Three-axis air-bearing based platform for small satellite attitude determination and control simulation

Abstract

A frictionless environment simulation platform, utilized for accomplishing three-axis attitude control tests in small satellites, is introduced. It is employed to develop, improve, and carry out objective tests of sensors, actuators, and algorithms in the experimental framework. Different sensors (i.e. sun, earth, magnetometer, and an inertial measurement unit) are utilized to assess three-axis deviations. A set of three inertial wheels is used as primary actuators for attitude control, together with three mutually perpendicular magnetic coils intended for desaturation purposes, and as a backup control system. Accurate balancing, through the platform’s center of mass relocation into the geometrical center of the spherical air-bearing, significatively reduces gravitational torques, generating a virtually torque-free environment. A very practical balancing procedure was developed for equilibrating the table in the local horizontal plane, with a reduced final residual torque. A wireless monitoring system was developed for on-line and post-processing analysis; attitude data are displayed and stored, allowing properly evaluate the sensors, actuators, and algorithms. A specifically designed onboard computer and a set of microcontrollers are used to carry out attitude determination and control tasks in a distributed control scheme. The main components and subsystems of the simulation platform are described in detail.

A Dynamic Testbed for Nanosatellites Attitude Verification

“…Despite being one order of magnitude higher than the typical disturbance expected for a CubeSat in LEO (≈10 −6 Nm), our result compares remarkably well with respect to the existing published data [28,29,43,44] (see Table 3), especially when considering the extremely low cost of our implementation, i.e., less than 500 Euro for IMU, actuators, control electronics, and balance masses. Once the balancing is completed, the residual disturbance torque, T D , is estimated, again through the sampling of free platform oscillations, by computing the angular accelerations retrieved from differenced IMU measurements.…”

“…Residual Offset r CM da Silva et al [28] >15 µm Liu et al [29] 5 µm Prado et al [43] ≈17 µm Young [44] <20 µm This work <1 µm…”

“…It can be cancelled only partially by design, and manual balancing does not lead to a guaranteed performance level [21]. Several automatic mass balancing systems have been proposed in the literature [28,29,36,37,43,44], as they can largely reduce the time necessary for the platform tuning while ensuring repeatability, and a more effective reduction of the gravity torque. Even so, the stated disturbance limit for testing nanosatellites can hardly be reached: assuming a total rotating mass (platform with balancing mechanism plus CubeSat) in the order of 10 kg, a matching between the CoR and CoM shall be achieved up to 10 nm level, if we want a torque in the order of 10 −6 Nm.…”

“…Residual Offset ‖ ‖ da Silva et al [28] >15 μm Liu et al [29] 5 μm Prado et al [43] ≈17 μm Young [44] <20 μm This work <1 μm Despite being one order of magnitude higher than the typical disturbance expected for a CubeSat in LEO (≈10 −6 Nm), our result compares remarkably well with respect to the existing published data [28,29,43,44] (see Table 3), especially when considering the extremely low cost of our implementation, i.e., less than 500 Euro for IMU, actuators, control electronics, and balance masses. Table 3.…”

A New Feature Points Reconstruction Method in Spacecraft Vision Navigation

“…Monocular vision navigation can be applied for spacecraft ground physical simulation platforms and spacecraft relative navigation [1][2][3]. Three-degree-of-freedom air bearing table is the key equipment of spacecraft ground test [4][5][6], which can simulate attitude motion in three directions. Air bearing table can be used in demonstration and validation of key technologies for space missions, such as spacecraft attitude determination, control actuator ground verification, control software development, autonomous spacecraft rendezvous and docking, space target detection and identification, target proximity and tracking control, demonstration and validation for precise pointing control of laser communication device, relative attitude cooperative control, microsatellite formation flying initialization, cooperative control, and autonomous operation.…”