ROOM
13
Special Report
On-orbit assembly provides a potential pathway
to address the size challenges of next generation
HDSTs. For example, consider the three-stage
evolvable space telescope concept described in
Polidan et al., (Proceedings of SPIE, 9143, 2014) and
shown schematically in Figure 3.
The idea is to assemble a large telescope in
space using hexagonal elements that are 4 m
across from one flat side to another. The telescope
would evolve over three launches that are
separated by budget cycles spread over several
years. In the first stage, the central circular
secondary mirror, and two hexagon elements
that form the primary mirror assembly (PMA) are
launched in a single stack and assembled on-orbit
to form an asymmetric aperture of 4.5 m x 12 m.
In the second stage, four additional hexagon
elements are launched in a single stack, and
assembled to form a symmetric aperture of
diameter 12 m. The third stage launches 12
additional hexagons that would be added to the
existing structure to complete a telescope with an
aperture diameter of 20 m. The exoplanet yields
provided by the three stages are indicated in
Figure 2.
In addition to enabling a scientifically
important increase in information return for
HDSTs by making it possible to evolve the
construction of the telescope over multiple years,
on-orbit assembly would likely provide significant
cost savings.
For Earth science, on-orbit assembly can
reduce the number of satellite launches for
weather and climate observations through the
The International Space
Station and the docked
Space Shuttle Endeavour
in May 2011 at the end of
the main construction
phase in LEO.
Figure 3. Three-stage
evolvable space telescope
concept leading to 20 m
aperture (Polidan et al.,
2014)
Stage 1
Stage 2
Stage 3
creation of a persistent platform assembled in
space. One illustration is the ability to use the
persistent platform to replace the A-Train series
of satellites that pass over the same spot on
the Earth within a few minutes of each other
collecting a variety of measurements. Sensors
could be added to the platform regularly, enabling
faster refresh than is currently feasible. Just as
importantly, assembly of multiple payloads (as
well as refresh) onto one platform would require
fewer launches, and provide launch savings of
several hundred million dollars.
Communications satellites
On-orbit assembly can also provide payoff for
telecommunications in geostationary orbit (GEO).
NASA
