ISEE-3: The Challenge of Long Duration Flight

by Paul Gilster on April 9, 2014

Some mission concepts for interstellar flight demand equipment that can stay functional not just for decades but for centuries. Do we know how to build such things? Missions like Voyager are encouraging in that we have two spacecraft that were never built for the kind of longevity we’ve demanded of them, and we’re still tracking their signals. But as Robert Forward once speculated, the problem may not be just in building the spacecraft, but in how we handle them.

Forward’s issue involved the changes on Earth that might occur over a long-duration spaceflight like the one he envisioned in Rocheworld (1984, first published as Flight of the Dragonfly). A crewed starship is actually on the way to Barnard’s Star, dependent on the massive laser installations in the Solar System whose beam will allow it to decelerate (through ‘staging’ the sail) into the destination star system. But there is a movement afoot on Earth to shut down the beam, motivated by money, politics and the usual cast of miscreants. The technology, in other words, works, but the question is whether the humans behind it will make the right decision.


Much goes on in Rocheworld and the question of shutting down the laser is but a minor theme, but the question Forward raises is intriguing. Consider what’s happening with the International Sun-Earth Explorer-3 (ISEE-3), a spacecraft launched in 1978 to make observations of the solar wind’s interactions with Earth’s magnetosphere. Back in 1983, ISEE-3 turned into ICE, the International Cometary Explorer, and in that guise studied comet Giacobini-Zinner and later Halley’s comet. NASA even turned the craft loose after that to study coronal mass ejections before decommissioning the probe and closing down its systems.

This August, as the Planetary Society’s Emily Lakdawalla has noted, the spacecraft in its heliocentric orbit will be catching up with the Earth from behind, which creates an interesting issue of its own. Although officially out of service, ISEE-3 has been broadcasting a carrier signal that was detected in 2008. It’s also known that as of last check — this was some time in the 1990s — twelve of its thirteen instruments were still working. Could we get the 36-year old spacecraft back in service? It’s a compelling thought, but a tough task to accomplish.

Image: The ISEE-3/ICE spacecraft. Can it be returned to use? Credit: NASA.

The problem isn’t with the data from the spacecraft, which can be accessed by the Deep Space Network. The issue is our ability to talk to the probe. The Goddard Space Flight Center team responsible for the craft maintains a Facebook page, from which Lakdawalla quotes:

The transmitters of the Deep Space Network, the hardware to send signals out to the fleet of NASA spacecraft in deep space, no longer includes the equipment needed to talk to ISEE-3. These old-fashioned transmitters were removed in 1999. Could new transmitters be built? Yes, but it would be at a price no one is willing to spend. And we need to use the DSN because no other network of antennas in the US has the sensitivity to detect and transmit signals to the spacecraft at such a distance.

However, all hope is not lost. ISEE-3’s signal has been detected by the Allen Telescope Array as well as by radio amateurs, and scientists at the Applied Physics Laboratory are studying potential new, lower-power ways of contacting the probe, as Lakdawalla reports in a later update. If the craft’s engines can be commanded to fire, it could be recaptured into a halo orbit at the L1 Lagrangian point and returned to service. The odds are long and time is short — the engine firing needs to be accomplished no later than early June — but the fact that the APL team is actively working on this inspires me to keep an eye on the ISEE3returns Facebook page.

ISEE-3 is not, obviously, a manned mission, so the question of reactivating it has none of the life-or-death drama of the Forward novel. But it’s an interesting commentary on how our technology can sometimes expose our weaknesses. In this case, we have a functioning spacecraft that could conceivably come back into use, one that is for now rendered impotent until we can pull the resources together to use it. The cost factor speaks for itself, and it’s understandable. But I’m reminded of our problems reading old data from the Pioneer days because the equipment has become obsolete. Truly long-term thinking involves planning for changing formats and technological upgrades, a subject about which we’ll be learning much more as we contemplate deeper and longer missions into the dark between the stars.



Optimal Worldship Populations

by Paul Gilster on April 8, 2014

Although we tend to focus on propulsion as the major obstacle to reaching another star, the biological problems that go along with journeys lasting decades or even centuries are equally daunting. If we could devise methods that would get us to Alpha Centauri within a century, we’d still face the need to keep a crew alive within a sustainable closed ecosystem for that amount of time. If we’re talking humans in starships, then, we need a lot more data about how people interact in isolated communities, stay healthy, and manage critical self-sustaining systems.


Image: A habitat for humans over generations, a worldship poses critical questions about survivability and genetic diversity. Credit: Adrian Mann.

Centauri Dreams readers will recall Cameron Smith’s interest in these matters, as reflected in his article Biological Evolution in Interstellar Human Migration, published here last March. The author of Emigrating Beyond Earth: Human Adaptation and Space Colonization (Springer, 2012), Dr. Smith (Portland State University) looks at these issues over the course of generations. How large does a starship crew have to be in order to keep the population healthy? This article in Popular Mechanics gives a nice overview of Smith’s findings, which were published in Acta Astronautica and flesh out his earlier essay in these pages. The work was performed as a contribution to Icarus Interstellar and its Project Hyperion.

Working with William Gardner-O’Kearney, Smith constructed simulations to create scenarios for interstellar travel with the help of MATLAB, a widely used tool for numerical computation. One immediate result was to draw into question earlier calculations by John Moore (University of Florida), who had found that a 2000 year voyage aboard a generation ship would require an initial crew of no more than 150. In sharp contrast, Smith found that a minimum of 10,000 was necessary, while 40,000 would be a safer number still given the perils of the journey. Starting population size, which the duo calculated over 30 generations, is a crucial matter.

A key issue, as you would expect, is genetic diversity. Small groups like the Amish and Ashkenazi Jews suffer higher rates of diseases like cystic fibrosis and Tay Sachs largely because of intermarriage between relatives. I’ll send you to the article for the bulk of the researchers’ graphs, but I’ll show one below, illustrating what happens within groups of different sizes over time. A ship starting out with a crew of 150 loses 80 percent of its genetic diversity after thirty generations. Even 500 is too small a number, for it does not represent a wide enough swath of the human population. Somewhere between 10,000 and 40,000 is where we find a starting population that can maintain 100 percent of its original genetic variation.


Image: The decline in genetic diversity among smaller populations over time is evident here. Note the 150 line in red at the bottom of the chart, with the most robust, in purple and representing a starting crew of 40,000, shown at the very top. This number maintains 100 percent diversity. Credit: Cameron Smith/Gardner O’Kearney.

Just as we preserve a healthy gene pool with a larger population, we also safeguard against external risks, the kind of catastrophe that could snuff out the entire population of a small ship. This work makes the case that housing tens of thousands of colonists in a single generation ship would be a mistake. Far better, when launching our expedition, to use multiple ships, traveling perhaps close enough together for trade and other human interactions, but separated so that a single disaster wouldn’t mean the end of the entire venture. I’m invariably reminded of the expedition led by Sky Haussmann in Alastair Reynolds’ novel Chasm City (2001), a fleet of starships that confronts a human-caused calamity.

