MANUFACTURERS OF CUSTOM, HIGH PRECISION INSTRUMENTATION AND SUPPORT EQUIPMENT

Projects

ISIR-AL

Time Period

May 1999 through December 1999

Project Description

The ISIR-Atmospheric Lidar (AL) is a Lidar system designed for use from the Space Shuttle cargo bay. The ISIR-AL system does not have its own laser transmitter, but uses the return signal from the transmitter on the accompanying Shuttle Laser Altimeter (SLA) system. The ISIR-AL system consists of a telescope which is an exact copy of that used in SLA. The light collected by the telescope is focused into a set of optics that collimates the beam, splits the light into two channels, and then focuses these two channels into fiber optics. The telescope assembly is shown in the cut-away view to the right. The telescope tube is the orange ribbed structure and the primary mirror is shown in blue at the bottom of the tube. The two fiber optic cables can be seen at the top of the telesocpe near the window (shown in green but actually clear). The fiber optics are held to the telescope tube with the three vanes shown in yellow. The entire telescope tube is lowered into a standard GAS (Get Away Special) can used for transporting instruments in the Space Shuttle cargo bay and is shown as the blue cut-away cylinder. Once in orbit, the lid of the cannister is opened and the ISIR-AL instrument views the Earth. The two fiber optic cables are routed to a pair of detectors (not shown) that are mounted to the brown plate shown at the bottom.

The final element of this project is the Risley Wedge assembly. It is shown to the right. A risley wedge assembly consists of at least one pair of wedged optics. The two elements of the pair can be rotated independently to steer a beam of light in a particular direction. The design shown to the right has two pairs of risley wedges. It is designed for use with the SLA laser which is mounted inside the same type of can as the ISIR instrument. This assembly allows ISIR-AL and SLA to be bore-sighted by adjusting the angle of the out-going laser beam. The outer ring (shown in brown) mates to the interface flange on the GAS cans and provides an airtight seal.

Challenges and Lessons Learned

The main challenge on this project was to keep costs at a minimum. Welch Mechanical Designs, LLC (WMD, LLC) took over the design from a competitor who ran significantly over budget and failed to produce a viable design. We created a design that met all of the requirements and even added an element that was not required. The extra element is a mechanism for adjusting the decenter (X-Y) of the optics at the top of the telescope tube. The extra mechanism was added to the design while still keeping the budget well below that used by my competitor.

This was also the first project where we had to perform rigorous safety analyses to qualify the design. The analyses are required to prove that the design is safe for use on the Space Shuttle and is not a safety threat to the human passengers.