Hypersonics History of Reentry

Lately, I have been examining the entire history of hypersonics research and technology, with a particular focus on the re-entry problem and ablation for small vehicles, such as those from ballistic missiles. While reviewing the writings of Wernher von Braun, I was amused to find that he joked about using frozen balsa wood as a potential material for re-entry vehicles. The re-entry challenge was initially posed to the scientific community by Theodore von Kármán of CalTech GALCIT and JPL as one of the most formidable problems to solve.

Early aerodynamic designs, borrowed from supersonic studies, often featured pointed shapes; however, these were soon discounted by experimental results at NASA and associated analysis. Test rocket programs, which explored ballistic trajectories at varying speeds and altitudes, revealed that aerodynamic ‘heating ‘heat barrier’ was the primary problem – unlike in supersonics, where the sound barrier was the main concern.

Ultimately, materials such as glass substrates and nylon were the first to be successfully used as ablative materials. This is quite different from today’s approaches, which involve advanced materials, composites, and sophisticated analyses for active cooling or modern ablative materials.

Words and Virginia Woolf

Finally, and most emphatically, words, like ourselves, in order to live at their ease, need privacy. Undoubtedly they like us to think, and they like us to feel, before we use them; but they also like us to pause; to become unconscious. Our unconsciousness is their privacy; our darkness is their light… That pause was made, that veil of darkness was dropped, to tempt words to come together in one of those swift marriages which are perfect images and create everlasting beauty. But no – nothing of that sort is going to happen tonight. The little wretches are out of temper; disobliging; disobedient; dumb. What is it that they are muttering? “Time’s up! Silence!”

Virginia Woolf, BBC, April, 29, 1937

Kelly Johnson on X-Plane Programs

Our present research airplanes have developed startling performance only by the use of rocket engines and flying essentially in a vacuum. Testing airplanes designed for transonic flight speeds at Mach numbers between 2 and 3 has proven, mainly, the bravery of the test pilots and the fact that where there is no drag, the rocket engine can propel even mediocre aerodynamic forms at high Mach numbers.

I am not aware of any aerodynamic or power plant improvements to airbreathing engines that have resulted from our very expensive research airplane program. Our modern tactical airplanes have been designed almost entirely on NACA and other wind-tunnel data, plus certain rocket model tests…. — Kelly Johnson

Navier-Stokes Equations and Practicality

Because an effort is likely impossible and impractical does not mean it is not worth attempting. The Navier-Stokes equations and turbulent flow represent the last great classical problem in physics. Since the time of Leonard Euler and Jean-Baptiste le Rond d’Alembert, many have devoted much of their lives to working on these problems. Although they have all failed, they may have made incremental progress toward understanding the physics and mathematics of these significant partial differential equations.

Eight Years at Florida

It has now been eight years since I joined the University of Florida. Years ago, the University was a very different place. Many things have changed due to external and internal factors. One thing is for certain: I am told that the academic community and academics are always changing. To be a successful professor, much like in biological theory, one must be adaptable.

Deming and Statistics

In God we trust. All others must bring data. — W. Edwards Deming

Deming revolutionized quality management with his emphasis on data-driven decision-making. His 1950s lectures on Statistical Product Quality Administration in Japan were instrumental in Japan’s post-war economic growth, helping it become the world’s second-largest economy. Deming was awarded the National Medal of Technology in 1987 by President Ronald Reagan. The Deming Prize, created by the Japanese Union of Scientists and Engineers, honors contributions to Total Quality Management.

On Websites at Florida

I have moved my faculty website to this website. My personal and faculty website are now located and combined here at saemiller.com. There is a redirect from https://faculty.eng.ufl.edu/fluids/

The university depends on academic freedom, and academic freedom depends on tenure. Without tenure there is no academic freedom, and without academic freedom there is no university. 

Gödel and Time

$\mathrm{LL}$ cosmological solutions with non-vanishing density of matter known at present ${ }^1$ have the common property that, in a certain sense, they contain an “absolute” time coordinate, ${ }^2$ owing to the fact that there exists a one-parametric system of three-spaces everywhere orthogonal on the world lines of matter. It is easily seen that the non-existence of such a system of three-spaces is equivalent with a rotation of matter relative to the compass of inertia. In this paper I am proposing a solution (with a cosmological term $\neq 0$ ) which exhibits such a rotation.

Kurt Gödel, Institute for Advanced Study, Princeton, New Jersey

Gödel circumvented the light-speed barrier by suggesting that a fast-spinning object could distort space and time, making their properties coalesce. At sufficiently high spins, returning to the starting point in space would coincide with returning in time. The limitation of Gödel’s concept is its reliance on a spinning universe, a condition not supported by current evidence. But, who knows if such a place exists.

Reference

Gödel, K. (1949). An example of a new type of cosmological solutions of Einstein’s field equations of gravitation. Reviews of modern physics, 21(3), 447.