Future spacecraft missions are trending towards the use of distributed systems or fractionated spacecraft. Initiatives such as DARPA's System F6 are encouraging the satellite community to explore the realm of collaborative spacecraft teams in order to achieve lower cost, lower risk, and greater data value over the conventional monoliths in LEO today. Extensive research has been and is being conducted indicating the advantages of distributed spacecraft systems in terms of both capability and cost. Enabling collaborative behaviors among teams or formations of pico-satellites requires technology development in several subsystem areas including attitude determination and control subsystems, orbit determination and maintenance capabilities, as well as a means to maintain accurate knowledge of team members' position and attitude. All of these technology developments desire improvements (more specifically, decreases) in mass and power requirements in order to fit on pico-satellite platforms such as the CubeSat. In this thesis a solution for the last technology development area aforementioned is presented. Accurate knowledge of each spacecraft's state in a formation, beyond improving collision avoidance, provides a means to best schedule sensor data gathering, thereby increasing power budget efficiency. Our solution is composed of multiple software and hardware components. First, finely-tuned flight system software for the maintaining of state knowledge through equations of motion propagation is developed. Additional software, including an extended Kalman filter implementation, and commercially available hardware components provide a means for on-board determination of both orbit and attitude. Lastly, an inter-satellite communication message structure and protocol enable the updating of position and attitude, as required, among team members. This messaging structure additionally provides a means for payload sensor and telemetry data sharing. In order to satisfy the needs of many different missions, the software has the flexibility to vary the limits of accuracy on the knowledge of team member position, velocity, and attitude. Such flexibility provides power savings for simpler applications while still enabling missions with the need of finer accuracy knowledge of the distributed team's state. Simulation results are presented indicating the accuracy and efficiency of formation structure knowledge through incorporation of the described solution. More importantly, results indicate the collaborative module's ability to maintain formation knowledge within bounds prescribed by a user. Simulation has included hardware-in-the-loop setups utilizing an S-band transceiver. Two "satellites" (computers setup with S-band transceivers and running the software components of the collaborative module) are provided GPS inputs comparable to the outputs provided from commercial hardware; this partial hardware-in-the-loop setup demonstrates the overall capabilities of the collaborative module. Details on each component of the module are provided. Although the module is designed with the 3U CubeSat framework as the initial demonstration platform, it is easily extendable onto other small satellite platforms. By using this collaborative module as a base, future work can build upon it with attitude control, orbit or formation control, and additional capabilities with the end goal of achieving autonomous clusters of small spacecraft.

A set of techniques is developed that allows the incorporation of flight dynamics metrics as an additional discipline in a high-fidelity aerodynamic optimization. Specifically, techniques for including static stability constraints and handling qualities constraints in a high-fidelity aerodynamic optimization are demonstrated. These constraints are developed from stability derivative information calculated using high-fidelity computational fluid dynamics (CFD). Two techniques are explored for computing the stability derivatives from CFD. One technique uses an automatic differentiation adjoint technique (ADjoint) to efficiently and accurately compute a full set of static and dynamic stability derivatives from a single steady solution. The other technique uses a linear regression method to compute the stability derivatives from a quasi-unsteady time-spectral CFD solution, allowing for the computation of static, dynamic and transient stability derivatives. Based on the characteristics of the two methods, the time-spectral technique is selected for further development, incorporated into an optimization framework, and used to conduct stability-constrained aerodynamic optimization. This stability-constrained optimization framework is then used to conduct an optimization study of a flying wing configuration. This study shows that stability constraints have a significant impact on the optimal design of flying wings and that, while static stability constraints can often be satisfied by modifying the airfoil profiles of the wing, dynamic stability constraints can require a significant change in the planform of the aircraft in order for the constraints to be satisfied.

The CanX-4/-5 mission currently under development at the Space Flight Laboratory will demonstrate sub-metre formation control in four separate formations consisting of two nanosatellites. Formation maintenance is performed using a propulsion payload providing one axis of thrust, resulting in frequent slewing to meet thrust targets. Navigation is GPS dependent, with both satellites equipped with a receiver and antenna pair. Presented is a mission simulation developed for evaluating formation flying algorithm performance and the effects of frequent slewing on GPS coverage. CanX-4 and CanX-5 will be joined for commissioning prior to commencing formation flying via a mechanism, the Intersatellite Separation System. Details regarding the performance testing and troubleshooting of the system are described. Integration and testing of CanX-4/-5 flight hardware into a functional “FlatSat” is presented. Additionally, a description of satellite operations for two nanosatellites is given, with an emphasis on the relevance to the work performed for the CanX-4/-5 mission.

