X-37b space plane’s microwave power beam experiment
thedrive.com
thedrive.com
Old designs from the 1970s were monolithic beasts, and would be horribly expensive even if launch were free. The new designs use a large number of small identical components (of seven or eight types), which self-assemble in orbit. That way you can mass-produce them.
I plugged SpaceX Starship launch costs into the book's estimate and got a total system cost of 5 cents/kWh, which is pretty good for steady clean power that doesn't need storage.
[1] The Case for Space Solar Power by John Mankins
One might say that space-based solar would operate 24/7 and so is better than normal solar panels. That's isn't reality. Low-orbit satellites spend half their day in darkness too. To hit a receiver on the night side of earth a satellite would have to be at a very high orbit, reducing beam efficiency and increasing launch costs.
Yes, and over 24 hours, they are 12 hours in darkness: on a 90-minute orbit, 45 consecutive minutes are spent in Earth's shadow => half the day, they are in darkness.
On the upside, they get full insolation during those 12 hours, unlike ground-based solar. On the downside, at night, the satellite will be in Earth's shadow whenever it's above the ground station, so LEO solar power satellites can't supply power at night (unless they carry batteries).
FWIW I don’t think that’s correct. The effect isn’t significant in really low orbits but going by my hasty maths even at the ISS’ orbit of 350km a satellite spends - at worst - about 10 hours a day in darkness. I say at worst because the plane of the orbit also has an effect here. I make it that you can roughly calculate it as: 24 * ((asin (EarthRadius/OrbitRadius) *2) / (2 pi radians)).
The satellite design uses a large area of mylar (or similar) reflectors, and a smaller area of solar cells collecting concentrated sunlight. Concentrated solar is costlier on Earth because the mirrors need to be a lot sturdier.
The ground collector covers a fairly large area but it's wire antenna and cheaper than solar panels.
The Falcon Heavy payload to GEO is 41% of its payload to LEO. I assumed a similar cost ratio for my estimate. Starship prices at scale aren't precisely known yet, but low enough that launch would be a relatively small portion of project cost anyway.
Large-scale grid storage is still quite expensive. Most "solar+storage" projects do not have enough storage to get through the night; if they did, it would cost significantly more than 5 cents/kWh.
https://www.vice.com/en_us/article/9a3y8d/the-man-who-turned...
A big issue with a project like this are unforeseen costs (being a space-based project) and engineering costs (sometimes needs government stimulus). I'm also bothered sometimes those solutions are advertised as panaceas for climate problem; while currently we have mostly a policy problem (clean energy is almost on par with carbon energy, we're just missing key incentives for the new tech and phasing out carbon plants quicker).
But indeed looks like a promising avenue of exploration.
They had a pretty detailed cost breakdown. The low cost is only once you have mass production and a large plant. They assume several smaller projects first, which would be quite expensive per kWh and include more R&D cost. Those would have to serve communities with very expensive power, like remote northern communities or military installations.
I wouldn't call it a climate panacea since it'll be quite some time before we can do it at scale. In the meantime we should phase out fossil energy as fast as we can with existing technology.
But it looks like in 15 or 20 years we'll have a thriving industry in space anyway, and it's possible that by then we'll be running up against the practical limits of wind/solar market penetration. SPS might play an important role then.
RF rectification is ~90% efficient, so that same 1000 W/m2 gives ~4.5x the power density of daylight PV, plus a capacity factor of nearly 100% gives 18x the energy density of terrestrial PV - and its baseload power.
Mankins will pitch you 100 W/m2 as a useful RF energy density to be competitive with terrestrial solar. You may also be able to include photovoltaics in your receiving antenna and have it both ways.
What really kills microwaves for power transfer is the minimum sizes of the transmitter/receiver thanks to diffraction. If your going from GEO to ground, I believe you need on the order of square kilometer sized arrays on both ends.
For ground to air applications, rectennas are too bulky and heavy to be practical. If you look at the last NASA power beaming challenge, all of the contestants went with optical power transfer because it was better in W/kg and in W/sq meter.
Disclaimer: I’m involved with free-space optical power transfer.
Lasers have definitely been considered for SPS. The main challenge is that clouds get in the way. (And you don't want the power density so high that it works as a weapon, but I imagine you can avoid that.)
