[HN Gopher] Electricity from Space: The 1970s DOE/NASA Solar Pow...
___________________________________________________________________
Electricity from Space: The 1970s DOE/NASA Solar Power Satellite
Studies
Author : valeg
Score : 81 points
Date : 2023-04-25 09:08 UTC (13 hours ago)
(HTM) web link (spaceflighthistory.blogspot.com)
(TXT) w3m dump (spaceflighthistory.blogspot.com)
| nickpeterson wrote:
| Dumb question but what about mirrors? Couldn't we redirect
| sunlight to a fixed point on earth that has solar panels?
| biomcgary wrote:
| I like the idea, but there are a few questions I have for the
| plausibility of this approach. 1. Does mylar (or weight
| equivalent have enough reflectivity and flatness) to target a
| ground station? 2. How much light can be concentrated before
| becoming a risk (e.g., birds above solar panels, human eyes in
| vicinity)? 3. How fast will the mirror material degrade from
| solar wind and micrometeorites?
|
| I assume someone has considered this scenario previously, but I
| imagine that SpaceX lift capacity and price might change the
| economics.
| Cthulhu_ wrote:
| Solar panels drop efficiency the warmer they get; focusing more
| sunlight on a space will heat that up.
|
| There's solar heat based power stations, using mirrors that
| focus light on a point or a pipe to heat up oil; the question
| there is, would they become more effective if they get more
| light?
|
| 1 square meter of ground currently receives 1370 watts of
| energy (if my quick google is accurate); if this can be
| captured, you can do a back of the napkin calculation of how
| much you need. It's already been posited that filling a
| relatively small patch of e.g. a desert can fulfil all of
| europe's energy needs - no space things needed.
| TrainedMonkey wrote:
| Possible but highly inefficient for power generation. Need
| massive amount of mirrors with pointing + stationkeeping. For
| medium orbits will need a huge amount of receiver sites + beefy
| prop & pointing systems. For Geo will need a truly staggering
| amount of mirrors + sophisticated focusing + massive receiver
| sites on the planet. Anywhere you point the beam will have
| massive ecology / weather disruptions... Probably not suitable
| for human habitation in a huge area due to atmosphere
| dispersing the beam. See
| https://en.wikipedia.org/wiki/Space_mirror_(climate_engineer...
| for more info.
|
| One cool thing we could do is slightly boost the amount of
| sunlight northern latitude cities receive. This will make solar
| panels there more viable and will make cities far more livable
| in the winter season. This could also be done seasonally. This
| is a cool example
| https://www.theguardian.com/world/2013/nov/06/rjukan-sun-nor...
| [deleted]
| usefulcat wrote:
| ".. President James Carter .."
|
| Weird, that's the first time in my life I've ever heard him
| referred to as 'James' rather than 'Jimmy'.
| dragonwriter wrote:
| I've seen James a fair amount, but almost never without also
| having "Earl" and "Jr."
| nirav72 wrote:
| I just got done reading Critical Mass by Daniel Suarez. The
| technology described and used in near future story of the book is
| based around this concept. Except in the book, they use it to
| power mass drivers to shoot cylinders of lunar regolith to a
| Lissajous orbit where it can be processed into raw materials.
| bglusman wrote:
| Came here to say the same! Though it's a bit fun that when they
| upgrade the moon to use a nuclear reactor to power several mass
| drivers, they mention how the satellite can be repurposed to
| provide power to earth now... which makes sense. The book (and
| its part 1 book, Delta-V) overall point about the value and
| utility of asteroid and lunar mining to bootstrap whole
| economies around the Lagrange points and that sending that
| matter back down to earth makes very little sense was pretty
| compelling, and relatedly that building a colony on Mars
| probably makes very little sense vs building in space with
| artificial gravity and artificial radiation shielding, where
| you're not subject to a giant gravity well to go back to
| earth/elsewhere in solar system.
| timthorn wrote:
| For those in the Cambridge area (or who have Zoom!), there will
| be a CSAR talk on Monday evening about the CASSIOPeiA Solar Power
| Satellite:
|
| https://www.csar.org.uk/lectures/2022-2023/20230501/
| milliams wrote:
| *[2016]
| mrguyorama wrote:
| This was an energy generation option in Sim City 2000 with the
| caveat that occasionally the ray of microwave energy would "miss"
| and cook some of your city.
