At each landing site on the surface of the Moon, the astronauts' activities are limited to distances of a few miles. In comparison with the total area of the surface of the Moon, the regions explored by the astronauts on foot or with the Rover are minuscule. They are frequently referred to as "point" samples. The desirability of extending our observations to larger areas is obvious. Indeed, several things can be done in orbit about the Moon that will allow us to extrapolate from the data obtained on the surface to the rest of the Moon. One of these things is photography; many photographs have been obtained from the command module on each of the previous Apollo missions. Both the number and quality of photographs obtained from lunar orbit on Apollo 15, and scheduled to be obtained on 16 and 17, have been greatly increased over those of earlier missions.
Several things other than photography can be done from lunar orbit. In these next few sections I will describe them.
The region of the Moon that was examined with orbital experiments on Apollo 15 is shown in figure 55. The coverage for the present mission, Apollo 16, is shown in figure 56. At the time of writing this guidebook (January 1972), the landing site for Apollo 17 had not been chosen. So I do not show the orbital coverage for Apollo 17. Nonetheless, I expect that the total coverage for these three missions will exceed 20% of the Moon's surface for several of the orbital experiments and will exceed 5% for each of them.
Although some photographic tasks will be done in the command module, most of the experiments for the orbital science will be done with equipment located in the service module. The various orbital experiments include the following-a chemical group of three experiments (gamma-ray spectrometer, X-ray fluorescence, and alpha particle spectrometer), S-band transponder, mass spectrometer, several photographic cameras with a laser altimeter, and a subsatellite (with S-band transponder, particle shadows/boundary layer, and magnetometer).
The equipment for the orbital science experiments, carried in the service module, are all housed in a section that is termed scientific instrument module (acronym SIM). The location of the SIM in the service module is shown III figure 57. The location of the equipment for the individual experiments in the SIM is shown in figure 58. The names and addresses of the principal investigator of each orbital experiment are given in Table 5.