| Spacelab |
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Class: Manned. Type: Space Station Module. Destination: Maximum Payload Orbit. Nation: USA. Agency: NASA-JSC. Manufacturer: Alenia. The Spacelab was designed by the European Space Agency to fit in the US space shuttle payload bay and allow extended experiments to be conducted by astronauts in orbit. Spacelab and the Canadian remote manipulator arm were the remnants of NASA's efforts to internationalize the shuttle program at its inception. In the absence of an American space station, Spacelab provided the only opportunity for America to carry out extensive man-tended experiments in space from the first Spacelab flight in 1983 until the Shuttle-Mir program in 1995. Spacelab's modules could be varied to meet specific mission requirements. Its four principal components were the pressurized module, which contained a laboratory with a shirt-sleeve working environment; one or more open pallets that exposed materials and equipment to space; a tunnel to gain access to the module from the shuttle cabin; and an instrument pointing subsystem. Spacelab was not deployed free of the orbiter, although ESA did consider free-flying configurations at various times over the years. On Sept. 24, 1973, a memorandum of understanding was signed between the European Space Agency, formerly known as the European Space Research Organization, and NASA with NASA's George C. Marshall Space Flight Center as lead center for ESA to design and develop Spacelab. An industrial consortium headed by ERNO-VFW Fokker (Zentralgesellschoft VFW-Fokker mbh) was named by ESA in June 1974 to build the pressurized modules. Five 10-foot-long, unpressurized, U-shaped pallet segments were built by the British Aerospace Corporation under contract to ERNO-VFW Fokker. The IPS was built by Dornier. The pressurized module, or laboratory, was available in two segments. One, called the core segment, contained supporting systems, such as data processing equipment and utilities for the pressurized modules and pallets (if pallets were used in conjunction with the pressurized modules). The laboratory had fixtures, such as floor-mounted racks and a workbench. The second, called the experiment segment, provided more working laboratory space and contained only floor-mounted racks. When only one segment was needed, the core segment was used. Each pressurized segment was a cylinder 4.12 m in outside diameter and 2.74 m long. When both segments were assembled with end cones, their maximum outside length was 7.0 m. The pressurized segment or segments were structurally attached to the orbiter payload bay by four attach fittings consisting of three longeron fitting sets (two primary and one stabilizing) and one keel fitting. The segment or segments were covered with passive thermal control insulation. The ceiling skin panel of each segment contained a 1.3 m-diameter opening for mounting a viewport adapter assembly, a Spacelab window adapter assembly or scientific airlock; if none of these items were used, the openings were closed with cover plates that were bolted in place. The module shell was made from 2219-T851 aluminum plate panels. Eight rolled integral-machined waffle patterns were butt-welded together to form the shell of each module segment. The shell thickness ranges from 1.5 to 3.6 cm. Because of the orbiter's center-of-gravity conditions, the Spacelab pressurized module or modules could not be installed at the forward end of the payload bay. Therefore, a pressurized tunnel was provided for equipment and crew transfer between the orbiter's pressurized crew compartment and the Spacelab pressurized module or modules. The transfer tunnel was a cylindrical structure with an internal unobstructed diameter of one meter. The cylinder was assembled in sections to allow length adjustment for different module configurations. Two tunnel lengths could be used-a long tunnel of 5.76 m and a short tunnel of 2.66 m. The joggle section of the tunnel compensates for the 1.07 m vertical offset of the orbiter middeck to the Spacelab pressurized module's centerline. There were flexible sections on each end of the tunnel near the orbiter and Spacelab interfaces. The tunnel was built by McDonnell Douglas Astronautics Company, Huntington Beach, Calif. The airlock in the middeck of the orbiter, the tunnel adapter, hatches, the tunnel extension and the tunnel itself permitted the flight crew members to transfer from the orbiter middeck to the Spacelab pressurized module or modules in a pressurized shirt-sleeve environment. The airlock, tunnel adapter, tunnel and Spacelab pressurized module or modules were at ambient pressure before launch. In addition, the middeck airlock, tunnel adapter and hatches permit crew members outfitted for extravehicular activity to transfer from the airlock/tunnel adapter in space suits to the payload bay without depressurizing the orbiter crew compartment and Spacelab module or modules. If an EVA was required, no flight crew members were permitted in the Spacelab tunnel or module. Some research to be accomplished on Spacelab missions requires that instruments be pointed with very high accuracy and stability at stars, the sun, the Earth or other targets of observation. The Instrument