IMP 8 (Explorer 50), the last satellite of the IMP series, was launched
October 26, 1973. It is a drum-shaped spacecraft, 135.6 cm across and
157.4 cm high, instrumented for interplanetary, magnetotail, and
magnetospheric boundaries stud ies of cosmic rays, energetic solar
particles, plasma, and electric and magnetic fields. Its initial orbit
was more elliptical than intended, with apogee and perigee distances of
about 45 and 25 earth radii. Its eccentricity decreased afte r launch.
Its orbital inclination varies between 0 deg and about 55 deg with a
periodicity of several years. The spacecraft spin axis is close to being
normal to the ecliptic plane, and the spin rate is approximately 23 rpm.
The data telemetry ra te is 1600 bps. The spacecraft is in the solar wind
for 7 to 8 days of every 12.2 day orbit. Telemetry coverage was 90% in
the early years, but only 50-70% through most of the 1980's and into the
1990's. The telemetry is VHF and the spacecraft i s tracked by Wallops
Island, VA; Redu, Belgium; Tasmania Australia; Santiago Chile; and Hawaii.
The objectives of the extended IMP-8 operations are similar to the
original goals with emphasis on providing solar wind parameters as input
for magne tospheric studies and as a 1-AU baseline for deep space studies,
and to continue solar cycle variation studies with a single set of
well-calibrated and understood instruments.
For additional information on IMP-8 see the IMP-8 Page at the NSSDC.