Looking at NASA’s Lunar Reconnaissance Orbiter (LRO) which has been in orbit around the Moon since 2009, people today might take it for granted that lunar missions are fairly routine affairs that are virtually guaranteed to be successful. But nothing could be further from the truth. While NASA’s recent lunar missions have been quite successful and make lunar missions look easy, these successes require a lot of work and come at the expense of many early lunar mission failures. As the Chinese are now learning with their trouble with the Yutu rover mission, successful lunar missions require the mastery of many new technologies, engineering techniques and project management skills – things that NASA learned the hard way a half a century ago.
NASA’s Rocky Start Towards the Moon
NASA’s first lunar missions were filled with one disappointing failure after another. Shortly after being founded in October 1958, NASA inherited a hodgepodge of lunar missions in various stages of preparation from the Department of Defense under the Pioneer program. In the end, one flyby and five lunar orbiter mission attempts launched between October 1958 and December 1960 ended in failure. Out of all of NASA’s initial attempts to launch probes towards the Moon, only the tiny six-kilogram Pioneer 4 built by the Jet Propulsion Laboratory (JPL) and launched on March 3, 1959, by a team at the Army Ballistic Missile Agency (ABMA) headed by Wernher von Braun (which would become the basis of NASA’s Marshall Space Flight Center), managed to escape the Earth to make a very distant 60,500-kilometer flyby of the Moon on its way into solar orbit (see “Vintage Micro: The Pioneer 4 Lunar Probe“).
Diagram showing the components of the Block I Ranger flown in 1961. This spacecraft would serve as the basis of the early Mariner probe to Venus. (NASA)
The initial flights of NASA’s first in-house lunar program approved at the end of 1959, Ranger which was built and managed by JPL, fared little better than the lunar Pioneers. The two flights of the Block I Ranger in 1961, which were designed to test the innovative Ranger design in extended Earth orbit, were stranded in short-lived low Earth orbits due to failures of the upper stage of the Atlas-Agena B launch vehicle. Despite the failures, the abbreviated flights of Ranger 1 and 2 did prove the three-axis stabilized design of Ranger which served as the basis of NASA’s first Mariner spacecraft launched to Venus in 1962 (see “The Prototype That Conquered the Solar System“.
Model of the Block II Rangers flown in 1962. The spherical hard -lander is the sphere on the top of the spacecraft. (NASA)
The three Block II Ranger flights, which were designed to hard-land a small probe on the lunar surface during 1962, fared little better than the Block I missions. While most of the launch vehicle issues were resolved, fatal malfunctions of key spacecraft components resulted in the complete failure of all of these missions. As 1962 was drawing to a close, the situation with the American Moon program looked bleak. The failure of the last Block II Ranger, Ranger 5 launched on October 16, 1962, was NASA’s sixth consecutive lunar mission failure in three years. Only 17 months after President John F. Kennedy committed the United States to landing a man on the Moon with Project Apollo, it was beginning to look as though the Americans would never make it (see “NASA’s First Moon Lander“).
Reviews by NASA and outside groups about the string of lunar mission failures produced a laundry list of engineering changes and management reforms for the next round of Block III Ranger flights which were intended to make observations of the Moon before they impacted its surface. Among the changes was for the Block III Ranger flights to concentrate exclusively on high-resolution imaging of the Moon. All other instruments and investigations were dropped in order to directly support the new Apollo program.
The first improved Block III Ranger, designated Ranger A, was finally ready for launch by the end of 1963. Much had been changed from the previous design. Ranger’s hexagon-shaped bus was similar to previous models with some notable exceptions. First, the framework of the bus was now made of aluminum due to its better thermal characteristics. A second battery to provide additional backup power was added. The course correction system was enlarged to provide a 60-meter per second velocity change capability representing a one-third increase over the earlier Block II Ranger. The sequencer which controlled spacecraft functions was redesigned to incorporate components which were not heat sterilized and included features that increased the chances of a successful mission in case of equipment failure. A second, independent attitude control system was added for redundancy.
Diagram showing the components of the Ranger Block III design. (NASA)
The bus was also fitted with new rectangular-shaped solar panels similar to the ones carried by Ranger’s successful cousin, the Mariner 2 Venus probe launched in 1962. This design had portions of the solar panels electrically isolated from each other to avoid a repeat of the total solar panel failure experienced by Ranger 5. All of these changes increased the mass of the Block III Ranger to 366 kilograms — the limit for the Atlas-Agena B launch vehicle for Ranger’s mission profile.
