The United States, too, had sought Jodrell Bank’s support soon after Sputnik’s launch, in what was meant to be a superconfidential arrangement, initiated in the spring of 1958 by a US Air Force colonel who had crossed the Atlantic with no announced reason except a desire to meet Lovell. As soon as the pair reached Lovell’s office, the colonel asked that the windows be shut and the doors locked, whereupon “the real conversation then began in a scarcely audible near-whisper.” The US Army had launched America’s first Earth satellite in January 1958; now the Air Force wanted to launch America’s first spacecraft to the Moon in August 1958 and to have Jodrell Bank track its journey. Discussion was out of the question; an immediate decision was required. Tracking equipment and technicians would be sent over from Los Angeles before the launch. Everything must remain completely secret.
Except that when the trailer that held all the equipment arrived, it displayed in giant letters the following ID: “Jodrell Bank, U.S. Air Force, Project Able.” So much for secrecy.
The Manchester Guardian broke the story in July. But the Pioneer 1 launch went ahead anyway, at 8:42 AM on October 11, and the Mark I picked up its signals at 8:52. This was NASA’s first-ever launch. Alas, early on October 13 Pioneer 1 fell back toward Earth and burned up upon re-entering the atmosphere, unable to reach the Moon because it never quite attained escape velocity and its launch angle was off by a few degrees.6 No matter. Occasional failures were inevitable, and officials stopped fretting over secrecy.
The next NASA–Jodrell Bank collaboration, Pioneer 5, was the opposite of a failure. On March 11, 1960, twelve minutes after the spacecraft launched from Cape Canaveral, the Mark I started tracking it. This time the radio telescope—“the only instrument which had any hope of transmitting with enough strength to the probe over distances of tens of millions of miles”—would not merely track the craft but also command it and receive scientific data from its onboard experiments:
At 1.25 p.m. when Pioneer was 5,000 miles from earth a touch on a button in the trailer at Jodrell transmitted a signal to the probe which fused the explosive bolts holding the payload to the carrier rocket. Immediately the nature of the received signals changed and we knew that Pioneer V was free, on course and transmitting as planned. For the rest of the day Pioneer responded to the commands of the telescope and when it sank below our horizon on that evening it was already 70,000 miles from earth. The next evening it was beyond the moon.7
For nearly four months, the radio telescope stayed in touch with the spacecraft. The last communication took place on June 26, 1960, at a distance of thirty-six million kilometers from Earth. In the deep vacuum of interplanetary space, with nothing to force a decay in its trajectory, Pioneer 5 continues to orbit the Sun every 312 days.
II.
Whereas radio waves have yielded all manner of benefits, both near at hand and far away, gamma rays are not generally regarded as beneficial. Quite the opposite.
Occupying the high-energy end of the electromagnetic spectrum, gamma rays were discovered as a by-product of radioactivity in 1900. By the 1950s, gamma rays from space were considered a possibility, but were not actually detected until 1961 by a short-lived, new kind of detector aboard NASA’s Explorer XI satellite.
Like X-rays, gamma rays are hard to detect, because they pass right through ordinary lenses and mirrors and thus can’t be focused the way radio waves and visible light can. What works for radio waves, microwaves, infrared, visible, and ultraviolet wavelengths doesn’t work for X-rays or gamma rays. Detectors in these bands require inventive designs. Plus, film registers only visible and UV light; to register signals from objects emitting in other bands, new recording methods were needed.
Explorer XI’s detector was a device called a scintillator, which is as distantly related to a telescope as a whale is to a spider. A scintillator is a tiny block of energy-sensitive material (cesium iodide, for instance) that pumps out tiny flashes of light—charged particles—each time a gamma ray barrels through it. Amplify the flashes with photomultiplier tubes, and you’ve got yourself a detection device. By measuring the energy of all those charged particles, you can tell what kind of radiation created them. During Explorer XI’s four months of tumbling through space, its detector gathered data for twenty-three days and snared a whopping twenty-two certifiable gamma rays.
