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Problem with Rocket Fuel Pressure Control Solved Quickly, Efficiently, with MATLAB and Simulink

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Challenge To design a control system for a rocket fuel tank that would ensure a continuous flow of liquid oxygen from the pressure tank to the turbine Solution Use MATLAB and Simulink to model, analyze, and implement a control system consisting of a series of flow-regulating valves, each with a different orifice Results An efficient and cost-effective design process A focus on finding solutions, not fixing code

Kistler K-1 space launch vehicle.

Challenge

GenCorp's Aerojet Division in Sacramento, California, needed to develop a control system that would maintain specified pressures in the propellant tanks of the Kistler Aerospace K-1 space launch vehicle.

When it is completed, the K-1 will be the first commercially available, fully reusable launch vehicle to provide low-cost access to space for low earth-orbiting satellites.

The K-1 is powered by modified Russian rocket engines, provided by Aerojet, that burn LOX (liquid oxygen) and kerosene. Thrust is produced when the appropriate mixture of LOX and kerosene is pumped into the combustion chamber and ignited.

Propellant pressures at the pump inlets must be controlled to prevent fluid cavitation and the resulting catastrophic engine failure. Pump inlet pressures are controlled by adding helium to the free volume, or ullage, at the top of each tank. Ullage pressures decrease rapidly as the engines fire and propellant levels drop. To restore pressure, propellants consumed during firing are replaced with helium from on-board storage bottles. But replacing propellants with helium creates a control engineering problem: constant changes in the pressure of the helium, the temperature governing the flow rate of the helium mass, and the engine thrust levels.

"I don't know how I would have solved this problem without [MATLAB] and Simulink."

Perry Stout
GenCorp Aerojet
 

Solution

Perry Stout, controls engineer for the project, developed a solution in which flow between the high-pressure helium storage bottles and the low-pressure propellant tanks is controlled by a series of solenoid valves, each with a different orifice. The control system selects specific combinations of valves to match helium flows with helium demand throughout the mission.

Stout used MATLAB and Simulink to design a control system that regulates the operation of the valves according to the system orifice needs. He began by deriving the physical equations that describe the process and writing them out on a sheet of paper. It was fast and easy to move these core equations into Simulink. He was then able to develop a model based on the equations, test them, and add heat transfer equations and closed-loop control laws graphically, without writing additional code. He could then analyze the design, using MATLAB, and modify it quickly and easily in search of optimal performance.

"I don't know how I would have solved this problem without [MATLAB and] Simulink," said Stout. "As a Fortran project, the control system design would have involved an entire team. A manager would have been required to divide the modeling, simulation, and control tasks among several people, closely monitor and coordinate all activity, and summarize the results."

Results

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