Space enthusiasts of a certain age, like myself, grew up learning about the trio of NASA’s unmanned programs which provided scientists and engineers with vital information about the Moon before the Apollo landings: Ranger which took TV images of the lunar surface before they were purposely crashed into the Moon; Lunar Orbiter which acquired high-resolution photographs of the lunar surface to scout out potential Apollo landing sites; and Surveyor which soft landed on the Moon. Almost forgotten all these decades later is the series of largely unsuccessful lunar missions which preceded these well-known achievements. While painfully disappointing at the time, these failure provided vital experience to develop the technology as well as engineering and management practices needed to ensure successful space missions to the Moon and beyond. Among these forgotten missions was NASA’s ambitious Pioneer P-3 lunar orbiter mission launched in November of 1959.
Origins
Before NASA was founded on October 1, 1958, the USAF had ambitious plans for space exploration. During the national debate that followed the launch of the Soviet Sputnik on October 4, 1957, the USAF was trying to position itself so that it could dominate the nation’s infant space program. Even after the Advanced Research Projects Agency (ARPA) was founded in February of 1958 and given the task of coordinating America’s military space programs, USAF efforts and plans figured prominently.
The original three USAF Pioneer lunar orbiters from 1958 all suffered from failures of their Thor-Able launch vehicles. (STL/John Taber)
The first step beyond Earth orbit for the USAF, called Project Able-1, was a series of attempts to place a small spacecraft into orbit around the Moon. These orbiters, along with a pair of small US Army-JPL lunar flyby probes, were part of the ARPA-sponsored Operation Mona, which was approved by President Dwight Eisenhower on March 27, 1958. Three launch attempts made by the USAF between August and November of 1958, now called Pioneers 0, 1, and 2, all failed to reach the Moon (see “The First Moon Race: Getting Off the Ground“). But even before these missions flew, the USAF, in conjunction with the builders of their first lunar orbiters, STL (Space Technology Laboratory, a division of TRW), began to study follow-on missions not only to lunar orbit but also to Venus to be launched during the 1959 launch window. Little was known about Earth’s near-twin at this time and many believed Venus ranked with Mars as a likely abode for extraterrestrial life, making it a desirable target for exploration.
The launch of the Thor-Able carrying Pioneer 1 on October 11, 1958. (USAF)
But these new missions would require a rocket larger than the Thor-Able used for the first unsuccessful USAF lunar orbiter attempts. The Thor-Able was essentially a Thor IRBM topped with modified versions of the upper two stages of the Vanguard originally developed by the Naval Research Laboratory to launch America’s first satellites (see “Vanguard TV-3: America’s First Satellite Launch Attempt“). Initially built for high-speed reentry tests of ICBM warheads, the Thor-Able was quickly adapted into a satellite launch vehicle and NASA eventually developed it into the famous Delta launch vehicle family based on improved versions of the Able upper stages. With more advanced upper stages still under development, a logical short-term solution to the problem of lofting the larger USAF probes was to place the Able upper stages on a still larger rocket. In the end the USAF selected their Atlas ICBM and the Atlas-Able launch vehicle was born.
The Atlas-Able Launch Vehicle
The first stage of the Atlas-Able consisted of a modified Convair-built Atlas D ICBM which was over twice the size of the Thor. The Atlas program began in February of 1954 when it was recognized that an ICBM was a feasible weapon. The Atlas, which used an RP-1 grade of kerosene and liquid oxygen as propellants, employed an innovative stage-and-a-half design where a pair of Rocketdyne LR-89 booster engines and their supporting structure were jettisoned after they were no longer needed during ascent. A LR-105 sustainer engine would then push the payload towards its target feeding off of the remaining propellants in the missile’s lightweight integral propellant tanks. The advantage of this arrangement was that all three engines, generating a total of 1,600 kilonewtons of thrust, were ignited on the launch pad, thus avoiding the need for the then untried procedure of starting a large rocket engine in flight. Given the issues encountered over the years with the ignition of smaller rocket engines at altitude, this seemed like a wise precaution.