While “gamma rays” are what we call the shortest wavelengths (and highest energy) of the electromagnetic spectrum, their swath of light is huge. But they’re not the only superhigh-energy stuff in the universe. So-called cosmic rays, which actually consist of particles, are competitively energetic. Hardly any of Earth’s daily dose of gamma rays that originate in deep space reach our planet’s surface. Atmospheric ozone—the three-atom version of the oxygen molecule—shields us nicely, though not entirely, from them, as well as from solar or anybody else’s UV and spaceborne X-rays. To detect gamma rays reliably requires specialized satellites in orbit above our atmosphere.
As you might suspect, high-energy phenomena breed high-energy light. Try to imagine the simultaneous detonation of all the nuclear bombs ever made, including those exploded during war or in preparation for war, together with those disassembled in the name of peace. Imagine a star a hundred times as massive as the Sun, collapsing in on itself at the hour of its death. Imagine a sprawling galaxy, formed during the first billion years of our universe’s lifetime, and the colossal black hole that lurks at its galactic center, entombing the substance of many billions of long-dead stars and continually swallowing everything within reach. Or imagine the remnant of an exploded giant star—a remnant so dense that a thimbleful would weigh a hundred million tons—spinning in faraway space at tens of thousands of times a second as it crashes into a neighbor. These fierce, violent configurations of matter, these superhigh-energy events, have superhigh-energy consequences. One of those consequences is a sudden, brief, often beamed burst of gamma rays: an explosion of astronomical proportions. A single burst can out-radiate an entire galaxy—as though the energy output of a hundred billion Suns were concentrated into a few moments of overwhelming brilliance. Wildly dramatic . . . and deadly, if you’re in the neighborhood.8
On average once a day, a gamma-ray burst occurs somewhere in the distant universe. The relatively weaker ones last less than a second; the rarer, highly energetic ones last as much as a few minutes. The source of all that energy is a mélange of gravitational, rotational, magnetic, and thermonuclear phenomena. The object releasing the energy might be a supernova, a kilonova, a hypernova, a blazar, or a quasar. Could also be stuff just before it falls into a black hole, or a nuclear explosion down here on Earth. Repeat: a nuclear explosion down here on Earth. Human ingenuity has conceived, invented, and deployed an equivalent of one of nature’s least friendly phenomena.
We still don’t have the full story on how cosmic gamma-ray bursts are generated. But before astrophysicists even knew cosmic gamma rays existed, both scientists and politicians knew that a terrestrial version would occur if and when a thermonuclear fusion bomb exploded.9 Whether the detonation was a test or an actual attack would make no difference, nor would it matter whether it took place in the middle of a desert, in the middle of Manhattan, or on the Moon. Nevertheless, when the twentieth century’s second all-out multinational war ended, the design of annihilation-class weaponry proceeded apace, causing as much fear and mistrust among the designers as among the bystanders. Einstein himself, acutely aware of the world’s newfound capacity for annihilation, said in a 1949 interview in Liberal Judaism, “I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones.”10
Faced with all that progress in destructive capacity and increasingly aware of the longer-term effects of radioactive fallout, the foreign ministers of the Soviet Union, the United States, and the United Kingdom signed the Limited Nuclear Test Ban Treaty in early August 1963. In this case, “Limited” left the door wide open for underground testing. Two months later, after the US Se
nate had ratified the treaty, President Kennedy signed it. On October 10 it attained the force of law.
Any political skeptic will tell you that abiding by a treaty is an entirely separate matter from signing a treaty. It now became necessary (and possible) to monitor from space any telltale signs of an impermissible detonation on Earth. To do so, the US would send up a few satellites carrying state-of-the-art gamma-ray detectors. These satellites were not telescopes. They were simply orbiting detectors, unable to pinpoint the exact spot of a thermonuclear explosion. But a set of them, each recording the exact arrival time of the gamma rays, would make it possible to triangulate the location. Furthermore, if the orbits were high enough, the satellites would escape the electromagnetic noise created by the Van Allen radiation belt—a region of space that one NASA writer memorably described as “two donuts of seething radiation” enveloping our planet.11
The ink was barely dry on the treaty when, on October 16, 1963, in the spirit of the military mantra “Trust but Verify,” the United States launched its first pair of Vela Hotel satellites, spaced 180 degrees apart, into a very high orbit—a hundred thousand kilometers, far beyond Earth’s atmosphere and well clear of the Van Allen belt. Their mandate was straightforward: to detect any gamma-ray emissions produced by any explosion of any nuclear bomb. Their detector was a scintillator.
