Reusing Space Shuttle External Tanks




Dave Randall Hunt


A Graduate Research Project Submitted to the Extended Campus

In Partial Fulfillment of the Requirements of the Degree of

Master of Aeronautical Science


Embry-Riddle Aeronautical University

Extended Campus

Hickam AFB Resident Center

September 1998


This Graduate Research Project was prepared under the

direction of the candidate’s Research Committee Member,

William A. Stickney, Adjunct Instructor III, Extended Campus,

and the candidate’s Research Committee Chair,

Frank W. Glazier, Full-time Faculty Member, Extended Campus, and has been

approved by the Project Review Committee. It was submitted

to the Extended Campus and partial fulfillment of

the requirements for the degree of

Master of Aeronautical Science






William A. Stickney, MS

Committee Member




Frank W. Glazier, MPA

Committee Chair




Writer: Dave Randall Hunt

Title: Reusing Space Shuttle External Tanks

Institution: Embry-Riddle Aeronautical University

Degree: Master of Aeronautical Science

Year: 1998

The External Tank is the largest component of the Space Shuttle system and is the only part that is not reused. Currently, the External Tank detaches from the Orbiter at approximately 95-98% of the way into orbit and burns up in the atmosphere with remnants falling into a remote part of the ocean. The technology exists to convert External Tanks into a space station, but it is perceived that changes could threaten the safety of the crew onboard. This research project analyzes how the External Tanks can be safely transformed into a space station and used for research, living quarters, and entertainment. This proposal also examines how the private sector can fund such a project and benefit financially from it.








Importance of the Research

Statement of the Problem








Liquid Oxygen Tank


Liquid Hydrogen Tank

Thermal Protection System

External Tank Hardware

Michoud Assembly Facility Production Capabilities

Super Lightweight Tank

Structural Verification Test


Future Uses

Converting the External Tank

Design Concepts

GEODE Project

Problems to Overcome

Maintaining a Circular Orbit

Disposing of Residual Fuel

Removal of Spray-On-Foam-Insulation

Raising Funds


Design of the Study

Data Description

Data Collection

Treatment of the Data








1 Idea and Safety Results

2 Problem Results

3 Technical Problem Results

4 Maintain Results

5 Design Results

6 Funding Results

7 Orbit Results

8 Time Results

9 Budget Results

10 Pay Results

11 Favorite Use Results




1 External Tank Components

2 Liquid Oxygen Tank Structure

3 Intertank Structure

4 Space Island

5 Prop Design

6 Star-Shaped Design



Importance of the Research

The External Tank (ET) on the Space Shuttle is the only piece of hardware that is not reused; it burns up in the atmosphere with remnants falling into the ocean after it is jettisoned from the orbiter. These tanks are produced and assembled at the Lockheed Martin Michoud Assembly Facility (MAF) and go through very vigorous testing to ensure a flawless Space Shuttle launch. The ET holds the liquid oxygen and liquid hydrogen, which is used up in the first eight and one-half minutes of the flight. Then it is separated from the orbiter and not used again (Damon, 1995).

A new Super Lightweight Tank (SLWT) has been designed to weigh less and provide more strength. This allows the Space Shuttle to carry more cargo into space and makes it possible for the orbiter to achieve a higher orbit. It is also possible for the Space Shuttle to carry the ET into orbit, then eject it into its own orbit. This would allow the ET to be reused for many innovative projects such as a refueling station or a space station for research, living quarters, and/or even entertainment.

The technology exists to convert these used ET’s into a space station, but the National Aeronautics and Space Administration (NASA) refuses to allow any changes to the ET that might jeopardize the safety of the crew onboard the Space Shuttle during the launch (Prado, 1997). The start-up costs for such a project are enormous, but there have been some creative ideas for financing construction of a space station by involving the private sector from around the globe. Most of the changes to the ET would be made on earth, and then the ETs would be joined together end-to-end into a huge ring while they are floating in space.

This research paper will analyze the benefits of converting these ETs and ways this could be profitable to the United States as well as to many of the businesses from around the world. Space can be looked upon as the next frontier in exploration and by reusing the ETs, this resourceful concept could become a reality.

Statement of the Problem

The purpose of this research project is to analyze how the ETs could be safely changed to be reused as a space station and how ETs could be assembled in space without endangering the lives of the astronauts involved, all within a reasonable time frame and budget.


1. Determine what changes will need to be made on the ET before it is used for a launch and how these changes might affect the launch capabilities of the Space Shuttle.

    1. Determine how the ET can maintain a circular orbit.

3. Determine how the residual liquid oxygen and liquid hydrogen can be purged from the ET.

4. Determine how the Spray-On-Foam Insulation (SOFI) can be removed from the outside of the ET without causing dangerous consequences.

5. Determine how the private sector can benefit financially by accepting the challenge of placing these ET’s in orbit for the purpose of research and entertainment.


ETs can be safely changed and reused as space stations without endangering the lives of astronauts, and this all can be accomplished within a reasonable time frame and budget.


This study will not consider the requirements and training required of astronauts to work in space.

The study will not determine where the astronauts will live while working in space or how they will be transported back and forth to Earth.

This study will not analyze the launch capabilities of the Space Shuttle.

This study will consider what attributes the ET contributes to the launch of the Space Shuttle.

This study will not consider what happened to the already used and jettisoned ETs.

The study will consider the results from the Internet survey web page, despite the fact that the results could be biased because only interested people will visit the site.


    1. The ET is constructed of material that will be safe when used in space.

2. There will be enough launches of the Space Shuttle in a specified time period to begin construction.

3. Lockheed Martin will be able to keep up with the demand and produce quality ETs.

4. ET testing is the most through and complete inspection one can expect from our technology.




The concept of a reusable spacecraft is nearly as old as that of flying machines itself. As the development of rocket propulsion systems increased, the idea of entering space became a reality. With this technology, the United States began its research to construct a vehicle that could be reused repeatedly. On January 5, 1972, President Nixon approved the three-element Space Shuttle consisting of an Orbiter, rocket boosters, and a disposable propellant-tank (Gatland, 1981). This was the answer that has worked since the first test flight on April 12, 1981 (Damon, 1995).

In 1975, the prime contractor for the ET was Martin Marietta Aerospace. The first ET was assembled at the Michoud Assembly Facility (MAF) in New Orleans, Louisiana in 1976. In July 1977, the fabrications for the first flight ET began. The intertank structural test program was completed in November 1977, and the first ET tanking test was conducted in December 1977. After all the testing was completed, the first flight ET (External Tank-1) was delivered to Kennedy Space Center in July 1979 (External Tank, 1997).


"The ET has three major components: the forward liquid oxygen tank, an unpressurized intertank that contains most of the electrical components, and the aft liquid hydrogen tank" (Dumoulin, 1988, p. 1). Below is an illustration of all the components.

Figure 1. External Tank Components. Note. From Introduction to Space (p. 137), by T. D. Damon, 1995, Malabar, FL: Krieger Publishing Company


It is 154 feet long and 27.6 feet in diameter and carries more than 535,000 gallons of cryogenic propellants that are fed to the orbiter’s three main engines (LaNasa, 1997). "Prior to propellant loading, the ET weighs approximately 66,000 pounds. But once liquid oxygen and liquid hydrogen are loaded into the vehicle beginning eight hours prior to Shuttle launch, the ET weighs 1.65 million pounds" (LaNasa, 1997, p. 1). The first five ETs weighed approximately 77,000 pounds inert, which was heavy compared to the 66,000-pound lightweight tank now used.

The weight reduction was accomplished by eliminating portions of stringers (structural stiffeners running the length of the hydrogen tank), using fewer stiffener rings and by modifying major frames in the hydrogen tank. Also, significant portions of the tank are milled differently to reduce thickness, and the weight of the ET’s aft solid rocket booster attachments were reduced by using a stronger, yet lighter and less expensive titanium alloy. Earlier several hundred pounds were eliminated by deleting the anti-geyser line. The line paralleled the oxygen feed line and provided a circulation path for liquid oxygen to reduce accumulation of gaseous oxygen in the feed line while the oxygen tank was being filled before launch. For each pound of weight reduced from the ET, the cargo-carrying capability of the space shuttle spacecraft is increased almost one pound (Dumoulin, 1988, p. 1).