| bradfa wrote:
| Any discussion on how much shooting giant microwave beams through
| the atmosphere would warm the atmosphere locally or globally?
| Clearly the beam won't be 100% efficient and that power loss is
| going to partly be absorbed by the atmosphere, causing it to
| warm.
| DennisP wrote:
| There's also waste heat from nuclear power and fossil plants.
| There's even some warming from the lower albedo of black solar
| panels. All of it is a tiny effect compared to the warming from
| greenhouse gases.
| cduzz wrote:
| Even things like electricity and water, which move pretty well,
| have "place value" -- people commonly move water from place to
| place by growing grain with the water and then moving the grain
| (not the water) to places that don't have enough water to grow
| the grain conveniently / economically. The same goes for
| electricity -- Iceland exports refined metals which require huge
| amounts of electricity to melt, effectively exporting the
| electricity entombed in the refined aluminum.
|
| What can be made in space that can allow moving this abundant
| energy? Obviously you can't haul ore up into space then refine it
| with a big magnifying glass and drop it back onto the earth.
| People talk about asteroids but they seem like they're a big
| delta-V away from where they'd be useful to put into Kia bumpers.
| GravitasFailure wrote:
| Anything where you need to manipulate the crystal structure or
| homogeneity of a mix, or cases where gravity will cause
| structural issues.
|
| It's possible to grow extremely high quality crystals in
| microgravity, so there's your semiconductor and optics
| industries.
|
| Bulk metallic glasses are easier to make in space for the same
| reason: crystals grow more slowly, and are easier to prevent.
|
| High quality vacuum on a scale never seen before for
| experiments and industrial processes.
|
| Imagine building the James Webb Space Telescope without needing
| to harden it against launch forces.
| [deleted]
| Faint wrote:
| antimatter :-P
| amitu wrote:
| Computation.
| jackmott42 wrote:
| That is a good point! GPT5 in space, beam down the model, not
| the energy.
| Faint wrote:
| With the speed GPT4 is replying, you could easily move
| inference to GEO as well, and no-one would notice.
| CorrectHorseBat wrote:
| Cooling is going to be a big problem for that
| mlyle wrote:
| Any use of energy in space is going to have pretty big
| cooling problems unless it's a fundamentally "hot" process
| that radiates away heat easily. Because any usage of energy
| in space all becomes heat.
| wongarsu wrote:
| There's probably a whole world of manufacturing processes that
| benefit from low gravity. The only one currently used is making
| high-quality optical fiber: producing ZBLAN fibers in 0g fixes
| a lot of problems with bubbles and crystal formation, allowing
| you to make better and much longer fibers. As access to space
| continues to get cheaper we will probably discover a lot of
| other cases where 0g is beneficial for manufacturing, and
| entombing energy might be another way to make those
| economically interesting.
| throwuwu wrote:
| Moon bricks. Ship regolith and dust into orbit from the moon,
| mix with water to make a moldable clay, form into bricks, bake
| inside the mother of all solar kilns and then drop them down on
| Earth. The water should be recoverable if the kiln is air
| tight. This would greatly reduce fuel needed on earth for
| construction. You could even make the reentry vehicle out of
| baked clay, only parachutes would need to be added. Extra
| points if you can make the whole thing buoyant and land them in
| the ocean.
| cfraenkel wrote:
| No need to waste the water. Melt the regolith scilicate in a
| vacuum and it forms anhydrous glass. (As strong as steel)
| sbradford26 wrote:
| So largely I believe the plan is to use microwaves to send the
| power back to earth so you don't have to have anything
| processed in space. This would usually involve ground stations
| that would receive the power.
| cduzz wrote:
| Right -- microwaving the ground is just moving the energy,
| which may or may not actually be efficient. On the face of it
| it seems silly, but so does making a rocket out of water
| towers and landing it on it's ass on the moon, so I've re-
| calibrated 'silly'.
|
| Nevertheless -- finding ways to move refined products around
| that embody a huge amount of energy is the traditional way to
| approach this problem.
|
| And anti-matter, if you could package it, is an obvious
| example....
| sbradford26 wrote:
| Yeah with space it is typically more efficient to move
| energy versus mass. The efficiency may not be great but you
| get to balance it with the increased efficiency of solar
| panels being located in space. So independent component
| efficiencies might be overshadowed by large end to end
| system efficiency gains.
