Alicat Pressure Controllers Enter NASA
Alicat's pressure controllers have been adopted by the National Aeronautics and Space Administration (NASA) for payload attitude control. Alicat's PC series of absolute pressure controllers provide the speed, accuracy, and durability required for mission-critical functions.
Some of NASA's sounding rocket payloads require pointing accuracy controlled to less than one arcsecond (1/3600th of a degree). Traditional attitude control systems (using solenoid valves) can cause excessive jitter and vibration and are not precise enough. Northrop Grumman, a NASA contractor, turned to Alicat for a solution compatible with its fragile optical instruments.
Alicat's PC series of absolute pressure controllers directly supply fuel to the payload attitude control thrusters. Four pressure controllers feed through a common argon manifold and operate at approximately 160 pounds per square inch gauge (PSIG). A standard Alicat multi-point RS-232 sends endpoint set commands to the controllers. Once the rocket altitude exceeds 100 kilometers, all controllers increase their absolute pressures to five pounds per square inch absolute (PSIA), balancing moments of pitch and yaw. By modulating the pressure command sent to the Alicat controllers, the spacecraft's attitude is changed.
Alicat's control precision allows extremely rapid changes in commanded pressure increments down to a minimum of 0.00234 psi or up to a maximum of 150 psi. NASA testing shows that the controller accurately tracks a 5 Hz sine wave signal with a response time of less than 32 milliseconds. Since there is no backup for the attitude control system, the Alicat pressure controller is considered a mission-critical component.
As the first choice for a range of applications, Alicat's PC series pressure controllers offer many output options and deliver fast, accurate, and repeatable results with their standardized design. Lower power consumption and robust construction give the PC series lower costs and longer life. With an industry-leading lifetime warranty against material and workmanship defects, users can be confident their application needs will be met.
To meet NASA's requirements, Alicat made minor modifications to the standard PC series controller by adding a capacitor and connector hardware. To enhance durability and reduce weight, the main circuit board is encapsulated in plastic, and the body is welded aluminum rather than traditional stainless steel. The controller easily passed NASA's shake, vibration, thermal cycling, and vacuum exposure tests and has successfully completed several missions. Northrop Grumman has ordered 28 controllers for this project over the next five years.
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