Autonomous navigation and guidance system for low thrust driven deep space missions

Presented herein is a concept of an Autonomous Navigation & Guidance System for electrically propelled deep space missions, including hardware configuration, algorithms for autonomous navigation and guidance, and estimates of potential guidance precision and mass consumption. This concept is actually a unified Navigation, Guidance and Attitude Control system. The unification is imposed by strong coupling between the orbital motion and the spacecraft attitude characteristic of low thrust space flights. The sensor set of the system consists of an optical instrument (Coupled Sun Star Tracker), and a block of four vector accelerometers. The propulsion subsystem is a set of nearly parallel Hall thrusters rigidly attached to the spacecraft body. The final stage of data processing is combining the thrust and torque programs and generating power and mass rate shares for every thruster. An end-to-end computer simulation provides guidance accuracy estimates versus the navigation data precision, flight time and available maximum thrust. Terminal guidance errors of a few tens of km in position and a few tens of cm/s in velocities are predicted under plausible assumptions on system parameters. Mass expenditures for the control are typically below one percent of total fuel mass budget.     

Proportional Navigation with a Maneuvering Target

A qualitative analysis of the trajectories of a missile pursuing a maneuvering target according to the proportional navigation law is presented. Conditions for a missile to reach the target from any initial state are determined. The existence of a boundary for the required missile acceleration is demonstrated.     

Missile Acceleration in Proportional Navigation

In a previous paper, the author obtained conditions for the acceleration of a missile pursuing a maneuvering target according to proportional navigation, to be bounded. This correspondence extends previous work, and new boundaries are obtained for the missile acceleration.     

Small satellite's role in future hyperspectral Earth observation missions

Along with various advanced satellite onboard sensors, an important place in the near future will belong to hyperspectral instruments, considered as suitable for different scientific, commercial and military missions. As was demonstrated over the last decade, hyperspectral Earth observations can be provided by small satellites at considerably lower costs and shorter timescales, even though with some limitations on resolution, spectral response, and data rate. In this work the requirements on small satellites with imaging hyperspectral sensors are studied. Physical and technological limitations of hyperspectral imagers are considered. A mathematical model of a small satellite with a hyperspectral imaging spectrometer system is developed. The ability of the small satellites of different subclasses (micro- and mini-) to obtain hyperspectral images with a given resolution and quality is examined. As a result of the feasibility analysis, the constraints on the main technical parameters of hyperspectral instruments suitable for application onboard the small satellites are outlined. Comparison of the data for designed and planned instruments with simulation results validates the presented approach to the estimation of the small satellite size limitations. Presented analysis was carried out for sensors with conventional filled aperture optics.     

The Closed-Form Solution of True Proportional Navigation

The closed-form solution of the equations of motion of an ideal missile pursuing a nonmaneuvering target according to the true propotional navigation law is obtained. An analysis of the solution is performed, and the conditions necessary for the missile to reach the target are determined.     

A Qualitative Study of Proportional Navigation

This paper represents a study of the trajectories of an ideal missile homing on a target according to the proportional navigation law. A qualitative study is performed and conditions are determined which enable one to demonstrate that: 1) the missile always reaches the target regardless of the initial conditions at launch; 2) the rotational rate of the line of sight is decreasing at the pursuit end.