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.