We report on coordinated high-altitude satellite observations in support of one of the first space-based VLF wave injection experiments, namely the USSR Aktivny mission. The Activny satellite (A) was designed to carry a VLF transmitter (nominal frequency ~10 kHz, transmitter power ~10 kW) coupled to a 20-m-diameter loop antenna in a nearly polar orbit (83¿ inclination, apogee ~2500 km, perigee ~500 km). We focus our attention on conjunction experiments between the Activny and DE 1 satellites. Because of problems in the deployment of the loop antenna, the radiated power capability of the antenna was significantly reduced. Although this substantially reduced the expectation of receiving detectable signal levels on the satellite, the DE 1/Activny conjunction experiments were nevertheless carried out as a means of possibly placing an upper limit on the radiated power. During the period November 1989 through April 1990, a total of 10 DE 1/Activny wave injection sessions were conducted. During each session the Activny transmitter operated at 10.537 kHz with 1 s on-1 s Off format, for a period of 6 min centered around the conjunction time. During three conjunction periods (December 12, 26, and 27, 1989) both DE 1 and Activny were in the southern hemisphere, and DE 1 was at relatively low altitudes (ranging from 6211 to 14,810 km), thus providing the best conjunction possibilities according to the ray tracing criteria developed above. On most days, Omega transmitter signals as well as commonly occurring natural wave phenomena such as whistlers (0+) and hiss were clearly seen well above the background level, but there was no evidence of the Activny 1 s On/1 s Off pattern. Though no Activny signals were detected by the LWR on the DE 1 satellite, the experimental constraints allow us to place an upper limit on the total power radiated by the Activny transmitter in the whistler-mode. Using experimental parameters, and the minimum detectable signal level of 0.05 &mgr;V/m for LWR, we find the upper limit on the total power radiated by the Activny satellite on the whistler-mode to be ~10 mW. Several recommendations for future space-based wave injection experiments are presented. ¿ American Geophysical Union 1994