A Technical Review by David Buth
First Published in L-5 Points, the Journal of the Minnesota Space Frontier Society in June of 1984. I was even threatened with a law suit if I published this one! Nothing ever came of it of course. Enjoy!
In 1979 and 1980, The Space Habitat Design Associates (SHDA), with the help of several other groups put together the Space Shuttle External Tank Habitability Study. It analysed the External Tank itself and its current use and possible modification in its introduction. The main body of the study dealt with bolt-on cargo sections, the Space Operations Center and its expansion to process STS External Tanks, as well as a large rotating habitat constructed from these same External Tanks.
The external Tank Torus (ETT) consists of a total of ten tanks, two in the central axis and eight in the outer octagonal rim. These tanks and their bolt on cargo sections are cut and welded together into an approximately 300 foot diameter space station. Although not mentioned in the study, the ETT would require over 3430 linear feet of welds on the tanks and about 530 linear feet of welds in the spokes. These figures don't include cuts for tank corrections or internal passageways or any other internal welding and cutting.
The rooms, bulkheads and passageways are formed from foam impregnated multi-layered inflatable structures hardened with microwave radiation. They can support "200 mpsi." (sic). Once complete, this station would rotate at 2.12 rpm to achieve 23% terrestial gravity (gs). It will support a permanent crew of 25 with 150 to 170 scientists, researchers, engineers, and technicians, and various other personnel including tourists. These people could live there for three, six or nine months, depending upon their own objectives.
In concept this modular design appears to be both aesthetically pleasing and functionally flexible. However, the study contains a few errors. Assuming no change in mission, the ETT requires major layout changes due to an error in physics. In each of the tanks, the decks were laid out parallel to the walls of the eight tanks. Therefore, the decks are at an angle of 45 degrees at either end, to the force of artifical gravity which is radial in nature. Only the center of the tank is perpendicular to the centrifugal force. To fix this results in reducing the three original continuous decks to two with lower rooms at the ends of the tanks and upper rooms in the center. As a result the maximm population of the space station is reduced from 200 to about 160.
Another factor in the new layout is the internal diameters and thicknesses of the five major ring frames in the external tank. The inner diameter of the 13 intermediate ring frames as well as their positions should also be considered. Their effect on internal layout is therefore not known by this author. The only measurements relating to the ring frames that were given in this study were the positions of the major ring frames.
I consider the lack of any description of any life support systems a drawback to the study as well. I suggest a life support system with eight "wheels" of eight algae tanks. These would be mounted in the axis and would be rotated at 7.8 rpm for an artificial gravity of .25 gs. Two sets of four tanks would counter-rotate for gyroscopic balance. With this system, each ten by three foot tank would supply oxygen for three people. This system, coupled with green plants scattered about the living quarters, would insure an adequate oxygen supply for the inhabitants. In fact, freeze-dried wastes may be oxidized to supply adequate C02 for all the plants. This greenery may also help to supply the inhabitants with food. Thus, the space station could get closer to a completely closed ecology. In order for this system to work, the axial tanks would have to be lengthened with forward and aft cargo compartments. to make room for the algae tanks.
In addition to this, some other modifications are in order. The study has the station oriented to the Sun to supply the solar collectors with power. Such control over orientation will require a good positioning system for the station. Many things on the station, including antennae, telescopes, and camera platforms, must be moved to the de-spin axis. If micro gravity research is to be conducted, some habitable modules should be attached to the de-spin axis as well.
Another modification to the station would consist of extending the length of these axes from 20 feet aprox. to 60 feet, the full length of the shuttle's cargo bay. This would enlarge the length of the ETT's axis to 546.5 feet. The number of shuttle missions needed would be increased from 12-14 to 14-16 to handle the increased tonnage for the station. This would allow plenty of room for the addition of algae tanks.
Different designs of space stations are possible for a variety of projects and budgets. (Figs D-G) Type "A" may be preferable for customers with a limited budgets. Type "B" may be used for a cardiac and critical burn hospital. Type "C" with its large shielding would be useful as an agricultural facility which would grow food for itself and other stations. Type "D" stations would be more stable with their counter rotating sections. This would cancel gyroscopic effects and would allow the stations much more mobility.
All things considered, the External Tank Space Station is a potentially very useful idea. I intend to consider its problems and potentinals in further detail as time permits, especially the life support systems. Our thanks to John Spencer, the study's executive director, and to SHDA for its preliminary work in this area and its dissemination for this and other useful ideas for our future in space.
[Ed. note: If we had saved all of the external tanks used to date we would have all of the tanks necessary to build this station. The Content is copyrighted 1984 © by Dave Buth.]
Click here for a tour of the Station
Standard Small Work Station:
Provides artificial gravity for crew as well as microgravity using 3 tanks.
Variable Gravity Station:
Provides variable gravity for burn or heart patients to slowly aclimate to normal earth gravity using 25 tanks.
Agricultural Station with Counter-rotating Assemblies:
This design can provide hydrponically grown food for many other stations when provided with their waste products using 68+ tanks.
Large Work Station with Counter-rotating Assemblies:
Provides multiple gravity environments for a large onsite work force using 30 tanks.
August 30, 1999 -