The First Atlas Test Flights

ULA’s Atlas V is one of the most powerful launch vehicles currently available in the United States and it is certainly among the most reliable rockets ever. Although it bears little resemblance to its ancestors as a result of decades of evolutionary changes and a major redesign at the beginning of this century, the Atlas V is the latest in the exceptionally long-lived Atlas family of launch vehicles. While today the Atlas is used to launch payloads into Earth orbit and beyond, this rocket actually started its career before the dawn of the Space Age as weapon system and, in contrast to its record of high reliability today, it was initially a very unreliable rocket.

The Birth of Atlas

The SM-65 Atlas program, which initially went by the name “Weapon System 107A”, began in February of 1954 after several studies had concluded that an intercontinental ballistic missile (ICBM) was a practical system for the long-range delivery of nuclear weapons. Because of its early ICBM-related research and development work, the Convair Division of General Dynamics (which today is part of Lockheed Martin) became the prime contractor of the Atlas program in January 1955. By June the project was given an “A-1” priority which placed it first in line for the nation’s engineering and material resources with an initial operational capability expected in the 1960 to 1962 timeframe.

Diagram illustrating the major components of an early production version of the SM-65 Atlas ICBM. Click on image to enlarge. (USAF)

Unlike most rockets at the time or since, the Atlas did not rely on conventional aircraft-style construction where the propellant tanks and exterior shell were attached separately to an internal framework which supported all the structural loads. Instead the Atlas used the same thin stainless steel structure to act as both the outer shell and propellant tanks with internal pressure providing the rigidity needed to keep it from collapsing. This balloon or integral tank-type structure was successfully tested by Convair on their MX-774 rocket which flew three times in 1948 from the missile range at White Sands, New Mexico. With a diameter of 3 meters and a total length of about 24 meters, the stainless steel structure of the Atlas was no thicker than one millimeter (about the thickness of an American dime) which resulted in an immense weight savings and a range of on the order of 15,000 kilometers without the need of a second stage.

The balloon or integral-type tanks used by Atlas were first flight tested by Convair on their MX-774 technology demonstrator in 1948.

Convair, working together with engineers from North American Aviation’s Rocketdyne Division (today part of Aerojet Rocketdyne), developed an innovative engine arrangement to power the Atlas. Rocketdyne already had practical experience with relatively large 500-kilonewton-class rocket engines as a result of their development work on the rocket boosters for the various incarnations of North American’s XSM-64 Navaho supersonic cruise missile. Derived from the XLR-43-series of engines, these power plants would serve as the starting point of not only the engines employed by the Atlas but the similar sized MB-3 used on Thor-based rockets as well as the H-1 employed by the Saturn I and IB launch vehicles. For the initial production versions of the Atlas, a pair of 687-kilonewton LR-89 booster engines were combined with a single LR-105 sustainer engine generating 253 kilonewtons of thrust in a propulsion system designated MA-2. A pair of LR-101 “vernier” engines producing just 4.4 kilonewtons of thrust each were mounted on either side of the Atlas to provide roll control during powered flight and trim the velocity of the ICBM after the larger engines had shutdown to ensure accurate targeting of its nuclear warhead.

Rocketdyne used its experience developing the engines for the rocket booster of the XSM-64 Navaho supersonic cruise missile to build the engines used for the Atlas. (USAF)

For the MA-2 propulsion system, all three of these engines would ignite on the launch pad to get the Atlas off the ground. After the ascending rocket had shed enough mass and gained sufficient altitude, it would jettison the pair of booster engines and their supporting structure. Greatly lightened, the Atlas would continue to accelerate towards its distant target powered by the single sustainer engine and the pair of verniers feeding off the remaining RP-1 grade kerosene and liquid oxygen (LOX) propellants in the tanks. This “stage and a half” arrangement eliminated the need of developing the untried procedure of igniting a large rocket engine at high altitude as would be required in a conventional multi-stage ICBM design and greatly improved the performance of the Atlas in the process.

