Technical paper: Wet Launch of Prefab Habitat Modules

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Technical paper: Wet Launch of Prefab Habitat Modules

Background: This was the formal peer-reviewed technical paper on the concept I originally called "CentriStation", short for "Centrifugal Station." I wrote the paper, prepared it as camera ready copy, traveled to Princetpn NJ, and gave teh presentation of teh paper at the SSI conference there, and it was published in the Space Studies Institute's 1995 space conference proceedings, published by AIAA.

This was not only the first formal technical paper I had created for presentation at a technical space conference, but it was the first such conference I had attended. It was a massive learning experience for me.

The idea for making the classic wheel-type space station in low earth Orbit, was that it was needed before committig to building the much larger 10,000-person self-sustating wheel type cities in GEO, which I had concluded was a useful purpose for my KESTS transportation structure concept, along with Solar Power Satellites in GEO. I hoped to give a paper on KESTS to GEO to the Space Studies Institute at Princeton NJ, but I felt I needed more experience before doing such a paper at that esteemed group; thus this paper was done first. Besides, I had long gotten the feeling that there was much resistance to my KESTS to GEO concept, among the aerospace community; and local members (in Los Angeles area) of the SSI were no exception. I had thought they all would be delighted with the whole KESTS to GEO concept and its enabled applications, but that clearly was not happening. I did not understand all that, made no sense to me; but I thought that maybe all they wanted was for me to present the concept in their accustomed format. So, a Centristation type concept paper would be a test run.

I was working as a lowly Electronics Technician for a small car alarm manufacturing company, VSE (Vehicle Security Electronics) in Chatsworth, CA, at the time. My computer was a new low end model 386SX without Windows, ran on DOS. The conference had a reequired formatting hich included part 1 column, part two column on the front page; none of my shareware word processing software would do that. Submission was by several hardcopies. So I made the camera-ready paper using poster making software, in which I was able to make each section of the page as a separate poster rectangle. That I did not make the columns quite exactly the same width, did not become apparent until years later when I attempted to recreate the paper using modern word prosessing software, which insisted on having all columns on a page the same width, of course.

The trip to Princeton by air to the hotel and conference went well, havign never done that before. I was one of the first paper presenters on th first day, and I quickly discovered that I was required t have viewgraphs to go along with my presentation. Frantically one of the conference helpers used a marker pen on sheets of blank viewgraph film, tracing the graphics from my paper, so that I would have at least that for my viewgraphs. Despite being afraid of public speaking, I did it, and was able to answer the questions in the usual question period afterwards. 

It was quite a morale boost when I finally had in my hands the hardbound conference proceedings:

Cline, J. E. David “Wet Launch of Prefab Habitat Modules” Space Manufacturing 10, Pathways to the High Frontier, Space Studies Institute, AIAA, 1995, 88-91


It was a shared copyright, so I include it below.


J. E. David Cline

Independent Researcher

9800 D Topanga Cyn Blvd. #118

Chatsworth, CA 91311

Copyright ©1995 by J. E. D. Cline. Published by the American Institute of Aeronautics and Astronautics, Inc, and Space Studies Institute, with permission.

Independent Researcher


It is proposed here that a technology be developed to build space modules which have a dual purpose, that of being both a prefabricated habitat segment and also temporarily being their own fuel tank during launch. Concurrently a re-useable unmanned winged engine control tug vehicle would be developed for the wet-launch of these modules, along with an additional flyback booster. This would provide a way to build economically a large diameter artificial gravity space habitat in LEO in which the majority of its structure would be built and emplaced prior to the first human presence there, reducing risk and cost. The toroidal space habitat would be built and assembled first on the ground in the form of the dual purpose modules, checked out, then disassembled and launched a segment at a time to the orbital site. Such wet launch enables the tank and launch vehicle structural mass to actually be part of the payload.


Payloads which have a very large volume/mass ratio, particularly those which are prefabricated segments of a full-diameter toroidal space habitat, can be designed to also serve as their own fuel tank during launch. Flyback re-useable engine tug systems are part of the technology. Utilizing this wet-launch technology, large diameter toroidal habitats can be built in orbit prior to human presence there. 1

With the development of a specific wet-launch technology, the component technologies used to create the Space Shuttle can be re-configured to enable serious consideration of major space projects squarely on the road to large scale space colonization in artificial colonies in Earth orbit. By the development of a technology for creating shell structure segment modules which are internally prefabricated with equipment, structures and supplies capable of withstanding cryogenic temperatures, and which are also designed to serve as the fuel tank during their own launch into orbit, new kinds of space projects can be seriously contemplated for the near future, particularly those of one- or two-mile diameter toroidal space habitats in Low Earth Orbit. Such a research semi-closed ecosystem habitat would pave the way for long-term homes for space manufacturing employees and their families, resort hotels, and prove out the basic artificial gravity space habitat concept for possible use in a massive ring of space habitats in the Clarke Belt. 2, 3

