(CNN) Space power plant and a mission to Mars: China’s new plans to conquer the final frontier. Quoting,
The completed solar farm would be placed in a geostationary orbit over a receiving station on Earth. It would transmit the energy — either in the form of a laser or as microwaves — to the Earth base, where it could be reconverted to electricity and distributed via the grid.
Power-in-space, this way, is nonsense. It has two possible purposes:
- Motivate creation of spin-off technology. The 60’s “space race”, to “put a man on the moon” gave us nothing directly, yet it laid much of the foundation of the modern world.
- Weaponization of space, with the ultimate satellite destroyer. The geosynchronous location, 22,300 miles above the surface of the earth, is not a good place for a power station, for reasons to be described.
Let’s do a napkin calculation. The current cost per pound of payload, to reach that high orbit, is about $12000 per pound. It is that low because of the huge number of communication satellite launches, with similar form factors and weights. This is not so with an orbiting power station, where the payload is accompanied by complex robotic machinery. But costs will decrease, so, projecting a decrease of 100X, our WAG is $120/lb, or, roughly $260/kg.
The CNN article offers a size of two square kilometers. For our purpose, it is more useful to start with a raw solar array power. Let’s make it 4 billion watts, 4GW, about the size of a large nuclear power station with several reactors. To convert this into mass, our benchmark is the newest, lightest solar array in space, the (TechBriefs) Flexible Array Concentrator Technology, developed by NASA. Furled on a carpet-like substrate, it unfurls to produce (at most) 400 watts/kilogram.
4 gigawatts of this weighs 10 million kilograms, about 22 million pounds. The “boost cost”, to get it into orbit, is $2.6BN. To keep things simple, we set the cost of building all the parts to be boosted at $2.6BN as well.
Now comes power conversion, the equivalent of an electrical substation in space, to combine all the power generated by the array into a form usable by the lasers. Anything that handles as much energy as a nuke plant (and, as we shall see, wastes most of it) is going to be large and massive. It also requires cooling. This space-plant requires dissipating heat similar to the cooling tower of a nuke.
The latest thing in lasers, the fiber laser, is touted for efficiency. But while the fiber and the diode pumps are themselves efficient, the “wall-plug” efficiency is only about 30%. The rest goes up in heat, so the lasers also have to be massively cooled.
All that A/C in space, 22,300 miles up. How do you do a service call? With a robot, which might not know what parts to bring. Sears won’t write a contract.
So for the plant required to get these watts back to earth, let’s put down $1.6BN to build, and $1.6BN to boost. With 30% efficiency, you have only 1.2GW of the original 4 headed towards earth, in the form of a laser beam.
Summing the costs:
- $2.6B for the solar array.
- $2.6B to boost it into orbit.
- $1.6B to build the power converters and lasers.
- $1.6B to boost the above.
Total: $8.4B, not including upkeep. (As John von Neumann said, there’s no point in being precise if we don’t know what we are talking about.) How much electric do we get for that price, and for how long?
It doesn’t all get back to earth. How much is absorbed by the atmosphere depends upon the location of the earth plant, and the color of the lasers. See (Humboldt State University) Atmospheric Absorption & Transmission.
If China has the good sense to put their ground receiving station on the Tibetan plateau, 3 miles above sea level, (see insolation chart), 75% of the laser beam could make it through. Visible light works the best, blue-green, but it’s also necessary to consider what color the solar cells on the ground prefer. Anyone who looks up would be instantly and permanently blinded. Alternatives to solar cells that can use safer near-infrared, such as a “heat engine” boiling-water-mechanical converter require that the laser beam be so concentrated it would fry eggs. That’s dangerous!
Let’s generously give the solar cells on the ground efficiency of 50%. Then 37.5% makes it out of the ground plant. Or the original 4 billion watts, only 450 megawatts is left, which has to be converted to grid power, with another loss, and more transmission losses to get it from the sunny Tibetan Plateau to consumer regions. This takes it down to about 300 megawatts. You can get that out of a single gas turbine. But wait!, you say. Gas turbines are not green. Well, neither is boosting 35 million pounds into geosynchronous orbit.
How durable would this accomplishment be? ( NASA) On-Orbit Performance Degradation of the International Space Station P6 Photovoltaic Arrays quotes give-or-take 0.3%/year. But the ISS is in low orbit, below the inner Van Allen radiation Belt. China’s power station is a much higher geosynchronous orbit, beyond the protection of earth’s magnetic field, exposed to a much harsher radiation environment. The radiation hazard is severe.
(ScienceDirect) Study of degradation of photovoltaic cells based on … suggests 10% over ten years. But another Carrington Event would destroy the station. We almost had one in 2012.
Microwaves are not an alternative for this distance. They will not focus. In near earth orbit, a few hundred miles up, microwaves become feasible. In low orbit, he radiation hazard to the solar cells is much less. Boost and servicing costs are reasonable. China would probably say the geosynchronous orbit is chosen so that the orbiting station can have fixed aim at the ground station.
It’s preposterous. The whole thing is, except as cover for an industrial activity too vast to conceal. In smaller scale, it is a feasible development for war in space, capable of frying satellites very efficiently and quickly.
Things being what they are, how would you shoot it down? Standard launch profiles reach geosynchronous orbit in about 5 1/4 hour, but with low speed relative to the target. Here time and speed are of the essence. But can we rely on automatic guidance?
That’s where the new Space Force comes in.
Where in Hell is Major Kong?