More thoughts on CM structure | Command module design | Forum

I've been thinking more about the internal structure of the CM and I've come to realise that we probably haven't really taken good stock of just how much of a boon the miniaturisation of electronics has been.  Thinking about the size of e.g. Crossbow's IMUs, standard commercial GPS receivers, netbook motherboards, etc., there's actually a quite sensible chance that we could fit all our electronics inside a single (radiation shielded) case the size of a medium-sized desktop computer case.

With this in mind, the diagram below shows the already discussed two-part pressure vessel, but with some more detail.

The large blue part of the pressure vessel is where the astronaut is steated.  The smaller green part at the front is a separate vessel for electronics, containing the one case mentioned above.  Two valves (shown in yellow – one atop another but in the actual capsule I assume they would be vertically aligned but on opposite sides of the cabin) allow flow between the two vessels when open – fans behind the valves, pointed in opposite directions, encourage mixing of the atmosphere between the two vessels, with heat generated by the electronics heating the entire cabin.  Prior to EVA, the valves are closed and the fans shut down.  The large vessel is vented while the smaller vessel remains pressurised.  Oxygen is fed into the pressure vessel from external tanks via the smaller electronics vessel, so that the fuel cells can still breathe during extended EVA.  With this arrangement, all of the electronics are in a pressurised environment all the time.  This makes testing of the electronics box on Earth extremely straight forward.

The smaller pressure vessel features two air-tight electrical plugs (shown as red circles) – one on top, by which the instrument panel is connected to the electronics box, and one at the front, by which the electronics box is connected to the first nose module (probably RCS).  The connection from the electronics box to the first nose module is not just those connections required for interfacing with that first module, but has several spare "channels" of cabling, which the first nose module simply passes through to subsequent nose modules, each of which have the same standard connectors on either end..  In this way, e.g. control signals can get from the electronics box to the RCS unit and parachute unit, and radio equipment in the electronics box can be connected to antennae in the nose, regardless of the order in which the nose units are attached.

The front panel of the smaller pressure vessel, shown in the diagram in darker green, features a hinged air-tight door.  Access to electronics on the ground is achieved by opening that door (which is hinged at the bottom, so that when open it lays flat on the floor) and pulling out the box, which is mounted on rails just like a drawer in a filing cabinet (but obviously with locks).  The entire box can be passed out through the EVA hatch for maintenance.  In this way, the CM avionics are almost entirely independent of the CM itself: cases can be slid in and out as required.

Thoughts?

Rocket-To-The-Moon said:

I like the design and the thought of using waste heat from the electronics for supplemental cabin heat.

Instead of having valves and fans to circulate air would it be a better idea to just have a hinged door between the electronics and the cabin. The door would open up into the electronics box. When preparing for EVA the astronaut would close the door. When the large pressure vessel is depressurized the door would self seal (rubber gasket) and the pressure inside the box would keep the door shut. I feel like this is a simple solution to this. It would still be possible to have a fan that induces a flow through the box or we could just rely on convection (I don't think convection works in 0g…a temperature gradient and conduction through the air).

Valves certainly may not be the simplest solution to the problem, I don't really have a lot of experience with these sorts of thing.  Your proposal sounds just as feasible to me and considerably simpler, so if nobody can find fault with it I'd have no objections to it at all.