A computer program facilitates the analysis and design of a radio-communication system for transmitting data from an orbiting spacecraft to ground stations. Input data provided by the user include primarily (1) parameters of the spacecraft orbit (including parameters that specify its position and orientation with respect to a coordinate system that translates with, but does not rotate with, the Earth); (2) either a specification of the gain pattern or else parameters needed to calculate the gain pattern of the antenna aboard the spacecraft; (3) type of spacecraft antenna aiming (nadir-pointed or articulated); (4) locations of the ground stations; (5) downlink bit rates and frequencies; (6) spacecraft instrument data rates; and (7) the angle (relative to the horizon) below which the line of sight from the spacecraft to each ground station is deemed to be blocked. The program calculates the spacecraft trajectory, the times when the spacecraft is visible from each ground station, the times (as functions of visibility and the antenna gain pattern) when radio communication is possible, the number of bits that a ground station can receive from the spacecraft during a given orbit, and the spacecraft data-storage capacity needed to hold data that are generated between communication intervals.

This work was done by Anil Kantak and Faiza Lansing of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Software category.

This software is available for commercial licensing. Please contact Don Hart of the California Institute of Technology at (818) 393-3425. Refer to NPO-20672