NASA RASL TELESCOPE SHIPS

 
 

DFM Engineering has completed and shipped the Raman Airborne Spectrographic Lidar (RASL) 24-inch Optical Tube Assembly (OTA) to NASA Goddard. The Optical Tube Assembly will be a major part of the RASL instrument to be mounted in various NASA research aircraft. The assembly met or exceeded all requirements, including the goal of the complete OTA weighing less than 200 pounds (it weighs 196 pounds) and passing through a 27-inch wide aircraft door (it measures 26.8 inches)

Achieving a low weight while maintaining a high stiffness was necessary to meet the high natural resonant frequencies required for aircraft use. High natural resonant frequencies are also very useful for ground based telescopes as they allow high performance pointing and tracking while minimizing wind induced vibrations. Ground based hardware can use less expensive steel construction, but for aircraft use an aluminum structure is theoretically, and from a practical standpoint, better. The tradeoffs of steel versus aluminum construction are further detailed in "Steel vs. Aluminum".

The RASL optical tube assembly also presented additional design and fabrication requirements including high strength to withstand the "G" loading of the aircraft and operation in any attitude. The mirror supports have to support the mirrors and maintain collimation (optical alignment) over the various "G" loads, directions, and temperatures. The wide temperature range requires the mirror supports and the mirror optical spacing to be fully passively temperature compensated.

DFM Engineering has used Invar (a metal with very low temperature expansion coefficient) spacers on most of their telescopes to minimize the focus shift with temperature changes. The RASL telescope required Invar spacers and additional temperature compensating elements to meet the focus stability requirement. Additional information on focus stability may be reviewed at "Performance Requirements for the Internet Telescope".

NASA will soon be integrating the RASL telescope with the Nd:YAG laser transmitter and the multi-channel filter-detector receiver. Laboratory tests and demonstrations will be followed by installing the RASL telescope into the airplane.

For more information on the original requirements and design specifications from NASA, please visit our related Newsworthy Articles.

• NASA Goddard original assignment features

• NASA Goddard project progress update w/photos

• Steel vs. Aluminum Article

• Performance Requirements for the Internet Telescope