You see, that's the point I'm making. Take any given solar cell: is it better to have on Earth or in orbit? What do you get from being in orbit? You get twice as much sun, best case. But you've got do do a conversion. You've got incoming photons that go to electrons, but you have to do two conversions you don't have to do on Earth. You've got to convert it to photons and then convert those photons back into electrons.And that double conversion is going to get you back to where you started basically! So why are you sending them to bloody space?And by the way, electron to photon converters are not free, nor is sending stuff to space. So then it obviously super-doesn't work.Case closed! You'd think case closed! But no, I guarantee it's gonna come up another ten times! I mean, for the love of god!
The solar arrays attached to a typical satellite generating 1.6GW in space and an average of 1GW on Earth would measure about 5 to 6 square kilometers and use a transmitting antenna array with a diameter of about 1 km.
I don't understand how you get to 10 times more in orbit than on the ground. The solar intensity at 1 AU is 1.36 kW. On the ground it is about 1 kW, depending on where you are, the weather, etc.
A space based solar power station would have to be in a geostationary orbit. So the BFS would have to be refueled for getting the panels into a high enough orbit, since its payload to GEO is relatively small.
I don't understand how you get to 10 times more in orbit than on the ground. The solar intensity at 1 AU is 1.36 kW. On the ground it is about 1 kW, depending on where you are, the weather, etc. A space based solar power station would have to be in a geostationary orbit. So the BFS would have to be refueled for getting the panels into a high enough orbit, since its payload to GEO is relatively small.
My losses? None I think the original NASA / Glaser studies assumed a fairly high DC-DC efficiency of about 80%.This link https://www.allaboutcircuits.com/news/wireless-power-transmission-of-solar-energy-from-space/ suggests:QuoteThe solar arrays attached to a typical satellite generating 1.6GW in space and an average of 1GW on Earth would measure about 5 to 6 square kilometers and use a transmitting antenna array with a diameter of about 1 km. https://spectrum.ieee.org/green-tech/solar/how-japan-plans-to-build-an-orbital-solar-farmThis talks about >70% for DC to microwaves, and >80% for microwaves to DC. (Also interesting stuff about Japanese R&D on this area. Their missing ingredient might be cheap launch costs).Anything above 50% (DC to DC) is not a major issue if BFR is as cheap as Musk hopes.
I assume it's the weather, but 10* is too pessimistic.Neglecting spectral effects (some of the 1.36kW is not going to be useful) and assuming that's claiming 136W/m^2 average insolation to solar panels. Or put another way, 1191kWh/year.Multiplying by a possibly optimistic 20% loss, that comes out to 900kWh/m^2/year. 900kWh/m^2 is beaten even in most of Scotland.In my part of Scotland, fixed panels get 1240kWh/m^2/year, 2 axis trackers 1600.In more moderate climates (middle of France) it's around 1520kWh/m^2/1990.And in Arizona/north-Africa like climates, 2110/2960.In the best climates, with trackers, it's much closer to 3* than 10*.10* is only gotten in places where people basically don't live.
This cost, and neglecting conversion losses are precisely why Musk eschews space solar.This thread is moot given Musk's stated objections un-addressed by proponents. Why in a SpaceX thread?If space solar ever happens, which I doubt, it will be done via a lunar construction base. Bezos?It's an act of faith on my part bolstered by advances in powerful magnets containment et. al. but fusion power in the 2030s will finally kill the Rube Goldberg scheme of space solar and its ground rectennas.
Quote from: speedevil on 05/01/2018 02:11 pmI assume it's the weather, but 10* is too pessimistic.Neglecting spectral effects (some of the 1.36kW is not going to be useful) and assuming that's claiming 136W/m^2 average insolation to solar panels. Or put another way, 1191kWh/year.Multiplying by a possibly optimistic 20% loss, that comes out to 900kWh/m^2/year. 900kWh/m^2 is beaten even in most of Scotland.In my part of Scotland, fixed panels get 1240kWh/m^2/year, 2 axis trackers 1600.In more moderate climates (middle of France) it's around 1520kWh/m^2/1990.And in Arizona/north-Africa like climates, 2110/2960.In the best climates, with trackers, it's much closer to 3* than 10*.10* is only gotten in places where people basically don't live.That is what I thought as well. I have seen similar math exercises and there never was a factor of 10 improvement.
(This might be a topic for elsewhere, but SpaceX might be a game changer for this, to the annoyance of Musk) Certainly, space solar power has long been dismissed, primarily due to 1. High launch costs (the original idea killer - coupled with falling oil prices)2. A lack of space capability meaning we can't make the power sats from asteroids or lunar material.And here is what Musk said, a few year back:QuoteYou see, that's the point I'm making. Take any given solar cell: is it better to have on Earth or in orbit? What do you get from being in orbit? You get twice as much sun, best case. But you've got do do a conversion. You've got incoming photons that go to electrons, but you have to do two conversions you don't have to do on Earth. You've got to convert it to photons and then convert those photons back into electrons.And that double conversion is going to get you back to where you started basically! So why are you sending them to bloody space?And by the way, electron to photon converters are not free, nor is sending stuff to space. So then it obviously super-doesn't work.Case closed! You'd think case closed! But no, I guarantee it's gonna come up another ten times! I mean, for the love of god!Case closed? Now, I know questioning Musk is unwise these days, but could BFR prove him wrong?*snip*
You've completely ignored Elon Musk's point: conversion and transmission losses. That's the number one problem with beamed space based solar power.
In England, you will normally get 1000KWh per year per KW(peak) of capacity. In GEO, you will get 365 * 24 = 8,760KWh per year per KW(peak) of capacity.You will also get more KW(peak) per m2 in space. Maybe not 1.36 times, but certainly more than 1. So your solar cells will deliver at least 10 times the energy of solar cells in England. In the months of December and January, when the energy is most needed, they'll deliver about 40 to 60 times as much energy. Northern Europe or Japan would be the most likely target markets.
Quote from: whitelancer64 on 05/01/2018 03:08 pmYou've completely ignored Elon Musk's point: conversion and transmission losses. That's the number one problem with beamed space based solar power. I specifically covered it. Conversion and transmission losses are much smaller than capacity factor loss. Which is why Space Solar power was originally proposed and studied in the 1960s.
Quote from: alexterrell on 05/01/2018 03:18 pmQuote from: whitelancer64 on 05/01/2018 03:08 pmYou've completely ignored Elon Musk's point: conversion and transmission losses. That's the number one problem with beamed space based solar power. I specifically covered it. Conversion and transmission losses are much smaller than capacity factor loss. Which is why Space Solar power was originally proposed and studied in the 1960s.Power loss from conversion and transmission through the atmosphere is something like 60% That's hardly trivial, and it's the cornerstone of why beamed space-based space power is not going to happen anytime soon. It works out to be about as effecitve to have solar panels on the ground rather than in space, without spending the billions needed to send them there.That's the entire point Musk is making - and you do not address it at all.
Quote from: whitelancer64 on 05/01/2018 03:50 pmQuote from: alexterrell on 05/01/2018 03:18 pmQuote from: whitelancer64 on 05/01/2018 03:08 pmYou've completely ignored Elon Musk's point: conversion and transmission losses. That's the number one problem with beamed space based solar power. I specifically covered it. Conversion and transmission losses are much smaller than capacity factor loss. Which is why Space Solar power was originally proposed and studied in the 1960s.Power loss from conversion and transmission through the atmosphere is something like 60% That's hardly trivial, and it's the cornerstone of why beamed space-based space power is not going to happen anytime soon. It works out to be about as effecitve to have solar panels on the ground rather than in space, without spending the billions needed to send them there.That's the entire point Musk is making - and you do not address it at all.How do those calculations work out for Mars high latitude facilities and for equatorial facilities on the Moon?
