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Saturday, April 23, 2016

Reading List: Coming Home

Launius, Roger D. and Dennis R. Jenkins. Coming Home. Washington: National Aeronautics and Space Administration, 2012. ISBN 978-0-16-091064-7. NASA SP-2011-593.
In the early decades of the twentieth century, when visionaries such as Konstantin Tsiolkovsky, Hermann Oberth, and Robert H. Goddard started to think seriously about how space travel might be accomplished, most of the focus was on how rockets might be designed and built which would enable their payloads to be accelerated to reach the extreme altitude and velocity required for long-distance ballistic or orbital flight. This is a daunting problem. The Earth has a deep gravity well: so deep that to place a satellite in a low orbit around it, you must not only lift the satellite from the Earth's surface to the desired orbital altitude (which isn't particularly difficult), but also impart sufficient velocity to it so that it does not fall back but, instead, orbits the planet. It's the speed that makes it so difficult.

Recall that the kinetic energy of a body is given by ½mv². If mass (m) is given in kilograms and velocity (v) in metres per second, energy is measured in joules. Note that the square of the velocity appears in the formula: if you triple the velocity, you need nine times the energy to accelerate the mass to that speed. A satellite must have a velocity of around 7.8 kilometres/second to remain in a low Earth orbit. This is about eight times the muzzle velocity of the 5.56×45mm NATO round fired by the M-16 and AR-15 rifles. Consequently, the satellite has sixty-four times the energy per unit mass of the rifle bullet, and the rocket which places it into orbit must expend all of that energy to launch it.

Every kilogram of a satellite in a low orbit has a kinetic energy of around 30 megajoules (thirty million joules). By comparison, the energy released by detonating a kilogram of TNT is 4.7 megajoules. The satellite, purely due to its motion, has more than six times the energy as an equal mass of TNT. The U.S. Space Shuttle orbiter had a mass, without payload, of around 70,000 kilograms. When preparing to leave orbit and return to Earth, its kinetic energy was about that of half a kiloton of TNT. During the process of atmospheric reentry and landing, in about half an hour, all of that energy must be dissipated in a non-destructive manner, until the orbiter comes to a stop on the runway with kinetic energy zero.

This is an extraordinarily difficult problem, which engineers had to confront as soon as they contemplated returning payloads from space to the Earth. The first payloads were, of course, warheads on intercontinental ballistic missiles. While these missiles did not go into orbit, they achieved speeds which were sufficiently fast as to present essentially the same problems as orbital reentry. When the first reconnaissance satellites were developed by the U.S. and the Soviet Union, the technology to capture images electronically and radio them to ground stations did not yet exist. The only option was to expose photographic film in orbit then physically return it to Earth for processing and interpretation. This was the requirement which drove the development of orbital reentry. The first manned orbital capsules employed technology proven by film return spy satellites. (In the case of the Soviets, the basic structure of the Zenit reconnaissance satellites and manned Vostok capsules was essentially the same.)

This book chronicles the history and engineering details of U.S. reentry and landing technology, for both unmanned and manned spacecraft. While many in the 1950s envisioned sleek spaceplanes as the vehicle of choice, when the time came to actually solve the problems of reentry, a seemingly counterintuitive solution came to the fore: the blunt body. We're all acquainted with the phenomenon of air friction: the faster an airplane flies, the hotter its skin gets. The SR-71, which flew at three times the speed of sound, had to be made of titanium since aluminium would have lost its strength at the temperatures which resulted from friction. But at the velocity of a returning satellite, around eight times faster than an SR-71, air behaves very differently. The satellite is moving so fast that air can't get out of the way and piles up in front of it. As the air is compressed, its temperature rises until it equals or exceeds that of the surface of the Sun. This heat is then radiated in all directions. That impinging upon the reentering body can, if not dealt with, destroy it.

A streamlined shape will cause the compression to be concentrated at the nose, leading to extreme heating. A blunt body, however, will cause a shock wave to form which stands off from its surface. Since the compressed air radiates heat in all directions, only that radiated in the direction of the body will be absorbed; the rest will be harmlessly radiated away into space, reducing total heating. There is still, however, plenty of heat to worry about.

