With the new push by the United States and other space faring powers to renew the exploration of the Moon, miniaturized spacecraft have been made part of the mix to test new technologies and perform scientific investigations of our nearest neighbor. But the use of such small probes to explore the Moon is hardly new. During the opening years of the Space Age, the US launched a number of lightweight spacecraft towards the Moon primarily due to the limited payload capabilities of the earliest American launch vehicles.
On March 27, 1958 President Eisenhower approved a plan for the Defense Department’s new Advance Research Projects Agency (ARPA) to launch a series of five missions to the Moon over the following year as part of “Operation Mona” with the hope of beating the Soviet Union to the Moon. The first missions to be launched were a United States Air Force (USAF) proposal to use their Thor-Able rocket, which had been originally developed for high-speed reentry tests, to launch three probes with the ambitious goal of orbiting the Moon. With masses just under 40 kilograms, these first orbiters of the USAF Project Able-1, as it was called, would meet today’s definition of “microsatellites”. Following these missions, a pair of more modest missions developed by the Army Ballistic Missile Agency (ABMA) and the Jet Propulsion Laboratory (JPL) at the California Institute of Technology would be launched to flyby the Moon.
A view of the lunar orbiter built for the USAF Project Able-1. (STL/John Taber)
The first Thor-Able carrying a lunar orbiter was launched on August 17, 1958 but exploded only 77 seconds into its flight due to an engine failure on the Thor first stage (see “USAF Project Able-1: The First Attempt to Reach the Moon”). But before the second launch was attempted, control of all of the ARPA-sponsored scientific space projects, including the lunar probes, was transferred to the newly formed NASA in October with the military relegated to an advisory role. NASA’s first official space mission, the second USAF Thor-Able lunar orbiter, was launched on October 11, 1958 and subsequently designated Pioneer 1. Unfortunately, Pioneer 1 ended up with a 152 meter per second velocity shortfall and reached a peak altitude of only 114,000 kilometers before falling back to Earth 43 hours after launch (see “Pioneer 1: NASA’s First Space Mission”). The final lunar orbiter mission of this initial round was launched on November 7 but Pioneer 2, as it was called, reached a peak altitude of only 1,550 kilometers due to an ignition failure of the Thor-Able third stage.
The ABMA-JPL Pioneers
The project which would launch the second round of American probes towards the Moon had its origin in a proposal by JPL (which would be transferred to NASA in December 1958) and ABMA (parts of which would become NASA’s Marshall Space Flight Center in 1960) to launch a pair of small space probes on escape trajectories using a modified version of ABMA’s Jupiter IRBM during the International Geophysical Year – a cooperative international scientific study of the Earth and its interaction with the Sun running from July 1957 to December 1958. JPL and ABMA were already involved in a number of cooperative space-related programs at this time including one that culminated in the launch of America’s first satellite, Explorer 1, on January 31, 1958 using a highly modified Redstone rocket known as the Juno I launch vehicle (see “Explorer 1: America’s First Satellite”). After the launch of the Soviet Union’s first two Sputnik satellites in the fall of 1957 (see “Sputnik: The Launch of the Space Age” and “Sputnik 2: The First Animal in Orbit”), development of a pair of lunar probes using what would become the Juno II launch vehicle started in November 1957 under the codename “Red Socks”.
Diagram showing the high-speed stage and trajectory to the Moon for JPL’s original Project Red Socks proposal. Click on image to enlarge. (JPL)
For the first stage of the Juno II launch vehicle, Jupiter’s RP-1 and LOX tanks retained their original 2.67-meter diameter but were lengthened by a total of 0.92 meters making the rocket 16.84 meters long. This prolonged the burn time of the 668 kilonewton thrust Rocketdyne S3D engine by 20 seconds to a total of 182 seconds. Mounted on top of the modified Jupiter first stage under an aerodynamic shroud was the “high speed assembly” consisting of an instrument compartment and a three-stage solid rocket cluster developed by JPL and similar to that used on ABMA’s Juno I rocket. This cluster of rocket motors was a spin-stabilized tub of 11 scaled-down JPL Sergeant rockets with a ring of seven used for the second stage, three for the third and a single motor for the fourth stage. Modifications of this cluster from the version used on the Juno I and earlier Jupiter-C used for high-speed reentry tests included filling the third and fourth stages with a higher performance propellant and changing the original stainless steel casing of the fourth stage to a lighter weight titanium casing. The 55-metric ton Juno II was designed to place 43 kilograms of payload in a 480-kilometer-high Earth orbit or up to 7 kilograms of useful payload on a direct ascent escape trajectory.
