11 We did design and fabricate actuator bobbins that separated the windings from the damping sleeves such  that they would not be coaxial, but we never had the opportunity  to test them. The more prevalent pole was  the BSM, and the BSM was designed to have much greater damping than the Scan Mechanism, so it appears that there is a relationship between the amount of damping and the prevalence of the pole. If a  non-coaxial design would reduce or eliminate the pole, phase margin could be greater  resulting in reduced  compensation output, better performance, and increased robustness . 

Sensor Fabrication Issue   Our Differential Impedance Transducer sensors vendor, Blue Line Engineering, did an excellent job of providing sensors to meet our specifications. The raw sensor behavior is non- linear, so the sensor  electronics undergo a tuning  process  to trade  off various performance parameters. The vendor was able to  predict very  well what they could achieve. We pushed them to the limits of what  was achievable for our  application and for their technology .    While the vendor certainly was under schedule pressure, there are usually multiple reasons for explanation of any mishap. An error occurred during manufacture of the flight sensors . The epoxy used for potting the  cables into the sensor bodies did not cure, which was one of the final steps in  manufacturing the sensors.  The root cause was an error in computing the mass of the components that were mixed, so the mix ratio  was in correct. It was necessary  to build a new set of sensors, resulting in a small schedule slip. The vendor  was very responsive and manufactured a new set of sensors very quickly.    While samples of pucks were provided for all epoxy mixes for outgassing testing, this process  did not  alleviate the risk of an error , but would catch the error after it occurs . Since significant work was at risk if an  error in mixing occurred, it would have been prudent to have more checks in place. One possibility could  have been to use premixed epoxy  stored at cold temperature that had already been tested for outgassing.      A process error such as this can always happen. This lesson is a reminder to elevate checks to prevent  such errors, dependent upon the amount of rework that is as stake if a  proces s fails.  

Schedule Pressure   In more recent times, pressure to meet schedule and budget has come under higher levels of scrutiny than  in the past . For this particular project, the in- house engineering team was turned on at the 11th hour to  produce the entire mechanism  from concept to flight . This put us on a tight schedule.    The BSM was initially determined to be supplied from a vendor, but the work was taken in- house after an  environmental test failure. The project originally chose the vendor as a cost savings  measure since it is  more cost effective to buy already developed hardware t han it is to develop hardware. However, it turned  out that the vendor’s hardware had design shortcomings such that flight qualification would require  redesign, so the perc eived cost savings evaporated. The project further benefited going in- house since  BSM requirements were  compromised in order to utilize the vendor’s hardware, so once the work was  brought in- house, optical requirements tightened up significantly.    Being on a tight schedule put us in the spotlight. Management was very concerned and preferred to ha ve  hardware sooner than later. Sometimes it is useful to develop some hardware early on to help with the  design process if analytical methods l ack fidelity , such that  the eas ier path is to build and test. In this case,  we determined that any early hardware development would not be of benefit , and also that  early hardware  development  would hurt cost and schedule. Though management desired a quick hardware cycle, we were  thankful that the team  was permitted to take the necessary time to design and analyze to the degree  deemed most efficient .  

It takes time a nd effort to develop hardware. Significant time is expended for procurement and fabrication,  followed by time and effort for assembly and testing. T he proper approach is to do all your homework and  design it right the first time.  Ideally, changes to the Engineering Model should be minimal in the F light Model.