Liquid Oxygen Tank

The upper tank carries 1.36 million pounds of liquid oxygen at minus 297 degrees Fahrenheit (F) at liftoff (Damon, 1995). It is 331 inches in diameter, 592 inches long, and weighs 12,000 pounds empty with a volume of 19,563 cubic feet (143,000 gallons). Below is an illustration of the liquid oxygen tank.

Figure 2. Liquid Oxygen Tank Structure. Note. From External Tank (p. 2), by J. Dumoulin, 1988


Dumoulin (1988) describes its construction as follows:

The liquid oxygen tank is an aluminum monocoque structure composed of a fusion-welded assembly of preformed, chem-milled gores, panels, machined fittings, and ring chords. It operates in a pressure range of 20 to 22 psig. The tank contains anti-slosh and anti-vortex provisions to minimize liquid residuals and damp fluid motion. The tank feeds into a 17-inch-diameter feed line that conveys the liquid oxygen through the intertank, then outside the ET to the aft right-hand ET/orbiter disconnect umbilical. The 17-inch-diameter feed line permits liquid oxygen to flow at approximately 2,787 pounds per second with the Space Shuttle Main Engines (SSMEs) operating at 104 percent or permits a maximum flow of 17, 592 gallons per minute. The liquid oxygen tank’s double-wedge nose cone reduces drag and heating, contains the vehicle’s ascent air data system (for nine tanks only) and serves as a lighting rod (p. 2).


"An intertank collar connects the two propellant tanks together and provides space for most of the electrical components" (Damon, 1995, p. 134). The intertank is 270 inches long, 331 inches in diameter, and weighs 12,100 pounds. Dumoulin (1988) better describes the configuration of the intertank as follows:

The intertank is a steel/aluminum semimonocoque cylindrical structure with flanges on each end for joining the liquid oxygen and liquid hydrogen tanks. The intertank houses ET instrumentation components and provides an umbilical plate that interfaces with the ground facility arm for purge gas supply, hazardous gas detection, and hydrogen gas boiloff during ground operations. It consists of mechanically joined skin, stringers, and machined panels of aluminum alloy. The intertank is vented during flight. The intertank contains the forward solid rocket booster (SRB)-ET attach thrust beam and fittings that distribute the SRB loads to the liquid oxygen and liquid hydrogen tanks (p. 3).

Below is an illustration of the intertank.



Figure 3. Intertank Structure. Note. From External Tank (p. 3), by J. Dumoulin, 1988

Liquid Hydrogen Tank

"The lower tank is about 2.5 times larger (383,000 gallons) and carries about a quarter of a million pounds of liquid hydrogen at minus 423 degrees F" (Damon, 1995, p. 133). It is 331 inches in diameter, 1,160 inches long, has 53,518 cubic feet of volume and weighs 29,000 pounds empty. The liquid hydrogen tank’s composition is specified below:

The liquid hydrogen tank is an aluminum semimonocoque structure of fusion-welded barrel sections, five major ring frames, and forward and aft ellipsoidal domes. Its operating pressure range is 32 to 34 psia. The tank contains an anti-vortex baffle and siphon outlet to transmit the liquid hydrogen from the tank through a 17-inch line to the aft umbilical. The liquid hydrogen feed line flow rate is 465 pounds per second with the SSMEs at 104 percent or a maximum flow of 47,365 gallons per minute. At the forward end of the liquid hydrogen tank is the ET/orbiter forward attachment pod strut, and its aft end are the two ET/orbiter aft attachment ball fittings as well as the aft SRB-ET stabilizing strut attachments (Dumoulin, 1988, p. 3).

Thermal Protection System

"The entire outer surface of the external tank is insulated with a half inch thick cork/epoxy layer covered with 1 to 2 inches of spray-on foam" (Damon, 1995, p. 134). "The system also includes the use of phenolic thermal insulators to preclude air liquefaction. Thermal isolators are required for liquid hydrogen tank attachments to preclude the liquefaction of air-exposed metallic attachments and to reduce heat flow into the liquid hydrogen. The thermal protection system weighs 4,823 pounds" (Dumoulin, 1988, p. 4) The two reasons protection is essential are that both propellants are very cold and they boil at very low temperatures. The following are problems that could happen if there were no insulation (Damon, 1995):

This poses two problems: excessive loss of hydrogen and oxygen through vent valves and buildup of excessive pressure in the tanks. Controlled boiling is necessary on the launch platform to keep the tanks pressurized for structural strength and also to assist the pumps in moving the propellants out of the engines. During flight, the tanks are pressurized by gases from the engines. In addition, because of the cold temperatures, if the tank were not insulated, water vapor in the air would readily condense as ice on the sides. At liftoff, the ice would break loose and damage the Shuttle (p. 134).

External Tank Hardware

The external hardware, ET / orbiter attachment fittings, umbilical fittings, electrical, and range safety system weigh 9,100 pounds. Each propellant tank has a vent and relief valve at its forward end. This dual-function valve can be opened by ground support equipment for the vent function during prelaunch and can open during flight when the ullage (empty space) pressure of the liquid hydrogen tank reaches 38 psig or the ullage pressure of the liquid oxygen tank reaches 25 psig (Dumoulin, 1988).

The liquid oxygen tank contains a separate, pyrotechnically operated, propulsive tumble vent valve at its forward end. At separation, the liquid oxygen tumble vent valve is opened, providing impulse to assist in the separation maneuver and give more positive control of the entry aerodynamics of the ET. There are eight propellant-depletion sensors, four each for fuel and oxidizer. The fuel-depletion sensors are located in the bottom of the fuel tank. The oxidizer sensors are mounted in the orbiter liquid oxygen feed line manifold downstream of the feed line disconnect. During space shuttle main engine thrusting, the orbiter general-purpose computers (GPC) constantly compute the instantaneous mass of the vehicle due to the usage of the propellants. Normally, main engine cutoff is based on a predetermined velocity. However, if any two of the fuel or oxidizer sensors sense a dry condition, the engines will be shut down (Dumoulin, 1988).

The locations of the liquid oxygen sensors allow the maximum amount of oxidizer to be consumed in the engines, while allowing sufficient time to shut down the engines before the oxidizer pumps cavitate (run dry). In addition, 1,100 pounds of liquid hydrogen are loaded over and above that required by the 6:1 oxidizer / fuel engine mixture ratio. This assures that main engine cut-off (MECO) from the depletion sensors is fuel-rich, since oxidizer-rich engine shutdowns can cause burning and severe erosion of engine components. Four pressure transducers located at the top of the liquid oxygen and liquid hydrogen tanks monitor the ullage pressures (Dumoulin, 1988).

Each of the two aft external tank umbilical plates mate with a corresponding plate on the orbiter. The plates help maintain alignment among the umbilicals. Bolting corresponding umbilical plates together provides physical strength at the umbilical plates. When the orbiter GPCs command external tank separation, pyrotechnic devices sever the bolts. The ET has five propellant umbilical valves that interface with orbiter umbilicals: two for the liquid oxygen tank and three for the liquid hydrogen tank. One of the liquid oxygen tank umbilical valves is for liquid oxygen; the other is for gaseous oxygen. The liquid hydrogen tank umbilical has two valves for liquid and one for gas. The intermediate-diameter liquid hydrogen umbilical is a recirculation umbilical used only during the liquid hydrogen chill-down sequence during prelaunch (Dumoulin, 1988).