Two independent chains of slow-scan vidicon cameras developed and built by RCA (a leading electronics manufacturer of the day, bought by GE in 1986 and subsequently dismantled) were enclosed in a 1.5-meter tall tower mounted on top of the bus. Clad in polished aluminum for thermal control, the 173-kilogram cylindrical tower tapered from 69 centimeters at its base to 41 centimeters at the top, where the low-gain antenna was mounted. A total of six cameras viewed the approaching lunar surface through a 33-centimeter square opening on the side of the tower. Their optical axes were canted at a 38° angle from the spacecraft’s long axis in order to get a clear view of the lunar surface during approach.
View of the Block III Ranger camera package. (NASA)
The full-scan camera set or “F-chain” consisted of a pair vidicon cameras that would provide 1,152-line images (comparable to today’s HD format) at a rate of about one image per camera each five seconds. The “A” camera had a relatively wide 25° field of view while the “B” camera had a narrower 8° field of view. The independent “P-chain” consisted of four vidicon cameras fitted with the same lenses as the pair of F-chain cameras but provided only partial, 300-line scans of their imaging plate. The P-chain camera images had the same resolution as the F-chain but only covered about 7% of the area. This was done so that images could be returned at a rate of five images per second in hopes of capturing at least a partial image a couple of tenths of a second before impact. At this altitude of only 300 to 600 meters, a resolution of 30 centimeters or better was possible.
Also enclosed inside the tower were two independent power supplies, camera sequencers, and batteries; one set for each chain of cameras. Each chain also possessed its own 60-watt transmitter to independently transmit images in real time back to Earth via the craft’s directional high-gain antenna. If the one set of cameras were to malfunction, the other was designed to operate independently. The bus still carried its own 3-watt transmitter which carried only engineering telemetry. With all these hardware changes, including redundant and more fault tolerant systems as well as 500 to 800 hours of prelaunch testing, the new Block III Ranger was much more likely to reach its target in working order.
Diagram showing the terminal maneuvers of the Block III Ranger to align its cameras to take images before it impacted the lunar surface. Click on image to enlarge. (NASA)
The Block III mission profile was very similar to the Block II up until the encounter with the Moon. About one hour before impact, the spacecraft would begin its terminal maneuver and reorient itself. This maneuver would aim the cameras along Ranger’s flight path towards approaching lunar surface with the high gain antenna turned to point towards Earth. Some 17 minutes before impact, the F-chain of cameras would be commanded to warm up for 90 seconds. The P-chain then would take its turn and warm up. Finally, 14 minutes before impact at an altitude of about 1,900 kilometers, the F-chain’s 60-watt transmitter would start beaming images back to Earth, followed by the P-chain about 150 seconds later. Transmission would continue until the spacecraft impacted the lunar surface at 2,600 meters per second. If everything worked perfectly, over 4,200 close-up television images of the lunar surface would be transmitted back to the Earth.
The First Block III Ranger Missions
The first launch of the new Block III, Ranger 6, took place on January 30, 1964. A course correction 16 hours and 41 minutes after launch was flawlessly executed putting Ranger 6 on course for an impact at 9.39° N, 21.51° E in the Sea of Tranquility. On February 2, as Ranger 6 passed the 2,076-kilometer altitude mark moving at 1,998 meters per second, the television cameras were switched into warm up mode with all systems functioning normally. When the time came for the cameras to switch to full power and start returning images, however, only static was received. Quickly a series of emergency commands were sent from Earth, but to no avail. Ranger 6 crashed into the lunar surface at a speed of 2,658 meters per second without returning a single picture.
Lunar Reconnaissance Orbiter image from October 29, 2009 showing the crater made by the impact of the unsuccessful Ranger 6 over 45 years earlier. (LRO/NASA)
Ranger 6 was definitely a very successful engineering test. With the exception of the cameras, all systems worked perfectly. In addition, the navigation accuracy was the best ever attained with the spacecraft impacting the Moon only 31 kilometers from its aim point and 0.3 seconds before its post-mid-course maneuver predicted impact time. Still, from the point of view of the public as well as the scientific community, this was NASA’s seventh consecutive lunar mission failure. NASA Headquarters formed another board of inquiry to investigate this mishap. The March launch of Ranger B was postponed pending the outcome of this new investigation. The pressure was on NASA with JPL and the Ranger program fighting for their lives.
