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IV Facilities to Support Microgravity Research and Applications There is a wide range of existing, planned, and proposed facilities to conduct microgravity research and applications activities. One class includes ground-based facilities, such as drop towers, aircraft flying parabolic trajectories, and sounding rockets. Another class includes facilities that are intrinsically tied to the Space Shuttle, ranging from "Get-Away-Special" canisters to Spacelab long modules. There are also orbital facilities, which include recoverable capsules launched on expendable launch vehicles, free-flying spacecraft, and space stations. Some of these existing, planned, and proposed facilities are non-U.S. in origin, but potentially are available to U.S. investigators. In addition, some are governmentally developed and operated whereas others are planned to be privately developed and/or operated. Major facilities that could support significant microgravity research and applications activity are discussed briefly in the following section. GROUND-BASED FACILITIES Ground-based facilities provide a microgravity environment with limited capabilities for research for short periods of time. Drop tubes, drop towers, aircraft flying a parabolic trajectory (e.g., KC-135, Learjet Model 25) provide microgravity conditions for periods of from 2 to 25 seconds. The gravitational accelerations range from about 10" g for the KC-135 to 10" g for drop tubes. Sounding rockets, of which there are at least 15 different types, provide microgravity durations of up to 10 minutes, although with the limitation that the orientation of the acceleration vector changes during flight. The acceleration environment is on the order of 10" g. 25

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Advantages: These facilities are relatively inexpensive compared to space-based facilities and are readily available. For the most part, the experimenter has access to the experiment until it is run, and retrieval is quick. SPACE SHUTTLE-BASED CAPABILITIES The following section describes a wide variety of facilities for microgravity experimentation that are closely tied to the Shuttle. The list treats current or planned major capabilities and is not exhaustive. For example, the West German SPAS (Shuttle Pallet Satellite) and the U.S. astronomical satellite, SPARTAN, both of which have been used to co-orbit with the Shuttle during flight, are not discussed. The potential effects of an Extended Duration Orbiter are discussed only briefly. Get-Away-Special Canister The concept of the Get-Away-Special canister, or GAS Can, was first introduced by NASA as a means of making available to a wide variety of users a relatively quick, inexpensive means of providing access to the space environment. The GAS Can has minimal interaction with the Shuttle: it is completely self-contained, and each experimenter is responsible for providing his or her own power, thermal control, data handling, and so forth, with only the on-off controls operated by an astronaut. The volume provided is 0.15 m , with each GAS Can able to carry up to 90.7 kg of payload. The GAS Cans can ride in many locations throughout the cargo bay, and a number of structures, bridges, and pallets have been designed to accommodate them. The experimenter must deliver the payload seven months before launch and can have access to them up to 60-90 days before launch. Advantages: Costs to users of GAS Cans are low, and flight opportunities are frequent. Status: As of early 1989, 39 GAS Cans had been flown. Space Shuttle Middeck "Middeck" refers to the middeck lockers that were originally provided to contain crew equipment (food, clothing, and personal effects), some number of which can be made available for experiments. Each locker can hold 0.06 m of equipment weighing up to 27 kg. About 115 W of power is available to each locker. The accelerations of gravity are in the 10" g range. Advantages: While the experiment volume is limited, the middeck experiments have become popular because of the flexibility permitted by the 26

