Development of a Cold Gas Propulsion System for the ... - SSL - MIT
Development of a Cold Gas Propulsion System for the ... - SSL - MIT Development of a Cold Gas Propulsion System for the ... - SSL - MIT
5.2.3 High Side of CGSE As mentioned previously, in order to use the flight regulator, it was necessary to construct the entire high side of the CGSE. As shown in Figure 3-3, this required fill and shutoff valves as well as tubing to connect them to the tanks and the flight regulator. Sizing of these valves and the tubing was based largely on practical assembly considerations; flow characteristics were also taken into account but without rigorous analysis. For instance, the tubing used to connect the two flight tanks to a single line to feed into the regulator needed to be rated for at least 4500 psia, but it should also be bendable, since this would allow for less mass and a wider range of possible angles as opposed to using elbow fittings for each turn in the tubing. These criteria led to the selection of 0.5 in. OD (0.334 in. ID) stainless steel tubing, which also interfaced well with the fittings in the necks of the tanks. Two lines of this tubing (one from each tank) came together at a three-way tee fitting, with the third branch leading to the flight regulator. Because this line to the regulator had to carry the flow from both tank lines, it was believed that its internal diameter should be larger than that of the two tank lines. Very few three-way tee fittings satisfied this, but the one selected had a 0.5 in. ID passage leading towards the regulator. This dimension was maintained by using 0.75 in. OD stainless steel tubing with 0.51 in. ID to complete a straight run to the regulator. The regulator had a main valve orifice of 0.375 in. [54], so it was believed that the tubing selections described would not restrict the gas flow more than the regulator itself would. The selection of high-side tubing helped to guide the selection of the fill and shutoff valves. Both of these valves are manually-actuated ball valves. The flow path through a ball valve is a simple straight line, so when the valve is fully open, it has a high flow capacity with minimal effect on the flow through it [56]. The ball valves selected for the CGSE were manually actuated with a quarter-turn handle, since electric or pneumatic actuators that could be controlled remotely were too large and heavy. Since the shutoff valve was to be placed in line with the single high side feed path to the flight regulator, it was chosen to have an internal diameter of 0.5 in. to match the rest of the line. The fill valve was chosen from the same family of valves as the shutoff valve, but it did not need to be as large since it was not in the main flow path. In fact, it was considered advantageous to have a smaller fill valve, since that would limit the flow rate during filling and allow more time for conditions to settle in the flight tanks, and also provide the opportunity for some mass savings. Thus, the fill valve was selected to have a size of 0.25 in. It was placed on the branch of a three-way tee fitting which had a run of 0.5 in. ID along the main flow path to the regulator. The high side of the CGSE built for single-stream characterization testing is pictured in Figure 5-5. 78
Figure 5-5. CGSE high side as constructed for single-stream characterization tests. As shown in Figure 5-5, a four-way cross fitting with pressure and temperature sensors similar to those used at the inlet and outlet of the thruster solenoid valve was placed just before the inlet of the regulator to measure conditions on the high side throughout the single-stream tests. With the construction of the high side, the third and final configuration for the single-stream characterization tests was as illustrated in Figure 5-6. Figure 5-6. Third configuration for single-stream characterization tests [38]. 79
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Figure 5-5. CGSE high side as constructed <strong>for</strong> single-stream characterization tests.<br />
As shown in Figure 5-5, a four-way cross fitting with pressure and temperature sensors similar to those<br />
used at <strong>the</strong> inlet and outlet <strong>of</strong> <strong>the</strong> thruster solenoid valve was placed just be<strong>for</strong>e <strong>the</strong> inlet <strong>of</strong> <strong>the</strong><br />
regulator to measure conditions on <strong>the</strong> high side throughout <strong>the</strong> single-stream tests.<br />
With <strong>the</strong> construction <strong>of</strong> <strong>the</strong> high side, <strong>the</strong> third and final configuration <strong>for</strong> <strong>the</strong> single-stream<br />
characterization tests was as illustrated in Figure 5-6.<br />
Figure 5-6. Third configuration <strong>for</strong> single-stream characterization tests [38].<br />
79
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