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.