An intermediate-range ballistic missile (IRBM) that was adapted for use
as a space launch vehicle and is the direct ancestor of the Delta rocket family. Development of the Thor was authorized in November 1955 to
give the United States Air Force an independent IRBM capability. At the
time, the Army Ballistic Missile Agency (ABMA)
was already developing the Redstone medium-range
ballistic missile and the Jupiter IRBM. Since the Air Force was now free to compete with the Army in creating
a similar weapon, a fierce rivalry broke out between the two services. The
Air Force requested proposals for a missile able to carry a nuclear warhead
at least 2,400 km – the distance from England to Moscow. The Douglas
Aircraft Company came up with a design that used the warhead and guidance
system already being developed for the Atlas and the engine from the Navaho. The resulting
missile could fit inside a Douglas C-124 Globemaster II for easy transportation
to a launch site. The first Thor was ready to fly in August 1956 and the
first operational Thors were deployed in England by the end of 1958. Two-thirds
of the Thor's body held the liquid propellants – liquid
oxygen and RP-1 – for the missile's
single-stage engine whose thrust capability was similar to both the Jupiter
IRBM engine and each individual Atlas ICBM booster stage engine. Two vernier
engines, similar to those on the Atlas, were attached at opposite sides
of the base of the Thor and burned the same fuel as the main engine. Advances
in ICBM technology led to the Thor's withdrawal from military service by
1965. But the Thor did not die: it remained critical to the evolution of
the American space program, serving as the core booster for many satellite-carrying
relatives, not the least of which was the Delta.
|Thor missile at USAF Museum, Patrick
A three-stage rocket that used the Thor IRBM as a core booster. Introduced
in 1958 and originally designed to support high-altitude Air Force and civilian
reentry vehicle research, the Thor-Able was
later modified to carry small satellites into orbit – the first Thor-based
variant to do so. Thor-Able was the first generation of what would become
the Delta family of space launch vehicles. The second and third stages were
adapted directly from the Vanguard rocket.
The first three Thor-Able launches were intended to test ablative materials
proposed for Atlas missile nosecones. But in addition, these flights carried
out groundbreaking biological research. Each of the three nosecones in the
series carried a mouse, electronic monitoring of which demonstrated that
animals could survive a long-range missile flight (see animals
in space). These tests would prove to be significant since the mice
would reach maximum altitudes of 960-1,600 km above Earth during their journey,
and experience long periods of weightlessness and gravity stress. These
Thor-Able flights did provide useful data on ablative nosecone technology,
but the mice did not fare so well. The first of these Thor-Able rockets
carried a mouse named "Mouse-In-Able-1" (MIA-1), nicknamed "Minnie Mouse"
and was launched on April 23, 1958. The rocket exploded due to a first stage
gearbox failure. The second of these Thor-Able rockets carried a mouse named
"Mouse-In-Able-2" (MIA-2) and was launched on July 9, 1958. The mouse survived
its entire flight, but recovery crews were not able to locate the nosecone.
The last Thor-Able mouse, named "Wickie Mouse" in honor of the nickname
of Cape Canaveral journalist Mercer "Wickie" Livermore, was launched on
July 23, 1958. This mouse also survived its flight, but recovery crews were
not able to locate the nosecone. Even though the nosecones were not recovered
in the two successful Thor-Able research flights, the fact that flights
of 9,600 km were achieved prompted Douglas Aircraft to propose an ICBM version
of the Thor called Thor-Intercontinental, or "Thoric." This proposal was
rejected by the Air Force since development of the Atlas and Titan ICBM
systems were already well underway. However, Thor-Able research rockets
were modified to launch satellites. Each Thor-Able was capable of carrying
a maximum 140-kg payload into low Earth orbit (LEO). Since the Thor-Able
ultimately evolved into a series of space launch vehicles, the initial version
is sometimes referred to as Thor-Able Zero.
A Thor-Able with an added fourth stage, designed specifically to send Pioneer spacecraft toward the Moon. The solid-propellant fourth stage motor remained
attached to the payload.
A version of Thor-Able used for high-altitude reentry vehicle testing instead
of launching satellites.
|Launch of a Thor-Able Star from Cape
Canaveral in 1961
A two-stage vehicle introduced in 1960 to carry military payloads into orbit.
By using improved Thor-Able first and second stages and eliminating the
weight of additional upper stages, Thor-Able Star was able to carry a large
LEO payload. The upgraded second stage engine could be restarted to augment
and adjust the orbit of the payload. Thor-Able Star was the last version
of the Thor-based rockets to be launched from Cape Canaveral carrying the
A two-stage vehicle that used the Lockheed-built Agena as the upper stage.
It served as the booster for the Discoverer
program, the United States' first series of spy satellites, and also launched Echo 2, Nimbus 1, and Alouette 1, among others.
| stage 1
| stage 2
| stage 3
| stage 1
| stage 2
| stage 3
MISSILES, AND LAUNCH VEHICLES