Centauri Dreams

Let’s start the year with a look back in time to 1957, a time when nuclear bombs were being tested underground for the first time at the Nevada test site some 105 kilometers northwest of Las Vegas. If this seems an unusual place to launch a discussion on interstellar matters, consider the story of an object that some argue became the fastest manmade artifact in history, an object moving so fast that it would have passed the orbit of Pluto four years after ‘launch,’ in the days of Yuri Gagarin and Project Mercury.

I’m bringing it up because the tale of the nuclear test known as Plumbob Pascal B is again active on the Internet, and it’s a rousing tale. Operation Plumbob involved a series of 29 nuclear tests that fed the development of missile warheads both intercontinental and intermediate. The history of such underground nuclear testing would make for an interesting book and indeed it has, in the form of Caging the Dragon (Defense Nuclear Agency, 1995), by one James Carothers.

But let’s narrow our focus to the nuclear devices known as Pascal A and B, the former used used in the first nuclear test below ground. This would have been the first such test in history, as the Soviet Union did not begin its underground program until 1961.

Image: The scene following the detonation of Ranier, an underground nuclear test similar to Pascal B. Credit: Plane Encyclopedia.

The key player here was Robert Brownlee (Los Alamos National Laboratory), who supervised the detonation of Pascal A and duly noted the fact that the yield was much greater than anticipated, so that a column of flame shot into the sky. The blast was not remotely contained. Pascal B was partially an attempt to fix that problem by lowering a 900-kilogram, 4-inch thick iron lid over the borehole. It seemed sensible to at least some at the time, but Brownlee himself evidently did not believe it would work to contain the blast, as indeed it did not.

The detonation of Pascal B caused the blast, like its predecessor, to climb straight up the borehole and escape. The interesting part is that the lid was never found. The only camera footage of the event caught the iron plate in only one frame, and that fact seems to be the source of the current interest. For Brownlee, extrapolating from the speed of the filming (one frame per millisecond) attempted a calculation on the speed of the object. He wound up with something on the order of six times Earth’s escape velocity, which would be 241,920 kilometers per hour, or 67.2 kilometers per second.

That’s an interesting figure! Voyager 1 is moving at about 17.1 kilometers per second and is more or less the yardstick for our thinking about where we are today in achieving deep space velocities. So what is commonly being described as a ‘manhole cover,’ which is pretty much what this object was, is conceivably the fastest moving object humans have ever produced.

Brownlee, recalling these events in 2002, described the iron cap as requiring a lot of ‘man-handlng’ to get it into place. And he goes on to say this:

For Pascal B, my calculations were designed to calculate the time and specifics of the shock wave as it reached the cap. I used yields both expected and exaggerated in my calculations, but significant ones. When I described my results to Bill Ogle [deputy division leader on the project], the conversation went something like this.

Ogle: “What time does the shock arrive at the top of the pipe?”
RRB: “Thirty one milliseconds.”
Ogle: “And what happens?”
RRB: “The shock reflects back down the hole, but the pressures and temperatures are such that the welded cap is bound to come off the hole.”
Ogle: “How fast does it go?”
RRB: “My calculations are irrelevant on this point. They are only valid in speaking of the shock reflection.”
Ogle: “How fast did it go?”
RRB: “Those numbers are meaningless. I have only a vacuum above the cap. No air, no gravity, no real material strengths in the iron cap. Effectively the cap is just loose, traveling through meaningless space.”
Ogle: And how fast is it going?”

This last question was more of a shout. Bill liked to have a direct answer to each one of his questions.

RRB: “Six times the escape velocity from the earth.”

Image: Los Alamos’ Robert Brownlee (1924-2018). Credit: American Astronomical Society.

According to Brownlee, the answer delighted Ogle, who had never heard of a velocity given in terms of escape velocity from the Earth. Brownlee himself notes that because the object was only caught in one camera frame, there was no direct velocity measurement. He could only summarize the situation by saying that the ‘manhole cover’ was “going like a bat!” But he also notes that neither he nor Ogle believed that the cap would actually have made it into space. And the story doesn’t end just yet.