The ET also has two electrical umbilicals that carry electrical power from the orbiter to the tank and the two SRBs and provide information from the SRBs and ET to the orbiter. A swing-arm-mounted cap to the fixed service structure covers the oxygen tank vent on top of the ET during the countdown and is retracted about two minutes before lift-off. The cap siphons off oxygen vapor that threatens to form large ice on the ET, thus protecting the orbiter's thermal protection system during launch (Dumoulin, 1988).

The range safety system provides for dispersing tank propellants if necessary. It includes a battery power source, a receiver/decoder, antennas, and ordnance. Various parameters are monitored and displayed on the flight deck and control panel. These parameters are then transmitted to the ground (Dumoulin, 1988).

Michoud Assembly Facility Production Capabilities

The following is an overview of what the Michoud Assembly Facility (MAF) is capable of producing and what tools are used throughout the facility (Ferrari, 1996):

The Michoud Assembly Facility is uniquely suited to large and small manufacturing operations that require wide bays, up to 40-foot clear height, access to production and material laboratories, and shipment by water, rail or highway. Michoud contains over 3.7 million square feet of manufacturing facilities, 700,000 square feet of office space, 200,000 square feet of laboratory space and a deep water port with convenient access to the Gulf of Mexico. Fully automated, computer-controlled weld equipment provides the most advanced welding for aluminum and aluminum-lithium alloys. Michoud uses state of the art delivery systems to apply thermal protection system materials to large space structures. The facility can conduct hydrostatic tests on pressure vessels up to 28 feet in diameter and 94 feet long. One of the largest automated facilities for interior and exterior cleaning of large aerospace structures is also available (p. 1).

Super Lightweight Tank

The first weight reduction of 10,000 pounds in April 1983 resulted in increased payload. Now a new design will weigh an additional 7,500 pounds less. This lighter weight will allow the Space Shuttle to carry heavier cargo into orbit, which is a key element in building the international space station (Cabbage, 1995).

Lockheed Martin Michoud Space System is assembling a super lightweight version of the ET. By substituting WeldaliteÒ , an aluminum-lithium alloy developed by Lockheed Martin, and incorporating weight-saving design changes and other efficiencies, the SLWT will weigh 7,500 pounds less than the current design and thus improve Shuttle payload capacity by an equal amount. Because the ET has almost reached orbital velocity with the orbiter at main engine cut-off, every pound removed from the ET equals approximately one pound of increased payload capability (Williams, 1997, p. 1).

The formulation for the aluminum-lithium, A1 2195, is one percent lithium, four percent copper, 0.4 percent silver, 0.4 percent magnesium, with the remainder being aluminum (Williams, 1997). "This alloy is weldable, 30 percent stronger and five percent less dense than the A1 2219 alloy previously used in the ET. The new alloy also provides higher fracture toughness at cryogenic temperatures, as low as minus 423 degrees F, versus room temperature fracture toughness" (Williams, 1997, p. 1). Besides the new material, the tank’s structural design has been improved. "The walls of the redesigned hydrogen tank are manufactured in an orthogonal waffle-like pattern, providing more strength and stability than the previous design" (NASA, 1997, p. 1). "Manufactures at NASA’s MAF will also try to keep the tank’s weight down with a new, more precise way of applying the insulating foam coating to the exterior" (Cabbage, 1995, p. 1). With the use of the new alloy, about 2.5 million dollars will be added to the ETs current 50 million dollar cost (Cabbage, 1995).

Structural Verification Test

Parker Counts, manager of the External Tank Project at the Marshall Space Flight Center said, "The new external tank has passed one of the most innovative structural verification test programs ever designed, culminating with these proof tests" (Rahn & Malone, 1997, p. 1). The following is a description of the state of the art test technology:

The proof test for the liquid oxygen tank was a hydrostatic, or water pressure test. The tank was placed vertically on the test stand at NASA's Michoud Assembly Facility in New Orleans, LA, and filled with water, which has similar density to liquid oxygen. The tests simulated conditions encountered during flights and validated the design changes. The liquid hydrogen tank was pressurized with gaseous nitrogen and subjected to conditions simulating the thrust of the orbiter's main engines and solid rocket boosters. Tests checked the new design by exposing the tank to harsher conditions than it will encounter in flight. After the tests, comprehensive X-ray and dye penetrant inspections will be performed to further verify the tank's flight worthiness. The proof tests completed March 25 were the final in a series of rigorous certification and structural verification tests (Rahn & Malone, 1997, p. 1).

In October 1997, a notable production milestone happened when the mating of the major components was completed. "The SLWT, designated ET-96, is currently in Final Assembly at MAF for completion of mechanical, electrical, and thermal protection system installations, and final acceptance tests. The tank is on schedule for delivery to NASA in January 1998 in support of the May 1998 launch of Space Shuttle mission STS-91, the final scheduled Shuttle/Mir docking mission concluding the joint U.S./Russian Phase 1 Program" (Nead, 1997, p.1).


The following is a schedule of events that happen to the ET during a Space Shuttle launch. The time is displayed first, followed by the event (Damon, 1995):

T - 4 hours 30 minutes: Begin filling liquid oxygen tank.

T - 2 hours 50 minutes: Begin filling liquid hydrogen tank.

T – 2 minutes 55 seconds: Oxygen tank at flight pressure.

T – 1 minute 57 seconds: Hydrogen tank at flight pressure.

T + 8 minutes 50 seconds: External tank separation (p. 143).

Basically the ET supplies the liquid hydrogen fuel and liquid oxygen oxidizer to the SSME’s during liftoff and ascent. During the first part of the flight, the emphasis is on gaining altitude. After getting through the dense part of the atmosphere, the orbiter increases horizontal velocity to reach orbital speed (Damon, 1995). The following is a description of when the ETs propellants are depleted and what happens to the ET once it leaves the orbiter:

When the hydrogen and oxygen in the ET are nearly consumed and the vehicle is just short of velocity, the orbiter’s main engines cut off. A vent valve at the top of the external tank opens and oxygen escapes through the nose cap. A few seconds later the tank is disconnected, the venting oxygen causing it to pitch away from the orbiter and start to tumble. Tumbling assures the atmospheric drag will cause it to break up as it falls back to Earth and lands in the Indian Ocean. There is some uncertainty as to where it will land because of the way it tumbles. The designated impact area is an oval 2,100 miles long by 62 miles wide (Damon, 1995, p. 146).

Mark Prado (1997) describes what happens to the ET and why it cannot be reused. "When more than 97 percent of orbital speed is attained, the ET is detached from the Shuttle Orbiter and directed to cross Earth’s atmosphere to burn up Skylab-like with remnants falling into a remote section of the Indian Ocean. The ET cannot be returned to Earth for reuse on later launches because it cannot be returned without burning up in Earth’s atmosphere, unlike the Boosters which detach themselves early before high speeds are attained. Currently, the ET is just thrown away" (p. 1).

Future Uses

There have been many ideas brought forward to use the ET as a space station or even a refueling station. "Martin Marietta has proposed modifying one tank to serve as a pressure vessel to house a gamma ray imaging telescope. Another possible use which has been proposed is as an orbital fuel storage facility to support on-orbit operations" (Bridwell, 1997, p. 2). "Some planners envision them clustered together as a space station, fitted with rockets and launched to the Moon for a lunar colony, or refitted a little at a time and used as orbiting gas stations for vehicles heading to the outer reaches of the Solar System" (Damon, 1995, p. 146).

Some looked at the 1,000 ETs scheduled to be taken up by the year 2000 and realized that if they were all left in orbit, converted into living and working quarters and joined into a single ring, they’d form an unbelievable structure three stories high and 30 miles round, housing over 36,000 people in condominium-like conditions! While a single 30-mile round ET Ring-station housing 36,000 people was theoretically possible, 80, one-third mile round Ring-stations holding 500 people each seemed far more practical. (Meyers, 1990, pp. 52-53)

The classic design is the 12-ET ring station along with two ETs joined end-to-end passing through the middle section. Below is a conceptual illustration of this arrangement.