| bglusman wrote:
| oh, whoops, somewhat duplicated your point, sorry!
| bglusman wrote:
| The book Critical Mass by Daniel Suarez is my only source,
| but, the efficiency of rectenna is discussed there, and
| particularly, though the efficiency of the transmission is
| somewhat low, the efficiency of solar panels in space is
| MUCH higher than on earth, and they can operate 24/7, so
| the overall system efficiency is still substantially higher
| than the equivalent solar panels on earth... at least,
| assuming you can build the solar panels in space from mined
| material as they do in the book, I imagine if you needed to
| launch all the material from earth, it would probably be a
| fairly different story, assuming you included that in the
| calculations.
| giantrobot wrote:
| > the efficiency of solar panels in space is MUCH higher
| than on earth
|
| Not really. The biggest difference between a panel on
| Earth and one in space is the space panel is illuminated
| 23 hours a day. So per panel you're getting 2-3x the
| illumination over the course of the day.
|
| The drawback is even at the absolute cheapest pie in the
| sky Musk estimates of cost to orbit ($10/kg), a space
| solar panel is orders of magnitude more expensive than a
| ground panel. You could just deploy 3x the number of
| panels on Earth for 3x the price vs deploying in space at
| x\^3 the price.
|
| Even with the near constant illumination of panels in
| space the losses from RF conversion, free space losses,
| atmospheric losses, and RF rectification eliminate a lot
| of your power gains. For those losses you also incur
| significant costs. So SBS is kind of a lose-lose problem.
| Every technology that would make SBS more practical could
| be applied on the ground for a tiny fraction of the cost.
| dabluecaboose wrote:
| >The biggest difference between a panel on Earth and one
| in space is the space panel is illuminated 23 hours a day
|
| Small nitpick, but as a GEO satellite navigator I want to
| point out that the solar panels are in sunlight
| constantly _except_ for "eclipse season" around the
| equinoxes. During eclipse season it can be in shadow for
| about an hour.
| giantrobot wrote:
| Thanks for the correction. So 23.76 hours a day (averaged
| over a year).
| oceanplexian wrote:
| It's not efficient for replacing power sources on the
| ground, but for airplanes, ships, and remote communities it
| could be genius. No need to carry heavy batteries around
| and your capacity is virtually unlimited (At least as far
| as it is feasible to build a massive orbital solar array).
| simonh wrote:
| If you need extensive industrial infrastructure in orbit, maybe
| make that from resources mined from asteroids. Ship high value
| finished goods down from orbit.
| GravitasFailure wrote:
| How much of that high value stuff will wind up in satellites?
| Cut the trip down the gravity well and just build in orbit,
| especially low value items that are expensive to launch but
| cheap to make.
| TrapLord_Rhodo wrote:
| read the delta-v series. Great book, and that's exactly what
| they do.
| Gravityloss wrote:
| George Crabtree et al from Argonne national lab are working on
| an automated chemistry lab that synthesizes and tests various
| flow battery chemicals on its own. Of course simulation and AI
| are used too but it's not enough. There are a lot of
| alternatives and a lot of different requirements / dimensions.
| Very fascinating video: https://youtu.be/yv_8xfwsKxE?t=1208
| michael1999 wrote:
| Gigawatt steerable carefully de-focused energy beam. That's a
| doomsday machine.
| JKCalhoun wrote:
| I loved _concept art_ (like the NASA /Boeing illustrations that
| accompany this article) until the artists started to go
| digital/CG in the 80's or whenever it was.
|
| I'm not a huge fan of the artist(s) depicting space concepts in
| this particular article though (still better than most rendered
| art). I tried to do a bit of googling to find something better
| but in 10 minutes the best I could come up with was this site:
| https://www.kuriositas.com/2013/08/space-shuttle-concept-art...
|
| I think there was more dynamism in the pre-CG concept art, often
| a bold use of color, sometimes an exaggerated use of
| shadow/light.
| gene-h wrote:
| One problem with this that wasn't as much of a problem in the
| 1970s is RF interference. The 1970s designs and many other
| designs use 2.45 GHz, so it will interfere with wifi and
| bluetooth, with bluetooth being more sensitive to interference.
|
| How far does this interference extend? Thousands of kilometers
| from the receiver[0, see page 250]. Because the transmitter is
| far, the beam spreads out quite a bit due to diffraction and
| because the transmit power is gigawatts there's hundreds of
| megawatts of stray power. Making bluetooth headphones and
| bluetooth low energy tags work worse will probably make people
| angry.