Power loss from conversion and transmission through the atmosphere is something like 60% That's hardly trivial, and it's the cornerstone of why beamed space-based space power is not going to happen anytime soon. It works out to be about as effecitve to have solar panels on the ground rather than in space, without spending the billions needed to send them there.That's the entire point Musk is making - and you do not address it at all.
Quote from: aero on 05/01/2018 04:06 pmQuote from: whitelancer64 on 05/01/2018 03:50 pmQuote from: alexterrell on 05/01/2018 03:18 pmQuote from: whitelancer64 on 05/01/2018 03:08 pmYou've completely ignored Elon Musk's point: conversion and transmission losses. That's the number one problem with beamed space based solar power. I specifically covered it. Conversion and transmission losses are much smaller than capacity factor loss. Which is why Space Solar power was originally proposed and studied in the 1960s.Power loss from conversion and transmission through the atmosphere is something like 60% That's hardly trivial, and it's the cornerstone of why beamed space-based space power is not going to happen anytime soon. It works out to be about as effecitve to have solar panels on the ground rather than in space, without spending the billions needed to send them there.That's the entire point Musk is making - and you do not address it at all.How do those calculations work out for Mars high latitude facilities and for equatorial facilities on the Moon?Much better, since there's little atmosphere on Mars and none on the Moon. The problem with the Moon is there are no lunar-stationary orbits, they are unstable because that altitude is outside the Moon's hill sphere. So you'd need a series of solar arrays orbiting the Moon that beam power when in sight of the Lunar station. It makes more sense if you have a lot of locations on the Moon that could benefit from these arrays, but then that becomes a cart-horse issue.
Quote from: aero on 05/01/2018 04:06 pmQuote from: whitelancer64 on 05/01/2018 03:50 pmQuote from: alexterrell on 05/01/2018 03:18 pmQuote from: whitelancer64 on 05/01/2018 03:08 pmYou've completely ignored Elon Musk's point: conversion and transmission losses. That's the number one problem with beamed space based solar power. I specifically covered it. Conversion and transmission losses are much smaller than capacity factor loss. Which is why Space Solar power was originally proposed and studied in the 1960s.Power loss from conversion and transmission through the atmosphere is something like 60% That's hardly trivial, and it's the cornerstone of why beamed space-based space power is not going to happen anytime soon. It works out to be about as effecitve to have solar panels on the ground rather than in space, without spending the billions needed to send them there.That's the entire point Musk is making - and you do not address it at all.How do those calculations work out for Mars high latitude facilities and for equatorial facilities on the Moon?In both instances, you have a problem of scale. This only works from about 4GW upwards on Earth.Mars is better as a Aerostationary orbit is only about half as far as GEO, so you can scale down to 2GW.The moon is a bit harder as you'd have to go to L1 or L2, which is actually further - I think 60,000km. On the moon, and perhaps Mars, with no/less atmosphere, lasers might be worth looking at. You drop from a DC to DC efficiency of about 60% (for microwaves) to perhaps 20% (for monochromatic lasers and PV cells), but minimum size would be MW rather than GW.
I'm not an electrical engineer and so am out of my depth when discussing antenna dimensions, but is there any way to use a smaller antenna? How does antenna diameter relate to electrical power, and to distance, and the size of the receiving rectenna?
On Earth, solar panels can be localized, as in individual buildings and home. You don't need a huge antenna in an isolated desert somewhere.
We need long term green solution to power generation. Fusion and SSP are only ones that can generate huge amounts of power need in the next few decades. Neither is proven, fusion is still an unknown, SSP is technically feasible, but needs lot more work and flying demo.Economically SSP is not viable if everything needs to be lifted from earth to GEO. Needs in space manufacturing, assembly and ISRU for both construction materials and fuel to reduce LEO to GEO transport costs. Ideally bulk mass is ISRU with high tech equipment coming from earth.
Quote from: Elmar Moelzer on 05/01/2018 01:42 pmI don't understand how you get to 10 times more in orbit than on the ground. The solar intensity at 1 AU is 1.36 kW. On the ground it is about 1 kW, depending on where you are, the weather, etc. Because capacity factors for fixed solar on the ground are between about 0.1 (Germany, England) and 0.2 (Atacama desert). ...
Two things....1. I am enjoying reading this thread. It's nice to have the issues/math laid out.2. Would this not be better in the Advanced Concepts section since, except for Musk's quote and the fact that BFS might be the only ship to pull it off if deemed economical, has nothing to really do with SpaceX?Thanks for the read so far!
Apologies to the OP, but IMO spaced based power will never make sense. Even if you could transport it to space for free. 1. The size of a 6GW (the OP's choice) array will be approx (assume 20% cell efficiency, so 272 watts/meter sq) > 22 million sq meters or roughly 8.5 sq miles. Or to make my point about the size, it's about 4000 football fields.2. What structure supports that monster array to keep it rigid?3. How do you keep the array pointed at the sun, without twisting and warping it? Does it use fuel? How long does the fuel last? Seems like you'd need hundreds of thrusters. What if one of them sticks on?4. How do you feed all that power to a microwave transmitter, which must be pointed in a constantly moving and different direction from the array? Even if you can use a phased array antenna, it's still a massive thing!5. How do you repair it when it gets hit by micrometeorites or simply fails?6. How do you protect it from a large solar flare?7. And, if we want a 20 year life, don't the panels need to be made from gallium arsenide? I recall silicon panels degrade rapidly in space.Even if you build smaller arrays it is still a space based construction task of a size that would dwarf all other space based projects ever done. Remember all the issues the ISS has had with their arrays? And that is tiny by comparison.On Earth, construction is easy. It doesn't require men in space suits or advanced robotics (that don't yet exist). Look how fast the array (admittedly small) in Boca Chica was installed by basic electricians in an unprepared field. On Earth, if a panel or system fails, some technician in a rusty Ford F150 wearing a t-shirt and jeans fixes the problem in 30 minutes. On Earth, solar panels can be localized, as in individual buildings and home. You don't need a huge antenna in an isolated desert somewhere.Just my 2 cents.
Quote from: alexterrell on 05/01/2018 02:00 pmQuote from: Elmar Moelzer on 05/01/2018 01:42 pmI don't understand how you get to 10 times more in orbit than on the ground. The solar intensity at 1 AU is 1.36 kW. On the ground it is about 1 kW, depending on where you are, the weather, etc. Because capacity factors for fixed solar on the ground are between about 0.1 (Germany, England) and 0.2 (Atacama desert). ...Wrong. The American Southwest has statewide<[ capacity factors of about 26%. Parts of Chile are even higher.Using Germany as an example is a red herring. It’s a terrible place for solar power. The vast majority of the world’s population and surface area gets vastly more sunlight.
I suspect Elon and SpaceX's attitude to a space-based solar-power satellite will be that they're not going to build one but if someone else wants to do so then they'll sell them the transportation to get their equipment into space - payable on delivery!Quote from: rickyramjet on 05/01/2018 07:37 pmOn Earth, solar panels can be localized, as in individual buildings and home. You don't need a huge antenna in an isolated desert somewhere.The receiving antenna will effectively be a power station embedded in a local or wider grid and therefore there will be distribution losses; with solar cells on the roofs of houses or factories etc, not so much.The advantage of consistent 24-hr supply can be overstated as there is not consistent 24-hr demand for electricity; night-time demand is a lot lower than daytime. Also, there are other sources of electricity at night (wind and hydro being the obvious renewable ones). Both factors lower the amount of storage needed. One should also note that daytime electricity is worth more than night-time!But it would be interesting to see a financial calculation. One would surmise that the first solar power satellite will be regarded as a riskier investment than ground-based solar, which is well understood. The rewards need to be commensurate!
