The Ranger Program
The Ranger program consisted of nine spacecraft missions with the ultimate objective of obtaining high-resolution photographs of the lunar surface. The development of the basic Ranger spacecraft system was initiated in 1959. The spacecraft was conceived as a fully attitude-stabilized platform from which lunar or planetary observations could be made. The Ranger spacecraft had three different configurations.
- Block I Missions
Block I, consisting of Ranger 1 and 2, were test missions. They were launched in 1961 for nonlunar-oriented engineering development.
- Block II Missions
These missions (Ranger 3, 4, and 5) were launched during 1962 to achieve rough lunar landings, obtain science data, and test approach television camera operations. These Ranger spacecraft experienced satisfactory vehicle performance but either missed the Moon (Ranger 3) or failed before impacting the lunar surface (Ranger 4 and 5).
- Block III Missions
The experience of the earlier phases of the program led to the Block III missions in 1964 and 1965: Ranger 6, 7, 8, and 9. These spacecraft were designed to achieve lunar impact trajectories and to transmit high-resolution photographs of the lunar surface during the final minutes of flight.
- Ranger 6 performed satisfactorily, but the camera failed to operate before lunar impact. However, Ranger 7, 8, and 9 fulfilled the mission objective and provided more than 17,000 photographs at resolutions not previously obtained. The Ranger 7 and 8 missions provided coverage of the two types of mare terrain in which they impacted. The first type is modified by crater rays, and the second is crossed by a complex system of ridges. Ranger 9 provided coverage of the highland region, impacting in the large central highland crater Alphonsus.
The Ranger photographs provided valuable information for future landing site selection for Surveyor and Apollo missions, and feature designation of surface detail not heretofore visible to Earth-based observations. For more on the individual missions, select from the list below.
Launch: July 28, 1964
Impacted Moon: July 31, 1964, at 13:25:49 UT
Landing Site: Mare Cognitum, 10.35°S lat., 339.42°E long.
The mission objective of Ranger 7, to obtain close-up pictures of the lunar surface that would be of benefit to both the scientific program and the manned program, was carried out flawlessly. The mission terminated with the acquisition of some 4000 television records of a preselected area of the lunar surface. The signals from the six television cameras aboard the spacecraft were transmitted during the last 17 minutes of the flight. The picture taking spanned a distance range from slightly more than a lunar radius to approximately 480 meters above the surface.
Selection of the Target Site
From the standpoint of the lunar manned spaceflight program, it was desired that the target area be one of typical mare and near the lunar equator. The selected region was a relatively detached mare or sinus between Oceanus Procellarum and Mare Nubium, bounded by the Riphaean Montes on one side and the bright cratered area containing Guericke Crater and Parry-Bonpland Crater on the other.
Launch: February 17, 1965
Impacted Moon: February 20, 1965, at 09:57:37 UT
Landing Site: Mare Tranquillitatis, 2.67°N lat., 24.65°E long.
The prime objective of the mission, to obtain high-resolution photographs of Mare Tranquillitatis, was met. During the 23 minutes the cameras operated before impact, a large swath of the Moon was photographed at high resolution for the first time. Excellent photographs of Delambre Crater, the southern shoreline of Mare Tranquillitatis, and the crater pair Ritter and Sabine were obtained. The last picture was taken 0.09 seconds before impact from an altitude of approximately 160 meters. The impact point was less than 20 kilometers from the selected point.
Selection of the Target Site
The basic objective in selecting the Ranger 8 target was to choose an area which, in conjunction with the Ranger 7 photographs, would be the most useful in increasing the knowledge of the lunar maria. Taking into consideration Apollo constraints, a point near the equator and 15° from the terminator was chosen.
Launch: March 21, 1965
Impacted Moon: March 24, 1965 at 14:08:20 UT
Landing Site: Alphonsus Crater, 12.83°S lat., 357.63°E long.
The Ranger 9 flight concluded the Ranger series in a spectacular manner, with the direct broadcast of the B-camera photographs over national television as the spacecraft approached the Moon. Unlike its predecessors, which photographed relatively simple mare terrain, Ranger 9 was directed to one of the more complicated areas of the Moon. The impact point was selected slightly northeast of the central peak of Alphonsus Crater. The last picture was taken 0.25 seconds before impact from an altitude of approximately 600 meters. The terminal resolution of 30 centimeters achieved exceeded that of both Ranger 7 and 8.
Selection of the Target Site
The criteria used in selecting the Ranger 9 target area were somewhat different than those applied to the Ranger 7 and 8 target selection. These missions had successfully provided high-resolution coverage to the two principal types of mare. Because of the similarities found in these areas, it was decided that photographs of other terrain types would be of more use. After due consideration, the crater Alphonsus was selected as the target.
The Television Cameras
The Ranger television equipment had the same construction and operational capabilities for all missions. Included in the system were six cameras. The six cameras were fundamentally the same with differences in exposure times, fields of view, lenses, and scan rates. The camera fields of view were arranged to provide overlapping coverage so that a nested sequence of photographs was obtained.
The camera system was divided into two completely separate channels designated P (partial) and F (full). Each channel was self-contained with separate power supplies, timers, and transmitters. The F channel had two cameras. The A camera was wide angle, and the B camera was narrow angle. The P channel contained four cameras designated P1 and P2 (narrow angle) and P3 and P4 (wide angle).
The last F-channel picture was taken between 2.5 and 5 seconds before impact (from an altitude of about 5 kilometers); the last P-channel picture was taken between 0.2 and 0.4 seconds (from an altitude of about 600 meters) from which the highest resolutions were obtained. The resolution achieved by Ranger 9 (0.3 meters) was a factor of 1000 better than any Earth-based views of the Moon.