Author Topic: Solar Power Satellites  (Read 32500 times)

Offline SICA Design

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Re: Solar Power Satellites
« Reply #40 on: 07/01/2014 10:42 AM »
You didn't understand the argument. With terrestrial solar panels, you capture as useful energy some energy which *would otherwise end up absorbed by Earth anyway*. With SBSP, the energy you capture and send to Earth *would otherwise fly past the planet*.

It does not matter whether you include terrestrial PV albedo (making light reflective sandy deserts much darker) or not:

It is still insignificant compared with total solar influx and GHG heat trapping.
« Last Edit: 07/01/2014 10:44 AM by SICA Design »

Offline gospacex

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Re: Solar Power Satellites
« Reply #41 on: 07/01/2014 10:45 AM »
You didn't understand the argument. With terrestrial solar panels, you capture as useful energy some energy which *would otherwise end up absorbed by Earth anyway*. With SBSP, the energy you capture and send to Earth *would otherwise fly past the planet*.

It does not matter whether you include terrestrial PV albedo (making light reflective sandy deserts much darker) or not:

It is still insignificant compared with total solar influx and GHG heat trapping.

I didn't say it matters. I said that your argument "but terrestrial solar PV also dissipates waste heat" is wrong, because that solar energy would arrive and be dissipated in this location *anyway*.
« Last Edit: 07/01/2014 10:47 AM by gospacex »

Offline SICA Design

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Re: Solar Power Satellites
« Reply #42 on: 07/01/2014 10:51 AM »
I didn't say it matters. I said that your argument "but terrestrial solar PV also dissipates waste heat" is wrong, because that solar energy would arrive and be dissipated in this location *anyway*.

I'm glad we agree it doesn't matter.

Offline dror

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Re: Solar Power Satellites
« Reply #43 on: 07/01/2014 12:56 PM »
I didn't say it matters. I said that your argument "but terrestrial solar PV also dissipates waste heat" is wrong, because that solar energy would arrive and be dissipated in this location *anyway*.

I'm glad we agree it doesn't matter.
It may not matter for one satelite.
How many satelites can you build befor it starts to matter?
50 GW?
500 GW?
5 TW?

Btw, tracking modules which combine concentrated thermal electric and pv can get 60 - 80% efficient.
"If we crave some cosmic purpose, then let us find ourselves a worthy goal. "
Carl Sagan, Pale Blue Dot

Offline JasonAW3

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Re: Solar Power Satellites
« Reply #44 on: 07/01/2014 01:20 PM »
Ok guys,

     This may seem like a dumb idea, but, instead of spending hundreds of billions of dollars to build a solar array in space, why not send up an inflatable array using thin film solar panels to convert sunlight to electricity, an inflatable directional microwave antenna on the back to transmit the energy back down to Earth and strategically placed solar electric thrusters to maintain attitude as needed.

     Using a thin mylar film as the inflatable structure, you should be able to get at least 1 kilometer of solar array per ton of mass.  Assuming the microwave antenna and gear plus the solar electric thrusters mss about 10 tons, bosting a 30 ton mass into Geosynch orbit should give us a 20 kilometer array that should be able generate at least 215 Gigawatts.

     There are a number of launchers that should be able to boost it into orbit and more than enough upper stages that can boost 30tons to Geosynch orbit.
My God!  It's full of universes!

Offline SICA Design

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Re: Solar Power Satellites
« Reply #45 on: 07/01/2014 01:21 PM »
I didn't say it matters. I said that your argument "but terrestrial solar PV also dissipates waste heat" is wrong, because that solar energy would arrive and be dissipated in this location *anyway*.

I'm glad we agree it doesn't matter.
It may not matter for one satelite.
How many satelites can you build befor it starts to matter?
50 GW?
500 GW?
5 TW?

World consumption in 2008 was about 16.4TW, it would need to grow by 8-10,000 times to reach parity with total insolation:
http://en.wikipedia.org/wiki/Solar_energy
http://en.wikipedia.org/wiki/World_energy_consumption

Quote
Btw, tracking modules which combine concentrated thermal electric and pv can get 60 - 80% efficient.

Ivanpah manages 2.7% peak efficiency at $19.6B/GW build cost.