Quote from: LM13 on 05/01/2018 02:31 pmI'm not an electrical engineer and so am out of my depth when discussing antenna dimensions, but is there any way to use a smaller antenna? How does antenna diameter relate to electrical power, and to distance, and the size of the receiving rectenna? The microwave antenna and rectenna are large for safety reasons. Sure they can be smaller, but the environmental impact study will be unkind if the power transmission system cooks birds as soon as the fly into the beam. Also has the nasty potential as a weapon system.
Solar might be useful in the tropics, but will always be a marginal player in northern latitudes, which is why Europe is actually a better example. Europe will need nuclear fission, nuclear fusion, or space solar power.
Quote from: RonM on 05/01/2018 08:33 pmQuote from: LM13 on 05/01/2018 02:31 pmI'm not an electrical engineer and so am out of my depth when discussing antenna dimensions, but is there any way to use a smaller antenna? How does antenna diameter relate to electrical power, and to distance, and the size of the receiving rectenna? The microwave antenna and rectenna are large for safety reasons. Sure they can be smaller, but the environmental impact study will be unkind if the power transmission system cooks birds as soon as the fly into the beam. Also has the nasty potential as a weapon system.Not quite. You can make the Earth receiver smaller (for a given transmission frequency) only by making the space transmitter bigger. That would then concentrate the microwaves to a higher density. I would suggest a legal maximum size of transmitter and power, which would physically limit the beam intensity. (Probably to 1KW/m2).That way, the only way a SF writer can conjure up death rays, would be by taking over multiple Solar Power Sats and pointing them all at the White House at the same time. (In which case, the President would need to shelter under some aluminium foil).
That's an awful lot of expense to get surface power equal to what the sun delivers for free.
The question for efficiency and cost effectiveness is one thing. But there are other questions..Maybe the most serious question with solar power is.. what do you do with all the grilled birds that fly through the beam?
Quote from: Semmel on 05/02/2018 07:51 pmThe question for efficiency and cost effectiveness is one thing. But there are other questions..Maybe the most serious question with solar power is.. what do you do with all the grilled birds that fly through the beam? Some of these can be mitigated by design choices.If your space power sat is at GEO, and has its antenna and solar panels the same size, if it is under xGW, for a given frequency, the power onto earth can't exceed 1kW/m^2 or whatever limit you think appropriate.More involved schemes are possible.
Al‐Asad (Iraq) includes 20,000 people living on 18 square miles, with an internal bus system, 48 1megawatt (MW) generators, 32 MW of continuous power demand, 1.1m gallons of water/day demand,1.2m gallons of water/day supply, 9 water wells, Reverse Osmosis Water Purification Unit (ROWPU),water treatment facilities treating 60 gallons/person/day, 6,771 facilities, and 193 spot generators...A 600 soldier FOB requires a convoy of 22 trucks per day to supply the base with fuel or waterand to truck away wastewater and solid waste...As of November 2007, 80 convoys were continuouslytraveling between Kuwait and Iraq (with 70% transporting fuel or water), exposing a critical vulnerabilityto Improvised Explosive Devices (IEDs) as they transported supplies from surrounding nations....FOB Planning Factors:500 man base camp -- 182 kW1,500 man " " -- 486 KW3,000 man " " -- 988 KW10,000 man " " -- 3,293 KW...The USMC Energy Assessment team calculated the contractor delivered fuel to CampLeatherneck in Afghanistan at $6.39 per gallon, and $11.70 per gallon to deliver the fuel to the tacticaledge (FOB Dwyer, 50 kilometers from Camp Leatherneck).148 An earlier estimate puts FY 02 standardDESC fuel price at $1.34 per gallon, a “true cost” of USAF tanker‐delivered fuel at $17.50 per gallon, and“hundreds of dollars per gallon for Army forces deep in the battlespace.”
You can sell power on a constant basis greatly reducing the need to ship a lot of mass of batteries too.You can plan independently of settlement details. A power sat can sell power to most locations on Mars surface. You just have to bet there will be a market for your power to start designing and building power sats.If there are unexpected finds and people want to set up new outposts to exploit them, you’re ready to sell them power.On the surface, PV would require more upkeep because of sand and dust than rectennas. PV is easier to deploy and fully automate in space.
Originally I wanted to address Musk's erroneous statements and ask whether BFR could enable Space Solar Power, rather than discuss the merits of Space Solar Power.
Quote from: AncientU on 05/02/2018 01:19 pmThat's an awful lot of expense to get surface power equal to what the sun delivers for free.It's a lot more than the sun delivers for free. In northern Europe...
Attached is a NASA study titled "Satellite Power Systems (SPS) Concept Definition Study" done by Rockwell in 1980.Page 14 states "power output must be decreased to satisfy the 23 mW/cm2 (0.23 kW/m2) RF energy constraint in the atmosphere to avoid potential microwave interference with the D and F layers of the atmosphere." Seems to be an issue with microwave power transmission through the ionosphere.
The main effect of the D region is to attenuate signals that pass through it, although the level of attenuation decreases with increasing frequency.
Northern Europe has about 30-50% of the world's demand for clean energy. Partly as a result, electricity is about double the price compared to the USA.
Quote from: RonM on 05/02/2018 09:16 pmAttached is a NASA study titled "Satellite Power Systems (SPS) Concept Definition Study" done by Rockwell in 1980.Page 14 states "power output must be decreased to satisfy the 23 mW/cm2 (0.23 kW/m2) RF energy constraint in the atmosphere to avoid potential microwave interference with the D and F layers of the atmosphere." Seems to be an issue with microwave power transmission through the ionosphere.Good study. It shows the system was feasible, with problems, with 1980s technology. It would be nice to update it to current tech.Regarding the atmosphere:http://www.radio-electronics.com/info/propagation/common/atmosphere.phpIt seems that a high density of radiation will ionise particles, which then block radio waves. However, this can't be the whole story because most radiation is coming from the sun (1.3KW/m2), so why would a weaker microwave signal make this worse?It does say:QuoteThe main effect of the D region is to attenuate signals that pass through it, although the level of attenuation decreases with increasing frequency.So it might be better to go to >5GHz signal. That reduces the transmitter size, which increases the heat problems.The efficiency chain was interestinghttp://prntscr.com/jd69buand they reckoned 30,000 tons: http://prntscr.com/jd69zlEven with BFR prices, that mass would need to come down a lot.
Quote from: alexterrell on 05/03/2018 10:55 amNorthern Europe has about 30-50% of the world's demand for clean energy. Partly as a result, electricity is about double the price compared to the USA.The world is growing, by the end of this century demand for energy is likely to be roughly proportional to population, making northern Europe niche. And the US has cleaner energy than much of Europe, such as Germany, but much lower prices (because Germany has particularly non-optimal clean energy policy combined with low sun).Again, Northern Europe is not an appropriate benchmark for global clean energy. And is a bad target for space solar power as well due to the high latitude.
Take any given solar cell: is it better to have on Earth or in orbit? What do you get from being in orbit? You get twice as much sun, best case.
At some point, the whole world should aim for European levels of power consumption.
Added:NOTE - For those worried about getting cooked the .23W/cm^2 is less than that produced by your cellphone of 1W/cm^2 next to your head.
Quote from: alexterrell on 05/03/2018 10:55 amNorthern Europe has about 30-50% of the world's demand for clean energy. Partly as a result, electricity is about double the price compared to the USA.The world is growing, by the end of this century demand for energy is likely to be roughly proportional to population, making northern Europe niche.
