April 1983:the Space Platform

The beginning of Space Shuttle operations has opened new doors to the use of space. For years, scientists have relied upon the costly method of individual, expendable satellites to perform on-orbit research. Now, however, the Shuttle offers routine two-way access to space.

For some time, work has been underway to develop the first Shuttle-based science and Earth applications research system: Spacelab. This joint project of NASA and the European Space Agency is a manned laboratory to be carried aloft in the payload bay of the Shuttle. It features a mix of habitable modules and U-shaped “pallets,” which are aluminium structures not unlike airline cargo containers. On these pallets, groups of experiment equipment can be prepackaged for placement in the Shuttle’s cargo bay.

Spacelab, set to become operational in September 1983, will represent a major advance in science and applications efforts in space. But, as good as it is, it has some limitations that the experimenters would like to overcome. The laboratory’s current maximum mission duration of about nine days is limited chiefly by the amount of power the Shuttle fuel cells can generate in orbit. The fact that all experiments must be carried inside the Shuttle cargo bay limits Spacelab’s pointing capability. When one instrument is observing a particular star, the entire Shuttle must be oriented toward deep space. This would prevent an Earth-observing experiment from functioning at the same time.

NASA has been working on an answer to these and other limitations. It will come in the form of a composite system that combines Spacelab with other equipment in an evolutionary way designed to meet growing needs with incremental hardware growth. The first step in this evolutionary process is expected to be a module known as the Space Platform.

1987: Year of the First Step

The Space Platform is a 26,000 lb (12,000 kg) module capable, among other things, of generating many kilowatts of solar power for indefinite periods of time. Far more power, in fact, and for much longer times, than the Shuttle can provide to experiments that operate from its cargo bay. Because of these platform advantages, experiments could be removed from the cargo bay and attached to special berthing ports on the plat¬form. In this way, long-duration experimentation could go on long after the Shuttle returned to Earth. Drawing energy from the Space Platform, these untended payloads could remain on orbit for six months or more. Periodically, the Shuttle would return to change the old experiment packages for new ones, and to maintain the platform itself.

An inherent capability exists to support Spacelab if the platform were to dock with the laboratory and thereby extend the length of Spacelab’s missions from about a week to approximately a month. The Space Platform would satisfy a wide range of science and applications objectives in the areas of high-energy astrophysics, astronomy, solar physics and atmospheric science. NASA proposes to "park” such a system in low Earth orbit by 1987.

Basic Features

The primary structure is a rectangular frame divided into three sections. The forward section contains most of the electrical and thermal control subsystems 'equipment. The central section contains most of the attitude control, communications, and data handling subsystems equipment. The aft section contains three berthing ports for payloads and a fourth for the Shuttle. These ports are located to permit easy access by the Shuttle's Remote Manipulator Arm, a robotic mechanism used to remove payloads from the cargo bay and install them at the ports on the platform.

The platform would gather its energy from the Sun by using wing-like solar arrays. Folded into the cargo bay of the Shuttle, the arrays would be deployed upon reaching orbit. Batteries in the platform would store the electricity so that power could be furnished even on the “night” side of the orbit. Present designs call for a power capability of about 12 kilowatts, but as payloads are later added, the demand for power will increase. These demands would be met by increasing the size of the solar arrays. The platform would, of course, provide more than power to attached pallets. Control moment gyros would provide stabilization and attitude control, and a reboost capability would keep the platform and its payloads at the proper orbital altitude. The platform would also provide heat dissipation, using a pumped coolant loop and a deployable radiatOT, and it would provide communications and high data rate telemetry. These features eliminate the need to send into orbit, as has been done in the past, separate support systems for individual satellites.

Another important feature of the Space Platform is that each of the pallets would be capable of individually pointing its instruments for its own scientific purpose without interfering with neighbouring payloads. One experiment package, for example, could be focused on the Sun; at an adjacent berthing port, an instrument could be studying the Earth in a natural resource observation; and at yet another pallet, an X-ray telescope could be monitoring distant nebulae. Such a capability eliminates the more costly approach of launching indi¬ vidual satellites to cope with the various instrument pointing needs of the scientific community.