As passed along by my ever-reliable buddy Al Jackson (Centauri Dreams readers will know of Al as astronaut trainer on the Lunar Module Simulator during the Apollo era, and as the author of numerous papers on interstellar propulsion), I point to a set of calculations by one R. Finden titled “The Fastest Object Ever: The Manhole Cover,” evidently sent in response to an article in a magazine called Business Insider in 2016. The note appeared originally on a Reddit thread. Finden notes that his or her work should be considered as a rough estimate because “flight at a mach number upwards of 200 has not been studied and may never be.” Good point.

Finden’s calculations show that the cover would have reached temperatures five times its melting point before it could ever escape the atmosphere. And then this:

If the steel plate were magical and did not burn in the atmosphere, it would have escaped the upper stratosphere (50km) at 53 km/s just 934ms from launch. This not only means it would have made it to space, but it would have eventually escaped our solar system (depending on the time of day at launch). What likely happened was the plate was initially launched parallel to the ground and rotated with oscillation into the upright position, and by that time the drag from the first second of flight decreased its speed enough to prevent it from entering the upper stratosphere.

Conclusion: No manhole cover in space. It’s worth recalling, the Finden note adds, that the Chelyabinsk meteor was moving at only one-third the speed and had 13,900 times the weight of the flying cover, and even this mass was unable to survive Earth’s atmosphere. I dislike this result, as the idea of an object ‘launched’ in 1961 escaping the Solar System while we were still trying to get to the Moon is utterly delightful. And because R Finden’s math skills are well beyond my pay grade, I can’t reach a definitive conclusion about the result. So maybe we can still dream of flying manhole covers even if the odds seem long indeed.

As I write, Voyager 1 is almost 166 AU from the Sun, moving at 17 kilometers per second. With its Voyager 2 counterpart, the mission represents the first spacecraft to operate in interstellar space, continuing to send data with the help of skilled juggling of onboard systems not deemed essential. Despite communications glitches, the mission continues, and it seems a good time to reprise a piece I wrote on the future of these doughty explorers back in 2015. Is there still time to do something new with the two probes once the demise of their plutonium power sources makes further communications impossible? The idea is hardly mine, and goes back to the Sagan era, as the article below explains. It’s also a notion that is purely symbolic, and for those immune to symbolism (the more practical-minded among us) it may seem trivial. But those with a poet’s eye may see the value of an act that can offer a futuristic finish to a mission that passed all expectations and will inspire generations yet unborn.

After Voyager 2 flew past Neptune in 1989, much of the world assumed that the story was over, for there were no further planetary encounters possible. But science was not through with the Voyagers then, and it is not through with the Voyagers now. In one sense, they have become a testbed for showing us how long a spacecraft can continue to operate. In a richer sense, they illustrate how an adaptive and curious species can offer future generations the gift of ‘deep time,’ taking its instruments forward into multi-generational missions of interstellar scope.

Now approximately 24 billion kilometers from Earth, Voyager 1, which took a much different trajectory than its counterpart by leaving the ecliptic due to its encounter with Saturn’s moon Titan, is 166 times as far from the Sun as the Earth (166 AU). Round trip radio time is over 46 hours. The craft has left the heliosphere, a ‘bubble’ that is puffed up and shaped by the stream of particles from the Sun called the ‘solar wind.’ Voyager 1 has become our first interstellar spacecraft, and it will keep transmitting until about 2025, perhaps longer. Voyager 2, its twin, is currently 138 AU out — 20.7 billion kilometers from the Sun — with a round-trip radio time of 38 hours.

Throughout history we have filled in the dark places in our knowledge with the products of our imagination, gradually ceding these visions to reality as expeditions crossed oceans and new lands came into view. The Greek historian Plutarch comments that “geographers… crowd into the edges of their maps parts of the world which they do not know about, adding notes in the margin to the effect, that beyond this lies nothing but sandy deserts full of wild beasts, unapproachable bogs, Scythian ice, or a frozen sea…” But deserts get crossed, first by individuals, then by caravans, and frozen seas yield to the explorer with dog-sled and ice-axe.

