Making semi-realistic command pods

[Armchair Rocket Scientist]

So I'm not sure if this is the best forum to put this in since this is mostly conceptual - mods please move it if necessary - but I'm working on preliminary ideas for a couple of "advanced" command pods for niches that neither the stock game nor current mods cover very well.

Configs for use with stock games will be included, but ultimately they're designed for "Kerbal-scale" RSS saves like 10x Kerbin, as well as RealFuels and comparable mods.

Currently the pods in development are:

A: A "high-density" 2.5m-1.25m capsule carrying six kerbals. Yes, six. This is meant to be a descent module similar to Soyuz, and would be used in conjunction with a Hitchhiker or other orbital module. The thing will be cramped, and when used with a life support mod should only offer 24 hours of accomodations with a full crew.

B: A set of 3.75m pods. Yes, I've heard of Taurus HCV, NovaPunch's Freyja, and the new 3.75m CM in Near Future Tech,, but none of them seem quite right: Freyja is rather flat, similar to the proposed Fuji spacecraft, the Taurus's enormous windows seem excessive on a capsule, and NFT's capsule has a bizarre shape (this is all personal opinion; nothing against any of these mods or their authors, I'm just looking for something a little different). Anyway, these will be conical capsules, probably with one 3.75m-2.5m variant and one 3.75m-1.25m variant.

Anyway, I have a couple questions regarding layout of exterior and interior.

1. Looking at most of the IVAs in the game, both stock and modded, the seats don't have headrests. This seems uncomfortable in a plane that might accelerate at 1 g, but for a capsule that could pull 5 gs, or 10 gs during a launch abort, it seems suicidal. Do we know of any reason Kerbal seats don't have headrests?

2. In most IVAs, kerbals are helmetless. This makes perfect sense for something like the Hitchhiker, but I was under the impression that during launch and landing astronauts always wore helmets in case of a cabin depressurization. However, Kerbal helmets are extremely bulky and restrict peripheral vision. Have there been any proposals for some type of flexible inflatable helmet that could be used to hold air in, but wouldn't need to survive radiation or micrometeoroids like a full EVA suit?

3. I've heard references to crew couches being able to fold away, allowing access to equipment or supplies stowed behind/underneath them. Will this be possible on the Dragon v2, which has multiple rows of seats? Are there any diagrams showing how the folding mechanism works?

4. Is there any rule of thumb for how much space nitrogen tanks, oxygen tanks, helium tanks for pressurizing the RCS system, etc. take up outside the pressure vessel?

5. I'd like for one version of the 3.75m capsule to be capable of propulsive landing similar to Dragon v2. However, the fuel required for this takes up a lot of space (no, I'm not including internal fuel tanks in the final model, but I want the capsule to actually have space for them). One possibility is putting reusable 3.75m (or a 5-3.75m) service bay underneath the capsule, followed by a heat shield. Is having the lower part of the spacecraft have essentially vertical sides viable with a lifting reentry?

6. Is there any information on how much SuperDraco engines actually weigh, as a baseline for the TWR of other liquid-fueled LES engines?

7. With the new stock heating model or new version of Deadly Reentry, is it preferable to have an integrated heat shield (and tweak away all the ablative when something else is directly below the pod on reentry), or have it as a second part? In the latter case, the pod's pressure vessel may extend below the transition between the frustrum and the spherical heat shield, possibly resulting in an IVA that's "bigger on the inside." Would the game have any problems with this?

[bazz]

I like this idea a lot modular command pods you can kit out according to the mission requirements.

4. Is there any rule of thumb for how much space nitrogen tanks, oxygen tanks, helium tanks for pressurizing the RCS system, etc. take up outside the pressure vessel?

Volume of Compressed Gas in a Cylinder

To find the volume of gas available from a compressed gas cylinder, we apply the Ideal Gas Law (PV = nRT). In a high-pressure cylinder, the volume will be affected by the content's compressibility factor Z (PV = ZnRT). For example, an AL cylinder of pure helium may contain 134 cu. ft. of gas while the same cylinder of pure air may contain 144 cu. ft. under the same conditions. For these practical calculations, however, we assume ideal gas behavior for simplicity.

The Ideal Gas Law PV = nRT

Where:

P is pressure

V is volume

n is the number of moles

R is the gas constant

T is the absolute temperature

When the temperature is kept constant, we can derive the equation:

P(1) x V(1) = P(2) x V(2)

Where:

P(1) is the pressure of the compressed gas in the cylinder (psi)

V(1) is the internal volume of the cylinder, often referred to as water volume (liter)*

P(2) is the atmospheric pressure (1 atm - 14.7 psi)

V(2) is the volume of gas at pressure P (2) (liter)

For example, an AL sized cylinder is filled with nitrogen at 2000 psi. What is the gas volume of nitrogen from the cylinder?

P(1) is 2000 psi

V(1) is the internal volume of AL cylinder 29.5 liter*

P(2) is 14.7 psi

V(2) is the unknown volume of gas

Solving the equation above for V(2) gives:

V(2) = [p(1) x V(1)]/P(2) = (2000 psi x 29.5 liters)/14.7 psi = 4013 liters

(approximately 140 cu. ft.)

*The water volume of the high-pressure cylinders can be found on this site under the Cylinder Specs and Packaging section.

http://www.alspecialtygases.com/volume_of_gas_in_a_cylinder.aspx

Also this...

[MainSailor]

3. I want to say that during the V2 reveal, the mechanism for folding the upper row of seats was shown, along with folding the control panel. I can't find a diagram or a photo right now though. I also know that the Apollo CM couches could move into a variety of positions, including flat against the bulkhead to provide more space in the capsule during zero g.

Edit: A related link that talks about the Apollo CM couches.

4. I don't have a number, but I know it's not that much space compared to the actual habitable volume.

Here's a photo of the Orion during assembly:

All the space along what I'd call the lower cone is used for various tanks used for RCS and atmosphere. Since this was for the EFT flight, I'm not sure these tanks were included.