Figure 4. Space Island. Note. From Space Manufacturing and Processing (p. 5), by Ball et al, 1997

The following is a simple idea for a space station:

Dozens of Station designs have been proposed, and the engineering for each has been worked out in considerable detail. The simplest would be to attach a habitable section at the base of the External Tank during the External Tanks construction. This Aft Cargo Carrier could be outfitted as living quarters for a half dozen astronauts. It would be roughly the size of a 2-story house. The crew would ride up in the shuttle, move to the habitable section once they'd reached orbit and begin converting the External Tank upper 16 stories into laboratory, production, and living areas. Once 2 or 3 of these single External Tanks are in orbit their crews could begin assembling additional External Tanks into a ring, or other design. A 12-External Tank ring would provide living quarters under one-quarter to full gravity conditions. The ring would be one-third mile round with a three deck interior holding living/working quarters and life support systems for up to 400 people (External Tank, 1997, pp. 1-2).

The Aft Cargo Carrier would be an inexpensive arrangement that could provide many benefits. Abstracts (1998) describes these benefits:

The External Tank (ET) Aft Cargo Carrier (ACC) is a low cost, low risk augmentation of the Space Transportation System (STS). It almost doubles the cargo volume of the STS while minimally impacting other STS elements (orbiter, ET and solid rocket boosters SRBs, launch facilities and STS operations. In addition to increasing the potential volume of cargo carried on a Shuttle launch, the ACC provides the following additional benefits: (1) Increased STS competitiveness for payloads; (2) Increased cargo manifest flexibility; (3) Increased spacecraft design options; (4) Alternate manifesting for special payloads; and (5) Future platform/station design options (p. 1).

"This has been dubbed a wet launch of a habitat. It solves most of the problems and expense of needing lots of robotic or human extravehicular activity in space to outfit the tank with its desired contents. However, since NASA has said that any use of the ET can’t have any effect on launch performance, and this design has a more massive tank with a resultant loss in payload capacity, it doesn’t look as if NASA will accept this. NASA doesn’t like any redesign of the manned Shuttle system due to the potentially lowering the safety to the crew by any mistakes due to redesign, e.g., structural dynamics" (Prado, 1997, pp. 3-4).

Gene Meyers, an industrial engineer and entrepreneur, is promoting a privately funded plan to use the ETs via the Space Island Project. He envisions also a giant ring formation that would allow for the production of gravity sensitive materials on a large scale. Other uses would be increased ease of cell farming for medical research, repairing and constructing satellites in space and, eventually, for entertainment (Ball, DeFilippo, Ritter, Skryd, and Ball, 1997).

The Space Islands Project has an intriguing scenario for a space resort hotel. Gene Meyers said, "The external tanks would be joined up end to end in the form of a ring with two more tanks joined up passing through the center like an axle through a wheel, like the orbiting Hilton in the 1969 movie, ‘2001: A Space Odyssey’" (Collis, 1997, p. 2). Marks (1997) describes how one of these hotels might pay for itself in a short amount of time:

In fact one option being considered is to design an early ET-station as a very exclusive hotel holding no more than a few dozen occupants at a time in spacious rooms, and limiting it to a total of 1,000 guests. After that its interiors would be torn out and divided up into smaller units for RregularS [SIC] tourists. Because of the exclusivity of that first, palatial orbiting hotel, some think that visitors on that first, historic guest list of 1,000 might pay as much as $10 million each for a one week stay. If that were true it would pay for the entire $10 billion station, meaning that later guest rates might be in the thousands, rather than millions. After the first decade or so of operations the costs could drop into the hundreds, and surveys show that at that rate there would be millions of takers. The view of Earth, the stars and the romantic possibilities of low or zero-gravity are just a few of the attractions (p. 4).

He also said, "Impatient space tourists may be startled to learn that the first 300-person, cruiseship-like station could be ready in about five years, and that some of the world’s major cruiselines, airlines, hotels and travel agencies are interested in joining forces with our group, Space Island Development Inc., to privately finance them" (Suter, 1998, p. C02).

Repairing satellites in space is another use for the ET. Gene Meyers (1998) says, "Our region’s satellite builders, TRW, Hughes and Loral, may lease station sections in advance for their own repair crews, since assembling, repairing and refueling their satellites in orbit (using "2001" space pods) could cut costs in half" (pp.M-2).

Most of these ideas where brought up in the past and nothing was done about them. Meyers (1998) had the following to say:

In 1978, Rockwell took the idea to their only customer, the National Aeronautics and Space Administration, which shelved it. At that time, the shuttle, then projected to ferry 100 passengers, was still three years from its first flight. NASA also had no intention of becoming a space hotel operator and preferred designing things from scratch rather than using recycled components, like ETs. Rockwell, for its part, had never sold products to anyone but the government. Building commercial space stations for tourism or satellite-repair markets was beyond its ken. Things are different today. The shuttles have flown nearly 100 flights, and NASA is keenly interested in privatizing them. Two years ago, Boeing bought Rockwell, and is desperately trying to find new business for the shuttered shuttle plants in Downey and Palmdale. But the Boeing space people have no idea how to interest the public in this dramatic option (pp.M-2).

Converting the External Tank

The following is a portrayal from Tom Abbott (1997), an ET enthusiast, of how an ET would be outfitted in orbit:

First the leftover hydrogen and oxygen must be vented from their respective tanks. The easiest and simplest way seems to be to use helium gas, from a tank mounted in the intertank section, to purge the tanks. After the tanks are purged, an astronaut would open the access hatch on the bottom of the hydrogen tank (opening the access hatch and astronauts passing through it in spacesuits has already been demonstrated in NASA's neutral buoyancy facilities). A docking adapter/airlock/propulsion unit would then be attached to the access hatch. All our ET outfitting hardware would be passed through the hatch into the ETs interior (all this would be done while the space shuttle is still attached, for support) and then we would seal it up and fill it with a breathable atmosphere. Let's go inside and take off our spacesuits. Once inside we can look down the length of the hydrogen tank. The other end is 96 ft away. Just inside the access hatch a few feet is the tank's main ringframe, which is more or less a circular girder. This main ringframe carries the lower attachments for the shuttle and solid rocket boosters, and the tanks walls are welded to it (and the others). We see this main ringframe protruding into the interior above the tank walls about four inches, all the way around the 27 ft diameter of the tank, and as you look farther into the tank you see that there are other ringframes at intervals (about 20 ft apart) all the way to the other end of the tank. Now, we take a 20-ft-long girder (part of our outfitting hardware) and we attach it so it spans the distance between the main ringframe and the next ringframe into the tank. We then take another girder and attach it to the same two ringframes, 180 degrees from the first girder. Both of these girders can be attached to the ringframes without penetrating the outer wall of the tank. We then take our 27-ft-long, 3-ft-wide flooring material and use it to span the distance between the two girders attached to the ringframes. The flooring attaches to the girders. Once this is done, the length of the hydrogen tank, we now have a floor 27 ft wide and 90 ft long, right down the middle of the tank (which I like to call the Main Deck), with a ceiling 13 ft above the main deck's floor. It's BIG! This whole process could be duplicated and another floor could be installed 8 ft below the Main Deck, and above for that matter, but my preference would be for a 13 ft ceiling. And the oxygen tank can be similarly outfitted. Now how hard would it be to put these basic floors together? Not very. It's just like tinkertoys. A couple of people could do it in a few weeks, especially since they will be working in shirtsleeves and have plenty of room to move around in. And how hard would it be to bolt all your other equipment to this basic deck arrangement. Like the astronaut said, All we have to do is tie our feet down and we can do anything in space. With two decks in an ET, it would have about three times more laboratory floor space than the international space station (pp. 1-2).

