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
fast response times on the order of ms. They were also lightweight, with masses of a few hundred grams. However, because they were space-rated hardware, these valves were prohibitively expensive. While solenoid valves from the other two classes tended to cost a few hundred or even just tens of dollars apiece, a single spacecraft solenoid valve might cost several thousand dollars. Also, there was generally a long lead time associated with the spacecraft valves – at least several weeks, or even longer for custom-made components. Thus, space-rated valves were not a viable option for the TALARIS CGSE. With all of these tradeoffs, very few COTS solenoid valves were found that would be suitable for the CGSE. The valve finally selected was the Omega SV128, with the optional 24 Vdc coil. Figure 4-5. Omega SV128 solenoid valve. The SV128 was essentially a process control valve, although it was slightly larger than most. It was one of the only valves in its class to meet both the pressure and flow rate requirements of the TALARIS CGSE, with a maximum differential pressure of 1500 psi and a
directly opens and closes the main valve orifice. This allows for a fast response time, but if the size of the orifice is large and the differential pressure across the valve is high, it can become impractical to install and power a solenoid strong enough to actuate the valve directly. By contrast, in a pilot-operated valve, the solenoid opens a smaller pilot orifice which then allows the upstream pressure of the fluid to help actuate the main orifice [53]. This method of actuation has the benefit of allowing a more reasonably sized solenoid to control stronger flows, but the process is more complex and thus takes longer to complete. For this reason, the SV128 had a somewhat slower response time than the other valves in its class. While other valves in the SV120 series which were direct-operated had opening and closing times of 4 to 15 ms, the SV128 was rated at 30 to 60 ms [52]. This was on the boundary of the acceptable range defined in the requirements in section 3.1.4, so it was deemed essential to focus on the time performance of the solenoid valve in component testing. However, the SV128 was relatively inexpensive and available for immediate shipping, and it was considered to be the best choice all around given the constraints of the TALARIS project. 4.2.2 Regulator In selecting the regulator for the CGSE, the inlet pressure requirement of 4500 psia, as set by the maximum rated pressure of the flight tanks, narrowed the field of COTS components significantly. Among the remaining candidates, there were several models found to have a sufficiently high
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fast response times on <strong>the</strong> order <strong>of</strong> ms. They were also lightweight, with masses <strong>of</strong> a few hundred<br />
grams. However, because <strong>the</strong>y were space-rated hardware, <strong>the</strong>se valves were prohibitively expensive.<br />
While solenoid valves from <strong>the</strong> o<strong>the</strong>r two classes tended to cost a few hundred or even just tens <strong>of</strong><br />
dollars apiece, a single spacecraft solenoid valve might cost several thousand dollars. Also, <strong>the</strong>re was<br />
generally a long lead time associated with <strong>the</strong> spacecraft valves – at least several weeks, or even longer<br />
<strong>for</strong> custom-made components. Thus, space-rated valves were not a viable option <strong>for</strong> <strong>the</strong> TALARIS CGSE.<br />
With all <strong>of</strong> <strong>the</strong>se trade<strong>of</strong>fs, very few COTS solenoid valves were found that would be suitable <strong>for</strong> <strong>the</strong><br />
CGSE. The valve finally selected was <strong>the</strong> Omega SV128, with <strong>the</strong> optional 24 Vdc coil.<br />
Figure 4-5. Omega SV128 solenoid valve.<br />
The SV128 was essentially a process control valve, although it was slightly larger than most. It was one<br />
<strong>of</strong> <strong>the</strong> only valves in its class to meet both <strong>the</strong> pressure and flow rate requirements <strong>of</strong> <strong>the</strong> TALARIS CGSE,<br />
with a maximum differential pressure <strong>of</strong> 1500 psi and a
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