A paper describes a process for imposing safety constraints on a spacecraft trajectory design. The conventional process has the ACS (Attitude Control System) team define geometric constraints, then the NAV (Navigation) team produces a compliant thrust direction profile for the spacecraft to execute. With time-varying thrust profiles, merely specifying geometric constraints is not sufficient. Because low thrust implies low agility under thrust vector control (TVC), even slowly developing spacecraft dynamics can be significant and geometric constraints can have dynamic implications. The thrust profile design process was modified to incorporate a new tool, known as qSTAT, which analyzes candidate thrust profiles for compliance with geometric and dynamic constraints by simulating an appropriately reduced set of spacecraft dynamics. qSTAT gives the navigation team a simplified attitude control simulation tool that can quickly be used to analyze multiple candidate thrust profile designs. The Dawn mission operation team uses this tool to improve productivity.
This work was done by Brett A. Smith, Charles A. Vanelli, and Allan Y. Lee of Caltech for NASA’s Jet Propulsion Laboratory.
The software used in this innovation is available for commercial licensing. Please contact Dan Broderick at
This Brief includes a Technical Support Package (TSP).
Quick Thrust Profile Design Analysis for Verifying Spacecraft Operational Capabilities
(reference NPO-48434) is currently available for download from the TSP library.
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Overview
The document discusses the challenges and solutions associated with the Dawn mission, which utilized solar electric propulsion (SEP) for low-thrust orbit transfers. It highlights the inadequacies of conventional maneuver design processes, particularly in managing long thrust durations with the relatively weak thrust force of SEP, which can reach a maximum of 91 mN. This weakness necessitated a reevaluation of how trajectory correction maneuvers (burns) are designed and executed, as they take considerable time and can be affected by safing events that may prevent thrusting.
To address these challenges, the Dawn team developed a time-efficient simulation tool known as the quick and Simple Thrust Verification Analysis Tool (qSTAT). This tool was designed to quickly verify the achievability of thrust profiles, allowing the navigation (NAV) and attitude control systems (ACS) teams to collaborate more effectively. The qSTAT tool is characterized by its simplicity, requiring minimal inputs while providing a reliable indication of whether a thrust profile will work. This approach enabled the mission team to overcome the complications associated with low-thrust orbit transfers and facilitated faster design verification before final delivery.
The document emphasizes the extraordinary flexibility that SEP offers in mission design, including the ability to carry significantly less fuel for the same change in velocity (∆v) compared to conventional propulsion systems. The specific impulse of SEP ranges from 1900 to 3200 seconds, compared to the typical 200-400 seconds for conventional systems, allowing for more ambitious mission objectives and launch dates.
However, the document also notes that the low thrust of SEP comes with trade-offs, particularly in the time required for trajectory corrections and the increased emphasis on quickly restoring thrust capabilities after any interruptions. The insights gained from the Dawn mission and the development of tools like qSTAT are expected to have broader applications in future aerospace endeavors, enhancing the efficiency and effectiveness of spacecraft maneuvering and operational capabilities.
Overall, the document serves as a technical support package that outlines the innovative strategies employed in the Dawn mission, showcasing the advancements in spacecraft agility and the potential for future applications in space exploration.
