Recent years have witnessed renewed interest in missions to the Moon. In addition to the United States and Russia, who dominated the exploration of the Moon during the first two decades of the Space Age, there are now many new players in the game, including the European Space Agency, Japan, China, and India. While recent missions continue to add much to our knowledge about the Moon, only half a century ago such voyages required the mastery of cutting-edge technology and frequently ended in disappointing failure. The problems encountered by these early efforts are exemplified by NASA’s first automated lunar lander built as part of their Ranger program.
The Ranger Program
During the opening years of the Space Age, NASA struggled to get probes to the Moon, initially with programs it had inherited from the military (see “NASA’s Forgotten Lunar Program”). Out of all of its attempts to launch probes towards the Moon, only the diminutive 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 break free of the Earth and make a distant flyby of the Moon (see “Vintage Micro: The Pioneer 4 Lunar Probe”).
By the end of January 1960, NASA’s first totally new lunar project, Ranger, had taken form. It was managed by JPL and would attempt to hard land a small package on the lunar surface while returning close up images during its descent. The first five flights of the new series would use two spacecraft types designated Block I and Block II that would be launched using the new Atlas-Agena B rocket. The first two flights would make use of the Block I spacecraft. They were meant to be engineering test flights that would place Ranger into an extended Earth orbit. These 307-kilogram three-axis stabilized spacecraft would be the forerunner of not only the Ranger Moon probes but also the Mariner spacecraft then being designed to explore the planets Venus and Mars (see “The Prototype That Conquered the Solar System”).
The main bus of the Block II Ranger was similar to the one used by the Block I test craft. It consisted of a hexagon-shaped magnesium frame bus 1.52 meters across. The various compartments of this bus contained the spacecraft’s central computer and sequencer which controlled the spacecraft, a battery to provide backup power, a radio transmitter, and the attitude control system. Attitude reference was provided by six Sun sensors, two Earth sensors, and three gyros. Extending from the sides of the bus were two solar panels holding 8,680 solar cells to provide up to 210 watts of electrical power for the spacecraft. Also extending from the base was a hinged dish-shaped high-gain communications antenna 1.22 meters across, which would be pointed at Earth with the aid of a light sensor. The spacecraft maintained its attitude using a set of ten gas jets supplied by 1.1 kilograms of compressed nitrogen gas held in three tanks.
Unlike the Block I Ranger, which was topped by an instrument-laden truss structure, the Block II bus carried a 150-kilogram package consisting of a small hard lander with a retrorocket that provided 22.6 kilonewtons of thrust. The hard lander, built by the Aeronutronic Division of the Ford Motor Company in Newport Beach, California, was a 64-centimeter diameter sphere with a mass of 43 kilograms. The exterior was composed of balsa wood designed to absorb the force of impact. Inside this impact limiter was a smaller 31-centimeter, 25-kilogram sphere that housed the lander’s systems. The primary instrument carried by the lander was a seismometer sensitive enough to detect the impact of a 2.3-kilogram meteorite on the opposite side of the Moon. The sensitive components of the seismometer were protected from the impact forces by a cushion of liquid heptane. Also included in the capsule was a 50-milliwatt transmitter, six silver-cadmium batteries, and a temperature-sensitive voltage oscillator. The lander was designed to survive an impact of 67 meters per second.
The hard lander’s interior temperature was controlled by a capsule containing 1.7 kilograms of water. During the hot lunar day, the interior would heat up to 30° C, at which point the water would start to boil under the ambient conditions. The temperature would rise no further until all the water had boiled away. During the cold lunar night, the warmed water, along with the heat generated by the lander’s internal electronics, would keep the interior temperature above freezing.
The 330-kilogram, 3.1-meter-tall Block II Ranger had additional modifications from its Block I predecessor. First, the battery was reduced in size to 11 kilograms, which provided one kilowatt-hour of reserve power. Another modification included the use of a 16-kilogram hydrazine-fueled course correction engine which generated 222 newtons of thrust to fine-tune Ranger’s aim as it approached the Moon. This engine could be fired for a maximum of 68 seconds, giving a total velocity change of 44 meters per second. Since any torques imparted during this engine’s operation could not be negated using the small attitude control jets, this engine was fitted with steering vanes at the exit nozzle.