The second pair of Vela Hotels was launched in July 1964, the third in July 1965, the sixth and last pair in April 1970. Work had begun in 1959 under President Eisenhower as a project of the Advanced Research Projects Agency, with help from the Atomic Energy Commission’s laboratories at Los Alamos. With each new pair, the sensitivity of the detectors and the precision of the timers improved. The Vela Hotels were a durable product, most lasting a decade or more beyond their planned life.12
As they circled Earth every four and a quarter days, one or another of the Vela satellites periodically registered hits from high-energy solar particles—nothing to worry about, nothing catastrophic. By contrast, if and when a thermonuclear weapon was exploded, it would register on all satellites in sightline of the event, showing up as an intense gamma-ray burst less than a millionth of a second in duration, followed by a leveling and then a fade-out, followed by hours or days of afterglow. Eventually, on July 2, 1967, the Velas did register a powerful gamma-ray event. The weird thing was, it didn’t fit the profile of a nuclear explosion. The recording shows a soaring initial peak lasting less than an eighth of a second, followed almost immediately by a second, somewhat lower peak lasting two seconds.13 Not a nuclear explosion. Also not a solar flare or a supernova, since none had been observed that day.
A couple of assiduous young astrophysicists at Los Alamos, Ray Klebesadel and Roy Olson, were the first to figure out what it was not and what it might be. But being scientists and also being attached to one of the country’s two classified national laboratories dedicated to developing nuclear weapons, they held off in hopes of gathering better evidence—which they got from upgraded pairs of Vela satellites, equipped with better instruments, that were launched in 1969 and 1970. After processing vast quantities of “noisy” Vela data, they and a colleague, Ian Strong, identified sixteen gamma-ray bursts between July 1969 and July 1972 that fulfilled their careful criteria (being recorded by at least two Vela craft within an interval of no more than four seconds). Those sixteen bursts reinforced the investigators’ July 1967 finding. In 1973, they published—which, in practice, means declassified—the results. It’s a typical scientific article for the Astrophysical Journal, calm and circumspect. The closest the authors come to saying they’ve identified something new and big in the universe is the understated assertion that “[i]nverse-square law considerations thereby place the sources at a distance of at least 10 orbit diameters”14—three billion kilometers minimum.
It’s not as though gamma-ray research and gamma-ray detectors didn’t exist prior to that article. But the findings of Klebesadel, Strong, and Olson stimulated a groundswell of new effort. The military’s interest in detecting extremely high-energy explosions ended up exploding what had previously been a low-profile branch of astrophysics. Space-based detectors came online, superseding ground-based detectors made from recycled World War II matériel.15
Incidentally, gamma rays and a myriad of subatomic particles are generated by the collision of superhigh-energy cosmic rays with Earth’s atmosphere. Within this cascade lurks striking evidence of time dilation, a feature of Einstein’s theory of relativity. Cosmic-ray particles move through space at upward of 99.5 percent the speed of light. When they slam into the top of Earth’s atmosphere, they break down into many subproducts, each with less and less energy per particle, forming an avalanche of elementary particles that descend toward Earth’s surface. Among the subproducts is a shower of gamma rays, which swiftly transform into electrons and their antimatter counterparts, positrons.