Diagram of the Juno II lunar mission launch sequence and the “Juno IIA” payload. Click on image to enlarge. (JPL/NASA)
On May 2, 1958 ABMA officially contracted JPL to develop and build four of the tiny lunar probes of which two would be launched on missions designated “Juno IIA” and “Juno IIA-Prime”. With a mass of just 6.67 kilograms each (which would qualify them as “nanosatellites” by today’s definition), the probes were a 23-centimeter-wide cone with an 8-centimeter spike antenna on the top. They were 51 centimeters long with an exterior housing constructed of gold-washed fiberglass. The exterior was gold plated and striped with paint for passive thermal control. The electrically conductive gold plating on the cone also served as an unsymmetrical dipole antenna element in conjunction with the spike antenna. At the squat cylindrical base of the probe was a despin mechanism consisting of two 1.5-meter-long weighted wires. A hydraulic timer would release the wires ten hours after launch. As the wires unwound, the payload’s spin rate would decrease from 400 to 11 revolutions per minute. Located inside the probe was a 500-gram UHF transmitter operating at a frequency of 960 MHz with an effective power of 180 milliwatts. The power supply for the transmitter and instruments consisted of a set of eighteen mercury cells.
Diagram showing the interior arrangement of the JPL Pioneer lunar probe. Click on image to enlarge. (JPL)
Originally these JPL-built lunar probes were to carry a tiny 35 mm photographic package capable of obtaining a single photograph of the Moon’s far side during a lunar flyby. A photoelectric triggering device would trip the camera’s shutter when the Moon was in the detector’s field of view and closer than 32,000 kilometers. The photograph would then be developed and scanned. By September of 1958, the design of this system had been finalized and parts of it were under development testing. But with the discovery of the Van Allen radiation belts surrounding the Earth by the first Explorer satellites during 1958, the JPL Moon probes’ primary instrument was changed to a pair of Geiger-Mueller tubes to obtain data on the radiation environment between the Earth and Moon. The original photoelectric triggering device along with the despin mechanism (needed to slow the probe’s rotation in order to allow photography) were retained as engineering tests for future systems.
An exploded view of an unflown Juno IIA payload currently in the Smithsonian National Air & Space Museum collection. (NASM)
With the new instrument, the desired mission of this probe was also altered. Instead of a close flyby, the probe was now intended to impact the lunar surface 33 hours and 45 minutes after launch when the Moon was best positioned to be seen by the Goldstone tracking station. But given the inherent inaccuracy of direct ascent trajectories, the relatively crude nature of the Juno II solid rockets and the guidance system, as well as the lack of any course correction capability, the JPL-ABMA probes would be lucky to make it anywhere near the Moon never mind hit it. Nonetheless, at this early stage of space exploration a lunar flyby was just as valuable scientifically as a direct hit. September of 1958 was initially set as the tentative launch date for their first ABMA-JPL Moon shot.
The 26-meter tracking antenna at the Goldstone Station that was used on early lunar and planetary missions as it appeared shortly after its completion in 1958. (NASA/JPL)
Tracking of the probes would be performed using a facility employing a 3-meter antenna in Mayaguez, Puerto Rico during the early phases of the mission. As the probe receded farther from the Earth, a 26-meter antenna at the new Deep Space Instrumentation Facility known as the “Goldstone Station” at Camp Irwin in California’s Mojave Desert would be used. This latter facility would become the basis of the Deep Space Tracking Network that would communicate with NASA’s lunar and planetary spacecraft for decades to come. The probe’s coordinates, Doppler velocity and telemetry data would be channeled directly from these tracking stations to JPL in Pasadena, California for reduction and analysis using a then state-of-the-art IBM 704 mainframe computer capable of up to 12,000 floating-point additions per second.
The First Launch Attempt
With the last Pioneer lunar orbiter flight launched in November 1958, NASA’s lunar hopes turned to the pair of smaller JPL-ABMA Pioneer flyby probes. Trajectory requirements to reach the Moon while the probe was in view of the Goldstone station dictated a 50-minute launch window on December 6 followed by daily 80-minute windows on December 7 through 12.
Pioneer 3 with the Juno II last stage shown being hoisted atop its launch vehicle on December 1, 1958. (NASA/MSFC)
With the Jupiter Round AM-11 already on its launch pedestal at Launch Complex 5 (LC-5) at Cape Canaveral by the end of November, the JPL-built high-speed assembly was added to the stack at 8:00 AM EST on December 1. With the final pre-launch testing completed, the countdown was started at T-9 hours at 12:40 PM EST on December 5. Including 185 minutes of built-in hold time in the countdown, launch was expected at just before 12:45 AM EST.
