Atlas

Atlas began as the first US intercontinental ballistic missile. At the same time Atlas was being developed as an ICBM, the Air Force began supplying the vehicles to the National Aeronautics and Space Administration (NASA) for space applications. In 1958 the first communication from space was broadcast from an orbiting Atlas with a recorded Christmas message from then President Eisenhower. Atlas went on to become a workhorse in the US space program, launching numerous government, military and civilian payloads.

Originally developed as a US Air Force weapon system, early in its development period, Atlas made the transition to become a space booster. Since it has undergone a series of improvements, including tank lengthening, engine performance increases, and system updating. The Atlas/Centaur launch vehicle, originally developed by General Dynamics for NASA, has launched a wide variety of spacecraft with over two decades of reliable operations. The vehicle has been continuously upgraded to launch progressively larger and heavier spacecraft. Vehicle characteristics included: efficient pressure-stabilized stainless steel structure for high stage mass fraction, advanced inertial guidance and control hardware and software for pinpoint accuracy and flexibility, high-energy liquid hydrogen and oxygen propellant upper stage.(1)

History(2)

The history of the Atlas ballistic missile field goes back to a US Army Air Force request for a proposal just after World War II. In October 1945, the Army Air Force invited industry to submit proposals for research and development of four types of missiles, the largest of which was to be a weapon with a 5,000-mile range.

By early January 1946, the Downey engineers had roughed out their ideas on two types of 5,000-mile missiles: one subsonic, winged, and jet powered and the other supersonic, ballistic, and rocket powered. A study program was proposed to the Air Force to determine which type would best serve the ultimate purpose.

In April, Convair received a contract for $1,400,000 for a year's study of under Project MX-774. Captive testing of the MX-774 research rockets began in San Diego in 1947. A year later, three MX-774's were test-launched at White Sands Proving Ground, New Mexico. The flights proved the value of three important innovations: gimbaled engines for directional control, lightweight, pressurized airframe structure, and separable nose cones. Defense cutbacks in 1947 forced the newly created United States Air Force to shelve the ballistic missile in favor of other weapon programs.

The outbreak of the Korean war resulted in increased defense appropriations. The US Air Force awarded Convair a new contract to study the respective merits of ballistic and glide rockets (Project MX-1593). In September 1951, Convair proposed a ballistic-type missile to incorporate design features validated by the MX-774. In 1953 (the year Convair merged with and became a division of General Dynamics), the Convair Division presented a plan to the Air Force for an accelerated program.

The largest propulsion problem in the early 1950's was that of ignition reliability. This was, at that time, less than 50 percent. It was this factor that led to the stage-and-a-half concept, wherein all engines are ignited prior to liftoff and the two booster engines are jettisoned during flight. This characteristic, employed for missile reliability, was retained in the Atlas space launch vehicles and permitted an assessment of propulsion system operation prior to commitment to actual flight.

A full go-ahead for the Atlas design was ordered in January 1955. The code name established for the Atlas weapon system was WS107A-l. The project was known at Convair division as the Model 7. In September 1955, the highest national research and development priority was assigned to the Atlas project, starting one of the largest and most complex production, testing, and construction programs ever undertaken. The first propulsion system and component tests were conducted in June 1956. The first captive and flight-test missiles were completed later the same year.

1957 witnessed the first Atlas flight test, in near operational configuration (minus sustainer engine), with a dummy nose cone. Following a successful launch, a propulsion system valve malfunction caused by excessive heating resulted in failure of one of the booster engines and the missile was destroyed by the range safety officer. Before the Atlas was destroyed, however, it experienced several seconds of violent maneuvering and tumbling, subjecting the airframe to structural loads much higher than design loads. The airframe remained intact, thus demonstrating the structural integrity of the Atlas. The second flight test missile, launched the same year, was partially successful. Then on 17 December 1957, missile 12-A, the third Atlas flight missile, made the first totally successful flight from Cape Kennedy (then Cape Canaveral). More flights followed, and in November 1958 the first full-range Atlas flight occurred, over a distance of 5, 512 nautical miles. Thus, all major design concepts were demonstrated, and development milestones passed generally ahead of or close to the original schedule.

The Atlas B had 10 successful tests between 1958 and 1959. The Atlas C used an improved guidance system and carried an operational reentry vehicle in tests conducted during 1958 and 1959. Atlas became fully operational as a weapon system in January 1959, when the Air Force declared Vandenberg Air Force Base operational. The Atlas D, the prototype for the operational system used a ground-based guidance system but carried the all-inertial guidance system that the Atlas E would use. The missile satisfied all research and development goals and became operational by August 1959. In September 1959, a crew from the Strategic Air Command marked the initial operational capability by launching an Atlas D from the Pacific Missile Range. The military deployed operationally Atlas D, E, and F as intercontinental ballistic missiles between 1960 and 1966. They phased out the Atlas D in 1964. Shortly thereafter, the Minuteman missile replaced the E and F models.