Quote from: Robotbeat on 05/01/2018 11:59 pmQuote from: alexterrell on 05/01/2018 02:00 pmQuote from: Elmar Moelzer on 05/01/2018 01:42 pmI don't understand how you get to 10 times more in orbit than on the ground. The solar intensity at 1 AU is 1.36 kW. On the ground it is about 1 kW, depending on where you are, the weather, etc. Because capacity factors for fixed solar on the ground are between about 0.1 (Germany, England) and 0.2 (Atacama desert). ...Wrong. The American Southwest has statewide<[ capacity factors of about 26%. Parts of Chile are even higher.Using Germany as an example is a red herring. It’s a terrible place for solar power. The vast majority of the world’s population and surface area gets vastly more sunlight.A capacity factor of 26% would mean 8.1 kWh/sq-m per day by my math (1.3*24*.26).This map shows that New Mexico is generally pretty close to that level but slightly shy:https://www.nrel.gov/gis/images/state-level-resource-maps/dni/New-Mexico-DNI-2017-01.jpg...
...Latitude is not problem. It just means elongating the receiver a bit. ...
It is a matter of economics. The rates the following document shows the actual comparison of various plat types and the costs of delivered power. Solar is marginally competitive with other conventional plant types. It is this competitive space that SSPS has to beat not just ground solar.https://www.eia.gov/outlooks/aeo/pdf/electricity_generation.pdfSolar is estimated to be competitive in the future with conventional due to rising environmental costs for new and older fossil fuel plants. Again SSPS will be built if it can compete economically in this space.
Understated forecasts are driven by overestimated costs. For example, the EIA recently estimated solar would cost $2,480 per kW in 2017. In fact, the Solar Energy Industries Association (SEIA) reports utility solar costs had already fallen to around $1,200/kilowatt (kW) last year.
Quote from: alexterrell on 05/03/2018 04:21 pm...Latitude is not problem. It just means elongating the receiver a bit. ......by the same argument, just install more solar panels.
Quote from: Robotbeat on 05/05/2018 04:45 amQuote from: alexterrell on 05/03/2018 04:21 pm...Latitude is not problem. It just means elongating the receiver a bit. ......by the same argument, just install more solar panels.Are you sure that's fair? I haven't thought through the physics carefully, but my gut says the elements of a tilted rectenna would need to be spaced further apart to accommodate the off-perpendicular beam, but that no more rectennas would be needed. This is in contrast to solar panels placed flat on the ground, whose total area would need to increase to let them cover the same projected area as seen from the Sun. But it's analogous to solar panels which can be individually tilted to face the Sun (but which would then have to be spread out to avoid shadowing each other).Kinda subtle.
Quote from: Exastro on 05/06/2018 09:05 pmQuote from: Robotbeat on 05/05/2018 04:45 amQuote from: alexterrell on 05/03/2018 04:21 pm...Latitude is not problem. It just means elongating the receiver a bit. ......by the same argument, just install more solar panels.Are you sure that's fair? I haven't thought through the physics carefully, but my gut says the elements of a tilted rectenna would need to be spaced further apart to accommodate the off-perpendicular beam, but that no more rectennas would be needed. This is in contrast to solar panels placed flat on the ground, whose total area would need to increase to let them cover the same projected area as seen from the Sun. But it's analogous to solar panels which can be individually tilted to face the Sun (but which would then have to be spread out to avoid shadowing each other).Kinda subtle.In both case you can tilt them to have about the same collection, just spread out. Solar is beamed fusion from the Sun, and the photovoltaic array is merely the receiver.
Here is a economic model equation to determine if a SSPS will be competitive. F - capacity factor increase of same weight in-orbit system over that of ground PV system at same location.C - cost of ground PV system/kg (there is likely some trade offs here for in-orbit but the average costs is likely to be a he same or very close)L - cost of launch $/kg(L+ C)/F <= CIf this is true then SSPS is competitive.Added:Or put another way. L<=(F-1)*CExample:If C is $10/kgAnd F is 5Then L would have to be <= to $40/kg for an SSPS to be competitive.
So the difference (as I understand it) is that the rectenna elements don't have to be tilted, just spread further apart. That should reduce the cost of accommodating a non-perpendicular beam relative to solar panels.
One of the most believable current proposals for bringing solar energy on a large scale to Europe is by connecting mega-grids to the MENAT (Middle East, North Africa, and Turkey) region, where huge amounts of investment and technology development are going into solar farms. Given that this is the current direction that green energy in Europe is likely to take, the question for the BFR providing us with space solar power, is can it make SSP cheaper than connecting our grids across to Morocco and Arabia?It's not really competing with large scale solar power on the ground in Europe, as at that point it's better to use large solar farms further South than to build them in our rainy lands.
The BFR has its own solar arrays for use in space. Could these be utilized on the surface of Mars? Or would they just collapse under gravity? Given the premium on cargo weight it would seem sensible to make full use of these panels if at all possible.
Quote from: Slarty1080 on 05/07/2018 12:01 pmThe BFR has its own solar arrays for use in space. Could these be utilized on the surface of Mars? Or would they just collapse under gravity? Given the premium on cargo weight it would seem sensible to make full use of these panels if at all possible.In principle, the arrays shown can be used on the surface, if they can either support their weight directly, or with the use of additional guy wires.As one sketch, if we assume there is a lifting hook fixture of some form at the top of the vehicle (perhaps not at the nose) , simply stringing an equilateral triangle of wire from that down to two anchor points on the ground, and adding two attach points for the inboard sides of the panels may let the panels lie in front of the wings in a usable attitude.It may make more sense to detach them.It is unclear if the solar panel design is more than notional.The panels shown are about 12m in radius, covering around two thirds of a circle, or 70m^2.At 25% efficiency, they produce around 20kW near earth.Landed on Mars, they produce around half a percent of the power needed for ISRU - it's not worth optimising very much for reusing them, though they could obviously be useful for short-term power.
Quote from: speedevil on 05/08/2018 10:37 amQuote from: Slarty1080 on 05/07/2018 12:01 pmThe BFR has its own solar arrays for use in space. Could these be utilized on the surface of Mars? Or would they just collapse under gravity? Given the premium on cargo weight it would seem sensible to make full use of these panels if at all possible.In principle, the arrays shown can be used on the surface, if they can either support their weight directly, or with the use of additional guy wires.As one sketch, if we assume there is a lifting hook fixture of some form at the top of the vehicle (perhaps not at the nose) , simply stringing an equilateral triangle of wire from that down to two anchor points on the ground, and adding two attach points for the inboard sides of the panels may let the panels lie in front of the wings in a usable attitude.It may make more sense to detach them.It is unclear if the solar panel design is more than notional.The panels shown are about 12m in radius, covering around two thirds of a circle, or 70m^2.At 25% efficiency, they produce around 20kW near earth.Landed on Mars, they produce around half a percent of the power needed for ISRU - it's not worth optimising very much for reusing them, though they could obviously be useful for short-term power.Perhaps ITS onboard solar arrays are no longer needed on the martian surface, as of 2018. Quantum dot solar cells presently have an exceptional rating of 15.2 kW/kg. While too fragile for use as ITS solar arrays, they could serve well on the martian surface, e.g., for scaled ISRU.One ITS payload of quantum dot PV panels could provide max power of ~ 1 GW on Mars. What do you think? Now that we're measuring martian PV performance in terms of "GW per payload", have we moved beyond the concern with ITS onboard solar array performance on Mars?--Dust devils would pose a real threat to these fragile quantum dot PV panels. How to protect? You could always add protective layers of course. But perhaps "canopy deployment" would provide sufficient protection itself, without addition of more layers. If panels were deployed overhead, using some tent-pole system, the panels would be positioned above the altitude of the dust devil's abrasive sand saltation region (<1 m altitude). Only fine dust would impact the panels. Conceptually:Practical energy storage remains a challenge, of course. How to store the midday peak PV terajoules through the night, or through dim winter months?
