467 connector rings. With the positive and negative high frequency data channels placed on adjacent rings, this  capacitance resulted in an impedance at the high frequency of the data signal sufficient  enough to block  the low voltage signal when combined with other losses in the complete system. By reordering the USB  channels through the connector such that  the ground channel of the USB DC power bus was placed on the  ring between the two data channels, the capacitance effect was disrupted and the impedance problem  eliminated.  

Beacon Activation and Battery Maintenance Challenges  

Since it was necessary to avoi d premature emission of radio  signals and draining of battery capacity, the  locat or beacon was not activated until the payload was ejected. D ue to the extended period of dormancy   from final battery charge until payload ejection,  it was necessary to minimiz e the power draw of the ejection  detection system in the payload. The EDR payloads included a custom designed activation circuit for the  ejection detection and battery charging functions. The coaxial nature of the phono plugs was susceptible  to brief short ing between adjacent conductors  during insertion and removal , which in combination with  peculiarities in the activation circuit design, led to a couple of challenging problems uncovered during later  phases of testing.  

Early versions of the activation design involved means of detecting severance of the USB data connection  circuit via cross connections to the battery charging circuit. T his cross coupling resulted in numerous  permanent failures of the payloads during testing, particularly to the COTS flash dr ives used for data  recording. Eventually it proved impossible to eliminate the failures with the original concept . A new system  of detecting payload ejection was developed. This method sens ed the severance of a short circuit between  terminals protruding fr om the side of the payload and shorted through contact with the wall of the alum inum  cartridge prior to ejection. This late design change  succe eded in eliminating the flash drive failures  due to  problematic coupling of the charging and data circuits . 

Due to inadequate voltage specification of certain components in the activation circuit , another  consequence of crossing conductors during coaxial plug insertion and removal was a propensity to damage  the activation circuit or battery, which accumulated  over r epeated cycles.  Delayed understanding of the  issue precluded redesign for properly sized components. Thus, the vulnerability was mitigated through  procedural safeguards and rigorous monitoring.  

A final redesign was undertaken to completely replace the act ivation circuit with an optically sensed circuit  for detecting payload ejection. While this completely resolved all of the remaining risks for operational  damage or premature battery drain of the payloads, the very late introduction in the schedule  precluded the  opportunity for full adequate testing of this design. In the end, a mixture of both redesigned versions of the  payloads was flown in order to balance these conflicting risks without disrupting the flight schedule.  

Conclusions  

The most challenging development issues were related to the custom designed payload activation circuit  and the software for writing data to the flash drives. Ironically, neither of these had been considered  noteworthy risk items at the beginning and had assumed to be within t he scope of routine developments.  In hindsight, the one noteworthy improvement to the development process would have been earlier  acceptance of the need for a change of design concept for these two items  and better integration between  mechanical and electr ical aspects of the design process in the crucial early phases . 

In operation, the EDR system performed almost flawlessly. It met all critical schedule milestones up to and  including flight , and without disruption to the overall AA -2 development and launch preparation schedule.  During the mission, all 12 data recorder payloads ejected exactly as planned and were successfully  recovered ahead of the anticipated timeline. Data was successfully  retrieved from all units and ultimately  proved to be a perfect reco rding of the telemetry stream on 11 of the units, with the only flaw being limited  disruption of the data on one of the payloads. The data loss was an intermittent issue with one of the data