Detection of solar wind at synchronous orbit

The detection of unshocked solar wind by the plasma detector on the ATS-5 synchronous satellite is reported. The fact that solar wind particles were detected means that the flow vector must have been nearly perpendicular to the spin axis of the spacecraft. Comparisons of fluxes and protons before and after the event tend to indicate that the flow vector in the magnetosheath is inclined not more than 20 deg to the equatorial plane.