A High-Precision Real-Time Pose Measurement Method for the Primary Lens of Large Aperture Space Telescope Based on Laser Ranging

Abstract

The aperture of space telescopes increases with their required resolution, and the transmission optical systems with long focal length and diffractive primary lens are becoming increasingly popular. In space, the changes in the pose of the primary lens relative to the rear lens group have a significant impact on the imaging performance of the telescope system. The measurement of the pose of the primary lens in real-time and with high-precision is one of the important techniques for a space telescope. In this paper, a high-precision real-time pose measurement method for the primary lens of a space telescope in orbit based on laser ranging is proposed, and a verification system is established. The pose change of the telescope's primary lens can be easily calculated through six high-precision laser distance changes. The measurement system can be installed freely, which solves the problems of complex system structure and low measurement accuracy in traditional pose measurement techniques. Analysis and experiments show that this method can accurately obtain the pose of the primary lens in real-time. The rotation error of the measurement system is 2 × 10^-5 degrees (0.072 arcsecs), and the translation error is 0.2 μm. This study will provide a scientific basis for high-quality imaging of a space telescope.

Keywords: high-precision; laser ranging; pose measurement; space telescope.

Figure 1

Schematic diagram of the telescope optical system.

Figure 2

Hexapod geometry Stewart Gough platform.

Figure 3

The schematic diagram of the pose measurement principle.

Figure 4

Principle and accuracy test for the laser rangefinder. (a) Principle of the laser rangefinder, which is based on Fabry-Perot interference. (b) Accuracy test for the laser rangefinder, the laser ranging accuracy is ±0.5 μm.

Figure 5

Test system. Three retroreflectors (red circles on the right of Figure 5) were attached to the edge of the frame, and six laser collimators (red circles on the left of Figure 5) were fixed to the edge of the relay mirror to verify the pose measurement method and its accuracy.

Figure 6

Test results of 1 × 10⁻⁴ degrees and 0.4 μm step test of the measurement system. (a) The tilt error of the measurement system is 2 × 10⁻⁵ degrees, (b) The decentration error of the measurement system is 0.2 μm.