by Paul Gilster | Jun 22, 2012 | Exoplanetary Science |
I’ve always had an interest in old travel books. A great part of the pleasure of these journals of exploration lies in their illustrations, sketches or photographs of landscapes well out of the reader’s experience, like Victoria Falls or Ayers Rock or the upper reaches of the Amazon. Maybe someday we’ll have a travel literature for exoplanets, but until that seemingly remote future, we’ll have to use our imagination to supply the visuals, because these are places that in most cases we cannot see and in the few cases when we can, we see them only as faint dots.
None of that slows me down because imagined landscapes can also be awe-inspiring. This morning I’m thinking about what it must be like on the molten surface of the newly discovered world Kepler-36b, a rocky planet 1.5 times the size of Earth and almost 5 times as massive. This is not a place to look for life — certainly not life as we know it — for it orbits its primary every 14 days at a scant 17.5 million kilometers. But if we could see the view from its surface, we would see another planet, a gaseous world, sometimes appearing three times larger than the Moon from the Earth.
That may sound like a view from the satellite of the larger planet, but in this case we have two planets orbiting closer to each other than any planets we’ve found elsewhere. The larger planet, Kepler-36c, is a Neptune-class world about 3.7 times the size of the Earth and 8 times as massive. While the inner world orbits 17.5 million kilometers from its star, Kepler-36c takes up a position a little over 19 million kilometers out, making for a close orbital pass indeed. Conjunctions occur every 97 days on average, at which point no more separates the two worlds than about 5 Earth-Moon distances. Now that would make for quite an image, but rather than just sketching a huge planet in the sky, the University of Washington’s Eric Agol, one of the researchers on this work, decided to show the unknown in terms of the familiar, as below:
Image: Sleepless in Seattle? This view might keep you up for a while. Adapted by Eric Agol of the UW, it depicts the view one might have of a rising Kepler-36c (represented by a NASA image of Neptune) if Seattle (shown in a skyline photograph by Frank Melchior, frankacaba.com) were placed on the surface of Kepler-36b. Credit: Eric Agol/UW.
We can only imagine the kind of gravitational effects the two planets are having on each other. It’s interesting to see as well the powerful uses the researchers, who report their work in Science Express this week, have made of asteroseismology, as noted in this news release from the Harvard-Smithsonian Center for Astrophysics. The sound waves trapped inside Sun-like stars set up oscillations that an instrument like Kepler or CoRoT can measure. Bill Chaplin (University of Birmingham, UK), a co-author of the paper on this work, says this:
“Kepler-36 shows beautiful oscillations. By measuring the oscillations we were able to measure the size, mass and age of the star to exquisite precision. Without asteroseismology, it would not have been possible to place such tight constraints on the properties of the planets.”
The more we know about the parent star, in other words, the better we can interpret the lightcurves we are gathering as we observe planetary transits. The pattern we’re familiar with in our own Solar System — rocky planets closer to the Sun, gas giants in the outer system — breaks dramatically here with two worlds of different compositions and densities in remarkably tight orbits. At Iowa State University, researcher Steve Kawaler was on the team that worked on these data. Kawaler describes the situation in a news release from the university:
“Small, rocky planets should form in the hot part of the solar system, close to their host star – like Mercury, Venus and Earth in our Solar System. Bigger, less dense planets – Jupiter, Uranus – can only form farther away from their host, where it is cool enough for volatile material like water ice, and methane ice to collect. In some cases, these large planets can migrate close in after they form, during the last stages of planet formation, but in so doing they should eject or destroy the low-mass inner planets.
“Here, we have a pair of planets in nearby orbits but with very different densities. How they both got there and survived is a mystery.”
Indeed, we have two planets whose densities differ by a factor of eight in orbits that differ by a mere 10 percent, offering a real challenge to current theories of planet formation and migration. The star, Kepler-36a, is about as massive as the Sun but only about 25 percent as dense, and it has somewhat lower metallicity. Researchers believe it is several billion years older than our star and has entered a sub-giant phase to attain a radius about 60 percent greater than the Sun’s.