Was the NASA challenge for SPS, or other applications?
Hydro is quite cheap, but it's not available everywhere and only scales to about 10% of global energy demand: https://dothemath.ucsd.edu/2011/12/how-much-dam-energy-can-w...
All other sources cost a good bit more than that. The US average is over 13 cents/kWh: https://www.electricchoice.com/electricity-prices-by-state/
If only the transmitter and receiver for space solar is a very significant fraction of the cost per kWh shipped at your house with profits of nuclear or hydro it can't be viable.
Canada's national average (this excludes the territories) is 10 cents (us)/kWh. Québec has the cheapest energy in Canada, primarily due to its proximity to hydroelectric sources, at 5.5 cents (us)/kWh. In parts of the US where hydroelectric is the dominant energy source, prices are comparable.
Including the territories Canada's average is 13 cents (us)/kWh.
13 cents/kWh is the US national average including all sources and regions, according to the link I posted.
If you keep the power down to the order of 10x sunlight, it doesn’t make a very good weapon.
1) False. You just have to find contexts where installing solar panels is undesirable or impractical. A forward military camp in the hills of Afghanistan?
2) It's quite easy to exceed the energy density of solar panels with a microwave rectenna to receive power. In fact, a lot of the old designs were dedicated to reducing the power density for safety reasons.
One might say that space-based solar would operate 24/7 and so is better than normal solar panels. That's isn't reality. Low-orbit satellites spend half their day in darkness too.
Zero cloud cover. Zero dust buildup. In terms of access to solar flux, there are a lot of advantages to being in orbit. Also, there's a "simple" way to get around the tyranny of the rocket equation and get stuff to geosynchronous orbit cheaply: mine the moon, manufacture the silicon solar panels there, and use lunar electromagnetic mass drivers to deliver bulk cargo to geosynchronous orbit. So I would agree with a lot of what you're saying about impracticality with that caveat: "short of having lunar industrial infrastructure."
But, given a major power that has the above, how is this so different from having fusion power?
EDIT: But if you carry forward this thinking a few steps, you get to...Oh NO!
So let's say that we don't get fusion power, but we do get to the point where lunar industrial infrastructure looks within reach. In that case, control over lunar resources will mean control over the most plentiful, clean, and convenient form of energy. Basically, more than half of the motivation behind major power wars in the last century and a half, has been control over resources, particularly energy. Having energy resources gives one military power which gives control over energy resources.
This dynamic would seem to set up the next major power conflict past the Taiwan issue. Space could well wind up being the Caucasus Mountains/Persian Gulf of the early to mid 21st century. A major power conflict over energy resources which fundamentally involves the power densities implied by space travel just seems like BAD NEWS.
Even worse. We first get the start of the above conflict. Then only afterwards does rapid wartime R&D finally yields military grade fusion power. Yup, we're living in our really nifty, really interesting Sci-fi future. "May you live in interesting times."
He3, Perhaps. That stuff would be worth it by weight to send back, especially if done by electromagnetic mass driver and not rocket.
Even though D-D emits neutrons, they're at an energy similar to fission neutrons, rather than the extremely energetic (and easiest) D-T reaction. It's almost certainly going to be cheaper to get your He3 from D-D fusion, and get energy in the bargain, rather than sifting through millions of tons of lunar dirt.
Fusion startup Helion, funded in part by YCombinator, is working on a hybrid D-D/D-He3 reactor, saying the combination will produce only 6% of its energy as neutron radiation, compared to 80% for D-T.
> It is now believed that a lunar mass driver several kilometers long, designed conservatively with present technology, should be able to deliver 600,000 tons a year to L-5, or more easily to L-2, at a cost of about $1 per pound, assuming only ten years of operation.
https://space.nss.org/l5-news-mass-driver-update/
If SpaceX succeeds in dropping launch costs below $50/kg with Starship, this doesn't seem like it'd be all that expensive.
By the way most huge companies are already international in some sense, geographically or by employing many nationalities and origins. This also helps avoiding conflicts.
Most of the proposed space-based solar power systems (SSPS) posit a reasonably large rectennas (like maybe 10 - 20 acres or 4 - 8 hectares) sized fields.
The challenge is to make the field low enough density such that things flying through it aren't harmed by it. Fortunately energy density falls off with the square of the area so if you have a enough open space you can make it arbitrarily low power per square foot or meter.
