The G-TAG software tool was developed under the R&TD on Integrated Autonomous Guidance, Navigation, and Control for Comet Sample Return, and represents a novel, multi-body dynamics simulation software tool for studying TAG sampling.

Comet Spacecraft Concept: Red arrows point to joints, blue arrows to spacecraft body components. The frame used for the simulation and for creating simulation movies is shown in the lower-left corner (x-axis completes coordinate system using the right-hand rule).
The G-TAG multi-body simulation tool provides a simulation environment in which a Touch-and-Go (TAG) sampling event can be extensively tested. TAG sampling requires the spacecraft to descend to the surface, contact the surface with a sampling collection device, and then to ascend to a safe altitude. The TAG event lasts only a few seconds but is mission-critical with potentially high risk. Consequently, there is a need for the TAG event to be well characterized and studied by simulation and analysis in order for the proposal teams to converge on a reliable spacecraft design.

This adaptation of the G-TAG tool was developed to support the Comet Odyssey proposal effort, and is specifically focused to address comet sample return missions. In this application, the spacecraft descends to and samples from the surface of a comet. Performance of the spacecraft during TAG is assessed based on survivability and sample collection performance.

For the adaptation of the G-TAG simulation tool to comet scenarios, models are developed that accurately describe the properties of the spacecraft, approach trajectories, and descent velocities, as well as the models of the external forces and torques acting on the spacecraft. The adapted models of the spacecraft, descent profiles, and external sampling forces/torques were more sophisticated and customized for comets than those available in the basic G-TAG simulation tool.

Scenarios implemented include the study of variations in requirements, spacecraft design (size, locations, etc. of the spacecraft components), and the environment (surface properties, slope, disturbances, etc.). The simulations, along with their visual representations using G-View, contributed to the Comet Odyssey New Frontiers proposal effort by indicating problems and/or benefits of different approaches and designs.

This work was done by Milan Mandic, Behçet Açıkmeşe, and Lars Blackmore of Caltech for NASA’s Jet Propulsion Laboratory.

This software is available for commercial licensing. Please contact Daniel Broderick of the California Institute of Technology at This email address is being protected from spambots. You need JavaScript enabled to view it.. NPO-47199

Topics:
Body structures Computer software and hardware Entry, descent and landing Entry, descent and landing Entry, descent, and landing Frames Reliability Simulation and modeling Software Spacecraft Spacecraft Tools and equipment Vehicles Vehicles
This Brief includes a Technical Support Package (TSP).
Document cover
Adaptation of G-TAG Software for Validating Touch-and-Go Comet Surface Sampling Design Methodology

(reference NPO-47199) is currently available for download from the TSP library.

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    This article first appeared in the September, 2011 issue of Software Tech Briefs Magazine (Vol. 35 No. 9).

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    Overview

    The document is a technical support package detailing the adaptation of the G-TAG (Guidance, Navigation, and Control for Touch-and-Go) software tool for validating a surface sampling design methodology for comet missions, specifically in support of the Comet Odyssey proposal. Developed by researchers at the Jet Propulsion Laboratory (JPL), the G-TAG software represents a novel multi-body dynamics simulation tool aimed at studying the complexities of touch-and-go (TAG) sampling on comet surfaces.

    The report outlines the objectives of the G-TAG tool, which include assessing spacecraft performance during TAG operations based on key factors such as survivability, sample collection efficiency, and antenna pointing accuracy. The simulations conducted with G-TAG consider various scenarios that account for different ground slopes, surface properties, and spacecraft design characteristics. This comprehensive approach allows for a thorough evaluation of how the spacecraft would interact with the comet's surface during sampling operations.

    Key findings from the simulations are presented, particularly focusing on survivability scenarios. For instance, the report discusses cases where the spacecraft experiences no thrusting and the implications of delays before ascent. It highlights that the spacecraft can handle ground slopes of up to 45 degrees and maintain a satisfactory contact force profile necessary for sample collection. The results indicate that the spacecraft's elbow joint and solar panel tips would remain clear of the comet's surface, with critical measurements showing that any delay beyond 7 seconds before ascent could lead to a crash.

    The document also emphasizes the importance of maintaining a low total angle of rotation for the spacecraft, which is crucial for antenna pointing requirements during operations. The findings are supported by various figures and subplots that illustrate the performance metrics and survivability of the spacecraft under different conditions.

    In conclusion, this report serves as a significant contribution to the development of methodologies for comet sample return missions, showcasing the capabilities of the G-TAG software in simulating and validating spacecraft operations in challenging environments. The research is conducted under the auspices of NASA, with acknowledgment of government sponsorship and the collaborative efforts of the JPL team.