Perhaps ITS onboard solar arrays are no longer needed on the martian surface, as of 2018. Quantum dot solar cells presently have an exceptional rating of 15.2 kW/kg. While too fragile for use as ITS solar arrays, they could serve well on the martian surface, e.g., for scaled ISRU.
Herein, we report an extremely lightweight and ultra-flexible CQD solar cell constructed on a polyethylene naphthalate substrate with a thickness of 1.3 μm.
A full 150mt payload with a system using such cells considering you are on Mars not Earth, structures, wiring/cables, and power conditioning with batteries the continuous output would be ~ 60MW.
Quote from: LMT on 05/16/2018 05:32 pmPerhaps ITS onboard solar arrays are no longer needed on the martian surface, as of 2018. Quantum dot solar cells presently have an exceptional rating of 15.2 kW/kg. While too fragile for use as ITS solar arrays, they could serve well on the martian surface, e.g., for scaled ISRU.These are far, far, far too fragile for use on the Martian surface
? Polyethylene naphthalate is a high-performance material: a common IC substrate, a tough fiber. The solar cells are reported having "durable mechanical properties" suitable for use on satellites, for example. Probably not suitable for the rigors of ITS adventures, but ok in space, generally.As for Mars, if you eliminate the sand saltation problem by elevating the panels, what's the remaining hazard that renders the panels "far, far, far too fragile" to just... sit there?
The windloads from martian winds may be approximately equal to 10m/s or so on earth, in storms, but even in more modest winds, this can excite flapping, which will destroy the film, as you can't guy it tight enough.
Quote from: oldAtlas_Eguy on 05/16/2018 06:24 pmPerhaps ITS onboard solar arrays are no longer needed on the martian surface, as of 2018. Quantum dot solar cells presently have an exceptional rating of 15.2 kW/kg. While too fragile for use as ITS solar arrays, they could serve well on the martian surface, e.g., for scaled ISRU.My original premise was that the economic challenges of Space Solar Power could be overcome by:1. Falling launch costs with BFR2. Falling mass requirements thanks to better solar cells and better structures.15KW/kg is ridiculously light. That is only about 500 tons of cells for an 8GW system, delivering 4GW to Earth.The lighter the cells, the lighter the supporting structures need to be - at least till dealing with solar wind becomes an issue. We're probably still talking 5,000 to 10,000 tons for mass to orbit, which, with BFR, is quite affordable.
If you put the solar arrays that low you lose the one big advantage that space solar has over ground based solar. It is shaded during the night.
Quote from: guckyfan on 06/05/2018 06:42 amIf you put the solar arrays that low you lose the one big advantage that space solar has over ground based solar. It is shaded during the night.Which is an even bigger problem - still - in northern latitude winters. Since it seems the power density of the Earth based rectenna is limiting factor, I'm not sure being so close to Earth is a major advantage at large scale.
Quote from: guckyfan on 06/05/2018 06:42 amIf you put the solar arrays that low you lose the one big advantage that space solar has over ground based solar. It is shaded during the night.No, there are many LEO SSP designs.
these sats would be in shadow half of the time, cutting their productivity by half.
If space solar has any advantage, it is providing power during the night.
Since it seems the power density of the Earth based rectenna is limiting factor, I'm not sure being so close to Earth is a major advantage at large scale.
Back on Earth, the [quantum dot panel's] 15KW/kg makes little difference. It still needs to be protected from hail and sand and pigeon muck, and the water jet used to clean the muck.
Quote from: alexterrell on 06/05/2018 11:32 amSince it seems the power density of the Earth based rectenna is limiting factor, I'm not sure being so close to Earth is a major advantage at large scale.?You understand that for any given rectenna, a 250-km orbit cuts the matching SSP system mass by ~ 10,000x, relative to geosync SSP mass, yes?Example:A rectenna set is matched with a single-launch, 150-ton SSP system that's piggybacked on the Terrestation @250.The equivalent geosync SSP hardware would mass 1,500,000 tons, plus all additional structure, for a total of perhaps 3,000,000 tons.SSP cargo mass saved @250 Terrestation: 2,999,850 tons.A major advantage.
Quote from: alexterrell on 06/05/2018 11:32 amQuote from: guckyfan on 06/05/2018 06:42 amIf you put the solar arrays that low you lose the one big advantage that space solar has over ground based solar. It is shaded during the night.Which is an even bigger problem - still - in northern latitude winters. Since it seems the power density of the Earth based rectenna is limiting factor, I'm not sure being so close to Earth is a major advantage at large scale.Im a fan of removing those limits and just making it a no-fly zone.
So do you think a multi-GW quantum dot PV farm is practicable on Mars?
Quote from: LMT on 06/06/2018 01:59 amSo do you think a multi-GW quantum dot PV farm is practicable on Mars?Try and lay out 50 square kilometres of cling film in the Atacama desert, and then we can assess whether this can be done on Mars. You will end up building a glass factory and sandwiching the cells between sheets of glass.
No, it cuts the rectenna mass by about 10,000 times.
lots of questions of station keeping (flying a parachute in the Thermoshpere)
Quote from: alexterrell on 06/06/2018 07:36 amNo, it cuts the rectenna mass by about 10,000 times. Here rectenna mass is fixed, hence "given". I was comparing the required SSP orbiting mass at the two distances, for a given rectenna's given power output. Focus first on that specific comparison. It's "the money", to first approximation.Quote from: alexterrell on 06/06/2018 07:36 amlots of questions of station keeping (flying a parachute in the Thermoshpere)I introduced ISEP into forum, in another thread. If you see big issues in the ISEP literature, or in the particular application, note them. OT here.
The difference in efficiencies of a Leo to geo system is that the rectenna output is 80% of SSP input transmitter power and the geo is 50%... Remember the transmitter antennas are phased arrays of greater than 1km in size.
Quote from: alexterrell on 06/06/2018 07:50 amQuote from: LMT on 06/06/2018 01:59 amSo do you think a multi-GW quantum dot PV farm is practicable on Mars?Try and lay out 50 square kilometres of cling film in the Atacama desert, and then we can assess whether this can be done on Mars. You will end up building a glass factory and sandwiching the cells between sheets of glass.? Why would you want a glass factory for martian panel deployment as below? Quantum dot solar cells were designed for use in space without glass or other high-mass layers, intentionally.
Designed for space. Mars surface is not the same as space. Whilst it's not as presented in "The Martian" you will still not be able to place materials as thin as a quantum dot array. Even deployment will probably be impossible.
Quote from: LMT on 06/06/2018 11:27 am? Why would you want a glass factory for martian panel deployment as below? Quantum dot solar cells were designed for use in space without glass or other high-mass layers, intentionally.Designed for space. Mars surface is not the same as space. Whilst it's not as presented in "The Martian" you will still not be able to place materials as thin as a quantum dot array. Even deployment will probably be impossible.
? Why would you want a glass factory for martian panel deployment as below? Quantum dot solar cells were designed for use in space without glass or other high-mass layers, intentionally.
Maybe it needs to be laminated on a 50 micrometer mylar sheet.
You might also consider Gorilla Glass...Perhaps aluminium foil backing and plastic over coating?