The quantitative feedback theory (QFT) of Horowitz is theoretically well developed for multivariable systems but there is not sufficient knowledge on its application to practical problems. A "flying machine" consisting of an airframe with two independently controlled sets of wings has been designed and constructed as a 2-input 2-output control problem. The airframe is constrained to move vertically on guide wires and to rotate about a pivot. Air flow over the wings is provided by two 7.SkW fans operated without any attempt at providing non-turbulent flow. The arrangement of the wings is such that in open loop, the dynamic behaviour of the airframe from the rear set of wings to the height is non-minimum phase. Additionally, the airframe is unstable for some flight conditions. This uncertain, non-linear and highly disturbed plant provides an ideal practical environment in which to test controller design theory. The construction, modelling, parameter estimation and simulation of the flying machine is described. Three different controller structures are disGussed, with actual controller designs arrived at from QFT understanding. The controller designs for the flying machine take into account parameter uncertainty and trade off disturbance attenuation against rate and amplitude saturation at the wing angle inputs. / Thesis (Ph.D.)-University of Natal, Durban, 1989.

The CanX-4/-5 mission currently under development at the Space Flight Laboratory will demonstrate sub-metre formation control in four separate formations consisting of two nanosatellites. Formation maintenance is performed using a propulsion payload providing one axis of thrust, resulting in frequent slewing to meet thrust targets. Navigation is GPS dependent, with both satellites equipped with a receiver and antenna pair. Presented is a mission simulation developed for evaluating formation flying algorithm performance and the effects of frequent slewing on GPS coverage. CanX-4 and CanX-5 will be joined for commissioning prior to commencing formation flying via a mechanism, the Intersatellite Separation System. Details regarding the performance testing and troubleshooting of the system are described. Integration and testing of CanX-4/-5 flight hardware into a functional “FlatSat” is presented. Additionally, a description of satellite operations for two nanosatellites is given, with an emphasis on the relevance to the work performed for the CanX-4/-5 mission.

In high density magnetic hard disk drives, both fast track seeking and extremely accurate positioning of the read/write head are required. A new piezoelectric microactuator with transverse and lateral control of the head positioning system for high density hard disk drives is proposed. First, the structure of the new piezoelectric microactuator is illustrated. Design of the new microactuator is based on the axial deformation of piezoelectric elements for lateral motion and the bimorph actuation of piezoelectric elements for transverse motion. Next, a mathematical model of the microactuator system is defined. Static properties associated with the displacement of the system are evaluated and then dynamic system equations of the system are evaluated. Frequency response of the system is studied based on the dynamic system equations of the actuator system. Dynamic properties of the system with a variety of system parameters are evaluated. Finally, the controller design for the actuator is presented. Simulation results show that the new actuator achieves a maximum stroke of displacement of more than 0.2m with servo bandwidth of more than 5 kHz in the lateral direction and the flying height is decreased to less than 6 nm with resonance frequency of more than 100 kHz under the 0.5 % damping assumption. The new piezoelectric microactuator improves performance of high density hard disk drives by increasing servo bandwidth and decreasing flying height.

A set of techniques is developed that allows the incorporation of flight dynamics metrics as an additional discipline in a high-fidelity aerodynamic optimization. Specifically, techniques for including static stability constraints and handling qualities constraints in a high-fidelity aerodynamic optimization are demonstrated. These constraints are developed from stability derivative information calculated using high-fidelity computational fluid dynamics (CFD). Two techniques are explored for computing the stability derivatives from CFD. One technique uses an automatic differentiation adjoint technique (ADjoint) to efficiently and accurately compute a full set of static and dynamic stability derivatives from a single steady solution. The other technique uses a linear regression method to compute the stability derivatives from a quasi-unsteady time-spectral CFD solution, allowing for the computation of static, dynamic and transient stability derivatives. Based on the characteristics of the two methods, the time-spectral technique is selected for further development, incorporated into an optimization framework, and used to conduct stability-constrained aerodynamic optimization. This stability-constrained optimization framework is then used to conduct an optimization study of a flying wing configuration. This study shows that stability constraints have a significant impact on the optimal design of flying wings and that, while static stability constraints can often be satisfied by modifying the airfoil profiles of the wing, dynamic stability constraints can require a significant change in the planform of the aircraft in order for the constraints to be satisfied.

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