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ability of experimenters to have late preflight and early postflight access and the ease of crew interaction. Status: Usually about ten lockers are available for research on each Shuttle mission. Material Science Laboratory and U.S. Microgravity Payload The Material Science Laboratory (MSL) is a structure that is mounted across the payload bay and provides power, data channels, thermal control, and an experiment mounting area sized to accommodate material science experiments. A payload mass of up to 925 kg can be accommodated on 4.8 m of mounting area. Remote operation of experiments by the Shuttle crew or ground investigators is intended. The U.S. Microgravity Payload (USMP) is approximately equivalent to two MSLs. Advantages: The MSL and USMP can enhance flight opportunities. Status: MSL was first flown on STS-24 in January 1986. One previously manifested MSL flight now has been replaced by USMP-01. Four USMP flights are manifested for the period from 1991 to 1993. Additional MSL flights have been requested but are not yet manifested. Spacelab Module Spacelab, developed by the European Space Agency (ESA), is a pressurized laboratory module that can accommodate two experimenters (mission or payload specialists) working simultaneously. Spacelab STS missions have been flown or are planned for the Federal Republic of Germany (D-l, D-2, and D-3), Japan (J-l), and DOD, as well as for U.S. life science and materials research. Both the German and Japanese missions have a large concentration of microgravity research experiments. The Spacelab elements are carried in the Shuttle payload bay. Spacelab has both short- and long-module configurations as well as unpressurized pallets that can be used for astronomy and materials experiments. The short module has never been flown, and the following data refer to the long module. Spacelab provides 7.7 kW peak power for 15 minutes every 3 hours and 3.4 kW maximum continuous power. Each flight can accommodate up to 4,550 kg of payload, with a volume of 8.07 m available to the user. Experimenters have access to their experiments up to 28 weeks before launch. Advantages: Spacelab currently provides the maximum available Shuttle-based laboratory accommodations in terms of volume, power, cooling, crew time, data management, and other resources. Status: Three joint U.S.-European missions have been flown, and the modules are scheduled to fly several dedicated U.S. missions, as well as joint missions with the Europeans and Japanese. Eleven additional non-DOD Spacelab long-module missions are manifested through FY 1994. 27

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Impact of Extended Duration Orbiter Current Shuttle flights are limited to a duration of ten days or less. For some time NASA has been studying the modifications required to provide an Extended Duration Orbiter (EDO) capability that could extend the maximum mission duration from ten to 16 or even up to 28 days (if concerns over potential pilot performance degradation on reentry are satisfactorily resolved). The required changes involve relatively minor modifications to the life-support systems and the provision of a new mission extension kit (cryogenic pallet). Shuttle OV-102 (Columbia) would be modified to be able to provide a 16-day mission capability, while the new OV-105 would be modified to provide a 16-day mission capability, which might then be extended to 28 days. Advantages: Extending the flight duration of the Space Shuttle provides the ability to perform more experiments and to have longer experiment run times, for example for crystal growth. Status: The 1990 budget proposal, which was under review at this writing, called for the EDO cryogenic kit to be privately financed and developed. Since the EDO has direct interface with vital Shuttle systems, there is some controversy about such an approach. PROPOSED U.S. FACILITIES The following subsections briefly describe a number of proposed U.S. facilities (listed in alphabetical order) that could be used to support microgravity research and applications activities. Specific information was supplied largely by the companies concerned. NASA has committed no microgravity payloads to specific commercial carriers. AMIGA (See the discussion of EURECA for details.) Under a Teaming Agreement, General Electric's Astro Space Division and MBB-ERNO propose to start acquisition activities for a spacecraft identical to the European Retrievable Carrier (EURECA) for the U.S. and international markets, with the possibility of launching AMICA as early as 1992. External Tank-Based Facilities A number of entrepreneurs have proposed on-orbit uses for the 8.5m diameter, 46 m long external tanks of the Space Shuttle. At present the tanks that supply fuel to the Shuttle's main engine are jettisoned when they are no longer needed. By the time they are jettisoned, they have reached 98 percent of full orbital velocity, and a relatively small effort is needed to carry them into orbit. Proposals have been put forth by 28

