Back when I was growing up in the heyday of the Apollo program, all young space enthusiasts like myself knew about NASA’s trio of unmanned lunar programs that had flown before the manned expeditions to the Moon: Ranger, Surveyor and Lunar Orbiter. But these missions were preceded by yet another NASA lunar program that is now almost completely forgotten. The Pioneer program, which NASA had inherited from the US Air Force (USAF) shortly after the space agency was founded in October 1958, included three attempts to launch an advance spacecraft to orbit the Moon between November 1959 and December 1960 six years before NASA’s first spacecraft in the Lunar Orbiter series was ever launched. Had these missions succeeded, they would have added greatly to our early understanding of the Moon and given the new NASA a spectacular space first. Unfortunately, the failure of all three of these missions not only quashed NASA’s early lunar ambitions, but relegated this short-lived program to obscurity.

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 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.

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. 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 was born.

The Atlas-Able

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.

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 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.

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 rocket. 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 Allegheny 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.

By the fall of 1959, the Able combination along with its cousin, the Vanguard upper stages, had an abysmal performance record. In total, Able and its relatives had flown successfully only six times out of their first sixteen opportunities. Combined with the less than stellar success record of the Atlas at that time, things were bound to go wrong with the Atlas-Able.

A Change of Plans

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 and the failure of not only the first three USAF lunar orbiters but the first Army-JPL probe, Pioneer 3, the near-term goals of the Pioneer program were redirected.

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 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-1 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.

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 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.

Despite the budget problems and tight schedule, the new STL-built lunar orbiters were the most advanced American spacecraft to date. The probe was a spin stabilized, aluminum alloy sphere one meter in diameter with a nominal mass of 165 kilograms. With no active attitude control system, the spinning probe essentially maintained the same orientation it had after 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. These paddles, with a total span of 2.7 meters once deployed, provided power to the probe’s systems as well as kept its NiCad batteries charged.

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 2.6-day 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. 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.

Thermal control was provided by 50 four-blade black and white butterfly fans controlled by bimetallic coils. As they heated and expanded, the butterfly fans would open, exposing more white and less black to reflect heat. When cooled, the butterfly fans would close, exposing more black to allow more heat to be absorbed. Also mounted to the exterior were a pair of square heat sinks to radiate heat generated by internal equipment. This complex thermal control system was required due to the amount of instrumentation carried and the more demanding thermal environment this mission would encounter compared to earlier spacecraft which employed a simpler, passive thermal control system.

Each probe carried 8.8 kilograms of instruments to measure the magnetic and radiation environment around the Moon. In addition, a simple scanning imager was carried to return the first images of the unseen lunar far side. Similar to models carried by the earlier USAF lunar orbiters, it would rely on a combination of the orbiter’s 120 to 180 rpm spin and its forward motion in lunar orbit to build up a crude 128 by 128-pixel image of the scene below. All of these instruments were tested by S-2 which was renamed Explorer 6 when it was launched on the first fully successful flight of the Thor-Able on August 7, 1959.

The Missions

The biggest obstacle for the new Pioneer Moon program was the availability of Atlas D missiles. 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 probes had lower priority than defense programs and NASA’s Project Mercury. In order to get their first new Pioneer launched on the scheduled date of 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. The Atlas C, in addition to continuing the testing of the series, was used for the training of missile crews. But the program suffered its first setback during what was suppose to be a 24-second flight readiness firing of the Atlas 9C at Launch Complex 12 at the Atlantic Missile Range (AMR) at Cape Canaveral, Florida on September 24, 1959. Seconds after starting the test, a propellant line ruptured starting a fire in the rocket’s aft compartment. Although the engines had shutdown after only a few seconds, the fire continued and eventually resulted in an explosion that destroyed the rocket and launch pad. Fortunately the payload was not attached (see the Related Video section at the end of this article for a brief video of this test).

For the next attempt, NASA diverted an Atlas D from its Mercury program. Atlas 20D was originally the backup launch vehicle for Mercury’s Big Joe unmanned test flight and was no longer needed (see “Giving Mercury Its Wings: The First Test Flights of NASA’s Mercury Program“). On November 26, 1959, Atlas-Able with the 169-kilogram Pioneer P-3 lifted off from Launch Complex 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 engine had ignited but the mission was already a complete loss. The problem was found to be excess pressure building up inside the shroud during ascent. This was corrected by drilling some tiny bleed holes into the shroud to help the pressure equalize.