10,000 seems to be the minimum number for success. Says Smith: “With 10,000, you can set off with good amount of human genetic diversity, survive even a bad disease sweep, and arrive in numbers, perhaps, and diversity sufficient to make a good go at Humanity 2.0.” That’s a large crew, but history has shown us that there are always pioneers, adventurers, misfits and any number of other psychological types willing to give up everything they have known to chance their future in unknown lands. The guess here is that if a fleet of five generation ships needing crews of 2000 each is ever built, it will not lack for volunteers.

The paper is Smith, “Estimation of a genetically viable population for multigenerational interstellar voyaging: Review and data for project Hyperion,” Acta Astronautica, Vol. 97 (2014), pp. 16-29 (abstract).



On the Enceladus Ocean

by Paul Gilster on April 7, 2014

The recent news about an ocean on Enceladus had me thinking over the weekend about a trip my wife and I took years ago to Michigan’s Upper Peninsula. There we had rented a cabin for the week on the shores of Lake Superior, twenty miles from the nearest town, unless you counted the small grocery store, art gallery and scattered houses up the highway as a town — if so, it was a tiny one. Looking out across the silver and gunmetal gray waves of Superior, you could imagine it an ocean, a cold, frothing place of treacherous currents and, that October, raw winds.

Lake Superior appears as the comparison in many of the reports on the Enceladus findings as they sketch out what appears to be a sea just as large, perhaps ten kilometers deep covered by an ice shell four times as thick. Given that the well known plumes of Enceladus are already known to contain organic molecules in addition to salty water, the inevitable question arises: Could some form of life exist beneath this frozen surface? There’s no way to tell as yet, but the imperative to probe still further into the tiny world (504 kilometers in diameter) continues to grow.


Image: This diagram illustrates the possible interior of Saturn’s moon Enceladus based on a gravity investigation by NASA’s Cassini spacecraft and NASA’s Deep Space Network, reported in April 2014. The gravity measurements suggest an ice outer shell and a low density, rocky core with a regional water ocean sandwiched in between at high southern latitudes. Views from Cassini’s imaging science subsystem were used to depict the surface geology of Enceladus and the plume of water jets gushing from fractures near the moon’s south pole. Credit: NASA/JPL-Caltech.

What we have in the latest work is the result of three Cassini flybys, two of them over the southern hemisphere, one over the north. The tiny deviation of the spacecraft from its trajectory — the velocity change was 0.2–0.3 millimetres per second — could be detected in Cassini’s radio signals, helping us measure variations in the gravity of the tiny world. The payoff is explained by Luciano Iess (Università La Sapienza, Rome), lead author of the paper in Science:

“By analysing the spacecraft’s motion in this way, and taking into account the topography of the moon we see with Cassini’s cameras, we are given a window into the internal structure of Enceladus. The perturbations in the spacecraft’s motion can be most simply explained by the moon having an asymmetric internal structure, such that an ice shell overlies liquid water at a depth of around 30–40 km in the southern hemisphere.”

These measurements are extraordinarily fine, but analysis of the Cassini signal can detect changes in velocity as small as 90 microns per second, according to this JPL news release. Although the southern polar region has a surface depression that affects the local pull of gravity, the magnitude of the gravitational dip is less than it ought to be given the size of the depression, which leads to the finding that a high density feature beneath the surface is the cause. Denser material, probably liquid water, compensates for the missing mass. This water may or may not be the source of the south pole plumes Cassini has observed in the past, but that possibility certainly exists.

Meanwhile, I’m recalling an earlier encounter with Enceladus. Freeman Dyson was talking about the moon as a target for the Orion spaceship in the late 1950s, and in a twelve-page report in 1958 called “Trips to Satellites of the Outer Planets,” he made the case for visiting the gas giant moons. Decades later, he would explain his thinking to his son George, as recounted in the latter’s Project Orion: The True Story of the Atomic Spaceship (Henry Holt, 2002):

“We knew very little about the satellites in those days. Enceladus looked particularly good. it was known to have a density of .618, so it clearly had to be made of ice plus hydrocarbons, really light things, which were what you need both for biology and for propellant, so you could imagine growing your vegetables there. Five-one-thousandths g on Enceladus is a very gentle gravity — just enough so that you won’t fall off.”

Amazing to recall that, at least for a time, the motto of Project Orion was “Saturn by 1970.” But it’s clear from everything we’ve learned about this moon since that Enceladus remains a primary object for study, even if we’ve now moved into the realm of astrobiology. What a surprise that would have been to the Orion team back in the 1950s!

The paper is Iess et al., “The gravity field and interior structure of Enceladus,” Science Vol. 344, No. 6179 (4 April 2014), pp. 78-80 (abstract).



Woven Light – Proteaa

by Paul Gilster on April 4, 2014

Heath Rezabek is concerned with information — how we uncover it, how we use it, how we store it against cataclysmic events. A librarian and futurist, Heath uses science fiction to explore how Vessels of preserved knowledge might be developed and maintained not only on Earth but in the far reaches of our Solar System and beyond. In today’s work, he traces resource discovery and archival technologies back as far as Vannevar Bush and forward into a future that has transformed our early experiments into endlessly morphing realms of human growth and preservation.

by Heath Rezabek


This is the fourth installment in a continuing series of speculative fiction here on Centauri Dreams. Feedback from prior installments helps shape the themes and direction of subsequent entries, but the purpose and focus of these pieces is to explore a timeline (or timelines) in which comprehensive, resilient archives of Earth’s biological, scientific, and cultural record — deep archives for deep time — are developed through unexpected means.

Woven Light (I) – Vessel Haven
Woven Light (II) – Adamantine
Woven Light (III) – Augmented Dreamstate
Woven Light (IV) – Proteaa

- – - -

Buckminster Fuller, in the process of designing and inventing a variety of structures based on geodesics, was at one point challenged by a patron to design a city which could float in Tokyo Bay. While this seems similar enough to the modern concept of seasteading, Fuller decided that the challenge was lacking in ambition. He instead developed a hypothetical framework for truly floating cities: Spherical structures which could drift above the surface of the Earth, configured internally however one wished.

Fuller believed such structures would not likely be built until pressures on Earth’s resources and settlement sustainability were much greater than they were at the time, and he somewhat whimsically called them Spherical Tensegrity Atmospheric Research Stations (STARS), or Cloud 9s. They were based upon the simple fact that if one enclosed a half mile (diameter) with a geodesic sphere, the structure itself would weigh but a thousandth of the weight of the internal air. Thus, if heated by a degree or more, the structure would lift and could become airborne.

Only glimpsed and hinted at here, we may see them again in future installments. As fantastical as they may seem, they bear a striking resemblance to an even more astounding thought experiment, also explored here.

Freeman Dyson, in his session for 2013’s Starship Century Symposium, proposed one of the most startling instances of a Vessel-like archive in my ongoing survey of such proposals: Called “Noah’s Ark Eggs” – I often refer to them as Dyson Eggs for short – their collections would be living biospheres, each self-contained and independent as a carrier of Earth-originating life to distances as far as you could wish, as randomly as you please. In this scenario, careful construction and glazing – aided by the engineering of viparious plants – would allow a Dyson Egg to contain enough heat to sustain a biome on starlight alone, as it drifted or was directed through the chilly reaches of space.