A long-exposure photograph of the roll back of the gantry at LC-5 prior to the launch of Pioneer 3 on December 6, 1958. (NASA)
The Juno IIA mission lifted off from LC-5 at 12:44:52.3 AM EST (05:44:52.3 GMT) on December 6, 1958 – just four seconds after the optimum launch time in its 50-minute launch window. While at first the launch of what was now designated Pioneer 3 looked good, a review of the launch telemetry showed that the Jupiter booster had cut-off 3.7 seconds too early due to a failure in the propellant tank depletion sensors resulting in a 382 meter per second velocity shortfall at the ignition of the high-speed assembly. Minor dispersions during the burns of the upper three stages resulted in a trajectory with Pioneer 3 travelling 1.1° lower and 4.6° farther south than planned. As a result, Pioneer 3 had failed to reach escape velocity just like its USAF predecessors.
This diagram illustrates the nominal launch sequence of Pioneer 3. Click on image to enlarge.
The initial plan was for the tracking facility in Mayaguez, Puerto Rico to acquire Pioneer 3 about five minutes after launch with the more capable facility at Goldstone station taking over about six hours after launch when the probe rose above the horizon in California. With Pioneer 3 now following the wrong trajectory, there was a scramble to acquire the receding probe’s signal and obtain whatever engineering and science data was possible in order to salvage something from the mission. The USAF Millstone Hill facility located in Westford, Massachusetts briefly tracked the probe but acquired no data. The Jodrell Bank radiotelescope located outside Manchester, England (now called the Lovell Telescope) tracked Pioneer 3 for a portion of its flight but suffered a temporary equipment failure. Eventually Goldstone acquired the wayward probe to continue tracking. Telemetry from Pioneer 3 indicated that its despin mechanism failed to operate at 15:30:00 GMT as intended leaving the probe spinning at the rate of 415 rpm instead of the slower 11 rpm. The probe’s passive thermal control system operated as designed with the internal temperature at 43° C.
Diagram showing the trajectory of Pioneer 3 through Earth’s Van Allen radiation belts with the distances measured from the center of the Earth. Click on image to enlarge (JPL/NASA)
Pioneer 3 reached a peak altitude of only 102,300 kilometers before it arced back to Earth and burned up at 16.4° N, 18.6° E over what is today the African nation of Chad at 19:51 GMT on December 7 some 38 hours and 6 minutes after launch. Despite the failure, data were received from Pioneer 3 for about 25 hours of its flight making measurements that confirmed the extent of Earth’s then newly discovered Van Allen radiation belt and found a second belt between 16,000 and 64,000 kilometers above the Earth. While scientifically important, it still did not make up for the fact that yet another American spacecraft had failed to reach the Moon.
This illustration provides a modern view of Earth’s Van Allen radiation belts. (JHU/APL/LASP)
With the failure of Pioneer 3 to reach the Moon, two additional probes – serial numbers 3 and 4 which were flight spares from the original Juno IIA mission – were modified and prepared so that one could be launched on the Juno IIA-Prime mission (see “Vintage Micro: The Pioneer 4 Lunar Probe”).
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Related Reading
“The First Race to the Moon: Getting Off the Ground”, Drew Ex Machina, November 8, 2018 [Post]
“Vintage Micro: The Pioneer 4 Lunar Probe”, Drew Ex Machina, August 2, 2014 [Post]
General References
Evert Clark, “Radiation Belt Explored by Army’s Pioneer III Probe”, Aviation Week, Vol. 69, No. 24, pp. 28-31, December 15, 1958
M. Eimer, A.R. Hibbs and R. Stevens, “Tracking the Moon Probes”, in Space Research: Proceedings of the First International Space Science Symposium, edited by Hilde Kallmann Bijl, Interscience Publishers, pp. 518-531, 1960
Conrad S. Josias, “Radiation Instrumentation Electronics for the Pioneers III and IV Space Probes”, Proceedings of the IRE, Vol. 48, No. 4, pp. 735-743, April 1960
William H. Pickering, “History of the Juno Cluster System”, in Astronautical Engineering and Science, edited by Ernst Stuhlinger, Frederick I. Ordway III, Jerry C. McCall, and George C. Bucher, McGraw-Hill Book Co., pp. 203-214, 1963
Allen E. Wolfe, “Juno Final Report Volume II Juno II: Space Probes”, JPL Technical Report No. 32-31, September 12, 1961
The Moon Probe Pioneer IV, NASA-JPL, c1959