Voyager and the Long Result

Space is stuffed with our imaginings, and despite our telescopes, what we find as we explore continues to surprise us. Voyager showed us unexpected live volcanoes on Jupiter’s moon Io and the billiard ball-smooth surface of Europa, one that seems to conceal an internal ocean. We saw an icy Enceladus, now known to spew geysers, and a smog-shrouded Titan. We found ice volcanoes on Neptune’s moon Triton and a Uranian moon — Miranda — with a geologically tortured surface and a cliff that is the highest known in the Solar System.

But the Voyagers are likewise an encounter with time. The issue raises its head because we are still communicating with spacecraft launched almost forty years ago. I doubt many would have placed a wager on the survival of electronics and internal mechanisms to this point, but these are the very issues raised by our explorations, for we still have trouble pushing any payload up to speeds equalling Voyager 1’s 17.1 kilometers per second. To explore the outer Solar System, and indeed to travel beyond it, is to create journeys measured in decades. With the Voyagers as an example, we may one day learn to harden and upgrade our craft for millennial journeys.

New Horizons took nine years to reach Pluto and its large moon Charon. To reach another star? An unthinkable 70,000 years-plus at Voyager 1 speeds, which is why the propulsion problem looms large as we think about dedicated missions beyond the Solar System. If light itself takes over 23 hours to reach Voyager 1, the nearest star, Proxima Centauri, is a numbing 4.2 light years away. To travel at even a paltry one percent of lightspeed, far beyond our capabilities today, would mean a journey to Proxima Centauri lasting well over four centuries.

What is possible near-term? Ralph McNutt, a veteran aerospace designer at the Johns Hopkins Applied Physics Laboratory, has proposed systems that could take a probe to 1000 AU in less than fifty years, giving us the chance to study the Oort Cloud of comets at what may be its inner edge. Now imagine that system ramped up ten times faster, perhaps boosted by a close pass by the Sun and a coordinated shove from a next-generation engine. Now we can anticipate a probe that could reach the Alpha Centauri stars in about 1400 years. Time begins to curl back on itself — we are talking trip times as great as the distance between the fall of Rome and today.

The interesting star Epsilon Eridani, some 10.5 light years out, would be within our reach in something over three thousand years. Go back that far in human history and you would see Sumerian ziggurats whose star maps faced the sky, as our ancestors confronted the unknown with imagined constellations and traced their destinies through star-based prognostications. The human impulse to explain seems universal, as is the pushing back of frontiers. And if these travel times seem preposterous, they’re worth dwelling on, because they help us see where we are with space technology today, and where we’ll need to be to reach the stars.

A certain humility settles in. While we work to improve propulsion systems, ever mindful that breakthroughs can happen in ways that no one expects, we also have to look at the practicalities of long-haul spaceflight. Both Voyagers have become early test cases in how long a spacecraft can last. They also force us to consider how things last in our own civilization. We have buildings on Earth — the Hagia Sophia in Constantinople, the Pantheon in Rome — that have been maintained for longer than the above Alpha Centauri flight time. A so-called ‘generation ship,’ with crew living and dying aboard the craft, may one day make the journey.

Engagement with deep time is not solely a matter of technology. In the world of business and commerce, our planet boasts abundant examples of companies that have been handed down for centuries within the same family. Construction firm Kongo Gumi, for example, was founded in Osaka in 578, and ended business activity only in 2007, being operated at the end by the 40th generation of the family involved. The Buddhist Shitennoji Temple and many other well known buildings in Japanese history owe much to this ancient firm.

The Japanese experience is instructive. Hoshi Ryokan is an innkeeping company founded in Komatsu in 718 and now operated by the family’s 46th generation. If you’re ever in Komatsu, you can go to a hotel that has been doing business on the site ever since. Nor do we have to stay in Japan. Fonderia Pontificia Marinelli has been making bells in Agnore, Italy since the year 1000, while the firm of Richard de Bas, founded in 1326, continues to make paper in Amvert d’Auvergne, providing its products for the likes of Braque and Picasso.