The bus of the Block II Ranger also carried its own set of instruments. A radar altimeter provided ranging information for lander deployment as well as data on the lunar surface’s radar characteristics. A gamma ray spectrometer mounted on an extendable 1.8-meter boom determined surface composition. A single television camera built by RCA and fitted with a JPL-designed 102-millimeter focal length lens was expected to return over 150 images of the approaching lunar surface composed of two hundred scan lines each (only about 40% of the number of lines in standard American television transmissions of that era).
In order to minimize the chances of Earth organisms reaching the Moon (which was still a concern in some circles during these early days), the entire spacecraft was sterilized first by baking components for 24 hours at 125° C and then all its parts were cleaned with alcohol before they were assembled. Finally, the entire spacecraft was saturated with ethylene oxide gas for 24 hours while in its launch faring.
There were many variables involved in choosing a proper launch window for Ranger. First, the length of the trip to the Moon was set to about 66 hours to maximize the payload while ensuring that Ranger would be in clear view of the Goldstone tracking antenna in California’s Mojave Desert— the most sensitive in NASA’s network of tracking stations — when it reached the Moon. Ranger also had to approach the Moon almost vertically at a precise speed because of the fixed velocity increment of the lander’s retrorocket. Because of the imaging requirements and the position of celestial references, the landing could only take place on the Moon’s visible face during a four- or five-day period centered on the Moon’s last quarter phase. Finally, the requirement that the hard lander’s antenna have Earth in view meant that it could not be placed more than forty-five degrees from the center of the Moon’s visible side. All of these constraints limited impact sites to near the lunar equator in the eastern part of Oceanus Procellarum.
A typical mission sequence for the Block II Ranger started with the modified Atlas D rocket placing the Agena B upper stage and Ranger spacecraft into a parking orbit after a short burn from the Agena B. After a preprogrammed time delay, the Agena B would reignite to place the spacecraft on a path to the Moon. Once its job was completed, the Agena B would separate from the probe and fired small retrorockets to distance itself from the Ranger. About five minutes after separation and around 48 minutes after launch, Ranger would then unfold its solar panels and high-gain antenna to begin its search for its first attitude reference, the Sun. Once acquired, Ranger would switch from its battery to its solar panels for power. It would then begin a slow roll until its antenna locked on to Earth, its final reference point, about four hours after launch.
If its trajectory needed refining, Ranger would be commanded to make a single mid-course correction about 15 hours after launch at a distance of 146,000 kilometers to ensure a lunar impact at the proper location and terminal velocity. During this time, the internal gyroscopes were used as an attitude reference as the spacecraft was pointed in the required direction. After the burn and cruise attitude had been reestablished, the relatively fragile gamma ray spectrometer boom would be deployed.
As Ranger approached the Moon, it would begin its terminal descent maneuver. The spacecraft would switch to its internal battery and turn so that its bottom was aligned with the Moon. After the high-gain antenna was once again pointed at Earth, the probe would begin to acquire television images starting about 32 minutes before impact at an altitude of 3,900 kilometers. Images would be taken every 13 seconds down to an altitude of 59 kilometers. Transmission of this last image, which was expected to reveal features as small as 3 meters across, would have been completed as the probe reached an altitude of only 24 kilometers.
Only 8.1 seconds before the bus crashed into the lunar surface at a speed of 2,900 meters per second, the radar altimeter would generate a fusing signal at an altitude of 21.4 kilometers. At that moment, bolt cutters would free the hard lander and retrorocket from the bus. A three nozzle spin motor would fire, lifting the package 0.8 meters above the bus and imparting a spin of 300 RPM. The retrorocket would then fire, slowing the capsule to a virtual stop at a height of only 335 meters above the lunar surface. Explosive bolts would cut the clamp holding the lander to its retrorocket and the two would be separated by springs. The hard lander would then free fall to the surface with an impact speed of 45 meters per second, give or take 9 meters per second.