Diagram showing the configuration of the Rocketdyne propulsion system developed for the Atlas. Click on image to enlarge. (Rocketdyne)

Considering the highly novel nature of its design, several different models of the Atlas were built and flown to evaluate various systems and allow the design to evolve into a working weapon system over time. The first model, called Atlas A, served as the initial test bed for the rocket and its technology. The goal of the Atlas A was to fly an abbreviated test flight travelling up to about 1,000 kilometers downrange to verify the soundness of the Atlas design. For this mission, the Atlas A required only a pair of booster engines to lift the 82.5-metric ton missile with its partial propellant load off the launch pad and send it on its way. With the MA-2 propulsion system still being developed, the booster engines from the interim MA-1 propulsion system consisting of a pair XLR43-NA-3 engines derived directly from the Navaho propulsion work would suffice. This pair of engines burned JP-4 jet fuel (consisting of a 50-50 mix of kerosene and gasoline) and LOX to produce a total of about 1,330 kilonewtons of thrust. Test firings of the Atlas A’s engines were performed between May and November 1956 at Stand 1-4 at Edwards Rocket Base in California’s Mojave Desert.

A simplified cutaway diagram of the Atlas A missile with some of its key specifications. (Convair)

The first complete MA-1 propulsion package with the detachable XLR43-NA-3 boosters and a XLR43-NA-5 sustainer engine required for longer range test flights would be used by the first flights of the Atlas B models which would benefit from the lessons learned from the Atlas A flights. Further design refinements including the more advanced MA-2 propulsion system employing early production versions of the LR-89/105 engine combination would be incorporated into the Atlas C which would also be used to start training of USAF launch crews. The first “operational” ICBM model would be the Atlas D.

The First Atlas Tests

The very first Atlas missile, Atlas 1A, was completed and “conditionally accepted” by the USAF on August 29, 1956 after which it was transported to Convair’s new test facilities in Sycamore Canyon, California. Located on land acquired from the US Navy 16 kilometers from Convair’s San Diego plant where the Atlas was being built, construction work on Convair’s two new captive test stands at Sycamore capable of accommodating a complete Atlas missile had started in February 1955. After additional work on the missile was finished on site, Atlas 1A was erected on test stand S-1 and conducted a short one-second startup test of its pair of Rocketdyne  XLR43-NA-3 booster engines on December 5. Unfortunately a second test firing on December 21 resulted almost immediately in a fire and explosion that totally destroyed the engine compartment of Atlas 1A and caused some damage to the test stand. This was not a promising start to the Atlas program.

An aerial view of Convair’s S-1 test stand at Sycamore Canyon where initial captive test firings of early-model Atlas missiles took place.

As repairs proceeded on the S-1 test stand, Atlas 3A was finished and shipped to Sycamore Canyon for captive testing. Starting on February 1, 1957, Atlas 3A performed five months of test firings of its pair of booster engines. Eight test runs totaling 446 seconds of engine firing time uncovered a series of hardware and procedural issues that were subsequently corrected. In the mean time, Atlas 2A was erected on March 25 at the first of two test stands, designated 1-A, dedicated to the Atlas program at Edwards Rocket Base located 330 kilometers from San Diego at Edwards Air Force Base. By the end of its series of 17 static test firings completed on December 1, Atlas 2A had logged 1,127 seconds of total firing time.

Atlas 4A as it appeared just before being erected at LC-14. Note the relatively long aft skirt or “boat tail” which contributed to some of the problems during the first two Atlas A test flights. (USAF)

As various parts of the Atlas ground test program proceeded, work pushed ahead in parallel to get the first test flights off the ground. The first flight article, Atlas 4A, was accepted by the USAF on November 29, 1956 and subsequently shipped to the Atlantic Missile Range at Cape Canaveral, Florida. Earlier in January 1956, construction work on four launch pad facilities, designated Launch Complexes 11 through 14, had started to support Atlas development flights. Two of these pads, LC-12 and LC-14, were earmarked specifically to support the first test flights of the Atlas A. After several months of on-site work on Atlas 4A and the new LC-14 to prepare them for launch, a brief flight readiness firing (FRF) of the engines was held on June 3, 1957 with the Atlas secured firmly to its launch pad. All was now ready for the first Atlas test flight.

Liftoff of the Atlas 4A on June 11, 1957 from LC-14 at Cape Canaveral, Florida. This was the largest American rocket ever flown up to this point in history. (USAF)

Atlas 4A successfully lifted off from LC-14 on June 11, 1957 at 4:37 PM EST only 2½ years after Convair received the Atlas contract. While all seemed to be going well at first, control of the ascending missile was lost after about 25 seconds of flight when one then the other booster engine shut down prematurely. The missile started tumbling and was finally destroyed by range safety after 50 seconds of flight. Although the missile was lost, the flight was still considered to be a partial success since the complex liftoff procedure had been successfully completed and the rocket remained intact even as it tumbled out of control convincingly demonstrating the strength of its unique construction.