We can hope that extreme systems like this can help us refine our thinking on planetary migration and its effects. The planets in this system, some 1200 light years from Earth in the constellation Cygnus, are puzzling but doubtless not alone in representing unusual configurations of the kind we’ll see more of as we continue to sift the Kepler results. The paper is Carter et al., “Kepler-36: A Pair of Planets with Neighboring Orbits and Dissimilar Densities,” published online in Science Express June 21, 2012 (abstract). See also this news release from the University of Washington.
by Paul Gilster | Jun 21, 2012 | Autonomy and Robotics |
My friend David Warlick and I were having a conversation yesterday about what educators should be doing to anticipate the technological changes ahead. Dave is a specialist in using technology in the classroom and lectures all over the world on the subject. I found myself saying that as we moved into a time of increasingly intelligent robotics, we should be emphasizing many of the same things we’d like our children to know as they raise their own families. Because a strong background in ethics, philosophy and moral responsibility is something they will have to bring to their children, and these are the same values we’ll want to instill into artificial intelligence.
The conversation invariably summoned up Asimov’s Three Laws of Robotics, first discussed in a 1942 science fiction story (‘Runaround,’ in Astounding Science Fiction‘s March issue) but becoming the basic principles of all his stories about robots. In case you’re having trouble remembering them, here are the Three Laws:
- A robot may not injure a human being or, through inaction, allow a human being to come to harm.
- A robot must obey the orders given to it by human beings, except where such orders would conflict with the First Law.
- A robot must protect its own existence as long as such protection does not conflict with the First or Second Laws.
Asimov is given credit for these laws but was quick to acknowledge that it was through a conversation with science fiction editor John Campbell in 1940 that the ideas within them fully crystallized, so we can in some ways say that they were a joint creation. As Dave and I talked, I was also musing about the artificial intelligence aboard the Alpha Centauri probe in Greg Bear’s Queen of Angels (1990), which runs into existential issues that force it into an ingenious solution, one it could hardly have been programmed to anticipate.
We are a long way from the kind of robotic intelligence that Asimov depicts in his stories, but interesting work out of Cornell University (thanks to Larry Klaes for the tip) points to the continued growth in that direction. At Cornell’s Personal Robotics Lab, researchers have been figuring out how to understand the relationship between people and the objects they use. Can a robot arrange a room in a way that would be optimal for humans? To make it possible, the robot would need to have a basic sense of how people relate to things like furniture and gadgets.
It should be easy enough for a robot to measure the distances between objects in a room and to arrange furniture, but people are clearly the wild card. What the Cornell researchers are doing is teaching the robots to imagine where people might stand or sit in a room so that they can arrange objects in ways that support human activity. Earlier work in this field was based on developing a model that showed the relationship between objects, but that didn’t factor in patterns of human use. A TV remote might always be near a TV, for example, but if a robot located it directly behind the set, the people in the room might have trouble finding it.
Here’s the gist of the idea as expressed in a Cornell news release:
Relating objects to humans not only avoids such mistakes but also makes computation easier, the researchers said, because each object is described in terms of its relationship to a small set of human poses, rather than to the long list of other objects in a scene. A computer learns these relationships by observing 3-D images of rooms with objects in them, in which it imagines human figures, placing them in practical relationships with objects and furniture. You don’t put a sitting person where there is no chair. You can put a sitting person on top of a bookcase, but there are no objects there for the person to use, so that’s ignored. The computer calculates the distance of objects from various parts of the imagined human figures, and notes the orientation of the objects.
Image: Above left, random placing of objects in a scene puts food on the floor, shoes on the desk and a laptop teetering on the top of the fridge. Considering the relationships between objects (upper right) is better, but the laptop is facing away from a potential user and the food higher than most humans would like. Adding human context (lower left) makes things more accessible. Lower right: how an actual robot carried it out. Credit: Personal Robotics Lab.
The goal is for the robot to learn constants of human behavior, thus figuring out how humans use space. The work involves images of various household spaces like living rooms and kitchens, with the robots programmed to move things around within those spaces using a variety of different algorithms. In general, factoring in human context made the placements more accurate than working just with the relationships between objects, but the best results came from combining human context with object-to-object programming, as shown in the above image.
We’re a long way from Asimov’s Three Laws, not to mention the brooding AI of the Greg Bear novel. But it’s fascinating to watch the techniques of robotic programming emerge because what Cornell is doing is probing how robots and humans will ultimately interact. These issues are no more than curiosities at the moment, but as we learn to work with smarter machines — including those that begin to develop a sense of personal awareness — we’re going to be asking the same kind of questions Asimov and Campbell did way back in the 1940s, when robots seemed like the wildest of science fiction but visionary writers were already imagining their consequences.
by Paul Gilster | Jun 20, 2012 | Culture and Society |
We all carry our assumptions with us no matter where we go, dubious extra baggage that can confuse not just our scientific views but our lives in general. That’s why it’s so refreshing when those assumptions are challenged in an insightful way. Think, for example, of the starship as envisioned by Hollywood. In our times it looks like something produced by the joint efforts of NASA, ESA and other governmental space agencies. No matter how diverse the crew, the model is always based on western culture, the assumptions reflecting our modern ethos.