As for aluminum foil, "plastic over coating", Mylar and the like... the record-setting QD solar cells were produced on PEN because it's mechanically better than those other films. Hence the record, hooray. You're petitioning for materials with lower tensile strength.
Quote from: LMT on 06/10/2018 01:29 pmAs for aluminum foil, "plastic over coating", Mylar and the like... the record-setting QD solar cells were produced on PEN because it's mechanically better than those other films. Hence the record, hooray. You're petitioning for materials with lower tensile strength. It is not one hundred times better.Thickness matters.Plus, you can't strain it anywhere close to its yield without damaging the cells adhered to it.
Quote from: guckyfan on 06/08/2018 06:28 pmMaybe it needs to be laminated on a 50 micrometer mylar sheet.Quote from: alexterrell on 06/10/2018 09:01 amYou might also consider Gorilla Glass...Perhaps aluminium foil backing and plastic over coating?So as you see, QD solar cells don't require glass, Gorilla or other. Multiple industrial examples make that clear enough.As for aluminum foil, "plastic over coating", Mylar and the like... the record-setting QD solar cells were produced on PEN because it's mechanically better than those other films. Hence the record, hooray. You're petitioning for materials with lower tensile strength.
Quote from: LMT on 06/10/2018 01:29 pmQuote from: guckyfan on 06/08/2018 06:28 pmMaybe it needs to be laminated on a 50 micrometer mylar sheet.Quote from: alexterrell on 06/10/2018 09:01 amYou might also consider Gorilla Glass...Perhaps aluminium foil backing and plastic over coating?So as you see, QD solar cells don't require glass, Gorilla or other. Multiple industrial examples make that clear enough.As for aluminum foil, "plastic over coating", Mylar and the like... the record-setting QD solar cells were produced on PEN because it's mechanically better than those other films. Hence the record, hooray. You're petitioning for materials with lower tensile strength. Cost is more important though. Aluminium and/or glass made on Mars might well be cheaper than mylar type films imported from Earth. But in space, you'd probably have nothing, with the solar film spread over carbon fibre trusses.
SOLAR ENERGY- no carbon emissions, unlimited supply and available to all. This renewable source is one of the answers to energy independence, but has been previously expensive to implement. Now, with advanced automated tetrapod quantum dot manufacturing, both cost and efficiency concerns are addressed. Although smaller than living cells, quantum.dots can absorb all wavelengths of visible sunlight plus the UV and Infrared. Using proprietary technologies, Solterra will manufacture very low cost solar cells utilizing Quantum Dot Technology for less than the cost of conventional solar cells. By combining Quantum Materials disruptive technologies of novel synthesis, QDX™ coating and automated production, quantum dot supply problems are solved. Solterra will also use R2R production methods invented by QMC Chief Science Officer, Dr. Ghassan Jabbour, that can be scaled by increasing R2R speeds.Our third generation quantum dot solar cells do not require custom made, expensive ,nor complex, processing equipment, and we do not use costly silicon or rare earth elements such as indium. Solterra instead will rely on low-cost screen printing and/or inkjet techniques applied to inexpensive substrates. Quantum Dot Solar Cells have extremely high potential efficiency, having demonstrated the production of multiple excitons from a single electron.Quantum Materials patented quantum dot synthesis, developed by Dr. Michael Wong of Rice University has been acquired by Quantum Materials for Solterra Renewable Technologies, Inc. By combining this proprietary, low cost QD manufacture process with automation QD manufacture, the quantities of tetrapod quantum dots needed to supply the daily use requirements of a solar cell plant production can be scaled into the Gigawatts/year range reducing the cost of solar generated electricity to little more than grid price at today's electricity prices. With grid prices expected to continue to increase, renewable solar energy using QMC Quantum Dot Technology will not only cost less but can also be good for the environment!Quantum Materials' Solar cells will come to market competitively priced with the opportunity to reduce prices even further as economies of scale come into effect. Additionally we believe our quantum dot manufacturing capability and print based cell manufacturing process will enable the rapid deployment of additional manufacturing sites across the globe.
Cost is more important though. Aluminium and/or glass made on Mars might well be cheaper than mylar type films imported from Earth.
https://www.youtube.com/watch?time_continue=72&v=_J4RxDZJ6Vg
Quote from: oiorionsbelt on 06/10/2018 04:16 pmhttps://www.youtube.com/watch?time_continue=72&v=_J4RxDZJ6VgI've never heard that one before.Musk was asked about solar, and seems very far from certain or enthusiastic. He describes one concept they evaluated, brings up nuclear, and says solar is "very important", as opposed to using any stronger description like "is the way to produce power on Mars".Hmmm.-----ABCD: Always Be Counting Down
One option for small improvement: add duplicate PV power plants up to 2000 km east and west of the SpaceX facility, and up to 2000 km toward the equator. Each plant is connected to the grid via thin, low-temperature HVDC power lines, which have high efficiency to that distance.
Doesn't Opportunity's situation put paid to the notion of using solar as the power source for a settlement?
If dust storms can radically reduce insolation for weeks at a time, wouldn't that seriously endanger a base?
Are there practical back-up systems/energy storage solutions that could cover that amount of time with severely reduced PV output?
even during major dust storms solar would yield at least 20% of normal values which would be enough by far to keep essential services running.
"After the last of these images were taken, Opportunity was forced to halt imaging -- and most other operations, including regular communication with Earth -- to conserve its battery power and ride out the storm."
And even harder than you indicated. The 2007 dust storm reduced light transmission by more than 95% for a period of ~ 3 weeks above Spirit, and ~ 4 weeks above Opportunity. Shutdown. Lemmon et al. 2015, Fig. 8.At a SpaceX facility "essential services" would be more than just a system clock. Propellant plant services, for example, and unavoidably. Earth-return launch windows must be honored, irrespective of weather or season. Winter storms occur: power systems must have scale and redundancy to accommodate.
Quote from: LMT on 06/14/2018 05:00 pmAnd even harder than you indicated. The 2007 dust storm reduced light transmission by more than 95% for a period of ~ 3 weeks above Spirit, and ~ 4 weeks above Opportunity. Shutdown. Lemmon et al. 2015, Fig. 8.At a SpaceX facility "essential services" would be more than just a system clock. Propellant plant services, for example, and unavoidably. Earth-return launch windows must be honored, irrespective of weather or season. Winter storms occur: power systems must have scale and redundancy to accommodate.PV power output is not entirely linear with direct optical transmission, since there is indirect light transmission.And propellant production absolutely DOES NOT have to continue during a dust storm. That's absurd. Just size the system assuming some weeks are lost to a storm, that is only a few percent of the time between synods.
xQuote from: envy887 on 06/14/2018 06:35 pmQuote from: LMT on 06/14/2018 05:00 pmAnd even harder than you indicated. The 2007 dust storm reduced light transmission by more than 95% for a period of ~ 3 weeks above Spirit, and ~ 4 weeks above Opportunity. Shutdown. Lemmon et al. 2015, Fig. 8.At a SpaceX facility "essential services" would be more than just a system clock. Propellant plant services, for example, and unavoidably. Earth-return launch windows must be honored, irrespective of weather or season. Winter storms occur: power systems must have scale and redundancy to accommodate.PV power output is not entirely linear with direct optical transmission, since there is indirect light transmission.And propellant production absolutely DOES NOT have to continue during a dust storm. That's absurd. Just size the system assuming some weeks are lost to a storm, that is only a few percent of the time between synods.When the atmosphere transmits < 5%, nonlinear response and indirect lighting aren't helpful.You realize those 4 weeks were just the peak of the storm, yes? The storm ran for 2 months. In martian winter, off-equator PV would be essentially disabled for the entirety of the storm. Imagine 5 months of winter in Hellas Basin, with daily clear-sky PV averaging 10% of summer max. Then intersperse 3 months of storms, all causing near-complete PV shutdown for the duration.Quantifying: What challenge does that scenario present to winter propellant production for, say, 10 spacecraft? How might you structure and scale things to accomplish the loading?