Focussing on the expansion of human civilization's well-being, particularly toward the potential of utilization of abundant space resources of solar energy, room to grow, and raw materials, it is conceivable that we could enable expansion of human civilization through space colonization in the near future, to alleviate the ongoing severe pressures on the earth surface ecosystem. The concept of technological re-configuration presented here was developed to be a significant step towards this early large-scale space colonization goal. 3


Building the interior of modular segments of a rotating space habitat to temporarily serve as oxidizer and fuel tanks involves cryogenic survivability, easy purging of residual fuel when in orbit, and easy removal and disposal of tank bulkheads.

The structural and materials technologies are interlaced. In the design, one needs to frequently refer to the overall picture, insofar as is possible; in this case, envisioning the completed toroidal habitat rotating in its LEO orbit. That wheel-like structure is an assembly of modules, linked end-to-end, and tensile reinforced by cables circling the toroid, compressing the segments together. Each of those segments served also as a fuel tank at one time, and as such had to survive fulfilling that function during its launch. 1

To launch a segment of the circumference of a toroidal space habitat while using the segment as its own fuel tank, it must be designed and built to function in the cryogenic environments within its oxidizer and fuel sections. Each equipment bay would need to be adequately sealed from penetration by the cryogenic liquids, or else easily decontaminated. Liners may be useful, to be removed upon initial manned entry of the orbiting space habitat. Residual traces of LOX would dissipate into the air which would infill the module, but residual hydrogen could be explosive or cause embrittlement of some metals. If a hydrocarbon fuel were used, it would need to be scrubbed out, possibly with a detergent. And there are houseplants and bacteria which digest petrochemicals, which might possibly be useful for recycling these residual fuel traces, perhaps later as part of the normal agricultural recycling process.

Bulkheads between the oxidizer and fuel sections of the module need to be easily removed and stored, along with bulkheads at the ends of the module. Design of such bulkheads also is a new task.


The engines used to launch the fuel-filled modules need to be re-useable. Drawing from the existing space shuttle design and technologies, one might envision a cluster of three SSME-like engines, as on the Space Shuttle orbiter, being used to launch the modules. Unpiloted, a streamlined minimum fuselage and airfoil would be included, heat-shielded for re-entry and autopiloted back to the launch site following each launch. 1

Since much of the payload doubles as airframe and fuel tank during its own launch, minimum booster requirements result. One might alternatively envision conventional air-breathing jet engines, two or three of them, connected by a saddle for the wet-launch module, and an airframe adequate to return it to the launch site following each boost. This craft might be piloted since it operates within the atmospheric portion of the launch.


The value is in the kind of space projects which are enabled by the technology. Developing a wet-launch technology enables near future economical construction of a full diameter toroidal research space habitat, which can lead to large scale space colonization, relatively economical construction of a space resort hotel, and habitats for long range manned space exploration. By enabling economical construction of large scale artificial gravity space habitats, the financing of space projects can be moved from the area of defense and pure science, over to fundings for commercial space resort hotels and even of artificial space habitat real estate development.


The structural walls of a payload module, and some of the interior structures, are designed to serve as the equivalent structures of fuel and oxidizer tanks during the module's own launch. This technology is limited to the launch of large volume-to-mass ratio payloads which can survive cryogenic temperatures and proximity to wet/gaseous oxidizer and fuels. Engine/control modules and boosters can be autopiloted during launch, orbital emplacement, teleoperated docking with earlier modules, and return to launch site.

Prefabrication and testing of the toroidal space habitat while it is on the ground, then effectively transferring it module by module to docked reassembly in orbit, eliminates nearly all of the dangerous, expensive time-consuming manned free-fall orbital construction time. 1


The technologies developed for use in the Space Shuttle and Skylab greatly enable this concept. Flyback systems, re-entry heat shielding, re-usable liquid fueled engine clusters, and the Skylab concept of building a pre-fitted space habitat module into what was originally designed to be a fuel tank area, all particularly enable this concept.


