Care to comment on what Elon Musk said? I think he's credible.
His analysis was simplistic. He also pushes Hyperloop, so he's known to sometimes be incredibly wrong on technical matters.

He points out, correctly, that SPS requires the conversion of electricity to microwaves, and then back to electricity. Definite losses. But solar panels on earth have definite problems compared to space based:
1) Terrestrial arrays need to be more complex: they have to track the sun. Or if fixed, you need a lot more of them.
2) A terrestrial array of the same power of an SPS rectenna would impact the environment far more: the arrays would blot out the sun, while the terrain under a rectenna would be usable for other purposes.
3) Terrestrial arrays add far more heat to the environment than space based.
4) Terrestrial arrays need to deal with not only the problem of day-night cycles on power generation and thus power storage (*vast* environment-damaging battery systems for when the sun ain't out), they need to deal with weather, dust, bugs, bird crap, lightning strikes, hail, tornados. This is not just a power fluctuation issue, it's a PV cell degradation issue.

SPS is hard and expensive. But lunar surface solar power is, after an initial *insanely* expensive startup cost, potentially the closest thing we have to "free power for the whole planet forever." Lunar regolith is surprisingly close to the ingredients that make up a PV cell. So large robotic factories that trundle along, eat the regolith and lay a road of PV cells behind them, could rather quickly supply all of Americas power needs... and then all planetary power needs.

A lunar factory that lays a layer of PV arrays ten meters wide and moves 1000 meters per day would lay down 3,650,000 square meters of PV arrays per year. If the cells are 20% efficient; and you only get 50% efficiency in the conversion to microwaves, transmission to intermediate platforms, reception on earth and conversion back to electricity; and due to the immobile nature of the array and the rotation of the moon they are only 25% as effective as an array permanently facing the sun... each year a single factory would be responsible for 1400 W/m2 X 365000 X .2 X .5 X.25 = 127.75 megawatts. In ten years that one factory will be responsible for 1.3 gigawatts of power. If you add one factory to the moon per year, in ten years you'll be adding 1.3 gigawatts of power per year. If you build the factory that builds the mobile factories on the moon itself using lunar resources, it could in principle become a sort of Von Neumann machine system that surprisingly quickly covers so much lunar terrain that you have more power than you know what to do with.

I recall an article many many years ago in I think Spaceflight that talked about the possibility of a Lunar Power Ring.
 
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As you can see, reaching high thermal exchanges to regulate a nuclear plant won't be too difficult.
Trying to use powdered glass as a medium to shed vast quantities of heat seems a dubious prospect. Note that the difference between 2 cm down and 10 cm down is around 100 kelvin. This indicates that lunar regolith is a *really* good insulator. Which means that it'd be a terrible medium to conduct heat away.
 
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And that's why lunar caves are such fantastic places for a base and for a colony.

Until the roof collapses. Keep in mind, no matter where you go in the universe nature is out to kill you.

So, sure, make use of lava tubes when possible. But buttress the bejeebers out of them. And by the time you have the construction infrastructure in place to make the lava tubes secure, you can now start building/excavating properly engineered facilities that will provide you just as much practical protection.
 
IIRC, NASA had a workable design for a back-hoe, optionally remote-controlled. The need for a several metres of regolith over the 'storm cellar' against 'not-even-worst-case' CMEs does concentrate minds...

Would it have been able to cope with the impact-sintered regolith ? I'm remembering several attempts to sample sub-surface sorta bouncing off. Hence the 'trad' sampling by whacking lumps off boulders. And let's not forget Mars probes have suffered similarly...

Uh, which two Apollos had a CME during gap ? IIRC, had it caught either, the crew would have probably lasted to hospital on Earth before dying unpleasantly. Perhaps a factor in Apollo missions' truncation...
 
There was a huuuuge CME in August 1972, right between Apollo 16 in April and Apollo 17 in December. Would have fried any Apollo crew.
 
And that's why lunar caves are such fantastic places for a base and for a colony.

Until the roof collapses. Keep in mind, no matter where you go in the universe nature is out to kill you.