Atlas 6A being prepared for launch from LC-14. (USAF)

A second test flight was prepared for launch after modifications were made to correct the presumed cause of the Atlas 4A failure. Atlas 6A lifted off from LC-14 at 4:57 PM EST on September 25, 1957 but once again control of the missile was lost during ascent forcing range safety to destroy the rocket after only 80 seconds of flight. Subsequent investigation showed that inadequate heat shielding at the base of the missile was the root cause of the two failures. The FRF on the launch pad, which had very different conditions compared to the static firings at Sycamore Canyon and Edwards, as well as conditions during flight were causing damage to electrical and mechanical components in the Atlas A aft compartment as exhaust gases made their way inside. To correct the problem, the Atlas’ “boat tail” was shortened with its original light aluminum heat shield replaced by a steel and fiberglass unit as well as flexible fiberglass boots added around the engine bells to keep hot exhaust gases out of the engine compartment. The geometry of the MA-1 propulsion system’s turbopump exhaust vent was also changed to expel the hot exhaust gases off to one side of the rocket instead of straight down.

Moving Into the Space Age

All of these changes and other systems modifications seemed to have finally worked on the next launch. Atlas 12A successfully lifted off from LC-14 at 12:39 PM EST on December 17, 1957. This time the Atlas A operated as planned and successfully flew its prescribed flight path about 800 kilometers downrange. This successful test flight was all the more important in light of the fact that the Soviet Union had successfully test flown its first ICBM, called the R-7, at full range just four months earlier then used a modified version of the same rocket to launch the first artificial Earth satellite into orbit on October 4, 1957 to usher in the Space Age (see “Sputnik: The Launch of the Space Age“).

Launch of Atlas 12A on December 17, 1957 from LC-14 on the first completely successful Atlas A test flight. (USAF)

Over the six months following the successful flight of Atlas 12A, Atlas A rockets were launched two more times from LC-14 and three times from the new LC-12. Although three of these five flights resulted in failure, enough was learned from them as well as from continued captive test firings of three A and the first B model missiles back in California to proceed with the next round of flights with the Atlas B starting in July 1958. The development of the Atlas, which was the largest American rocket to have flown up to this point in history, was now well on its way.

View of Atlas 10B on the pad at LC-11 that was used for the first Atlas satellite launch as part of Project SCORE on December 18, 1958. (USAF)

Although the Atlas would continue to experience problems and many failures, a specially modified “hot rod” version of the Atlas B was eventually used during the ongoing test program to launch a payload into orbit on December 18, 1958 for Project Score starting the Atlas’ long career as a satellite launch vehicle (see “Vintage Micro: The Talking Atlas”). The following year, the Atlas D was selected by NASA to launch its Mercury manned spacecraft into orbit (from LC-14 where the first Atlas A flights were launched, no less) and it subsequently became America’s first operational ICBM. While its role as a weapon ended by 1965 because of the availability of the Titan II and then the solid-propellant Minuteman I ICBMs, the increasingly reliable Atlas fitted with a variety of upper stages would continue its role as a highly successful satellite launch vehicle for over a half a century to come.

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Related Video

Here is documentary from the USAF about the Atlas ICBM development program up to the end of 1957 entitled “Atlas: The ICBM”.

Here is a Convair report about the Atlas 6A test flight launched on September 25, 1957.

Related Reading

“Vintage Micro: The Talking Atlas”, Drew Ex Machina, December 18, 2014 [Post]

“Riding Piggyback on an ICBM”, Drew Ex Machina, January 21, 2015 [Post]

“The Launch of Atlas-Centaur 5”, Drew Ex Machina, March 2, 2015 [Post]

“Sputnik: The Launch of the Space Age”, Drew Ex Machina, October 4, 2017 [Post]

General References

David Baker, The Rocket, Crown Publishers, 1978

J.D. Hunley, Preludes to U.S. Space-Launch Vehicle Technology: Goddard Rockets to Minuteman III, University Press of Florida, 2008

Chuck Walker with Joel Powell, Atlas: The Ultimate Weapon, Apogee Books, 2005