Conclu sions  and Nex t Steps 

The d esign of the HCM was valid ated t hrough our q ualificatio n testing. Th e effort also provi ded valu able  informatio n about o ptimizi ng the  flight mech anisms while  on-orbit and how to i mprove  future de signs for  similar motors . 

Several ope rations rule s are re comm ended ba sed on  the results of  the testing s eque nce. First, because it   was sho wn that the HCM is mo st repeatable when th e move an gle was 90° or greater, key m oves of the   HCM  during observations will be at least this l arge with a nominal  observing rotation of 120°. Rotations  that are small er than 30° will be pre ceded by a full rev olution. Seco nd, while it is intended th at little or no   adjustment in  the HCM delay settings be required during th e SECCHI prim e missi on. Increases in th e  flight mechan ism delay set tings may be requi red in extreme cases to offset in creasi ng friction in order to   maintain hig h repeata bility. Evidence in  the coro nagraph ima ges will be exploi ted to indicat e chan ging  repeatability in the mech anism. Finally,  adjustme nts to the delay setting may also be requi red sho uld the  instru ment te mperature  be lower or hig her than th e nominal proje cted temp erature. While the me chanism   itself can not provide sufficient feedba ck to make th ese adj ustme nts, the temper ature feedb ack avail able  while on orbit  will be used to re-tune the mechani sm during the mi ssion.  

The lesso ns learned in thi s study provided valua ble desig n information for th e developm ent of a similar  hollo w-co re motor for the Helio seismic Magneti c Imager (HMI) on  the Sola r Dynamics Observatory (S DO)  (Scherrer 20 02). T he HMI HCM  is to have a minimum apertu re of 3 5.6 m m and  will be expe cted t o  perfo rm m ore than 8 0 million op eration s during a five-year n ominal  missi on with t he same  repeatability as  the SECCHI HCM. Th e design r elies on the use of a smalle r bea ring with a one -piece, phe nolic retain er,  instea d of th e Teflon to roid separated bearin g used in the SE CCHI HCM. Nye 2001B oil  will be used as a  lubricant. Wit h the ad dition al de sign differen ce of much lo wer cog ging torque t han the SE CCHI HCM, thi s  arrangement is anticipated to produ ce much less variability in the bea ring fri ction – and less torque noise  – during the lifetime of the mechani sm. This will allow for high lifetim e repeatabil ity performance. A control   system id entical to that used for SECCHI will be u sed for HMI. The sm aller cogging to rque will allo w for  much si mpler correlation between del ay setting and motor stoppi ng position a nd less vari ability in the   beari ng fri ction will en sure that the stoppi ng po sition is as re peata ble as po ssible.  

The challenges in this design will be characterizi ng the motor friction through a comprehensive lifetime  testing and careful correlation of fri ction data to  delay setting s for on-orbit tu ning. Th e variation i n the  beari ng friction will be mea sured during low speed operation  and an attempt will be made  to measure th e  mech anism repeata bility continuo usly d uring the course of the vacuum lifetime operation. 

Referen ces 

1. Akin, David, et al. “Th ree High Duty Cycle, Spa ce-Qualified Me chanism s.” Proceedings of t he 27th   Aerospace Mechanisms Symposium  (1993)  2. Brue ckner, G.E., et al. “The L arge A ngle Spectroscopic Coron agraph (LAS CO).” Solar Phy sics,  Volume 16 2, pp 357 -402 (1995 )  3. Conley, Peter L. Ed. Space Vehi cle M echanisms: E lements of a Successful Desig n. John Wile y &  Sons , Inc. pp. 315 (19 98)  4. Harri s, Tedri c A. “Rolling Bearin g Analysis.” John Wiley & Sons, Inc . pp. 452 (20 01)  5. Howard, R.A ., Mose s, J. D. and S ocker, D.G. “T he La rge Angle Spe ctroscopic Coro nagraph   (LASCO).” Proce edings of the SPIE , Volume 413 9, pp  259-2 83 (20 00)  6. Sche rrer, P. H. “Th e Heli oseismic and Magn etic Imager fo r the Sola r Dy namics O bservatory.”  American Ge ophysical Union, Fall Meeti ng (2002)  7. Thomp son, William T., et al. “Th e COR1 Inner Coronag raph for STEREO-SE CCHI.” Proce eding s of  the SPIE , Volume 485 3 (2003).  8. Wülser, J.-P., et al. “EUVI:  The STE REO-SECCHI E xtreme Ult raviolet Image r.” Proceedi ngs of the   SPIE , Volume 5171 (200 3).  27