ISS Solar Power

There is a coding contest now for programmers to find the best algorithm for pointing the ISS solar arrays to avoid shadowing the masts during parts of the orbit which causes them to shrink from the cold and possibly buckle. Given that the station is in its’ second decade now,  I would think that this should have been a problem solved quite some time ago. Since there is a contest to solve that problem, it would seem that I’m wrong. It seems to me that the basic problem is that the ISS is large and unwieldy enough to have inflicted this problem on itself. Since eventually there will be even larger and more convoluted orbital platforms depending on solar energy, it might be worth taking a look at different options for power.

One option is a co-orbiting solar power satellite dedicated to ISS power. If maximum distance can be kept under a hundred miles, the ISS side rectenna would be a fairly small piece of hardware that should have far less effect on the ISS microgravity environment. An ISS dedicated SPS could be upgraded at will (or ability) without affecting the ISS at all. Even though some power would be lost to efficiency issues, a solar array ten or a hundred times as large could make up the difference and then some.

The co-orbiting SPS could also serve as an embryonic transport node for ISS and points beyond. An SPS based tug could capture ISS bound payloads for sorting and repackaging before drifting them over to the station at the time of need or convenience. This would considerably relax the requirements on ISS bound supply transports. The ISS visiting vehicle requirements apparently cut the effective payloads by a considerable amount with the last Falcon IX delivering a small fraction of its’ advertised payload. The tug meeting all the visitor requirements on a permanent basis would also be a safer option for ISS delivery than a constant mix of American, Japanese, Russian, and ESA ships arriving at various intervals.

The transport node would make an effective storehouse for items not yet needed or no longer required on the ISS. By relaxing the timing of deliveries via available storage, all the supplying entities could launch at earliest convenience rather than somewhat arbitrary schedules based on the latest delay by the other guy. By using the tug to remove unwanted stuff from the station, more room would be available for the researchers doing the real work.

The co-orbiting SPS would make a useful safe haven for ISS crew that needed to evacuate. With available tugs and taxis, the ISS staff should be able to increase to a dozen or so if escape requirements are still the bottleneck for crew size.

For points beyond, the SPS could provide considerable early power to electric propulsion vehicles during the gravity well climb out. The assembly and check out portions would allow on board techs to add used ISS gear to outbound missions that could use it.

All these suggestions are old. It just seems that a NASA contest to solve a power problem is a good time to rehash them.

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18 Responses to ISS Solar Power

  1. e.p. says:

    My guess would be the inefficiencies haven’t been a problem until now due to a combination of degradation of the solar arrays (less power out) and demand (more experiments, equipment, reduced efficiency of older batteries, etc.).

    -e.p.

  2. Adam G. says:

    Doesn’t tacking on a tug, docking facilities, and storage facilities to your SPS recreate some of the problems that the ISS is experiencing now?

  3. Chris (Robotbeat) says:

    I think the prize is an excellent idea to wring extra performance from a $100 billion facility.

    The prize is, what, $30,000? That’s like the cost of a toothbrush on ISS. Spending a small amount on optimizing the solution is going to be far cheaper and easier than developing another platform.

    I’m always surprised by people who want to propose elaborate engineering solutions to problems that are much more easily and cheaply solved with some analysis and a little cleverness. Like for instance, we could have an elaborate artificial gravity system, OR we could, you know, try some anti-osteoporosis medications? (This isn’t to say there’s no use in artificial gravity, but it’s the small, cheap solutions that you should always try first.)

  4. Chris (Robotbeat) says:

    ISS’s solar arrays are WAY obsolete. They are far lower in efficiency than modern arrays with modern cells and are far heavier than current solar array technology like UltraFlex and the like.

    The ISS’s cells are 14% efficient (at least, they were). Nowadays, ~30% efficiency space-rated solar cells are very common. You could more than double the power output simply by using modern cells!

  5. john hare says:

    Adam G,
    If the focus was on power production rather than microgravity quality, then the facility could be optimized around that. The problems should be less, though not entirely gone.