As living archive, each instance would develop by natural selection from a single-set in countless directions, ultimately carrying those finely honed living ingredients and blueprints to unknown worlds like dandelion wisps on the wind. This idea was mentioned in a prior Vessel Open Framework entry, discussing the possibility of individual habitats throughout the asteroid belt as a way to mitigate Xrisk.

If Dyson Eggs could be engineered for human (or transhuman, or posthuman) purposes as well as those of plant life, another unknown avenue for Earth-originating archives and civilization would open up. We also ask: if in space Dyson Eggs are possible, then are Fuller Spheres / STARS / Cloud 9s possible as well, above the surface of the Earth or elsewhere? If not as extended-purpose habitats, might our fictional version of Vessel Labs give them a try, for limited-population Vessel archives, in a timeline yet to be explored?

Although discussed most fully in the course of the narrative, one last design fiction is to be mentioned here as well, and that is Vannevar Bush’s Memex, as detailed in his 1945 Atlantic article, As We May Think. His original proposal has much more in common with nascent augmented intelligence than it does with what we now have at hand in our current digital networks; that original article is always worth a new look as we weigh our future aspirations against the technologies envisioned by our predecessors.

- – - – -

image-01-precursorae-wikipedia copy

Image: ‘Precursorae’, Heath Rezabek. Adaptation of photography CC BY-SA Wikimedia.

Shimmering, barely a flicker against the wall of night, a slim circumference slides stars aside at its edges, falling through the space between.

Inside thrives a verdant darkling jungle, weightless and entangled. Structurally, its mass is a mesh of entwined greenery, countless conduits, endlessly connecting.

Its warmth is fed by the barest of starlight; its mission knows no fixed end.

Amidst the brambles, prowlers make their slow way from one kill to the next, as the smaller ones scurry between safer perches, instinctually, perpetually, all one in their motion.

At a glance, the apex is red in tooth and claw. But appearances can deceive, in light as lost as this shadowing. The true apex belongs to beings who’ve smoothed their subtler instincts until they’ve fused with logic and language alike. Were there a way for us to witness them, grappling and gliding between boughs, we would be excused for mistaking them as human. Yet human — strictly speaking — the Avaai are not.

The name is emergent and generative, like their language. It means, more or less, “Those who remain through departing.” They are, in some ways, our descendants; but in timeless reaches, their science reborn as generative myth, even they will come to be known as precursors. And they are few among many, splayed afield and bound far from their fellows by a gambit: a seed, a sphere, an impossible Aleph.

Of the many names given to these starborne terraria in the deeps of their time, Precursorae was one. Ark Ovae another. Dysonae, a third. They are adrift; but they are never alone.

The Avaai have two eyes and ears, yet they share thought with myriad nearby forms who have nothing of the sort. The Avaai have two legs and two arms, yet their movements are lithe and their forms are stretched by weightless dance. Their features are more angular, their aspect more severe; their thoughts a fog of mind shared with all around them. They are organic, but they are not, so to speak, biological. They are synthetic, but they are not, as it were, artificial. Like koans, like the Tao, they are better described through what they are not.

They are Proteaa, and like everything else here, they share a basis in Protean cells.

Like Protean cells themselves, the Avaai are transmortal, able to pass from one form into another, able to share their thoughts and lives with the flora and fauna all around them, with which they are inextricably bound.

The fog of mind is their medium; fluid sometimes, particulate at others. They craft artifacts, in which every atom carries an echo of the whole. They are solid state; yes, and liquid as well.

But one thing they do not know, collectively or alone, (for they can recede and retreat if they wish) is how long they have been, and how long they might be. The deep well of remembrance harbors a mythology which has mapped the slow drifting of their constellations into shapes entirely other than the ones they’d known before.

These ever changing all-surrounding starfields — the personae retraced upon them — are their mythemes, the most basic of forms. Formulae and hypotheses, a scattered suspension of salt in the waters. ~For matter is slumbering light~

Their inheritance is a deep-healing habit of retreat, where solitude and union cleave and renew. And when they look closely, turning inwards, they can gaze into a place that is also time. They can convene and converse with a dark mind made clear through its gravity, known to them as the Kainadhren, Ancient Light. And through its channels and conduits, they can quite nearly reach other times and far places. Quite nearly: pushing at that membrane which reflects all times and places, an infinity-etched horizon.

We would find life within a Protean Precursorae to be brief and delirious. But we can guess in some sense at the transmutable lives of the Avaai, because we were the ones who observed the emergence of the Proteaa. And together, we’ve run the simulations.

- – - – -

image-2-cc-by-sa-wikipedia-vannevar-bush copy

Image: Adaptation of ‘Vannevar Bush’ CC BY-SA Wikimedia.

Before Thea Ramer was a research scientist in holographic cartography, she was a writer of speculative fiction, part of a writing group with several instances around the world. As part of this club, she’d developed a series of writing exercises to banish forever the excuse of writer’s block. One of her inspirations in this had been a now-mythic proposal by a wartime scientist named Vannevar Bush, titled As We May Think.

Although history would see this work as having been a key inspiration in the development of her era’s still-capitalized Internet, the original proposal had much more to do with memory and association than it did with switching or even linking. His thought-experiment prototype, which he called aMemex, was to be a way for thinkers to track and trace the sinuous pathways of their own inspirations and memories, as they sparked and resparked one-another, clustering and growing over time.

For Vannevar Bush, tasked with assisting in the collective remembrance of a generation of scientists at work in dark days, this was a way for thinkers to organically archive and pass down their best associations and kernels of discovery. But Thea saw something different in the latent potential of Bush’s original model. “Writing is a way of thinking in traces,” she would say; and she had glimpsed a means for regenerating a primordial soup of ideas through association, whether done alone or as a game between players. And so a set of writing (which is thinking) exercises emerged.

The exercises could be used by anyone with a challenge to overcome; and indeed, she herself would apply these methods much later in her work on holographic syntax, which would eventually yield hologlyphs, which would come to find a home deep down in the living code of Protean cells.

At the time of her efforts on her speculative fiction, The Tracer Guild, her use of these tools were in full swing. Though it would be years before they were adapted for work on the Avatamsaka synthetic mind, already she’d called the resulting pool a Codex – partly in honor of the Memex, and partly from an understanding that before there were books, there were bundles bound by hand and over time. To Thea, a Codex was bound not by thread but by association, theme, subject, intent.

Any given project might have a codex built up around it, filled with its influences and fragments of its form. In this way, a codex became a kind of random access archive of materials and raw ingredients, in which orderly arrangement was much less important than withdrawing sets and samples in a way that sparked sensemaking. In its earliest forms, the Vessel Codex which would ultimately drive Avatamsaka’s pattern-sampling technique was initially a very manual approach.

image-3-cc-by-sa-heath-rezabek copy

Image: ‘Wildcards.’ CC BY-SA Heath Rezabek.