Offline SICA Design

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Re: Solar Power Satellites
« Reply #46 on: 07/01/2014 01:24 PM »

Offline Asteroza

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Re: Solar Power Satellites
« Reply #47 on: 07/02/2014 12:33 AM »
Maybe I'm not understanding correctly, but what happens when the SPS lines up with the day/night terminator line while near the top of the Molniya loiter then, unless you phase orbits to avoid that scenario?

HESPeruS is never in Earth's shadow when other beam constraints are met. A Molniya orbit is inclined at 63.4deg taking it WAY above the northern hemisphere. The diagram is not to scale (obviously), but the solar angle (shown from Earth's tilted perspective) and orbit proportions are correct. The "SPS" represents a small section of one module - the tiered arrangement is at ~25mm scale.

Were you considering something similar to 70 minute GEO outtages during Spring/Vernal equinoxes?

No no, it wasn't equinox outages. I had pictured HESPeruS to be a single contiguous flat panel, along the lines of currently proposed sandwich panels for SPS, thus only showing one large contiguous planar area (where the emitters would be mounted across the entire area of the panel) and one nadir edge to earth. Thus, if edge on to earth or close, you go beyond the reasonable beam steering limits of a phased array. The stepped venetian blind structure you show where the emitters line the long linear strip panel edges neatly sidesteps that problem. Are the steps a fully fixed structure then? Though that makes for interesting orientation issues, likely compensated by smart precession and beam steering.


Bad thought of the day, the high speed pass portion is pretty low (as you say, 450 Km perigee).  Is there the possibility of using the beamed power of the SPS to power an LV upper stage or orbital tug during the high speed pass, as nominally the odds of a terrestrial power user being in the footprint of the high speed pass would be low? At such close range, the beam spot is much tighter and have utility in various ways. An inflated ring rectenna for an orbital tug could power electric propulsion systems, and Parkin's microwave thermal rocket work would be applicable (AKA microwave Skylon variant of Henson's laser Skylon, and the associated SPS bootstrapping)

Offline SICA Design

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Re: Solar Power Satellites
« Reply #48 on: 07/02/2014 08:18 AM »
Asteroza,

HESPeruS has some commonality with sandwich panels including:
* modular construction
* short distance power distribution
* no single point power bottleneck, such as a rotating joint

As shown, the "venetian blind" sections combine into a hexagonal module <4.8m across vertices. Each module is actually a subtle 3D tetrahedron for rigidity, which is continued across multiple fractal scales (eliminating the requirement for additional truss sections or other support backbone). I have done some further work which solves high density stacking issues within the Skylon hold (must be limited by payload mass not volume!).

The diagram also shows the option for thin-film or concentrated PV at each element. Quad junction CPV has been demonstrated at 44.7% efficiency (40% assumed). Thin film PV (eg perovskite) offers lower mass, but cannot yet match efficiency (though huge gains have been made in a short period, from 3% to currently 19%).

I have discussed the possibility of boot-strapping construction (using one SPS to boost the components for another into Molniya via microwave thermal propulsion) with Keith Henson. However, he suggests the orbital phasing and beam times will not work in its favour.

[Edit]
Quote
Though that makes for interesting orientation issues, likely compensated by smart precession and beam steering.
The boresight beam axis is also the rotation axis, aligned normal to the ecliptic. The whole SPS rotates once per year to maintain PV (or concentrating fresnel reflectors) face-on to the sun. At perigee, the SPS will be travelling mostly edge-on to the residual atmosphere. Not quite GOCE streamlining, but better than the alternative if drag is to be minimised. OTOH, there is no junkyard orbit required for end-of-life modules; only a small nudge will ensure re-entry happens in a predictable timeframe.

Beam steering is retrodirective, based on synchronised sampling and time-reversal of the incoming 40.68MHz pilot beam wavefront (with minimally accurate targeting performed by the rectenna ground facility). The SPS requires no "knowledge" of where the rectenna actually is, but may need to perform small phase corrections (e.g. linear prediction) to allow for RF time-of-flight delays.

« Last Edit: 07/02/2014 12:17 PM by SICA Design »

Offline Hanelyp

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Re: Solar Power Satellites
« Reply #49 on: 07/02/2014 07:51 PM »
How does HESPeruS keep modules on opposite sides of the array in phase for beam forming?

