A document discusses a method of controlling touch and go (TAG) of a spacecraft to correct attitude, while ensuring a safe ascent. TAG is a concept whereby a spacecraft is in contact with the surface of a small body, such as a comet or asteroid, for a few seconds or less before ascending to a safe location away from the small body.
The report describes a controller that corrects attitude and ensures that the spacecraft ascends to a safe state as quickly as possible. The approach allocates a certain amount of control authority to attitude control, and uses the rest to accelerate the spacecraft as quickly as possible in the ascent direction. The relative allocation to attitude and position is a parameter whose optimal value is determined using a ground software tool.
This new approach makes use of the full control authority of the spacecraft to correct the errors imparted by the contact, and ascend as quickly as possible. This is in contrast to prior approaches, which do not optimize the ascent acceleration.
This work was done by Lars James C. Blackmore of Caltech for NASA’s Jet Propulsion Laboratory. NPO-47192
This Brief includes a Technical Support Package (TSP).
Six Degrees-Of-Freedom Ascent Control for Small-Body Touch and Go
(reference NPO-47192) is currently available for download from the TSP library.
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Overview
The document from NASA's Jet Propulsion Laboratory (JPL) presents a comprehensive overview of a new six degrees of freedom (6-DOF) control approach for spacecraft ascent from small planetary bodies, such as comets and asteroids, following a Touch and Go (TAG) sampling operation. The TAG concept involves a spacecraft making brief contact with a small body to collect samples, which poses unique challenges for ascent due to the forces and torques imparted during contact.
The primary focus of the report is on the difficulties faced by spacecraft after performing a TAG operation. When the spacecraft contacts the surface, it can experience significant angular displacement and angular rate changes, which can lead to potential collisions with the small body if not corrected promptly. The document emphasizes that the limited thrust available for both ascent and attitude control complicates the situation, as the problems of rotational and translational control are interlinked.
To address these challenges, the report proposes a combined approach for attitude and position control, allowing for safe ascent after TAG. The methodology involves the use of torque and force equations to manage the spacecraft's movements effectively. The document outlines the notation used in the control approach, including the representation of torque and force delivered by thrusters, and the constraints on thrust allocations to ensure safe operations.
The introduction highlights the importance of the TAG operation, which can involve devices like a brushwheel sampler that collects material from the surface in a matter of seconds. The report also discusses the implications of not being able to fire attitude control thrusters during contact, which can lead to unwanted angular displacements that must be corrected immediately after sampling.
Overall, the document serves as a technical support package that not only details the innovative control strategies for ascent from small bodies but also underscores the broader implications of this research for future space missions. It invites further exploration and collaboration in the field of aerospace technology, emphasizing the potential applications of these advancements in various scientific and commercial contexts.