Wildcards worked like this: You needed at least three players, each with a stack of blank index cards. The seeker (whose turn it was) would write on a blank (or draw if need be) something on their minds, on which they were seeking input. They’d lay it out, and the others would pen their response, based on what they knew of the seeker and the subject. The seeker would take stock, and pick the most useful response. They’d get to keep all the cards as payoff, and the turn would pass to the one with the favorite response, who’d get to be seeker in turn. The mechanic wasn’t perfect, and they were always tweaking it; but this was its basis.

Though it’d be tedious to detail the turns of their session here, it’s worth noting that this evening Thea walked away with five cards whose contents would come to influence her work more than she could have guessed.

[ Pathfinders ]
[ Shadow-forms gather around the core ]
[ The riverbed splits at a massive, ancient tree ]
[ Albino traders make the best maps of the deeps ]
[ These passages go on forever ]
[ Ancient Light ]

She, in turn, had supplied these responses to her friends:

[ White dwarf stars ]
[ Rebuilt every twenty years ]
[ That which does not expand forever, eventually contracts ]
[ Tales of the Kami ]
[ All their constellations would differ from ours ]
[ Calligraphy, Astronomy, and Swordsmithing ]
[ Perhaps the solution is not chemical but mathematical ]
[ Customs are a form of Etiquette ]

Home again, Thea shuffled these cards into file with uncounted others. She had once spent her time typing them into an aging, soon to be extinct digital platform called HyperCard, the clack-clacking of her Centris a kind of hypnosis; but she’d come to trust both the durability and even the labor-intensity of her pen-scratched cardstock.

Thea Ramer surveyed the card files as she slid the last one into unsorted slumber. “There, now. Dream awhile,” she muttered, and reached for her wine. She would not draw any of these particular cards out in a pattern-sample for months — in several cases, she’d never lay eyes on them again. Yet there they lay and waited; a glimpse now and again was enough to plant seeds deeply in the imagination…

- – - – -

image-4-cc-by-sa-wikipedia copy

Image: Adaptation of photography CC BY-SA Wikimedia.

Dr. Kaasura stood, faltering in the low light of the cavern. Before him lay the crates, one — the white one he’d carried from the flooding road, splayed open, leaning on stone. He reached out, pulling it to rest level at his feet. The crate’s white material was dense, with a feel almost like sanded wood. Its matte sides, unscarred by the storm or his trials, reflected nothing of the cavern’s aqua glow. Jota wiped a stray leaf away, small bits of mangled fern sticking to his fingers.

Inside it was a very cubic looking box, quite black, also matte, and so featureless that, at this angle, it seemed to Jota’s eyes a dark hexagon, a gap in space, no edges to be seen.

A flicker skimmed the white inner surface of the crate. Kaasura walked closer, looking at the side wall, and found it lit with tiny squares of different hues. “Projections?” he muttered, looking back at the surface of the inner box. Pitch black, no signs of life. But another look at the projections was enough to resolve them clearly.

Arrayed against the white insides, countless little pinholes, neither square nor round, all different, faded in and out. Bringing his focus to bear on a small spot, Jota Kaasura could see a sea of impressions shimmer and fade: an iron teapot, or the image of one. His aunt, in a scene he could not recognize. Beside her, in another tiny scene, a small child bounced a ball, running in some game. A ruined landscape, scarred by a massive red orb, feral and fading… An apple; an overturned wheelbarrow; sunrise over a stormy sea. A slipstream sail gliding through depthless night.

Kaasura stumbled back, awestruck at the sight. Countless images, faded in and out as if clouds were passing in front of stars. He turned to face the wooden crate, then, as if to forget the black in white. It too looked identical to the one overturned by the truck, but its sides were dry, unmuddied, unbruised. Jota looked at the edges, and found them nailed shut. His fingers felt at his pockets, expecting the pocketknife they found there. He started prying at the lid, unsurprised when it released so easily from the crate. Unsurprised, but not untroubled.

Inside, old packing strips, shredded and brown; and nestled within – a kind of a globe. Several feet across, each tiny pane in its varied surface was triangular, miniature, geodesic. The glass was gritty, each edge a wiry seam. Jota braced himself to lift it — and failed. It was cold to the touch, even to his cold fingers.

Dr. Kaasura stood and sighed, turning to the metal crate. It seemed to have three latches, each with its own lock and perhaps with its own key. He was suddenly very tired.

“Who are you?”

Kaasura turned with a start. A woman stood in the far corner of the cavern, a staff turned towards him. He couldn’t make out her face, but she was short and her stance was strong. Jota held out one hand, open-palmed…

“Why are you here? How did you get here?” She took a half-step forwards, the end of her staff alight with countless fibres. Electrified?
He held up his other hand, nodding. “My name is Jota. I came here to shelter from the storm.” He gestured back to slick rockface behind him, the subsiding rains down below. “I… certainly didn’t expect to find anyone else here…”

She frowned at his nudge for information, hesitating before motioning towards the rear of the cavern. “I live here. Not here,” she motioned at the dim room around them, “back there; our skycity’s docked.”

She looked around then, almost nervously, as Kaasura considered what to say. She interrupted before he could.

“You can’t be here.”

“Why not?”

“It’s just not allowed. You have to be escorted.”

“Well, surely you could escort me, couldn’t you?”

“I don’t know you. I don’t know where you came from, or what your intent is, here.” She was on the edge of helping him; he could feel that much. He raised his hands higher, his arms wider, gesturing towards these ends.

“I only meant to shelter from the storm. I was fleeing for my life — well, that and… I was trying to save these crates.” He motioned, then, at the three mysteries tumbled on the floor.

She looked down at them, a worried look on her face. When she glimpsed the geodesic sphere in its shredded bed, she stopped short and her look turned strangely. “Where did you get that..?”

Eyes fixed upon the geodesic sphere, he watched her as he hesitated. She made her way towards the black box in its white crate. “What are they?”

“I’m not sure,” Kaasura said truly. “And without my laboratory, it’s hard for me to find out. I need a place to rest, and to work.”

She looked at him, long and low, weighing her factors.

“What is your name. I’m Jota. You..?”

Hesitation. Concern.

“… Call me Miira.”

He tried it: “Mirra?”

She shook her head, no longer so stern. “M i i r a”.


She nodded — “Wait here.” — and turned.

A few steps towards a dark way he hadn’t seen, she paused. “That is, you’re free to go. Back the way you came. But don’t try to come after, until I return.”

Then in shadows, she was gone.

Jota blinked, hands still outstretched, the room suddenly vast in its silence. He walked towards the corner into which she’d disappeared, his eyes adjusting to the dim aquamarine light. Although there are fewer of the cracks he’d noticed on his way up the channel, he could still make out a few slim rivulets of mossy luminescence spreading out and down a smoothly carved tunnel, as if in glacial pursuit of Miira’s faded footfalls.

He stopped and examined the doorframe. Although the room of the cavern was roughly hewn, as if by nature and effort, at the rear a triangular bracing cut the wall, thick and apparently metal. The cavern that cut forth from there carried its angular lines, but split and bifurcated as it sliced through the stone.