Let's consider the Mercury capsules in which the first U.S. astronauts flew. They reentered blunt end first, with a heat shield facing the air flow. Compression in the shock layer ahead of the heat shield raised the air temperature to around 5800° K, almost precisely the surface temperature of the Sun. Over the reentry, the heat pulse would deposit a total of 100 megajoules per square metre of heat shield. The astronaut was just a few centimetres from the shield, and the temperature on the back side of the shield could not be allowed to exceed 65° C. How in the world do you accomplish that?

Engineers have investigated a wide variety of ways to beat the heat. The simplest are completely passive systems: they have no moving parts. An example of a passive system is a “heat sink”. You simply have a mass of some substance with high heat capacity (which means it can absorb a large amount of energy with a small rise in temperature), usually a metal, which absorbs the heat during the pulse, then slowly releases it. The heat sink must be made of a material which doesn't melt or corrode during the heat pulse. The original design of the Mercury spacecraft specified a beryllium heat sink design, and this was flown on the two suborbital flights, but was replaced for the orbital missions. The Space Shuttle used a passive heat shield of a different kind: ceramic tiles which could withstand the heat on their surface and provided insulation which prevented the heat from reaching the aluminium structure beneath. The tiles proved very difficult to manufacture, were fragile, and required a great deal of maintenance, but they were, in principle, reusable.

The most commonly used technology for reentry is ablation. A heat shield is fabricated of a material which, when subjected to reentry heat, chars and releases gases. The gases carry away the heat, while the charred material which remains provides insulation. A variety of materials have been used for ablative heat shields, from advanced silicone and carbon composites to oak wood, on some early Soviet and Chinese reentry experiments. Ablative heat shields were used on Mercury orbital capsules, in projects Gemini and Apollo, all Soviet and Chinese manned spacecraft, and will be used by the SpaceX and Boeing crew transport capsules now under development.

If the heat shield works and you make it through the heat pulse, you're still falling like a rock. The solution of choice for landing spacecraft has been parachutes, and even though they seem simple conceptually, in practice there are many details which must be dealt with, such as stabilising the falling craft so it won't tumble and tangle the parachute suspension lines when the parachute is deployed, and opening the canopy in multiple stages to prevent a jarring shock which might damage the parachute or craft.

The early astronauts were pilots, and never much liked the idea of having to be fished out of the ocean by the Navy at the conclusion of their flights. A variety of schemes were explored to allow piloted flight to a runway landing, including inflatable wings and paragliders, but difficulties developing the technologies and schedule pressure during the space race caused the Gemini and Apollo projects to abandon them in favour of parachutes and a splashdown. Not until the Space Shuttle were precision runway landings achieved, and now NASA has abandoned that capability. SpaceX hopes to eventually return their Crew Dragon capsule to a landing pad with a propulsive landing, but that is not discussed here.

In the 1990s, NASA pursued a variety of spaceplane concepts: the X-33, X-34, and X-38. These projects pioneered new concepts in thermal protection for reentry which would be less expensive and maintenance-intensive than the Space Shuttle's tiles. In keeping with NASA's practice of the era, each project was cancelled after consuming a large sum of money and extensive engineering development. The X-37 was developed by NASA, and when abandoned, was taken over by the Air Force, which operates it on secret missions. Each of these projects is discussed here.

This book is the definitive history of U.S. spacecraft reentry systems. There is a wealth of technical detail, and some readers may find there's more here than they wanted to know. No specialised knowledge is required to understand the descriptions: just patience. In keeping with NASA tradition, quaint units like inches, pounds, miles per hour, and British Thermal Units are used in most of the text, but then in the final chapters, the authors switch back and forth between metric and U.S. customary units seemingly at random. There are some delightful anecdotes, such as when the designers of NASA's new Orion capsule had to visit the Smithsonian's National Air and Space Museum to examine an Apollo heat shield to figure out how it was made, attached to the spacecraft, and the properties of the proprietary ablative material it employed.

