Shop Talk

  Archived Shop Talk

This project completed in September of 2003 indicates some of the varied capabilities of ScopeCraft. It is a fore optic for a LIDAR system. LIDARs are used to study the upper atmosphere by pulsing a LASER beam into the atmosphere and collecting the return reflected/scattered light and analyzing it. In order to collect enough light LIDARs use large collecting fore optics. BY pulsing the LASER and timing the light collection, various levels of the atmosphere can be studied. The LIDAR fore optic can be considered as a large non-moving optical tube assembly. The optical configuration with this system is a classical Cassegrain with a third turn mirror just above the primary to bring the collected light beam out to the side.

The primary mirror is a 36 diameter 5 thick Cervit blank with a 12 Pyrex secondary. The tertiary mirror is a 6-inch Pyrex diagonal. The requirements for maintaining collimation and focus were very tight which required the use of carbon fiber truss members with a zero coefficient of thermal expansion. These specifications were compounded by the additional requirement that the system was to be mounted in an over seas shipping container and would be subjected to g-forces of up to 10 g's as the container was shipped. The primary, which normally weighed over 460 pounds, now represented a force of 4600 pounds under these loads. In order to meet these high loads the 18-point support for the primary mirror needed to be very robust.
The next design challenge was the secondary mirror support. After calculating the required support it was decided to make the secondary mirror assembly removable and packed in a separate crate. This then added an additional challenge of being able to be re-attached to the main part of the structure without needing recollimation and focusing. This implied a kinematic mount for the removable portion of the secondary.

The entire steel portion of the structure was powder coated in flat black and the individual carbon fiber truss members were painted flat black enamel.

The entire project from detailed design to delivery took 90 days and included all CAD files, assembly instructions, and collimation instructions.