Exploring the Unknown: Selected Documents in ... - The Black Vault

50
First Steps into Space: Projects Mercury and Gemini
Document I-2
Document Title: H. Julian Allen and A. J. Eggers, Jr., NACA, “Research
Memorandum: A Study of the Motion and Aerodynamic Heating of Missiles
Entering the Earth’s Atmosphere at High Supersonic Speeds,” 25 August 1953.
Source: Folder 18674, NASA Historical Reference Collection, NASA History
Division, NASA Headquarters, Washington, DC.
In the later 1940s aerodynamicists began research on the best means of reentry to Earth from
space, where the high speeds caused atmospheric heating in excess of 1,800°F. These investigations
found that a blunt-nose body experienced much less heating than a pointed body,
which would burn up before reaching Earth’s surface. The blunt reentry body, discovered in
1951 by H. Julian Allen, an engineer with NACA’s Ames Research Center, created a stronger
shock wave at the nose of the vehicle and dumped a good deal of the reentry heat into the
airflow, making less heat available to heat the reentry vehicle itself. Allen’s work led to the
design of wide-body bases for spacecraft, giving the capsules their characteristic “teardrop”
shape, and to the use of the ablative heat shields that protected the Mercury, Gemini, and
Apollo astronauts as their space capsules reentered Earth’s atmosphere. This document represents
one of Allen’s earliest contributions to understanding the reentry problem. Coupled with
his later contributions, as well as with the research of others including his early collaborator
Alfred Eggers, Allen’s research made possible human spaceflight in the 1960s.
NACA
RESEARCH MEMORANDUM
A STUDY OF THE MOTION AND AERODYNAMIC HEATING OF MISSILES
ENTERING THE EARTH’S ATMOSPHERE AT HIGH SUPERSONIC SPEEDS
By H. Julian Allen and A. J. Eggers, Jr.
Ames Aeronautical Laboratory
Moffett Field, Calif.
August 25, 1953
SUMMARY
A simplified analysis is made of the velocity and deceleration history of missiles
entering the earth’s atmosphere at high supersonic speeds. It is found that,
in general, the gravity force is negligible compared to the aerodynamic drag force
and, hence, that the trajectory is essentially a straight line. A constant drag coefficient
and an exponential variation of density with altitude are assumed and generalized
curves for the variation of missile speed and deceleration with altitude
are obtained. A curious finding is that the maximum deceleration is independent
of physical characteristics of a missile (e.g., mass, size, and drag coefficient) and