Offline SICA Design

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Re: Solar Power Satellites
« Reply #50 on: 07/02/2014 09:53 PM »
How does HESPeruS keep modules on opposite sides of the array in phase for beam forming?
The key is synchronisation, both inter-module and intra-module (between all 25 billion elements). Its covered over several pages, but I'll try and summarise:

* Distribute a synchronised timing reference across the whole system, linked to the Pilot Beam frequency (40.68MHz)
* Perform synchronised sampling of the Pilot Beam wave-front at several points across each module to determine phase values (three points on a plane).
* Use time-of-flight knowledge and recent phase history to predict small phase corrections for RF round-trip delay.
* Distribute two time-reversed phase values (and the timing reference) to each element in a linear string.
* At each element, synchronise a 1:143 PLL to the position-weighted average of the two phases to generate a local 5.8GHz power beam.

Inter-module uses 100GHz duplex fibre (as for standard Ethernet) at the six module sides - there are no electrical connections between modules. One module is designated as "Master" (could be any; not position dependent).

A unique duplex path is determined between all functioning modules (routes around any failures). The Master sends out a regular timing burst passed module-module until it reaches the End Node, where it is reflected back along the same duplex path to the Master - averages about 62ms for the million modules.

At any module, the timing reference is defined as the average of the outbound and return bursts. The outbound and return paths are regularly swapped to eliminate path length errors.

The same thing happens intra-module, but at 40.68MHz and broadcast (not element-to-element).




Offline Asteroza

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Re: Solar Power Satellites
« Reply #51 on: 07/02/2014 11:36 PM »

I have discussed the possibility of boot-strapping construction (using one SPS to boost the components for another into Molniya via microwave thermal propulsion) with Keith Henson. However, he suggests the orbital phasing and beam times will not work in its favour.


That's a little unexpected, but possible. Skylon dumping direct to a Molniya inclination but a sub-450 km circular parking orbit seemed to be a good choice at first. After that trade against full construction then apogee raising of a completed SPS or apogee raise all parts module by module before joining. Single module apogee raising using something like a microwave powered Flyut while the bootstrap SPS sweeps towards perigee seems doable even if microwave Skylon itself is unattractive due to launch site distance from perigee ground track specific to the Molniya orbit you wish to service.

Offline SICA Design

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Re: Solar Power Satellites
« Reply #52 on: 07/03/2014 05:46 AM »

I have discussed the possibility of boot-strapping construction (using one SPS to boost the components for another into Molniya via microwave thermal propulsion) with Keith Henson. However, he suggests the orbital phasing and beam times will not work in its favour.

That's a little unexpected, but possible. Skylon dumping direct to a Molniya inclination but a sub-450 km circular parking orbit seemed to be a good choice at first. After that trade against full construction then apogee raising of a completed SPS or apogee raise all parts module by module before joining. Single module apogee raising using something like a microwave powered Flyut while the bootstrap SPS sweeps towards perigee seems doable even if microwave Skylon itself is unattractive due to launch site distance from perigee ground track specific to the Molniya orbit you wish to service.

I haven't tried to model this; Keith has for laser-thermal GTO, but I'd presume not for Molniya. Would anyone here like to have a go?

The diffraction limit at 5.8GHz, from a 4.4km diameter antenna down to a 1 metre spot, gives <35km beam distance, which is one reason for pessimism.

[Edit]
Could make a good anti-missile defence for the SPS though; provided the missiles abide by the rules and don't try to attack the non-beaming side!  :)

[Edit2]
...and the missiles agree to play fair and send out a 40.68MHz homing signal  :) :)

« Last Edit: 07/03/2014 05:53 AM by SICA Design »

Offline Hanelyp

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Re: Solar Power Satellites
« Reply #53 on: 07/03/2014 05:15 PM »
[Edit2]
...and the missiles agree to play fair and send out a 40.68MHz homing signal  :) :)
If you were serious about anti-missile capability on the solar array, a less directional system could illuminate a target missile with the homing signal.  Though with a 40MHz homing signal the warhead bus might be made too small to reflect the signal well.

Offline Asteroza

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Re: Solar Power Satellites
« Reply #54 on: 07/04/2014 12:11 AM »

I have discussed the possibility of boot-strapping construction (using one SPS to boost the components for another into Molniya via microwave thermal propulsion) with Keith Henson. However, he suggests the orbital phasing and beam times will not work in its favour.

