A thermal vacuum chamber is used to simulate thermal environments of a test satellite in orbits where daily temperature variations range from 80 K to above 400 K. The test facility is complex and consists of expensive parts. Modification of control software is discouraged as the modification may cause unexpected system failure. This paper describes a study that develops a real-time dynamics model of the thermal vacuum chamber that can be used to create control algorithms and simulate electrical inputs and outputs for interface with a programmable logic controller (PLC). The dynamics model is represented by simulation software and exported to a target PC in the Microsoft® Disk Operating System (DOS) mode to exploit the real-time kernel of the DOS software. The model is executed in real-time and communicates with a microprocessor-based input/output (I/O) board via a serial port to emulate electrical inputs and outputs.
The target process to model is the gaseous nitrogen (GN2) mode in which GN2 circulates in a closed loop through thermal shrouds encompassing a test object. A blower boosts the GN2. Injected liquid nitrogen (LN2) and an electric heater control the set temperature of the GN2. The realized simulator dynamics are quite similar to those of the thermal vacuum chamber and serve as an appropriate system to verify the control performance of a programmed PLC.