Quote from: LMT on 06/14/2018 07:30 pmQuantifying: What challenge does that scenario present to winter propellant production for, say, 10 spacecraft? How might you structure and scale things to accomplish the loading?Hellas at mostly 40+ degrees south is probably further than you want to go with solar as primary, and more equatorial locations are better initially. But even there, just make it bigger, and do propellant production mainly in the summer.
Quantifying: What challenge does that scenario present to winter propellant production for, say, 10 spacecraft? How might you structure and scale things to accomplish the loading?
As part of the study, we are looking at the leading three SBSP concepts, from the USA (SPS Alpha), UK (CASSIOPeiA) and China (MR-SPS). SBSP experts John Mankins (USA) and Ian Cash (UK) – the inventors of the first two concepts – are supporting our study.
Not sure if this has been covered, but this thread seems a good place for it:https://www.fnc.co.uk/discover-frazer-nash/news/frazer-nash-exploring-viability-of-space-based-solar-power-to-help-deliver-net-zeroThe UK Government is looking for risky ventures, perhaps to try and compensate for the Brexit damage. They have now commissioned a study into Space Solar Power.This is relevant to SpaceX because if the cost of launching a solar power station is less than the cost of building the solar arrays, then it might be possible to make a business case for it. Launch cost = System Weight x Cost per unit massQuoteAs part of the study, we are looking at the leading three SBSP concepts, from the USA (SPS Alpha), UK (CASSIOPeiA) and China (MR-SPS). SBSP experts John Mankins (USA) and Ian Cash (UK) – the inventors of the first two concepts – are supporting our study.
I can't help but feel the idea will run aground somewhere on the rocks of transmission loss,
continually dropping solar panel prices
and the technical uncertainties around massive solar arrays in orbit. But we shall see. It's a neat idea but I question the practicality / economics of it.
Would it be possible to harvest static electricity generated during dust storms to offset solar loss?
Quote from: Slarty1080 on 11/21/2020 01:35 pmI can't help but feel the idea will run aground somewhere on the rocks of transmission loss, JPL found ways to phase lock cavity magetrons (something that was not believed to be possible) to make low cost high power phased array transmitters in the 1970's. Quote from: Slarty1080continually dropping solar panel prices Which only work during the day. Above 800Km daylight is 24 hours long. At GEO there would be no pointer shifting but much higher losses. Quote from: Slarty1080and the technical uncertainties around massive solar arrays in orbit. But we shall see. It's a neat idea but I question the practicality / economics of it.And yet somehow the ISS stays in orbit.
Quote from: alexterrell on 11/18/2020 07:28 amNot sure if this has been covered, but this thread seems a good place for it:https://www.fnc.co.uk/discover-frazer-nash/news/frazer-nash-exploring-viability-of-space-based-solar-power-to-help-deliver-net-zeroThe UK Government is looking for risky ventures, perhaps to try and compensate for the Brexit damage. They have now commissioned a study into Space Solar Power.This is relevant to SpaceX because if the cost of launching a solar power station is less than the cost of building the solar arrays, then it might be possible to make a business case for it. Launch cost = System Weight x Cost per unit massQuoteAs part of the study, we are looking at the leading three SBSP concepts, from the USA (SPS Alpha), UK (CASSIOPeiA) and China (MR-SPS). SBSP experts John Mankins (USA) and Ian Cash (UK) – the inventors of the first two concepts – are supporting our study.Problem with using SBSP en-masse is and always has been MMOD.Micrometeoroid impacts blast away ~100x as much mass as the original impactor, and SBSP offers a huge target (you almost couldn't design something worse for MMOD unless you launch buckets of sand or something). So even if you dodge the big chunks, your solar panels will slowly get "eroded away" by untrackable MMOD. Since each impact multiplies the amount of tiny debris, you don't need too many SBSP installations before you're substantially increasing the MMOD environment in your chosen orbit.Note that while the Kessler syndrome runaway threshold depends only on the total mass in a certain orbit, a large area satellites will be eroded away into fragments faster than a compact satellite.
Interesting. Does this then, by extrapolation, ultimately invalidate the idea of a Dyson swarm as well?
by 2025 you're launching... reactors
Quote from: alexterrell on 11/18/2020 07:28 amNot sure if this has been covered, but this thread seems a good place for it:https://www.fnc.co.uk/discover-frazer-nash/news/frazer-nash-exploring-viability-of-space-based-solar-power-to-help-deliver-net-zeroThe UK Government is looking for risky ventures, perhaps to try and compensate for the Brexit damage. They have now commissioned a study into Space Solar Power.This is relevant to SpaceX because if the cost of launching a solar power station is less than the cost of building the solar arrays, then it might be possible to make a business case for it. Launch cost = System Weight x Cost per unit massQuoteAs part of the study, we are looking at the leading three SBSP concepts, from the USA (SPS Alpha), UK (CASSIOPeiA) and China (MR-SPS). SBSP experts John Mankins (USA) and Ian Cash (UK) – the inventors of the first two concepts – are supporting our study.Problem with using SBSP en-masse is and always has been MMOD [micrometeoroids and orbital debris].
Are there any reactor programs that have a prayer of being ready by then?
Quote from: Twark_Main on 11/23/2020 12:20 amAre there any reactor programs that have a prayer of being ready by then?Kilopower might be ready for a field trial.
The product follows the need. Until today, why would anyone invest in nuclear space power? The only customer could be once in a decade probe of Nasa which might or might not come.
With real plans to set up bases on the moon & Mars there is a real need & market for such devices. I'd be really surprised if a leading space transportation company doesn't have an internal development program or at least ordered some.
Wouldn't this argument against solar power in space also apply to space nuclear power? They also need large surface areas to radiate away heat. Im not sure if they all circulate liquids through the radiators but wouldn't that make them particularly vulnerable?
MMOD is really an issue in LEO (and GEO, to a lesser extent).
The main distinction between the populations of cataloged and uncataloged large debris is more a product of sensor capabilities than of any inherent differences in the objects. For example, a fragment 30 cm in diameter that would almost certainly be cataloged if it were in LEO would not be cataloged if it were in GEO.
VLEO and GEO have similar cataloged debris fluxes.
SSP area in GEO is ~ 10,000x larger, hence the debris issue.
Quote from: LMT on 11/26/2020 04:28 pmVLEO and GEO have similar cataloged debris fluxes.According to your own (outdated) chart, the density in LEO is 100x what it is in GEO. Flux equals density times orbital velocity, so the flux difference in LEO vs GEO is even larger.
Your source (buried two links deep) is yourself, hand-waving with the inverse square law.However I know of no actual proposals where they take a LEO SSP design and relocate it to GEO without any redesign (a proposal which, according to your own numbers, would be at most 0.001% efficient; yes sunlight in space is abundant, but equipment is not).Is this 10,000x number actually based on a serious SSP proposal that I somehow missed, or just a figment of imagination?
There are several problems with VLEO solar power. Atmospheric drag on large solar panel arrays will be high and require a lot of effort to maintain altitude. Receiving rectenna will only see a satellite for a short time, so the satellite constellation would need thousands of satellites. One of the biggest advantages of space based solar power is near constant sunlight and VLEO throws that away. It would be far easier and cheaper to install solar panels where needed on Earth.