Diagram illustrating the major components of an early production version of the Atlas ICBM. Click on image to enlarge. (USAF)
The Atlas A through C models were used for test flights starting in June of 1957 at first to validate then, later, refine the design of this large missile (see “The First Atlas Test Flights”). A stripped-down “hot rod” version of the Atlas B was even launched into Earth orbit on December 18, 1958, carrying an experimental communication payload as part of ARPA’s Project SCORE (see “Vintage Micro: The Talking Atlas”). The Atlas D, eventually deployed operationally as an ICBM, was also designated for use as the booster for USAF launch vehicles with upper stages like the Agena and the advanced, hydrogen-fueled Centaur then under development (see “The Launch of Atlas-Centaur 5”). The Atlas D was also selected by NASA as the launch vehicle for the manned Mercury orbital missions. The first Atlas D test launch in April of 1959 failed, as did the next three attempts. The first Atlas D to meet its goals finally flew on July 28. After another successful flight from the Pacific Missile Range in California on September 9, the Atlas D was declared operational. But with only a 61% success record by November 1959, the Atlas D may have been considered “operational” but it was not yet very reliable.
A schematic diagram of the Atlas-Able launch vehicle. Click on image to enlarge. (STL)
The upper stages of the Atlas-Able, which were the responsibility of STL, were nearly identical to those used in the Thor-Able which in turn were adapted from the upper stages of the Vanguard launch vehicle. The second stage was 84 centimeters in diameter and about 6.7 meters long, 0.65 meters longer than the version flown on the Thor-Able. The other major difference in the second stage was the substitution of the lighter Aerojet AJ10-101 engine for the AJ10-42 used in the Thor-Able. The AJ10-101 used a highly toxic combination of UDMH (Unsymmetrical DiMethyl Hydrazine) and IRFNA (Inhibited Red Fuming Nitric Acid) to generate 34 kilonewtons of thrust. The X-248 solid rocket motor built by the Allegany Ballistic Laboratory topped off the stack, as it did on the Thor-Able and later versions of the Vanguard. It generated about 14 kilonewtons of thrust for 40 seconds. At launch, the Atlas-Able stood about 30 meters tall and weighed in at about 120 metric tons. Using a direct ascent trajectory (which does not use an interim parking orbit typically used today – a procedure yet to be developed) would allow the Atlas-Able to send payloads as great as 200 kilograms into an escape trajectory to the Moon or beyond.
Technicians preparing the Able second stage and its AJ-10 engine (to the left) for flight. (STL/John Taber)
The Birth of NASA’s P-3 Probe
After NASA started operations in October of 1958, virtually all purely scientific space programs run by the military were eventually transferred to the new civilian space agency. This included not only the remaining flights originally part of ARPA’s Operation Mona, but also the follow-on probes the USAF was planning. In November of 1958 NASA essentially adopted the existing USAF plans as part of their nascent Pioneer program and started work to launch a pair of probes to Venus during the June 1959 launch window. After this a lunar orbiter mission was planned. But these plans changed during the spring of 1959. After the successful launch of the Soviet Luna 1 in January 1959 (see “The Dream: The First Probe to the Moon”) and the failure of not only the first three USAF lunar orbiters but the first Army-JPL probe, Pioneer 3 (see “Pioneer 3: JPL’s First Moonshot Attempt”), the near-term goals of the Pioneer program were redirected.
NASA Explorer 6 satellite (also known as “Able-3” and “S-2”), launched in August of 1959, served as a prototype to test equipment to be used in STL’s future “paddle-wheel” probes like the Pioneer lunar orbiters. (NASA)
The new plan called for a series of spin-stabilized probes built by STL to be launched with each mission building on the experience of the earlier ones. The first was the “Able-3” mission. Designated as S-2 by NASA, this satellite was scheduled to be launched into an elongated 12-hour Earth orbit in August of 1959 using the Thor-Able. It would test the basic paddle-wheel spacecraft design and instruments while providing new data on the space environment close to the Earth. The next planned mission was the “Able 4 Atlas” mission, whose payload was designated as P-3 by NASA. The goal of this mission was to launch a probe into lunar orbit in September of 1959 using the new Atlas-Able. In November, “Able 4 Thor”, designated P-2 by NASA, would be launched on a deep space mission towards the orbit of Venus using a Thor-Able since there was insufficient time and resources to build and launch the originally planned Venus probe in time for the June 1959 launch window (see “Vintage Micro: The First Interplanetary Probe”).
