Fields and Particles Data from Explorers 33 and 35

The Explorer 33 and 35 spacecraft, also referred to as Anchored IMP (AIMP) 1 and 2, were launched in 1966 and 1967 towards lunar-centric orbits. Explorer 35 achieved a 5 Rm lunar orbit, but Explorer 33 went into a moderately eccentric, geocentric orbit of about 15 day period, 70 Earth radii apogee for most of its life. Their principal periods of coverage were 7/1/66-1/14/70 and 7/19/67-2/23/72. Intermittent Explorer 33 data were acquired up to 5/31/71; Explorer 35 coverage declined during the last two years of its principal period. The spacecraft carried instruments to measure in situ magnetic fields (Ness and Sonett), plasmas (Bridge), and energetic particles (Anderson and Van Allen). In addition, Van Allen's Geiger tubes measured 2-12 Angstrom solar X-rays. Many data sets from these IMP spacecraft are held at NSSDC, whose catalogs should be consulted for further details on the instruments and data sets. The Explorer 33 orbit was such that the local time of apogee was at midnight in July for 1966-1968. A 'lunar encounter' in early 1969 yielded a 45-day, 140 Re apogee orbit