Evaluation of Robot-assisted Spacecraft Alignment

Abstract

The Reusable Flight Experience (ReFEx) is a spacecraft developed by the German Aerospace Center (DLR), which aims to provide design and flight data as well as operational experience on aerodynamically controlled Reusable Launch Vehicles (RLV) stages. The constant knowledge of the position and orientation in 3D space is essential for a successful mission. The alignment and transformation matrices between the individual component’s local coordinate systems within different subsystems of ReFEx must be determined before the flight. They are required as inputs for the Guidance, Navigation and Control (GNC) algorithms controlling the flight path during the spacecraft’s mission. A generalized alignment process was developed which guides the operator through the required measurements and concludes with the desired results. An industrial robot was implemented for an increased generalization with different Devices under Test (DUT). Additionally, the industrial robot was used to implement a feature that reduced the time effort for a performed alignment process by 42 min or up to 41.6 % compared to a non robot-assisted alignment process. A custom Python script was developed to support the operator with the numerous calculations performed in the background. The measured data and results of the alignment chain were visualized in a Graphical User Interface (GUI). The alignment process was tested and verified using a custom designed and constructed test rig with a test alignment cube. The alignment cube had a measured angle between two autocollimated mirror faces of 90.000 429 7◦ ± 0.000 384 7◦. That was a difference from the perfect 90◦ of 4.297 · 10−4◦ ± 3.847 · 10−4◦ or 1.547 arcsec ± 1.385 arcsec.