Hz, with a 20-dB per decade decrease for higher frequencies. Except for the flipper failure, the experiment functioned normally from launch to spacecraft turnoff on 24 June 1973. Low-Energy Integral Spectrum Measurement Experiment A planar multi-grid sensor programmed as a retarding potential analyzer was used to observe the intensity of the electron and ion components of the low energy plasma near the Moon. Integral spectra were obtained for both ions and electrons in the energy range from 1 to 500 eV. A complete spectrum was obtained every 80-seconds. Micrometeorite Flux This experiment was designed to measure the ionization, momentum, speed, and direction of micrometeorites, using thin film charged detectors, induction devices, and microphones. Plasma Probe A multigrid, split-collector Faraday cup mounted on the equator of the spacecraft was used to study the directional intensity of solar wind positive ions and electrons with particular emphasis on the interaction of the solar wind with the moon. Twenty-seven integral current samples (requiring about 4.3 s) were taken in an energy-per-charge window from 80 to 2850 eV. Then the current was sampled in eight differential energy-per-charge windows between 50 and 5400 eV at the azimuth where the peak current appeared in the previous series of integral measurements. These measurements (integral and differential) took about 25 s. Both the sum and difference of collector currents were obtained for positive ions. Only the sum was obtained for electrons. A complete set of measurements (two collector plate sums and one difference for protons, and one collector plate sum for electrons) required 328 s. The experiment worked well from launch until its failure in July 1968. Selenodetic Studies Range and range-rate tracking data of the Explorer 35 satellite as it orbited the Moon were used to obtain selenodetic gravity field information based on the perturbations to the satellite orbit imparted by the lunar mass distribution. End of Mission After successful operation for 6 years, the spacecraft was turned off on 24 June 1973. The orbit would have naturally decayed after this point, resulting in an impact on the Moon at an unknown time and location. Explorer 35 (or Explorer XXXV) was also known as the Anchored Interplanetary Monitoring Platform-2 (AIMP-2 or IMP-E). See also Explorer 33 Explorer program References 1967 in spaceflight Missions to the Moon Explorers Program Satellites orbiting the Moon Spacecraft launched in 1967 Interplanetary Monitoring Platform NASA space probes