So, sure, make use of lava tubes when possible. But buttress the bejeebers out of them. And by the time you have the construction infrastructure in place to make the lava tubes secure, you can now start building/excavating properly engineered facilities that will provide you just as much practical protection.

Well yeah, but most of the surviving ones have already been there for ~4 billion years, so probably not a huge risk.
 
Well yeah, but most of the surviving ones have already been there for ~4 billion years, so probably not a huge risk.

They've spent those four billion years without being tampered with. No drilling, excavating, demolitions; no heavy earth-moving equipment trundling around above or within; nobody hosing down the interior walls with sealant and pressurizing. No constant vibrations from reactors, actuators, motors, toilets flushing, cryogenic compressors running, the 2045 Annual President Kardashian Memorial Twerking Contest.
 
Well yeah, but most of the surviving ones have already been there for ~4 billion years, so probably not a huge risk.

They've spent those four billion years without being tampered with. No drilling, excavating, demolitions; no heavy earth-moving equipment trundling around above or within; nobody hosing down the interior walls with sealant and pressurizing. No constant vibrations from reactors, actuators, motors, toilets flushing, cryogenic compressors running, the 2045 Annual President Kardashian Memorial Twerking Contest.

Shame on you. I mean, someone had to say it.
 
They'll need one of these:


$549 seems a bit much for a paperback. At least the shipping is free...

The Department of Defense will gladly sell you a hammer for $500.
Incorrect. the DoD will sell me a used hammer at auction for a buck fitty. But if I ramp up my BS'ing skills, I could sell it back to them for a grand.
 
As a side note to the discussion, over a decade ago, my company worked with JPL on space based power transmission systems, both laser and microwave. At that time there were a number of show stoppers, some of which have been mitigated with new technology.

One of the big ones is that the system would require a geosynchronous orbit, unless your receivers were located on the equator, but that proved not to be practical. As a result, for any type of efficient transmission active aiming would be required. At the time, that was easier said than done.

Another issue was system size. At the time, the orbital system mass was on the order of 8.5 thousand metric tons. That is a fairly daunting task (similar to launching a navy destroyer into orbit in a bunch of little pieces). With the improved technologies, both in system mass and throw capability, those numbers come down, but are still somewhat disconcerting.

Additionally, even though you can transmit through the atmosphere, beam dispersion was an issue. As a result, the efficiencies started to fall way off.

At the end of the day, and after 4 years of investigation, the idea was put of the shelf, the consensus was to throw a nuclear reactor up there and get on with business. Of course, that had a whole new set of problems, some of which are mentioned in this thread. I will save those discussions for another day. I get a headache thinking of this stuff for very long - LOL.
 

As a side note to the discussion, over a decade ago, my company worked with JPL on space based power transmission systems, both laser and microwave. At that time there were a number of show stoppers, some of which have been mitigated with new technology.

One of the big ones is that the system would require a geosynchronous orbit, unless your receivers were located on the equator, but that proved not to be practical. As a result, for any type of efficient transmission active aiming would be required. At the time, that was easier said than done.

Another issue was system size. At the time, the orbital system mass was on the order of 8.5 thousand metric tons. That is a fairly daunting task (similar to launching a navy destroyer into orbit in a bunch of little pieces). With the improved technologies, both in system mass and throw capability, those numbers come down, but are still somewhat disconcerting.

Additionally, even though you can transmit through the atmosphere, beam dispersion was an issue. As a result, the efficiencies started to fall way off.

At the end of the day, and after 4 years of investigation, the idea was put of the shelf, the consensus was to throw a nuclear reactor up there and get on with business. Of course, that had a whole new set of problems, some of which are mentioned in this thread. I will save those discussions for another day. I get a headache thinking of this stuff for very long - LOL.

Yeah, just throw a reactor up there. Elon Musk said it would be tough to get up to 50% via microwaves. Anyway, I still think they're going to do it, in stages. Spread out the cost and so on. Geosynchronous orbit is a given.
 
