Following the success of this probe, Canada and the United States signed an agreement to launch further satellites under a new program known as the International Satellites for Ionospheric Studies (ISIS) Program. In 1965, a refurbished backup model of Alouette-I was launched as Alouette-II. There were five types of ionospheric measurements that this satellite conducted. It was equipped with a sweep-frequency ionospheric sounder, a VLF receiver, an energetic particle experiment, a cosmic noise experiment, and an electrostatic probe. The primary objective of this probe was to extend the scope of Alouette-I’s mission, both in altitude coverage and number of parameters investigated. In addition, Aloutette-II contained various technological upgrades compared to Aloutette-I, including modifications to the antenna system, which was enhanced by adding highly reflective plates at the ends of the longer antennas because of excessive spin rate decay discrepancies.
ISIS-I was far more complex than either of the Alouette probes which was partially due to the data collected by the Alouette probes. It was later understood that for proper interpretation of ionospheric behaviour, which was revealed by the sounder, additional information such as ion mass, electron temperature, and ion temperature were required. ISIS-I was the first of the satellites from the program to incorporate the swept and fixed frequency sounder combined with a complete set of direct measurement experiments — active spin maintenance, spin axis orientation control, and onboard tape recorder for data storage. This last element was especially important as it allowed data to be collected at pre-selected times, even if the satellite was not in sight of a telemetry station. Furthermore, the clock acted as a master spacecraft oscillator which was used to synchronize the probe’s experiments.
Due to fiscal limitations, ISIS-II was generally quite similar to its predecessor and as a result, the number of system designs carried over from ISIS-I were maximized. Nonetheless, there were changes made to increase the frequency marker accuracy and output power of both the sounder transmitters. Furthermore, a significant change was made with the addition of the Automatic Ionogram Transmission (AIT) which allowed automatic operation of the sounder every three minutes. In addition, the scope of the VLF was increased to include antenna impedance measurements on the sounder’s short dipoles. However, the most significant addition to the probe was two optical experiments designed and built in Canada (the Red Line Photometer and the Auroral Scanning Photometer). Their purpose was to study atmospheric optical emissions.