Making Missions that Last

We have long-term thinking in our genes, as the planners of the Pyramids must have assumed. The Long Now Foundation, which studies issues relating to trans-generational thinking and the long-term survival of artifacts, has pointed out that computer code has its own kind of longevity. Enduring like the Sphinx, deeply planted software tools like the Unix kernel may well be operational a thousand years from now. Jon Lomberg and the team behind the One Earth Message — an attempt to transmit a kind of digital ‘Golden Record’ to the New Horizons spacecraft as a catalog of the human condition — estimate that the encoded data will survive at least one hundred thousand years, and perhaps up to a million if given sufficient redundancy.

‘Deep time’ takes us well beyond quarterly stock reports, and even beyond generational boundaries, an odd place to be for a culture that thrives on the slickly fashionable. It’s energizing to know that there is a superstructure that persists. The Voyagers are uniquely capable of keeping this fact in front of us because we see them defying the odds and surviving. Stamatios “Tom” Krimigis (JHU/APL) is on record as saying of the Voyager mission “I suspect it’s going to outlast me.”

Krimigis is one of the principal investigators on the Voyager mission and the only remaining original member of the instrument team. His work involves instruments that can measure the flow of charged particles. Such instruments — low-energy charged particle (LECP) detectors — report on the flow of ions, electrons and other charged particles from the solar wind, but because they demanded a 360-degree view, they posed a problem. Voyager had to keep its antenna pointed at the Earth at all times, so the spacecraft couldn’t turn. This meant that the tools needed included an electric motor and a swivel mechanism that could swing back and forth for decades without seizing up in the cold vacuum of space.

The solution was offered by a California company called Schaeffer Magnetics. Krimigis’ team tested the contractor’s four-pound motor, ball bearings and dry lubricant. The company ran the motorized system through half a million ‘steps’ without failure. The instruments are still working, still detecting a particle flow that is evidently a mix of solar and interstellar particles, one that is moving in a flow perpendicular to the spacecraft’s direction of travel, so that it appears we’re just over the edge into interstellar space, a place where the medium is roiled and frothy, like ocean currents meeting each other and rebounding.

One Last Burn

Although the spacecraft are expected to keep transmitting for several more years, we’ll continue to see both Voyagers suffering from power issues. But there is a way to keep them alive, if not in equipment then as a part of our lore and our philosophy. They will take about 30,000 years to reach the outer edge of the Oort Cloud (the inner edge, according to current estimates, is maybe 300 years away). Add another 10,000 years and Voyager 1 passes some 100,000 AU past the red dwarf Gliese 445, which happens to be moving toward the Sun and will, by this remote date, be one of the closest stars to the Solar System. As to Voyager 2, it will pass 111,000 AU from Ross 248 in roughly the same time-frame, at which point the red dwarf will actually be the closest star to the Sun.

Carl Sagan and the team working on the Voyager Golden Record wondered whether something could be done about the fact that neither Voyager was headed for another Solar System. Is it possible that toward the end of the Voyagers’ active lifetimes (somewhere in the 2020s), we could set up a trajectory change that would eventually lead Voyager as close as possible to one of these stars? Enough hydrazine is available on each craft that, just before we lose radio contact with them forever, we could give them a final, tank-emptying burn. Tens of thousands of years later, the ancient craft, blind, mute but still more or less intact, would drift in the general vicinity of a star whose inhabitants, if any, might find them and wonder.

A trajectory change would increase only infinitesimally the faint chance that one of these spacecraft would someday be intercepted by another civilization, and neither could return data. But there is something grand in symbolic gestures, magic in the idea that these venerable machines might one day be warmed, however faintly, by the light of another sun. Our spacecraft are our emissaries and the manifestations of our dreams. How we conceive of them through the information they carry helps us gain perspective on ourselves, and shapes the context of our future explorations. Giving the Voyagers one last, hard shove toward a star would speak volumes about our values as a questioning species determined to confront the unknown.