we would need a decent view so that could be accurately docked.

Not that I have any objection to ensuring a decent view from the cockpit, but it's not strictly necessary for docking - we could also have cameras mounted on or near the tip of the nose, feeding images to a screen on the instrument panel.  Even if we can manage to achieve good visibility, docking cameras may be worth implementing anyway.

noumena said:Lookin' peachy keen. I didn't quite understand the window at first either. I have another question regarding it now that I do. I've never seen a window that big or at an angle quite like that on a rocket. Is there a precedent for this or are you striking out into new territory? It looks really neat :-) Should give the pilot a heck of a view.

The window is based on what I have seen with other capsules, albeit a little bit larger. It should probably be made a smaller so that we don't waste so much internal volume. We were discussing the possibility of using a magnet on the tip of the nose to dock with the lander so we would need a decent view so that could be accurately docked.

Luke Maurits said:Actually, I just realised the same sort of "scooped out window" design was in fact used on Gemini, check out this diagram, it's quite clear.  I would love to know the rationale behind this design.

 I'm pretty sure that the primary reason is so that docking could be accomplished.

My thoughts were that we would have ultra high pressure oxygen cylinders (~10,000psi (second link) is about as high as I could find) in the "nose" of the module.

I wonder about how much room we will have/need in the nose.  I suppose we can make it arbitrarily long if we need to, but in addition to it looking a bit silly I am sure that keeping it shorter will have positive aerodynamic effects and I worry about vibration with a relatively long, thin part of the craft sticking out from the opposite end of the booster.

I assume that a lot of the nose will be taken up by parachute / paraglider stowage.  This seems to be the case in Mercury and Gemini, I assume that parachutes haven't miniaturised since those days since the entire operating principle depends on surface area.  I also really like the way Gemini's RCS is localised entirely to a block at the base of the nose (whereas Mercury has jets at the base of the cone and the fuel storage behind the astronaut's back, necessitating a lot of plumbing) and figure we should emulate that too.  This may not leave much room in the nose for gas storage.

I was thinking about long, cylindrical oxygen tanks, parallel to the nose, being stored in the space under the seat.  Here is a terrible concept diagram:

I suppose it will be hard to start planning this kind of stuff in detail without some sort of CAD solution where we can specify sizes for things and see what actually fits where.

This is sort of outside the scope of this thread, but at one point we talked about pumping the cabin air into a storage vessel prior to EVAs. This would probably be relatively easy to do and (nearly) the entire volume could fit into a fairly small low pressure tank (standard 450psi 31bar oxygen bottle). Upon repressurization one would simply vent the bottle's contents into the cabin. Then fine tune the mixture with nitrogen and/or oxygen until it reaches the desired pressure/mixture.

The weight of the pump/storage bottle might not be worth the effort though.

Safer, I suppose, but it's still dangerous. I'm against it. We really wouldn't need all that big a tank of Nitrogen, for example, to contain several habitable volumes worth of the stuff. We'd want to have a few extra, though, in case unschedualed EVAs are required for some emergency or there is a leak or something, but it should still be reasonable.

My thoughts were that we would have ultra high pressure oxygen cylinders (~10,000psi (second link) is about as high as I could find) in the "nose" of the module. The pure O2 would be fed into the life support mixer that controls the flow of pure oxygen and recycled air (CO2 scrubbed air). Prior to reentry the nose would be jettisoned (reducing the mass of the reentry vehicle and thus reducing the thickness of the heat shield, but also increasing the peak acceleration…which we would have to keep an eye on). Prior to the separation the cabin air would be enriched with oxygen so that the scrubber can keep a habitable atmosphere until the capsule is recovered.

In order to determine how much oxygen we need I guess that we need to determine how much oxygen a person uses in 1 day.

This is from a website:

I found a web site which stated that an average adult each day consumes 4 lb
of food, 2 lb of water, and 6 lb of oxygen. I could not find a
corroborating site, but the numbers seem roughly reasonable. Assuming 6 lb
of oxygen per day is right, how large a room do you have to seal?
Incidentally, an exercising adult uses oxygen at about 15 times this rate,
so remain calm!

