E-1 (rocket engine)

Rocketdyne's E-1 was a liquid propellant rocket engine originally built as a backup design for the Titan I missile. While it was being developed, Heinz-Hermann Koelle at the Army Ballistic Missile Agency (ABMA) selected it as the primary engine for the rocket that would emerge as the Saturn I. In the end, the Titan went ahead with its primary engine, and the Saturn decided to use the lower-thrust H-1 in order to speed development. The E-1 project was cancelled in 1959, but Rocketdyne's success with the design gave NASA confidence in Rocketdyne's ability to deliver the much larger F-1, which powered the first stage of the Saturn V missions to the Moon.

In July 1954 the Air Force Scientific Advisory Board's ICBM working group advised the Western Development Division (WDD) on their doubts about the Atlas missile that was then under development. Atlas used a number of unconventional features in order to meet its performance goals, and they felt that there was undue risk that if any of these proved unworkable in practice then the entire design would fail. The group suggested that a second ICBM project be started as a risk mitigation effort.

SAC's concerns were taken to heart within the Air Force, and they directed Ramo-Wooldridge to study the issue. Ramo responded by inviting Lockheed and the Glenn L. Martin Company to propose alternative ICBM designs. Based on these reports, Ramo suggested that the Air Force begin development of a new missile that used a conventional airframe in place of the Atlas's "balloon tanks", and replaced the "stage and a half" layout with a two-stage design.

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