Design Concepts

Besides the ring shape designs, many other ideas have been proposed. Examples of a few of these designs are described below (Meyers, 1990):

One was to join eight or 10 ETs together end-to-end, then spin the whole structure slowly, like a propeller. Rather than each ET’s interior being divided lengthwise into three decks (like an oceanliner), this Prop-station design would have each ET’s interior divided crosswise into 18 "floors," each about the size of a modest two-bedroom apartment. Ten ETs joined in this manner would produce a 180-story "ET-skyscraper" of Donald Trump proportions. One of the unique features of this design is that the centrifugal (or spinning) force would produce different gravity levels on each "floor." If the whole structure were spun at two revolutions per minute, a 200-pound person standing in either of the two end-floors would feel gravity levels identical to Earth’s. They’d "weigh" 200 pounds. But as that person climbed "up" through the 90 floors between the station’s end and its center, he or she would feel about 1% lighter on each floor. When they [SIC] got to the station’s center, they’d [SIC] actually float about as the astronauts do today aboard the shuttle (p. 53).

Below is an illustration of the prop design.



Figure 5. Prop Design. Note. From ET-Solutions (p. 54), by G. Meyers, 1990, West Covina, CA: Space/Life Project

This design can also be altered to accommodate any number of ETs. Gene Meyers, (1990) describes what changes could be made:

A variation on this design called for two or four additional ETs to be attached at right angles to the station’s center; one sticking out in front of the propeller-like station, and the other sticking out behind it. If these two ETs were attached by magnetic "slip-coupling" which allowed the station to slowly spin while the two right angles ETs were not spinning, the two would become enormous, airtight zero-gravity labs or construction bays. (The same slip-couplings would allow the two end-to-end ETs in the ring design to behave the same way.) Other designs used additional ETs to form 3-, 4-, or 6- bladed propeller shapes, while others added a complete ring around the outside edge of the propeller-like design (p. 55).

Another design sketched out by Hughes aircraft engineers was the star-shaped version. Their plan was to build satellites in space because it would be less expensive (Meyers, 1990). The following is an illustration of the star-shaped design:



Figure 6. Star-Shaped Design. Note. From ET-Solutions (p. 112), by G. Meyers, 1990, West Covina, CA: Space/Life Project

B. Bierman describes the same type of design in more detail:

I propose arranging the tanks like an asterisk, as spokes of a wheel, but with no rim. Joining them would require only one hub module, which would fit in the shuttle cargo bay. Additionally, two tanks would be mounted along the axis of rotation, like an axle, to provide areas of micro-gravity for recreation and experimentation. Eight tanks would be required in all, six "spokes" around the hub module, and one tank on each end of the hub module, forming the "axle." The entire structure could be secured with tension cables joining the bottom (blunt end) of the tanks around the perimeter and out to the ends of each "axle" tank. The tanks would all attach to the hub module via their pointed ends. The hub module would be built so the tanks need merely to have a sealant applied, dock with the hub, be drilled and bolted in place, or welded with a solar powered arc welder, and have their points cut off to form a hole for people and baggage and equipment to pass through. When completed, docking with the space station would take place at the blunt end of either "axle" tank, and a pre-fabricated docking module, that would fit in the shuttle cargo bay, could be easily designed. Window modules could be mass produced and flown up to be placed on the tanks. An added bonus to this arrangement is that the six-tank "asterisks" could be stacked as more tanks become available. If the stack gets too "tall" it would probably become unstable in rotation, but a stack of about five asterisks with an "axle" tank on each "end-asterisk" would probably be fine. That would be 32 tanks in all. One aspect of this design that might be considered as a flaw is that the artificial gravity would increase as you get farther from the hub. In the tanks forming the "spokes" of the "asterisk" or "rimless wheel", "up" would be toward the pointed end of the tank. The farther "up" you were, the less you'd weigh. This may not be a disadvantage at all. Tourists may want to experience different gravities. There could be "Moon Rooms" where the "gravity" is 1/6 of a "G" and decorated in a lunar theme. There could be "Mars Rooms" at the 1/3 of a "G" level. Experience would show what level of gravity the tourists prefer, and the most preferable rooms would cost more, as they currently do on cruise ships (personal communication, May 1, 1998).

Free-floating designs have also been considered. These could be used for zero gravity production facilities or honeymoon suites. These single units could be located a quarter of a mile away from the larger design to provide a get away for couples to enjoy a zero gravity atmosphere (Meyers, 1997). A depiction of a 20-ET facility design is described by Marks (1997). "A wheel-shaped, rotating station with 12 ETs in the 3-deck, 1/3-mile round living quarters, 2 more end-to-end as a 32-story "axle" through its center and 6 free-floating ETs beside it for isolated commercial production" (p. 1). In my opinion, the free-floating tanks could be used for experimentation on anything from agriculture to manufacturing unnatural crystals.

GEODE Project

"Mark Holderman, a NASA engineer at Johnson Space Center in Houston has conceived of a Commercial/Industrial Process and Applications Platform (CIPAP) called GEODE" (Ball, et al, 1997, p. 5).

GEODE: This is not a cleaver acronym, but simply the utilization of a geology term that describes a stone with a rather unimpressive surface, but contains surprisingly beautiful gem-like crystals located within its interior hollow space. The External Tank is a rather unimpressive structure on the outside, but configured appropriately, could possess the jewels of the next industrial revolution within its aluminum walls (Holderman, 1998, p. 3).

Ball, et al (1997) states:

The purpose of the GEODE project is to provide an opportunity for the commercial and academic sectors to participate in space activities while maximizing the potential for profit. Holderman stated in a recent interview with Space News that, "GEODE is not a research platform...GEODE is meant to be the vanguard space production platform for commercial manufacturing work." Holderman believes that it would take a total of nine shuttle launches to realize the completion of GEODE. A first launch would place one ET in orbit, and three subsequent launches would be sufficient to construct an operational GEODE. The delivery of additional hardware would be completed over five more shuttle flights. In its final form, GEODE would have a docking port, a crew module, and a transport vehicle so that crew members could return to earth in the event of an emergency. Holderman projected that the price tag on GEODE would be close to five billion dollars, not including the cost of the nine shuttle launches it would take to complete the project. He is confident, though, that the project will actually end up costing half as much because of cost savings for minimized launches, reduced logistics, and pay back due to the products being manufactured. He believes that much of the return on the investment in GEODE will be realized in the form of the profits generated from the emerging fields of Nanotechnology and MEMS (Micro-Electro-Mechanical-System). Nanotechnology sensors would enable significant medical advances, such as the constant and unobtrusive monitoring of internal organs like the heart. The promise of such emerging technologies causes Holderman to believe that, "The environment of space may truly be the cradle for the next Industrial and Economic Revolution" (p. 5).

Holderman (1998) describes the concept as follows:

The technical aspects of the GEODE concept are substantially unique in that they impose virtually no modifications to the operational Space Shuttle Program (SSP). It utilizes existing and/or certified hardware without impacting the NASA manifest or depleting hardware assets (i.e., SSME, Orbiter, etc.). It is intended to be the vanguard space production platform for commercial production and manufacturing activities. Embedded in its design is the capability for duplicate platforms to be built, allowing specialized production environments to be precisely tailored for unique/exclusive process support. The intent of the GEODE concept is to offer the Commercial and Academic sectors (other than traditional Aerospace) a real and genuine opportunity to participate in the exclusive space environment while maximizing the potential for profit. This Orbiting Commercial/Industrial Product and Applications Platform (CIPAP), will be capable of supporting a number of production environments and requirements. It is planned to be efficient, flexible, and supportive of commercial needs, and for GEODE to be capable of duplication, thereby enabling opportunity for specific applications on a number of orbiting platforms. The GEODE is intended as an adjunct to the International Space Station Alpha (ISSA), capable of complete operational status 3 years after ISS completion. Additionally, no technical issues or concerns exist that would preclude earlier delivery and operation. This effort is experiencing the challenges associated with creating the initial "ground swell" of momentum and support that any new approach must weather. Specifically, the GEODE concept is attempting to surface from within a global space infrastructure that is currently focused on negotiating its gestation period regarding commercialization activities. The political environment in the past was perhaps not as conducive towards commercial space activity as that which has currently come into affect. An advancement of the agenda of commercial space is definitely at hand, and the GEODE concept supports all the tenets of that effort. A new Industrial/Economic Revolution, with space as the focus, could be on the immediate horizon (pp. 10-11).

