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Dave, freezing is a problem, particularly for water in the radiator. I don't know how to get away from using water in the radiators. It's also tricky because you can't let more than perhaps 80% condense before the radiators get waterlogged. CO2 as a working fluid can probably be kept in a...

moltenmetal re "Without hot air," http://withouthotair.blogspot.co.uk/2014/09/solar-power-from-space.html

The article on how to get the transport cost down was posted today: http://theenergycollective.com/keith-henson/485571/power-satellite-progress

davefitz, Efficiency is only one consideration. The point of the entire design to cost effort is to get the cost of electric power delivered to the power grid on earth well below the cost of coal. For microwave optics reasons and the minimum forward voltage of the receiver diodes, power...

davefitz, as far as I know, PV and nuclear are the only power sources ever used in space. Thermal cycles are possible, but it isn't easy to get rid of the waste heat. If you can start at a really high temperature, and take energy out in stages, then the size of the radiators is reduced...

Design of a thermal type power satellite proceeds. The big tubes are the radiator, the red hot object is the boiler. https://drive.google.com/file/d/0B5iotdmmTJQsSWpzTHZUS2diQWdvY055WmdPVS1sOWt2MGJj/edit?usp=sharing Larger view showing the concentrating mirrors on tracks that follow the sun...

tbuelna, the fluids used had more to do with the external regime the Shuttle was in. On the way up, before reaching orbit and being able to open the doors, they used water evaporating into vacuum or near vacuum. On the way back down, they used evaporating ammonia to get rid of waste heat when...

tbuelna, this document http://spaceflight.nasa.gov/shuttle/reference/shutref/orbiter/eclss/atcs.html could sure use diagrams. Freon, water *and* ammonia.

tbuelna, I agree with you re designing vehicles like Skylon. However, I am predicating my limited focus on an assumption that Reaction Engines knows what they are doing with (among other things) reentry thermal protection. I am trying to figure out how Skylon can be used to solve the energy...

tbuelna, I have worked on this off and on since 1975. I have an *intimate* appreciation of the economics of the problem. I came here not to discuss economics or business financing problems, but to see if this engineering forum had any thoughts on thermodynamic cycles to skim off more of the...

tbuelna, you completely missed the goal. Even if it is an easier problem to solve, reducing the cost of launching payload to GEO by 50% will not contribute to the goal of economical solar power from space. Also, I am not much interested in becoming extremely wealthy. ESA's review of Skylon...

tbuela, you are looking at a long conceptual development process. The low cost delivery of cargo to GEO depends on a UK project, Skylon, recently funded by $350 million, a combination of a grant by the UK and private investment. If you look at the price/volume market curve, there is a huge...

moltonmetal, I am really disappointed in getting what amounts to political dogma responses from a group that's supposed to be technical heavies. Nothing new either, read the comments here http://www.theoildrum.com/node/5485 "Perhaps it is incorrect of me to assume they are in favor of a die...

If trying to figure out a technical way to get the human race out of the energy jam is "idealism" so be it. Ammonia, however, is a candidate for a bottoming cycle, not a topping cycle...

I guess this site isn't as useful as I hoped it might be. I am intimately familiar with space elevators, having presented a paper at the Microsoft sponsored conference some years ago, and with the Orion nuclear propulsion concept by Ted Taylor and Freeman Dyson. In fact, I know Freeman Dyson...

The operative word in your post is "currently." If Skylon flies in 2021 (and they have money to develop the engines) it is expected to fly every other day. It takes off from a runway and you could probably fly them off at 6-8 per hour. But ignoring the transport cost, you do mention that it is...

Tbuelna, your objection is economic rather than physics, but I am happy to discuss it. First, you are right, the current cost to GEO is close to $20,000/kg. Boeing used something close to your number in this study, http://www.sspi.gatech.edu/aiaa-2009-0462_ssp_alternatives_potter.pdf They got...

I know that combined cycle power plants can go just a bit over 60%. I would like to go that high for space based solar power plants. 60% thermal efficiency with a non-steam topping cycle reduces the size of the radiators. Potassium Rankine may be a good choice. One document makes a case for...