The NASA investigation into the failure of the Ranger 6 camera package was released on March 17, 1964. The 75-page report pinned the problem squarely on the RCA camera package itself. The completely redundant camera system was found not to be perfectly so since there was a single line that carried commands to both camera chains. It was discovered that when the Atlas 199D carrying Ranger 6 dropped its booster engines, about 180 kilograms of unburned propellants were expelled and subsequently ignited by the sustainer engine as usually happened during Atlas flights. While this was not normally an issue on previous launches, this time the detonation wave produced worked its way into a mechanically sealed umbilical door on the Agena second stage. The umbilical pin that controlled the camera package for ground testing was 6 millimeters from another pin carrying twenty volts. The burning fuel vapor was conductive enough to short the two pins briefly and cause the camera package to turn on prematurely burning out the redundant power supplies which were designed to only operate at full power in the vacuum of space. Changes were made to the camera system design and prelaunch testing procedures to not only prevent this failure mode but improve its operation and reliability.
Launch of Ranger 7 on July 28, 1964 for what would be NASA’s first completely successful lunar mission. (NASA)
With the threat of cancellation hanging over the Ranger program, Ranger B was modified and scheduled for launch in late July 1964 before the Atlas-Agena facilities were to be dedicated to the launch of the upcoming Mariner missions to Mars. Several targets were considered by the Ranger science team for the first day of the launch period on July 27, 1964 along 7° E longitude between 21° N and 14° S latitude. The launch on this first day was scrubbed due to problems with the ground-based portion of the guidance system, however. Finally, on July 28 (50 years ago today), Ranger 7 successfully lifted off at 12:50 PM EDT only 7.9 seconds into its launch window aimed at 11° S, 21° W in the northwest portion of Mare Nubium. The Atlas 250D operated perfectly as did the modifications that prevented the cameras from prematurely activating when the Atlas dropped its booster engines. After a brief burn from the Agena B 6009 second stage, the Agena and Ranger entered its temporary Earth parking orbit.
With a good injection burn from the Agena B a half hour after launch, it was calculated that Ranger 7 would skim over the leading edge of the Moon and impact on its far side. A 50-second course correction burn the day after launch brought the predicted impact point within the intended target area. About 20 minutes before impact on the morning of July 31 with Ranger 7 2,277 kilometers above the lunar surface traveling at 1,917 meters per second, the F-chain cameras were placed into the ninety-second warm-up mode followed by the P-chain. Much to the relief of JPL and NASA officials, pictures from the F-chain cameras started streaming back to Earth 17 minutes and 30 seconds before impact, followed 3 minutes and 33 seconds later by the P-chain.
First image of the Moon returned by Ranger 7 (or any American spacecraft) on July 31, 1964. (NASA)
By the time Ranger 7 plowed into the lunar surface 68 hours, 35 minutes, and 42 seconds after launch, 4,316 pictures had been transmitted back to Earth. The last image, only a portion of which was transmitted before the probe’s destruction, was acquired at an altitude of only 300 meters, showing features as small as a meter across. Ranger 7 had impacted at 10.7° S, 20.7° W only 13 kilometers from its aim point. It was the first major American lunar mission success after almost six years of attempts.
The pictures returned by Ranger 7 confirmed that the lunar mare regions are quite smooth and apparently free of major hazards for the Apollo Lunar Module. Because of the size and shape of the craters and the topography observed during the approach, it seemed unlikely that the lunar surface was coated with a deep dust layer that could bury a lunar lander upon touchdown, as some had feared. With the successful flight of Ranger 7, it now appeared that a safe landing on the lunar surface was possible. It also ended up saving the Ranger program from cancellation and salvaged JPL’s sagging standing in the American space program. With the next Ranger flight now scheduled for February 1965, scientists and engineers began the process of choosing the next impact site to support the upcoming Surveyor unmanned lunar landing program and the Apollo missions to follow.
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Related Video
This excellent NASA-produced period documentary, “Lunar Bridgehead”, tells the story of the Ranger 7 mission.
Related Reading
“The Prototype That Conquered the Solar System”, Drew Ex Machina, September 15, 2015 [Post]
“NASA’s First Moon Lander”, Drew Ex Machina, January 26, 2016 [Post]
“The Mission of Ranger 8”, Drew Ex Machina, February 17, 2015 [Post]
“Vintage Micro: The Pioneer 4 Lunar Probe”, Drew Ex Machina, August 2, 2014 [Post]
General References
R. Cargill Hall, Lunar Impact: The NASA History of Project Ranger, Dover Publishing, 2010
Raymond L. Heacock, “Ranger: Its Mission and Its Results”, TRW Spacelog, Summer 1965
Michael M. Mirabito, The Exploration of Outer Space with Cameras, McFarland, 1983
H. M. Schurmeier, R. L. Heacock, and A. E. Wolf, “The Ranger Missions to the Moon”, Scientific American, January 1966
Paolo Ulivi with David M. Harland, Lunar Exploration: Human Pioneers and Robotic Surveyors, Springer-Praxis, 2004