NASA’s Pioneer 5 probe (also known as “Able 4 Thor” and “P-2”) was launched into solar orbit in March 1960 to explore interplanetary space. (NASA)
Ideally NASA officials would have wanted more time to improve the reliability of the Atlas-Able by replacing the Able stages with enhanced versions being developed for their Thor-Delta rocket program. But budget limitations brought on by the spiraling costs of other NASA programs, a lack of time and the fear of what the next Soviet space spectacular would bring did not allow for this option.
Technicians working on the Pioneer P-3 lunar orbiter. (STL/John Taber)
Despite the budget problems and tight schedule, the new STL-built P-3 lunar orbiter was the most advanced and massive NASA scientific spacecraft to date. The probe was a spin stabilized, aluminum alloy sphere one meter in diameter and a total height of 1.4 meters (including antennas) with a nominal mass of 169 kilograms. With no active attitude control system, the spinning probe essentially maintained the same orientation it had following launch for its entire mission. Attached to the exterior were four paddles 60 centimeters square each covered with 2,200 solar cells that would be deployed after launch to provide a maximum of 66 watts of electrical power. These paddles, with a total span of 2.7 meters once deployed following launch, provided power to the probe’s systems as well as kept its NiCad batteries continuously charged. The exterior also sported four aluminum dipole antennas to support the probe’s telecommunications system.
Diagram showing the Pioneer P-3 in its launch configuration inside its fiberglass launch shroud on top of the Atlas-Able. Click on image to enlarge.
At each end of the probe was a small monopropellant rocket engine generating 90 newtons of thrust. Either could be used in bursts of up to four seconds for course corrections during the 62-hour flight to the Moon while the forward-facing engine would provide a velocity change of 1,070 meters per second to place the probe into lunar orbit. The forward-facing engine was designed for up to two firings while the aft-facing engine was capable of four firings for midcourse and orbital maneuvers. For the first mission, a 5,060 by 5,420 kilometer orbit inclined 42° to the lunar equator with a period of 12 hours was planned for a nominal one-year mission. In case of an unexpected deviation in the approach trajectory and/or orbit insertion maneuver, mission objectives could be achieved with a perilune as low as 1,600 kilometers and an apolune as high as 16,000 kilometers. The 63 kilograms of hydrazine propellant for these engines was kept in a pressurized 66-centimeter diameter sphere at the heart of the probe. The hydrazine would spontaneously decompose inside the throat of the engines after it had passed over a bed of an aluminum oxide catalyst that had been preheated to 250° C at engine ignition by a 0.2-second hypergolic reaction between the hydrazine a small amount of nitrogen tetroxide injected into the engine at ignition.
The propulsion system for NASA’s Pioneer lunar orbiter was dominated by the spherical hydrazine tank in the center. One of the two diametrically opposing rocket engines is visible at the top along with nitrogen pressurization tanks. (STL/John Taber)
Thermal control to maintain the interior temperature in the required 4° C to 29° C range (with an ideal value of about 21° C) was provided by 52 four-blade black and white butterfly “fans” controlled by bimetallic coils. As they heated and expanded at temperatures above 24° C, the butterfly fans would open, exposing more white and less black to reflect heat. When cooled below 10° C, the butterfly fans would close, exposing more black to allow more heat to be absorbed. Also mounted on the exterior were a pair of square heat sinks to radiate heat generated by internal equipment like the transmitter and power converters. This complex thermal control system was required due to the amount of instrumentation carried as well as the more demanding and varied thermal environment this mission would encounter compared to earlier spacecraft which employed a simpler, passive thermal control system.
The Pioneer P-3 Scientific Payload
The P-3 probe carried an impressive suite of scientific instruments with a total mass of nine kilograms. These instruments included:
Diagram showing the arrangement of internal equipment of the Pioneer lunar orbiter. Click on image to enlarge. (NASA)
A cosmic ray telescope developed by the University of Chicago. This 2.3-kilogram instrument consisted of a cluster of seven argon-filled cylinders wrapped in a thin layer of lead used to detect electrons with energies greater than 12 MeV and protons in excess of 70 MeV from cosmic rays, trapped radiation in the Earth’s magnetic field or coming from the Sun.
