Inertial Confinement Fusion

When nuclear physicists were able to make the transition from fissile atomic bombs to fusion-driven thermonuclear bombs in less than a decade, it seemed that the harnessing of fusion power for the electrical grid was imminent. At the time nuclear fusion was considered the energy source of the future, and today it remains just that. It turned out that containing a miniature star in a magnetic bottle was much harder than initially anticipated. Taking in this melancholy state of affairs, by the 1970s researchers decided to try to make fusion easier by adding giant lasers to the reactor. The result was a serious effort toward using shock and swiftness rather than magnets to contain the fusing material that remains in work today. You can read more about the concept here:

Inertial confinement fusion

The heavy nuclei required for fission reactors are naturally unstable, and only need a slight touch from their neighbors to cleave apart, releasing energy in the process. By contrast, fusion aims to bring nuclei together that are content to remain themselves, and the reactor has to push each nucleus up a long hill of electrostatic repulsion to bring them close enough to embrace. The energy release from each union of two hydrogen atoms is several times more potent per unit mass than that from each split of a uranium or plutonium atom, and either reaction is staggeringly powerful compared to the chemical reactions of molecules. Fusion also has the distinct advantage over fission of using fuel abundant in nature (or readily available in our nuclear stockpiles, at least) that leaves behind no vile radioactive residue. But how to bring the hydrogen together?

Three things are required for such nuclear wizardry - heat, density, and time. Stars, the natural reactors that light up the universe, have all three in abundance. Since waiting billions of years for two nuclei to fuse doesn't make many friends on the power grid, typical fusion reactor designs speed up the reaction by using heavier isotopes of hydrogen more amenable to attachment, and by cranking the temperature above that at the center of the Sun. Under such conditions, the average nucleus of deuterium or tritium will spend a matter of seconds or minutes in the reactor before fusing. Inertial confinement reactors aim to fuse everything in a matter of microseconds by exceeding the Sun in both temperature and density.

Inertial confinement fusion's principle of operation is charmingly simple. For a few trillionths of a second, the reactor delivers trillions of watts of laser light into a pinhead-size pellet of fuel. The flash transforms the surface of the fuel into an explosive shock wave of plasma rocketing both outward and inward toward the fuel's center. On the way in, the wave sweeps up fuel along with it, knocking atoms closer and closer until the pellet, or what's left of it, is up to a hundred times denser than lead and six times hotter than the center of the Sun. At this point, the fuel ignites, and if all goes well it releases about the amount of energy of a barrel of oil without all those pesky carbon dioxide emissions.

Predictably things are a bit more complicated than that, but although inertial confinement reactors quickly advanced to the efficiency of the best magnetic confinement reactors of the time could do in the 1980s, progress since has been slow. Physicists found that while the push of the shock front is considerable, it isn't overwhelming, and turbulence in the wave tends to cause mixing before full compression. Like engine knock in a car, some of the fuel burns to early and fouls the reaction, keeping it from producing more power than the lasers provide. The tolerances required of the laser beams and pellet geometry are formidable, and make fueling the reactor for more than a few experimental shots a severe challenge. Modern lasers are horridly inefficient, and it's unclear if it's possible to unleash more energy from the fusion reaction than the lasers deliver without a fundamental breakthrough in the physics of coherent light. None of this means that power from inertial confinement fusion is impossible, but it leads the curious to consider other options.

Since the harnessing of gravity seems beyond the scope of our current understanding of physics, the only credible alternative is magnetism. Most experimental fusion reactors use intense magnetic fields to bottle up the plasma like a battery of lightning. My friend who does research on plasmas and their application to spacecraft propulsion likens this problem to "holding up a ball of water with a whole bunch of sharpened pencils." Magnetic boxes are really more like nets, and the hottest atoms tend to leak out first, leaving the bulk too cold to light up. This is an exotic physics regime where the outlands of heat, nuclear forces, magnets, and fluid dynamics share an uneasy border. Nobody quite understands what happens here, and the reactors still don't unlock more energy than it takes to light them.

Will fusion, magnetically- or inertially-confined, always be the power source of the future? Kim Stanley Robinson thought not. In Blue Mars he imagines great spaceworthy liners powered by inertial-confinement fusion plying back and forth between the planets in a matter of days, their engines doubling as gravity simulators since the ships never stop accelerating. The imagery bewitches the mind, but for now it's a mirage. Some day, maybe with lasers, maybe with magnets, I'm confident that we'll master the ways of hydrogen and helium. The solar system will seem a little more human-sized then, but for now it remains as vast as the Pacific to those who first set foot on the islands of Polynesia.