In December 1958, an entire Atlas B launched itself into an earth-orbit, carrying an Army Signal Corps instrumentation package which broadcast from outer space President Eisenhower's Christmas message to the world. This launch, Project Score, began the new launch vehicle era for the Atlas as well as providing one of the first propaganda "wins" for the United States. A series of scientific space probes and Air Force space project launches followed.

The design of the basic Atlas changed very little over the years. The Atlas is a liquid-propellant vehicle that includes a booster section and a sustainer section. The booster section consists of two high-thrust engines which ignite at lift-off. The craft jettisons them approximately two minutes into the flight. The sustainer section has a single engine that ignites at lift-off and operates throughout the flight.

The unique 1 1/2-stage design concept of the Atlas space launch vehicle allows it to be used without an upper stage for missions requiring relatively low orbital altitudes. Any type of mission may be performed by adding available upper stages to the Atlas, such as the Agena and Centaur, the most commonly used Atlas upper stages. An additional upper stage, Burner II, permits even greater mission flexibility in the Atlas family of space launch vehicles. Burner II is a small, solid propellant upper stage containing its own guidance and control system and hot- and cold-gas reaction control engines. Hydrogen peroxide engines provide thrust for separation from the lower stage, reaction control thrust during engine firing, and velocity vernier thrust after main engine firing. Gaseous nitrogen thrusters are used for attitude control during coast, spacecraft spinup, and retrothrust at spacecraft separation.(3)

The first Centaur contract was awarded to General Dynamics by the Advanced Research Project Agency in 1958. As the first space vehicle to use liquid hydrogen fuel, Centaur necessitated development of a whole new technology. The problem of materials, handling behavior, fabrication, and testing for liquid hydrogen in a space application had to be solved not only to make Centaur a success, but also because the was the fuel planned for many elements of the Apollo program. Also in 1958, Pratt & Whitney Aircraft was awarded a contract to develop Centaur's RL-10 engines. At the same time, the US Air Force built the first large-quantity liquid hydrogen production facility. NASA's Lewis Research Center (LeRC) did much pioneering work in developing liquid hydrogen technology. LeRC first fired an experimental LO2/LH2 engine of 5,000 pounds thrust in 1953.

In 1962, LeRC was assigned technical management of Centaur. At the same time, the Centaur project was given a DX priority, the nation's most urgent aerospace priority. This reflected its importance to the Surveyor lunar exploration program and to the development of liquid hydrogen technology.

The first successful flight of Centaur atop Atlas occurred in November 1963. This was the world's first inflight ignition of a hydrogen powered vehicle. Centaur's first mission was to inject Surveyor moon landers into trans-lunar orbit. The first operational Centaur mission, in May 1966, was an outstanding achievement. Surveyor 1 landed within eight miles of its lunar target. Centaur performed the first successful space restart of liquid hydrogen engines in October 1966. With this flight, the Centaur R&D phase was completed.

General Dynamics was given go-ahead on the contract for the D-l Improved Centaur program in April 1969. Objectives of the D-1 were to achieve increased reliability and lower recurring, mission-peculiar, and boost vehicle integration costs. The Atlas/Centaur D-1A launch vehicle was used for a variety of planetary, commercial, military, and scientific space missions. Major improvements over its predecessor, Centaur D, were incorporated into Centaur D-l. Primary changes were in avionics and payload area structures. Many former hardware functions were performed by the flight software, including a software digital autopilot. Lower cost and greater mission flexibility were achieved by this approach.(4)

Notes

1. General Dynamics Space Systems Division, Atlas Centaur Mission Planners Guide, (April 1983, Revised November 1986), Arlington, Virginia and San Diego, California.

2. Adapted from: General Dynamics Convair Division, Atlas Space Launch Vehicle Systems Summary, GDC-BGJ67-001, February 1967;

Air Command and Staff College (Lt Col Curtis D. Cochran, Lt Col Dennis M. Gorman, Maj Joseph D. Dumoulin {editors}), Space Handbook - AU-18, (Air University Press, Maxwell Air Force Base, Alabama, January 1985); and

General Dynamics Space Systems Division, Atlas Centaur Mission Planners Guide, (April 1983, Revised November 1986), Arlington, Virginia and San Diego, California.

3. Adapted from: General Dynamics Convair Division, The Atlas Launch Vehicle Family for Spacecraft Contractor Planning, GDC-BGJ67-002, April 1967.

4. General Dynamics Space Systems Division, Atlas Centaur Mission Planners Guide, (April 1983, Revised November 1986), Arlington, Virginia and San Diego, California.