A total radiation flux counter, developed by the University of Minnesota, which consisted of a 1.2-cm in diameter metal ball filled with argon acting as an ionization chamber to measure integrated radiation exposure and a Geiger-Mueller tube similar to those carried earlier by the JPL-built Pioneer 3 and 4 probes (see “Vintage Micro: The Pioneer 4 Lunar Probe”) and Explorer satellites. This 0.9-kilogram instrument was designed to detect medium-energy radiation in the space environment.
A scintillation counter consisting of a 2.5-centimeter cylinder of plastic fitted with a photomultiplier tube which would detect flashes of light generated by radiation passing through the device. Developed by STL, this 1.5-kilogram instrument was designed to characterize low-energy radiation.
A 1.1-kilogram flux-gate magnetometer developed by STL was carried to measure the magnetic fields of the Earth and Moon as strong as 0.32 teslas along one axis of the P-3 spacecraft.
A search-coil magnetometer was also carried to measure the magnetic field strength. Built by STL as well, this 0.5-kilogram instrument used a sensor consisting of a mu-metal (a soft ferromagnetic alloy of iron and nickel) core surrounded by 5,000 turns of fine No. 40 copper wire. This instrument was capable of measuring magnetic fields in the 10-4 to 0.1 tesla range. The combination of the data from this instrument and the flux-gate magnetometer would allow the measurement of the strength, direction, and distribution of the magnetic field in the space environment.
A micrometeoroid detector was carried by the P-3 probe. It consisted of a pair of metal plates mounted on the exterior of the probe which were fitted with microphones to sense and characterize impacts.
The P-3 also carried a primitive scanning imager to create images of the Moon including the first views of the previously unseen far side. This 1.1-kilogram instrument consisted of a 5-centimeter mirror that focused an image onto a photocell whose measured brightness was converted into one of eight possible values that were recorded on magnetic tape for later transmission back to Earth. With the device canted at a 45° angle to the satellite’s spin axis, the imager relied on the 150 rpm spin of the probe to scan a line across its target and the probe’s forward motion to build up an image one scan line at a time. With each rotation of the satellite, a single brightness value along the scan line was measured and recorded. This process was repeated 128 times for each line of the image before the scanning of the next 128-pixel line started. A prototype of this instrument was successfully tested on Explorer 6 to produce the first (very crude!) image of the Earth acquired by an orbiting satellite (see “First Pictures: View of the Earth from NASA’s Explorer 6 – August 14, 1959”).
This is the publicly released image of the Earth taken by Explorer 6 on August 14, 1959. (NASA)
A small but highly sensitive VLF receiver built by Stanford University was carried to monitor natural radio emission at a frequency of about 15 kHz using a simple dipole antenna protruding from the bottom of the probe. These observation were expected to provide information on the motions of plasma in the environment and give additional insights on the radiation and magnetic fields in space.
The P-3 spacecraft also carried a pair of radio transponders which could be used to measure the electron density between the Earth and probe by means of subtle time delays in the round trip time of the signals.
In order to determine the orientation of the spinning P-3 probe to help interpret the data collected by its instrument, an aspect sensor consisting of a small photocell on the exterior of the spacecraft was carried to measure the angle relative to the Sun.
The P-3 probe carried a pair of redundant five-watt UHF transmitters operating at a frequency of 378 MHz. Data were typically transmitted back to Earth in real time using the STL-developed Telebit digital telemetry system. When the satellite was not in view of an Earth-based tracking station, data could be recorded for subsequent download. A pair of redundant command receivers were carried with provisions to initiate 20 different functions including the control of the probe’s propulsion system. The total mass of the scientific instruments, telemetry system, and the power supply was 55 kilograms.
The solar panels of the Pioneer P-3 payload being attached in preparation for launch. (General Dynamics/SDASM)
The P-3 Mission
The biggest obstacle for getting the new Pioneer P-3 lunar orbiter mission off the ground was the availability of Atlas D missiles for the probe’s launch vehicle. The assembly lines at General Dynamic’s Convair division in San Diego, California simply could not keep up with the demand for the missile. While still important to national prestige, NASA’s new Moon probe had lower priority than defense programs and NASA’s Project Mercury. In order to get their first new Pioneer launched during a four-day launch window opening on October 3, 1959, officials decided to substitute a surplus Atlas C as the booster—the only C-model to be used in a space shot.