Problems to Overcome

The technical challenges of placing an ET into orbit include the circularization and maintenance of orbit, the cleanup and evacuation of residual liquid oxygen and liquid hydrogen, and dealing with the foam insulation (Fitch, 1997). There have been many different ideas of how to solve these problems.

Maintaining a Circular Orbit

The first problem is to get the ET into a circular orbit and keep it there. "If left in a very low Earth orbit, the tanks would have to be periodically boosted to higher altitude to keep them from becoming a hazard to traffic and from eventually burning in. A costly alternative is to strap on rockets and boot them to a higher stable parking orbit" (Damon, 1995, p. 146). With that, some form of attitude jets would need to be attached, plus a way to remotely control them. Tom Abbott said, "In all on-orbit ET space station conversion proposals, a propulsion system is installed just as soon as is practical and the ET remains attached to the Space Shuttle until this is accomplished. Positive control of the ET at all times is the only acceptable way to operate" (Fitch, 1997, p. 1).

Disposing of Residual Fuel

When the Space Shuttle jettisons the ET, there are from 5 to 20 tons of residual fuels remaining in the tank, and something has to be done with them (Fitch, 1997). Tom Abbott said, "According to a study undertaken at the direction of the ET Project Office, there are three ways to accomplish this: (a) through the Orbiter’s fill and drain valves, (b) through the Orbiter’s engines, and (c) through the ET vent and relief valves. The first method is recommended. The second method has the disadvantage that the vented hydrogen could affect the engine unfavorably, and the third method requires modifications to the ET" (Fitch, 1997, p. 3).

Holderman (1998) provides the following solution:

Martin Marietta has persistently studied (IR&D) L02 scavenging techniques for the cryogenic LO2 residuals remaining after MECO. A large percentage of the LO2 residing in the feedline would be applied towards establishing the habitable atmosphere in the "bladder" of the ET volume being utilized (e.g. LO2 tank). The hardware associated with this system would be located in the intertank and would be positioned so as to not perturb the integrated stack CG and to also meet the required loads and vibro-acoustic environments of NSTS 07700, Vol. X. The Bladder would have built-in conduits (soft) that would be tied into a recirculation vent and distribution system in order to avoid stratification within the 22,000cuft L02 tank volume (usable volume would be less). Condensation concerns would also be addressed by the same system with a direct link to a water reclamation loop being an integral part of the Bladder design (although this would not be part of the initial bladder deployment) (p. 17).

Removal of Spray-On-Foam-Insulation

There is concern that the Spray-On-Foam Insulation (SOFI) could erode in orbit and cause annoying and potentially dangerous debris (Fitch, 1997). Tom Abbott suggests his solution. "After the ET reaches orbit, it can be held in a 170 mile high orbit while the SOFI is scrapped [SIC] off. One study predicts it would take less than a week to strip the SOFI, and debris would deorbit in from hours to a couple of days, depending on the size of the piece. Another is to leave the ET in a 160 mile orbit for about a month and all the SOFI would oxidize off of it" (Fitch, 1997, p. 4). Meyers (1990) describes several ideas to remove the foam:

Without the paint to hold it in place, small bits of the orange foam shed on the way up to orbit, and figuring out how to remove it in space has soaked up quite a bit of NASA’s time. It turns out that it can best be removed by using something like a gigantic, single wire cheese cutter with an electric current running trough it to heat it up. Some engineers think the foam could be removed from the "welder paths" using this method; others think the entire station should be cleaned in order to spray additional aluminum onto the outside walls; still others think as much of the foam as possible should be left in place for added protection; and yet another group wants to leave the foam there, but place the entire station in some sort of flexible, tube-shaped bag to keep loose chunks from breaking off and fouling the station’s path in orbit (p. 128).

Holderman (1998) concerns about the foam are described below:

Debris on orbit has always been a concern for the ISS. The TPS/SOFI (Thermal Protection Sys/Sprayed On Foam Insulation) on the External Tank is often viewed as being fragile and prone to "popcorn" type effects. In fact, the rhine on the outer surface of the SOFI has been demonstrated to be UV resistant (terrestrial test) and extremely "tough". The adhesion qualities are excellent and outgassing appears to not be a concern (as evidenced by Orbiter Umbilical -well cameras and hand held photos from SSP DTOs). Most "debris" from TPS/SOFI is generated during ascent, with indications to date indicating that the SOFI will persistently remain adhered to the ET, accepting with ease the minute dimensional changes that ET will experience from the on-orbit thermal environment (ie., passing in/out of the terminator as well as solar basting). If atomic oxygen has a severe effect on the rhine of the SOFI, very small particulate debris would result. However, the aero erosion of ascent could be considered much more abrasive than would result from on-orbit conditions. Additionally, the work of J. Loftus at JSC has indicated that the SOFI debris, being of such small mass, would begin to deorbit after one revolution thereby leaving the GEODE's immediate vicinity and not presenting a problem condition. MMC/MAF has investigated a multitude of options to totally eliminate any threat of debris emanating from the SOFI. Design solutions have included deployable MLI-kevlar shields, new anti-debris coatings applied at MAF to the SOFI, and containment sheaths that could be erected (pp. 16-17).

Raising Funds

First, we should consider what the ET would cost private enterprise’s to orbit. It is surprising what NASA has already agreed to (Jones, 1998):

NASA has already agreed to turn tank ownership over to anyone (who can control the orbit/maintenance/decommissioning of ETs) for FREE!!! Congress when shown how much money and potential is being wasted by throwing away this resource should be compelled to act! All External tanks should be recovered and stockpiled for future use. A separate Agency needs to be created to recover and refurbish ETs in orbit and sell them to industry! This will reduce government waste and help foster business development. An Orbital Transfer Vehicle (OTV) will be necessary to place the ETs is stable orbits, perhaps private industry can do this perhaps it should be governments role to provide this. Either way ET recycling is accomplished should be done in a way that most benefits the building of business economies in space. I believe that ETs should be used as a (low cost) supplement to the International Space Station (ISS) and be provided to Industry that can benefit by using Microgravity/High vacuum in production processes. With private enterprise moving into the launch industry it is time to start providing stations that the private sector will need for industry, tourism, exploration, and colonization (p. 2).

Engineers have detailed how ETs can be safely left in orbit, and Meyers (1997) has described the costs associated with building these space stations:

They’ve even calculated that a complete, 20-ET station complex could be commercially built for less than $15 billion even with the expensive launch costs of today’s first-generation shuttles. The second station would cost $7 billion, the third and fourth, less than $5 billion each. These experts believe the first station, or Space Island, could be built by 2002, and by leasing 10-by-20-foot suites to tourists or space manufactures for several thousand dollars a day, it could pay for itself in three years. The three largest US. Aerospace-engineering societies have endorsed the concept’s technical feasibility. Even more stunning: If ETs were "sold" to developers in orbit for $500 million each, even NASA’s prototype shuttles profitably could carry supplies or passengers for free (p. 16)!

