Abstracts of External Tank Technical Reports

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 space platform/station design options.

The results of ascent, deployment and disposal studies of the effectiveness of an External Tank/Aft Cargo Carrier (ET/ACC) space facility for the Space Shuttle are reviewed. It is shown that the ET/ACC, could perform an active role in Low-earth orbit as a space platform or space-station element. Several of the important design criteria needed to develop an effective ET are described in detail. Some of the applications of the ET/ACC system would include: an extended orbit base for a manned crew or experiment package beyond a Shuttle mission duration; a microgravity experiment and processing facility; an earth observation facility; and a terminal for preparing payloads and boosters headed for higher orbits.

The orbital recovery of the external tank (ET), backbone of the U.S. space transportation system, can be considered enormously important for the future development and colonization of space. America's ability to respond to the many space opportunities on the horizon of research, commercialization and planetary science depend on the resiliency of the space transportation system, and especially on the use of the external tank in space. The use of ET's -- as launch stages for planetary exploration, as large platforms in either low Earth orbit or geosynchronous Earth orbit to coorbit with other payloads requiring human interaction, or as an element of support for the next part of space station Freedom -- could be of fundamental importance. The purpose of this paper is to describe a method for the orbital construction of the device and the corresponding recovery of the ET.

This paper deals with the possibility of converting an expended Space Shuttle External Tank into a Space Station, a permanently manned orbital facility. The Space Station was designed economically by using much off-shelf hardware developed for earlier space projects. It is compatible with the Space Transportation System, which will operate in the 1980s. It is proposed that mission-dependent experimental equipment be carried aboard Spacelab-type modules, which should be exchanged during periodic revisits by the Space Shuttle. The key functions of the proposed Space Station are discussed, such as power supply, thermal control, trajectory corrections, etc. The project arrived at a Space Station carrying a permanent crew of 8 people, orbiting the Earth at an altitude of about 390 km, resupplied by STS once in 80 days.

The use of the Space Shuttle external tank (ET) and aft cargo carrier (ACC) as orbital-platform structures is proposed. The ET and ACC are described; the relatively low cost of orbiting the ET rather than discarding it is indicated; and a basic orbital-platform design using the ET as strongback for payloads and an ACC module to provide utilities is presented. Consideration is given to a large-area gamma-ray telescope of gas-Cerenkov type (installed in the ET on orbit by EVA) and a solar furnace capable of melting the ET for use as an on-orbit materials resource. Photographs, drawings, diagrams, and graphs are provided.

An account is given of the prospects for constructing a large, multiuse manned space station on the basis of discarded Space Shuttle External Tanks (ETs). The station, designated 'Space Base 1', is scaled to begin operations with a crew of 25 and expand to as many as 170. It will encompass variable-gravity processing and training facilities, recreational/physical fitness facilities, individual crew quarters, agricultural facilities, and a partially-closed life support system. The ETs used in Space Base 1's initial, 25-crewmember structure will be obtained from eight launches of an unmanned launch system similar to NASA's proposed Shuttle C; four standard Space Shuttle flights will carry the crewmembers.

An evaluation is made of the potential contribution of the Space Shuttle's discarded External Tanks (ETs) to the LEO infrastructure system requirements of 21st-century solar power satellites, lunar outposts, and human exploration missions to Mars. Such infrastructure will require manned and man-tended laboratories, fuel-storage depots, and orbiting hangars for assembly and refurbishment of large spacecraft. Each empty ET contains over 70,000 cu ft of volume that is pressurizable to about 30 psi. The most simple uses of the ET are that of 'trash basket' for Space Station wastes and of a source of Al alloy for on-orbit construction.

This is the report of a study group which met in La Jolla, California, 23-27 August 1982, to examine possible uses of the shuttle external tank in orbit, especially uses which might apply to a future space station. The decisions which will be made about space station functions and structures cannot, of course, be foreseen at this time. However, a few points are clear, and these form the bases of assumptions for the work. They are: the station or stations should be developed so as to permit staged or incremental growth; some key functions of a space station can be compared to the concept of an automotive service station in terms of refueling, service, and repair; the station must provide, or assist, the capability of raising large payloads to geosynchronous orbit, or putting them into other special orbits; and that there are major opportunities to serve other constituencies, both civilian and military. This report addresses these issues and discusses many ways in which the shuttle external tank could contribute dramatically to the future utilization of space.

Proposed uses for orbiting Space Shuttle External Tanks are examined. Consideration is given to the use of residual oxygen and hydrogen in spent External Tanks, using the tanks for Space Station waste disposal, linking the tanks with cables to make a gravity research facility, and outfitting a tank with solar arrays and an attitude control system to serve as a mounting platform for Shuttle launched instrument pallets or commercial systems. Other possible uses include tethering an external tank to a satellite and using the tanks' aluminum for constructing the future orbital infrastructure.

It is suggested that the Space Shuttle External Tank (ET) may after fuel depletion and separation from the Orbiter be considered an orbital source of aluminum, which can be reprocessed in situ and fabricated into useful systems. If this course were followed, transportation cost savings of $9.5 billion would be accumulated by the year 2000. Structural elements which may be manufactured from ET-derived aluminum include such unique products of microgravity processing as thin spherical shells and foamed aluminum. In addition, the ET may be used as the modular basis of space station structures.

