This design required a large-force high-stroke actuator. This could be made possible with the use of a  very long stroke spring and the same actuator. This would be simple conceptually, but resulted in high loads causing an increase in weight. It also would have limited extensibility to larger or smaller designs  and higher pressure systems. The MSFC Wedge Disk design incorporated a wedge to support a thin disk internally. The wedge would  support the PA loads on the disk. The disk was to be thin enough to rupture reliably at roughly ½ the minimum MDP (hence 100% margin). The biggest unknown was how the loads would scale with the pressure and disk size. Quick calculations showed it should scale linearly and assuming a very high coefficient of friction (0.9), the spring loads required for a wide pressure range were manageable. The NESC actuator could easily handle these variable loads. The valve could be made to have a relatively short stroke and a high equivalent square edged orifice diameter.  The pilot design was conceived to use one of the other concepts as a pilot system to balance scaling for  pressure or size. The idea was to develop a small pilot system that was reliable and light, and then build a valve that had internal force balancing of the PA and Sp loads. As this concept was developed, it became  clear that it was going to be costly and complex. But the valve looked feasible and was the most scalable of all the designs considered. The GSFC valve used a fracture plate that supported the inlet pressure, but could be overloaded with the  addition of a high force, low stroke actuator. This concept had much heritage to previous work and was  simple, scalable within a range of sizes and pressures, and was a fairly mature concept. The main issue was the original concept used a Nitinol bar stroke actuator. This actuator, although reliable and capable of very high loads, was very slow and depending on the initial temperature, varied in response time. So,  MSFC and GSFC conceived a magnetostrictive actuator. This actuator was based on MSFC-patented  valve concepts, but is high force, low stroke as required, and is very fast. These two concepts (the GSFCvalve and the modified MSFC actuator) were combined into the GSFC valve that was included in the trade space. Trade Study With the five concepts fleshed out, each was evaluated by a team of MSFC and GSFC personnel. The  first step was to develop a methodology for evaluation. This consisted of a matrix of figures of merit andweighting factors in a pair-wise analysis to provide a ranking of each concept.  The figures of merit were derived from the performance requirements shown in Table 1, but downselected to those felt most critical. Team members each voted on a weighting factor for each requirement. Table 2 and Table 3 show the teams suggested figures of merit and weighting factors, respectively. Down Selection The results of this trade showed that two concepts, the MSFC Wedge Seat Design and the GSFC  Fracture Disk Design, were nearly equal in performance.  With GSFC needing to develop a detailed analysis of the actuator, but having a nearly completed the  valve design, and MSFC only needing to complete the NESC actuator design started to do a new valve  design. It appeared there was manpower available to do both designs. A review of the budget showed that with the rapidly de-escalating costs of SLM due to increased competition in the market, there was  budget to build and test an example of each. With the total cost to design, build, and test both valves within the available resources allocated for this program, the decision was to produce both designs and  have a real hardware trade study down-select at the end of the program. 476