Protected from the force of impact by its balsa wood shell, the lander would roll to a stop. The capsule floating freely inside the shell on a layer of liquid Freon was made to be bottom heavy so that it would settle into a horizontal position. After twenty minutes, plugs are blown out, allowing the 225 milliliters of heptane protecting the seismometer and the Freon to evaporate into the lunar vacuum, thus fixing the capsule in place and allowing the seismometer to operate correctly. The package would then transmit its findings on lunar seismic activity for the next one to three months. If it worked, the United States would have the first high-resolution pictures of the Moon as well as the first hard landing on its surface.
The Block II Ranger Flights
The first Block II Ranger, designated payload P-34 by NASA, lifted off on at 3:30 PM EST on January 26, 1962, after a four-day delay to fix a ruptured intertank insulation bulkhead in the Atlas 121D booster. As the Atlas-Agena B ascended towards its parking orbit, a component in its guidance system failed, disabling the radio command system needed to shutdown the engines at the precise time. Relying on its internal autopilot system, the Atlas placed the Agena 6003 escape stage and Ranger 3 into a parking orbit a bit higher and faster than planned. After a short coast, the Agena B came to life again and boosted the 330-kilogram Ranger 3 into an escape trajectory. Because of an incorrect constant in the Agena guidance program, Ranger 3 was thrown even farther off course. Early tracking indicated that Ranger 3 was operating properly but it would reach the Moon’s orbit 14 hours too early and miss the Moon by 32,000 kilometers – far too wide a miss for Ranger’s relatively small course correction engine to negate.
Since an impact was out of the question, NASA decided to exercise the various functions of the new Block II spacecraft as an engineering test and perform some flyby photography of the Moon. The first test was to perform a mid-course correction that would also bring Ranger 3 closer to the Moon. The course correction was performed the day after launch at 2:00 AM PST as instructed with an accuracy one quarter of one percent of speed and two and one half degrees of direction. Unfortunately, an undetected sign inversion in the instructions sent to the spacecraft resulted in the maneuver taking place in the wrong direction. Instead of pushing Ranger closer to the Moon, it moved the probe farther away, resulting in a flyby distance of 36,785 kilometers.
Forty hours after the attempted course correction and some 50,000 kilometers from the Moon, Ranger 3 was instructed to turn towards the Moon and begin imaging. Telemetry initially showed that everything was going according to plan, but Ranger’s computer and sequencer suddenly malfunctioned resulting in the spacecraft slowly rolling and unable to lock its high gain antenna on the Earth. The camera turned on and started transmitting images as instructed but, because of the misaligned antenna, only noisy images showing the camera’s fiducial marks illuminated by light scattering off of the spacecraft were received. Unable to properly transmit its images or accept further commands from Earth, Ranger 3 continued past the Moon and into a solar orbit with a perihelion of 147 million, an aphelion of 174 million kilometers and a period of 406 days. On January 31, Ranger’s supply of attitude control gas ran out and the spacecraft started tumbling effectively ending the mission. The only scientific data returned by the wayward lunar probe were 30 hours of background radiation readings from the gamma ray spectrometer.
On April 23, 1962 at 3:50 PM EST, the second Block II spacecraft, Ranger 4, was launched—after some delays—in the middle of its allotted launch window on Atlas 133D topped with Agena 6004. For the first time in the Ranger series, the Atlas-Agena B operated flawlessly, injecting the 331-kilogram Ranger 4 into a collision course with the Moon. Unfortunately, during the first tracking pass of the receding probe, it was discovered that Ranger’s master clock had stopped and the computer was not responding to ground commands. Unable to perform any functions, Ranger 4 continued on to the Moon and was tracked using the hard lander’s transmitter.
After sixty-four hours, the lifeless probe (whose batteries were depleted just hours earlier) skimmed the leading edge of the Moon and crashed on its far side at 15.5° south latitude and 130.5° west longitude in a crater later named Paschen. Ranger 4 became the first US probe to hit the Moon, but not quite in the manner that its designers had hoped. The second Ranger failure in a row indicated the need for much better quality control measures especially given the spacecraft’s lack of redundancy.