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Global Outposts, Inc., Space Phoenix Program (initiated by the University Corporation for Atmospheric Research), and others that would use the external tanks as platforms for microgravity research, among other activities. Advantages: Costs can be expected to be low since an aerospace frame designed for other purposes will be used with no extra launch costs. No manifesting is required on the Shuttle. Status: As part of President Reagan's commercialization initiative, as well as under congressional urging, NASA will make tanks available to the private sector and recently conducted a competition to select a small number of projects to pursue. Neither of the above two companies or others that the committee approached have a flight-readiness timetable. Space Phoenix had earlier negotiated a Memorandum of Understanding with NASA to use five tanks for suborbital research. Industrial Space Facility The Industrial Space Facility (ISF) is a privately developed, pressurized, orbiting laboratory proposed by the Space Industries Partnership (SIP)* that can be utilized as a free-flyer or as a human-tended facility when attached to the Shuttle. Its internal dimensions are 11 m long and 3 m in diameter (providing to the user space for seven Space Station double racks and six modular containers for user experiments). The ISF depends on the Shuttle for transportation to orbit, resupply, and servicing, and it is intended to use off-the-shelf technologies. SIP has proposed that the facility could be used for technology validation and to work out potential Space Station solutions in such areas as docking system design, operation and utilization of Space Station racks, as well as for microgravity research or production. The ISF would remain on orbit rather than return to Earth with the Shuttle and thus would provide long-duration exposure to the microgravity environment. It is designed to stay in space for three years without a revisit if necessary. Experiments conducted in the free-flying mode would require specifically designed automation and/or teleoperation capabilities. As a free-flyer, ISF is predicted to have an optimal microgravity level of 10" or 10" g. When it is attached to the Shuttle at an angle extending out of the payload bay, some deterioration in the quality of the microgravity environment can be expected because the ISF will not be at the center of gravity of the configuration and also will be subject to transient g accelerations due to the presence of humans. *Space Industries Partnership was set up by Space Industries, Inc., Westinghouse Electric Corp., Lockheed Missile and Space Corp. (the solar array contractor), and Boeing Commercial Space Company (the docking system and rack contractor). 29

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However, human interaction with experiments is possible in this mode. Power available to payloads in the free-flying mode is expected to average 7 kW, with 10 kW of peak power. SIP has indicated that the ISF can be available for flight within 36 to 42 months from a commitment. Experimenters are expected to have access to their experiments up to 28 weeks before launch. One-half of the Shuttle payload bay will be required for resupply visits to the ISF. Advantages: When the ISF is in the attached mode, SIP believes that the ISF could extend the capabilities of the Shuttle up to 21 days without an EDO. In this mode, it provides a shirt-sleeve environment. As a free-flyer, ISF has the advantage of remaining on orbit and not requiring relaunch. ISF racks will be compatible with those of the Space Station. Status: ISF engineering design has been completed and the Preliminary Design Review with NASA has taken place. In addition, the Payload Implementation Plan, detailing operations and interfaces with the Shuttle, has been signed. SIP has a 1985 Space System Development Agreement with NASA stipulating that SIP may reimburse NASA for two and one-half Shuttle flights at 12 percent of their cash flow starting two years after the launches. The ISF is currently manifested on three Shuttle flights for orbital insertion and revisits beginning in January 1993. No payloads are known to be committed to the ISF. Financing arrangements currently await the decision of the U.S. government on an anchor tenant contract. Leasecraft Leasecraft is an unpressurized, unmanned, multimission modular spacecraft (MMS) proposed by Fairchild Space Company for payloads up to 6,800 kg. The MMS was used for the Solar Maximum mission and for the Explorer series. The Extreme Ultraviolet Explorer is scheduled to be launched on a Delta ELV, after which it will scan the sky for approximately 13 months, then rendezvous with the Shuttle. At that time the instrument module, which is designed to be readily removable, will be exchanged for the X-Ray Timing Experiment, and so on. A pressurized module can be carried on Leasecraft if desired. Continuous power ranging from 1 to 7.3 kW can be made available to the payload, depending on the configuration. Advantages: In conjunction with the Shuttle or co-orbiting with a Space Station, Leasecraft could provide long-duration exposure in a free-flyer based on an existing spacecraft design. Depending on the payload configuration, Leasecraft can be launched on the Delta ELV and avoid complete dependence on the Shuttle. Status: In 1987, Fairchild and NASA revalidated a Joint Endeavor Agreement for the commercial development of Leasecraft under which NASA would provide a free launch and the first servicing flight along with flight test planning and test resources. 30

