other for redundan cy, incre ased foot print, and decre ased pe rmea bility. (The spri ng tube se als consist of a   loose In conel wire mesh shape d into  a tube, wra pped with  braided Nextel cera mic fa bric, and filled with  Saffil ceramic batting.) The tube s were stitched to th e Incon el mounting plate with Inconel safety wire  and  were al so captured betwe en a lip in th e fusel age skin therm al protection tile s and a lip i n the top of the   mounting plate. This d esign was cho sen both for it s ability to withstan d the te mperature and oxidation  conditions, and becau se it provided a soft contact su rface with the  arc, whi ch was critical to prote cting the   cerami c coating of the lower arc the rmal prote ction shell from ab rasion damage. Ho weve r, it was al so  necessa ry for the se ctor g ear teeth to p ass thro ugh t he se al for th e flap to achi eve full extension d uring  testing and post re-entry fl ight. To prevent ab rasion damag e to the seal by the  gear teeth, the p ortion of  the se al co ntacted by the teeth wa s covered with an  Incon el plat e or ‘shoe’ th at covere d bot h tube s and  prevente d the spri ng tube s from prot ruding into the gear teeth. T o prevent the  ‘shoe’ from abrading the   cerami c coating of the lower arc,  the a ssembly of bot h spring tub es and th e ‘sh oe’ wa s wra pped with a   layer of wove n Nextel fabri c, with  the ‘ shoe’ a nd ove r wrap held in place by the  Inco nel stitchi ng. The  seal  mounting pl ate wa s fixed to a small, re movable sect ion of the fuselage skin to aid installati on and was  mounted with a flange ca ptured b etween the skin secti on a nd a  capture plat e such that it could sli de  slightly in  the plane  of the  skin to  accommodate  dislocation s of the  arc path caused by th ermal expa nsion  and ae ro loa ding of the system (Figu re 9). 

       DRIVE  UNIT  LOWER ARC  WITH CO VER  SEAL Figure 8.  Section thr ough Flap and   Actuator Sy stem  Figure 9. Clo se-up Sectio n throug h   Thermal Sea l

Actuator Driv e Unit  The CRV Body Flap Actu ation co ntrol system (actu ator & control lers) was de signed, built a nd qualified b y  the System s Group  of M oog In c (Fi gure 11). It was one of th e first spa ce-rated, du al-fault tole rant,  electrome chanical p rimary flight  control actuatio n syst ems. 

The a ctuato r was de signed to provid e full torqu e and spee d perfo rman ce after any two ele ctrical o r  controlle r channel failures. Drive trai n mechanical redunda ncy was not provide d due to the weight impa ct  and th e effe ct of addition al com plexity o n overall relia bility. Instead , large  margins of safety and fail safe  designs were integrated int o the individual components to over come the reliabilit y concerns. 

 As sho wn in the sch ematic (Figu re 10) three  redundant moto rs were  torque summed aroun d a common   bull ge ar; whi ch input into a cycl oidal drive. The sy stem wa s designed such th at in the eve nt of a moto r  channel failu re the other channel(s) would drag al ong the faile d motor. Thi s eliminate d the need for  clutche s and the problem s asso ciated  with impl ementing such d evices. T he output of the cy cloidal drive  in turn was connec ted by a floating crowned spline shaft, whic h drove the sector pinion gear and  subsequent sector g ear arc of the flap. T he overall a ctuator drive ratio wa s 248 6.6:1. 

Three brushless DC, rare earth, sam arium cobalt magnet mot ors provid ed powe r. The  rotors we re  band ed with steel sleeves to p revent  a roto r / stato r jam due to possibl e faile d ma gnet retention since  peak ope rating speeds of 1530 0 rpm were p ossible. A cycloid al drive transmi ssion wa s chosen be cause  385