Pedantic, but for LEO there are dawn-dusk SSO orbits that ride the terminator [1] so they get continuous sunlight, you could power some peoples evenings depending on how far the grid spans into the dark side. Not a solution for getting power at 2am though.
Might be able to compete if the cost if a rectenna is cheaper/kwh than solar panels (and free as sunlight). Then you can use your same battery solution for night time.
> satellites in geostationary orbit will spend some time in the shadow during what we call “eclipse seasons.” Each eclipse season lasts 44 days, during which the time that a satellite spends in eclipse (shadow) builds gradually from about a minute or two at the start of the season, to a maximum of 72 minutes at each equinox. It then gradually retreats over the next 22 days, at which point the solar arrays are again in the sunlight on a 24×7 basis.
https://corpblog.viasat.com/how-satellites-are-affected-by-t...
So you do have a little bit of downtime, but so do coal, gas, and nuclear plants. The few hours of shadow per year still leaves a capacity factor of over 99%.
Wired ran a story featuring him last year:
https://www.wired.com/story/how-to-get-solar-power-on-a-rain...
The main news in it was this:
https://www.robins.af.mil/News/Article-Display/Article/19980...
[1] https://attend.ieee.org/wisee-2020/wp-content/uploads/sites/...
A space based solar power array is a large solar sail. As it orbits, its angle of incidence to the solar wind will change, perturbing its orbit.
Lightsail 2 [1] showed the solar wind can be used to raise orbit. I wonder if such effects would be critical for space-based power systems, or just another design constraint.
[1] https://www.planetary.org/explore/projects/lightsail-solar-s...
Wireless power transmission would be ideal for a lot of applications, transportation (electric cars, planes, maybe trains, UAVs, boats) chief among them.
You could shave a lot of weight out of an electric plane by reducing its battery capacity to an emergency supply. This would also greatly reduce the carbon impact of flight transportation, while making a case for bootstraping a beamed power constellation and ecosystem.
I guess that's something Nikola Tesla first envisioned :)
Unfortunately, from what I know, microwaves are not really harmless, unless diffused over a large area, and you then need a large collector. An airliner could do, if big enough. I don't know either if a beam can be steered fast enough, and what would the economics behind be.
So, ballpark 7 MegaWatts, more during ascent, and add a bit if passengers want to watch movies, eat hot meals, drink soft drinks, etc.
On the plus side, if the airplane doesn’t have to carry fuel, carrying capacity could go up (with some redesign to make the plane strong enough to land fully loaded), so that 737 might be equivalent to a 747.
That 737-300 has about 125m² of wing area, and, guessing, about the same are for the body, so that would be 7MW/250m² = 28kW/m². The sun delivers about 1,400W/m², so that’s 20 times what the suns delivers on a cloudless day.
Now, most of the time, the ground station (or solar space array) beaming the energy wouldn’t be directly below/above the plane, so the required power/m² could go up a lot ⇒ I would make sure that any windows in the plane wouldn’t let the microwaves through.
Doable? Possibly, but on ground level, I guess it would be wise to use a lot more area for sending that amount of power up, to prevent killing birds.
Might be a problem at the base station, but there should be multiple of those for greater fault tolerance anyway.
I don't know if this reasoning is correct or not, but definitely has nothing to do with the speed of light in air. I'm not even sure why you are bringing it up.
A 737 has a wing area of 125 square meters. To deliver 7.5MW to those wings will need 60kW/square meter.
That's a far greater energy density.
As for "time in beam" of a moving beam. Presumably one end of the beam is fixed, and depending on the target's velocity the beam might not be moving much at all (oncoming plane).
So, picking 30,000 feet for flight height and 250m/s for the plane’s speed, at 900 feet the beam’s speed would be 7½ m/s. That’s quite doable for birds.
More importantly, if the beam isn’t sent from directly below the plane, and the plane flies more or less directly towards or away from the beam’s source, the speed at which it moves horizontally goes down considerably (1/cos(α), where α is the deviation from the vertical, I think), and its width when flying through it in the direction of the beam’s source at constant height will go up considerably.
The beam’s width, and, with it, intensity, will likely be larger on the ground, but my gut feeling is this won’t be enough to correct for both these factors in all cases (corrections welcome)
That said, I was mostly imagining space-based stations.
