329 MOPITT Mechanisms :  16 Years In -Orbit Operation on Terra  

Andrew S.  Gibson1, Florian Nichitiu2, Dwight Caldwell3, John Hackett4,   Robert Deschambault5 and James R. Drummond6  Abstract  

The 16th anniversary of the launch of NASA’s Terra  Spacecraft was marked on Dec ember 18, 2015, with   the Measurements of Pollution in the Troposphere (MOPITT) instrument  being a successful contributor to  the NASA  EOS flagship . MOPITT has been enabled by a large suite of mechanisms, allowing the  instrument to perform long- duration monitoring of atmospheric carbon monoxide, providing global  measurements of this important greenhouse gas  for 16 years . Mechanisms have been successfully  employed for scanning , cooling of detectors , and to optically modulat e the gas path length within the  instrument by means of pressure and gas cell length variation . The instrument utilizes  these devices to  perform correlation spectroscopy , enabl ing measurement s with vertical resolution from the nadir view ,  and has  thereby furthered understanding of source and global transport effects of carbon monoxide.  Given the design requirement for a 5. 25-year lifetime , the stability and performance of the majority of  mechanisms hav e far surpassed design goals.    With 16 continuously operating mechanisms in service on MOPITT, including 12 rotating mechanisms   and 4 with linear drive elements, the instrument was an ambitious undertaking. The l ong life requirements  combined with demands for  cleanliness  and optical stability made for difficult design choices including  that of the selection of new lubrication processes . Observations and lessons learned with regards to  many aspects of the mechanisms and associated monitoring devices  are discussed here. Mechanism   behavior s are  described, including  anomalies, long- term drive current/power , fill pressure, vibration and  cold-tip temperature trends . The effectiveness  of particular lubrication formulations and the screening  method implemented is discussed in relation to continuous rotating mechanisms and stepper motors ,  which  have exceeded  15 billon rotations and 2.5 billion steps  respectively . Aspects of gas cell hermeticity,  optical cleanliness, heater problems and SEU effects on accelerometers are also discu ssed.                                                                                                                                                   1 Canadian Space Agency, St -Hubert, QC, Canada                4 Canadensys Aerospace Corp., Bolton, ON, Canada  2 University of Toronto, Department of Physics,  ON, Canada     5 Christie Digital Systems , Kitchener, ON, Canada   3 COM DEV International Lt d., Cambridge, ON, Canada            6 Dalhousi e University, Halifax, NS, Canada 

Copyright © 2015 Government of Canada. NASA has been granted permission to publish and disseminate this work  as part of the Proceedings of the 43rd Aerospace Mechanisms Symposium, NASA Ames Research Center, May 4-6,  2016. All other rights are retained by the copyright owner .  Stirling Cryocoolers (2)           Displacer                   Compressor  Length Modulated Cells (4)   Scan  Mirrors   (4)  Chopper  Mechanisms  (4)  Pressure Modulated Cells (2) 

MOPITT Instrument Layout  (showing mechanism locations)  Carbon Monoxide Average Mixing Ratio (in ppbv)  (measured June- July 2015)