|
| Different frequencies could be used, but that requires allocating
| spectrum, which is a pretty difficult task politically. In the
| US, there are a couple bands in the sub-10 GHz range where power
| beaming works best that have few users. So it's not impossible,
| but still politically difficult.
|
| [0]https://ieeexplore.ieee.org/document/9318744
| [deleted]
| mNovak wrote:
| I bet the military would love/hate it (depending where
| deployed), because all that stray illumination would make for a
| perfect bistatic radar source. Suddenly many radars can be
| passive, and stealth techniques take a serious hit.
| mlyle wrote:
| This is a really good point.
|
| I know super narrow notch filters up in the gigahertz are
| difficult, but has anyone thought at all about how narrowband
| the power transmission could reasonably be? Because then at
| least notching would be possible to squeeze out adjacent
| spectrum.
| techdragon wrote:
| There are techniques. And generally speaking the bandwidth
| can be much narrower than the sort of things designed back
| then. Even a lot of modern systems are designed with less
| than state of the art tech for various reasons...
| reliability, cost, etc.
| fourseventy wrote:
| This idea never made any sense to me. Why the heck would you
| spend billions of dollars to launch solar panels into space to
| gather sunlight then beam it to earth when you could just wait
| for the sunlight to get to earth naturally for free...
| kybernetikos wrote:
| Putting the cells in orbit means that there's almost no night,
| and there's less loss due to the atmosphere.
|
| Of course, there are loads of problems with the idea but I can
| see why it's intuitively appealing.
| jackmott wrote:
| there is loss from the atmosphere when you beam it down
| pfdietz wrote:
| Not much, typically.
| MrOwnPut wrote:
| I think 60% over a kilometer is the best efficiency thus
| far.
|
| What is the "typically" you are referencing?
| pfdietz wrote:
| Microwave beams are attenuated in heavy rain. Typically,
| the beam is not going through heavy rain.
|
| The 60% over a kilometer is not due to atmospheric
| absorption, it's due to losses at the transmitter and
| receiver (and beam spread exceeding the size of the
| receiver.) If microwaves lost 40% of their energy in a
| kilometer radar would have a hard time working.
|
| Millimeter waves are more strongly absorbed in clear air,
| so they are not as good for this use case. They may be
| good for powering aircraft.
| kybernetikos wrote:
| yes, but you can concentrate the beam more than sunlight so
| that there's less atmosphere involved. You can also choose
| a beam technology (wavelength etc) based on it going
| through the atmosphere well, rather than having to stick
| with sunlight's properties.
| Cthulhu_ wrote:
| The loss from the atmosphere is not the issue; plenty of
| energy still hits the earth while the sun is out, plenty of
| methods of capturing it (solar panels, mirrors to focus the
| heat, etc), the issue is that someone actually has to build
| it and it goes off at night. That, and transport.
| kybernetikos wrote:
| Indeed, and this project is a way of fixing the "it goes
| off at night" problem by making all the other problems
| massively harder.
| nine_k wrote:
| The fact that a powerful microwave beam shooting precisely from
| the orbit is _also_ a weapon platform (if directed outside the
| receiver) might have played some role.
| MrOwnPut wrote:
| A real-life Hammer of Dawn (gears of war)
|
| Really though I don't see this scaling to energy production
| for the masses due to the beaming logistics.
|
| It'll mainly be used to recharge drones that never land and
| possibly fry enemy systems / missiles / etc.
| DennisP wrote:
| Not with a satellite in geostationary. The beam concentration
| on the ground would be too low to hurt anyone. You'd need a
| collector miles wide.
|
| With modern modular designs using phased array transmitters,
| even getting that much focus requires a reference signal from
| the ground target.
| Faint wrote:
| Yeah, no night, no atmosphere, constant power output, lot's of
| real estate, and panels in space do not need heavy
| superstructure to withstand weather or gravity, thus they could
| potentially be extremely light for the area (micrometers to
| tens of micrometers thick at most needed for light absorption).
| And in far future, if they are built of materials taken from
| moon or meteorites, you could also bypass most of the lifting
| cost for even that. Of course, that would need huge scale to
| justify the R&D to pull it off.