In the above case, I talked about ground-based stations at airports. Unfortunately, those would require high angular velocities, but would already be in bird-restricted areas (airports use all sorts of tricks, including drones, sounds, people chasing them, etc, to scare away birds). You could also conceivably drastically lower the beam energy output by using multiple beams that concentrate at a single point.
Now, a fun calculation: what would be the tipping point between birds saved by not emitting carbon dioxide and birds killed by the towers, if there is one?
One last point: I'd hazard that the bird is likely to change direction if it starts running into a beam and it has time to (ie, it is not killed "instantly"). This drastically lowers the dangerous altitude range, as the bird is less likely to fly in the same path as the beam (how likely was it in the first place? One would need to go faster than the other to catch up, but not too much to actually dispense the lethal dose? I haven't done the math, but I'd say it's quite unlikely).
A small battery, and/or a ground station at the airport could provide a bit of extra power during ascent, and the battery recharged during flight. I guess the extra power shouldn't amount to a lot more than 10kW...
Depending on the wavelength, it should be fairly easy to have the plane act as a Faraday cage to shield its passengers. I guess the geometry could be slightly tweaked as well to make a larger surface area, possibly using trailing metallic wires to improve the energy collection area at a minimal cost (I get that cylindrical wires are the worst aerodynamic shape, but it should be less of a problem behind the wing).
If the wavelength is low enough, a coarse mesh could collect power quite efficiently, but you'd have to worry a lot more about radio interference.
If you go slower, you need bigger wings (also no one really wants longer, slower flights in cramped airplane cabins).
Answering to a cousin comment, buses and trains can't compete when you need to cross water :)
I like to approach problems this way. Plus, one can have dreams, can't they?
Once you've shown it can theoretically work, it's time to consider the side effects: best/worst. With the above, someone now controls a multi-gigawat orbiting power source.
Upsides: well, it can power useful stuff just about anywhere on (two third of) earth when there's nothing else to do. That would be really useful to compensate renewables, or other grid fluctuations. One could even imagine making airplanes slower of faster depending on demand.
Downsides: well, somebody really does control that :)
So it seems drag isn’t taking most of that power.
Also, “I guess the extra power (for ascent) shouldn't amount to a lot more than 10kW” seems unlikely to me. It’s too low compared to the 7MW used at cruise height.
Also, if my math is correct, 1kWh lifts one kilogram about 360,000 meters, or 36,000kg (less than the weight of an empty 737) by 10 meters. So, 10kW would lift the plane by only 100 meters in an hour.
But the safety question is more serious. The beam is dangerous to birds, unshielded aircraft, and persons on the ground. I don't think it's great giving the US military even more power to start a fire anywhere on earth with zero warning.
Single antenna apertures are limited to about 90 dB of gain, and I doubt that is near enough, but I’d have to run some calculations.
They already have hydrogen bombs :-)))
This is a bit like complaining about a knife in a gun shop :-)
Are lasers like this detectable? If not, seems like a good way of creating targeted brain tumors. Disrupting soft infrastructure nodes etc.
If you get hit by a megawatt beam, you're going to get burned regardless of the wavelength (unless either it's short enough to pass through you, or somehow you reflect 100% of it).
As another comment points out, you can beam steer quite fast. You only care about angular rate, and an airliner at cruise altitude moves fairly slowly (eg you can follow it with your eyes easily).
Actually, yes, the article explicitly mentions the possibility of powering unmanned aerial vehicles.
Ya. The public report on the super-secret space plane touts that it is studying far-off green energy solutions when those same technologies have much more immediate military effects. It's like the USAF saying that it is studying lasers in order to build better CD players. Everyone takes such statements with a grain of salt. Nobody thinks that we are getting the full story behind these experiments and we chuckle a bit at the poor junior officer instructed to "be creative" with descriptions in public statements.
You're not wrong about low orbit sats in general, but it's only one of many potential military (and/or civilian) uses. And it's not the use the article focuses on.
The step zero could also be using Earth's deserts.
And then step one is using a space shell of satellites. Because the available surface at a large distance of Earth is huge, even considering the constraints of not creating too much shadow for life's photosynthesis.
Further in the future could be step two, some flotilla at Lagrange points or even directly in a solar orbital between Earth and Mars (so that this will never create any shadows to us).