6 lb is about 2.73 kg. Since a mole of oxygen has a mass of 32 gm = 0.032
kg, an adult needs about 85 moles per day. Since a mole under standard
conditions (atmospheric pressure, 300 C) occupies 22.4 liters, 85 moles
occupies about 1900 liters or 1.9 m^3. But air is 21% oxygen, so about 9.1
m^3 of 321 ft^3of air is required for one adult for one day.

So according to this we would need ~1900 liters per day of pure oxygen (at standard atmospheric pressure). Assuming that we use a 690 bar tank (10,000psi) we could squeeze that 1900 liters down to 2.75 liters (did I get that correct?…ideal gas law pV=nRT) per day. Multiplying this by a 10-12 day mission duration comes out to about 27.5-33 liters of pure oxygen @ 690 bar starting pressure. For those who have trouble visualizing things in metric units (myself included), this comes out to a tiny 1.165 ft^3 for 12 days of oxygen. Of course we need some sort of re breather system to scrub CO2 from the cabin.

What kind of atmosphere do we want? The ISS uses a composition similar to air. Do we dare forget Apollo 1 and go with a pure oxygen cabin? The real issue with Apollo 1 is that they had pure oxygen at sea level which meant that the absolute pressure was atmospheric plus the overpressure. Is pure oxygen safe if we only use .7atm while in space (532 mmHg)?

Rocket-To-The-Moon said:

I'm also curious why you think that ours needs to be scaled up (compared to Mercury)? My main concern is that it is big enough so that the astronaut can don the moon suit.

Mercury was really small.  Wikipedia says: "Because of their small size it was said that the Mercury spacecraft were worn, not ridden.  With 1.7 cubic meters of habitable volume, the spacecraft was just large enough for the single crew member".

I think some scale up will be needed, mainly because we will need to fit more stuff in than Mercury did and our astronaut will need more mobility.  The longest Mercury flight was 1 day, 10 hours, and the earliest ones were less than an hour.  We will need to store a lot more oxygen, food, water, etc. than those flights would have needed for our mission which will be at least 6 days long as possibly longer.  I doubt it could all fit into something Mercury sized.  Also, given the short average flight time, I assume the toilet solution for Mercury was "just hold it in".  We will need a better solution which will require a bit of mobility on behalf of the astronaut, more than you could get in Mercury, where you just stayed strapped in the whole time.  Mercury didn't support any EVA options, so the hatch could afford to be smaller and getting into/out of the capsule could be more of a struggle.  To be able to get into and out of our capsule during EVA easily and safely we will probably need a bigger hatch and more spare room.  And, like you mentioned, there is the need for enough room to be able to put on the moon suit.

Don't worry, I'm not talking about scaling it up much.  I think our module will have to be larger than Mercury but would probably be smaller than Gemini (which is basically just Mercury scaled up enough for a second seat, with some stuff shifted into a "service module" at the back).  It would definitely be Gemini-sized in the worst case – never larger.

Slightly unrelated, but I've also found a nice diagram of the insides of Gemini.  If you imagine removing the second seat, there is a lot of spare room, it should be enough to fit all of our supplies – although I'm a little bit nervous about oxygen.  Has anyone done the maths on not just how much O2 we would need but how much space it would take up if stored at a realistic pressure?  Maybe we will need a service module approach for this after all.

Luke Maurits said:

I don't quite understand how it works, then.  The astronaut is lying perpendicular to the long cylindircal nose, facing upward, right?  How can they see out of that window?  Is there a mirror or something?  Even if there is a mirror, why would we want a view facing backward rather than forward?  Won't the angle of the CM's conical section lead to much of the view out that window being obscured?

What was your reason for going with the "bulge" shape instead of a simple flat window directly infront of the astronaut's face?  The kind of thing you can see in this cut-away view of Mercury (which I love, by the way, I picture our module basically being a scaled up version of it).

I think that the 2d picture may be confusing you. When on the launch pad the window is facing directly forward and the astronaut is laying on their back with their face behind (below) the window. Here is a video to help you visualize it.
I'm also curious why you think that ours needs to be scaled up (compared to Mercury)? My main concern is that it is big enough so that the astronaut can don the moon suit.

What was your reason for going with the "bulge" shape instead of a simple flat window directly infront of the astronaut's face?  The kind of thing you can see in this cut-away view of Mercury (which I love, by the way, I picture our module basically being a scaled up version of it).