|
| Anyway, space based solar power is the end game. Nothing on
| earth will ever provide the quantities of power (not even
| nuclear, fusion or fission) that capturing solar energy can.
| sidewndr46 wrote:
| You do realize the Earth doesn't have "night" as a globe-wide
| event right? If it's night here, it must not be night
| somewhere else.
| DennisP wrote:
| Yeah everybody knows that. But transmission by wire halfway
| around the globe would be pretty expensive, and carry
| geopolitical risks.
| pengaru wrote:
| > and carry geopolitical risks.
|
| And a solar death ray aimed at the planet doesn't?
| DennisP wrote:
| As I noted in another comment, it's not a death ray. Even
| with a reference signal from the ground, it's not
| concentrated enough to cause harm.
|
| Regardless, I don't think long-distance transmission is a
| viable solution to solar intermittency.
| sidewndr46 wrote:
| Is transmitting power from a satellite in low-earth-orbit
| going to be cheaper?
| DennisP wrote:
| Possibly. Long-distance high-voltage wires get pretty
| expensive. At Starship launch costs with modern designs,
| SPS actually looks pretty economical.
| sidewndr46 wrote:
| If someone has compiled a cost comparison of
| transcontinental HVDC links compared with the alternative
| spaceborne solution I'd certainly love to see it.
|
| The space based solution is possibly actually more
| reliable, as there are actually less components involved
| that could fail.
| oceanplexian wrote:
| > They could potentially be extremely light for the area
| (micrometers to tens of micrometers thick at most needed for
| light absorption).
|
| This is really the key, if you can make a solar panel that's
| as light and thin as say mylar, and then unfold it when you
| get to space, we could put up several kilometers of solar
| panels without requiring much mass at all. It's not like
| there's wind or rain up there to wear it down.
| ZeroGravitas wrote:
| > constant power output
|
| Worth noting this isn't as much of a benefit as it's made out
| to be.
|
| If you were designing a perfect power source, it would match
| demand, so produce more in winter in polar regions, and more
| in summer for regions with lots of AC. Similarly, you'd
| generally want more power during the day than at night.
|
| This is part of the reason a mix of solar and wind that
| varies by latitude is an ideal mix.
|
| Space power might get more bang for buck if it could target
| its power to different regions e.g. swapping from north to
| south as the seasons change, and/or following the day/night
| cycle and/or weather to maximise energy price.
| DennisP wrote:
| The satellites would be in geostationary, with phased-array
| transmitters, focused by a reference signal from the ground
| target. They actually could be repointed to various
| receivers. The ground stations would be relatively cheap so
| it wouldn't be all that important to maximize their
| utilization.
|
| (Source: _The Case for Space Solar Power_ )
| spacemark wrote:
| No night? Where are you putting these satellites? The only
| orbit that doesn't eclipse is sun synchronous, an already
| crowded orbit. Even GEO satellites experience eclipse.
| c54 wrote:
| > Glaser had noticed that a satellite in geosynchronous
| Earth orbit (GEO), 35,786 kilometers above the equator,
| would pass through Earth's shadow for only a few minutes
| each year.
|
| The article addresses this. To my mind 4 minutes per year
| is equivalent to the parent's layspeak "no night" comment.
| cfraenkel wrote:
| 4 minutes??? Not even close. Each eclipse varies from a
| few seconds for the first one to practically an hour in
| the middle, then gets shorter again, over roughly 30
| eclipses each season (2 per year)
| etskinner wrote:
| They address this in the article: Only twice per year are
| the panels in shadow, at the equinoxes. Presumably all the
| rest of the time they're slightly above/below the earth
| with respect to its orbit. It's the same reason the moon is
| lit nearly all the time.
| mlyle wrote:
| > It's the same reason the moon is lit nearly all the
| time.
|
| The moon is 10x further away, so the Earth
| subtends/shades a much smaller angle.
| DennisP wrote:
| A geostationary satellite gets eclipsed more than the
| moon but it's still in full sun 99.5% of the time.
| mecko23 wrote:
| Respectfully, I believe you are inaccurate on both
| accounts, sun synchronous orbits (SSO) only have no eclipse
| if their orbital plane is within a very degrees of the
| terminator, this of course widens with altitude but there
| exists far more possible SSOs with eclipses than without.
