John Lee Junkins

Texas A&M University | TAMU · Department of Aerospace Engineering

An innovative electro-optical navigation system called Optical Navigation System (OptoNav) for Autonomous Landing consisting of a machine vision camera, and a set of co-registered structured light beacons is proposed. OptoNav is used to directly sense the altitude and two orientation states of an air vehicle with respect to the flight path directio...

A supervised stochastic learning method called the Gaussian Process Regression (GPR) is used to design an autonomous guidance law for low-thrust spacecraft. The problems considered are both of the time- and fuel-optimal regimes and a methodology based on ``perturbed back-propagation'' approach is presented to generate optimal control along neighbor...

This paper proposes an overarching trajectory-power-propulsion co-optimization framework by incorporating actual discrete operation modes of electric thrusters within the optimal control formulation of spacecraft trajectory design. An interplanetary trajectory from Earth to comet 67P/Churyumov-Gerasimenko is formulated and solved using a spacecraft...

Application of idealized constant-specific-impulse, constant-thrust electric thruster performance models or curve-fitted polynomials is quite common for spacecraft trajectory design. However, incorporation of realistic performance models of multi-mode electric thrusters leads to notable challenges, and at the same time, offers unprecedented system-...

An innovative approach to identify the rotation rate of a tumbling rigid and autonomously deploy a payload package is presented in this paper. The experimental prototype of a delivery system, including the sensor system, and computational vision algorithms for identification of the deployment site and the ground robots at the Land, Air and Space Ro...

High precision propagation for satellites orbiting a large body with a highly nonlinear gravity field (planets, moons, asteroids) require accurate computation of the gravitational acceleration at each integration step. This is a computationally expensive operation that depends mainly on the orbit geometry and the accuracy to which the solution is r...

High precision propagation for satellites orbiting a large body with a highly nonlinear gravity field (planets, moons, asteroids) require accurate computation of the gravitational acceleration at each integration step. This is a computationally expensive operation that depends mainly on the orbit geometry and the accuracy to which the solution is r...

As is well known in celestial mechanics, coordinate choices have significant consequences in the analytical and computational approaches to solve the most fundamental initial value problem. The present study focuses on the impact of various coordinate representations of the dynamics on the solution of the ensuing state/costate two-point boundary-va...

Application of optimal control principles on a number of engineering systems reveal bang-bang and/or bang-off-bang structures in some or all of the control inputs. These abrupt changes introduce undesired non-smoothness into the equations of motion, and their ensuing numerical propagation, which requires special treatments. In order to alleviate th...

The problem of time-optimal, rest-to-rest slewing of a flexible spacecraft through a large angle is studied. These maneuvers are known to have bang-bang control profiles, which lead to undesirable excitation of higher frequency vibrations. It is common to approximate the dynamics using the assumed modes method; and formulate and solve the resulting...

The orthogonal Chebyshev polynomials are commonly used to approximate functions. The approximation accuracy is dependent on the nature of the approximated function, its domain, the Chebyshev series degree, and the number sampling nodes. In this paper, we show how to optimally choose the degree of Chebyshev expansion to achieve a prescribed accuracy...

A novel application of Modified Chebyshev Picard Iteration (MCPI) to differential correction is presented. By leveraging the Chebyshev basis functions of MCPI, interpolation in 1 dimension may be used to target plane crossing events, instead of integrating the 42 dimensional variational equation required for standard step integrators. This results...

Modified Chebyshev Picard Iteration is an iterative numerical method for solving linear or non-linear ordinary differential equations. In a serial computational environment the method has been shown to compete with, or outperform, current state of practice numerical integrators. This paper presents several improvements to the basic method, designed...