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Shielding against hypervelocity impacts is a thing, like a whipple shield. Easy enough for many things, like various habitat modules.

But radiators are required to be very large in size, particularly for new applications where those are very high-energy. Depending on what you're doing, the radiator could be most of your surface area. This is made even worse by the need for it to actually function, like flowing fluid through to transfer heat. Any impacts are likely to cause leaks or degrade function. So it would seem like you would want to have a missile shield, but the requirements for a missile shield go almost entirely against the requirements of a radiator for heat rejection. The only possible ways I can think to make this work are:

  1. Have a shield that is transparent to the thermal wavelengths. This will be expensive and very imperfect.
  2. Maybe, speculatively, you could have a wire mesh above the radiator surface, but only if that wire mesh occupied an acceptable fraction of the total area, and if the mesh size was smaller than the expected missiles that you're worried about. Because thermal photons are small, you can get a selective effect here.

I tried to ask ChatGPT, but it seemed to fundamentally blunder the problem. It did find a patent that's at least relevant:

https://patents.justia.com/patent/12415625

Which it took as it was describing (2), but reading myself, I think it's describing (1) but it's language is so hard to read I'm legitimately not sure. Also unclear if it's actually a patent because other search engines do not return it.

But I guess my question is, are either of these things viable? Is there any serious proposals for any radiator shield?

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    $\begingroup$ Of course there isn't a good way to link to a patent from the USPTO itself, but the basic search ppubs.uspto.gov/basic and patent number 12415625 will get you to the proper patent that includes the actual figures. Hopefully that will clarify what the patent is about $\endgroup$ Commented 2 days ago
  • $\begingroup$ The shuttle didn't have anything like this. Late in the program (1998) automatic leak isolation was added in case a radiator got a significant puncture, but no shielding. $\endgroup$ Commented 2 days ago

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(Oh fun, I know the guy who is the inventor on that patent.)

The short answer is no, we don't typically shield radiators, but also yes, we design radiators so that they can withstand the expected environment with a prescribed probability.

Much of the approach depends on what kind of radiator we are talking about.

There are two main types of radiator used on spacecraft -- or rather, there are two main methods of transferring heat from the heat sources to the radiators: heat pipes and pumped fluid loops. Heat pipes are passive and self-contained, but they have limited capacity. Pumped fluid loops can reject far more heat, but they are more complex and more vulnerable to failure.

The general construction of a radiator is some type of structural panel -- typically honeycomb -- into which the flow tubes are embedded. Within the radiator, the flow tubes will have some sort of conductive structure that brings the heat from the fluid in the flow tubes to the radiator surface where it can be rejected to space. Very often this structure is just a solid chunk of metal.

Radiator failure would happen as a result of not being able to meet heat rejection requirements. In general, this means penetrating one or more flow tubes such that the working fluid leaks. Depending on your vehicle design and mission, it may be one leak or it may require multiple.

Heat pipe systems are, in general, easier to include redundancy in, as each heat pipe is a standalone item, so loss of one heat pipe does not affect other heat pipes. Whether losing a single heat pipes causes any avionics failures depends completely on the particular design.

Pumped fluid loop systems are far harder to create redundancy. Either you need to have fully separate loops, or you need to be able to isolate sections. Both of these options are mass-heavy and still carry risks of sneak single points of failure.

The general approach to hardening a radiator to MMOD comes in varying three design aspects:

  1. Adding redundancy to permit loss of a flow tube. This is "easy-ish" for heat pipe systems but very difficult with pumped fluid loops unless it has been planned for since the beginning of the vehicle design.
  2. Adjusting the flow tube density on the radiator. Fewer total inches of flow tube within the panel means less vulnerability. The radiator does not care if the structural honeycomb gets hit. This is another basic sizing decision that needs to be made early in the design.
  3. Adjusting the design of the conductive structure that thermally bonds the flowtube to the radiator surface. This is the easiest option to do later in the design. This can be as simple as thickening the extrusion so the flowtube is set farther back, hollowing out the extrusion so that it acts like a whipple shield itself, or other choices, adding doublers to the facesheets, and other choices.

This pertains specifically to the panels themselves, but especially with deployable pumped fluid loop radiators, there is a lot of vulnerability in the supporting equipment themselves -- manifolds, return pipes, flex hoses, etc., that are somewhat outside the scope of this question.

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  • $\begingroup$ Are there any radiative fluids that would be appropriate for self-sealing? That is, you get a mimpact but the system simply loses a bit of fluid pressure rather than needing to actually shut off that loop? $\endgroup$ Commented yesterday

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