Marks (1997) describes the same concept and gives ideas for paying off the station in a years time:

The concept's real economic show stopper is that each ET could be "sold" to a commercial station operator for $400 million in orbit, more than recovering the construction and launch costs of both the manned and unmanned versions. Even if this price escalated to $500 million per outfitted ET, a 20-ET would cost $10 billion. A dome of solar cells would cover the ring. The whole system would contain 1.5 million cubic feet of interior space, half of which would be needed for station and occupant support. (Life support costs - from showers and toilets to food-producing gardens and recycling systems - would be far lower in partial gravity than in zero-g.) Leasing the other 750,000 cu. ft. at $50/cu. ft./day (tended by trained station staff) would generate over $30 million/day, paying for the entire station in about a year. This profit potential is so enormous that when single-stage-to-orbits (SSTO's) become operational, station operators might cover all their launch and operating expenses, much as the early railroads offered free tickets to Easterners whoUd [SIC] eventually buy or rent railroad-owned land in the West. The numbers can be slid around ($10/cu. ft. would mean a 5-year payback, perhaps tied to royalties on the materials produced on the stations), but they're definitely in a very exotic ballpark. This whole concept is familiar to airline executives who keep their craft in the air - producing income - as much as possible. It keeps most of the unmanned shuttle components earning income "in the air" for at least 20 years, rather than just during the 8-1/2 minute launch phase. Another design would replace the SRBs with liquid boosters having 2-3 shuttle engines/booster. The booster tanks could be carried into orbit to become the "spokes" of the wheel-shaped station, and the engines could either glide back or be refurbished on the stations and used to send planetary probes on their way for NASA or move these closed cycle stations into Lunar or Martian orbits (p. 1).

Cooperate sponsorship of the first space station would make it possible to get this idea started. Collis (1997) gives indications of who could sponsor the building of the first space station:

Meyers and his group are looking to corporate sponsorship to meet the $10 billion to $15 billion cost of building the first space station. You’d need about 16 of these external tanks. If we can get companies like Coca-Cola and General Motors to sponsor them for $500 million each, you’d cover big chunks of your costs for the first station; the second station would cost roughly half as much, and the third and fourth stations would be about 10 to 15 percent less. Space Islands Project is privately funded right now. We’ve budgeted $20 million for the first push to bring in some of the larger sponsors. The payback for them will be enormous. Coca-Cola, for example, spends $8 billion a year on marketing. So we’ve suggested that if they were to pay the cost of a shuttle launch - $400 million to $500 million – they could have the external tank painted white with their logo splashed all over it. This would give them two to three years of broad international exposure. We’re talking to Carnival Cruises, Hilton Hotels, Universal Studios, Radisson Hotels and Disney to support the project (p. 2).

Meyers (1998) also states:

Space Islands asserts it can attract enough corporate sponsorship and contract-TV coverage to cover most of the first ET-station’s five-year, $10-billion construction and launch costs. The Beverly Hills-based Hilton Corp. has already expressed interest, as have Radisson, Marriot and three major airlines. Boeing’s largest rival, Airbus Industrie, is even discussing beating Boeing to the punch, offering airline clients several dozen free passes to the first station if they buy new Airbus airliners. Another group, the Downey-based Aerospace Legacy Foundation, says a "space theme park" could be built on the 200-acre, nearly abandoned, former Rockwell site in Downey, where the space shuttles and much of the Apollo program were designed. NASA owns most of the land and has been told by Congress to sell it as surplus. The group has approached Universal Studios about building a new theme park, highlighting 50 years of space exploration’s past and 50 years of its future. With a three-story "thick" ET-station as its centerpiece, Space Island sponsorship funds may cover part of its cost. The site’s huge buildings could make ideal sound stages; the station mock-up and other space attractions could allow filming of a movie or TV series built around the concept, and much of the actual station design work could be done behind glass walls, resembling the "Jurassic Park" set (pp. M-2).

Who might benefit from this concept?

Ironically, NASA might benefit the most from this concept. These islands would be large enough to grow food and recycle their air and water, and they’d have their own shuttle-style engines to change orbit. This means that with extra fuel, entire stations loaded with lab equipment and 100 scientists could be flown into orbit around the moon (or to Mars!) for a half-billion dollars a month. In 1988 NASA estimated that an eight-person, two-year trip to Mars would cost $500 billion (Meyers, 1997, p. 16).

In the long term, people on Earth can benefit from having an ET space station in orbit. Hardersen (1997), an activist in the National Space Society, believes space exploration is important for two reasons:

To explore the unknown and to help improve the lives of humans on Earth. Economic gains would generally fit into the second rational, but they only benefit a small part of the global population. The real promise of space lies in the realization that the resources of the solar system can dramatically raise the standard of living of the poorest people on our planet. Imagine what cheap and limitless electricity could do to help people in the less developed countries in the world (pp. 75-76).



Design of the Study

This project was designed to analyze if the ET can be placed into orbit and constructed into a space station by utilizing funds from the private sector. By determining that the ET can be safely reworked to incorporate the characteristics of a livable area within the constraints of resources, a space station could be built in a short amount of time. A further look determined if the plans for this concept are within reach and if they can be determined to be accurate and credible. Once it is decided that the ET can be safely constructed into a space station, business interests throughout the world will have the opportunity to get involved with this new method of research and entertainment.

Data Description

The data for this project varied from simple solutions to these problems to complex engineering changes that could be made to the ET. Also data from interviews was used to determine if the private sector is interested in supporting this concept. Also three main sets of data were required to complete this study. They are:

1. Test data providing support from interested businesses that are willing to support this concept.

2. Test data from people who would be interested in taking a vacation to these space stations for entertainment purposes.

3. Test data from Lockheed Martin and NASA stating the pros and cons of implementing this as an alternative to the International Space Station.

The test data consisted of reports and interviews published on the Internet.

Data Collection

The data was collected in several different ways. The test data was compiled through the Internet by creating a survey web page. Also sites dedicated to this idea were used for data collection. Magazine, newspaper, and online articles, along with interviews of people directly involved with this project, were used. Lockheed Martin was also used as a resource for technical information regarding the ET.

Treatment of the Data

The data for this study was reviewed and applied to the project subproblems in the following manner:

1. First Subproblem. Determine what changes will need to be made on the ET before it is used for a launch and how these changes might effect the launch capabilities of the Space Shuttle.

To determine what changes would need to be made, an analysis was determined from technical engineering studies that have already been conducted and interviews that have answered some of these concerns.

2. Second Subproblem. Determine how the ET can maintain a circular orbit.

The data to determine how the ET can maintain an orbit was reviewed and the possible solutions were analyzed.

3. Third Subproblem. Determine how the residual liquid oxygen and liquid hydrogen can be cleaned out of the ET.

The data to determine how the ET could be cleaned out was reviewed and the possible solutions were analyzed.

4. Forth Subproblem. Determine how the Spray-On-Foam Insulation (SOFI) can be removed from the outside of the ET without causing dangerous consequences.

The data to determine how the SOFI can be removed safely was reviewed and the possible solutions were analyzed.

5. Fifth Subproblem. Determine how the private sector can benefit financially by accepting the challenge of placing these ET’s in orbit for the purpose of research and entertainment.

This was reviewed and the possible benefits were adjusted to decide if the private sector should invest in this theory.



I used descriptive research when collecting data to answer questions that were placed on two different Internet survey web pages. The findings of the first three questions are in Table 1.

Table 1

Idea and Safety Results






Have you ever heard of this idea before?




Did you review More Info and the Links to learn more about this idea?



Do you think it is possible to safely convert these External Tanks into a Space Station?



Note. From "External Tank Survey" by D.R. Hunt, 1998

What do you think is the biggest problem with this idea? A summary of this question is presented in Table 2.

Table 2

Problem Results


Response Percentage

Funds to get the idea started


Safely converting the ETs


Political problems


Disposing of the residual fuel


Maintaining a circular orbit


Removal of the Spray-On-Foam-Insulation (SOFI)



Note. From "External Tank Survey" by D.R. Hunt, 1998

The same type of question was asked on another survey web page. What do you see as being the most challenging technical problem in securing the ET after launch? The results are included in Table 3.

Table 3

Technical Problem Results

Technical Problem

Response Percentage

Guidance and orientation control of the tank


Gaining manned entry to the interior


Venting the residual 02 and H2 in the tank


Circularizing its orbit


Dealing with the insulation


Emergency re-entry safety concerns


Note. From "External Tanks in Orbit – Survey" by C.A. Fitch, 1998

Once in orbit, how would you propose to maintain the ET in orbit? The results for this question are in Table 4.