As a NASA publication, this book is in the public domain. The paperback linked to above is a republication of the original NASA edition. The book may be downloaded for free from the book's Web page in three electronic formats: PDF, MOBI (Kindle), and EPUB. Get the PDF! While the PDF is a faithful representation of the print edition, the MOBI edition is hideously ugly and mis-formatted. Footnotes are interleaved in the text at random locations in red type (except when they aren't in red type), block quotes are not set off from the main text, dozens of hyphenated words and adjacent words are run together, and the index is completely useless: citing page numbers in the print edition which do not appear in the electronic edition; for some reason large sections of the index are in red type. I haven't looked at the EPUB edition, but given the lack of attention to detail evident in the MOBI, my expectations for it are not high.

Posted at 19:25 Permalink

Saturday, April 16, 2016

Reading List: Obsessive Genius

Goldsmith, Barbara. Obsessive Genius. New York: W. W. Norton, 2005. ISBN 978-0-393-32748-9.
Maria Salomea Skłodowska was born in 1867 in Warsaw, Poland, then part of the Russian Empire. She was the fifth and last child born to her parents, Władysław and Bronisława Skłodowski, both teachers. Both parents were members of a lower class of the aristocracy called the Szlachta, but had lost their wealth through involvement in the Polish nationalist movement opposed to Russian rule. They retained the love of learning characteristic of their class, and had independently obtained teaching appointments before meeting and marrying. Their children were raised in an intellectual atmosphere, with their father reading books aloud to them in Polish, Russian, French, German, and English, all languages in which he was fluent.

During Maria's childhood, her father lost his teaching position after his anti-Russian sentiments and activities were discovered, and supported himself by operating a boarding school for boys from the provinces. In cramped and less than sanitary conditions, one of the boarders infected two of the children with typhus: Marie's sister Zofia died. Three years later, her mother, Bronisława, died of tuberculosis. Maria experienced her first episode of depression, a malady which would haunt her throughout life.

Despite having graduated from secondary school with honours, Marie and her sister Bronisława could not pursue their education in Poland, as the universities did not admit women. Marie made an agreement with her older sister: she would support Bronisława's medical education at the Sorbonne in Paris in return for her supporting Maria's studies there after she graduated and entered practice. Maria worked as a governess, supporting Bronisława. Finally, in 1891, she was able to travel to Paris and enroll in the Sorbonne. On the registration forms, she signed her name as “Marie”.

One of just 23 women among the two thousand enrolled in the School of Sciences, Marie studied physics, chemistry, and mathematics under an eminent faculty including luminaries such as Henri Poincaré. In 1893, she earned her degree in physics, one of only two women to graduate with a science degree that year, and in 1894 obtained a second degree in mathematics, ranking second in her class.

Finances remained tight, and Marie was delighted when one of her professors, Gabriel Lippman, arranged for her to receive a grant to study the magnetic properties of different kinds of steel. She set to work on the project but made little progress because the equipment she was using in Lippman's laboratory was cumbersome and insensitive. A friend recommended she contact a little-known physicist who was an expert on magnetism in metals and had developed instruments for precision measurements. Marie arranged to meet Pierre Curie to discuss her work.

Pierre was working at the School of Industrial Physics and Chemistry of the City of Paris (EPCI), an institution much less prestigious than the Sorbonne, in a laboratory which the visiting Lord Kelvin described as “a cubbyhole between the hallway and a student laboratory”. Still, he had major achievements to his credit. In 1880, with his brother Jacques, he had discovered the phenomenon of piezoelectricity, the interaction between electricity and mechanical stress in solids. Now the foundation of many technologies, the Curies used piezoelectricity to build an electrometer much more sensitive than previous instruments. His doctoral dissertation on the effects of temperature on the magnetism of metals introduced the concept of a critical temperature, different for each metal or alloy, at which permanent magnetism is lost. This is now called the Curie temperature.

When Pierre and Marie first met, they were immediately taken with one another: both from families of modest means, largely self-educated, and fascinated by scientific investigation. Pierre rapidly fell in love and was determined to marry Marie, but she, having been rejected in an earlier relationship in Poland, was hesitant and still planned to return to Warsaw. Pierre eventually persuaded Marie, and the two were married in July 1895. Marie was given a small laboratory space in the EPCI building to pursue work on magnetism, and henceforth the Curies would be a scientific team.