Starting from a long range objective of expanding civilization while removing much of civilization's pressures on the earth's ecosystem, the verification of the fundamentals of space settlement functionality needs to be made. This might be done by building a full one- or two-mile diameter rotating toroid in orbit, outfitted for use as a nearly self-sufficient space habitat, would test and refine concepts so long held as self-evident, such as functionality of artificial gravity through centripetal acceleration within a rotating wheel-like space habitat, and the myriad interactive functions of a closed-cycle, semi-self-sufficient city/agriculture system integrated with a mechanical structure. With the proof of such fundamental space colonization concepts, serious consideration can be made for the development of massive earthsurface-to-orbit transportation systems such as the kinetic energy supported railway bridge concepts, which in turn enable a vast ring of earthsurface-like space habitats ringing the Earth in the Clarke Belt, a potential home for hundreds of billions of people. 3, 5, 6


Skylab was built out of that which was originally built to serve as a fuel tank for an Apollo lunar landing launch.

The Space Shuttle's external tank has tempted many people to dream of its structural use for building a habitat in space despite the large amount of manned free-fall construction effort required.

The concept of a wheel-like, rotating artificial gravity space habitat has been around for at least 40 years, yet one has yet to be built. The tremendous amount of raw materials, and in-orbit manned assembly time has been far too expensive to do, considering the expected benefits of such a construction project.

The Biosphere 2 semi-sealed closed ecological test in recent years in Arizona has been the best prior testing we could do.


Maximum use of existing technologies developed for the Space Shuttle suggest a high likelihood of success of the launch system. Laterally-coupled launch vehicle structures, heat-shield materials, liquid hydrogen and oxygen fuel systems, reusable SSME engines, orbital docking systems, and Skylab pre-fitted tank module experience all contribute to the liklihood of success. Generic basic module structure for the toroidal habitat segments enable relatively quick replacement of modules lost during launch. The technique of building the complete wheel-like space habitat on the ground first, for checkout of the multiple interdependent systems, makes for earlier and easier debugging, thus also contributing toward the success of the mission.


Testing of equipment bays designed to be filled with fuel or oxidizer can be done on the ground. An expendable launch could be modified so its second stage is a test module equipped with prefabricated internal equipment bays, to test survivability of equipment in proximity to cryogenic liquids in launch conditions, ability to purge residual fuel, and operational functionality of the equipment following launch. The SSME cluster tug could be drop-tested and autopiloted to a specified runway landing. The jet engine powered booster needs to be flown as an individual aircraft as well as part of the launch vehicle.


Wet-launch technology could be tested using an upper stage of an expendable launch to test materials and survivability. Nearly all of the technologies utilized in this concept already exist, except the techniques for creating modules which are wet-launchable. Thus the cost to develop would be far less than that to develop the space shuttle. Demonstration of the concept might also be done with a specially built external tank used in an actual launch of a space shuttle, although the risk of losing an orbiter cautions this approach. Production costs are lowered due to the large number of similar structures, including the many SSME-type engines, conventional jet engines, and duplicate airframes; the modules themselves would have only a half dozen basic shell types, the rest of their diversity for habitat use would be through individual installation of specific wet-launchable equipment. 4


1. Ground testing of equipment bays designed to be in contact with cryogenic liquid hydrogen and oxygen.

2. Launch to LEO of a test prefab module built from a modified second stage of an expendable launch vehicle.

3. Drop test of a SSME cluster tug airframe, and autopiloted runway landing.

4. Flight test of jet engine powered booster as an independent aircraft.

5. Wet-launch of a prefabricated test module, by the reuseable tug and booster.

6. Construction on the ground of a toroidal space settlement, made of wet-launchable segments, perhaps 1 mile in diameter, made of 166 segmental modules which are 100 feet long, with 3 half-mile long spokes made of similar modules.

7. Completion of 236 successful orbital emplacements assembling the first toroidal space habitat in upper LEO. With a booster and tug turn around time of 1 week, and 14 sets of booster/tugs available, 14 launches per week are made, or two per day. If no modules are lost during the launch series, then assembly time is 17 weeks to complete launch and assembly phase of the settlement, about 5 months to emplace in orbit. A lost module would need to be modified from a set of generic modules, and launched in an added orbital emplacement boost. If each tug uses a cluster of 3 SSME-type engines, and 14 tugs are built, then initially 42 SSME reaction engines are needed for the project.

8. If each booster uses standard commercial aircraft jet engines, then the same 14 sets of booster and tugs initially would require 28 jet engines. If a pair of toroids are built in the project, one spun up and the other left at zero-g, and if an initial 14 sets of booster/tugs are built, then it would take at least 8 months to complete orbital emplacement; if half of the booster/tugs are lost through attrition, then the project still takes less than 16 months to completely launch and assemble them in orbit.

