[The following is an excerpt from a letter to Allen Meece]

[Updated 4 September 2002]

I've been playing with an old idea for the crew hab, using it as a starting point for new hab ideas. This is a basic "plastic hab", constructed inside an airtight 3.5m x 6.5m PET tank and using a similar 2.5 x 2.5m tank for an airlock. The crew cabins of both tanks are supported by additional aluminum frameworks built into each tank.

The 3.5m diameter tank used for the main crew quarters is cramped, but with a 2.2m ceiling has considerable room for storage and machinery both under the floor and overhead. Using the frame, lockers can be built into the curve of each wall, providing additional space.

The walkways inside are slightly wider than absolutely necessary, but have lockers and equipment shelves opening into them over the entire length of each wall, with a small gap by the pilot's station for a side window. Using a design like this would require the crew to use all kinds of space saving measures. For example, the plan given above does not expressly include beds for the crew, which are intended to be foldable hammocks or cots which are stored when not in use. The hab bath essentially consists of a big plastic bucket with a shower door and plumbing in it, intended to serve as both latrine and shower stall. More importantly, note that the workroom can only really be configured for three work stations, which saves even more space by making assumptions about crew rotation and distribution of labor. (Six bunks still fit in the crew cabin, though, along with the most essential item shown here: beanbag chairs! :) )

The air-lock, with its smaller diameter, could have only enough space above and below 2.2m ceilings for plumbing. Everything else, including the necessary compressed air tanks, would have to be stored in lockers and panels along the sides of the airlock or outside the pressure vessel.

Additional volume is required outside the hab for insulation and some storage, adding another 0.6m to the diameter of each module. This leaves the diameter of the crew module at 4.1m or more. This is too wide to fit inside a keel of reasonable width. A better option in terms of distributing the weight is to suspend the hab beneath the keel. Placing the hab atop the keel or within it requires the keel to resist strain without the ability to distribute the load, via tension, to other parts of the platform.

Note that in addition to being wider than a comfortable keel, the hab module's length is also a fair fraction of the platform length. With its weight, this means that its placement relative to the center of rotation is critical if we don't want the platform to tip. In addition, it would be desirable to lower a hab of this design even further because it would produce a useful lowering of the center of mass, adding stability to the platform.

The disadvantage of this is that the hab is at some remove from the keel, requiring the crew to climb up to gain access to it. Partial solutions can be had by suspending the hab as close to the keel as possible and by including a walkway around the hab for use by all EVA's that do not expressly require access to the keel. The full hab is sufficiently long that its air lock end can be placed relatively close to the tether even though its center of mass remains some distance away. Extending the platform around the hab so that the tether passes through it could help solve the problem of how to dock the elevator to the platform. Since the platform and elevator will both always face into the wind, and the tether is ahead of the platform's center of rotation, the elevator can dock with the suspended platform without having to -- or even being able to -- ascend to the tether mount.

A ladder can be used to ascend to the keel, but that won't be useful for hauling up equipment to maintain the antenna arbor or other systems that require access to the keel. A gin pole and winch can be employed as a small crane to hoist a bucket elevator to and from the keel.