Alicat Pressure Controllers Rocket Into the Atmosphere

Modified PC Series used in sounding rocket payload attitude control systems
Tucson, Arizona (September 21, 2011) – Pressure controllers from Alicat Scientific  have been selected for use in NASA sounding rockets to control payload attitude. Alicat PC Series absolute pressure controllers provide the speed, accuracy and durability required for this mission-critical function.

Alicat controllers modulate the pressure commands to adjust altitude on this NASA sounding rockets' payload section.

Alicat controllers modulate the pressure commands to adjust attitude on this NASA sounding rockets' payload section.

The payload sections of some NASA sounding rockets are required to achieve pointing accuracies of finer than 1 arc second (1/3600 of a degree). Conventional attitude control systems (using solenoid valves) introduce too much shock and vibration, and are imprecise. NASA contractor Northrop Grumman turned to Alicat for a solution that would work with its delicate optical instruments.

The Alicat PC Series absolute pressure controllers are used to directly feed the payload’s attitude control jets. The four pressure controllers are fed from a common gaseous argon manifold at approximately 160 psig, with a stock Alicat mulitdrop RS-232 sending set-point commands to the controllers. As soon as the rocket passes 100 km in altitude, all controllers are brought up to 5 PSIA with both pitch and yaw moments balanced. The spacecraft’s attitude is then modified by modulating the pressure commands sent to the Alicat controllers.

Alicat’s control precision enables commanded pressure changes in increments as small as .00234 psi or as large as 150 psi, with extreme speed. NASA’s testing demonstrated the controllers accurately track a 5 hz sign wave, correlating to a response time faster than 32 milliseconds. As there are no backup systems for altitude control, the Alicat pressure controllers are considered to be mission-critical pieces of equipment.

A top choice for a variety of applications, the Alicat PC Series pressure controllers are available with numerous output options in a modular design that delivers fast, accurate and repeatable results. Low power consumption and a rugged design result in lower cost over the course of its long service life. With an industry-leading Lifetime Warranty against defects in materials and workmanship, users can feel confident that their application needs will be met.

To fit NASA’s requirements, the stock PC Series controllers were modified slightly with a different capacitor and connector hardware. To enhance durability and reduce mass, the main electronics board was potted in plastic and the bodies were fabricated from aluminum, rather than the typical stainless steel. The controllers passed NASA testing for shock, vibration, thermal cycling and exposure to vacuum without difficulty, and have completed several successful missions. Northrop Grumman has ordered 28 controllers over a five year period for this application.

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