Geosynchronous is not a given. It's an enormous waste of sun exposure.
Sat com don't even work like that since their inception. Harvesting sun light is just an added variable in the equation.
 
Well yeah, but most of the surviving ones have already been there for ~4 billion years, so probably not a huge risk.

They've spent those four billion years without being tampered with. No drilling, excavating, demolitions; no heavy earth-moving equipment trundling around above or within; nobody hosing down the interior walls with sealant and pressurizing. No constant vibrations from reactors, actuators, motors, toilets flushing, cryogenic compressors running, the 2045 Annual President Kardashian Memorial Twerking Contest.
LOL.

But no, the Moon is still getting bumped around a fair bit.
The moon is still tectonically active, like Earth, generating moonquakes as our planet creates earthquakes, a new study based on Apollo mission data found...

Seismometers at four Apollo landing sites on the moon recorded 28 shallow moonquakes between 1969 and 1977, ranging from magnitude 1.5 to 5 on the Richter scale. Some of these shallow quakes might in theory result from activity on lunar faults, but the locations and depths of the sources of these quakes were uncertain.
 
Those lava tubes:

 
Microwave satellites for feeding into grids are lame. The true potential of space power lies in application of energy from space directly. In practice this means transmission in visible and IR bands with lasers.

Notice a crime in action at night? Call the space grid with any cell phone and TURN ON THE LIGHTS, anywhere.

Feel cold on a mountain top? Call the space grid and get HEAT RAYS.

Electronics low on power? Unfold solar panels and CALL THE POWER.

Even just a small total capacity can be revolutionary in a lot of low duty cycle "just in case" applications. For high value use cases it enables a completely unmatched product. Mobile applications is just far better than, a few power satellites can make HAPS aircraft a lot more cost effective and nevermind demands from lifestyle reasons. (for example people spend time and money climbing mountains)

If space infrastructure gets to a low cost point due to asteroid/luna industry, it is imaginable that fuels are no longer used in transports as power just gets beamed all over the place, with bother with the eye sore and organization issues that is logistics infrastructure? Imagine the problems with building a pipeline with populations a order of magnitude more wealthy and NIMBY-Y than today, to take a straight extrapolation of social evolution.

The thing to really imagine is what kind of culture would grow out of available power anywhere. Van life what happens with motor vehicles. Beam power grid in space leads or what kind of life?
 
Microwave satellites for feeding into grids are lame. The true potential of space power lies in application of energy from space directly. In practice this means transmission in visible and IR bands with lasers.
What you are after is a power density (watts/square meter) that is not only likely impossible to achieve, but *dangerous.* You would not be able to focus a laser beam to the size of a small vehicle from geosynchronous, so it would have to be lower... *much* lower. Meaning the beam emitter would have to be able to precisely target a fast-moving target, and presumably *millions* of them. All with a beam power on par with "weapons potential."

Nations won't object too strenuously to SPS microwave beam powers as low as generally projected. But a beam powerful enough to power a car, tight enough to fit within, say, the hood of a car, fast and precise enough to target a moving car? Yeah, that's a weapon, just the thing for setting fires to forests, crops, buildings, fuel supplies, ammo dumps. The whole UN would be up in arms.

Never mind the problems caused by scintilation of the IR beam off of low-level dust. You might not be able to see an infrared beam, but that won't stop you going blind.

View: https://www.youtube.com/watch?v=aa_tCzIMJjE
 
Low level power beaming achieved

A plus for solar growth
 
You would not be able to focus a laser beam to the size of a small vehicle from geosynchronous, so it would have to be lower... *much* lower. Meaning the beam emitter would have to be able to precisely target a fast-moving target, and presumably *millions* of them. All with a beam power on par with "weapons potential."
From the perspective of previous epoch technology, new "civilian" technology are "horrifyingly" powerful weapons.