With the loss of the P-3 payload, in April of 1960 NASA authorized the building of a new pair of 176-kilogram “Able-5” probes designated P-30 and P-31. Similar to the earlier P-3, these probes included a number of minor design refinements and replaced the camera with additional instruments to characterize the radiation environment near the Moon. Since the Soviet Luna 3 had already photographed the far side of the Moon in October 1959, the comparatively primitive camera carried by Pioneer was now considered redundant (see “Luna 3: Casting Light on the ‘Dark Side’ of the Moon“). The new probes would be placed into a 2,300 by 4,000 kilometer orbit around the Moon. A shortage of Atlas D missiles, a lack of funding, and scheduling conflicts with other programs for the only two available Atlas launch pads at Cape Canaveral forced NASA to delay the next Pioneer lunar orbiter launch. In the mean time, NASA’s P-2 deep space probe, rechristened Pioneer 5, was launched on March 11, 1960, using a Thor-Able. Despite months of delays, Pioneer 5 would prove to be the most successful of the original STL-built Pioneer spacecraft (see “Vintage Micro: The First Interplanetary Probe”).

After a months-long wait for an Atlas booster and an available launch pad, another Atlas-Able and its Pioneer P-30 payload were prepared for a launch from the rebuilt LC-12 scheduled for September 23, 1960. After a postponement due to high winds and heavy rain from Tropical Storm Florence, NASA’s first launch of the Atlas-Able V series finally lifted of at 10:13 AM EST on September 25, 1960. While the Atlas 80D booster operated as intended with a 275-second burn, the oxidizer system in the second stage’s AJ-10 engine malfunctioned resulting in the engine developing only 70% thrust. A further malfunction caused the ascending rocket to start tumbling. The third stage fired upon command from the ground and the probe, which would have been called “Pioneer 6”, successfully fired its own propulsion system to separate from the spent rocket motor making it the first time a spacecraft successfully ignited its own engine in space. But without attaining the proper velocity and far off course, the payload was destroyed upon reentry 17 minutes after launch.

The last Pioneer lunar orbiter, P-31, was launched from Pad 12 at 3:40 AM on December 15, 1960. Like too many Atlas flights at that time, the Atlas 91D booster exploded at an altitude of 12 kilometers after only 68 seconds of powered flight. A subsequent investigation cleared the Atlas D and showed that the second stage had ignited prematurely, resulting in the collapse of the Atlas missile’s forward bulkhead and destruction of the ascending rocket. With this last failure, NASA had nothing to show after an expenditure of $40 million (about $300 million in today’s dollars). Given the poor performance of the Atlas-Able and the fact that lunar missions with newer designs were already being developed (see “The Prototype That Conquered the Solar System”), the Pioneer lunar orbiter program was cancelled.

In the end, seven out of eight of America’s first probes to the Moon launched between August 1958 and the December 1960 were failures. Only the diminutive 6.1-kilogram Army-JPL Pioneer 4 launched on March 3, 1959, by a team led by famed German rocket engineer Wernher von Braun managed to escape the Earth and make it anywhere near the Moon (see “The First Moon Race: Reaching Our Neighbor“). During this same time, the Soviet Union managed three spectacularly successful missions that were the first to fly by the Moon (Luna 1), the first to impact the Moon (Luna 2), and the first to photograph the unseen far side (Luna 3). Although the Soviet Union also suffered a half-dozen failures during this period, they were kept secret, unlike America’s very public failures. Today’s lunar missions owe much to the lessons learned from the successes and failures of these early Soviet and American missions.

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Related Video

Here is silent footage of the failure of the Atlas 9C booster during the static test firing of the first Atlas-Able on September 24, 1959.

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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]

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

Michael Yaffe, “Scientists Analyze Lunar Orbit Failure”, Aviation Week, p. 34, October 3, 1960

“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

“’Propeller Blades’ Control Able IV Heat”, Aviation Week, p. 28, September 7, 1959

“Attempt to Launch Lunar-Orbiting Payload Fails”, Aviation Week, pp. 52-53, December 7, 1959

“Atlas Able IV”, STL Space Log, Vol 1., No. 2, pp. 19-20, September 1960