1 ATLAS Beam Steering Mechanism Lessons Learned  

Kenneth A. Blumenstock*, Alex ander K.  Cramer *, Alan B. Gostin *, Claef  F. Hakun* , Paul G. Haney *,  Matthew R. Hinkle *, Kenneth Y.  Lee*, Carlos F. Lugo* , Adam J. Matuszeski *, Armando Morell *,  Nerses V. Armani **, Joseph Bonafede **, Molly I. Jackson **, Peter J. Steigner ** & Juan J. Stromsd örfer** 

Abstract  

This paper describes the design, testing, and lessons learned during the development of the Advanced  Topographic Laser Altimeter System (ATLAS)  Beam Steering Mechanism (BSM). The BSM is a 2 degreeof-freedom tip-tilt mechanism for the purpose of  pointing a flat mirror to tightly control the co- alignment of  the transmitted laser and the receiver tel escope of the ATLAS instrument. The high resolution needs of the  mission resul ted in sub- arcsecond pointing and knowledge requirements, which have been met .  Development of the methodology to verify performance required significant effort . The B SM will fly as part  of the Ice, Cloud, and Elevation Satellite II Mission (ICESat II) , which is scheduled to be launched in 2017.  The ICESat II primary mission is to map the E arth’s surface topography for the determination of seasonal  changes of ice sheet thickness and vegetation canopy thickness to establish long- term trends.   

Introduction  

The primary purpose of this paper is to focus upon “Lessons Learned” that came about during the development of the ATLAS Beam Steering Mechanism (BSM). A secondary purpose is to review the configuration and design features of the BSM, as well as to gain understanding of the reasoning behind  some of the design features.      Light, Detection, and Ranging ( LiDAR ) systems have been used for numerous spaceflight missions. Highpowered laser pulses fired from the spacecraft are reflected off the Earth’s surface and back to the  spacecraft , where they are detected. Measurement time from firing to detection determines t he distance to  the surface, and signal characteristics reveal  additional properties of the atmosphere and surface. ATLAS  maps  the topography of our planet  to monitor seasonal changes in ice sheet and vegetation canopy  thickness, which is very important in gaining understanding of long- term trends . 

As technology advances, there is always a desire to gain bett er resolution of measurements. ATLAS has  the smallest transmitted beam, smallest receiver field of view, and smallest alignment margin among  NASA/GSFC space -borne laser altimeters. This  result ed in the stringent requ irements imposed upon the  BSM , which led to further challenges in verifying that those requirements were met .  

Design  

Overview   An exploded v iew of the BSM is in Figure 1. Not shown in that figure  are both the actuators and the position  sensors , which  can be  seen in the cross sections of Figure 2.  

Mirror   The BSM mirror, which reflects a high- powered laser, required a dielectric coating to provide very high  reflectivity a t the wavelength of the laser. A metal mirror would not support a dielectric coating, resulting in                                                              * NASA Goddard Space Flight Center, Greenbelt, MD   ** Stinger Ghaffarian Technologies Inc., Greenbelt, MD  

Proceedings of the 43rd Aerospace Mechanisms Symposium, NASA Ames Research Center, May 4-6, 2016