Roll Control Test Unit
The Roll Control Test Unit (RCTU) is a full mockup of the roll control system for LAD and for Starscraper in the future. A challenge to becoming flight ready has been successfully and accurately testing our control logic and the required electronics. We have experimented in the past with actively controlling ASTRo, a small solid rocket with servo-controlled fins built specifically for testing the control system, but the practicality of having to fly a reasonably large rocket every time we wanted to test the controls system dramatically limited our ability to experiment and test successfully.
RCTU is designed from the ground up to be a complete mimic of the Starscraper and LAD cold-gas roll control system: identical valves, control electronics, and components, all mounted to a large free-spinning platform weighted to have the same mass characteristics as the rocket it is simultating. With RCTU operational, iterating the control system is as easy as changing a few lines of code on the onboard electronics, filling the cold gas tank, and running the program. Sensors onboard the setup record performance data in real time, showing us exactly how well the system works.
RCTU also allows us to test and debug the entire hardware loop for the control system. Between the raw control logic and the roll control thrusters is a complex electromechanical system composed of fluid components, power supply equipment, a sensitive IMU (Inertial Measurement Unit, which tells the controller how fast the rocket is spinning), and electronic boards running a real-time operating system. All of these need to work together for the system to function; RCTU gives us a simple way of insuring the entire system works together in the same configuration we will be using for flight.