Pointing Subsystem (IPS) provided precision pointing for a wide range of payloads, including large single instruments or a cluster of instruments or a single small-rocket-class instrument. The pointing mechanism could accommodate instruments of diverse sizes and weights (up to 7 metric tons) and could point them to within 2 arc seconds and hold them on target to within 1.2 arc seconds. Each pallet was more than a platform for mounting instrumentation; with an igloo attached, it could also cool equipment, provide electrical power and furnish connections for commanding and acquiring data from experiments. When only pallets were used, the Spacelab pallet portions of essential systems required for supporting experiments (power, experiment control, data handling, communications, etc.) were protected in a pressurized, temperature-controlled igloo housing. The pallets were designed for large instruments, experiments requiring direct exposure to space or systems needing unobstructed or broad fields of view, such as telescopes, antennas and sensors (e.g., radiometers and radars). The U-shaped pallets were covered with aluminum honeycomb panels. A series of hard points attached to the main pallet structure was provided for mounting heavy payload equipment. Up to five segments could be flown on a single mission. Each pallet train was held in place in the payload bay by a set of five attach fittings, four longeron sill fittings and one keel fitting. Pallet-to-pallet joints were used to connect the pallets to form a single rigid structure called a pallet train. Twelve joints were used to connect two pallets. The Spacelab electrical power distribution subsystem controlled and distributed main, essential and emergency dc and ac power to Spacelab subsystems and experiment equipment. Orbiter fuel cell power plants 2 and 3 provided dc power to orbiter main buses B and C, respectively. The orbiter electrical power distribution system was capable of distributing 7 kilowatts maximum continuous (12 kilowatts peak) power to Spacelab subsystems and experiments during on-orbit phases. If a single fuel cell failed on orbit, the system remained operational with a maximum power level of 5 kilowatts continuous and 8 kilowatts peak. The primary dc power received in the Spacelab from the orbiter primary payload bus was nominally 28 volts, a maximum of 32 volts and a worst-case minimum of 23 volts. The Spacelab command and data management system provided a variety of services to Spacelab experiments and subsystems. Most of the CDMS commands were carried out through the use of the computerized system aboard Spacelab, called the data processing assembly. The DPA formatted telemetry data and transferred the information to the orbiter for transmission, received command data from the orbiter and distributed them to Spacelab subsystems, transferred data from the orbiter to experiments, and distributed timing signals from the orbiter to experiments. The CDMS included three identical computers and assorted peripherals. One computer was dedicated to Spacelab experiments, one supported Spacelab subsystems, and the third was a backup. The flight crew monitored and operated Spacelab subsystems and payload experiments through data display and keyboard units. The three identical MATRA 125/MS computers had a main memory capacity of 64K 16-bit words. These three computers were later changed to the upgraded AP-101SL orbiter computers. The Spacelab pressurized module video system interfaced with the orbiter closed-circuit television system and the orbiter Ku-band signal processor. The orbiter CCTV system accepted three video inputs from the Spacelab system. The Spacelab intercom master station interfaced with the orbiter audio central control unit and the orbiter EVA/ATC transceiver for communications through orbiter duplex (simultaneous talk and listen) audio channels. The Spacelab environmental control subsystem consisted of the atmosphere storage and control subsystem and the atmosphere revitalization system. The atmosphere storage and control subsystem received gaseous oxygen from the orbiter power reactant storage and distribution system and gaseous nitrogen from a tank located on the Spacelab module's exterior. The Spacelab ASCS regulated the gaseous oxygen and nitrogen pressure and flow rates to provide a shirt-sleeve environment for the Spacelab module compatible with the orbiter cabin atmosphere. Gaseous oxygen from the orbiter PRSD entered the Spacelab module through the upper feed-through in the Spacelab forward end cone at 7 bar and a maximum flow rate of 6 kg per hour. The Spacelab cabin depressurization assembly was primarily for contingency dump of Spacelab cabin atmosphere in case of fire that could not be handled by the Spacelab fire suppression system, The module would be depressurized at 0.2 kg per second. The Spacelab active thermal control subsystem consisted of a water loop to remove heat from the Spacelab module and a Freon loop to remove heat from equipment on any pallets that were flown with the pressurized module. Typical orbit: 253 km circular orbit, 39 deg inclination. Length: 7.00 m (22.90 ft). Maximum Diameter: 4.12 m (13.51 ft). Spacelab Chronology
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