Thermal control | Spacecraft Engineering Workgroup | Forum

Not much substance in this post, just pointing out that, as a group, we have rather significantly neglected the issue of thermal control in all of our discussions.  By this I mean making sure all parts of the spacecraft are kept within a range of acceptable temperatures to keep them operating properly (this is distinct from thermal protection, which deals with reentry heat).

This will be particularly salient for the Single Craft proposal.  The common CM in that plan will need to be able to keep all its parts at appropriate temperatures both during the trans-lunar cruise (where the only sources of heat are the sun and onboard electronics, and there is a lot of surrounding dark space to radiate into) and during its stay on the lunar surface (where heat is being conducted through the landing legs, as well as coming from the sun and the sun's reflection off the moon, and there is less dark space to radiate into without back-reflection).  This is a more challenging problem than maintaining a comfortable temperature in only one of those environments.

brmj said:

For the lunar lander, I see this as a smaller issue if the heat balance is such that heat would normally need to be disposed of. On the surface, we can use the ground as a heat sink, which ought to be considerably more effective than just radiating into vacuum. If, on the other hand, it works out so that we need to be heating the cabin, this works against us for the same reason. However, the legs could be designed to be much more or less conductive of heat depending on this, so we ought to be able to optimize for either adequately.

We will definitely need to be disposing of heat while on the surface – a lot of it.  While in trans-lunar glide I think we are more likely to need to be heating the cabin, although probably not too much beyond what natural heating we get from the astronaut and the electronics.

Using the lunar surface as a heat sink is not going to work because the lunar surface gets up to 123 degrees C during the day.  If our lander is at a temperature lower than that (and it had better be!), heat is going to flow from the moon into the lander, not the other way around.  We will need to try to insulate the landing gear from the craft itself as much as possible, and we will certainly still have to get rid of some heat somehow.  The Apollo LM's ascent stage had an ice sublimator in it for this purpose, and the Soviet LK lander had an alcohol vaporiser for the same.  I think we will need some sort of active cooling device like these, either that or a set of deployable radiators.

One of my concerns is that if we design the CM to be thermally best suited for the lunar surface (and since that is by far the more extreme of the two environments, it makes sense to me to do this) then we will do things like e.g. cover it in really shiny, reflective foil, like the Apollo LM, in order to reflect back as much as we can of all the incoming sunlight.  This is probably quite suboptimal for the trans-lunar part of the flight, though: if you look at a Soyuz module, they're usually covered in dark, thick-looking blankets designed to keep heat in.  A lunar-surface optimised CM might tend to get very cold while in space, which means we will probably have to put more work into heating the cabin.  The alternative would be to design the CM to be thermally best suited to open space, i.e. to try to retain some heat, and in that case it's going to get very hot on the moon very quickly, requiring a pretty impressive cooling system to keep it manageable.