Truck can mow down horse cavalry and infantry squares like nothing
Transport air plane can bomb cities
Cell phone can be modified into autonomous weapons with help of propulsion and warhead

And with space, all the relevant energies means all the tech is extremely effective weapons from the view of previous epoch tech:

Heavy Reuseable rocket with the right payload can sink entire surface fleets with fractional orbital bombardment
Any spaceship drive enabling human time scale inter-planetary mobility result in nuclear level damage potential

--------
Perhaps early into the space age such technology may seem too much like a military escalation. Most will not care after anyone make a serious militarization effort: Once the SDI defense grid (or something similar) is started by anyone, power satellites without fire control systems to hit hypersonics, without hardening to deal with counterbattery and likes would not really raise a eyebrow. The future is a long time.

Space to space sail based transport infrastructure would likely be consider centrally controllable and safer than nuclear drives everywhere as well.

I am sure the media-complex at the time frame will certain throw a fit like all previous eras (remember how TNT was suppose to make war too horrible? remember all the crying over airpower and strategic bombardment? all the crying over nukes? all the crying over robotics? blah) but some will just push it through if it is worthwhile, and maybe someone will repeat the mantra: "Whatever happens, we are the ones with orbital Kill-sats~"

---------
From a near term application perspective:

Solar + Storage type setup is increasingly attractive for a lot of use cases. No need for complications of power lines or fuel logistics and pretty low costs in general. The problem is imperfect reliability, but power satellites putting solar-level energy flux onto the ground cleanly deals with the problem without expensive backup generator, power line or other large storage system. Even if many people will prepare a on the ground backup system, many others would not while backups to backups can also fail: always a stream of potential users.

Solar level power density for lumination and heating is quite sufficient to human users.

For transportation purposes solar level power density is obviously very insufficient outside of specially designed vehicles. I'd expect more vehicles to get solar capability for convenience as prices drop (no flat battery when you leave it idle, run the monitoring electronics), and power sats can again be used in emergency to enable some mobility.

Environmental shaping effects of the power sats can also be interesting: burn a firebreak to control a fire would be interesting. Massive weather engineering for special events may become the norm once capacity is built up.

Given the relative costs of sensors to high energy systems, it would be the most monitored thing near the planet. If future society is to coordinate over high powered space infrastructure at all, this would be a relatively easy problem, just compare it to fleets of heavy and fast spaceships or even mere space garbage.
 
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View: https://twitter.com/DrPhiltill/status/1583106346538311680


This is article is a good overview of current thinking on SBSP. I will add a little about how I was changed from skepticism to cautious optimism to actual optimism. A short /1




2/ Maybe 20 years ago I was skeptical simply because I was always skeptical of every idea and especially those which come from enthusiasts, since enthusiasts are more likely to suffer cognitive bias. I was careful to *never* suggest that SBSP may be a benefit of space. But…




3/ …the skepticism of another skeptic shook me out of that funk because I could see he went too far. It was Pete Worden, former head of Reagan’s Star Wars program and later head of NASA Ames. Pete was never known for technological timidity, and yet he was a disbeliever in SBSP.




4/ But one time I heard him give a talk where he said that SBSP is too expensive by five orders of magnitude (100,000x more costly) compared to putting solar on the ground — e.g., by coating a desert with PV to supply national or regional energy needs. So I checked his numbers…




5/ It turns out he made a basic mistake, one which most skeptics of SBSP still routinely make. He was comparing the cost of SBSP, which is 24/7 100% market penetration baseload power, vs PV without storage or a smart grid to turn it into baseload, at ~30% market penetration.




6/ And he was using Space Shuttle or similar launch costs since newer heavy lifts were not available back then. And he was assuming no technological progress in SBSP. When you correct those, you get to within an order of magnitude of terrestrial renewables, where the latter…




7/ …are still at less than 100% market penetration — which is really hard and costly with renewables since they are mostly intermittent. (Exceptions like hydro are geographically limited and power-limited.) So if we are within 1-2 orders of magnitude, then maybe it is possible.




8/ So about 15 years ago I began to argue that SBSP is still not economically viable until after we have a full industrial supply chain operating outside Earth’s gravity well, but then it should become viable. That still pushes SBSP decades into the future.




