Space platforms: multi-use facilities for a cost-paring age

Cost-conscious space planners are studying the concept of orbiting ''carpools'' to make more efficient use of near-earth space. Here a leading space engineer explains how this may transform humanity's use of this new frontier.

Many of the satellites that go into low-earth orbit have common needs for such things as electric power or temperature control. Consequently, a share-the-ride era is emerging in space.

The interest of NASA (National Aeronautics and Space Administration) in more economical space operations has spawned the concept of large, multi-use facilities in low earth orbit called space platforms. A number of suggested designs are now being studied by McDonnell Douglas, under contract to Marshall Space Flight Center. Unmanned as well as manned platforms are planned; both will be ''plugged'' into a new, common utility-provision vehicle, a boxlike structure with large winglike solar panels and radiators that will provide 12-25 kw of solar-derived power, heat rejection, data handling, a ground communications link , attitude control, and orbit-reboost propulsion.

The multi-use facilities will orbit many payloads (in cost-effective, ''carpool'' fashion) both for scientific and commercial applications. The facility will be delivered into orbit in sections, assembled and activated with shuttle support, and then visited on a three-month cycle. The platforms are designed for easy loading and unloading. The periodic shuttle visits will allow crews to exchange payloads, as well as modifying, maintaining, or replenishing those on board.

The unmanned platform version planned for late in this decade will initially consist of a central utility vehicle with three short arms. Here payloads can be mounted and rotated independently to serve the three different viewing objectives of solar, astronomical, and earth-oriented instruments and their respective scientists at the consoles in the Payload Operations Control Center on earth. Ultimately, scientists hope to replace the three initial short arms with 12-meter ones to accommodate the much larger telescopes and antennas planned by NASA for later years.

Benefits of the unmanned platform lie in the efficiency and consequent economy inherent in numerous payloads using centralized spacecraft services, a single communications link with ground stations, and a single orbital destination for the shuttle to deliver, service, and retrieve its cargo.

Scientists hope that in the late '80s manned platform modules can be plugged into the same central utility-provision carrier.The manned platform will provide a valuable ''workbench in space.'' Here the crew can unload, assemble, and align such large structures as multi-segment mirrors for large telescopes or antennas. Manned-platform activities will also include development and testing of advanced equipment and operating procedures. Manipulators for assembling large structures in space and other experimental technologies for future space vehicles or manned platforms can also be tested. All of these require considerable time and human involvement and thus long-term residence in orbit.

The manned platform would consist of a group of interconnected, pressurized cylindrical aluminum modules of a diameter that fits into the shuttle cargo bay, plus a ''workbench'' operations beam of lightweight, high strength graphite-epoxy trusswork with numerous berthing positions. These modules can use much of the technology developed on the shuttle and spacelab vehicles.

The early manned platform will accommodate a crew of three to four. These may rotate every 90 days, depending on changing needs. Like the unmanned platform, the manned platform assemblage is plugged into the central utility vehicle via the airlock-adapter, which contains the central passageway; a restroom; EVA exit point (access to outside); and, for emergency situations, a safe haven with food , water, and supplies. Attached to the airlock-adapter are the Control Center Habitat Module, the Payload Modules, and the Logistics Module. Aft of the Habitat is mounted the ''workbench'' operations beam where outside assembly and other services are performed.

Inside of the Control Center Habitat is a control console, a workbench, food preparation rack, some payload racks, and three staterooms, each complete with a sleeping bag, entertainment center (stereo, library, etc.), and personal stowage lockers. The payload modules will contain racks of life-science experiments and pharmaceutical or materials-processing equipment.

The Logistics Module, exchanged every second visit of the shuttle (or every 180 days), has two sections, one pressurized. The pressurized section will hold supplies such as food, more disposable clothing, and other items for crew use, new experiments, and payloads or consumables for payloads which will continue to stay in orbit. Water replenishment tanks are also stowed inside of this Logistics Module. The unpressurized (outside) section holds tanks for oxygen and nitrogen for replenishing the breathing atmosphere inside the manned platform.

The shuttle allows men to fly in orbit for a week. However, long-term manned capability in orbit is one category of service yet remaining to be provided for the US space program. This service was available in Skylab for several years in the early '70s. But since then only the Russians have had men in long-term orbital residence.

People are irreplaceable for many important functions in orbit. Manned platforms, therefore, possibly operating in the late '80s, would thus provide the long-term residency in space to further capitalize on those unique surroundings.