Abstract
In this paper, a homodyne single-beam interferometer for three degrees of freedom (DoF) measurement is used to assess the dimensional stability of a deployable telescope for small spacecraft. The interferometric system is based on a Michelson interferometer concept, and the number of components is kept to a minimum. The rig is composed of a HeNe laser at 632.8 nm, two lenses, a prism, a beamsplitter and a CMOS camera. This makes the setup very attractive for low-cost and low-complexity solutions, and its performance can be readily improved by upgrading the hardware according to need. The algorithm is based on the Discrete Fourier Transform (DFT) of the spatial interference pattern detected by a CMOS sensor. Spectral information on fringe density and orientation can be translated into both relative displacements and tilts. The system can easily measure displacements with nanometer resolution and angle variations with microrad resolution. The developed architecture was suitable to determine the thermal deformations of the optical payload. Maximum relative displacements of about 30 microns and angle variations of the order of 0.1 mrad were obtained experimentally, with good repeatability.