged shuttle and a damaged docked Soyuz that involved 10 aboard for an indefinite stay? Too improbable? If the incoming Soyuz had lost re-entry capability that day too (way too improbable?!), ISS would have had to accomodate 13. As the article points out, now that there are six ISS crew members, the same scenario would have resulted in 16 on the ISS. The planning for six crew members started a long time ago, when the shuttle’s future was more uncertain — I wonder if contingency plans for 13 or even 16 aboard were ever drawn up.

  8. It may have changed when it became obvious there would be no American CRV, but the original USOS life support system was spec’ed out for a crew of four which, when combined with the Russian side crew of three, yielded a seven-man crew. That would be three Russians, three Americans, and one international (rotating among Europe, Japan, Europe, Japan, and Canada, IIRC) on-orbit at all times.

    Mike

  13. I wonder if there were contingency plans for that mission for a damaged shuttle and a damaged docked Soyuz that involved 10 aboard for an indefinite stay? Too improbable?

    Too improbable. There are contingency plans for either a stranded shuttle or a stranded Soyuz, but not both at the same time.

    If the incoming Soyuz had lost re-entry capability that day too (way too improbable?!), ISS would have had to accomodate 13.

    Yes, way too improbable. Now you’re three independent failures deep.

    As the article points out, now that there are six ISS crew members, the same scenario would have resulted in 16 on the ISS. The planning for six crew members started a long time ago, when the shuttle’s future was more uncertain — I wonder if contingency plans for 13 or even 16 aboard were ever drawn up.

    No. Shuttle crews to ISS have generally been six since the ISS crew went to six, so no more than 12 need be accommodated at once. Failure of both a shuttle and Soyuz is not a scenario that is protected.

  14. IS the decision to limit the Shuttle crew to six due to the kind of ISS design constraints that Rand might be interested in? (Or more simply: why is the Shuttle crew limited to six now?)

    Also: the following question might be tangential to Rand’s inquiry, but I’m wondering if the answer would reveal anything about the capabilities of the ISS. At the end of March 2009, with seven visiting from the shuttle, three ISS crew members, and a relief crew already on orbit in an incoming Soyuz, if the Shuttle’s undocking had been delayed for a non-life-threatening reason (similar to this last week’s Soyuz undocking delay), would the incoming Soyuz have docked anyway, temporarily increasing the crew of the ISS+Shuttle+Soyuz assembly to 13?

  16. The limitation of six is (AFAIK) driven by the fact that they only have that much capacity for evacuation via Soyuz.

    Will, I hadn’t really thought about that, but yes, I would assume they’re doing additional experiments (perhaps less energy-intensive ones), or maintenance, or just developing a bigger data base for health effects of weightlessness. They’re doing more of whatever it is we think that ISS crew are supposed to be doing.

  17. Rand, I’m not sure if you were answering me, but if so, my question is why only a crew of six (as opposed to seven) on the Shuttle as described by Nemo above, for a total of 12 temporarily on the ISS when a Shuttle visits. There still would be twice the capacity of the two docked Soyuzes, so maybe it has to do with life-support requirements.

  18. If additional crew are expected to do more of what the crew is doing now, then additional volume and power for more experiments will be needed. As a data point, consider that back when ISS was supposed to have a crew of seven at final assembly, it was expected to have more modules, (particularly the CAM) and more power from the Russian Power Module.

    Less than that and a crew of seven will be underemployed.

  19. There are many considerations to be dealt with. I worked as an illustrator at Holloman AFB and illustrated many concepts and configurations for space travel. Primarily Life support is the major problem. Secondarily is the equipment to live comfortably, and the weight of the support equipment. I worked with Dr Steinhoff as our chief scientist and he was concerned primarily with these three items. All of that has to go up there somehow. Finally, the cost of putting it there. That is always a concern. I think from my experiences, that weight and life support are the main concerns.

  20. Will, that assumes that an ISS crew of six is enough to fully utilize the power and volume available now. The problem is a bit more complicated. When I was working these issues in the early 1990’s, we estimated that it would take three crew to operate and maintain the space station. Until May 2009, the crew was only three and I read that they managed to spare only 15 hours per week for research. Even when the crew went to six, it didn’t mean that a full three were immediately available for research. They ramped up over time and I don’t know whether the productive research crew is up to three people yet.

    I wonder if they know yet whether the a crew of six can fully utilize ISS capabilities. Three people doing research doesn’t seem like much to me for such a large and complex facility. If they could increase the crew by one, it would increase their research time by a third, not a sixth, so it’s a very high-leverage question.

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