Also in the mix you’ll find muons, which are the high-energy, heavy version of the electron. They’re not particularly stable. After a half-millionth of a second, on average, they decay into other, less energetic particles, one of which will always be an electron. Compared with the life expectancies of many other subatomic particles, a half-millionth of a second is an eternity. But because the particle shower moves so fast relative to us and our detectors on Earth’s surface, the muons experience the passage of time more slowly than we do. Enter the bizarre world of Einstein’s special theory of relativity. This branch of physics doesn’t care who or what you are, whether you’re an animal, vegetable, or mineral. If you travel fast, several weird things happen. One is that your inner time clock will appear to tick more slowly, as seen by all those who observe you. Your time “dilates.” And muons in a cosmic-ray cascade offer one of the most striking tests of this phenomenon. Because they travel at such high speeds, we see them living ten times longer before they decay—and, as a result, reaching much deeper into Earth’s atmosphere—than they “should.”
If you don’t happen to be going as fast as a muon, you’ll still experience a little time dilation. Spend six months on the International Space Station, which is traveling five miles per second around Earth (a mere 0.0027 percent the speed of light), and you will have aged 0.005 seconds less than everybody else on Earth.
III.
Since everything warmer than absolute zero radiates heat, detecting infrared at a distance means, in principle, detecting everything. Period. As a result, every astrophysicist as well as every general, counterrevolutionary, spy, cop, and drone that needs to identify an otherwise invisible target could search for it in infrared. But what the warfighter must also do is distinguish what is from what is not a threat. Simply detecting a patch of oddly intense infrared isn’t enough. Surveillants need to know the “heat signature” of their target so they can isolate and differentiate it from the manifold other infrared sources that crowd the theater of operations.
Out there in the cosmos, the cooler residents—those with temperatures below about 1000 kelvins (700 degrees Celsius), which includes planets, failed stars, cosmic dust, and assorted clouds in galaxies, especially those about to give birth to star systems—emit more infrared than any other band of light. Anything hotter than that also begins to glow in the visible part of the spectrum, rendering it plainly visible to anybody looking, initially appearing “red hot” but then, as its temperature rises further, “white hot” and finally “blue hot.” So if you want to see cool objects, best use an infrared telescope.
Also, infrared light escapes clouds of gas and dust much more readily than does visible light, even when the visible light is highly luminous. This is where an all-sky survey and the US Air Force’s Infrared Celestial Backgrounds program enter the picture.
To distinguish the infrared signature of a missile in the sky headed for the presidential palace from the infrared signature of a cosmic object, the general needs a sky map. The general provides the funding. The astrophysicist provides the map. Whereas the discovery of gamma-ray bursts was a serendipitous by-
product of the normal work of military surveillance, comprehensive infrared sky maps were the intentional result of a military initiative meant to furnish surveillance with a necessary tool. As an Air Force fact sheet explains it:
Ballistic missile defense is an important mission with the need to develop technologies for detecting and tracking theater and strategic ballistic missiles from launch to intercept. . . . Effective tracking of cold-body and dim targets in the IR spectral region requires the IR signature of the target to be distinguished from the background against which the target is observed. The issue is that the background can mask or mimic the target. Therefore, [a] key technical goal is to measure and model the full range of backgrounds, particularly challenging backgrounds, in order to design IR sensor systems which will maximize the visibility of the target signature.16
This problem is not unique to infrared. Any measurement of anything by any means risks getting confused with background noise. We’re all familiar with literal noise. An intimate conversation between you and a loved one can occur without confusion in a quiet room, whereas at a crowded cocktail party you will need to speak well above a whisper to be heard and understood—to be detected. “Noise” includes any unwanted signal that contaminates the target of measurement.
When the earliest infrared investigations took place, most scientists presumed radiant heat and visible light to be two different things, although in 1835 André-Marie Ampère published a note proposing that they were both the result of “vibratory motion.”17 Early IR detectors were upgraded versions of the thermometer, suited to modest achievements such as measuring the heat signature of a cow a quarter mile away. But in the summer of 1878, when infrared wasn’t yet called infrared—its discoverer, William Herschel, had used the term “calorific rays”—an unnamed commentator in Scientific American described Thomas Alva Edison’s ambitious proposal for a sky survey of invisible sources of heat. To carry out the survey, Edison’s own heat-sensitive astronomical invention, the tasimeter, would be attached to a large telescope in order to “explore those parts of the heavens which appear blank”:
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