| Secondly with GEOs as with any very high altitude orbit the
| eclipse time trends towards zero so effectively at a GEO
| the eclipse time is minimal compared to the illuminated
| time. Of note the length for the eclipse time of GEO varies
| throughout the year.
| spacemark wrote:
| Respectfully, you are not correct that eclipse in Geo is
| insignificant. It drives many engineering constraints for
| spacecraft systems. Look I get why people are excited
| about space space solar power, but I've been in this
| industry for 15 years and when you dig into the numbers
| and understand the realities of spacecraft engineering,
| SBSP just seems like a fool's errand. It may not always
| be that way, but the technical challenges are extreme and
| costs are still nowhere near what would be required to
| make it work.
|
| You can chalk my comments up to a grumpy engineer tired
| of the cyclical SBSP pushes that never go anywhere.
| mecko23 wrote:
| Hmm, well I totally understand how it drives spacecraft
| design and I don't know off the top of my head the length
| of greatest eclipse but it cannot be greater than a small
| fraction of the period (upwards of 1/12). This is
| significant for a spacecraft itself but as far as a
| regionally integrated power grid is concerned it is a
| clear improvement over current solar PV systems. I get
| that there maybe some fatigue here with the idea and blue
| sky optimism that comes with SBSP, I think there are
| valid criticisms to level at it orbit selection and
| corresponding ground tracks and eclipses are not one.
| mlyle wrote:
| > It drives many engineering constraints for spacecraft
| systems.
|
| Here the only thing it's going to drive are thermal
| requirements-- which are admittedly significant problems.
| There's no need to continue to use large amounts of power
| for comms, etc, like on most GEO birds.
|
| And, of course, the grid needs to deal with the power
| disappearing for an hour in the middle of the night for
| short periods of the year.
| spacemark wrote:
| It drives electrical and battery system requirements more
| than anything else. Thermal effects impact pointing/ADCS,
| which impacts propulsion, etc.
| mlyle wrote:
| There's no real intrinsic electrical or battery system
| requirements for a giant solar power satellite. The
| energy use is comparably trivial: no big transponders to
| run in eclipse like a comsat.
|
| But you do need everything to survive the cold and
| thermal cycling.
| giantrobot wrote:
| Not just thermal cycling but a giant solar collector is
| literally a giant solar sail. There would be significant
| force applied to a giant collector.
|
| You'd need propulsion to maintain position and
| orientation. You'd also need a number of propulsion units
| to balance solar pressure gradients as the collector
| entered and existed the Earth's shadow as well as the
| thermal expansion/contraction of the structure.
|
| It's likely not a lot of power but a non-trivial amount
| of fuel.
| mlyle wrote:
| You probably maintain orientation with a control moment
| gyro and periodically desaturate it with thrust. You also
| use thrust to reboost and stay in orbital slot.
|
| High-impulse ion engines, etc, are a good match for this
| task.
| giantrobot wrote:
| You'd need a rigid structure to keep the gyro from
| ripping itself loose from the structure. Even constructed
| as a giant space frame, that's a lot of mass to deal with
| the torsion of the structure rotating.
|
| A structure 100m on a side would be just at the bounds of
| current technology (the ISS's control moment gyros). With
| 30% efficient panels that's only about 4MW before
| conversion and path losses.
|
| The high impulse ion engines to desaturate the gyros
| would still need to be refueled regularly. I think you're
| hand waving a lot of complexity that even if completely
| solved still leaves a solution that's orders of magnitude
| costlier than solar panels on the ground.
| dabluecaboose wrote:
| This is exactly how the NOAA GOES sats work. Every day at
| a proscribed time we used to desaturate the reaction
| wheels, so they could more or less keep running
| constantly and keep the satellite pointing where it
| should be.
| mlyle wrote:
| Yup. This would be big enough that a control moment gyro
| would be "worth it," too-- and could store a whole lot of
| momentum and allow less frequent desaturation burns.
| mecko23 wrote:
| Why in this case would it cause significant problems? Are
| you referring to the heating (that would make sense with
| such a large surface area of panels)? Concerning cooling-
| with such short times in eclipse I can't imagine that it
| would have enough time to have cooling issues beyond
| flexing of the superstructure (if made from metals). Be
| interested to hear though if I'm missing something.
|
| As to power disappearing with an adequately
| geographically integrated grid I don't forsee that as
| really too much of a problem. Currently the grid deals
| with short term outs fairly well especially if they are
| planned for months in advance.