When an assumption is ripe for questioning, along comes a writer like Michael Bishop. Consider the starship Kalachakra, carrying a crew of 990 to a planet in the Gliese 581 system, as envisioned in Bishop’s ‘Twenty Lights to the Land of Snow,’ a novella in the Johnson/McDevitt book Going Interstellar. Most of the crew spends the flight in hibernation using the wonderfully named drug ursidormizine — thus slumbering ‘bear-like’ — but each crewmember must emerge every couple of years to avoid the deterioration the process creates in the sleeping ‘somnacicles.’
Image: The culture aboard a starship may be nothing like what Hollywood so often envisions. Speculations along these lines are fine fodder for science fiction, and remind us that an interstellar future is multi-disciplinary, demanding our best efforts not just in science but in philosophy, sociology and culture. Credit: Adrian Mann.
Kalachakra carries Free Tibetans escaping a tyrannical government, the most prominent among its crew being the Dalai Lama, who inconveniently dies early on and must be replaced. I won’t get into plot details because in my estimation, the cover price of Going Interstellar would have been justified even if the Bishop story were the only thing in the book. You’ll want to read this for yourself, and anticipate along with me the novel that will surely come out of it. You’ll especially enjoy the defeat of expectations at every turn. Here, for example, is a look into the hangar where the Kalachakra carries the lander that will be used on arrival:
An AG [anti-gravity]-generator never runs in the hangar because people don’t often visit it, and our lander nests in a vast hammock of polyester cables. So we levitated in a cordoned space near the nose of the lander, which the Free Federation of Tibetan Voyagers has named Chenrezig, after that Buddhist disciple who, in monkey form, sired the first human Tibetans. (Each new DL [Dalai Lama] automatically qualifies as the latest incarnation of Chenrezig). Our lander’s nose is painted with bright geometric patterns and the cartoon head of a wise-looking donkey wearing glasses and a beaked yellow hat. Despite this amusing iconography, however, almost everyone on our strut-ship now calls the lander the Yak Butter Express.
That last bit, the donkey in the yellow hat, is just right — no somber United Federation of Planets logo or some such aboard the Kalachakra! In the story, the journey at one-fifth of light speed is funded by a United Nations charter and all sorts of diplomatic maneuvering designed to solve a political crisis by creating a new ‘land of snow’ in the high mountains of Gl 581g’s terminator. Never mind that Gl 581g most likely doesn’t exist, for it was thought to be there when Bishop wrote the story, and it shows up elsewhere in Going Interstellar as well, a reminder of how fast our exoplanet knowledge is changing. The point is, this journey is all about coming of age, learning who you are, and creating meaning out of uncertainty. It’s just a great read.
Perils of the Book Reviewer
Now and again I’m asked about the ‘What I am Reading’ window on the Centauri Dreams main page, and why it takes me so long to get through a book. I’m not actually as slow a reader as it appears. Going Interstellar was up there for several weeks because I never read a single book at a time, but usually have several going simultaneously. I always try to put the book of most interest to my readers up in the window, but I only have room for one. The pace — and the blog format — have changed the way I review books in general. Rather than writing a single, monolithic review as I used to do for newspapers, I’m more prone to write about a book while it’s in progress, coming around to it again and again before moving on to the next volume.
Thus it has been with Going Interstellar, about which a few more thoughts. You’ll recall that this is a collection of essays and fiction, mixing them in the fashion of Arthur Clarke’s 1990 book Project Solar Sail. I had mentioned the similarity before but was startled to find Mike Resnick’s story ‘Siren Song’ at the end of the book. Like the Clarke volume, which includes Clarke’s ‘The Wind from the Sun,’ the Johnson/McDevitt book includes a story about a solar sail race, or I should say in this case a race in which a single solar sail appears. Resnick’s is a moody little evocation of Odysseus that’s less interested in showing solar sailing at work than in mining the mythic ore that our move into the Solar System will invoke.
