A vision-based DSP embedded navigation sensor

Abstract

Spacecraft missions such as spacecraft docking and formation flying require high-precision relative position and attitude data. Although a global positioning system can provide this capability near the earth, deep space missions require the use of alternative technologies. One such technology is the vision-based navigation (VISNAV) sensor system developed at Texas A&M University. VISNAV comprises an electro-optical sensor combined with light sources or beacons. This patented sensor has an analog detector in the focal plane with a rise time of a few microseconds. Accuracies better than one part in 2000 of the field of view have been obtained. This paper presents a new approach involving simultaneous activation of beacons with frequency division multiplexing as part of the VISNAV sensor system. In addition, it discusses the synchronous demodulation process using digital heterodyning and decimating filter banks on a low-power fixed point digital signal processor, which improves the accuracy of the sensor measurements and the reliability of the system. This paper also presents an optimal and computationally efficient six-degree-of-freedom estimation algorithm using a new measurement model based on the attitude representation of modified Rodrigues parameters.

Visual Detection and Servoing for Automated Docking of Unmanned Spacecraft

“…[1][2][3][4][5][6][7][8][9][10] Automatic docking require precise relative pose estimation of the target spacecraft. Many developed space-faring countries have deployed a number of manned and unmanned spacecraft with ARD capability: Progress and Soyuz by RKA in Russia, ATV by ESA in Europe, ETS-VII by NASDA, HTV by JAXA in Japan, the unmanned XSS-11 by the U.S. Air Force, DART by NASA in the USA, Dragon by SpaceX in the USA, and Tiangong 1 and Shenzhou 8 by CNSA in China.…”

“…Such ARD techniques can be implemented using range, optical, and imaging sensors for longitudinal and lateral guidance. [1][2][3][4][5][6][7][8][9] When these are combined with an onboard navigation system using GPS/INS aids and a star tracker, a spacecraft can automatically maneuver toward a target and perform docking with greater accuracy. 10) For unmanned missions, the ARD system uses an adjustable light source and three or more reflective element clamps (i.e., retro-reflectors) as point-like features to detect the relative distance and orientation between the chaser and target vehicle based on prior information about reflector locations on the visual marker.…”

“…10) For unmanned missions, the ARD system uses an adjustable light source and three or more reflective element clamps (i.e., retro-reflectors) as point-like features to detect the relative distance and orientation between the chaser and target vehicle based on prior information about reflector locations on the visual marker. [3][4][5][6][7][8] Other ARD systems based on visual detection have been demonstrated for unmanned spacecraft in recent years. [7][8][9] In particular, model-based visual detection algorithms for a single vision sensor or a combined vision/LiDAR sensor have been used successfully to estimate the orientation of a target without a visual marker.…”

Real time simultaneous localization and mapping: towards low-cost multiprocessor embedded systems

“…Digital signal processors (DSP) are usually used in vision systems [29]. They integrate a number of resources that serve to enhance image processing versatility.…”

Vision-Based Relative State Estimation Using the Unscented Kalman Filter

“…Vision-based discrete-time attitude measurements for a single sensor are given by Crassidis and Markley (2003), Gunnam et al (2002), Junkins et al (1999), and Kim et al (2007) (16) Int'l J. of Aeronautical & Space Sci. 12(1), 24-36 (2011) where b  i denotes the i th observation and the sensor error v i is characterized as being approximately Gaussian.…”