Facing the Heat Barrier - NASA's History Office

Facing the Heat Barrier: A History of Hypersonics
ing. Thus, in December Vannevar Bush, wartime head of the Office of Scientific
Research and Development, gave his views in congressional testimony:
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“There has been a great deal said about a 3,000 miles high-angle rocket.
In my opinion, such a thing is impossible for many years. The people have
been writing these things that annoy me, have been talking about a 3,000
mile high-angle rocket shot from one continent to another, carrying an
atomic bomb and so directed as to be a precise weapon which would land
exactly on a certain target, such as a city. I say, technically, I don’t think
anyone in the world knows how to do such a thing, and I feel confident
that it will not be done for a very long period of time to come. I think we
can leave that out of our thinking.” 1
Propulsion and re-entry were major problems, but guidance was worse. For
intercontinental range, the Air Force set the permitted miss distance at 5,000 feet
and then at 1,500 feet. The latter equaled the error of experienced bombardiers
who were using radar bombsights to strike at night from 25,000 feet. The view at
the Pentagon was that an ICBM would have to do as well when flying all the way
to Moscow. This accuracy corresponded to hitting a golf ball a mile and having it
make a hole in one. Moreover, each ICBM was to do this entirely through automatic
control. 2
The Air Force therefore emphasized bombers during the early postwar years,
paying little attention to missiles. Its main program, such as it was, called for a missile
that was neither ballistic nor intercontinental. It was a cruise missile, which was
to solve its guidance problem by steering continually. The first thoughts dated to
November 1945. At North American Aviation, chief engineer Raymond Rice and
chief scientist William Bollay proposed to “essentially add wings to the V-2 and
design a missile fundamentally the same as the A-9.”
Like the supersonic wind tunnel at the Naval Ordnance Laboratory, here was
another concept that was to carry a German project to completion. The initial
design had a specified range of 500 miles, 3 which soon increased. Like the A-9,
this missile—designated MX-770—was to follow a boost-glide trajectory and then
extend its range with a supersonic glide. But by 1948 the U.S. Air Force had won
its independence from the Army and had received authority over missile programs
with ranges of 1,000 miles and more. Shorter-range missiles remained the concern
of the Army. Accordingly, late in February, Air Force officials instructed North
American to stretch the range of the MX-770 to a thousand miles.
A boost-glide trajectory was not well suited for a doubled range. At Wright Field,
the Air Force development center, Colonel M. S. Roth proposed to increase the
range by adding ramjets. 4 This drew on work at Wright, where the Power Plant
Nose Cones and Re-entry
Laboratory had a Nonrotating Engine Branch that was funding development of
both ramjets and rocket engines. Its director, Weldon Worth, dealt specifically with
ramjets. 5 A modification of the MX-770 design added two ramjet engines, mounting
them singly at the tips of the vertical fins. 6 The missile also received a new name:
Navaho. This reflected a penchant at North American for names beginning with
“NA.” 7
Then, within a few months during 1949 and 1950, the prospect of world war
emerged. In 1949 the Soviets exploded their first atomic bomb. At nearly the same
time, China’s Mao Zedong defeated the Nationalists of Chiang Kai-shek and proclaimed
the People’s Republic of China. The Soviets had already shown aggressiveness
by subverting the democratic government of Czechoslovakia and by blockading
Berlin. These new developments raised the prospect of a unified communist empire
armed with the industry that had defeated the Nazis, wielding atomic weapons, and
deploying the limitless manpower of China.
President Truman responded both publicly and with actions that were classified.
In January 1950 he announced a stepped-up nuclear program, directing “the
Atomic Energy Commission to continue its work on all forms of atomic weapons,
including the so-called hydrogen or super bomb.” In April he gave his approval to a
secret policy document, NSC-68. It stated that the United States would resist communist
expansion anywhere in the world and would devote up to twenty percent of
the gross national product to national defense. 8 Then in June, in China’s back yard,
North Korea invaded the South, and America again was at war.
These events had consequences for the missile program, as the design and mission
of Navaho changed dramatically during 1950. Bollay’s specialists, working with
Air Force counterparts, showed that they could anticipate increases in its range to
as much as 5,500 nautical miles. Conferences among Air Force officials, held at
the Pentagon in August, set this intercontinental range as a long-term goal. A letter
from Major General Donald Putt, Director of Research and Development within
the Air Materiel Command, became the directive instructing North American to
pursue this objective. An interim version, Navaho II, with range of 2,500 nautical
miles, appeared technically feasible. The full-range Navaho III represented a longterm
project that was slated to go forward as a parallel effort.
The thousand-mile Navaho of 1948 had taken approaches based on the V-2 to
their limit. Navaho II, the initial focus of effort, took shape as a two-stage missile
with a rocket-powered booster. The booster was to use two such engines, each with
thrust of 120,000 pounds. A ramjet-powered second stage was to ride it during
initial ascent, accelerating to the supersonic speed at which the ramjet engines could
produce their rated thrust. This second stage was then to fly onward as a cruise missile,
at a planned flight speed of Mach 2.75. 9
A rival to Navaho soon emerged. At Convair, structural analyst Karel Bossart
held a strong interest in building an ICBM. As a prelude, he had built three rockets
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