The fiction in this book is spry and interesting. Along with the Bishop and Resnick, I thought particularly highly of Les Johnson’s ‘Choices’ and Sarah Hoyt’s ‘The Big Ship and the Wise Old Owl,’ which plays entertainingly off the clues afforded by nursery rhymes on a starship journey to reveal the dangerous machinations that may complicate an interstellar arrival. Jack McDevitt’s ‘Lucy’ takes us into the mind of an AI pushed into what can only be called an ‘awakening’ at system’s edge, one that questions our human limitations and makes us wonder just who is likely to make that first interstellar crossing, machine or human? Ben Bova’s ‘A Country for Old Men’ taps into the same theme, with the notion that there are tricks up the sleeve of our species that even the wisest AI may not be able to fathom.
Fictional Threads in Science
What I appreciate about the mixed format of a book like this is that it keeps you grounded in the possible. The ideas used to get big ships moving into the interstellar deep in these stories are all based on extensions of our current engineering and ideas in line with contemporary physics. We have chapters on antimatter and fusion (Greg Matloff), solar and beamed energy sails (Les Johnson) and Richard Obousy’s introduction to Project Icarus, the ongoing redesign of the British Interplanetary Society’s Project Daedalus starship. I like what Obousy has to say about the project’s objectives, especially in training a new generation of designers:
To maintain the healthy vision of a future where interstellar travel is possible, a new generation of capable enthusiasts is required. Project Icarus was designed with this specific motive in mind, and a quick glance at the Icarus designers reveals an average age close to thirty. Thus, one hope is that upon completion of the project, an adept team of competent interstellar engineers will have been created, and that this team will continue to kindle the dream of interstellar flight for a few more decades until, presumably, they too become grey and find their own enthusiastic replacements.
Starship design brings challenges galore, the chief of these perhaps being the issue of deceleration. As a consultant for Project Icarus, I was privileged to throw my two cents in on the debate over whether Icarus should, like Daedalus, be a flyby mission, or whether incorporating deceleration at the target should be attempted. I was agog at the notion of deceleration given what this would do to the mass ratio, but the more I thought about it, the more I came around to the idea that the team was right. A flyby gives you precious little data for the decades you’ve spent reaching the target, and sooner or later we’re going to have to face the deceleration problem, so better to get working on it now. A solution to this problem alone would be an unforgettable contribution to interstellar studies, if Project Icarus can provide one.
There’s much more of interest in Obousy’s essay, including the fact that the inertial confinement fusion strategy favored by the Daedalus designers — firing deuterium and helium-3 pellets into a reaction chamber at a rate of 250 pellets per second, where they are ignited by electron beams — calls for an improvement of 21 million times over the ignition rate expected from the National Ignition Facility at Lawrence Livermore Laboratory. To say there is much work to be done is to state the obvious, a fact cheerfully acknowledged by this band of visionary designers.
In any case, I’ve rambled on about Going Interstellar without getting into the meat of several of its essays, but I’ll be drawing on these in coming days as we look at further propulsion possibilities. We’re also going to be looking at how rocketry studies were influenced by science fiction in the era between the two World Wars as I draw on John Cheng’s Astounding Wonder: Imagining Science and Science Fiction in Interwar America (University of Pennsylvania Press, 2012). The new book up in the ‘What I Am Reading’ window is Kelvin Long’s Deep Space Propulsion (Wiley, 2011).
Have I mentioned that I need new reading glasses? I’ll have to get them soon because interstellar ideas are popping up all over the place. I also have Centauri Dreams reader Jim Essig’s new title Call of the Cosmic Wild (2012) ahead. And although it’s not on an interstellar theme, I’m soon going to be talking about Mark Anderson’s The Day the World Discovered the Sun (Da Capo, 2012), received too late to read before the transit of Venus, but telling a tale of transit study in the 18th Century that reminds us what minds fired by curiosity can do with the tools of their time. We’re not in so different a position than those 18th Century astronomers who set sail around the globe to view the 1769 transit. Like them, we work with tools that following ages will find primitive, and in starship terms, our goals are far beyond our grasp. It is the hope of closing that gap even a little that impels the interstellar community to keep trying.
by Paul Gilster | Jun 19, 2012 | Culture and Society |
Tau Zero founder Marc Millis is interviewed by Bruce Dorminey in Forbes this week, the logical first question being where interstellar flight ranks on our list of priorities. A case can be made, after all, that we have yet to get humans beyond the Moon, and that while we have managed robotic missions to the outer planets, our technologies need development closer to home. Should a Moon base get our attention, or a Mars mission? Millis argues that pursuing next steps like these should be managed in tandem with the pursuit of more far-reaching advances that force us to look beyond existing methods.