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SPACEHAB Established in 1983, the SPACEHAB Corporation will provide a commercially developed pressurized module designed to augment the available Space Shuttle middeck volume. It is patterned after the pressure vessel designed for Spacelab and is intended to fit in the forward end of the payload bay with a short tunnel providing accessibility for researchers that is nearly identical to that of the middeck lockers. It is 3 m long, 4.1 m in diameter, and provides 31 m of pressurized volume. In an all-middeck locker configuration, the SPACEHAB would contain 69 usable lockers with a total volume of 4.6 m. It can also be configured with standard Space Station racks replacing all or some of the lockers. The SPACEHAB Corporation anticipates that half of its payloads will be non-U.S. and that NASA will lease the other half. Advantages: SPACEHAB is designed to reduce the amount of time required from identification of a payload to flight to 12 months and to provide a rapid turnaround so that results are available quickly to the investigator (with turnaround estimated by SPACEHAB Corporation to be four times as rapid as Spacelab). Astronauts will have ready access to experiments. Because its computer systems do not rely on those of the Shuttle, operations are quicker and cheaper than for Spacelab. In addition, SPACEHAB may be easier to manifest than payloads that require the entire payload bay. Status: A 1988 Space Systems Development Agreement between The SPACEHAB Corporation and NASA provides a commitment for six shared Shuttle flights. NASA is to be reimbursed for standard Shuttle services within 30 days subsequent to each launch. The SPACEHAB Corporation has contracted with McDonnell Douglas to fabricate three units, two of which will be flight articles. It is manifested five times from late 1991 through 1994, and four additional flights have been requested. SPACEHAB officials indicated that by the summer of 1989 they will have firm payload commitments and deposits from Europe and Japan. They have identified sources and are completing financing arrangements for all funding needed to complete development and production of the module. Space Station Freedom The Space Station Freedom will be a multiuser, on-orbit facility with three pressurized laboratory modules and numerous attachment points on its truss structure for unpressurized payloads. It is scheduled to be available for human-tended operations in late 1995, with permanent manning in late 1996, and an intended lifetime of 30 years. The Space Station is projected to provide a quasi-steady (<0.001 Hz) microgravity environment of no worse than 2 x 10 g inside the pressurized laboratory modules, and 10" g within a substantial fraction of that volume. Total pressurized volume for user equipment is estimated to be approximately 60 m (120 31

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standard 19-inch racks). This level of microgravity environment is required to be available for six continuous periods per year of at least 30 days each. Transient disturbances are anticipated from the following: Shuttle Orbiter docking (about 10 g, four to five times per year); Space Station reboost (about 10 g for two to three hours, four to five times per year); various moving mechanisms, especially the mobile servicing system (about 10 g at 0.17 Hz, when in use); crew exercise (although the effects are not yet known and understood, they are expected to be manageable with suitable isolation); and other crew activity inside the modules (about 10" to 10" g, if not isolated--the degree of isolation possible is still under study). Advantages: The unique characteristics of the Space Station for microgravity research and applications work are the availability of high user power levels (up to 45 kW total), large user experiment volumes, continuing human interaction with experiments, and long experiment run times. Status: The Space Station has completed several requirements reviews and is in the preliminary design phase. Assembly of the Space Station on orbit is scheduled to begin in 1995, with a human-tended capability expected by late 1995. NON-U.S. FACILITIES EURECA EURECA (European Retrievable Carrier) will be an unmanned, free- flying, retrievable orbiting facility. Its development is sponsored by the European Space Agency, and it is being built by MBB-ERNO. It is not human-tended. (AMICA is an identical commercial facility proposed by the European firms and General Electric's Astro Space Division.) Initiated as a Spacelab follow-on activity, hardware development for EURECA began in 1985, and EURECA is manifested for a Shuttle launch in 1991 and retrieval six months after launch. The initial mission has a complement of 15 instruments and facilities dedicated to a variety of science and applications experiments. Additional missions are scheduled for 1993 and 1995. EURECA has a recoverable payload capability of 1,000 kg, with at least 8.5m of payload volume available to users. Average power available to payloads is 1.0 kW with a 1.5 kW peak. Microgravity levels are expected to be from 10 to 10 g in the low-frequency (< 0.1 Hz) range. A turnaround time of 1.5 years is required between retrieval and the next launch, but studies are underway to reduce that time to one year. The EURECA platform's expected life is five missions over ten years. Advantages: EURECA is designed to provide flexibility and ease in integrating experiments into the system and thus reducing costs to users. AMIGA'S cost is estimated at $110,000 per kilogram. 32

