This scenario was created to demonstrate the use of a fuzzy-logic closed-loop control system used to simulate proximity operations. The fuzzy-logic application called “FuzzyTech” is used through an Astrogator Engine Model Plugin (via VBscript) to control when an Astrogator Engine is on or off in order to control the approach of a chase vehicle with a target vehicle. In this case the chase vehicle is represented as the CEV, and the target is the ISS.
[Note, before the scenario can be run, please execute the batch file called “FuzzyDocker.bat”. This file registers the FuzzyTech dll with the following command “regsvr32 FuzzyDocker.dll” so that the DLL may be accessed by the plugin scripts.
The user enters an offset in both position and velocity for the chase vehicle (WRT the target) and then the fuzzy logic controller will be used to determine when the engine fires. Engine firings can be seen in the 3D window.
The user can first attain the current conditions by using the ‘Get Current Values’ in the HTML utility shown below. Then, the user can change these numbers and set them into the scenario using the ‘Set Values’ button. Finally, if the user selects the ‘Re-calculate’ button, the new trajectory is created, using STK/Astrogator and the fuzzy-logic controller.
Once the trajectory has been created, the user can animate the scenario to see the engine firings, and the progress of the trajectory.
Note that the scenario is only setup to deal with relative positions that are close to the ISS and velocities that are small. Also, the fuzzy logic assumes that the vehicle is approaching the ISS from the –X direction (i.e. the x value is negative). It will work best if the offset is between -100 to -500 m in the +X, and -100 to 100 in the +Y, -Y, +Z and –Z. Velocities should be between -2 and +2 m/sec.
You can experiment with other values, but assumptions made in the STK scenario may prevent the scenario from reaching a solution.
Michel E. Loucks
President, Space Mission
Engineer
Space Exploration
Engineering Corp.
360.378.7168
360.317.5527 (cell)