    Chris,
    Modern cells would certainly be better. It would be much cheaper, faster better, if they can optimize around the current hardware. It is almost always better to look at the cheaper solutions first.

    I don’t think that the looking should be restricted to those easier ideas in the early stages. It sometimes happens that the easier solutions don’t work as well as one would like. Then it becomes useful to already have an idea of alternatives. If it later becomes necessary to replace large masses of solar cells with the more efficient modern ones, then it would be useful to have alternatives already in mind. Even if you just need the real data to stop proposals like this one.

  6. Andrew Swallow says:

    The ISS is a space station rather than a transport vehicle so it does not undergo large accelerations. It can therefore tow its solar arrays. A simple way of keeping them out of its shadow.

  7. john hare` says:

    That is a trully superior idea Andrew.

  8. Peterh says:

    If power production were the only criteria, a trivial solution would seem to exist. But with microgravity quality, drag that has to be countered by a thruster, attitude control in a gravity gradient, and perhaps other factors, an optimal solution becomes much trickier.

  9. Rand Simberg says:

    ISS can’t tow anything without disturbing its microgravity environment. It really does need a separate facility. This is an interesting idea, John, that is complementary to one that I have for a safe haven. ISS shouldn’t be a facility, but a co-orbital cluster of them.

  10. Pingback: Transterrestrial Musings - ISS Solar Power

  11. Tom D says:

    I vaguely recall from my orbital mechanics classes that any two things in low earth orbit will gradually drift apart due to perturbations, node regression, drag, etc. unless there is active station keeping (thrust) or a physical tether between the two. There is no such thing as being co-orbital for more than a few days (or weeks, I can’t remember).

    A solar power station (or free flyer or whatever) will need some amount of active propulsion to stay in sight of the ISS. This is not necessarily a problem, but it is an important complication.

  12. Tom D says:

    By the way, I really, really like the idea of a power beaming facility in orbit. This could be a very useful utility for powering ISS, other stations, satellites, and maybe even high power/high efficiency earth orbit-escape stages using ion or VASIMR rockets. Seems like this would be a natural for commercial development and operation too.

  13. johnhare says:

    I had assumed an orbit with just enough eccentricity to keep it in a similar plane and period, but not actual station keeping. The solar panels would possibly provide some solar sail properties, or failing that, power for electric station keeping. It shouldn’t be necessary to maintain a constant distance or vector from the station as long as it maintained line of sight to the rectenna.

  14. ken anthony says:

    There’s your problem. The I.S.S. isn’t a commercial entity. Separate facilities working in cooperation is a no brainer for commercial entities. What is power worth? You don’t know until two or more competing entities are trying to sell it.

  15. ech says:

    “The ISS visiting vehicle requirements apparently cut the effective payloads by a considerable amount with the last Falcon IX delivering a small fraction of its’ advertised payload. ”

    I’m not sure that the VV requirements are that mass-intensive. I did an analysis of them a while back and the only hardware additions would be, IIRC, position lights (i.e. strobes), an RF link to ISS with data to ISS and limited commanding back (i.e. stop and abort were the minimum commands), and the propellant needed to stop at a few points during the rendezvous and prox ops to ask for permission to continue.

    I think the Dragon mission ran light because the ISS program didn’t want to risk high value cargo on a test flight.

  16. Karl Hallowell says:

    Like for instance, we could have an elaborate artificial gravity system, OR we could, you know, try some anti-osteoporosis medications?

    What is the simpler solution again? A moderately complex dynamical system which you can figure out in a couple of launches (and which we know would work once we have it figured out) or medication that differs in effect by astronaut and by its interactions with any other medications that the astronauts’ take. And which hasn’t tested on time frames relevant to any missions that would need to consider artificial gravity. And which might not actually be sufficient over that time frame to prevent bone loss or related medical problems.

  17. ken anthony says:

    Get Bigelow to sell them power?

  18. PeterH says:

    Regarding a co-orbiting power station, it occurs to me that 2 objects in orbits of slightly different eccentricities but common period could appear to orbit each other. But not a lot of room for a variant eccentricity for a station following the low orbit ISS.

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