In the final years of the nineteenth century “rays” were all the rage. In 1896, Wilhelm Conrad Röntgen discovered penetrating radiation produced by accelerating electrons (which he called “cathode rays”, as the electron would not be discovered until the following year) into a metal target. He called them “X-rays”, using “X” as the symbol for the unknown. The same year, Henri Becquerel discovered that a sample of uranium salts could expose a photographic plate even if the plate were wrapped in a black cloth. In 1897 he published six papers on these “Becquerel rays”. Both discoveries were completely accidental.

The year that Marie was ready to begin her doctoral research, 65 percent of the papers presented at the Academy of Sciences in Paris were devoted to X-rays. Pierre suggested that Marie investigate the Becquerel rays produced by uranium, as they had been largely neglected by other scientists. She began a series of experiments using an electrometer designed by Pierre. The instrument was sensitive but exasperating to operate: Lord Rayleigh later wrote that electrometers were “designed by the devil”. Patiently, Marie measured the rays produced by uranium and then moved on to test samples of other elements. Among them, only thorium produced detectable rays.

She then made a puzzling observation. Uranium was produced from an ore called pitchblende. When she tested a sample of the residue of pitchblende from which all of the uranium had been extracted, she measured rays four times as energetic as those from pure uranium. She inferred that there must be a substance, perhaps a new chemical element, remaining in the pitchblende residue which was more radioactive than uranium. She then tested a thorium ore and found it also to produce rays more energetic than pure thorium. Perhaps here was yet another element to be discovered.

In March 1898, Marie wrote a paper in which she presented her measurements of the uranium and thorium ores, introduced the word “radioactivity” to describe the phenomenon, put forth the hypothesis that one or more undiscovered elements were responsible, suggested that radioactivity could be used to discover new elements, and, based upon her observations that radioactivity was unaffected by chemical processes, that it must be “an atomic property”. Neither Pierre nor Marie were members of the Academy of Sciences; Marie's former professor, Gabriel Lippman, presented the paper on her behalf.

It was one thing to hypothesise the existence of a new element or elements, and entirely another to isolate the element and determine its properties. Ore, like pitchblende, is a mix of chemical compounds. Starting with ore from which the uranium had been extracted, the Curies undertook a process to chemically separate these components. Those found to be radioactive were then distilled to increase their purity. With each distillation their activity increased. They finally found two of these fractions contained all the radioactivity. One was chemically similar to barium, while the other resembled bismuth. Measuring the properties of the fractions indicated they must be a mixture of the new radioactive elements and other, lighter elements.

To isolate the new elements, a process called “fractionation” was undertaken. When crystals form from a solution, the lighter elements tend to crystallise first. By repeating this process, the heavier elements could slowly be concentrated. With each fractionation the radioactivity increased. Working with the fraction which behaved like bismuth, the Curies eventually purified it to be 400 times as radioactive as uranium. No spectrum of the new element could yet be determined, but the Curies were sufficiently confident in the presence of a new element to publish a paper in July 1898 announcing the discovery and naming the new element “polonium” after Marie's native Poland. In December, working with the fraction which chemically resembled barium, they produced a sample 900 times as radioactive as uranium. This time a clear novel spectral line was found, and at the end of December 1898 they announced the discovery of a second new element, which they named “radium”.

Two new elements had been discovered, with evidence sufficiently persuasive that their existence was generally accepted. But the existing samples were known to be impure. The physical and chemical properties of the new elements, allowing their places in the periodic table to be determined, would require removal of the impurities and isolation of pure samples. The same process of fractionation could be used, but since it quickly became clear that the new radioactive elements were a tiny fraction of the samples in which they had been discovered, it would be necessary to scale up the process to something closer to an industrial scale. (The sample in which radium had been identified was 900 times more radioactive than uranium. Pure radium was eventually found to be ten million times as radioactive as uranium.)

Pierre learned that the residue from extracting uranium from pitchblende was dumped in a forest near the uranium mine. He arranged to have the Austrian government donate the material at no cost, and found the funds to ship it to the laboratory in Paris. Now, instead of test tubes, they were working with tons of material. Pierre convinced a chemical company to perform the first round of purification, persuading them that other researchers would be eager to buy the resulting material. Eventually, they delivered twenty kilogram lots of material to the Curies which were fifty times as radioactive as uranium. From there the Curie laboratory took over the subsequent purification. After four years, processing ten tons of pitchblende residue, hundreds of tons of rinsing water, thousands of fractionations, one tenth of a gram of radium chloride was produced that was sufficiently pure to measure its properties. In July 1902 Marie announced the isolation of radium and placed it on the periodic table as element 88.