9/ Then I was part of a very large proposal team for a gargantuan project (that was surprisingly *almost* funded) to directly work on that off-Earth supply chain with the goal of making SBSP viable. I worked with pro-SBSP John Mankins on that team, and got to hear his arguments.




10/ Mankins argues for hyper-modularity of the system so that large reductions in manufacturing cost can occur. If 90% of the mass consists of a small number of low-cost, easily manufactured modules, then we may get a 1-2 order of magnitude cost reduction, easily.




11/ About 4 years ago I was at a conference luncheon where Mankins was the speaker. He argued that SBSP is economically viable. Pete Worden was in the audience. After the talk, Worden immediately raised his hand and said, “I think you have convinced me.”




12/ Mankins was (and is) arguing for a version of SBSP where we don’t have to wait for off-Earth industry. The story only gets better as we add off-Earth industry. I gave a talk on this at @esa’s recent workshop.




13/ When we have lunar propellant manufacturing, the cost of boosting SBSP from LEO to GEO is cheaper. I know there are skeptics of that, too, but I have a paper that proves it currently in peer review. I will share that ASAP.




14/ Another early application of space resources for SBSP could be structural elements. That is only about 20% of the mass, so it may be a real business opportunity for metal production but by itself it is not a major reason to be optimistic or pessimistic of SBSP.




15/ In the long-run, I am very optimistic about SBSP and I think it will be crucial to health of our planet. Studies predict that energy use on Earth will continue to increase *despite* calls for sustainability.




16/ The 1-sigma estimate of published studies is that power demand may increase by a factor of 5 by 2100. That means the entire supply chain, making and then using the power, will increase by a factor of 5. Very bad for planet Earth! But we are a short-sighted & divisive species.




17/ (image in prior: education.nationalgeographic.org/resource/pollu…) A practical solution to solving Earth’s climate and environment problems should not expect a magical rewriting or human nature to succeed. We should plan for increased energy use. But make it clean, and move the supply chain off-Earth




18/ To make that approach really sustainable, we will need even more recycling, which requires even more energy! The beauty of SBSP is that, in the long run, about 95% of the energy sector *and the supply chain that supports it* can be moved off planet. And with it…




19/ …most of the computing sector and its supply chain can be moved off-planet. By 2100 that could be ~half of our environmental burden moved off planet. One thing will become inexorably more costly: real estate on Earth. Everything else drops in cost. SBSP becomes viable.




20/ But that is really long-term, decades in the future requiring ongoing progress in robotics and AI for off-Earth industry. I am convinced we will get there in the long term. But what about near term? Should we be convinced of SBSP like Mankins and now apparently Pete Worden?




21/ I think we need continued tech progress to really prove it — that’s the way it always is with technology —, but ESA just commissioned two studies which both came back with positive responses that it is achievable. It may help the climate crisis so it is a tiny cost to try it.




22/ I am convinced it is a no-brainer to place this bet. Even if it takes a bit longer to become economic than what we think, programs like SBSP communicate confidence in the future. This motivates education among young people and a more optimistic world.




23/ And because it is a space project focused on saving Earth instead of a minority of people settling on Mars, it is likely to gain broader political support, which helps space overall (and therefore also helps the economics of settling Mars). End






















 
Overview article from Science, focused on recent development: Space-based solar power is getting serious—can it solve Earth’s energy woes?

Late last month in Munich, engineers at the European aerospace firm Airbus showed off what might be the future of clean energy. They collected sunlight with solar panels, transformed it into microwaves, and beamed the energy across an aircraft hangar, where it was turned back to electricity that, among other things, lit up a model of a city. The demo delivered just 2 kilowatts over 36 meters, but it raised a serious question: Is it time to resurrect a scheme long derided as science fiction and launch giant satellites to collect solar energy in space? In a high orbit, liberated from clouds and nighttime, they could generate power 24 hours a day and beam it down to Earth.

“It’s not new science, it’s an engineering problem,” says Airbus engineer Jean-Dominique Coste. “But it’s never been done at [large] scale.”