He looked at the stone, then, as if for the first time. Pumice? Tiny dark cells in a petrified foam. He was exhausted.

Kaasura stepped backwards, once; twice; turning, he found support on the white crate, collapsing to the floor beside it, still soggy and cold.

Leaning his head against its sides, Jota sat facing the triangular passageway. He could hear dripping throughout the cavern, and far behind, the slow washing of sea and storm subsiding.

Echoes and stones, falling far in the distance, down the maze of twisty passages, along the way which Mirra had made her way, along the way…

And he begins to nod.

And he begins to dream.

image-5-wiki-Reflection_in_a_soap_bubble_edit copy

Image: Adaptation of ‘Reflection in a Soap Bubble.’ CC BY-SA Wikimedia.

And in the dream, Kaasura sees a bubble, adrift, floating high above the land. At first he thinks it’s a blown bubble, blown out over grass or a field. Its bright surface mirrors sharply the sky.

As he looks more closely, he can see features. The surface of bubble is riddled with layers and lines and portals and intaglio. There’s a texture to it, not quite consistent, but definitely patterned; definitely there.

Gigantic and ponderous, it drifts over the shoreline. He senses the scale, because far below he can see the ruins of the power plant. Smoke is rising from one of the crumpled generators. Steam billows as superheated runoff collides with the sea.

The sphere sails on, over the tips and tops of the mountain range (he can make out the cleft he climbed into) and on past the mountains. He follows as if in flight far above, freely falling through its wake. Below, mountain peaks cut coldly, impassably. It passes and passes them by.

The sphere reaches a wide open plain. As it opens up over that expanse, he can see that it’s a desert, cold and worn, under a ruddy sky. The ground has the strangest textures. Ancient and empty, crumpled and swept. Nothing breaks the surface of frozen red rock and rubble.

But in the distance, beyond the bubble by a far misty mile, he sees another. And then another; and he realizes that they’re getting smaller, as he rises higher.

More appear as they cluster and shrink beneath his altitude; they’re not near each other, but all of them drift as if part of the same current, eddying in waves as wide as landscapes, buoys and beacons on a sea of risen air. Signal lights flicker on their edges; warmer lights waver in their hearts.

And as Dr. Kaasura rises also, he begins to see an arcing curve to the land which lifts those bubbles, until they seem as if they’re afloat upon the surface of a bubble that’s far larger. And just as he feels the fragility can’t hold, he awakes — and finds he’s no longer in a cavern.

He takes a breath, and rubs his eyes. And far above his resting head, a skydome is traced, a prismatic array.



Small Payloads to the Stars

by Paul Gilster on April 3, 2014

Making things smaller seems more and more to be a key to feasibility for long-haul spaceflight. Recently I went through solar sail ideas from the 1950s as the concept made its way into the scientific journals after an interesting debut to the public in Astounding Science Fiction. We also discussed Sundiver missions taking advantage of a huge ‘slingshot’ effect as a sail skims the photosphere. These could yield high speeds if we can solve the materials problem, but the other issue is making the payload light enough to get maximum benefit from the maneuver.

It puzzles me that in an age of rapid miniaturization and increasing interest in the technologies of the very small, we tend to be locked into an older paradigm for starships, that they must be enormous structures to maintain a crew and carry out their scientific mission. Alan Mole’s recent paper reminds us of an alternative flow of work beginning in the 1980s that suggests a far more creative approach. If we’re going to extrapolate, as we must when talking about actual starships, let’s see where nanotech takes us in the next fifty years and start thinking about propulsion in terms of moving what could be a very small payload instead of a behemoth.

I think sails connect beautifully with this kind of thinking. Mole envisions a sail driven by a particle beam, with the beam generator in Earth orbit fed by ground-based power installations, but we continue to look at other sail concepts as well, including laser and microwave beaming to ultralight sails made of beryllium or extremely light metamaterials. Payload-inefficient rockets don’t scale nearly as well to the kind of interstellar missions we are thinking about, but sails leave the propellant behind to enable fast missions delivering extremely small payloads.

This kind of thinking was already becoming apparent as early sail work emerged in the hands of Konstantin Tsiolkovsky, Fridrickh Tsander and others, and I’ll point you back to From Cosmism to the Znamya Experiments for more on that. For now, though, have a look at the marvelous Frank Tinsley illustration below. Here’s a startlingly early version (1959!) of sails in action, painted before Cordwainer Smith’s “The Lady Who Sailed the Soul” and Arthur C. Clarke’s “Sunjammer” ever hit the magazines. When Robert Forward began working on laser-pushed lightsails, he would have had images like this from popular culture to entice him.


Image: An early look at the solar sail from a 1959 advertising image by Frank Tinsley. Credit & copyright: GraphicaArtis/Corbis.

Tinsley’s career is worth lingering on. A freelance illustrator known for his cover paintings for pulp magazines, he covered a wide range of subjects in magazines like Action Stories, Air Trails, Sky Birds and Western Story, with a stint in the early silent film industry in New York City in the 1920s, where he served as a scenic artist and became friends with William Randolph Hearst. By the 1950’s, he was illustrating articles for Mechanix Illustrated. A representative sample of the latter work can be seen here, packed with speculations about futuristic technologies.

But back to sails carrying small and innovative payloads. In a 1998 paper in the Journal of the British Interplanetary Society, Anders Hansson, who had two years earlier described what he called ‘living spacecraft’ in the same journal, reported on NASA Ames work into spacecraft consisting of only a few million atoms each. The study speculated that craft of this size would travel not as single probes but as a swarm that could, upon arrival at a destination system, link together to form a larger spacecraft for exploration and investigation.

Gregory Matloff, who along with Eugene Mallove wrote the seminal paper “Solar Sail Starships: The Clipper Ships of the Galaxy” for JBIS in 1981, has recently discussed the design advantages of solar sail nano-cables that would be much stronger than diamond. Nanotechnology in one form or another could thus influence the design even of the large sail structures themselves, not to mention the advantages of shrinking the instruments they deliver to the target. We may one day test out these ideas through nanotech deployed to asteroids to harvest resources there, teaching us lessons we’ll later apply to payloads that assemble research stations or even colonies upon arrival.

The Hansson paper is “From Microsystems to Nanosystems,” JBIS 51 (1998), 123-126. Greg Matloff’s 1981 paper with Eugene Mallove is “Solar Sail Starships: The Clipper Ships of the Galaxy,” JBIS 34 (1981), 371-380.



The Probe and the Particle Beam

by Paul Gilster on April 2, 2014

For those wanting to dig deeper into Alan Mole’s 1 kilogram interstellar colony probe idea, the author has offered to email copies of the JBIS paper — write him at For my part, writing about miniaturized probes with hybrid technologies inevitably calls to mind Freeman Dyson, who in his 1985 title Infinite in All Directions (Harper & Row) discussed a 1 kilogram spacecraft that would be grown rather than built. Here’s Greg Matloff’s description of what Dyson whimsically called ‘Astrochicken’:

Genetically engineered plant and animal components would be required in Astrochicken. Solar energy would power the craft in a manner analogous (or identical) to photosynthesis in plants. Sensors would connect to Astrochicken’s 1-gm computer brain with nerves like those in an animal’s nervous system. This space beast might have the agility of a hummingbird, with ‘wings’ that could serve as solar sails, sunlight collectors and planetary-atmosphere aerobrakes. A chemical rocket system for landing and ascending from a planetary surface would be based upon that of the bombardier beetle, which sprays its enemies with a scalding hot liquid jet.