NASA initiated studies in 1991 of the possibility of defining a relatively inexpensive space station predicated on Space Transportation System hardware and accordingly designated STS-Lab. This station configuration would use a modified Space Shuttle Orbiter with a permanent laboratory in its payload bay, as well as an external fuel tank structure and a solar power photovoltaic array. This option offers the ability to double or even triple the productivity of many Spacelab missions, beginning no later than 1995.

The purpose of this study is to determine whether the External Tanks of the Space Transportation System, when carried into LEO, can be reduced economically to a form of readily usable construction material. A scenario is assumed in which the first tank is partially dismantled and then becomes the facility for dismantling additional tanks, storing products and constructing space structures. A set of tools is identified to autonomously accomplish the tasks of cutting, transport of crude stock, removal of spray-on form insulation, and product storage. Astronaut setup and takedown of tools is required for each tank reduction. Power requirements are determined for the reduction task, and an electrical power system is specified. An orbit model projects the annual facility fuel requirements, predicts the orbital decay of the facility, and estimates the orbital decay rates of any debris which may escape during the salvage operation. Life cycle costs are projected based upon reducing four tanks per year. It is shown that more than 52,000 pounds of structural aluminum, primarily in the form of I-beams and strip, can be salvaged annually in a manner that is cost competitive when compared to equivalent products delivered as orbiter payload.

A concept for using a spent External Tank from the National Space Transportation System (Shuttle) to derive a Lunar habitat is described. The concept is that the External Tank is carried into Low-Earth Orbit (LEO) where the oxygen tank-intertank subassembly is separated from the hydrogen tank, berthed to Space Station Freedom and the subassembly outfitted as a 12-person Lunar habitat using extravehicular activity (EVA) and intravehicular activity (IVA). A single launch of the NSTS Orbiter can place the External Tank in LEO, provide orbiter astronauts for disassembly of the External Tank, and transport the required subsystem hardware for outfitting the Lunar habitat. An estimate of the astronauts' EVA and IVA is provided. The liquid oxygen tank-intertank modifications utilize existing structures and openings for human access without compromising the structural integrity of the tank. The modification includes installation of living quarters, instrumentation, and an air lock. Feasibility studies of the following additional systems include micrometeoroid and radiation protection, thermal-control, environmental-control and life-support, and propulsion. The converted Lunar habitat is designed for unmanned transport and autonomous soft landing on the Lunar surface without need for site preparation. Lunar regolith is used to fill the micrometeoroid shield volume for radiation protection using a conveyor. The Lunar habitat concept is considered to be feasible by the year 2000 with the concurrent development of a space transfer vehicle and a Lunar lander for crew changeover and resupply.

A concept for using the spent external tank from a National Space Transportation System (NSTS) to derive a lunar habitat is described. The external tank is carried into low Earth orbit where the oxygen tank-intertank subassembly is separated from the hydrogen tank, berthed to Space Station Freedom and the subassembly outfitted as a 12-person lunar habitat using extravehicular activity (EVA) and intravehicular activity (IVA). A single launch of the NSTS orbiter can place the external tank in LEO, provide orbiter astronauts for disassembly of the external tank, and transport the required subsystem hardware for outfitting the lunar habitat. An estimate of the astronauts' EVA and IVA is provided. The liquid oxygen intertank modifications utilize existing structures and openings for man access without compromising the structural integrity of the tank. The modifications include installation of living quarters, instrumentation, and an airlock. Feasibility studies of the following additional systems include micrometeoroid and radiation protection, thermal control, environmental control and life support, and propulsion. The converted lunar habitat is designed for unmanned transport and autonomous soft landing on the lunar surface without need for site preparation. Lunar regolith is used to fill the micrometeoroid shield volume for radiation protection using a conveyer. The lunar habitat concept is considered to be feasible by the year 2000 with the concurrent development of a space transfer vehicle and a lunar lander for crew changeover and resupply.

The Space Shuttle external tank, which consists of a liquid oxygen tank, an intertank structure, and a liquid hydrogen tank, is an expendable structure used for approximately 8.5 min during each launch. A concept for outfitting the liquid oxygen tank-intertank unit for a 12-person lunar habitat is described. The concept utilizes existing structures and openings for both man and equipment access without compromising the structural integrity of the tank. Living quarters, instrumentation, environmental control and life support, thermal control, and propulsion systems are installed at Space Station Freedom. The unmanned habitat is then transported to low lunar orbit and autonomously soft landed on the lunar surface. Design studies indicate that this concept is feasible by the year 2000 with concurrent development of a space transfer vehicle and manned cargo lander for crew changeover and resupply.

In response to the ever-present need for a very large gamma-ray detector for energies greater than 100 MeV, a concept to build a telescope of 250,000 sq cm sensitive area using a Space Shuttle External Tank (ET) is presented. In the Space Station era, for the first time, large detectors can be constructed on-orbit which would otherwise be limited in size by the launch vehicle. The ET will serve both as the spacecraft and the Cherenkov pressure vessel. The significant feature is that the sensitive area will be forty times that of the high energy detector on GRO and will be able to locate even the faintest sources from the GRO survey to a few arc minutes. The detection technique is based upon that originally proposed by Greisen.