Table 4

Maintain Results


Response Percentage

Connect it to a docking and guidance module


Use a LOX/H engine powered by fuel scavenged from the ET


Pioneer the use of a powerful ion engine


Pre-installed thrusters in the inter-tank region


Attach hydrazine thrusters, like those on the shuttle


Use hardware from the ISS


Use a docked Soyuz craft



Note. From "External Tanks in Orbit – Survey" by C.A. Fitch, 1998

The results for the design of an ET space station follow in Table 5.

Table 5

Design Results

My favorite ET space station configuration is

Response Percentage

Anything that actually got flown


A ring station, spun for gravity


Several ETs arranged parallel, connected


A star shaped, connected at their tops


A hybrid of ETs and conventional station modules


Free-floating single ETs


A linear "propeller" of ETs placed end-to-end


Note. From "External Tanks in Orbit – Survey" by C.A. Fitch, 1998

Where do you feel the funding for the project should come from? The results for this question are found in Table 6.

Table 6

Funding Results


Response Percentage

Any business interested


The travel industry


The Aviation/Aerospace community




The hotel industry


Note. From "External Tank Survey" by D.R. Hunt, 1998


When should putting an External Tank into a stable orbit be tried? The results for this question are found in Table 7.

Table 7

Orbit Results


Response Percentage

ASAP with the existing shuttle configuration


With minor modifications to make the ET more safe


With a ground integrated AFT Cargo Carrier attachment


Only with an unmanned shuttle derived configuration


When hell freezes over


Note. From "External Tanks in Orbit – Survey" by C.A. Fitch, 1998

How long do you think it will be until the first ET is in orbit and is converted into a space station? The responses for this question are in Table 8.

Table 8

Time Results


Response Percentage



In the next 5-10 years


In the next 10-20 years


Over 20 years from now


In the next 1-5 years


Note. From "External Tank Survey" by D.R. Hunt, 1998

What do you feel is a reasonable budget to get this idea started? The results for this question are found in Table 9.

Table 9

Budget Results


Response Percentage

Between $1-$5 Billion


Under $1 Billion


Over $10 Billion


Nothing – This idea will not work


Between $5-10 Billion


Note. From "External Tank Survey" by D.R. Hunt, 1998

How much would you be willing to pay to take a vacation in space for a 2 week stay? The results for this question are in Table 10.

Table 10

Pay Results


Response Percentage







$100,000 and above


Note. From "External Tank Survey" by D.R. Hunt, 1998

The survey results for what the ET should be use for are included in Table 11.

Table 11

Favorite Use Results

My favorite proposed use of a Shuttle External Tank in orbit is for

Response Percentage

A space station module


An interplanetary craft


Raw materials


Fuel storage


Indian Ocean fishbait


A telescope shell


A lunar habitat


Note. From "External Tanks in Orbit – Survey" by C.A. Fitch, 1998



The results indicate that the majority of people surveyed have heard of this concept and believe it is possible to convert these ETs into a space station. Also, most of the people surveyed wanted to learn more about this idea and were interested in how this dramatic idea could become a reality. 80% of the people believed that the ET should be used for a space station but they also believed that the first ET would never make it into orbit. 50% of the people surveyed believe that the ET should be placed in a stable orbit as soon as possible without making any changes to the ET, while 81% believe that the ET can be safely converted and used as a space station.

As for the changes that might affect the launch capabilities of the shuttle, only 23% believe that only minor modifications would need to be made to the ET. Only another 17% believe that an Aft Cargo Carrier should be attached. Overall, most of the technical problems during the launch were not a major concern for the people surveyed.

Guidance and orientation control of the ET concerned only 27% of the people surveyed and only 6% thought that maintaining the ET in orbit would be a problem. The other survey came up with a 10% concern for circularizing the ETs orbit. This problem does not seem to worry these people surveyed. 30% of the responses believed that connecting the ET to a docking and guidance module would solve the orbit problem, while other ideas of using different engine configurations to maintain the ET in orbit could be used.

When asked what the biggest problem with this idea only 9% of the people were concerned with the residual fuel. As for the most technical problem, 20% thought that venting the residual fuel could cause difficulty. Furthermore, 27% believed that the residual fuel could be used to maintain the ET in orbit.

Removal of the SOFI did not trouble anybody when asked what the biggest problem with this idea was. 10% believed that this was a technical problem and might cause some challenge when the ET is in orbit.

One of the biggest problems was where to get the funds to start implementing this idea. 40% were concerned but believed that 57% of any business interested could fund this project. Funding from the travel industry came in at 40% and the aviation/aerospace community, as a funding source, made up 34% of the responses. It was also believed that NASA and the hotel industry could fund this project with 26% of the responses assigned to each. It was also determined that 34% of the people surveyed believe that $1-$5 billion could get this idea started, while the rest of the majority, at 30%, believe that this idea could get started with less than $1 billion. As for how much an individual would pay to take a vacation in space, 64% of the people surveyed would pay anywhere in-between $1,001-$10,000.



The ET is a valuable resource and many people believe that this idea could happen in the near future. By getting the public to accept this idea, I believe that this project could be completed in the next five years. Rockwell and NASA have worked out most of the technical problems in the past, but no one ever took the first step to get this idea started. Through my research, I concluded that Gene Meyers is taking this step by making people aware of this impressive idea. His work shows that all of the technical aspects have been considered and he also reveals how private business can get involved in making this project come to life.

All of the problems considered with my research have both been resolved by engineers from the past or present and examined by curious business investors that would like to be the first in space. The problem with the launch capabilities starts at NASA because they do not want to change anything that might affect the safety of the crew on board. Privatization of the shuttle launches will solve this problem. Throughout this research, many businesses have shown interest in this idea and Gene Meyers has even put up his own money to get this idea started. But there needs to be that first business to make that first step. This will help others to invest so the funds will be there to get that first ET space station in orbit.

Gene Meyers has also worked out all of the costs involved with starting and maintaining this idea. He believes there is a market that will support space tourism and these ETs will give people a place to visit while in space. I believe space is the next frontier to explore and there is much more out there that can be learned to help mankind. By placing ETs in orbit and using them for all humanity, not just NASA or other governments, human beings can begin to explore and investigate space on there own. This is what drives me to research an idea that has so much potential, but all the governments want to do is find the flaws and not consider all the positive outcomes this would have for all the people on Earth.

My conclusion is to use this valuable resource before the opportunity passes us by. It is a shame that such a well-constructed and tested piece of equipment is only used for 8 and one half minutes and then is discarded and not reused. There is always a risk in anything we do and the majority of people believe that ETs can be safely converted and used as space stations. So, take that first step and space will not be as far away as it is today.



From the results of the research project, I would recommend that a private business or businesses get together and launch an ET into orbit. With the help from NASA and other experts it could then be determined if the ET is capable of maintaining its orbit, seeing what can actually be done with the residual fuel, and how the SOFI will accept the elements of space. This would produce real factual data instead of the guesswork that we now have.

At first, I would recommend free-floating an ET for a month to see how it holds up. During that time, astronauts could begin converting the interior with items brought up on the orbiter. After this concludes successfully, I would recommend the Aft Cargo Carrier be attached to the next ET sent into orbit. This would make more room available in the orbiter for tools and astronauts to build the space station.

At this point, if all were prosperous, I would recommend sending up as many shuttles as necessary to complete a ring station. This design seems to make the most sense because it can be spun to create artificial gravity. I realize that most people wanting to enter space would like to feel weightlessness all the time, but this design makes it more practical for normal living activities. You would feel total weightlessness in the center of the station and as you move towards the outside, more and more gravity would be felt. I feel this experience would be something that would be hard to create on Earth and many people would find this appealing.

As far as what business need to get involved, I would recommend any business that has an interest with space, travel, hotels, aviation, and anyone else who would like to step into the next frontier. This is an opportunity that has passed us by for far too long and I recommend that we act today so in five years we can learn, experience, and affect the way all humankind will live in the future.


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