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Status: While the initial EURECA flight in 1991 is fully manifested, largely with European payloads, EURECA representatives are actively seeking customers for subsequent flights. FSW FSW is a retrievable Chinese capsule orbited by the Long March 2 expendable launch vehicle. Missions of 6-15 days are possible with 100 W of power and maximum payloads of 300 kg. However, deceleration of about 13 g is encountered on recovery of the capsule. Advantages: FSW is competitively priced, and it is possible to integrate and fly some types of experiments within a relatively short period (< 1 year) once an agreement with the Chinese has been reached. Status: The first non-Chinese experiment payload was carried on an FSW-1 capsule launched on August 5, 1987, and retrieved on August 10 under an agreement between the Great Wall Industry Corporation and Matra Espace. The payload included an ESA microgravity accelerometer experiment and a biological experiment dealing with algae growth. In 1988 the German company Intospace launched a microgravity test facility with 104 protein crystal samples on a Long March 2, and a number of follow-on flights are planned. Japanese Free-Flyer The Japanese Space Flyer Unit (SFU) will be a reusable, free-flying platform suitable for microgravity materials experiments. As currently planned, the SFU would be an 8,000-kg (gross weight) platform first launched by the Japanese H-II rocket in early 1993 and retrieved by the Space Shuttle about 6 months later. The experiments to be carried out on the first flight would include space observation, advanced technology experiments, flight tests of advanced industrial technologies, and verification of the exposed facility of the Japanese Experiment Module of the Space Station. It is likely that the SFU will initially be filled to capacity with Japanese materials and life sciences experiments. Advantages: As a free-flyer, the SFU should provide a high-quality microgravity environment. Reusability should lower costs for flying experiments. Status: The SFU is in the development phase. SFU retrieval is manifested for the STS 70 mission in mid-1993. Photon Photon is a Soviet recoverable capsule launched on an SL-4 expendable launch vehicle to a 220 to 400 km orbit, typically at an inclination of 33

