Release No. 95-98
STS-74 Photogrammetric Appendage Structural Dynamics Experiment
(PASDE):
Understanding How Solar Arrays Move in Space
What Is PASDE?
The Photogrammetric Appendage Structural Dynamics Experiment
(PASDE) was developed to study vibrations in a solar
array attached to the Russian space station Mir.
The structural stability of solar arrays is crucial for the
International Space Station and future spacecraft. PASDE data will
help engineers understand how solar panels move in space and how to
improve future solar panel designs.
What Is Photogrammetry?
Photogrammetry involves photographing an object with one or more
cameras, from two or more locations. Since the object is viewed
from many different angles, three-dimensional coordinates can be
determined from the two-dimensional measurements on the film. This
is done by a process known as optical triangulation. Photogrammetry
provides a cheap, accurate and versatile means of measuring the
dynamic motions of an object. This technique, used by PASDE, will
enable engineers to discern movements as small as 1/10 inch in the
tips of the Mir solar arrays.
Why Fly PASDE Aboard The Space Shuttle?
The objective of PASDE is to develop and demonstrate advanced
photogrammetric techniques to monitor on-orbit movements. The use
of photogrammetric techniques for these on-orbit measurements can
be a low-cost alternative to standard instrumentation, such as
accelerometers, that need to be directly attached to the object
being studied.
How Does PASDE Work?
Photographic images of two panels on a solar array on the Mir
Kvant-2 module will be recorded by six 8-mm video recorders, along
with a timing signal provided by the space shuttle. The timing
signal will allow the images of the solar arrays to be correlated
with planned test activities. Since these images are viewed from
different angles, three-dimensional position data can be obtained
from the film by optical analysis. The images and time histories
will be processed for different points on the solar array to
determine array vibrations and movements during the various
on-orbit tests.
What Components Make Up PASDE?
PASDE is made up of three Get-Away-Special (GAS) canisters
mounted in the payload bay of the Space Shuttle Atlantis (STS-74).
The six PASDE video cameras, two per GAS can, will focus on two
sections of the Mir Kvant-2 solar arrays, photographing their
movements during docking, thermal expansion and other planned
on-orbit events. In the illustration below, the Kvant-2 module and
its solar arrays are to the right, near the tail of the orbiter,
and the three PASDE GAS canisters are shown in their positions in
the payload bay.
How Will The PASDE Data Be Used?
The data returned by PASDE can be used to help eliminate
unacceptable vibrations on the solar arrays of the International
Space Station and other space structures. Additionally, analysis of
PASDE data may provide considerable cost savings by assisting
spacecraft designers in the development of the optimum weight and
stiffness of future solar arrays.
Who Funds PASDE?
The PASDE project is part of the International Space
Station’s Phase-1 flight program to the Russian Space Station
Mir.
A color photo of a PASDE camera array in a GAS can structure
(L-95-3413) and a color or B/W copy of the illustration shown above
are available upon request. For more information on the PASDE
project, please contact the NASA Langley Office of Public Affairs
at (757) 864-6124.
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