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
Figure 4-7. Drawing of CGSE nozzle [55]. The nozzle was machined from 9/16 in. aluminum hex stock in the MIT AeroAstro machine shop. The overall external length of the nozzle was 0.961 in.; this included 0.400 in. of ¼ in. male NPT threads 5 cut externally on the inlet end of the nozzle, as well as a hexagonal segment wide enough to be gripped firmly by a wrench, so that the nozzle could be screwed tightly into the outlet of the SV128 solenoid valve. The exact geometry of the converging side of a rocket nozzle is not particularly important, since the flow in this region is subsonic and can be easily turned without much pressure loss [ 28], so the inlet side of the nozzle was simply drilled out to an internal diameter of 0.25 in., and the angled tip of the drill bit was used to make a short tapering transition to the nozzle throat. (This did create a relatively small chamber-to-throat area ratio, which can cause a small additional pressure drop, but the estimated thrust loss that would result was less than 5% [28].)The diverging section of the nozzle was cut on a CNC lathe, using computer assistance to maintain the 15° half-angle of the cone. While the nozzle was being designed and machined, the Tescom regulator and an Omega SV128 solenoid valve had been ordered. Once all of these flow control components had been obtained, testing could begin to verify that these components had been appropriately sized for the CGSE. 5 In NPT sizing, the dimension given is a nominal pipe size, related to the inner diameter (ID) of the fitting. 72
5 Single-Stream Component Testing An incremental program of testing for the TALARIS CGSE was designed with three major steps. First, the individual components of the system, which had been selected based on the results of the MATLAB model as well as other considerations, would be tested to verify that their performance met the requirements of the CGSE. Next, a full eight-thruster system would be constructed, and the verification tests would be repeated. The main purpose of this step would be to ensure that components which met requirements on their own would continue to do so even when they had to interact with a greater number of components in a complex system. For instance, the regulator would have to be capable of maintaining pressure on the low side of the CGSE with higher mass flows resulting from multiple thrusters firing at once. Finally, the eight-thruster system would be fully integrated with the rest of the TALARIS hopper and tested under actual flight conditions. In this phase, the idea was to move from verification to validation. It would be necessary to ensure that the CGSE interacted effectively with the other subsystems of the TALARIS hopper in order to produce the desired result: a controllable vehicle capable of completing a demonstration hop. To achieve this goal, it would be necessary to have not only properly functional hardware and software, but also skilled and practiced vehicle operators. Thus, additional goals throughout these three phases of testing were to gain operational experience and to develop procedures and protocols for optimal operation of the CGSE that also ensured the safety of every person involved with TALARIS. For the first step in the three-step plan, a single Omega SV128 solenoid valve was purchased, in order to verify its suitability before proceeding with the purchase of enough valves to build a full eight-thruster flight system. A single aluminum nozzle was machined, designed for 425 psia chamber pressure as described in section 4.3. The Tescom 44-1363-2122-408 regulator was also purchased. Finally, tubing and fittings were purchased and assembled to connect the components together. Since this setup fed gas to a single thruster, as opposed to the multiple branching flow paths that would be needed in the full eight-thruster system, this first round of component tests was also referred to as single-stream testing. 5.1 Objectives Several measurable outcomes of the single-stream component tests were defined. The first was to characterize the thrust output of a single CGSE thruster. The maximum amount of force that the thruster could produce when fed through the flight regulator would be determined. It was assumed that 73
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Figure 4-7. Drawing <strong>of</strong> CGSE nozzle [55].<br />
The nozzle was machined from 9/16 in. aluminum hex stock in <strong>the</strong> <strong>MIT</strong> AeroAstro machine shop. The<br />
overall external length <strong>of</strong> <strong>the</strong> nozzle was 0.961 in.; this included 0.400 in. <strong>of</strong> ¼ in. male NPT threads 5<br />
cut<br />
externally on <strong>the</strong> inlet end <strong>of</strong> <strong>the</strong> nozzle, as well as a hexagonal segment wide enough to be gripped<br />
firmly by a wrench, so that <strong>the</strong> nozzle could be screwed tightly into <strong>the</strong> outlet <strong>of</strong> <strong>the</strong> SV128 solenoid<br />
valve. The exact geometry <strong>of</strong> <strong>the</strong> converging side <strong>of</strong> a rocket nozzle is not particularly important, since<br />
<strong>the</strong> flow in this region is subsonic and can be easily turned without much pressure loss [ 28],<br />
so <strong>the</strong> inlet<br />
side <strong>of</strong> <strong>the</strong> nozzle was simply drilled out to an internal diameter <strong>of</strong> 0.25 in., and <strong>the</strong> angled tip <strong>of</strong> <strong>the</strong> drill<br />
bit was used to make a short tapering transition to <strong>the</strong> nozzle throat. (This did create a relatively small<br />
chamber-to-throat area ratio, which can cause a small additional pressure drop, but <strong>the</strong> estimated<br />
thrust loss that would result was less than 5% [28].)The diverging section <strong>of</strong> <strong>the</strong> nozzle was cut on a CNC<br />
la<strong>the</strong>, using computer assistance to maintain <strong>the</strong> 15° half-angle <strong>of</strong> <strong>the</strong> cone.<br />
While <strong>the</strong> nozzle was being designed and machined, <strong>the</strong> Tescom regulator and an Omega SV128<br />
solenoid valve had been ordered. Once all <strong>of</strong> <strong>the</strong>se flow control components had been obtained, testing<br />
could begin to verify that <strong>the</strong>se components had been appropriately sized <strong>for</strong> <strong>the</strong> CGSE.<br />
5 In NPT sizing, <strong>the</strong> dimension given is a nominal pipe size, related to <strong>the</strong> inner diameter (ID) <strong>of</strong> <strong>the</strong> fitting.<br />
72
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