A view of the Atlas 9C and its Able stages with the rocket’s gantry rolled back on September 21, 1959. (General Dynamics/SDASM)
In preparation for the launch of the Pioneer P-3 mission, Atlas 9C was erected on the pad at Launch Complex 12 (LC-12) on Cape Canaveral on August 27, 1959. Following its initial checkout on the pad, the Able upper stages were added to the stack. The program suffered its first major setback during what was supposed to be a routine 24-second flight readiness firing of the Atlas 9C on September 24. Seconds after starting the test, a propellant line in the Atlas ruptured starting a fire in the rocket’s aft compartment. Although the engines had shut down after only a few seconds, the fire continued and eventually resulted in an explosion that destroyed the rocket and badly damaged the launch pad. Fortunately the P-3 payload was not attached.
For the next attempt, NASA diverted an Atlas D from its Mercury program to serve as the booster. Atlas 20D was originally slated to be the backup launch vehicle for Mercury’s Big Joe unmanned test flight and was no longer needed after the mission met its objectives (see “Giving Mercury Its Wings: The First Test Flights of NASA’s Mercury Program“). With insufficient time to meet the next launch window opening at the end of October, the launch attempt was moved out to a window opening on November 26. With LC-12 out of commission, Atlas 20D was erected on the pad at LC-14 on October 19 to begin preparations for a launch. Unfortunately, the Soviet Luna 3 mission launched on October 6 had already successfully returned the first images of the lunar far side so NASA had once again lost out on another potential space first (see “Luna 3: Shedding Light on the ‘Dark Side’ of the Moon”). Mating of the Able upper stages began on November 9 with the P-3 payload topping the stack 13 days later.
The erection of Atlas 20D on the pad at LC-14 on October 19, 1959. (General Dynamics/SDASM
On November 26, 1959, the first Atlas-Able with the 169-kilogram Pioneer P-3 lifted off from LC-14 at 2:26 AM EST. All was going well until about 45 seconds into the flight when the bulbous fiberglass payload shroud ripped away under the aerodynamic loads, destroying the third stage and probe in the process. The second stage continued transmitting telemetry for another minute and radar confirmed that its AJ-10 engine had ignited but, the mission was already a complete loss.
The launch of the Pioneer P-3 lunar orbiter on November 26, 1959 from LC-14 at Cape Canaveral, Florida. (USAF)
A subsequent investigation into the problem found that excess pressure building up inside the shroud as the exterior air pressure rapidly decreased during ascent caused a structural failure of the new launch shroud. This was corrected by simply drilling some tiny bleed holes into the shroud to help the pressure equalize more quickly. But, with limited funds and no Atlas D rockets readily available to launch a successor to the Pioneer P-3 lunar orbiter, NASA would have to wait ten months before there was a reflight of this ambitious spacecraft.
Related Reading
“Vintage Micro: The First Interplanetary Probe”, Drew Ex Machina, April 17, 2015 [Post]
“The First Moon Race: Getting Off the Ground”, Drew Ex Machina, November 8, 2018 [Post]
“The First Moon Race: Reaching Our Neighbor”, Drew Ex Machina, September 14, 2019 [Post]
“First Pictures: View of the Earth from NASA’s Explorer 6 – August 14, 1959”, Drew Ex Machina, August 14, 2024 [Post]
General References
P.F. Glaser and E.R. Spangler, “The Able-5 Lunar Satellite”, STL report, 1960
Keith J. Scala, “Atlas-Able: A Forgotten Failure”, Quest, Vol. 4, No. 1, pp. 36-37, Spring 1995
Chuck Walker with Joel Powell, Atlas – The Ultimate Weapon, Apogee Books, 2005
“A Development Plan for Two Interplanetary Probes (Able 4)”, STL report, 14 January 1959
“Development Plan for Able 3-4 (Earth Satellite, Lunar Satellite, Deep Space Probe)”, STL report, 1 June 1959
“Atlas Able IV Vehicle Destroyed”, Aviation Week, Vol. 71, No. 13, p. 30, September 28, 1959
“Attempt to Launch Lunar-Orbiting Payload Fails”, Aviation Week, Vol. 71, No. 23, pp. 52-53, December 7, 1959
“Atlas-Able IV Instrumentation Detailed”, Aviation Week, Vol. 71, No. 24, pp. 53-57, December 14, 1959
“Atlas Able IV”, STL Space Log, Vol 1., No. 2, pp. 19-20, September 1960