The passage is from Matloff’s Deep Space Probes (2nd ed., Springer, 2006), which goes on to discuss the need to master nanotechnology so that we can manipulate objects on the scale of atoms. He even speculates, citing Alan Tough, that nanotechnology could produce a hyperthin communication antenna for relaying information to Earth from an interstellar probe, constructing it from resources in the destination star system. And he cites Anders Hansson’s 1996 paper in JBIS that sketches an interstellar Astrochicken, one with

…miniaturised propulsion subsystems, autonomous computerised navigation via pulsar signals, and a laser communication link with Earth. The craft would be a bioengineered organism. After an interstellar crossing, such a living Astrochicken would establish orbit around a habitable planet. The ship (or being) could grow an incubator/nursery using resources of the target solar system, and breed the first generation of human colonists using human eggs and sperm in cryogenic storage.

Infrastructure for the Probe

Just as Project Icarus is an attempt to update the Daedalus design of the 1970s, Alan Mole’s work re-examines ideas like these in light of recent work. Yesterday we looked at the trends he thinks make probes with this degree of miniaturization possible. For getting the probe to destination at 0.1 c, he relies on a magnetic sail which draws on studies performed by Dana Andrews in the 1990s. Andrews was talking about a 2000 kg payload, but Mole’s 1 kg payload could be accelerated at 1000 g to cruising speed, with an acceleration distance he calculates at only 0.3 AU, using 1/9th the kinetic energy of the Andrews probe.

To push the magnetic sail a particle beam produced by an accelerator is demanded. Here is Mole’s description:

The probe interacts with the beam by having a magnetic sail, a loop of superconducting wire. This is ejected from the probe and a large current introduced. The magnetic field repels all parts of the wire, so it naturally inflates to a circular loop. For one kg and 0.1 c the acceleration distance is only 0.3 AU and the loop diameter…is just 270 m. After cruise, it is possible to slow the probe by reintroducing a current into the sail and using “friction” from interstellar magnetic fields. This method seems to scale successfully.

The beam generator in Earth orbit would be powered by beamed power from the Earth’s surface. Mole describes the installation as ‘an orbital solar power farm in reverse,’ with the advantage of tapping directly into Earthbound power resources. He points out that NASA drew up studies of a Solar Power Satellite system in 1981, coming in at a cost of about $4 billion to beam power to Earth by microwaves. The Mole plan reverses the process to power an orbital beam generator that would accelerate the magsail, with an estimated beam generator cost of $17 billion.


Image: We’ve long imagined beaming power down to Earth to tap the Sun’s abundant energies. But is there a case for beaming power up to drive an interstellar beam technology? Credit: Mafic Studios/National Space Society.

Mole believes the cost of such a beam generator might actually come in considerably lower than $17 billion, but the appendix to his paper shows a wide range of possible costs. In a recent email, Mole wrote me that he is offering a stipend of $5000 (negotiable) for a suitable expert to design and produce cost estimates for the beam generator. Those interested should apply to Mole directly at the email address given at the top of this article. The cost estimates are significant, to say the least, and getting them right should illustrate the value of moving to a smaller probe.

In terms of energy use, by Mole’s figures, a 2000 kg probe of the sort Dana Andrews discussed in his 1994 paper, would require 560 times the US capacity for power generation today. A 1 kg probe would require 28 percent of the US generating capacity, making it far more feasible for a civilization at our stage of development over the next fifty years. The author adds:

Large probes and worldships inspire readers to imagine the vast civilizations that could afford them, but not to start work in hopes of seeing them launched in the readers’ lifetimes. In contrast, a 1 kg probe is plausible for the present civilization. If discussion begins now such a probe could be launched in fifty years.

Sail technologies, whether beamed by microwave, laser or particle beam, come to the fore in discussions like these because we’re already beginning to build experience with solar sails in space. Laboratory experiments have shown that sail beaming works, with the added benefit — shown in Greg and Jim Benford’s experiments — that materials can undergo ‘desorption,’ providing additional acceleration. Now we need to learn how well particle beams can drive a magnetic sail because, like all these sail concepts, this one requires no propellant aboard the spacecraft, a huge plus given the challenge of pushing even a 1 kilogram payload to a tenth of lightspeed.

The paper we’ve been discussing is Mole, “One Kilogram Interstellar Colony Mission,” Journal of the British Interplanetary Society Vol. 66, No. 12, 381-387 (available at the site). The Dana Andrews paper referred to above is Andrews, “Cost considerations for interstellar missions,” Acta Astronautica 34, pp. 357-365,1994. The Hansson paper is “Towards Living Spacecraft,” JBIS 49 (1996), 387-390.



Small Probes, Hybrid Technologies

by Paul Gilster on April 1, 2014

Reducing the size of a starship makes eminent sense, and as we saw yesterday, Alan Mole has been suggesting in the pages of JBIS that we do just that. A 1 kilogram interstellar probe sounds like it could be nothing more than a flyby mission, and with scant resources for reporting back to Earth at that. But by Mole’s calculation, a tiny probe can take advantage of numerous advances in any number of relevant technologies to make itself viable upon arrival.

Just how far can nanotech and the biological sciences take us in creating such a probe? For what Mole proposes isn’t just an automated mission that uses nano-scale ‘assemblers’ to create a research outpost on some distant world. He’s talking instead about an actual human colony, one whose supporting environment is first guaranteed by nanobots and, in turn, the robots they build, and whose population is delivered through the hatching of human embryos or perhaps even more exotic methods, such as building humans from DNA formulae stored in memory.


Let’s look at some of the factors the author lists, and bear in mind that we are trying to sketch out the shape of technologies that will have advanced in ways we can’t predict by the time such a probe is ready to fly, even if we allow it the relatively short time-frame (by interstellar scales) of fifty or sixty years of development before launch. From the “One Kilogram Interstellar Colony Mission” paper, here are the key points:

1) Increases in memory density show no sign of slowing. Mole cites small media memory chips that will soon carry two terabytes, but I’d point to Charles Stross’ fascinating discussion of ‘memory diamond,’ which sets theoretical limits on memory density by manipulating carbon atoms. If we need to pack vast amounts of memory into tiny spaces, the future is increasingly bright.

2) Within fifty years, nanotechnology may be able to produce tiny machines — nanobots — capable of complex tasks including self reproduction. The key question then becomes, can such technologies build humans? Mole recognizes the size of the challenge:

“Whether nanomachines can build full humans is unknown. It is physically possible — nature does it when a single fertilized egg cell grows into a human or animal. The DNA of a bacterium has been produced from stored ones and zeros in a computer. Granted, this required a full laboratory of equipment, but in five decades nanobots may be able to do it.”