So thinking more about this I realized that regardless of whether the Friis Transmission Equation is the correct equation to apply to this context, there is a better way to think about it.Imagine a cone. The microwave emitter is not a point source radiating in all directions. It is trying to emit all of the photons (and their energy) in one direction. But that beam is going to spread. So our emitter is the tip of this cone and the receiving antenna will be at the base of the cone. High transmission efficiencies demand that the receiving antenna be the same size or larger than the cone created by the slowing spreading microwave photons.And therefore the size of the receiving antenna that we need in order to get high transmission efficiencies gets four times larger for every doubling of distance.So the size of the receiving antenna needed if the energy is coming from an emitter in GEO is vastly larger than if it's coming from LEO.So this reinforces what LMT has said above and it may be that I've just restated the Friis Transmission Equation in a different form (or a particular case covered by that equation) but even so I prefer thinking about it in terms of cones. And one of the benefits of thinking about it this way is that it suggests a possible solution to this problem.Here's the key question. How efficient can we get at doing microwave energy transmission in space? Because if we can get really efficient, like say 99%, then we can imagine a chain of intermediate receiving and emitting stations that can conduct energy from one point to another with relatively little loss.So if we can do 99% for one step, and there were ten steps, that's 0.99^10, aka 90% efficiency over that total distance. And the larger the receiving antenna, the larger the distance covered by a particular step.Anyways this is just speculation. But I do have the impression, or an idea I got somewhere, that very high efficiencies are possible for microwave energy transmission in the ideal case.
I do have the impression, or an idea I got somewhere, that very high efficiencies are possible for microwave energy transmission...
Quote from: mandrewa on 11/30/2020 03:04 pmSo thinking more about this I realized that regardless of whether the Friis Transmission Equation is the correct equation to apply to this context, there is a better way to think about it.Imagine a cone. The microwave emitter is not a point source radiating in all directions. It is trying to emit all of the photons (and their energy) in one direction. But that beam is going to spread. So our emitter is the tip of this cone and the receiving antenna will be at the base of the cone. High transmission efficiencies demand that the receiving antenna be the same size or larger than the cone created by the slowing spreading microwave photons.And therefore the size of the receiving antenna that we need in order to get high transmission efficiencies gets four times larger for every doubling of distance.So the size of the receiving antenna needed if the energy is coming from an emitter in GEO is vastly larger than if it's coming from LEO.So this reinforces what LMT has said above and it may be that I've just restated the Friis Transmission Equation in a different form (or a particular case covered by that equation) but even so I prefer thinking about it in terms of cones. And one of the benefits of thinking about it this way is that it suggests a possible solution to this problem.Here's the key question. How efficient can we get at doing microwave energy transmission in space? Because if we can get really efficient, like say 99%, then we can imagine a chain of intermediate receiving and emitting stations that can conduct energy from one point to another with relatively little loss.So if we can do 99% for one step, and there were ten steps, that's 0.99^10, aka 90% efficiency over that total distance. And the larger the receiving antenna, the larger the distance covered by a particular step.Anyways this is just speculation. But I do have the impression, or an idea I got somewhere, that very high efficiencies are possible for microwave energy transmission in the ideal case.Does this mean we can replace all the high voltage transmission lines? Or has the maths gone wrong somewhere?
Quote from: mandrewa on 11/30/2020 03:04 pmI do have the impression, or an idea I got somewhere, that very high efficiencies are possible for microwave energy transmission...The Friis formula gives max transmission over any appreciable distance (far field).Image: a worked example, Sophocles 2003, Ex. 16.6.1.You might rework the example to illustrate: 1. shift to VLEO (250 km)2. apply plausible SSP frequency and gain numbers3. scale to some commercial gigawattsRefs.Sophocles, J., 2003. Electromagnetic waves and antennas.
could it be that the Friis Transmission Equation doesn't apply to an antenna emitting a directed beam?
Quote from: mandrewa on 11/30/2020 06:22 pmcould it be that the Friis Transmission Equation doesn't apply to an antenna emitting a directed beam?No, it works as-is. Use a practical microwave, e.g. 5.8 GHz (5.2 cm), and try variations. Transmission efficiency is never like a power line of course, but some variations work better than others.
Yes, I got that. That's what I meant when I wrote Reply #151, and plugged in a few numbers and got an absurdly low level of energy transmission.So how do we explain the idea of solar power satellites?*snip*
Quote from: Twark_Main on 11/28/2020 09:38 pmQuote from: LMT on 11/26/2020 04:28 pmVLEO and GEO have similar cataloged debris fluxes.According to your own (outdated) chart, the density in LEO is 100x what it is in GEO. Flux equals density times orbital velocity, so the flux difference in LEO vs GEO is even larger.VLEO, not LEO.
Or do you think invisible 30 cm debris is harmless in GEO?
Quote from: Twark_Main on 11/28/2020 09:38 pmYour source (buried two links deep) is yourself, hand-waving with the inverse square law.However I know of no actual proposals where they take a LEO SSP design and relocate it to GEO without any redesign (a proposal which, according to your own numbers, would be at most 0.001% efficient; yes sunlight in space is abundant, but equipment is not).Is this 10,000x number actually based on a serious SSP proposal that I somehow missed, or just a figment of imagination?Weird. No, I posted the Friis formula right here. A given SSP system delivers ~ 10,000x more power from VLEO than from GEO, due to inverse square propagation, and subtracting VLEO night shutdown. It's a fundamental SSP calc.
I can only assume this "10,000x" larger station was never seriously proposed by anyone, and is nothing but a hypothetical napkin math strawman.
@Twark_Main and @LMT, your constant mutual sniping is really tiresome for everybody else to read. You are in a public forum. It's basically the equivalent of standing in the street and arguing at 3am and waking up the whole neighbourhood. Please.
Now you know the Friis formula, so you can see why no one is "hand-waving with the inverse square law".
"Indonesia invited SpaceX to assess the possibility of setting up a rocket launch site in the country, according to a ministry statement.President Joko Widodo discussed the idea with SpaceX founder Elon Musk during a phone call on Friday, the Coordinating Ministry for Maritime and Investment Affairs said in the statement. Musk intends to send a team to Indonesia in January to study partnership opportunities, it said."
At 34:55 into the video (Space Solar Power: A New Beginning - Sergio Pellegrino - 10/31/2018) is the slide: "Levelized Cost of Electricity (LCOE) GEO vs. MEO"This assumes a fifteen year operational lifetime for a solar power satellite that has been launched on the Atlas V 551.If the weight of the basic solar power satellite element can be brought down to 0.16 kg/m2 then the electricity from a solar power satellite in GEO should cost about $2.06 per kilowatt-hour or $1.77 per kilowatt-hour if it comes from five solar power satellites equally spaced around the earth at MEO.Now that's a higher number than you see on your electric bill. But there are three things to remember here. First this is a baby-in-the-bathwater situation. Assuming there isn't something fundamentally wrong with this cost estimate, these numbers will only get better with time. And second, maybe it would be more appropriate to compare to the cost of electricity produced by solar cells on the earth instead of in general, and although that's going to be a controversial subject, so much so that I wonder if I should go there, but still it may be that looked at from that perspective that this is a genuinely economically competitive idea even at the baby-in-the-bathwater stage.And third, of course, what does it do to the cost estimate if instead of launching on the Atlas V 551 it is launched on Starship?
I suspect this extremely rapid response time is why the Caltech team thinks they can aim multiple phased array antennas at a target on earth and consistently hit it with all of them. And intuitively it seems to me, although I don't really know, that as long as they have rapid feedback, so they know when they are hitting their target or not, that they should be able to do this.