Engineering: quotes, facts and reflections - Page 3

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Christine Darden, a NASA engineer, wrote computer programs to predict sonic booms, the thunder-like bangs made by aircraft flying faster than sound. Her research showed that reshaping a plane's nose and wings could make them softer on the ground.

Darden, a mathematics graduate of Hampton Institute, joined NASA's Langley Research Center in 1967 as a 'human computer', doing calculations for engineers. She pressed her managers to move her into engineering, and in the 1970s they did. A sonic boom forms when the shock waves from an aircraft's nose, wings and tail merge into one sharp jolt that reaches the ground. Darden's programs modelled those waves and pointed to shapes that keep them from merging, so people below hear a softer thump. She earned a doctorate in engineering from George Washington University in 1983, led NASA's sonic boom team from 1989 and wrote more than 50 papers. NASA's X-59, which first flew on 28 October 2025, was built to test this idea. Her story is also told in Margot Lee Shetterly's book Hidden Figures.

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Annie Easley joined NACA, NASA's forerunner, in 1955 as a 'human computer' doing calculations by hand, then became a programmer. Her code supported the Centaur rocket stage, which later sent probes such as Voyager and Cassini into space, and research on energy and batteries.

Easley was born in Birmingham, Alabama, in 1933. When she joined the Lewis Flight Propulsion Laboratory in Cleveland, Ohio, she was one of only four Black employees among about 2,500. As machines took over the arithmetic, she learned the programming languages FORTRAN and SOAP. Centaur, a rocket stage that fires after the first stage is spent, was the first to burn liquid hydrogen with liquid oxygen, and her programs supported its analyses. Her energy work included simulations that supported early battery research for hybrid vehicles. She finished a mathematics degree at Cleveland State University in 1977 while working full time. As an equal employment opportunity counsellor, she helped resolve discrimination complaints, and she encouraged girls and minority students to take up science. She retired in 1989.

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Radia Perlman, an American engineer, invented the spanning-tree algorithm, which stops data from circling endlessly in computer networks that have duplicate connections. It keeps the spare links switched off and brings one back into use when a cable fails.

When a network has more than one path between two points, a message can loop round and round, copying itself until the network jams. Perlman solved this in the mid-1980s while working at Digital Equipment Corporation. Her method lets the switches that connect a network agree among themselves, with no central controller, on one loop-free set of routes shaped like a branching tree; the extra links wait on standby. If a link breaks, the switches recalculate and a standby link takes over. The IEEE, the body behind many networking standards, adopted the method as 802.1D in 1990, and it and its faster successors still keep office and campus networks running. Perlman even described the algorithm in a short poem, “Algorhyme”.

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WonderScience

The scanning tunnelling microscope, invented at IBM's Zurich laboratory in 1981, can show individual atoms on a surface. It moves a needle-sharp tip just above the sample and measures the tiny electric current that leaks across the gap, which changes sharply with distance.

In everyday physics an electron cannot cross an empty gap, but when the gap is only about a billionth of a metre wide, quantum mechanics lets some electrons slip across anyway; this is called tunnelling. The current drops roughly tenfold for every extra tenth of a nanometre, so the tip's height can be controlled with extraordinary precision. A feedback system keeps the current steady as the tip scans, and the recorded height traces the surface. The method needs samples that conduct electricity. Gerd Binnig and Heinrich Rohrer built the first working instrument in 1981, and in 1983 they published an image of a silicon surface resolved atom by atom. They shared the 1986 Nobel Prize in Physics with Ernst Ruska, inventor of the electron microscope. In 1989 IBM researchers used such a tip to spell the company's name in 35 xenon atoms.

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Electron microscopes use beams of electrons, focused by magnets instead of glass lenses, to show details far smaller than any light microscope can, down to viruses and even rows of atoms. Ernst Ruska and Max Knoll built the first one in Berlin in 1931.

A light microscope cannot separate details much smaller than about half the wavelength of light, roughly 200 nanometres. Electrons also behave as waves, and when accelerated their wavelength becomes many thousands of times shorter. Ruska and Knoll used magnetic coils to focus them in 1931, and by 1933 Ruska's instrument could show finer detail than any light microscope. Siemens sold the first commercial model in 1939. Transmission electron microscopes send electrons through very thin slices; scanning electron microscopes sweep a beam across a surface and build a three-dimensional-looking picture from the signals that come back. Samples must sit in a vacuum and be carefully prepared, but the images opened up the inner structure of cells, viruses and materials. Ruska shared the 1986 Nobel Prize in Physics.

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Photogrammetry measures real objects from photographs. By matching the same points in pictures taken from different positions, it calculates distances, shapes and exact 3D positions, and it is how many maps, building surveys and 3D models are made.

When a camera moves, nearby things seem to shift against the background more than distant ones. This effect, called parallax, is also why a finger held close to the face seems to jump when each eye is closed in turn. If the camera positions are known or can be worked out, software matches corresponding points across several views and triangulates where each one sits in space. The French army officer Aimé Laussedat began making maps from photographs in the 1850s and is often called the father of the field; the German architect Albrecht Meydenbauer coined the word “photogrammetry” in 1867 while recording historic buildings. Photographs taken from aircraft later made it the standard way to map large areas. Today it produces maps, building surveys and 3D records of objects too fragile to handle, and drones and phone apps use the same principle.

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