In June of 1903, Marie defended her doctoral thesis, becoming the first woman in France to obtain a doctorate in science. With the discovery of radium, the source of the enormous energy it and other radioactive elements released became a major focus of research. Ernest Rutherford argued that radioactivity was a process of “atomic disintegration” in which one element was spontaneously transmuting to another. The Curies originally doubted this hypothesis, but after repeating the experiments of Rutherford, accepted his conclusion as correct.

In 1903, the Nobel Prize for Physics was shared by Marie and Pierre Curie and Henri Becquerel, awarded for the discovery of radioactivity. The discovery of radium and polonium was not mentioned. Marie embarked on the isolation of polonium, and within two years produced a sample sufficiently pure to place it as element 84 on the periodic table with an estimate of its half-life of 140 days (the modern value is 138.4 days). Polonium is about 5000 times as radioactive as radium. Polonium and radium found in nature are the products of decay of primordial uranium and thorium. Their half-lives are so short (radium's is 1600 years) that any present at the Earth's formation has long since decayed.

After the announcement of the discovery of radium and the Nobel prize, the Curies, and especially Marie, became celebrities. Awards, honorary doctorates, and memberships in the academies of science of several countries followed, along with financial support and the laboratory facilities they had lacked while performing the work which won them such acclaim. Radium became a popular fad, hailed as a cure for cancer and other diseases, a fountain of youth, and promoted by quacks promising all kinds of benefits from the nostrums they peddled, some of which, to the detriment of their customers, actually contained minute quantities of radium.

Tragedy struck in April 1906 when Pierre was killed in a traffic accident: run over on a Paris street in a heavy rainstorm by a wagon pulled by two horses. Marie was inconsolable, immersing herself in laboratory work and neglecting her two young daughters. Her spells of depression returned. She continued to explore the properties of radium and polonium and worked to establish a standard unit to measure radioactive decay, calibrated by radium. (This unit is now called the curie, but is no longer defined based upon radium and has been replaced by the becquerel, which is simply an inverse second.) Marie Curie was not interested or involved in the work to determine the structure of the atom and its nucleus or the development of quantum theory. The Curie laboratory continued to grow, but focused on production of radium and its applications in medicine and industry. Lise Meitner applied for a job at the laboratory and was rejected. Meitner later said she believed that Marie thought her a potential rival to Curie's daughter Irène. Meitner joined the Kaiser Wilhelm Institute in Berlin and went on to co-discover nuclear fission. The only two chemical elements named in whole or part for women are curium (element 96, named for both Pierre and Marie) and meitnerium (element 109).

In 1910, after three years of work with André-Louis Debierne, Marie managed to produce a sample of metallic radium, allowing a definitive measurement of its properties. In 1911, she won a second Nobel prize, unshared, in chemistry, for the isolation of radium and polonium. At the moment of triumph, news broke of a messy affair she had been carrying on with Pierre's successor at the EPCI, Paul Langevin, a married man. The popular press, who had hailed Marie as a towering figure of French science, went after her with bared fangs and mockery, and she went into seclusion under an assumed name.

During World War I, she invented and promoted the use of mobile field X-ray units (called “Les Petites Curies”) and won acceptance for women to operate them near the front, with her daughter Irène assisting in the effort. After the war, her reputation largely rehabilitated, Marie not only accepted but contributed to the growth of the Curie myth, seeing it as a way to fund her laboratory and research. Irène took the lead at the laboratory.

As co-discoverer of the phenomenon of radioactivity and two chemical elements, Curie's achievements were well recognised. She was the first woman to win a Nobel prize, the first person to win two Nobel prizes, and the only person so far to win Nobel prizes in two different sciences. (The third woman to win a Nobel prize was her daughter, Irène Joliot-Curie, for the discovery of artificial radioactivity.) She was the first woman to be appointed a full professor at the Sorbonne.