| mlyle wrote:
| > Concerning cooling- with such short times in eclipse I
| can't imagine that it would have enough time to have
| cooling issues
|
| Lots of thin structure with 70 minutes to radiate, with
| the only thing shining on it the earth's albedo
| subtending a tiny angle. I'd imagine it creates rather
| significant demands on structure and electrical
| connections.
|
| I've not run the numbers on a GEO solar spacecraft, but
| the smallsat group that I'm mentoring that would be
| "thicker" than a lot of the GEO craft... gets down to
| -30C without heaters during its 40 minutes in eclipse
| while much closer to Earth.
|
| > As to power disappearing with an adequately
| geographically integrated grid I don't forsee that as
| really too much of a problem. Currently the grid deals
| with short term outs fairly well especially if they are
| planned for months in advance.
|
| Yup, that's the point I'm making. A space based solar
| power craft has smaller problems from eclipse than a
| typical comsat. Batteries, etc, are not nearly as much of
| a concern. It's mostly the thermals that are left.
| dabluecaboose wrote:
| Solar Radiation Pressure is non-negligible for navigation
| and attitude dynamics as well. Eclipse season changes
| things for the NAV team.
| mlyle wrote:
| So, let's cut down the pedantry a bit. Even in the most
| pessimal reasonable orbits, up to an hour of outage in the
| middle of the night for 3-4 months per year is a very
| different beast from getting just several hours of sun per
| day.
|
| Why?
|
| - You still get better duty cycle from the panels
|
| - The time the power is missing is very small
|
| - The need for storage, etc, is low because it's a short
| period of relatively low demand that is missing.
| sandos wrote:
| Conclusion: everyone will eventually live in orbit!
| XorNot wrote:
| I mean probably? We can't manufacture more real estate down
| here as easily as you could up there (once certain
| technologies are common place).
| cosgrove wrote:
| I think it's neat that they did all these studies on feasibility
| and projected a start date into the 2000s.
|
| Also neat that we ended up with complimentary energy generation
| and storage technologies to fix the "it gets dark at night"
| problem of solar electricity generation!
| mhandley wrote:
| Has anyone updated the economic feasibility studies based on
| using SpaceX's Starship as the heavy-lift reusable launcher? At
| first glance, it seems like this, combined with today's greatly
| improved robotics and ion thrusters to move components from LEO
| to GEO, may be the key enablers.
| [deleted]
| jackmott wrote:
| [dead]
| T-A wrote:
| There has been a surge of interest over the past year:
|
| https://spacenews.com/nasa-to-reexamine-space-based-solar-po...
|
| https://www.esa.int/Enabling_Support/Space_Engineering_Techn...
|
| https://spaceenergyinitiative.org.uk/
|
| https://www.spacesolar.co.uk/
|
| https://www.solarspacetechnologies.com.au/
|
| Here's a nice recent summary (despite the publication date):
|
| https://aerospaceamerica.aiaa.org/features/harvesting-sunlig...
| ZeroGravitas wrote:
| It's probably the lower cost of earthbound solar and batteries
| that are the bigger factor in updating the feasability,
| trending in the opposite direction.
| simonh wrote:
| Musk is on record saying it's a complete non-starter. There are
| all sorts of problems with it. Beam spreading is a huge
| problem, the ground receiver would generally have to be about
| 10x the diameter of the transmitter and these would need to be
| really big arrays. A 1km transmitter is ballpark. Targeting the
| receiver is tricky as even minuscule angular offsets mean you
| would miss completely. Losses from transmission and reception
| are huge, and the enormous emissions leakage means you have to
| clear the big chunk of orbital 'real estate' of other
| satellites or they'd suffer serious problems.
| dexterdog wrote:
| If he says it can't be done either it really is seriously
| unrealistic, or somebody else already has a lead on him.
| xbmcuser wrote:
| He has the cheapest way to get to space locked in for a few
| years so if he says it is not feasible than it probably is
| not feasible. Looking at how ground solar and battery
| prices are still falling 10-15% a year I think it will be
| hard for space solar to be economically viable let alone
| viable when you take it into account pollution.
| DennisP wrote:
| People sure put a lot of weight on an off-the-cuff comment
| Musk made in 2012, before Starship was even a gleam in his
| eye. That was the same year NASA published their SPS-ALPHA
| study[1] on modern SPS design, so Musk may not have been
| aware of it.