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62.8 degrees. Mission duration is 14-30 days. The maximum payload mass is 500 kg, and the available volume is 4.7 m . Four hundred watts of power can be supplied to the payload, rising to 700 W for 1.5 hours a day. The acceleration levels inside the craft are 10 g and lower during the flight, but deceleration levels during reentry can reach eight to ten g's. The facilities that have flown aboard Photon include the Zona 1 and Splav-2 electric furnaces and the Kashtan electrophoresis unit. Advantages: As of early 1989, flight opportunities on the Photon capsule were being offered commercially by Glavcosmos at $15,000 per kilogram. This price is negotiable if either the data received from the experiment or the new hardware developed for it are shared with the Soviets. Status: The Soviets first orbited the Photon capsule in 1983, and it has flown three times since. The French have a firm commercial contract for use of the Photon, and negotiations have begun with other potential customers. Space Station Mir The Soviets claim a microgravity environment of 10" to 10" g for the Mir space station. Mir's current total power is approximately 10 kW, down from 11.6 kW due to solar panel degradation. The solar panels of a new module scheduled to be added to Mir in late 1989 are expected to double the available power. Another module also is scheduled for late 1989. Mir operational requirements use approximately 1.0 kW. There currently is little space available within Mir for new experiments, and major new research facilities will need to go either on the exterior or in additional modules. A current bottleneck in the Mir system appears to be the return of items from Mir to Earth, in that only 120 to 150 kg can be returned via Soyuz two or three times a year, at least until the Soviet Shuttle enters service. Reentry g levels are on the order of six to seven g's. Advantages: Mir allows long-duration microgravity exposure (on the order of years), with the capability for extensive manned interaction. Status: Mir was put into orbit in 1986, and it has been continuously occupied since 1987. SUMMARY OF INFORMATION ON SPACE-BASED FACILITIES The list of facilities discussed in this chapter is not meant to be an exhaustive one. For example, OSSA is studying the development of a recoverable capsule, Lifesat, for life sciences research. Similarly, a non-U.S. company, Dornier, is developing a recoverable capsule called Space Courier, which it intends to offer commercially. Additional facilities are likely to be proposed over the next few years. 34

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Table 1 summarizes available information on the characteristics and capabilities of some of the previously described space-based facilities. IMPACT OF SPACE TRANSPORTATION SCHEDULE ON MICROGRAVITY RESEARCH Almost all of the U.S. capabilities and some of the non-U.S. ones, such as EURECA, depend on the Space Shuttle for launch into orbit and/or servicing. Thus, the frequency of the microgravity research missions carried on the facilities depends both on how quickly the facility can be made ready for another flight and on Shuttle flight rates. The current Shuttle manifest (January 1989 through September 1994) includes microgravity payloads (excluding middeck experiments) given in terms of Shuttle-equivalent flights, that is, equivalent to the balance of the payload bay, as shown in Table 2. The NASA payloads shown reflect requirements for microgravity research identified by the NASA Office of Space Science and Applications and the Office of Commercial Programs, although the manifest does not satisfy all proposed requirements. NASA payloads account for 2.87 and 2.70 Shuttle-equivalent flights in 1993 and 1994, respectively, while non-U.S. microgravity payloads account for 0.70 in each of those years. SPACEHAB and ISF manifested space accounts for two and one and one-half Shuttle-equivalent flights in FY 1993 and FY 1994, respectively. However, the microgravity experiments they would carry are as yet undefined. The number of launches anticipated by NASA. in the most recent manifest (January 1989) builds up to 13 to 14 per year in the FY 1993 to 1994 period after the replacement fourth orbiter, OV-105, becomes operational. The ability to reach and sustain such flight rates can be described as optimistic or "success oriented," especially since NASA does not set aside a flight contingency reserve. While a recent National Research Council study estimates a sustainable rate of 11 to 13 flights per year for a four-orbiter fleet, it cautions that "these estimates do not account for contingencies" that, aside from the obvious ones of loss or major damage to an orbiter, include "diverted landings; weather delays; late manifest and/or flight plan changes; unforeseen payload delays; facility or support system downtime; lack of timely availability of spares/logistic support." Should Space Shuttle launch rates of 13 to 14 per year not materialize, some microgravity research goals may not be achieved in the desired time frames since there is no readily available alternative for Shuttle-transported microgravity payloads. Some Shuttle flights that are presently booked, however, may be freed up, and that might help to compensate for lower flight rates. If there is a serious shortfall in Shuttle launch rates, many research goals will not be met. If NASA management and the national leadership believe it important to promote research in the microgravity sciences, they must make an effort to ensure that flight opportunities for microgravity research do not suffer disproportionately during remanifesting. In addition, NASA and the 35

