Mark Post

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.

Hydraulophone design considerations: absement, displacement, and velocity-sensitive music keyboard in which each key is a water jet

We present a musical keyboard that is not only velocity-sensitive, but in fact responds to absement (presement), displacement (placement), velocity, acceleration, jerk, jounce, etc. (i.e. to all the derivatives, as well as the integral, of displacement).Moreover, unlike a piano keyboard in which the keys reach a point of maximal displacement, our keys are essentially infinite in length, and thus never reach an end to their key travel. Our infinite length keys are achieved by using water jet streams that continue to flow past the fingers of a person playing the instrument. The instrument takes the form of a pipe with a row of holes, in which water flows out of each hole, while a user is invited to play the instrument by interfering with the flow of water coming out of the holes. The instrument resembles a large flute, but, unlike a flute, there is no complicated fingering pattern. Instead, each hole (each water jet) corresponds to one note (as with a piano or pipe organ). Therefore, unlike a flute, chords can be played by blocking more than one water jet hole at the same time. Because each note corresponds to only one hole, different fingers of the musician can be inserted into, onto, around, or near several of the instruments many water jet holes, in a variety of different ways, resulting in an ability to independently control the way in which each note in a chord sounds.Thus the hydraulophone combines the intricate embouchure control of woodwind instruments with the polyphony of keyboard instruments.Various forms of our instrument include totally acoustic, totally electronic, as well as hybrid instruments that are acoustic but also include an interface to a multimedia computer to produce a mixture of sounds that are produced by the acoustic properties of water screeching through orific plates, as well as synthesized sounds.

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.

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.

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.

Bayesian decision making for planetary micro-rovers

This study focuses on the implementation of a simple statistical algorithm to classify and map objects sensed by a micro-rover proto-implementation of a simple statistical algorithm to classify and map objects sensed by a micro-rover proto-type in real world testing.

Design of a novel wheeled tensegrity robot: a comparison of tensegrity concepts and a prototype for travelling air ducts

Efforts in the research of tensegrity structures applied to mobile robots have recently been focused on a purely tensegrity solution to all design requirements. Locomotion systems based on tensegrity structures are currently slow and complex to control. Although wheeled locomotion provides better efficiency over distances there is no literature available on the value of wheeled methods with respect to tensegrity designs, nor on how to transition from a tensegrity structure to a fixed structure in mobile robotics. This paper is the first part of a larger study that aims to combine the flexibility, light weight, and strength of a tensegrity structure with the efficiency and simple control of a wheeled locomotion system. It focuses on comparing different types of tensegrity structure for applicability to a mobile robot, and experimentally finding an appropriate transitional region from a tensegrity structure to a conventional fixed structure on mobile robots. It applies this transitional structure to what is, to the authors’ knowledge, the design of the world’s first wheeled tensegrity robot that has been designed with the goal of traversing air ducts.

Autonomous navigation with ROS for a mobile robot in agricultural fields

Autonomous monitoring of agricultural farms and fields has recently become feasible due to continuing advances in robotics technology, but many notable challenges remain. In this paper, we describe the state of ongoing work to create a fully autonomous ground rover platform for monitoring and intervention tasks on modern farms that is built using inexpensive and off the shelf hardware and Robot Operating System (ROS) software so as to be affordable to farmers. The hardware and software architectures used in this rover are described along with challenges and solutions in odometry and localization, object recognition and mapping, and path planning algorithms under the constraints of the current hardware. Results obtained from laboratory and field testing show both the key challenges to be overcome, and the current successes in applying a low-cost rover platform to the task of autonomously navigating the outdoor farming environment.

FPGA hardware nonlinear control design for modular CubeSat attitude control system

CubeSat attitude control systems must be compact, fast, and accurate to achieve success in space missions with stringent control requirements. Nonlinear control strategies allow the creation of robust algorithms for orbit and attitude control, but can have higher processing requirements for effective operation. In addition, It is desirable to distribute components of a CubeSat control system across hardware as much as possible to decrease the load on a central computing unit and to make the system more tolerant to point failures. Field Programmable Gate Array technology has become a popular solution to the limited electronic space and demanding processing requirements present in new-generation CubeSat systems. This paper will focus on demonstrating the feasibility and effectiveness of a proposed nonlinear adaptive fuzzy controller implemented on a Field Programmable Gate Array as part of a highly-integrated space hardware system that is under development.