HST Solar Array  3 Latches 

Mike Garrah* 

Abstract 

The Hubbl e Space Tele scop e Servi cing Mission 3B , complete d succe ssfully in  March of 2 002, incl uded  installatio n of two new So lar Array (designated SA3 ) Assem blies. The SA3 s are of a completely ne w  design that minimizes o n-orbit jitter, and maximize s power generation. T he SA3 Latch es, develope d by  Swales  Aerospace under contrac t with NASA Goddard Space Flight Cent er, were used to carry the SA3s  into o rbit in  the Sp ace T ransportation  System 1 09 Cargo  Bay. Th ese latche s were engin eered to m eet a   wide a rray of requi reme nts cove ring almost the enti re spectrum of mech anism desig n. Du ring the course  of this pre sentation, the details of the overall latch system desig n, as well a s the desi gn of each individu al  latch will be presented. An overview of the lat ch environm ental  test program will  be presented with  empha sis on solutio n of probl ems encountered du ring that p rocess. Be cause this h ardware h as been  successfully designed, tested, and flo wn, there i s a vast a rray of practical information availa ble that will b e  of definite v alue to  mechani sms en gineers. A summa ry of “le sson l earned ” during the developm ent  process will b e provide d at the end of this pre sentation.  

Introduc tion 

The des ign of large Extra-vehic ular Activity (EVA)  releas ed structures such as the SA3 As semblies ,  carrie d into  space by th e Space  Tran sportation  Syst em, is p redicated on addressin g a wide rang e of  unique requirements. These include mi ssion safety, EVA timelines, human  factors, tool capabilities, and  weight and v olume constraints. To support the repl acem ent of the arrays, th e hardware had to be first  carrie d to o rbit using a system of uni que latche s that could accommodate th e launch environ ment a s well  as on -orbit th ermal di stortions. Upon reaching orbit, the latche s had to allow f or tool a ssisted ast ronaut  actuatio n for relea se of the arrays. Th e design, fabri cation, qualifi cation, an d successful mi ssion operatio n  of these latch es, kn own as the SA3/RAC Latche s is th e subj ect of this presentati on.  

Overall Sy stem Desc ription 

The SA3 Latch system consists of two sets of five discre et latche s (for a total of 10), mou nted on oppo site  sides of a vertical structu re known as the Cente r Support Stru cture  (CSS), which is in turn m ounted to a  pallet in th e shuttle bay. E ach set of five latch es structurally supports one SA3  during la unch and  landing  (if re quired). Four of the  latches (designated Latch 1 thro ugh Latch 4 ) support the re ctangular shaped  SA3 at each of its four corners. T he la st latch (d esignated Latch 5) s upports a deployable m ast on the top  of the SA3. Fi gure 1 illu strates the SA3/RAC Lat ch lo cation s with t he sto wed SA3 and ma st.   

Latch 1, sh own in the up per rig ht corner of Figure  1, consi sts of an active half mounted  to the SA3   structure, an d a passive  half mount ed to the CSS. T he SA3 m ounted side incorpo rates an internal  7/16 ”  (11-mm) h ex drive ACME scre w that picks up a floatin g ball nut insi de of the coni cal pa ssive h alf mounted   to the CSS. A  semi -sphe rical fitting on th e end of the  active L atch 1 housing mates with an  interior conical  surfa ce on th e passive (CSS) side which aids i n alignment an d provides 3 degrees of constraint. Latch 2,  shown in th e lower right corner of Figu re 1, is a vise -type latch with an  integ ral 90° bevel ge ar set drive n  throug h a rotary input shaf t. A 7/16” (11 -mm) h ex drive located on the Latch 1 h ousing, co upled to a drive   extension rod, transmit s torque to th e input shaft. Thi s latch incorporat es a “V” gui de and clamps down on  a semi-cylind rical swivel  fitting on  the SA3, providi ng 2 deg rees of constraint. Latch 3, sho wn in the upp er  left corn er of Figure 1, is a  vise-type lat ch with a directly driven semi-sphe rical pad that cl amps down on  an attach ment fitting at the uppe r left corner of the SA3 . The front (clampi ng) portion of the latch is hinge d                                                    * Swales Aerospace, Beltsville, MD 

Procee dings of the 37th Aeros pace Mec hanisms Sy mpos ium, Joh nson S pace Ce nter, May 19-2 1, 200 4  131