Even if a treaty did ban these weapons it wouldn't be "illegal" for a major power in any meaningful sense. These mutual arms restriction treaties are only followed by the major power as long as they see a mutual interest in doing so.
Sorry, but this really rubs me the wrong way. The whole reason we have these kind of treaties is to protect nations which don't have the power to defend their interests should a conflict arise.
Saying that it is normal for a nation to just ignore a treaty they have ratified IMHO instills a very wrong mindset. If a nation ignores a treaty, the reaction should not be "Oh, that was to be expected".
Without external forces (a higher authority or some sort of coalition of the weak) to check the impulses of the strong, the strong get to make and break the rules as they please.
This is inevitable and a fundamental fact of reality.
A nation can withdraw from a treaty instead of ignoring it. The US just withdrew from the INF treaty. In retaliation, Russia withdrew too (they were the only signatories).
In 1936 Japan withdrew from the Washington Naval Treaty and built the formidable battleship Yamato (armed with 18 inch guns, by far the largest in WW2). What was the world supposed to do? The US imposed various sanctions on Japan. At some point the sanctions became so hard that they amounted to an economic death sentence. WW2 was not averted.
The unpleasant truth is that international treaties are not worth a whole lot. For the simple reason that there's no international equivalent of law enforcement.
Yes, as far as I can see both the INF and the Outer Space Treaty explicitly include the possibility for a withdrawal (with prior notice).
At least this publicly signals the intent of a nation to do something which would violate the treaty instead of just silently ignoring it.
It’s blatantly naive. The reason we have these restrictions is because it’s simply more efficient not to have an arms race.
If it was really about small countries we would already gotten rid of nuclear weapons.
Don’t forget that the amount of countries having the capability to detect the launches of nukes is even less than the amount of countries having nukes.
I can't count the number of times I saw the usual armchair experts confidently state online that Trump's proposed Space Force would "violate the Outer Space Treaty!".
It's one thing to not be completely familiar with the details of a treaty signed 50 years ago, but how is anyone today ignorant of the military (the US's and other countries') large presence in space?
It was designed to prevent the nuclear powers form parking their nukes in space because that would reduce the warning time to the point where MAD might break as a first strike without a chance of retaliation could then be possible.
https://en.wikipedia.org/wiki/Wardenclyffe_Tower
I remember reading a Repairman Jack novel about it. I think it was Conspiracies.
[1] https://www.popularmechanics.com/technology/a8101/elon-musk-...
What makes you think he did?
1. How much power could a satellite generate, realistically? 2. How many targets could it serve simultaneously?
I imagine there is a huge difference between being able to support a single, ultra lightweight drone and, say, hundreds of reapers.
What is considered a "reasonable" orbit depends on our ability to collimate the microwave beam's rays, which is not an easy task
For comparison, the ISS generates 240kW when in sunlight. So for the 7MW mentioned upthread to power an airliner (or half a Eurostar train), you need something 28 times larger than the ISS.
in city telecom microwave antennas on top of buildings already kill thousands of bird every day.
maintenance checklist start with "clean the dead birds from base of antenna"
Please show a source if I’m mistaken.
https://en.m.wikipedia.org/wiki/Towerkill
TIL.
it's power that kills. you can make a death ray with light, vhf, whatever, given enough power, which decay geometrically. most of the dead birds are on antennas without cover, where the birds would perch up and get fried. thousands of dead birds every day on top of builds is the sole reason all microwave antennas have that white half-cone cover on them.
Reliable high density power beaming could enable fully automated cargo drone aircraft. These would have fundamental advantages in operations costs due to weight savings, the simplicity of electric motors, and reduced personnel costs.
If we could generate large amounts of power in space and use sufficiently large transmitters (re: diffraction limits) to beam it to VASIMR thruster spacecraft, we could substantially reduce transit times to Mars, as one example. Alternatively, we could also greatly increase mass fractions of cargo delivery to Mars.
Does this mean it's possible to have a satellite in geostationary orbit that is never eclipsed by the Earth? Or does it mean you have more than one satellite serving a power receiver?
There have even been proposals to put transmitters on the Moon, but that's stretching things.
