14 thoughts on “Space Solar Power”

  1. They’re talking about solar panels as collectors. I hope that’s just a reporter not understanding what they’re talking about; solar thermal is the way to go, with the cold side in the shade at 3 Kelvin.

    Colonel M.V. “Coyote” Smith to the white courtesy phone…

    1. We have decades of experience with solar panels in space. We have zero with solar thermal. The technology readiness levels are vastly different (you have to deal with a working fluid, which could spring leaks). That may be the ultimate solution, but the soonest one is solar panels.

      1. Nah. We have decades of experience with space thermal, only in reverse. Instead of generating power from a temperature difference, we have tons of experience applying power to create a temperature difference. A prime example is the cryocooler used on the James Webb Space Telescope. It is a thermo-acoustic Stirling cycle cooler, which can cool the infrared optics of JWST below 4 Kelvin. These coolers are used on a great many spacecraft, and have essentially an infinite working life. And, as with any refrigeration cycle, it can be operated in reverse. Given a temperature difference, it generates electrical power. Northrop Grumman (who made the JWST cryocoolers, and is the preeminent manufacturer of such devices) has demonstrated, without much effort, 30% efficiency in heat to electrical energy conversion. So why isn’t this technology the standard? Well, it’s Northrop Grumman (for which both my wife and I worked many years), and Northrop Grumman a) won’t develop anything on its own nickel, and b) won’t bid on anything that requires it to manufacture something unless it’s an airplane – or a mind-blowingly expensive government spacecraft. The technology is there, TRL 10, just waiting for someone to use it. Oh, and that 30% efficiency is without any effort to concentrate the hot side or enhance the cold side emissivity. There’s no reason it can’t be in the 80% range.

          1. The one in Mojave uses parabolic reflectors. The demonstration unit I built at San Jose State in 2008 used Fresnel lenses, and while Sandia got up to 32% efficiency on their reflector-based unit, which cost millions, ours was getting 40%, and the most expensive part was our turbine, which cost us something like 20 grand.

            And that’s with our cold side right around 30 F. With a cold side at 3 Kelvin, you only need the hot side to get up to 300 Kelvin to get 99% efficiency. You could lose half in transmission losses and still be better than the best solar panels (~14%).

            Aluminized mylar is a hell of a lot cheaper than photovoltaics.

          2. The scale of the pulse tube/Stirling system on JWST using a Joule-Thompson loop at 7 K (JWST removes less than a watt: https://webb.nasa.gov/content/about/innovations/cryocooler.html)? We’ve started to expand the cryocooler side, but of course ran into funding hiccups with NASA HQ (https://cryocooler.org/resources/Documents/C21/115.pdf#page=1, https://cryocooler.org/resources/Documents/C21/107.pdf#page=1, https://cryocooler.org/resources/Documents/C21/387.pdf#page=1). There are general sizing limits, at least on the cryocooler side where efficiency starts to tail off on individual stirling units. Thermo-acoustic based cycles are much worse efficiency wise than the pulse-tube varients, at least for coolers.

            On the power conversion side – it seems like the large developments are focused around NASA kilopower concept: https://ntrs.nasa.gov/citations/20210010322. Once you get bigger than that, again, you tend to focus more on Brayton cycle systems: https://ntrs.nasa.gov/citations/20220002293, it doesn’t matter whether the source of heat is solar or nuclear (for cycle selection, it probably does matter a bit in the details of things though).

            There may be developments on the black side of DoD I’m not aware of though. But yes, scaling for space applications of thermal conversion, both hot and cold, requires investment.

    2. Solar Thermal has always intrigued me. The mirror just seems less problematic than acres of photovoltaic cells, for example.

      Thermal inertia of the boiler has always suggested to me that the satellite will not be as “nervous” about solar cell orientation and power drop off if it orbits into shadow — making it usable in lower orbits perhaps. If and when in situ manufacturing starts up in space many of the parts are less sophisticated than the PV panels as well. Something to watch, I guess.

      1. I know that when Gerard O’Neill was around, he considered any SPS study which didn’t include solar thermal to be incomplete, liked the efficiencies, and pointed out that if using space resources, the greater mass might be less of a issue.

  2. Better start thinking about ways to counter the Greenies, because they’re bound to be against space based solar power, and raise hell. “OMG! Microwaves! They’ll do terrible things to the atmosphere! Rectennas are ugly, and there’s endangered animals there/nearby! Microwaves!”

    I’m all for space based power, but Greenies hate anything that doesn’t come from their tiny little minds. So get ready for pushback the closer we get to building and deploying the satellites.

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