STEREO / SECCHI Coronagrap h Hollow -Core Motor Development and Testing 

Augustu s S. Moore*, Alexande r D. Price**, David J . Akin*, Ralp h Hor ber†

Abstract 

A hollow-core  motor was develope d by the Lo ckhe ed Martin Sola r and Ast rophysics L aboratory for u se in  two coronagraph tele scopes in  the Sun Ea rth Connection Coronal  and Heli osphe ric Inve stigati on  (SECCHI) in strument suite  on the two spacecraft of Solar Te rrestrial Rel ations Obse rvatory  (STEREO).  The HCM ha s a 48-mm a pertu re and rotates a pol arizer on the  optical axi s of the tele scope s. Here  we  descri be the developm ent of the mech anism a nd test ing metho ds as well a s the re sults of te sting an d life  simulatio n. The HCM wa s proven to be  robu st and c apabl e of performing in ex cess of its pri me mission   life. In addition, we pre sent the limitations to the design and the le sson s lea rned for future me chanisms. 

Introduc tion 

A hollow-core  motor (HCM) wa s devel oped to be i ncorpor ated into t he two coronagraph tele scope s in the   Sun Earth Conne ction Co ronal and Hel iospheric Investigatio n (SECCHI) suite  of instrum ents on ea ch of  the two  spa cecraft of th e STEREO  missi on th at will be launched in early 2006. Two coronagraph  telescop es are bei ng developed: COR1, whi ch will h ave a fiel d  of view of 1.3 – 4 Rsun that is being develope d by the Go ddard  Space Flight Center, and COR2, which will have a fi eld of  view  of 2 – 15 R sun and is bei ng develo ped by the Nav al Research  Labo ratory. Each of the two STERE O spa cecraft will carry a  COR1 an d CO R2 tele scope. The Naval Research  Labo ratory   principal inv estigato r respon sible for the ove rall SECCHI  program is Dr. Russell  Howard [5]. T he Lockhee d Martin Sp ace  System Com pany Solar a nd Astrop hysics La boratory (LMSAL)  is develo ping two other tel escop es for t he SECCHI p rogram (th e  Extreme Ultraviolet Imag er an d the Guide T elescop e) and is  respon sible for the coro nagraph shutter motors a nd HCM s [8].                                                          *  Lockheed Martin Spa ce System Com pany, Solar a nd Astro physi cs Laboratory, Palo Alto, C alifornia  **  Lockhe ed Martin Spa ce System Company, Solar and Astrop hysics Labo ratory, Palo Alto, Californi a  and Dartmo uth Colle ge, Ha nover, Ne w Hampshire  †  H. Magnetics In c., Marshfield, Massa chusetts 

Procee dings of the 37th Aeros pace Mec hanisms Sy mpos ium, Joh nson S pace Ce nter, May 19-2 1, 200 4   Solar corona grahs like COR1 and COR2 are  designed to  observe the faint coro na that is norm ally only visible to the  naked eye d uring a sol ar eclipse [2]. Coron agraphs accompli sh  this by blo cking the view of the visibl e sol ar disk in ord er to  observe  the faint extende d corona  whose inten sity is severa l  orders of magnitude le ss bright than t he sola r disk. The light  from the co rona origi nates in the photosphere and is Thomp son  scattered  into the field of  view of the corona graph telescop es.  As a result, the dete cted light is significantly pola rized. By taking   advantag e of this polari zation, the true coronal emi ssion can be   isolate d from backg round and instrument al sources. T he HCM is  placed o n the opti cal axi s of th e coronag raph (Fig. 1) and  contai ns a linear pol arizer. During observation s, the HCM will  rotate the pol arizer so ima ges may be a cquired in m ultiple polari zation state s. 

Figure 1.  Location o f the SECCHI  HCM in th e CO R1 Teles cope Polarizer   in HCM  

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