GEO satellites go dark for about an hour a night for about 6 weeks a year.
https://www.stephenmack.space/blog/geostationary-satellite-e... Contains a video of them
Aka laser ASAT platform. Seems like one of those read between the lines Space Force press releases. References to laser beam UAV kills, original research by Revolutionary Munitions Directorate etc. All the remote power through atmosphere interference sounds pretty fanciful TBH, whereas crippling adversary satellites using beam energy instead of kinetic impactors (=space debris) seems like the most parsimonious application.
I would question if there really is such a strong push for even more US ASAT tools in the USSF, though given the current administration I guess the "kill 'em all" mentality has a good wind in their sails.
https://www.space.com/russia-anti-satellite-missile-test-202...
Beyond just needing the capability, media releases like this seems to be oblique posturing as well.
Edit: apparently posting to fast? Reply to below:
>ASAT warfare is hugely advantageous to them
Most threat models anticipate disrupting space assets in peer to peer conflicts to mitigate technological edge. All the old ASAT tests have been missiles that create debris (or potential debris in deliberate near misses), Recipe for kessler syndrome if executed at scale. So moving to beam ASAT that can disrupt / destroy sensors precisely without adversely risking the space commons might not be a terrible development in terms of space arms race.
Also if memory serves some of the new Chinese satellite used to track SCS shipping (US aircraft carriers) are in a high orbit that can't be hit by current ASAT at all. So this might be developing new capabilities. It certainly makes sense to hit other objects in space vacuum at speed of light than to power drones through clouds.
(To be clear, the USA already posses ASAT capability, demonstrated most recently in 2008)
Um, lowering barriers for using weapons is obviously a bad thing: it means they are more likely to be used, and cause a response by the adversary. So unless you mean that this beam-tech should be freely shared all you're doing is increasing the risk to the commons.
But my larger point is this: the incredibly costs of space weapons only make sense if you think your adversary doesn't have any counter-move, this is what I meant by my supposition that USSP thinks space warfare is advantageous.
To illustrate: remote detection can be counteracted by masking and decoys, both of with are much more mundane than ASAT capabilities but will work pretty good for a fraction of the cost and without any risk at all to the commons.
[edit: possibly a spoiler?]
Other possibility is to use stratospheric balloons as receiver stations. Could then use softer power links to the ground. Would some system of cables be doable then?
(I wrote that in the optics of a Dyson's sphere [thus connecting space solar stations to an on-ground power grid] instead of the proposed direct powering of drones.)
And in 2015, the optical rectenna: https://www.me.gatech.edu/featured_colarectenna
Laser and microwave beams, while they do suffer from losses over distance, aren't anywhere near that bad.
“It is not a dream, it is a simple feat of scientific electrical engineering, only expensive — blind, faint-hearted, doubting world! […] Humanity is not yet sufficiently advanced to be willingly led by the discoverer’s keen searching sense. But who knows? Perhaps it is better in this present world of ours that a revolutionary idea or invention instead of being helped and patted, be hampered and ill-treated in its adolescence — by want of means, by selfish interest, pedantry, stupidity and ignorance; that it be attacked and stifled; that it pass through bitter trials and tribulations, through the strife of commercial existence. So do we get our light. So all that was great in the past was ridiculed, condemned, combatted, suppressed — only to emerge all the more powerfully, all the more triumphantly from the struggle.”
Why go through all this trouble when there's this?
https://www.amprius.com/amprius-silicon-nanowire-lithium-ion...
While 25 days is the record, I'm sure this thing can remain aloft for at least a week at a time.
To me the solution from the article appears expensive and suspiciously deathray-ish.
Noone is going to deploy satellite network just to power some semi-gliders.
I checked and the Zephyr S has a 5kg payload - not much, but enough for instrumentation. And they're making an even bigger one.
Is it a laser or a focused microwave beam? Will it hurt if a bird or airplane flies through the beam?
Maybe targeted at someones head it might pay for itself, but still pretty sci-fi if it was possible.
Just send from a blimp.
Or send the power up to the satellite to power them, it's good as free from the ground, if this stuff is possible.
[edit] I would have ruled out this being a ruse to confuse people from the military's side, since it's so crazy no one would believe solar panels in space transmitting energy to earth was possible. But maybe not it seems..... I assume IRL it's for communications, or jamming, shooting a missile out of the air?
Drone Mothership