|
| Modern designs use a phased-array transmitter, and a
| reference signal from the ground for targeting. Overall
| energy loss is 40 to 60% according to the book _The Case for
| Space Solar Power_.
|
| [1] https://www.nasa.gov/pdf/716070main_Mankins_2011_PhI_SPS_
| Alp...
| ben_w wrote:
| 60% loss is also what you would get with a single 1GW
| existing HVDC cable, connecting anywhere on Earth to its
| antipode.
|
| IIRC, for _n_ identical parallel resistors of rO, S = nrO,
| so this only gets better for bigger systems.
| giantrobot wrote:
| Elon Musk's most fantastic/unrealistic prediction for
| Starship cost to orbit is $10/kg. To get to GEO roughly
| doubles that cost because the cargo Starship needs to
| rendezvous with a tanker for the fuel to GEO then back
| home. Intermodal surface freight reaching most of the
| planet is about $1/kg on the _high end_.
|
| To even begin to make sense, space freight to would need to
| be 1/10th of Musk's overly optimistic $10/kg. You could
| ship the panels air freight and still beat those numbers by
| a huge margin.
|
| That says nothing of the construction costs. Which for SBS
| will cost orders of magnitude more than day laborers in
| t-shirts assembling arrays on the ground.
|
| Every aspect of SBS is ridiculously expensive and requires
| as-yet entirely undeveloped space-based construction
| technologies. There's no near-term horizon where it's
| anywhere close to competitive with ground-based solar. This
| holds even if you assume over-building surface solar to 3x
| to match the duty cycle of SBS.
| ben_w wrote:
| Only 1km? Given the usual claims I hear about power density
| and total power, it's normally 100km^2, or square 10km on the
| side.
| mikepurvis wrote:
| That's pretty sobering, since you can produce/capture quite
| a lot of energy with 100km^2 of clear, flat ground that has
| a view of the sky.
|
| Not least by just putting normal solar panels on it and
| jettisoning the whole space part.
| DennisP wrote:
| Yes but with SPS, that 100km^2 is mostly just antenna
| wire, and you don't need any sort of energy storage.
| ben_w wrote:
| At 6cm spacing, a 10km by 10km ground array with 1mm^2
| cross section wires has total 1667 m^3 volume; this is as
| much conductor as you would get in the equivalent of a
| 1111 km long 1 GW HVDC cable: https://www.wolframalpha.co
| m/input?i=10km*10km%2F6cm*1mm%5E2...
|
| It's not exactly the same thing, of course, but it means
| 40 such ground stations would use as much metal as a 1 GW
| line looping all the way around the planet and back to
| itself, and a global grid is another way to obviate
| storage.
|
| That's 1 GW with standard existing cables; I assume if
| you actually want to go that far one can improve the
| design as the optimisation goals are different. Parallel
| cables lower resistance.
|
| I'm also not sure how much maximum current would scale in
| such cases.
| simonh wrote:
| For the receiver yes that's ballpark. I'm talking about the
| size of the microwave transmitter array in orbit beaming
| power down to the surface.
| ben_w wrote:
| Ah! I misread. Thanks :)
| blincoln wrote:
| The article mentions that limited agriculture could be conducted
| at the rectenna sites. I wonder if it could have actually been
| beneficial. A lot of middle America (where most of the sites
| would have been located) gets VERY cold in the winter. Would
| microwave warming of the rectenna sites allow growing more crops
| there for more of the year?
| ben_w wrote:
| Yes, but a thin sheet of plastic over the farmland also
| massively boosts output in similar cases, and there are more
| issues than just temperature:
|
| https://en.wikipedia.org/wiki/Polytunnel
| DennisP wrote:
| NASA completed another study in 2012, with a vastly cheaper and
| more practical design enabled by new technologies. Here's a
| description: https://space.nss.org/sps-alpha-a-novel-approach-to-
| space-so...
|
| and the study itself:
| https://www.nasa.gov/directorates/spacetech/niac/2011_Practi...
|
| A book-length treatment of modern SPS designs is _The Case for
| Space Solar Power_. It has detailed cost figures but was written
| before SpaceX had accomplished much, estimating a cost at
| gigawatt scale of 15 cents /kWh. I plugged in Starship launch
| costs and it came to 4 cents/kWh, which is not bad for 24/7 clean
| power without storage.
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