The R-36

The largest intercontinental ballistic missile ever fielded was a two-stage Soviet rocket called the R-36, which was later upgraded and re-dubbed the R-36M. Both variants were powered by a hypergolic mixture of unsymmetrical dimethylhydrazine and nitrogen tetroxide, could carry a payload of 8 metric tons across the globe in less than an hour, and are among the most terrifying engines of war ever put into mass production. You can read more about the vehicle family here:
R-36

Large rockets are always spectacular when they leave Earth, but the R-36 launches with particular flair. Unlike American ICBMs, which light their engines in the silo and emerge from the ground under their own power, the R-36 is hurled forth with a large black-powder-driven piston like a giant mortar shot. Once the missile clears the surface, the protective piston is thrown away under rocket power, the main engines ignite, and the the R-36's powered flight begins. This may seem excessively baroque, especially for a design from an engineering culture better known for robust simplicity, but it protects the missile and silo from thermal and acoustic damage from running mind-blowingly loud and hot rocket engines in an underground tube. It's also mesmerizing to watch on video:

The payload carried by the R-36 is the stuff that night terrors are made of. Early models carried a single warhead with a yield of up to 25 megatons, while later versions are capable of launching a flotilla of up to 10 warheads in the 500 kiloton range and dozens of decoys, jammers, and other penetration aids. Large single bombs are useful for destroying hardened targets or for causing continent-scale blackouts with electromagnetic pulses in the ionosphere, but clusters of smaller bombs (each still at least 30 times as powerful as the atomic bombs dropped on Japan in World War II) are more useful for destroying large areas like cities.

It's important to understand just how different large thermonuclear bombs are from the relatively small fission bombs deployed in the 1940s. The bombs dropped on Hiroshima and Nagasaki were awe-inspiring devices, but the large single warheads carried by early R-36s were able to unleash a thousand times more energy. James Cameron was a physics major in college, and unsurprisingly the most accurate depiction of large thermonuclear weapons that I know of appears in his movie Terminator 2. It's easy to find on youtube if you want to see it. Suffice it to say that because of the way physics works small bombs deliver much of their energy in pressure waves while big bombs are dominated by a star-like pulse of heat energy. There's an interesting discussion to be had on why this is the case, but the more relevant question is "Why do you want this?"

I'm not suggesting that anyone (or at least any sane person in a position of power) actually wants to burn Moscow, Washington, or Beijing to the ground, but the superpowers have spent trillions of dollars over the last half century to be able to set any city of their choice on fire in 45 minutes or less. Clearly this capability is wanted, and not just by a select few. There's a plausible argument to made that big bombs and fast delivery systems discourage anyone from being dumb enough to start a peer-to-peer war among Earth's armed forces, but it's disingenuous to think of these systems as direct engines of peace. Global diplomatic harmony doesn't emerge in the law of mass action when UDMH is burned with nitrogen tetroxide.

The R-36's history as an enabling device for thermonuclear madness is troubled, to say the least, but out of this thuggish background a much more practical second life has emerged for those missiles decommissioned by the START weapons reduction treaties. For a time during the Cold War some R-36s were equipped not to ride straight to their targets but to linger in Earth orbit for a short time before descending to their destinations. This reduces the missiles' payload, but enables a strike anywhere in the world on any heading from any launch site, confounding the adversary's defenses. This makes nuclear war profoundly confusing in addition to its basic hellishness. When the parking of nuclear weapons on orbit was explicitly banned by the SALT II treaty, this system was phased out, but the R-36 remained a creature worthy of plying the space beyond Earth.

When the statues of Lenin fell, first in Berlin, then in Moscow, and Americans and Russians began sharing space stations and the other fruits of advanced technology, the machines made to drive fright into the heart of every American began lofting their spacecraft into orbit, at a reasonable price. Among other payloads, two experimental space stations designed by Bigelow Aerospace have been launched so far. Weapons of mass destruction remain an infection we'd do well to eradicate, but for now at least there's some progress that shows a more civilized world ahead.

The Inception Button

There exists a page on the internet that was created for the sole purpose of providing the dramatic sound from the Inception trailer when pressed. That page is located here.

That'ts all for now. On a housekeeping note, I'm planning on returning to a regular schedule on this blog, this time Monday-Wednesday-Friday to allow more time for meaningful commentary without getting in the way of all the other goings-on of my life. I anticipate most posts will be more meaningful than this one.