Regina Lee

Design of attitude control systems for cubesat-class nanosatellite

We present a satellite attitude control system design using low-cost hardware and software for a 1U CubeSat. The attitude control system architecture is a crucial subsystemfor any satellite mission since precise pointing is often required to meet mission objectives. The accuracy and precision requirements are even more challenging for small satellites where limited volume, mass, and power are available for the attitude control system hardware. In this proposed embedded attitude control system design for a 1U CubeSat, pointing is obtained through a two-stage approach involving coarse and fine control modes. Fine control is achieved through the use of three reaction wheels or three magnetorquers and one reaction wheel along the pitch axis. Significant design work has been conducted to realize the proposed architecture. In this paper, we present an overview of the embedded attitude control system design; the verification results fromnumerical simulation studies to demonstrate the performance of a CubeSat-class nanosatellite; and a series of air-bearing verification tests on nanosatellite attitude control systemhardware that compares the performance of the proposed nonlinear controller with a proportional-integral-derivative controller.

Calibration and in-orbit performance of the Argus 1000 spectrometer - the Canadian pollution monitor

Argus 1000 is a new generation miniature pollution-monitoring instrument to monitor greenhouse-gas emission from the space. Argus was launched on the CanX-2 micro-satellite April 28, 2008. Operating in the near infrared and in a nadir-viewing mode, Argus provides a capability for the monitoring of Earth-based sources and sinks of anthropogenic pollution. It has 136 near infrared channels in the spectral range of 0.9-1.7 µm with an instantaneous spatial resolution of 1.25 km. With a mass of just 228 g in flight-model configuration, the instrument is a demonstrator for a future micro-satellite network that can supply near-real time monitoring of pollution events in order to facilitate the detection of the sources causing climate change. In this Letter, we describe the instrument, the analysis concept behind Argus 1000 and its in-orbit performance. Recent spectral data taken over Ontario, Canada, are presented.

Demonstration of a compressive-sensing Fourier-transform on-chip spectrometer

We demonstrate compressive-sensing (CS) spectroscopy in a planar-waveguide Fourier-transform spectrometer (FTS) device. The spectrometer is implemented as an array of Mach-Zehnder interferometers (MZIs) integrated on a photonic chip. The signal from a set of MZIs is composed of an undersampled discrete Fourier interferogram, which we invert using l1-norm minimization to retrieve a sparse input spectrum. To implement this technique, we use a subwavelength-engineered spatial heterodyne FTS on a chip composed of 32 independent MZIs. We demonstrate the retrieval of three sparse input signals by collecting data from restricted sets (8 and 14) of MZIs and applying common CS reconstruction techniques to this data. We show that this retrieval maintains the full resolution and bandwidth of the original device, despite a sampling factor as low as one-fourth of a conventional (non-compressive) design.

Nanosatellite attitude air bearing system using variable structure control

This paper details a novel fault tolerant variable structure control law using sliding mode control which can be used to improve fault tolerance in nanosatellite attitude control systems. A locally asymptotically stable adaptive fuzzy first order sliding mode controller is used to solve the local attitude control tracking problem. Simulation results validate the tracking and fault tolerant performance of the proposed controller in the presence of noise and reaction wheel faults. The controller is also tested with embedded attitude control hardware on a spherical air bearing system and compared with a PID controller and 2nd and 3rd order sliding mode controllers. The proposed controller is more tolerant to faults and uses less energy for attitude control, and has a steady-state error of 0.8 degrees while PID accuracy in the same system is 5 degrees.

Nanosatellite air bearing tests of fault-tolerant sliding-mode attitude control with unscented kalman filter

This paper documents the development and testing of a fault tolerant sliding mode attitude control algorithm for a nanosatellite with reaction wheel control actuation.

Geolocation of Argus Flight Data

In this paper, we briefly describe the Argus spectrometer and its mission. We then focus on the process to determine the geolocation of the spectrometers flight data. For the Canadian Advanced Nanospace eXperiment 2 (CanX-2) Argus flight, we have used Simplified General Perturbations 4 (SGP4) propagation for position determination. Two sets of flight data are presented as examples. We estimate the uncertainty in the geolocation of Argus data using this method and investigate potential improvements for future Argus flights.

Robust Adaptive Unscented Kalman Filter for Spacecraft Attitude Estimation Using Quaternion Measurements

AbstractA robust unscented Kalman filter based on a multiplicative quaternion-error approach is proposed for high-precision spacecraft attitude estimation using quaternion measurements under measur...

Real-Time Nonlinear Attitude Control System for Nanosatellite Applications

This paper develops a fault-tolerant attitude controller for next-generation nanosatellites. The proposed fault-tolerant attitude control algorithms in this study are based on first-order and high-order sliding-mode control theories as well as fuzzy logic systems to achieve low cost and real-time autonomy. A locally asymptotically stable adaptive fuzzy first-order sliding-mode controller is chosen as the best solution to the local attitude control tracking problem. This novel fault-tolerant controller is validated by simulation results with reaction wheel Coulomb friction, saturation, noise, dead zones, bias faults, and external disturbances. Simulation and testing results presented in the paper demonstrate that the attitude control system can provide successful pointing and tracking in the presence of system uncertainties for a specified class of reaction wheel failures.

Spherical Air Bearing Attitude Control Simulator for Nanosatellites

Spherical Air Bearing systems have been used as a testbed for attitude control systems for many decades. With the advancements of nanosatellite technologies as a platform for scientific missions, there is an increased demand for comprehensive, pre-launch testing of nanosatellites. Several spherical air bearing systems have been developed for larger satellite application and add too much parasitic mass to be applicable for nanosatellite applications. This paper focuses on the design and validation of a Spherical Air Bearing Attitude Control Simulator for Nanosatellites. The simulator consists of the physical design of the system, a complete electronics system, and validation of the simulator using low-cost reaction wheels as actuators. The design of the air bearing platform includes a manual balancing system to align the centre of mass with the centre of rotation. The electronics system is intended to measure the attitude of the platform and control the actuator system. Validation is achieved through a controlled slew maneuver of the air bearing platform.

Study for femto satellites using micro Control Moment Gyroscope

Femto-satellites can be used for distributed space missions that can require hundreds to thousands of satellites for real time, distributed, multi-point networks to accomplish remote sensing and science objectives. While suitable sensors are available using micro-electro-mechanical system technology, most femto-satellite designs have no attitude control capability due to the power and size constraints on attitude control actuators. A novel femto-satellite design that uses a micro-electro-mechanical system Control Moment Gyroscope is studied in this paper. We focus on the principal design, modelling, and discussion of the proposed Control Moment Gyroscope while detailing a controllable femto-satellite design that can make use of attitude control for simple sensing missions.