Refill Strategy for Two-Tank Cold Gas Systems

Presenter Information

Samuel Wood, Georgia Institute of TechnologyFollow
Glenn Lightsey, Georgia Institute of TechnologyFollow

Session

Weekend Poster Session 1

Location

Utah State University, Logan, UT

Abstract

Heritage

• The Glenn Lightsey Research Group (GLRG) in the Georgia Institute of Technology Space Systems Design Laboratory (SSDL) designs, builds, and tests cold gas propulsion systems for use in a variety of CubeSat volumes
• A GLRG cold gas propulsion system (CGPS) is operating on NASA’s Biosentinel mission
• CGPS are delivered or nearing delivery for the SunRISE, SWARM-EX, and VISORS missions

• The propellant, R-236fa, is stored as a saturated liquid-vapor mixture in the main tank
• A refill valve connects a plenum to the main tank. The plenum is kept below saturation pressure to store gaseous R-236fa for actuation
• Each tank contains a temperature and pressure sensor
• The temperature range of these systems is typically between -20 to 50 °C

• Refilling directly injects liquid propellant into the plenum when the refill flow path is covered by liquid
• Closing the refill valve when the plenum has reached a high refill limit, defined as a fraction of the main tank pressure, leads to significant pressure overshoot as the saturated liquid transitions to gas
• Liquid in the plenum causes higher than expected thrust and lower operational efficiency

• The new refill strategy will have two logical components implemented on the CGPS controller
1. Predict how long the refill valve needs to be open to reach a desired plenum pressure given the current state of the system
2. Predict when the plenum has reached a steady-state pressure after the refill valve is closed