Lesso ns Lea rned 

Tailor requi rements an d design concepts for su ccess   The utili zatio n of the ri sley prism con cept made it p ossible to d evelop a flig ht qualified p recision boresi ght  adjustment mech anism i n <4 mo nths. The  alig nment capa bility of the m echanism all owed loo se  installatio n alignment requireme nts and mad e the BAM a viabl e risk redu ction o ption th at co uld be  impleme nted late in th e I&T pha se of the G LAS instrument . By thoroug h engi neering and  trad e  negotiatio ns, we were able  to tailor most of the BAM design requi rements to readily availabl e resources.  We mad e our job as easy as po ssible while still meet ing the goal s of providing a  preci sion me chanism to   reduce the ri sk of margin al boresight alignment stability performance  of the GLA S instrument.  This l esson  can a nd sho uld be ap plied to every proje ct at every pha se of  instrum ent mech anism developm ent.  Always loo k to ways that can red uce se nsitivity and increa se the r obustness of a desi gn.     Photograph s May Prove to Be Invaluable   The BAM utilized spare risley pri sms from the la ser assemblies. The paper  work documenting the  characterization of  the prism assem blies was exa mined and the two closest mat ching prisms were  selected for the B AM. Great care was taken not  to contaminate  the p risms as mole cular or parti culat e  contami natio n could be f atal to the transmi ssion of the relativel y high po wer lase r radiation ref racting  throug h the prisms. After final assem bly and ba seline pe rform ance testing  the protoflig ht unit wa s  vibrated. The  BAM assem bly was in spected po st vibrat ion for a ny signs of pot ential failure s. A chip was  “discove red” in one of the  prisms. Th e record s of all of the sp are risley p risms were in vestigated to   determi ne whether the  chip wa s pre-existing o r a result of the vi bration te st. The do cumentation of the  spare risleys wa s lacking. They were re legated  to sp are statu s because of le ss than perfect coatin gs or  matche s to other risleys. I t was imp ossible to d etermine wheth er or not th e chip had  existed prior to  vibration. After micro scopic insp ectio n of the area in questio n, and review of n umerous photog raphs taken  durin g the assembly and t esting of the  BAM, it was det ermined  that there was evidence that the chip  existed prio r to vibration. Unfort unately , it had not b een noted during th e cursory visu al inspectio ns that   were limited  by the de sire to minimi ze potential contamination  of the prisms. A lesson  learned here is to  fully insp ect “alrea dy qu alified” or  “spares” items a nd to take  numerous pictu res during the developme nt  process.  

Utilize Off-th e-Shelf/Spare parts fo r other Proje cts an d Indust ry Contacts   When time is of the esse nce the de sign engin eer must utilize t he part s that are availabl e and de sign  around them.  In order to d evelop a viab le flight wo rthy mechani sm desig n in an extremely sh ort peri od of   time, it is essential th at the propo sed design reflec t hard ware that is availa ble within th e developm ent  sched ule re quired. Conta cts mad e through a ssociation with the Aero space Mecha nism Symposium   undo ubtedly were cruci al to the timely d evelopme nt of the BAM. It was believed that the longe st lead item   would be the  procurement  of the actua tors a nd fligh t qualified el ectro nics. Th e vendor of the actu ators  acted extre mely quickly an d delivere d 4 fight units in ~6 wee ks. As it turned out, the delivery fit perfectly  into the development sch edule and di d not cau se any impact to th e developm ent program. The BAM and   BAME desi gns were fo unded on what wa s imm ediately available o r easily fabricated with minim al  modificatio n of otherwi se off the shelf parts.  

Keep it Simple   The ol d axio m axiom "Ke ep It Simple" does pay off and was demonstrated i n the de signs of both the BA M  and the BAM E. The BAM utilized a basic sp ur-ge ar train to p rovide the req uired angul ar resolution to  meet the beam stee ring require ment s levied on th e BAM. Given th e limited command li ne resource s and  spare parts available, the extremely si mple BAME des ign prove d to be a reliable and rob ust sol ution for  driving th e BAM. The BA M is a good example of a simpl e yet clever d esign impleme ntation, exe cuted  unde r a seve re time and re source co nstraint. 

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