Author Topic: What wavelength would be chosen to beam power from space to the martian surface?  (Read 1780 times)

Offline gin455res

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If a space based solar power station was built in aereostationary orbit, would it be designed the same as one in geostationary orbit?

Would mars's thinner atmosphere allow laser power beaming?
   (what about dust storms?; if yes could such a system be implemented on an early martian-base-sized small scale?)

Is there much advantage from the fact that this orbit is half as wide as the equivalent geostationary orbit. So there is less beam divergence, and a more concentrated beam?
« Last Edit: 11/27/2011 12:19 PM by Chris Bergin »

Offline Proponent

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Despite the earth's dense atmosphere, lasers are considered even for geocentric space solar power systems.  The recent study by the  International Academy of Astronautics, for example, considers both laser  and microwave systems, though it concludes that a microwave system is  better.  Like you, I suspect dust storms would be the key issue: if power must be beamed through them, then it seems likely microwaves would be preferred.
 
The lower altitude of areostationary orbit would indeed reduce the  spread of the beam and would enable the use of smaller antennas.  They are still going to be big, though, and I find it hard to imagine the space solar power would be attractive on Mars for a very long time, if ever (of course, I'm also very skeptical about its economic viability on earth).
« Last Edit: 11/28/2011 01:15 AM by Proponent »

Offline alexterrell

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The problem with microwaves is that you need very large apertures of transmitter and receiver. That makes them suitable for multi GW applications on Earth. Mars is easier, but you still want 100s of MW. The moon (from L1/L2) is tricky because of distance as well.

traditional microwaves talk about 2.4GHz. You could go to higher frequencies -100 GHz or so - but there is a loss in efficiency.

The problem with lasers is the inefficiency. I've heard you can get 50% at each end, so a total of less than 25% efficient. They would make a nice solution for a lunar base - they could beam down to individual trucks. Mars should be feasible - I think 6mbar won't cause the beam to diverge significantly and absorption not an issue as long as you can avoid CO2 absorption lines.

Dust storms would be a problem. 

Offline kevin-rf

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Dumb question, with the orbit being lower than Deimos and higher than Phobos what are the chances of debris passing through the MSO orbit and causing a problem? The to moons do not have very deep gravity wells and it is very easy to liberate debris from them.
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Offline RanulfC

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If a space based solar power station was built in aereostationary orbit, would it be designed the same as one in geostationary orbit?

Would mars's thinner atmosphere allow laser power beaming?
   (what about dust storms?; if yes could such a system be implemented on an early martian-base-sized small scale?)

Is there much advantage from the fact that this orbit is half as wide as the equivalent geostationary orbit. So there is less beam divergence, and a more concentrated beam?

Been looked into, see the following examples for a start:

"POWOW an alternative power source for Mars exploration"
http://www.sciencedirect.com/science/article/pii/S0094576502000735

"POwer WithOut Wire (POWOW): A SEP Concept for Space Exploration"
http://www.mendeley.com/research/power-without-wires-powow-sep-concept-space-exploration/

"Powow revisited beamed power for mars exploration"
http://www.mendeley.com/research/powow-revisited-beamed-power-mars-exploration/

"Energizing the Future of Space Exploration: Applications of Space Solar Power"
http://www.nss.org/settlement/ssp/library/2008-EnergizingTheFutureOfSpaceExploration.pdf

PoWoW is an interesting "pre-cursor" concept mission that would use the Solar Array to power a SEP cargo craft to Mars (or Venus, and the Moon are also suggested) and once there they would beam power to surface missions, rovers, and facilities.

Design differences between an Earth and Mars power-sat are mostly due to the differing distance from the Sun. Orbital parameter requirements and Line-Of-Sight access would also be a factor. As mentioned in the last paper cited some Lunar base concepts would be unable to use beamed power due to LOS issues with orbiting satellites.

Randy
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Offline gin455res

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Thanks very much Randy,
I'll take a look at those later today.

Offline HIPAR

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Here on earth, radio band atmospheric attenuation is easily manageable up to (about) 15 GHz.  I'd suspect we can go much higher without transmission on Mars.  But, there are absorption lines to be considered.  These result from atomic/molecular resonances.  I'd suspect those problems will be minimal on Mars with its thin atmosphere and general absence of water vapor.

These effects are well understood so they can be modeled; we have extensive knowledge about the composition of the Martian atmosphere.

Here on earth rain scatter becomes a major issue for frequencies higher than (about) 5GHz.  The dust would be our major transmission problem at Mars.  It's always somewhat present so analysts will need to model its specific attenuation (dB/km).   I'm guessing the dust problem will set an upper limit in the Ku band maybe around 12 GHz. 

The atmospheric loss La is the sum of gaseous attenuation and dust scatter.

For typical radio applications, it is common to find Free Space Path Loss in dB with f measured in units of MHz and d in km:

FSPL = 20log(d) + 20log(f) + 32.45

Then you need to know the receive Gr and transmit Gt antenna power gains in dB to calculate the received power Pr:

Pr = Pt + Gt + Gr - FSPL - La

You need to express power of transmitter Pt in dB referenced to a power unit .. usually a milliwatt dBm or watt dBw.

You can design your favorite solar collector to provide Pt.  You can decide how big the antennas need to be for assessing Gt and Gr.

Interesting, the antenna efficiency adds a loss of 3dB at each end of the link.  The maximum power that can be transmitted from a source to a load is 50% from simple network theory.  So reduce antenna gains by 3dB.

When you actually go through the numbers it becomes obvious this is not a practical system but yet it's an idea that refuses to go away.

Reality check:

Now that I thought about it a bit more, I'd say it would be more sensible to skip the transmission apparatus just building your solar collector on the Martian surface!  It's not like there's a real estate shortage there.

---  CHAS

« Last Edit: 12/04/2011 12:12 AM by HIPAR »

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