The urgent need for green energy, cheaper access to space, and improvements in technology could finally change that, proponents of space solar power believe. “Once someone makes the commercial investment, it will bloom. It could be a trillion-dollar industry,” says former NASA researcher John Mankins, who evaluated space solar power for the agency a decade ago.
 
A recent overview article of the solar power topic.

When inventor Charles Fritts created the first crude solar photovoltaic cells in the 1880s, one might have thought the achievement would rapidly revolutionize global electricity production. There is, after all, no power source cheaper, cleaner and more ubiquitous than sunlight. Yet despite enormous (and ongoing) technical advances making solar power ever more capable and affordable, some 140 years on it still supplies less than 5 percent of the world’s electricity. For all its benefits, solar power does have drawbacks that can limit its use—chief among them the fact that half the planet’s surface is in darkness at any given time.


Tactical Wireless Power Beaming Technologies for Energy Web Dominance Request for Information

This Request for Information (RFI) from the Defense Advanced Research Projects Agency (DARPA)’s Tactical Technology Office (TTO) seeks technologies and innovative solutions for efficient, kilometer-range radio frequency (RF) kilowatt-class power beaming, distributed apertures for dynamic coherent beamforming, the conversion of RF to electrical energy, and RF energy relays in a lightweight, size-limited payload.

Responses to this RFI will be used to inform and explore future programs within the Tactical Technology Office that advance the ability of multiple ground assets to dynamically move energy across a network of small aircraft equipped with energy receiving and relay technologies. This RF power beaming and relay concept is expected to serve as a component of a more expansive energy web of power generation, transfer relays and receiving solutions, enabling the DoD to dynamically distribute energy resources to more flexibly deliver military effects.

Intellectual or other privileged or proprietary information contained in responses to this RFI will not be distributed outside of the Department of Defense (DoD) or U.S. Government employees from other Government agencies who are working with DARPA on this RFI. In the event that a new DARPA program is developed in response to this RFI and a solicitation is issued, no intellectual or other proprietary information received in response to this RFI will be divulged to entities outside the U.S. Government.

 
China intends to use its newly-completed Tiangong space station to test key technologies required for space-based polar power, according to a senior space official.

Robotic arms already operating on the outside of Tiangong will be used to test on-orbit assembly of modules for a space-based solar power test system, Yang Hong, chief designer of the Tiangong space station said in a presentation at the ongoing China Space Conference.

The test system will then orbit independently and deploy its solar arrays and other systems. It is likely to test and verify capabilities such as power generation, conversion and transmission.
 
Northrop Grumman has completed ground-based tests to demonstrate critical technology required for a 2025 demonstration of space-based solar power.

“As far as the technologies go, we’re very confident in our design and we’ve proven it out,” Tara Theret, Northrop Grumman’s Space Solar Power Incremental Demonstrations and Research (SSPIDR) program director, told SpaceNews. “Now, it’s just building, testing and integrating the rest of the hardware on a challenging timeline.”

Northrop Grumman announced Dec. 15 the successful demonstration of a key element of SSPIDR, the ability to beam radio frequency energy toward various antennas by steering the beam. The testing was conducted in one of Northrop Grumman’s anechoic test chambers in Baltimore.
 
While going 100% Green would take time, and Space harvested solar energy is the way to go, the authors should not discard the relocation of traditional power generation like nuclear outside of earth as an input to close the gap.

Naturally, space exploration will need their power stations to move at the required pace and a business model could well prosper by rappatriating any excess of energy, or specifically produced energy, to earth. Especially with the moon that is closer to us.

Like mentioned before and elsewhere, nuclear or local fossil fuels burn on a planet devoid of atmosphere is easy. The lower gravity of the Moon will also accelerates power station expansion and shipping back to earth.

It could well end as a serious competior to generate electricity.

Hence, Green is not the main variable to describe the process. Locally it is, because of Earth's population will. Politics is the variable.

And, as a side remark, there is so much momentum potentially to restore the dignity of that word today, setting up the footsteps of humanity in space, that, it is bewildering to see the scarce interest of that subject in international politics.
 
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