All 2015 Content
Session
Technical Session VI: Ground Systems and Communications
Abstract
This paper proposes a new system to enable rapid slew and settle (or retargeting) for small satellites. The rapid slew and settle is a critical element to low Earth orbit (LEO) laser communication in which the latency during slew should be minimized and precision pointing should be established right after the slew. The proposed system is comprised of four single degree-of-freedom (DOF) control moment gyros (CMGs) with variable speed flywheels (equivalently, reaction wheels (RW)), called hybrid CMGs (or HCMGs), and an embedded optimizer to solve a new constrained time-optimal control (TOC) and momentum management problem together in real-time. The four HCMGs effectively combine four CMGs and four RWs to meet the strict size, weight and power (SWaP) requirements of small satellites. The new constrained TOC problem effectively addresses the critical singularity issue of the HCMGs and uniquely incorporates momentum management of the RWs, which is discovered to speed up the slew and settle while controlling momentum of the RWs. In this paper, the proposed TOC problem is solved offline by GPOPS and SNOPT that have been proven to be an efficient tool to solve this kind of problem. It makes progress in developing an embedded optimizer that may efficiently solve this optimal control problem in a sequential way by initializing the current optimization process using the previous optimal solution. Due to continuity in the nature of the optimal problem and its solution, the sequential process typically requires only a few iterations to reach the optimal solution and is suitable for real-time optimization.
Rapid Slew and Settle of a Small Satellite in LEO Laser Communication
This paper proposes a new system to enable rapid slew and settle (or retargeting) for small satellites. The rapid slew and settle is a critical element to low Earth orbit (LEO) laser communication in which the latency during slew should be minimized and precision pointing should be established right after the slew. The proposed system is comprised of four single degree-of-freedom (DOF) control moment gyros (CMGs) with variable speed flywheels (equivalently, reaction wheels (RW)), called hybrid CMGs (or HCMGs), and an embedded optimizer to solve a new constrained time-optimal control (TOC) and momentum management problem together in real-time. The four HCMGs effectively combine four CMGs and four RWs to meet the strict size, weight and power (SWaP) requirements of small satellites. The new constrained TOC problem effectively addresses the critical singularity issue of the HCMGs and uniquely incorporates momentum management of the RWs, which is discovered to speed up the slew and settle while controlling momentum of the RWs. In this paper, the proposed TOC problem is solved offline by GPOPS and SNOPT that have been proven to be an efficient tool to solve this kind of problem. It makes progress in developing an embedded optimizer that may efficiently solve this optimal control problem in a sequential way by initializing the current optimization process using the previous optimal solution. Due to continuity in the nature of the optimal problem and its solution, the sequential process typically requires only a few iterations to reach the optimal solution and is suitable for real-time optimization.
