The Complete Book of Spaceflight: From Apollo 1 to Zero Gravity

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America’s first intercontinental ballistic missile
(ICBM), from which evolved a hugely successful
family of space launch vehicles. A modified Atlas was
used to launch the orbital flights in the Mercury Project,
and modern versions of the Atlas continue to
play a central role in the U.S. space program. (See
table, “Current Atlas Family,” on page 46.)
History
Atlas has its roots in October 1945, when the U.S.
Army Air Corps sought proposals for new missile systems.
A contract was awarded to the San Diego–based
Consolidated Vultee Aircraft (Convair) Corporation
to develop the so-called MX-774 “Hiroc” missile with
a range of about 11,000 km and some unusually
advanced features for its time. Among these was a single-wall
construction of stainless steel so thin that the
missile was kept from collapsing only by the internal
pressure of its fuel tanks—a design that remains
unique to the Atlas family. The weight saved meant
increased range. Other new features included a detachable
payload section and gimbaled rocket engines
for more precise steering instead of exhaust deflector
vanes, which were then common.
Despite these innovations, the MX-774 project was
canceled in 1947 and priority given to developing
the Navaho, the Snark, and the Matador. However,
Convair built and test-launched three of the missiles
originally authorized. None was a total success, but
Convair continued research and conceived another
revolutionary idea that would eventually find its way
into the Atlas and become its most defining feature.
This is the “stage-and-a-half” propulsion system in
which three engines—two boosters and a sustainer
engine—are fed by the same liquid oxygen/RP-1
(kerosene mixture) propellant tanks and all ignited at
liftoff. During the first few minutes of flight, the
boosters shut down and fall away (to save weight),
while the sustainer continues burning.
In 1951, with the outbreak of the Korean War and
rising Cold War tensions, Convair received a new Air
Force contract to develop a long-range nuclear ballistic
missile incorporating the main features of the MX-
774. It was called “Atlas,” a name proposed by Convair
lead engineer Karel Bossart and approved by the Air
Atlas
Force. In September 1955, Atlas was given the highest
national development priority and by 1959 was being
deployed as an ICBM. But operational versions of the
Atlas missile, known as the Atlas D, E, and F, were
destined to be not only weapons. Having proved
themselves reliable and versatile, they became the
core boosters for a range of space launch vehicles, including,
in chronological order, the Atlas-Able, Atlas-
47, 200, 228
Mercury, Atlas-Agena, and Atlas-Centaur.
Atlas-Able
A four-stage rocket with an Atlas D first stage and
Able upper stages. After being used in three unsuccessful
attempts to send early Pioneer probes to the
Moon, the short-lived Atlas-Able was retired in 1960.
Atlas-Mercury
See Mercury-Atlas.
Atlas-Agena
A series of rockets based on Atlas first stages and Agena
second stages. Two were important in the space program.
The Atlas-Agena B used an Atlas E or F first stage
and an Agena B—the first Agena to have multiple restart
capability—as the second stage. Among the spacecraft
launched by Atlas-Agena Bs were the Ranger lunar
probes, Mariner 1 and 2, OGO-1, and the MIDAS and
Samos military satellites. The Atlas-Agena D featured
an improved and lightened Agena second stage and, in
one of its configurations, solid Burner third and Star 17
fourth stages for geosynchronous launches. Atlas-Agena
Ds were responsible for many launches including those
of the Lunar Orbiters; Mariner 3, 4, and 5; OAO-1;
and the Vela and other reconnaissance satellites. Atlaslaunched
modified Agena Ds were used as target vehicles
in Gemini rendezvous and docking missions.
Atlas-Centaur
A family of Atlas-based first- and upper-stage combinations
that evolved from the Atlas D and remains in use.
The original Atlas-Centaur, introduced in 1962, used
the D as first stage and the powerful liquid oxygen/liq-