Breakthroughs can change everything, and Millis is, after all, the former head of NASA’s Breakthrough Propulsion Physics project, which came to an abrupt end in 2002 when a congressional earmark to build a propulsion laboratory in Alabama — one that cost more than all NASA’s BPP research put together — scarfed up what could have been research money. And as Millis tells Dorminey, we’re left after all this with the continuing question of how to build a viable space effort using less than one half of one percent of our national resources.
While we ponder the near-term economics, a major driver for interstellar flight is to create a backup plan for our species in the event of a natural or man-made catastrophe that could threaten the Earth. But we don’t have to think far into the future to a time when a changing Sun will make conditions here unlivable. We can take solid steps toward creating a Solar System-wide infrastructure in the next several centuries, along the way developing the technologies for interstellar journeys. As Millis says:
The crux of the starflight benefit is developing such things as closed-loop life support that could also be applied for earth’s surface survival. The starflight option forces the need for that feature more than Moon and Mars colonies which can still depend on earth for their survival. But by also reaching for the more demanding requirements of starflight, we increase our chances of developing the independent survival capacity sooner. We don’t know our real expiration date. This is about hedging our bets for all the risks along the way.
I notice, too, that Marc was recently referenced on the Washington Post‘s WonkBlog, where Ezra Klein looks at his calculations on when humanity will have the ability to generate the energies needed for interstellar flight. The power needed to reach Alpha Centauri and decelerate is daunting and our energy production inches up but slowly:
For the past three decades, the total energy produced by the world has grown at a modest pace — around 1.9 percent per year. And humans have devoted just a tiny fraction of that to spaceflight. Unless either of those trends changes radically, Millis calculates, we won’t have the energy needed to launch an Alpha Centauri probe until sometime around the year 2463, at the earliest.
The good news, Millis notes, is that we could probably have a small colony ship that contained a bunch of humans ready even sooner, by the year 2200 or so. This ship couldn’t necessarily travel to other stars — it wouldn’t be nearly as fast as the Alpha Centauri probe — but it could pack about 500 people in, with supplies. This might be a good backup plan in case we end up trashing the Earth beyond repair and need to ensure the survival of the species.
More on all this in Marc’s paper “Energy, Incessant Obsolescence, and the First Interstellar Missions.” The paper was presented at the 61st International Astronautical Congress of the International Astronautical Federation, held in Prague in late 2010. Also note (see comments) that an updated version is available: Millis, “First Interstellar Missions, Considering Energy and Incessant Obsolescence,” JBIS 63, (2010), pp. 434-443.
100 Year Starship Call for Papers
Individuals and organizations from all disciplines are invited to participate in the upcoming public symposium of the 100 Year Starship organization, which published its call for papers yesterday. The theme of the session will be ‘Transition to Transformation: The Journey Begins.’ About the theme, the organization says this:
[It] acknowledges the accomplishments of space exploration to date and calls for authors to consider what changes are needed in how we currently envision and “do space” to truly push forward humanity’s journey to another star. Discussions this year should focus within each topical track on those transformative ideas and processes that make the leap to new breakthroughs. Papers accepted will be included in the 100YSS™ 2012 Symposium Proceedings and may be considered for publication in the coming Journal of Interstellar Studies.
Note that last item: I’ll have more for you about the Journal of Interstellar Studies as we move forward, but suffice it to say that the field has long needed its own journal, going back to the days when Robert Forward and Eugene Mallove were compiling interstellar bibliographies back in the early 1980s. The Journal of the British Interplanetary Society has done an outstanding job at keeping interstellar ideas current with its ‘red cover’ issues, but the hope here is that the new venue will offer still more opportunities for scientists — especially the upcoming generation of researchers now being drawn to interstellar studies — to interact with the community.