9. Removal of the internal bulkheads from the assembled toroid segments, and purging of residual fuel within it.

10. Launch and orbital modular linking of a second, but non-rotating adjacent toroid for zero-gee materials processing. 6

11. Arrival of first construction workers, and start up of first habitat quarters area.

12. Stringing tensile cable through loops in the modules to act as safety cable, compressing the toroidal structure and its spokes into a rigid structure.

13. Spin-up of the wheel-like space habitat gradually to a full 1-g at its perimeter. Egress to the habitat limited to through the central hub airlocks.

14. Stocking of the habitat with supplies which could not have survived the wet-launch process, including agricultural plants and animals.

15. Human population of the space habitat.

16. Stabilization of the system for providing feedback information which coordinates all of the biological, electrical and mechanical systems interlinked within the space habitat.


Preparation for possible large scale space colonization in near-earth orbits such as the Clarke Belt, which could expand civilization greatly while also reducing the pressure on the earthsurface ecosystem. Space resort hotels, which could provide financing and opportunity for average people to experience life in space.


Mankind needs daily drama in life just like the need for food and shelter. Witness the lure of television shows, movies and newspaper headlines. This project supplies the drama of space colonization started in the 1950's, and could begin to be implemented in the 1990's. Life in space needs to encompass all the functions of being human, in addition to being interesting, sometimes adventurous, and potentially within the reach of personal experience of many people in the near future. Life there needs to be shown to be capable of being very comfortable, safe, and supporting all the mating and family-raising activities that humans normally need. The drama of achieving these in the vast room and resources of space can excite the imagination of humanity, supplying a new confidence in the future of humanity and of planet earth's ecosystem. And the habitat could be modified for relocation at Mars' moon Phobos, or be boosted to GEO if-and-when KESTS (Kinetic-Energy-Supported Transportation Structures) are operational. 1

An alternative way of financing this project thus might be to present it as an ongoing TV series, real-time, from inception to completion, showing also the spinoffs developed by this project, such as recycling, functional understanding of multiple interacting life systems in a semi-closed environment, agriculture, and group lifestyle forms in action. The rotating ring, or toroid shape, has long been in American awareness as the design for a permanently occupied space station, because it provides the artificial gravity needed for normal bodily function. The centripetal force simulated gravity is assumed to be able to provide the means to overcome the unhealthy effects of weightlessness, such as immune system disfunction, bone loss and muscular atrophy; and allow a human being to have normal bodily functions such as ordinary bathroom activities. And people need the companionship and ecological balance of other lifeforms; these animals, fish and plants also need "gravity" to function normally. While it is a testing ground for the Stanford Torus much larger design ... to be built from lunar raw materials later ..., it will test those self-sufficient agricultural processes and family lifestyles in the relatively nearby LEO. The habitat additionally serves as home to workers for adjacent free-fall, hard-vacuum manufacturing facilities, and is comfortable waystation for early manned missions back to the moon and perhaps beyond . 1, 5, 6


Development of a modular wet-launch technology and its specialized launch tugs and boosters, enables the early economical construction of true mid-sized artificial gravity earth-normal-interior space habitats which have been so long envisioned in the imagination of far-seeing people. In turn, within such a habitat the concepts of closed cycle agricultural support systems can be developed, along with the myriad of other normal life function systems. If the concepts of artificial near-earth-normal-interior semi-closed-ecosystems are proven out, then the serious design and development of large scale earthsurface-to-space transportation systems can be begun. A ring of such habitats located in the Clarke Belt, accessed by surface-to-GEO kinetic-energy-supported transportation structures, could easily accommodate many times the entire current population of our planet, enabling continued large scale expansion of humanity and its companion earth life forms. More immediately, this space launch and construction technology could be also used to build a resort hotel in space, bringing the potential for a real personal experience of living in space to many otherwise average people. Modular wet-launch technology can be a key to true space colonization in a much earlier time frame.


1. "Centristation III" by j.e.d.cline1, GEnie Space and Science Library file #1071, December 17, 1989

2. "HWY TO EARTH GEO RING" by j.e.d.cline1, GEnie Space and Science Library file #747, February 9, 1989

3. "6TOGO" by j.e.d.cline1, GEnie Space and Science Library file #4405, April 9, 1994

4. "Toward a Space Habitat" by j.e.d.cline1, GEnie Space and Science Library file #1718, July 1, 1991

5. "Space Settlements, A Design Study", NASA SP-413, 1977

6. "Centristation IV, Multi-goal Space Station" by j.e.d.cline1, GEnie Space and Science Library file #2931, April 3, 1993

Copyright ©1995 by J. E. D. Cline. Published by the American Institute of Aeronautics and Astronautics, Inc, and Space Studies Institute, with permission.

Independent Researcher