A launch window study for GEOTAIL's double lunar swingby trajectory

The GEOTAIL spacecraft of the International Solar-Terrestrial Physics Program will use a series of paired lunar swingbys to explore distant parts of the earth's magnetic tail. A 21-day launch window has been calculated for GEOTAIL, in July and August 1992, to start its distant-tail phase with a first lunar swingby (S1) on September 8, 1992. The main launch window in July utilizes 4.5 revolutions in a transfer orbit to S1, with a mid-August contingency window that uses 2.5 transfer-orbit revolutions before S1. Designing a good distant-tail trajectory, and then accurately matching it at S1 for every day in the launch window, seems to be the easiest and most reliable strategy. However, the total delta-V costs of the current designs can probably be reduced, possibly with the help of new interactive software that can be run on personal computers.