3) I would feel better about the nanotechnology cited above if we took that fifty year restriction out of the equation, but even without humans ‘built’ by nanotech, we still have the option of sending embryos. Here the relevant citation is a 1989 Japanese project to incubate a goat fetus in an artificial womb, where the fetus grew to birth size but did not survive. Using vast numbers of human embryos on a colony ship, to be raised by robots at destination (robots that have themselves been built by nanobots), allows humanity to spread without large ships and without the need for hibernation (the large ships may be less feasible than the hibernation).

4) That Mole’s proposal is audacious is underlined by the fact that artificial intelligence may be its least controversial feature. Not everyone agrees with Ray Kurzweil that within three decades we’ll be able to essentially duplicate a human mind and run it as a program on a computer. But watching the trends in memory and recent work in brain architecture, including the Blue Brain Project, makes the prospect of uploaded minds at least possible. In any event, we are talking about running some kind of artificial intelligence on tiny CPUs that can manage the activities of nanobots as they build androids that go on to create a human colony. We’re in Singularity territory now, and in the nature of things, that makes predictions tricky indeed.

All of this grows out of a foundation of thinking that combines biology and silicon in interesting ways. Back in June of 1999, then NASA administrator Daniel Goldin spoke before the American Astronomical Society. It had been two years since he announced (in the same year that the Pathfinder probe landed on Mars) that reaching another star would be a new goal for NASA. That was startling enough, but Goldin went on to speak about a combination of lightsail technologies, artificial intelligence advances and hybrid systems tapping advances in biology.

It was an exciting time, even if the interstellar vision was quickly submerged in NASA’s more immediate goals and the ever present challenge of funding work in low Earth orbit. But Goldin’s probe — he described it as a space vehicle about the size of a Coke can — was meant to build itself by scavenging an asteroid, using the abundant supplies of carbon, iron and other materials such an object could provide. Mole’s paper reminded me of Goldin’s quote from that time:

“This reconfigurable hybrid system can adapt form and function to deal with changes and unanticipated problems. Eventually it will leave its host carrier and travel at a good fraction of the speed of light out to the stars and other solar systems… Such a spacecraft sounds like an ambitious dream, but it could be possible if we effectively utilize hybridized technologies.”

With Goldin as with Mole, the intent was to craft a starship without the need to push thousands of tons of payload, using the ability of technology to build and extend itself with local materials. In any case, we’re getting better and better at working with small spacecraft. Consider the Viking landers, each of which massed about 1200 kilograms (the Viking orbiter was 2300 kg). Mars Pathfinder’s lander came in at 100 kilograms, while the Sojourner rover itself massed only 12 kg.

Freeman Dyson laid out a concept for a 1 kilogram probe back in 1985 that set the stage not only for increased miniaturization but the fusion of biology with digital tech. Tomorrow I’ll get into some of Dyson’s ideas as a way of framing what Alan Mole is discussing, and then we need to focus in on the propulsion question. Getting anything — even something as small as a 1 kilogram probe — to another star is an extraordinary undertaking. But finding ways to leave the propellant behind can make it more feasible.

The paper under discussion is Mole, “One Kilogram Interstellar Colony Mission,” Journal of the British Interplanetary Society Vol. 66, No. 12, 381-387.



Interstellar Probe: The 1 KG Mission

by Paul Gilster on March 31, 2014

Reading Charles Adler’s Wizards, Aliens and Starships over the weekend, I’ve been thinking about starflight and cost. Subtitled ‘Physics and Math in Fantasy and Science Fiction,’ Adler’s book uses the genres as a way into sound science, and his chapters contain numerous references to writers like Poul Anderson, Larry Niven and Robert Heinlein. On the matter of speculative propulsion systems, he lingers over fusion and describes the work of Project Daedalus back in the 1970s, when an ad hoc team of volunteer scientists and engineers put together a serious starship study.

Like the vessels written about in the science fiction of that era and before, Daedalus was simply a mammoth craft — 53 million kilograms! — but that corresponded with what SF had been telling us all along. We would travel to the stars aboard vessels not so different from ocean liners, perhaps big enough to be livable on a daily basis, or at least big enough to pack thousands of humans into cryogenic containers for a trip under suspended animation. It’s a natural enough thought: Long journeys demand big vessels. Scenarios like this burn up plenty of energy, as Adler is quick to note:

…the implication of an interstellar probe [like Daedalus]…is that we possess an extremely energy-rich society. The cost of Project Daedalus was estimated at $10 trillion. Using the rule of thumb that prices for everything double every 20 years, the estimate comes in at about $40 trillion today, dwarfing the U.S. GDP. This amount of money is about equal to the GDP of the entire world. Energetics tell us why this is so: the total energy contained in the payload is about 10% of the total world energy usage for one year. This is too expensive for any current world civilization to undertake, and it may well be too expensive for any civilization to undertake under any circumstances.

Adler, a professor of physics at St. Mary’s College in Maryland, is a lively writer who is well versed in both science fiction and fantasy, making this an entertaining volume indeed. He doesn’t mention the ongoing Project Icarus study, but it will be interesting to see how the ensuing years have modified the original Daedalus concept to produce a less costly, more viable design. Even so, the assumption is that a fusion starship as designed today is going to be a large vehicle because it has to deliver enough of a payload to make the journey to the star worthwhile.

Realm of the Small

Enter Alan Mole. A retired engineer, Mole is an aerospace stress analyst who has worked at the University of Colorado Laboratory for Atmospheric and Space Physics, and as a contract engineer for Ball Aerospace, McDonnell Douglas, Pratt and Whitney, Thiokol-ATK and other firms. A recent issue of the Journal of the British Interplanetary Society contains his paper “One Kilogram Interstellar Colony Mission,” which reverses the big starship paradigm and looks to deliver a seriously effective payload at a sharply reduced cost. Mole is, he tells me, interested not only in physically possible ways to solve difficult problems, but also in making the solutions economically feasible.


Image: The Milky Way over Ontario. As we ponder a human future in the stars, can nanotech and biology breakthroughs show the way forward? Credit & Copyright: Kerry-Ann Lecky Hepburn.

The difficulty of the problem is hard to overstate. It was not some skeptical bystander but Anthony Martin himself, a major player in the Daedalus design effort, who noted the cost to the society that chose to build Daedalus: “It seems probable that a Solar System wide culture making use of all of its resources would easily be wealthy enough to afford such an undertaking.” But Alan Mole is not the first to point out that we are developing lower cost alternatives. If we can create a smaller payload and find a propulsion method that scales down to meet its requirements, we can start talking about an interstellar effort that would prove economically viable while offering choices for human expansion including interstellar colonization.

