A report proposes a technique for onboard updating of the orbital period of an aerobraking spacecraft in order to estimate the time of the next periapsis. The time of periapsis is nearly centered in the middle of the drag pass, and provides a convenient reference time for events in the sequence that controls the activities taking place onboard the spacecraft. Heretofore, updates of periapsis times have been computed on Earth on the basis of radio tracking data, then uplinked to the spacecraft. Onboard updating could increase operational efficiency and reduce costs by reducing the amount of ground and tracking support needed.
This work was done by Daniel T. Lyons of NASA's Jet Propulsion Laboratory, Robert H. Tolson of George Washington University, and James Longuski of Purdue University. To obtain a copy of the report, "Simple Autonomous Timing Update During Aerobraking," access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Mechanics category.
NPO-30155
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Onboard Estimation of Times of Periapsis During Aerobraking
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Overview
The document presents a technical report on a novel technique for onboard estimation of periapsis times during aerobraking maneuvers, developed by Daniel T. Lyons from NASA’s Jet Propulsion Laboratory, Robert H. Tolson from George Washington University, and James Longuski from Purdue University. The primary focus of the report is to enhance the operational efficiency of spacecraft by enabling them to update their orbital period autonomously, rather than relying on ground-based calculations.
Traditionally, periapsis times—critical for timing various onboard activities—were computed on Earth using radio tracking data and then transmitted to the spacecraft. This process required significant ground support and resources. The proposed method aims to streamline this by allowing the spacecraft to perform these calculations onboard, thereby reducing operational costs and the need for extensive ground tracking.
The technique involves integrating the outputs from accelerometers aboard the spacecraft to determine the total change in velocity during the drag phase of an orbital pass. This change in velocity is then used to calculate the change in orbital period through a polynomial function that is dependent on the current orbital period. The report details the testing of this method on all 630 orbits of the Mars Global Surveyor spacecraft, demonstrating its effectiveness.
The results of the testing were promising, showing that the time of the next periapsis could be predicted with a high degree of accuracy—within 90 seconds. This level of precision is well within the 300-second tolerance required for the timing of command sequences executed by the spacecraft, indicating that the onboard estimation method is both reliable and efficient.
The report emphasizes the potential benefits of this technique, including increased autonomy for spacecraft, reduced reliance on ground support, and overall cost savings for space missions. It highlights the importance of advancing onboard processing capabilities to improve mission operations and enhance the success of future aerobraking maneuvers.
In summary, this document outlines a significant advancement in spacecraft operations, showcasing a method that allows for real-time updates of orbital parameters, thereby improving the efficiency and effectiveness of space missions. The work represents a collaborative effort between leading experts in the field and underscores NASA's commitment to innovation in space exploration.
