The current state of affairs, rearranging forums to suit? | Spacecraft Engineering Workgroup | Forum

Since there has been a lot of rethinking about the CM lately, this is an attempt to summarise how things seem to look so far.

Basically, to summarise the shift in thinking: NASA used three craft ultimately in the lead up to putting a man on the moon.  Mercury, to learn how to safely put a man in space and get them back; Gemini, to learn how long a man could stay in space and to see if they could leave the craft while in space (EVA); Apollo to use the knowledge gained from Mercury and Gemini to go to the moon.

Since we do not have NASA's budget and do have a lot of their knowledge, we're basically going to do the work of all 3 of these projects in one, CLLARE.  That means that the CLLARE spacecraft has to be able to operate in "Mercury mode", "Gemini mode" and "Apollo mode".  i.e. we want to be able to just do suborbital and EVA-free orbital flights as well as a moon mission.  This restriction basically rules out the Apollo project's strict CM-SM dichotomy – we cannot put things like power generation, communication equipment, etc. in a separate, lunar-specific module instead of in the crew's module, because those things will be necessary even on the "Mercury mode" flights where there is no lunar module.

This leads us to a design where essentially instead of a CM which contains as little as necessary for its job and then a jettisonable SM which contains everything else and an engine, we will have a "self-contained" spacecraft, like Mercury, that we can send up all by itself for suborbital and short orbital fights, but which we can attach a big engine to (our "orbital bus") for lunar missions.  You could still think of this in SM/CM terms, but the SM would contain only an engine and its fuel, so you may as well call it a propulsion module or something.

So, the CLLARE spacecraft (do we still want to call it the CLLARE command module even though it looks like there will no longer be a CLLARE service module?) should probably look like this:

• A craft which can contain entirely within itself all the power generation and atmosphere maintaining equipment and materials necessary for a stay in space of, say, at least 8 days; but…
• …which could have extra modules attached to it to provide supplies for longer missions if we want to do them (this would be like the Apollo SM).
• A craft which contains its own attitude control (RCS) system and no significant means of self propulsion; but…
• …which could have extra propulsion modules attached to it to supply more than just attitude control.  These propulsion modules could be small and weak (a simple solid fuelled system for reentry burns on orbital missions) or large and powerful (a cryogenic fuelled system for lunar missions).
• A craft which supports EVA via an ingress-egress hatch like those seen on Gemini.

I am thinking it would be great to have a standardised module connection system so that you can treat the modules like lego bricks: you start with just the CLLARE spacecraft by itself, and if you're only going suborbital that's good enough.  But behind that you can attach an arbitrary number of "mission extension modules" (which contain extra oxygen, methanol, water, whatever), so that you can stay up there as long as you like, and behind those you can attach an arbitrary number of propulsion modules (you use the outermost one first and then jetisson it when you're done to use the next one).  If you wanted to go somewhere far, far away for a long, long time, your arrangement could look like this:

[Prop module]=[Prop module]=[Prop module]=…=[Ext module]=[Ext module]=[Ext module]=…=[CLLARE spacecraft],

which would have the appearance of a long cylinder with a truncated cone on its end.  Of course, with only one crew member you probably wouldn't want to do something extreme like that, but if we were clever about it we could make sure that if we designed a 2 or 3 seat version of the CLLARE spacecraft in future, it was compatible with the same kinds of propulsion and extension modules.  This would involve either the bigger spacecraft having a larger radius at the end of its cone and using a "shrinking adaptor" between it and the train of modules, or keeping the spacecraft radius the same by putting crew members infront of one another instead of alongside one another, kind of like you see in 2-crew jet fighters.  That stuff's in the distant future for now, anyway.

For the lunar mission, the arrangement would simply be:

[Prop module]=[CLLARE spacecraft]

Do people agree that this is a sensible way to divide things up, so that we can use the one craft for Mercury, Gemini and Apollo style missions?

If there is agreement that this approach is best, what should we do with the forums?  At the moment there are explicit CM and SM subforums that would have to be deleted or potentially renamed.  This is easy enough to do, but I worry that if we do this now we may change our minds later and have to change it again, etc, etc.  Perhaps the best thing to do for now would be to have non-lander related spacecraft engineering discussion happen in the main SEW forum and then create subforms once we are more certain about our situation?

brmj said:

I think the varient that would consist of including an extension module on our moon flight and ratting the command module alone for perhaps a day or two might also be worth considering.

Actually, this probably makes a lot of sense, in that it will help us keep the size and mass of the base capsule down.  We can simply jetison both the extension module and propulsion module (possibly as a single unit) after any reentry burns.

My only concern with the nose approach is that there just won't be enough room unless we make the nose look ridiculously long.  This is based mainly on intuition, though, and could be very wrong.  If someone can do some rough hand-waving calculations and show that (i) moving everything other than RCS out of the nose into the cone won't take up too much room in the cone and (ii) putting enough gas/liquid in nose tanks for a lunar mission can be achieved without the nose length exceeding some realistic limit, then I would be more than happy to consider it.

I wonder what the aerodynamic implications of a long nose on a short cone vs a short nose on a cone with cylindrical modules on the back would be?

With regards to your concerns about simplicity of stacking modules to be later separated: in some sense this is a false dichotomy because even if we put gas and liquid into nose tanks, we will still need an external propulsion bus to be attached to the back of the capsule for lunar and Earth injection, and that will need to be separated` before reentry.  If we discard the extension and propulsion module as one unit then we don't actually require any extra separation events.  Also, if you check out figure 2-11 on pdf page 39 of the Vol 1 Gemini Familiarisation Manual, you'll see that the mechanism by which their reentry module is attached to the crew module is astonishingly simple – they basically just have a few short titanium straps bolted to both modules.  The straps have shaped charges around them which break the straps in two upon detonation and that appears to be about it!  It's amazing how simple some of this stuff is.