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The ISS EEATCS radiator ORU Centaur co-generation experiment A NASA SBIR 2015 proposal

April 24, 2014

The ISS EEATCS radiator ORU Centaur co-generation experiment; A NASA SBIR 2015 proposal


The proposed decadal small fission reactor sadly is far in our future, so how to test the possibility of a small fission reactors radiators being used as a secondary power source? or a better question, how can this concept be used in non nuclear systems?

lets take the largest spacecraft radiator system now flying as an example, what if these radiators were incorporated into an empty in space stage tank filled with Xenon and with a stirling engine system? Or what if the ISS Ammonia system replaced the role of the Xenon? would Ammonia do damage to the Centaur fuel tank?  would Ammonia damage the stirling engine?.

Not having radiators geometry inside the fuel tank would be a weight savings Docking a centaur with ISS with fluid connections to the ISS The EEATCS radiator ORU system or better stated replacing the radiator with the Centaur might be a tall order and what would 70 kW per hour provide to a stirling engine?  remaining waste heat after the stirling engines recovered energy radiate through the Centaur in space stage hull.

The NASA radiator paper,


The EEATCS radiator ORU is a direct flow, deployable and retractable radiator system with two independent cooling loops Two MBSU cold plates, each designed to remove 495 watts at 80 lbs/hr. Three DDCU cold plates are each designed to remove 694 watts at 125 lbs/hr. The EATCS is designed to provide 35 kW of heat rejection per loop for a total capability of 70 kW


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  1. Hi,

    To use the tank as a radiator, you would need to keep it quite cold. The ammonia in the ISS system is under pressure at 300 psi, that makes it a liquid. To use it in the centaur stage it would need to be a gas, since the stage is most probably incapable of maintaining 300 psi, and the weight of ammonia would be too much anyway. Ammonia is used because water would freeze at the temperatures the radiators are operated at.

    If you radiated out from an ammonia circuit into the tank, you would need to keep the tank colder than the ammonia circuit to do useful work. This would make it very cold, and my guess is the sterling engine would then be incapable of extracting much energy.

    Work my office has done with sterling cycles at low tempertures (but higher than what the ISS uses) has yielded efficiencies of 14% and less. So a stirling engine might at best extract 5 kW from the 70 kW of cooling. Probably much less. My guess is that the equivalent weight of solar cells would provide more power.

    My guess is that the centaur stage as a radiating system would be more useful at higher temperatures.

    One interesting possibility is to use it as a element in a condensing system, with gas coolant injected into the center, that cools and condensates on the outside walls, is recuperated( I don’t quite know how) and is then pumped back into a heat exchanger that cools a reactor and turns the fluid back into gas, completing the cycle.

    You might look up articles with names similar to this:
    ‘Rotating Bubble Membrane Radiator for Space Nuclear Power Systems’

    I wil be posting on Brayton cycles and other cooling cycles in my next posts. I hope you can find useful data in them.


    Michel Lamontagne


  2. Michel, thanks for the insights!
    Of course my first thought was of the decadel survey small fission reactor radiator at 400 C in one of the fuel tanks


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