A research programme has been conducted, the objective of which has been the determination of unsteady force coefficients for a range of parachute canopy models. These coefficients are required for prediction of the aerodynamic stability of full scale parachutes under conditions of unsteady motion during descent. The method of obtaining these coefficients required the collection of force and acceleration data for parachute canopy models which were tested in unsteady conditions. This was achieved by imposing oscillatory motion on individual canopies during towing tests, which were conducted under water in a ship testing tank. Two modes of unsteady motion were imposed on a canopy under test; one in which it was oscillated along its axis, and one in which it was oscillated laterally. A mathematical model describing such modes of motion consists of a general equation for the unsteady force developed on a bluff body. In this model the force F(t) is expressed using two components; a velocity dependent force component, and an acceleration dependent force component. Each component of the aerodynamic force contains an unknown parameter denoted by the terms ‘a’ and ‘b’ in the equation, which is shown below; F( t ) = a( t ) • V²( t ) + b( t ) • V( t ). An identification technique is used to determine the mean values per cycle of each parameter by substitution of the data obtained from these tests as functional variables in the mathematical model. Mean values of the velocity dependent force and stability coefficients; CT and ∂CN/∂α, and the added mass coefficients k11 and k33 are then obtained from these parameters. The results of this programme indicate a strong dependence in oscillatory motion of the mean value per cycle for the axial added mass coefficient k11 on the unsteady force parameter called the Keulegan-Carpenter number KC; KC = Û • T/DO. Where; Û = the velocity amplitude of the oscillation, T = the period of an oscillation, and DO = a typical canopy dimension. The velocity dependent axial force coefficient CT exhibits a similar, although not as substantial dependency. Good agreement has been obtained between steady-state test results from this programme and results from other independent work. The effects of values obtained in this investigation are considered in the linearised dynamic stability model developed by Doherr and Saliaris (1), and their influence on the descent characteristics of full-scale parachutes is assesed.

Many landing sites of scientific interest on Mars including most of the Southern Hemisphere at elevations above 2km Mars Orbiter Laser Altimeter reference are inaccessible due to current limitations in precision entry guidance and payload deceleration. Precision guidance and large payload deceleration is challenging due to the thin Martian atmosphere, large changes in free stream conditions during entry, and aerothermal and aerodynamic instability concerns associated with control systems with direct external flow field interaction. Such risks have descoped past Mars missions to unguided entry with the exception of Mars Science Laboratory's (MSL) bank angle guidance. Consequently, prior to MSL landing ellipses were on the order of 100's of km. MSL has approached the upper limit of payload deceleration capability for rigid, blunt body sphere cone aeroshells used on all successful Mars entry missions. Hypersonic Inflatable Aerodynamic Decelerators (HIADS) are in development for larger payload deceleration capability through inflated aeroshell diameters greater than rigid aeroshells constrained by the launch rocket diameter, but to date there has been limited dynamics, control, and guidance development for their use on future missions. This dissertation develops internal moving mass actuator (IMMA) control systems for improving Mars precision entry guidance of rigid capsules and demonstrating precision guidance capability for HIADs. IMMAs provide vehicle control moments without direct interaction with the external flow field and can increase payload mass delivered through reducing propellant mass for control and using portions of the payload for the IMMAs. Dynamics models for entry vehicles with rotation and translation IMMAs are developed. IMMA control systems using the models are developed for two NASA vehicle types: a 2.65 m, 602 kg Mars Phoenix-sized entry capsule and an 8.3 m, 5.9 metric ton HIAD approaching payload requirements for robotic precursor missions for future human missions. Linear Quadratic controllers with integral action for guidance command tracking are developed for translation and rotation IMMA configurations. Angle of attack and sideslip guidance laws are developed as an alternative to bank angle guidance for decoupling range and cross-range control for improved precision entry guidance. A new variant of the Apollo Earth return terminal guidance algorithm is implemented to provide the closed-loop angle of attack range control commands. Nonlinear simulations of the entire 8 degree of freedom closed-loop systems demonstrate precision guidance to nominal trajectories and final targets for off-nominal initial entry conditions for flight path angle, range, cross-range, speed and attitude. Mechanical power studies for IMMA motion show rotation IMMA require less total mechanical power than translation actuators, but both systems have low nominal mechanical power requirements (below 100 Watts). Precision guidance for both systems to terminal targets greater than 38 km down-range from an open-loop ballistic entry is shown for low mechanical power, low CM displacement, (< 4.5 in) and at low internal velocities (< 2 in/s) over significant dynamic pressure changes. The collective precision guidance results and low mechanical power requirements show IMMA based entry guidance control systems constitute a promising alternative to thruster based control systems for future Mars landers. / Ph. D.