The tracks for the conference are laid out in the call for papers, ranging from ‘Time-Distance Solutions’ to ‘Becoming an Interstellar Civilization,’ with special sessions on topics like spinoffs and commercial applications. Note that there is a ‘No Paper, No Podium’ rule in effect, with papers due on August 17th. The abstracts themselves are due on July 8. The symposium is to be held from September 13-16 in Houston, TX (when the Texas heat should have nicely subsided), and there is a form on the 100 Year Starship site allowing you to be notified when registration opens. Last year’s session in Orlando is going to be a tough act to follow, but the list of topics promises lively discussion and the chance to mingle with the major players in this burgeoning field.
by Paul Gilster | Jun 18, 2012 | Outer Solar System |
It should come as no surprise to anyone who follows Centauri Dreams that I am a great admirer of Ed Stone, the former director of the Jet Propulsion Laboratory (from 1991 to 2001) and more than any single scientist, the public face of many of our missions to the outer Solar System. Stone’s work on space projects began as far back as 1961 with the cosmic ray experiments he designed for the Discoverer satellites, but it was as project scientist for the Voyager missions that he became a familiar figure to audiences worldwide. His tenure at JPL saw missions like Mars Pathfinder, the Sojourner rover, Deep Space 1 and the launches of Cassini and Stardust.
That, of course, is only a partial list, but it gives you the drift. This morning I’m thinking about Stone again because of a quote he provided for a recent JPL news release. Here again he’s talking about the Voyagers, which are pushing up against the edge of the system:
“The laws of physics say that someday Voyager will become the first human-made object to enter interstellar space, but we still do not know exactly when that someday will be. The latest data indicate that we are clearly in a new region where things are changing more quickly. It is very exciting. We are approaching the solar system’s frontier.”
Image: Dr. Stone (center) and members of the Voyager mission discuss the spacecraft’s closest approach to Jupiter, March 1979. Credit: NASA/JPL.
As seems to be a habit of the Voyagers, they are again approaching an exciting encounter. In the other room I still have the VCR tapes I made of Voyager II’s 1989 Neptune flyby — amazing to think it’s been so many years! — and I recall remarking to my wife that night that these doughty machines still had some life in them, and that, who knows, they might keep giving us information for another decade or so. If I had done my homework back then, I would have realized that we might get both spacecraft through to 2020 or so, when the power output of their radioisotope thermoelectric generators will decline too steeply for operations to continue.
A morning check shows that Voyager 1 is 16 hours, 39 minutes and 2 seconds light travel time from us, while its sister ship is 13 hours, 35 minutes and 13 seconds of light travel time away. Impressive for journeys that began in 1977 and a real tribute to our ability to build systems that can last. The Voyagers’ interstellar mission is all about studying not only the Kuiper Belt but the heliosphere and the elusive boundary between the region of the Sun’s influence and true interstellar space. That included the famous ‘Pale Blue Dot’ image showing a group portrait of the Solar System, including the faint Earth, as seen from outside. And while it is true that New Horizons left Earth faster than either Voyager, our Pluto/Charon probe is now moving at 15 kilometers per second, while Voyager 1 maintains a brisk 17.26 kilometers per second.
An indication that interstellar space looms near is that Voyager 1, in the period from early 2009 to early 2012, has measured a 25 percent increase in galactic cosmic rays, with an even more rapid increase in the spring of 2012. The science team will now be watching for a change in the intensity of energetic particles generated inside the heliosphere, a kind of ‘bubble’ of charged particles inflated by our star’s solar wind. A sharp dropoff will be another flag for leaving the system, as will a major change in the direction of magnetic field lines around the spacecraft.
As for Ed Stone, he’s on record as saying that the biggest surprise of the Voyager missions was the discovery of Io’s volcanoes, but he notes that as the missions unfolded, they continually surprised us. Doubtless even our best estimates of the passage into interstellar space will come up short of the reality as we learn more about the boundary through which all future interstellar craft will have to pass. Says Stone:
“When the Voyagers launched in 1977, the space age was all of 20 years old. Many of us on the team dreamed of reaching interstellar space, but we really had no way of knowing how long a journey it would be — or if these two vehicles that we invested so much time and energy in would operate long enough to reach it.”
For that matter, who knew how long we’d be able to work with these spacecraft even if they did approach the margins of the Solar System? The numbers are daunting but our deep-space tracking antennas are up to the job: The signal that the Voyager probes return to Earth is 10-16 watts, which works out to one part in 10 quadrillion. The Voyager Interstellar Mission team notes that a digital watch operates at a power level 20 billion times greater than this, and yet we’re still hoping for another decade or so of data. If power were not a problem (and low hydrazine levels), we might be talking about another century or more of contact with the spacecraft unless they lost their lock on the distant Sun.
And after the Voyagers reach interstellar space? The next boundary will be the region where the Sun’s gravity is no longer dominant, a distance about halfway to the nearest star (although neither spacecraft is pointed at Proxima Centauri). It should take the long-silent Voyagers about 37,000 years to reach that threshold.
