456 will be presented at the IEEE Aerospace Conference in March 20201. This paper expands upon the previous  paper with focus on key design decisions and a non- traditional development process at NASA that enabled  success of the EDR subsystem , within the constraints of limited resources and a compressed schedule.  

Figure 2.  Six of the twelve flight payloads near completion.  

Aggressive cost and schedule limits for the AA -2 program, exacerbated by the late addition of the EDR  subsystem, forced development to proceed along an accelerated path with resource limitations that did not  allow for a typical process of developing requir ements, defining environments, and analytically validating  design solutions. With an incomplete set of requirements, engineering judgment guided the identification of  design parameters with the most uncertainty, and/or highest risk of not converging on an acceptable  solution. These parameters were pursued with demonstration testing as early as possible in the  development process, which provided the necessary evidence regarding those  requirements with the  highest sensitivity to the design parameters . Require ments definition matured concurrently with testing  progress . The design was explicitly driven to maximize potential for large margins in parameters with high  uncertainty and low sensitivity. The design also allowed for radical redundancy –  twelve data recorders  were flown, but only one needed to be recovered to obtain the full flight data set.  

Unique Challenges  

The principal  challenge was to determine how to eject a recorder from the CM. Detailed knowledge of the  local environments at the time of ejection was not available, but the ejection system needed to ensure  confidence in successful retention and separation of the data recorder payloads during the anticipated  tumbling of the CM during uncontrolled flight. Due to the cost and schedule constraints of the project,  making use of an off the shelf solution was preferable to a new development. Early on it was recognized  that the US Air Force AN/ALE -47 flare and chaff dispenser system had many features that seemed to be  congruent with the EDR objectives.  

The standard ALE -47 dispenser system required an enhanced capability in two critical aspects. The  anticipated flight vibration environment of the CM during the test flight greatly exceeded certified limits of  the ALE -47 system. In addition, the ALE -47 syste m was designed for dispensing passive decoy payloads  and did not have provisions for separable power and data connections between the payloads and host  vehicle. Thus, modifications to the ALE -47 system were required to meet these needs for the AA -2 test  flight. 

Bounded by the  standard capabilities of the ejection system, the defined characteristics of the payload data  storage and beacon electronics, and the requisite operational environments, the dominant aspect of the  payload design was the balance of pac kaging the components into the available mass and volume limits of  the standard ALE -47 cartridge,  while still maintaining adequate robustness. Not only did multiple electronics  need to fit within the volume allotted by the cartridge, but the mass was const rained by the need for sufficient  buoyancy to ensure the payloads would float in the ocean with adequate stability for antenna pointing, yet  have sufficient structural integrity to survive the water impact at a terminal velocity of approximately 150  mph.