Marie Curie died of anæmia in 1934, probably brought on by exposure to radiation over her career. She took few precautions, and her papers and personal effects remain radioactive to this day. Her legacy is one of dedication and indefatigable persistence in achieving the goals she set for herself, regardless of the scientific and technical challenges and the barriers women faced at the time. She demonstrated that pure persistence, coupled with a brilliant intellect, can overcome formidable obstacles.

Posted at 20:46 Permalink

Monday, April 11, 2016

Reading List: Blue Gemini

Jenne, Mike. Blue Gemini. New York: Yucca Publishing, 2015. ISBN 978-1-63158-047-5.
It is the late 1960s, and the Apollo project is racing toward the Moon. The U.S. Air Force has not abandoned its manned space flight ambitions, and is proceeding with its Manned Orbiting Laboratory program, nominally to explore the missions military astronauts can perform in an orbiting space station, but in reality a large manned reconnaissance satellite. Behind the curtain of secrecy and under the cover of the blandly named “Aerospace Support Project”, the Air Force was simultaneously proceeding with a much more provocative project: Blue Gemini. Using the Titan II booster and a modified version of the two-man spacecraft from NASA's recently-concluded Gemini program, its mission was to launch on short notice, rendezvous with and inspect uncooperative targets (think Soviet military satellites), and optionally attach a package to them which, on command from the ground, could destroy the satellite, de-orbit it, or throw it out of control. All of this would have to be done covertly, without alerting the Soviets to the intrusion.

Inconclusive evidence and fears that the Soviets, in response to the U.S. ballistic missile submarine capability, were preparing to place nuclear weapons in orbit, ready to rain down onto the U.S. upon command, even if the Soviet missile and bomber forces were destroyed, gave Blue Gemini a high priority. Operating out of Wright-Patterson Air Force Base in Ohio, flight hardware for the Gemini-I interceptor spacecraft, Titan II missiles modified for man-rating, and a launching site on Johnston Island in the Pacific were all being prepared, and three flight crews were in training.

Scott Ourecky had always dreamed of flying. In college, he enrolled in Air Force ROTC, underwent primary flight training, and joined the Air Force upon graduation. Once in uniform, his talent for engineering and mathematics caused him to advance, but his applications for flight training were repeatedly rejected, and he had resigned himself to a technical career in advanced weapon development, most recently at Eglin Air Force Base in Florida. There he is recruited to work part-time on the thorny technical problems of a hush-hush project: Blue Gemini.

Ourecky settles in and undertakes the formidable challenges faced by the mission. (NASA's Gemini rendezvous targets were cooperative: they had transponders and flashing beacons which made them easier to locate, and missions could be planned so that rendezvous would be accomplished when communications with ground controllers would be available. In Blue Gemini the crew would be largely on their own, with only brief communication passes available.) Finally, after an incident brought on by the pressure and grueling pace of training, he finds himself in the right seat of the simulator, paired with hot-shot pilot Drew Carson (who views non-pilots as lesser beings, and would rather be in Vietnam adding combat missions to his service record rather than sitting in a simulator in Ohio on a black program which will probably never be disclosed).

As the story progresses, crisis after crisis must be dealt with, all against a deadline which, if not met, will mean the almost-certain cancellation of the project.

This is fiction: no Gemini interceptor program ever existed (although one of the missions for which the Space Shuttle was designed was essentially the same: a one orbit inspection or snatch-and-return of a hostile satellite). But the remarkable thing about this novel is that, unlike many thrillers, the author gets just about everything absolutely right. This does not stop with the technical details of the Gemini and Titan hardware, but also Pentagon politics, inter-service rivalry, the interaction of military projects with political forces, and the dynamics of the relations between pilots, engineers, and project administrators. It works as a thriller, as a story with characters who develop in interesting ways, and there are no jarring goofs to distract you from the narrative. (Well, hardly any: the turbine engines of a C-130 do not “cough to life”.)

There are numerous subplots and characters involved in them, and when this book comes to an end, they're just left hanging in mid-air. That's because this is the first of a multi-volume work in progress. The second novel, Blue Darker than Black, picks up where the first ends. The third, Pale Blue, is scheduled to be published in August 2016.

Posted at 22:51 Permalink