ISIS 1 (International Satellite for Ionosphere Studies) was an ionospheric observatory
instrumented with sweep- and fixed-frequency ionosondes, a VLF receiver, energetic and
soft particle detectors, an ion mass spectrometer, an electrostatic probe, an
electrostatic analyzer, a beacon transmitter, and a cosmic noise experiment. The sounder
used two dipole antennas (73 and 18.7 m long). The satellite was spin-stabilized at about
2.9 rpm after antenna deployment. Some control was exercised over the spin rate and
attitude by using magnetically induced torques to change the spin rate and to precess the
spin axis. A tape recorder with 1-h capacity was included on the satellite. The satellite
could be programmed to take recorded observations for four different time periods for each
full recording period. The recorder data were dumped only at Ottawa. For non-tape-recorded
observations, data for the satellite and subsatellite regions could be acquired and
telemetered when the spacecraft was in the line of sight of telemetry stations. The
selected telemetry stations were in areas that provided primary data coverage near the
80-deg-W meridian and in areas near Hawaii, Singapore, Australia, the UK, Norway, India,
Japan, Antarctica, New Zealand, and Central Africa. NASA support of the ISIS project was
terminated on 1 October 1979. A significant amount of experimental data, however, was
acquired after this date by the Canadian project team. ISIS 1 operations were terminated
in Canada on 9 March 1984. The Radio Research Laboratories (Tokyo, Japan) then requested
and received permission to reactivate ISIS 1. Regular ISIS 1 operations were started from
Kashima, Japan, in early August 1984. ISIS 1 was deactivated effective January 24,
1990.
ISIS 2 was an ionospheric observatory instrumented with a sweep- and a fixed-frequency
ionosonde, a VLF receiver, energetic and soft particle detectors, an ion mass
spectrometer, an electrostatic probe, a retarding potential analyzer, a beacon
transmitter, a cosmic noise experiment, and two photometers. Two long crossed-dipole
antennas (73 and 18.7 m) were used for the sounding, VLF, and cosmic noise experiments.
The spacecraft was spin-stabilized to about 2 rpm after antenna deployment. There were two
basic orientation modes for the spacecraft, cartwheel and orbit-aligned. The spacecraft
operated approximately the same length of time in each mode, remaining in one mode
typically 3 to 5 months. The cartwheel mode with the axis perpendicular to the orbit plane
was made available to provide ram and wake data for some experiments for each spin period,
rather than for each orbit period. Attitude and spin information was obtained from a
three-axis magnetometer and a sun sensor. Control of attitude and spin was possible by
means of magnetic torquing. The experiment package also included a programmable tape
recorder with a 1-h capacity. For nonrecorded observations, data from satellite and
subsatellite regions were telemetered when the spacecraft was in the line of sight of a
telemetry station. Telemetry stations were located so that primary data coverage was near
the 80-deg-W meridian and near Hawaii, Singapore, Australia, England, France, Norway,
India, Japan, Antarctica, New Zealand, and Central Africa. NASA support of the ISIS
project was terminated on 1 October 1979. A significant amount of experimental data,
however, was acquired after this date by the Canadian project team. ISIS 2 operations were
terminated in Canada on 9 March 1984. The Radio Research Laboratories (Tokyo, Japan) then
requested and received permission to reactivate ISIS 2. Regular ISIS 2 operations were
started from Kashima, Japan, in early August 1984. ISIS 2 was deactivated effective 24,
1990.