[the link for this free pdf is at the bottom of this page]
I recently went back to my copy of Space Commerce by John L. McLucas because The Space Studies Institute has a project simmering called SSI G-Lab and I recalled there being some mention of related potential options.
G-Lab is a free flying spinner at LEO planned to accommodate research on multiple generations of vertebrates at various reduced gravities – research that cannot be performed on the surface of the Earth because of the overriding 1 g. This is an important project because without it all bets are off when it comes to extended visits or permanent settlement of other planetary surfaces in the Solar System. We can ‘just go’ and find out when the first child is born but for a fraction of the cost and risk we could have some indication of the hazards and an easy place to test mitigation ideas.
In the 1991 book McLucas (Former DOD Deputy Director of Defense Research & Engineering, Director of the National Reconnaissance Office, Administrator of the FAA, Fellow of the AIAA, Secretary of the Air Force, Chairman of NASA’s Advisory Council, Chairman of External Tanks Corporation and board member of Orbital Sciences Corporation) brings up this same issue of the need for variable gravity research and artificial gravity labs and adds to it a plan that could have possibly been done back in that day, the use of spent STS external main engine tanks:
“One area of research where the tank may actually be better than the Space Station is in studying the effects of artificial gravity. Although we may not need to simulate 1 g, it is probably impossible to do so within the confines of the current Space Station Design; it is just too small. With a diameter of 15 feet, the largest centrifuge you can squeeze into the Space Station as now configured has a radius of about 6 feet. It is impossible to envisage getting useful results by putting a person in such a device. Such rapid spinning would upset the basic measurements on the effects of artificial g. The external tank, on the other hand, is large enough for a centrifuge of 12-foot radius. While still not ideal, this is much more workable.
We may very well decide to rig up two platforms tied to each end of a tether so that we can spin the whole thing, thus achieving a large fraction of 1 g at a very slow rotation rate. Two external tanks tied together and rotating about a common center of gravity would make an excellent lab for testing the effects of artificial gravity of different levels.”
- pages 173-174
The discussion of using spent STS main tanks for artificial gravity testing goes on for several more paragraphs in both the section “The Shuttle’s External Tanks” and the following “Industrial Space Facility.” It is fascinating reading.
McLucas wrote the book in 1990-91 and according to Wikipedia “In 1990, it was suggested that the external tank be used as a lunar habitat or as an orbital station.” Farther back, in the 1988 SSI edition of The High Frontier, Gerard K. O’Neill writes similar ideas of using, instead of throwing away, those massive external tanks:
“In the ‘Low Profile’ plan, those tanks would be carried into orbit, at a very small cost in shuttle payload. We would set up a storehouse of empty tanks in orbit; some would be fitted out as living quarters, each tank providing about twenty comfortable, private apartments for as many workers. In Shettler’s plan [**], those modular apartment houses would turn up everywhere in the early days of space manufacturing: in low orbit, for the training and final screening of workers in the special world of zero gravity; in high orbit, for the workforce tending the processing plants, at L2, for times when the mass-receiver there may need repair, and on the lunar surface.”
O’Neill doesn’t in that paragraph mention testing artificial gravity in the tanks as his idea was to just make rotating habitats that simply were at 1 g, but it was a part of SSI’s External Tank concepts, as we see in the 1985 SSI Report on Shuttle External Tank Applications written by SSI SA J. Alex Gimarc:
“The use of tethers with the ET also provide significant advantages to the future space program. These advantages include artificial gravity, momentum exchange, electrical power generation, electric propulsion, and significant enhancements in shuttle and space station missions.
The physics of tethers allows artificial gravity to be generated in two ways. First, two tanks can be attached to each other by a tether and stored in a gravity gradient mode . This is useful in liquid storage applications. Second, the system can be made to rotate. Artificial gravity levels of 1 ‘G’ can be induced by a system 200 meters in diameter rotating at 2-3rpm. This artificial gravity will negate the undesirable effects of long term weightlessness on the body and lengthen crew stays on station. “
Of course, the days of throwing away giant first stage tanks are behind us, landing them and re-using them is the current and potentially game-changing route. However, once the re-use technology matures beyond prototypes, when a tank has finished its run of launches there is a chance that a company would consider leaving it on orbit if someone could find a use for it in its final state.
SpaceX’s use of “easier” to store RP-1 (kerosene) or methane means for a sticky inside and difficult cleanout but if Blue Origin or some other yet to appear company uses hydrogen with a helpful insulation system then a cleaner purge might be possible.
How possible? In the end Skylab was launched “dry” as a facility built on the ground not “wet” and constructed in Space, it was simply less complicated, but we should be careful before completely ruling out the option if the day comes that launching is not as huge a deal as it was in the Apollo era – or still is today. Some motivator might come along to put a dual use tank back on the table and the bullet points in chapter seven of Space Commerce (plus the points made in The High Frontier and the SSI ET Report) may come around again as just those important needs.
Reading a book on Space Tech from 1991 or 1988 or 1985 may seem to be a silly exercise, logic says that new books come out every year and new companies come along that completely re-write the fundamentals. Well, not necessarily. Space is definitely hot again with new players battling for bragging rights but overall it’s still a very slow moving business and old resources are where engineers go first not only to see if they can shave development time and cost but also to look for sell-able ideas that just were too far ahead of their time.
With that in mind, The Space Studies Institute is proud to re-release the SSI Report on Space Shuttle External Tank Applications. We hope that you find in its pages some great ideas that can help us all reach The High Frontier. Click the link below for your free copy.
-Robert Smith March 2017
**- J. Peter Vajk, Joseph H. Engel and John A Shettler. “Habitat and Logistic Support Requirements for the Initiation of a Space Manufacturing Enterprise”. NASA SP-428 Space Resources and Space Settlements (technical papers from the 1977 Ames Summer Study on Space Manufacturing and Industrialization Using Nonterrestrial Materials)