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October 1995

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.

Image of PASDE video camera
Video Camera Portion of the STS-74 Photogrammetric Appendage Structural Dynamics Experiment (PASDE)

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 (804) 864-6124.
 

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