DESTINATION MOON: A History of the Lunar Orbiter Program
Other Potential Experiments
[145] Although the Block I spacecraft carried only the four experiments described above, the Lunar Orbiter Program Office was Planning a greater number of more sophisticated scientific experiments for the Block II Orbiter. They included: 1) a gamma ray experiment to determine the presence and relative abundance of natural, long-lived radioisotopes on the surface of the Moon; 2) an infrared experiment for mapping the lateral variations in the Moon's surface temperature; 3) a bi-static radar experiment for determining the average radar cross-section, surface roughness correlation functions, altitude measurements, reflectivity, and the dielectric properties of the lunar surface; 4) a photometry/colorimetry experiment to determine variations in the photometric function and the color of lunar surface materials; 5) a radiometer experiment for measurement and determination of lunar surface thermal gradients; 6) an X-ray fluorescent experiment to detect the relative abundance of iron and nickle on the Moon's surface; 7) a solar plasma experiment to study the spatial and temporal flux variation [146] and energy distribution of low-energy protons and electrons of the plasma; 8) an experiment to investigate the magnetic field In the vicinity of the Moon; and, finally, 9) a lunar ionosphere experiment to determine the presence of a low-density ionosphere in the immediate vicinity of the Moon's surface.12
These experiments, spanning a wide range of scientific fields of investigation, demonstrated that the Lunar Orbiter Program envisioned in a second block of spacecraft a series which would conduct primarily scientific investigations and not necessarily more photography of the lunar surface. NASA had already designated the Block I Orbiters for missions which would gather photographic data of the lunar surface vital for miss ion planning of the Apollo Program.
Moreover, the first Lunar Orbiters would explore some aspects of the Moon's environment and complement the work which the Surveyor spacecraft would carry out when they landed on the Moon. The Orbiter concept, expanded in a second series of spacecraft, could achieve major advances in knowledge about Earth's natural satellite, a philosophy consistent with the mainstream of thought in the Office of Space Science and Applications. However, lack of funds eventually precluded the Block II Orbiters and curtailed a [147] major U.S. scientific thrust in exploring the Moon.