If Daedalus totalled 53 million kilograms, Mole thinks we should be looking at a single kilogram as sufficient for our colony probe. Making something like this even imaginable involves advances in artificial intelligence, computer memory, materials science, nanotechnology and biology that we can imagine continuing throughout the century, barring the kind of societal catastrophe that disrupts civilization itself. The kind of probe Mole envisions is a world in itself or, I should say, the seed of a world to come, for it uses technology to raise a human colony at destination:

Consider a one kg colony probe sent to a nearby extrasolar planet at about 0.1 c. It will land and nanobots will emerge to build ever larger robots and greenhouses etc. for colony infrastructure. The nanobots will be powered by batteries and recharged by solar cells, building larger arrays of these as work progresses. They will then hatch human embryos (millions per gram) or build humans directly from DNA formulas stored in memory (as was done for a simple bacterium in the artificial life experiments in 2010.) The probe will transmit no data to Earth but if the colony is successful it will eventually build transmitters and establish contact.

Charles Adler doesn’t suggest science fictional treatments of such ideas, but I know current authors must be working this turf, and I’d appreciate pointers from readers. I’m reminded of Robert Freitas’ ideas about self-reproducing probes, a concept I discussed in Centauri Dreams (the book) in the context of an earlier Freitas idea called REPRO, which involved probes on a Daedalus scale that built replicas of themselves and continued out into the galaxy. By reducing the probe to the size of a sewing needle, Freitas envisions sending just enough nanotechnology to turn assemblers loose at destination to build a station to take scientific measurements, report findings back to Earth and, eventually, move on to another star.

Alan Mole is likewise intrigued by the world of the small, but as the above quote demonstrates, he’s thinking in terms of biology as well. Tomorrow I want to explore the implications of Mole’s thinking, looking first at previous ideas for very small payloads from the likes of Freeman Dyson, Dan Goldin and Gregory Matloff. Then we’ll talk about the propulsion systems that could make such a concept work. For it may not be feasible to carry our propellant with us, opening the door for a variety of beamed energy concepts whose cost is far less onerous than the alternatives.

The paper we’ll be discussing for the next few days is Mole, “One Kilogram Interstellar Colony Mission, Journal of the British Interplanetary Society Vol. 66, No. 12, 381-387.



Rosetta: Target in Sight

by Paul Gilster on March 28, 2014

The European Space Agency’s Rosetta spacecraft, having traveled for ten years, is on track for its close-up investigation of comet 67P/Churyumov–Gerasimenko to begin later this year. Three years ago we had the first actual image of the comet, a 13-hour exposure taken shortly before the craft entered a lengthy period of hibernation. On the 20th of January, Rosetta was ‘awakened’ and controllers are in the process of commissioning its onboard instruments. As part of the process, we have two ‘first-light’ images taken on March 20 and 21.


Image: Comet 67P/Churymov-Gerasimenko in the constellation Ophiuchus. This image was taken on 21 March by the OSIRIS Narrow Angle Camera. The comet is indicated by the small circle next to the bright globular star cluster M107. The image was taken from a distance of about 5 million kilometres to the comet. A wide-angle image was taken on 20 March. Credit & copyright: ESA © 2014 MPS for OSIRIS-Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA.

We’re seeing Rosetta from a distance of 5 million kilometers, from which vantage we see its light in less than a pixel through a series of 60 to 300 second exposures. Even so, the sense of exhilaration in the words of OSIRIS principal investigator Holger Sierks (Max-Planck-Institut für Sonnensystemforschung, Göttingen) is palpable:

“Finally seeing our target after a 10 year journey through space is an incredible feeling. These first images taken from such a huge distance show us that OSIRIS is ready for the upcoming adventure.”

Keep in mind the relevance of Rosetta’s mission not only to the evolution of the Solar System but also to future propulsion ideas. One area of interest is the interaction between the solar wind and cometary gases, needed information as we deepen our knowledge not only of the solar wind itself but how its stream of charged particles might be used in electric and magnetic sail concepts. The solar wind’s variability is one key issue about which we have much to learn.

Rosetta’s studies will be wide-ranging. The spacecraft flies with eleven science instruments onboard, fine-tuned to study everything from the comet’s surface geology to its internal structure and the dust and plasma that surround it. OSIRIS (Optical, Spectroscopic and Infrared Remote Imaging System) has both a wide-angle and a narrow-angle camera involved in the capture of the early images, all part of six weeks of activity as all eleven instruments are checked out for arrival in August.

This ESA news release offers more, noting that on its current trajectory, the spacecraft would pass approximately 50,000 kilometers from the comet at a speed of 800 meters per second. It will be in May that a series of maneuvers are begun to reduce Rosetta’s velocity relative to the comet to 1 meter per second, with the aim of bringing it within 100 kilometers by the first week of August. The re-activation of OSIRIS now gives way to checks on the other instruments as we prepare for what ought to be a memorable encounter. The Philae lander is scheduled to attempt its landing in November.


{ 1 comment }

Habitability: The Case for F-Class Stars

by Paul Gilster on March 27, 2014

When it comes to habitable planets, we focus naturally enough on stars like our own. But increasing attention has been paid to stars smaller and cooler than the Sun. M-class dwarfs have small but interesting habitable zones of their own and certain advantages when it comes to detecting terrestrial planets. K-class stars are also interesting, with a prominent candidate, Alpha Centauri B, existing in our stellar back yard. What we haven’t examined with the same intensity, though, are stars a bit more massive and hotter than the Sun, and new work suggests that this is a mistake.

Manfred Cuntz (University of Texas at Arlington), working with grad student Satoko Sato, has been leading work on F-class stars of the kind normally thought problematic for life because of their high levels of ultraviolet radiation. Along with researchers from the University of Guanajuato (Mexico), Cuntz and Sato suggest that we take a closer look at F stars, particularly considering that they offer a wider habitable zone where life-sustaining planets might flourish.

Cuntz thinks the case is a strong one:

“F-type stars are not hopeless. There is a gap in attention from the scientific community when it comes to knowledge about F-type stars and that is what our research is working to fill. It appears they may indeed be a good place to look for habitable planets.”


Image: The habitable zone as visualized around different types of star. Credit: NASA.

The team’s paper in the International Journal of Astrobiology makes this argument based on its studies of the damage that ultraviolet radiation can cause to the carbon-based macro-molecules necessary for life. Its estimates of the damage that would accrue to DNA on planets in F-class star systems covered calculations for F-type stars at various points in their evolution. Planets in the outermost regions of the habitable zone experience much lower levels of radiation. This UT-Arlington news release quotes the paper:

“Our study is a further contribution toward the exploration of the exobiological suitability of stars hotter and, by implication, more massive than the Sun…at least in the outer portions of F-star habitable zones, UV radiation should not be viewed as an insurmountable hindrance to the existence and evolution of life.”

F-type stars represent 3 percent of the stars in the Milky Way, as compared with G-class at about 7 percent and K-class at approximately 12. And then there are M-dwarfs, which may account for over 75 percent of all main sequence stars. In any event, the more we widen the prospects for astrobiology beyond stars like the Sun, the more we address the possibility of a galaxy suffused with life, even if we still have no direct evidence. Just as intriguing: If it turns out life is abundant, is intelligence abundant as well?

The paper is Sato et al., “Habitability around F-type Stars,” International Journal of Astrobiology, published online 25 March 2014 (abstract).