# Is a refrigeration laser thermodynamically possible?

Taking the argument to extreme, we are talking about covering an area of the sun and dumping the heat flux across that area to a heat sink of nearly absolute zero temperature. That is what the sun is already doing and it retains its high 'surface' temperature anyway.

If we take the argument to a[n il]logical maximum, the sun is entirely surrounded by our heat gathering surface and the energy is collected in a single location where our 'communication laser' pumps all that heat into space. If our laser is 1/1,000,000 the surface area of the sun, it would need to pump out a million times the solar output. Meanwhile, the entire surface of our solar shell must furiously work to concentrate heat toward the laser.

Q1. Is this a correct scenario?
Q2. Does the 'total coverage' aspect negate some or all of this scenario?
Q3. Can a refrigeration laser operate under this scenario?
Q4. If the sun operated at 500 degrees Fahrenheit or even 5000 degrees Celsius, would we even be having this debate?

Assume that we would still need to cool the 'Sundiver' for an indefinite period.

Having written the preceding, there are two lasers at work in the scenario. The first is the refrigeration laser that cools the inward-facing shell. The second is the communication laser transmitting to space.

Okay, so what is going on here is that we have outward thrust supplied by the comms laser and heat absorption from the inward-facing heat sink generated by the cooling effect of the refrigeration laser.

Excuse me for brainstorming a bit. First time encountering this forum.

So, we have inward force applied by the outward radiation at/near perihelion. If we maintain inward orientation throughout the passage, then the thrust should have relatively little effect on the orbital characteristics since no acceleration or deceleration is applied; instead it is applied orthogonally with the orbital path. Or have I got that wrong? I think it might make the orbit increasingly elliptical. Never could master that orbital dynamics video game on my dad's Timex Sinclair.

Mapes said:
However, if there were a large energy source on board, a very high power laser beam might be produced that would carry away the same amount of entropy that is received from the Sun. I can't see any problems with this scenario. It wouldn't be self-renewing, however; eventually the energy source would be depleted.
So, given a large enough internal supply of energy, a refrigeration laser is possible, but not self-renewing, as the supply will eventually be depleted. I still don't understand how to actually build one, even in theory.
The solar physicists might have gone on resignedly burning up probes in exchange for fleeting bursts of information had Tina Merchant not offered another way. "Why don't you refrigerate?" she asked. "You have all the power you want. You can run refrigerators to push heat from one part of the probe to another."
You have all the power you want? From the sun, right? You can't extract heat energy thermodynamically, but maybe that's not the only power source available from the sun. Can't you use photovoltaics to absorb light energy? Maybe capture energetic electrons magnetically? Or occasionally refuel a self-sustaining fusion reactor from stellar hydrogen?
iffydroplight said:
Taking the argument to extreme, we are talking about covering an area of the sun and dumping the heat flux across that area to a heat sink of nearly absolute zero temperature.
The heat sink being 4 kelvin outer space, right? If it were that easy, we could just plant a refrigeration laser on the surface of the Earth, point it into space, and get free energy! After all, Earth is about 288 kelvin, and even hotter in some places. There, global warming crisis solved. Get cheap renewable power plants literally anywhere exposed to open sky, and as a bonus, they actually refrigerate the planet! No way this could really work...

Wait, could this actually work?

Refering to my limelight space cooler:
russ_watters said:
The thermodynamic efficiency of any kind of heat pump is dependent on temperature: the larger the temperature difference between the hot and cold side, the lower the efficiency. So yes, you could do what you suggest, but you could do very little cooling with it.
I think this is more of an engineering problem, but maybe it isn't necessary to achieve 1000 Kelvins for the space cooler to work. I've heard that cheap green lasers are actually infrared lasers and a frequency doubler. Maybe you can generate light from a much lower temperature? Or do frequency doublers only work on lasers?

Never forget that Overall head transfer = Overall heat transfer coefficient * Area * (Temperature of hot surface - Temperature of cool surface). That is, Qdot=UA(deltaT). So, with the sun radiating into space's 4 Kelvin heat sink it is working at max heat transfer rate for the surface area until and unless we raise the effective surface temperature of the sun with our RHL (Ridiculously Hot Laser), lower the temperature of space (heh!), or increase the 'effective surface area' of the sun.

Much more likely to work is a Gattling Gun cooling scheme wherein cold slugs that become its temporary heat sinks are fired to the probe. Following use, they are recycled into space to escape the sun's influence and cool down far enough away that the temperature is appropriate - or - they are plunged into the sun for disposal.

On the modeling or proof-of-concept side, can we make a free-floating balloon with solar cells on its sunward side that can decrease the temperature of the air surrounding its entire surface (minus the side with the 'communication laser')? If we can do that, then the model is workable and the only thing left is to scale up the solution to match the target environment. I remain skeptical.