That's a little unexpected, but possible. Skylon dumping direct to a Molniya inclination but a sub-450 km circular parking orbit seemed to be a good choice at first. After that trade against full construction then apogee raising of a completed SPS or apogee raise all parts module by module before joining. Single module apogee raising using something like a microwave powered Flyut while the bootstrap SPS sweeps towards perigee seems doable even if microwave Skylon itself is unattractive due to launch site distance from perigee ground track specific to the Molniya orbit you wish to service.

I haven't tried to model this; Keith has for laser-thermal GTO, but I'd presume not for Molniya. Would anyone here like to have a go?

The diffraction limit at 5.8GHz, from a 4.4km diameter antenna down to a 1 metre spot, gives <35km beam distance, which is one reason for pessimism.

[Edit]
Could make a good anti-missile defence for the SPS though; provided the missiles abide by the rules and don't try to attack the non-beaming side!  :)

[Edit2]
...and the missiles agree to play fair and send out a 40.68MHz homing signal  :) :)

Fore reference, what are the distances for 2,3,4,5, and 10m spots? I suspect even then the distances would be unattractive for a Skylon but potentially usable for a orbital tug which can open up a large rectenna via an inflatable ring with 10m not being unreasonable.

It's probably unrealistic to do the external heating for a Skylon via microwave if you have to do the heating as two smaller spots on the wing upper surface of the current Sklyon configuration. Which is why I always imagined externally heated Skylon to be a flipped configuration, with the wing on the top of the fuselage and the payload bay opening towards the bottom. This allows a much larger single receiver surface which can double as thermal protection for reentry, provided you did reentry upside-down. That 180 roll before and after reentry is the obnoxious part (since a passenger module will need seats that rotate 180), but it keeps the hot side uninterrupted with landing gear doors. 180 degree roll is potentially a deal-breaker, but then again, many nose first reentry VTVL SSTO designs had "swoop-of-death" maneuver that people felt was acceptable.

Perhaps a different bootstrap concept might be in order. If one could accept the bootstrap/demo sat can't be reasonably used for continuous utility power service, a low SSO SPS riding the day/night terminator to supply dedicated propulsion power might be possible. How that propulsion power is beamed (Henson uses laser, but microwave might work here) determines the utility of it. Oddly enough, that would force you to do predawn and post-dusk Skylon flights or tug boosts.

Offline SICA Design

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Re: Solar Power Satellites
« Reply #55 on: 07/04/2014 07:47 AM »
The diffraction limit is approximated by the inequality:

(A x D) / (λ x R) > 2.44

where A is antenna aperture (diameter), D is rectenna diameter, λ is the wavelength (51.7mm for 5.8GHz) and R is the beam distance. So the maximum beam length will change in proportion to the spot size if everything else stays constant.

I like the idea of a Skylon without breaks in the TPS for wheel wells, but as recently commented on 'Skylon Thread 4', it's not designed for combat manouvres - which I guess includes barrel rolls!

Offline SICA Design

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Re: Solar Power Satellites
« Reply #56 on: 10/15/2014 08:25 PM »
Article on HESPeruS published in the IET's magazine recently:

http://eandt.theiet.org/magazine/2014/10/space-based-solar-power.cfm


Offline Robotbeat

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Re: Solar Power Satellites
« Reply #57 on: 10/15/2014 11:43 PM »
Should use lasers and find a customer that needs a lot of power and is willing to pay a LOT more than $0.10/kWh and lives above the clouds and could use a system at the hundreds of kW range to start.
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Offline QuantumG

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Re: Solar Power Satellites
« Reply #58 on: 10/16/2014 12:51 AM »
Should use lasers and find a customer that needs a lot of power and is willing to pay a LOT more than $0.10/kWh and lives above the clouds and could use a system at the hundreds of kW range to start.

Cloud servers in the clouds.

I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

Offline Vultur

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Re: Solar Power Satellites
« Reply #59 on: 10/17/2014 06:26 AM »
How much would a HESPeruS satellite cost? (not including launch costs as obviously that's highly dependent on how cheap Skylon and/or SpaceX reusability turn out to be in actual practice...)