The need arose to apply the state determination algorithms developed for the Advanced Video Guidance Sensor autonomous rendezvous and docking (AR&D) sensor onto a commercial off-the-shelf (COTS), smartphone-based platform to create a lower-mass, lower-cost sensor for small satellite and CubeSat applications. Prior techniques used for state determination suffer one or more of the following problems: large mass, large volume, high cost, or computationally intensive calculations.
The Smartphone Video Guidance Sensor (SVGS) uses COTS hardware and simple geometric techniques to extract the desired relative state information. The SVGS provides a low-cost, integrated rendezvous and proximity operations sensor system to allow an approaching spacecraft to determine the position and attitude of a target spacecraft. The target vehicle carries an array of target retroreflectors. The SVGS images these targets using a smartphone-type camera, and then processes the image using photogrammetry techniques to determine the range and relative orientation (6-DOF state) of the target vehicle. All image-capture and processing operations are performed internally by the SVGS with the resulting state vector. This state vector would then be provided to the chaser spacecraft’s other subsystems for consumption. The SVGS illumination source is separated from the camera by a significant distance. There fore, the return illumination from the retroreflectors to the camera includes a small inherent angular error. The closer the illumination source is to the camera, the smaller the angular error will be.
The retroreflectors are illuminated by the camera flash on the smartphone and imaged by the smartphone camera. The resulting image is processed using photogrammetry algorithms running on the smartphone to extract the relative X, Y, and Z distance and relative orientation, expressed as a roll, pitch, yaw angle sequence.
This work has resulted in an Android smartphone application capable of running on suitable Android devices, which validates the SVGS concept. The SVGS application was tested in the MSFC Flight Robotics Laboratory (FRL). Following future tailoring of the SVGS hardware to give it the fit, form, and function required for space environments, potential applications of this technology will include CubeSat or other small satellite proximity operations and formation flying missions.
SVGS test results show successful relative state calculations at ranges from 0.3 to 45 meters. SVGS state calculations showed relative range accuracy of 0.1 meters or better at ranges up to 10 meters, and attitude accuracy of 1 degree or better. The range accuracy at 30 meters was within 0.5 meters, and attitude accuracy of better than 2 degrees.
Although the SVGS was implemented on a smartphone platform running the Google Android operating system, the functionality could easily be redeveloped for use on other platforms such as Apple’s iOS or other smartphones with integrated cameras.