The Last Flight and Aftermath
All hopes now rode with the last Block II flight of Ranger 5. After an analysis of the previous failures, engineers made several improvements to the spacecraft. A hydraulic backup timer activated by the separation of the Agena escape stage was included to operate automatic functions and a ground commanded backup timer in the command encoder was included to allow direct ground control. Both changes would help avoid a repeat of the previous two failures. The modifications and addition of backup systems increased the mass of Ranger 5 to 342 kilograms.
Ranger 5 finally lifted off from LC-12 at Cape Canaveral at 12:59 PM EST on October 18, 1962. As it accelerated towards orbit, a portion of the guidance system of Atlas 148D failed — the same component failure that started a chain of events which led to the loss of Ranger’s cousin, the Venus-bound Mariner 1, just three months earlier. Fortunately, the error in the guidance program of the Atlas 145D that carried Mariner 1 was corrected in this booster’s program and Ranger 5 was successfully placed on a trajectory towards the Moon after the final burn from Agena 6005.
Unfortunately, Ranger’s recovery from its close brush with failure at launch was all for naught. About 75 minutes after getting underway, as Ranger 5 was obediently settling into its cruise attitude, a short circuit developed in its solar panels. Although the panels’ isolation diodes protected the power supply from immediate failure, Ranger now had no means of powering itself except with the small backup battery. Within hours, Ranger 5 died from lack of power just as a midcourse maneuver was being attempted as an engineering test. The probe was tracked to a distance of 1.27 million kilometers using the lander’s transmitter after Ranger 5 passed only 724 kilometers over the Moon’s trailing edge. The inert Ranger 5 continued on into a solar orbit with a perihelion of 142 million kilometers, an aphelion of 157 million kilometers and a period of 365 days.
With the loss of the last Block II Ranger, the entire program was deemed to be an utter failure. Investigations into the failure of the Ranger program started on October 30, 1962, and a month later NASA Headquarters released the findings of its inquiry. In brief, the report recommended streamlining management and changing the mission goals to be more in line with the needs of the new Apollo Moon program. The report also called for a thorough re-evaluation of the Ranger design, modifying vulnerable systems and including more backup systems. More extensive testing of systems and better quality control for components were recommended. Most of all, the report called for the immediate abandonment of sterilization. Sterilization was pinpointed as the cause of many of Ranger’s system failures and it was now felt to be unnecessary, given that the hostile lunar environment was unlikely to harbor any indigenous life forms. Unless these changes were made, the new Block III Rangers (which would carry an enlarged suite of television cameras to secure high resolution pictures of the lunar surface all the way to impact) were likely to suffer the same fate as its predecessors.
With these recommendations in hand, JPL set about redesigning and rebuilding the new Block III Rangers. The scheduled launch of what would be Ranger 6 was postponed to late 1963 (see “50 Years Ago Today: The Launch of Ranger 7”). NASA would now have to wait for the first launch of JPL’s new Surveyor spacecraft to get a shot at landing on the Moon. In the mean time, the Soviet Union started ramping up its efforts to land on the Moon first with their troubled E-6 spacecraft (see “50 Years Ago Today: The Launch of Luna 5”).
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Here is some silent newsreel footage from 1962 showing the preparation of Ranger 3 for launch.
Here is a brief newsreel of the launch of Ranger 3
Here is another brief newsreel about the launch of Ranger 4 (and an early Block I Saturn I launch).
“The Prototype That Conquered the Solar System”, Drew Ex Machina, September 15, 2015 [Post]
“50 Years Ago Today: The Launch of Ranger 7”, Drew Ex Machina, July 28, 2014 [Post]
“50 Years Ago Today: The Launch of Luna 5”, Drew Ex Machina, May 9, 2015 [Post]
R. Cargill Hall, Lunar Impact: The NASA History of Project Ranger, Dover Publishing, 2010
Paolo Ulivi with David M. Harland, Lunar Exploration: Human Pioneers and Robotic Surveyors, Springer-Praxis, 2004