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TABLE 1 Summary of Orbital Facilities1 Capabilities Estimated jLl-g Gravity (g) Crew Facilities Developer Duration Level Interaction Shuttles: Existing Getaway Specials NASA 4-7 days* io-3 Payload bay; Crew ha* on/off switches only MSL NASA 4-7 days* ID'3 Payload bay; Remote operation Middeck NASA 4-7 days* ID'3 Crew-tended Spacelab (Long Module) ESA/NASA 4-7 days* ID'3 Crew-tended Shuttle: Proposed Spacehab Spacehab Co. McDonnell- Douglas Aeritalia 4-7 days* ID'3 Crew-tended ISF (Facility Space Industries Partnership years io-6-io-6 Crew-tended in attached mode; Free-flyer capability Module) Eureca/Amica ESA 6 months io-5-io-7 Free-flyer; Shuttle deploy &r return Japanese Free- Flyer Japan 6 months N/A Free-flyer; Shuttle return Leasecraft Fail-child years N/A Free-flyer; Shuttle return Photon USSR 14-30 days sic"5 Untended Free-flyer FSW China 6-15 days N/A Untended Free-flyer Space Station Mir USSR years io-3-io-B Crew-tended Space Station Freedom NASA, ESA, Japan, Canada years io-5-io-6 Crew-tended *Can be extended with EDO capabilities. Sources: NASA, Teledyne Brown Engineering, ESA, Private Companies 36

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Flight Frequency Year Available (Projected) Power to Payload Payload Volume Maximum Payload Mass Up to 50/year (Shuttle) Operational Supplied by Experimenter 0.15 m* 90 kg 5/year (Shuttle) Operational 1.41 kW (Ave) 2.59 kW (Peak) 4.85 m2 mounting area 925kg Up to 14/year Operational 115 W/locker .06 m3/locker (~10 lockers/ mission) 27 kg/locker MO lockers/ mission) (Shuttle) 1-4/year (Shuttle) Operational 3.4 kW (Ave) 7.7 kW (Peak) 8.07 m3 4,550 kg 1-3/year (Shuttle) 1991 3.2 kW (Ave) 6.7 kW (Peak) 4.6m8 1,360 kg (69 lockers) ~3/year revisit! (Shuttle) 1993 7 kW (Ave) 10 kW (Peak) (Free Flyer) 9.50 m3 2,950-6,220 kg by orbiter ~l/year (Shuttle) 1991 1 kW (Ave) 1.5 kW (Peak) 8.5m3 1,000 kg N/A 1993 N/A N/A N/A N/A In abeyance 1-7 kW (Ave) N/A 6,800kg N/A Operational 400 W (Ave) 700 W (Peak) 4.7 m3 500kg N/A Operational 100 W N/A 300kg Continuous Operation Operational ~10 kw total power; should 90 m3 total volume N/A increase Continuous Operation 1996 45 kw total user power (Ave) 60 m3 total usable Lab volume > 68,200 kg (120 std racks) 37

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TABLE 2 Manifesting of Microgravity Payloads Fiscal Year Summary in Shuttle-Equivalent Flights (Shuttle Cargo Bay Fayloads Only) 1990 1991 1992 1993 1994 NASA 1.00 1.65 2.60 2.87 2.70 Non-U.S. Spacelab-J (Japanese) Spacelab-D2 and D3 (German) EURECA (ESA) SFU (Japanese) Commercial SPACEHAB ISF 0.45 0.25 0.25 0.50 0.50 0.20 0.25 1.75 0.70^ 0.50 1.00 Total 1.00 2.35 4.05 5.57 4.90 -Being Negotiated (Source: NASA) 38

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national leadership should continue to develop mixed fleet options for access to space so that microgravity activities in orbit are not completely Shuttle-dependent. To effectively use expendable launchers and free- flyers, however, greater emphasis will be needed on automation, robotics, and telescience, as discussed in the following chapter. NOTES 1. National Research Council, Committee on NASA Scientific and Technological Program Reviews. 1986. Post-Challenger Assessment of Space Shuttle Flight Rates and Utilization pp. 7-8. 39

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