Happy 75th Birthday Greg Benford!

Young Greg (left) and Jim (right) Benford war with the descendants of dinosaurs, er, chickens.

Young Greg (left) and Jim (right) Benford war with descendants of dinosaurs, er, chickens.

Best wishes to Greg and Jim Benford, twin brothers born this day in 1941, renowned scientists, sf fans, and authors.

They discovered fandom in the 1950s while their father was in the Army and stationed in Germany. There, jokes Greg, he and his brother both had to learn a foreign language: “I had to learn English – because I’m from Alabama.” The two began Void, one of the zines most closely identified with the iconoclastic spirit many remember as the best thing about fandom in those days. Also, Greg attended his first convention in 1956.

Greg and Jim in Germany in 1956.

Greg became a Professor of Plasma Physics and Astrophysics at the University of California, as well as one of the most accomplished hard sf writers. He’s a two-time Nebula winner, and has been nominated for the Hugo 13 times. A new collection of his short fiction, The Best of Gregory Benford, edited by David G. Hartwell, was published last July.

Greg Benford and David G. Hartwell sitting in President Taft's chair.

Greg Benford and David G. Hartwell sitting in President Taft’s chair.

Jim and Greg have worked on a number of things together, such as the concept of “Benford beacons”, theorizing that an alien civilization striving to optimize costs and make its signaling technology more efficient, would prefer signals that are pulsed, narrowly directed and broadband in the 1-to-10-gigahertz range.

In 2013, they helped organize the Starship Century Symposium where participants asked, “Is this the century we begin to build starships? Can we? Should we?”

The brothers Benford hope “Yes” is the answer to all three questions.

Jim and Greg at Tri Alpha Energy, a company doing advanced work in magnetic field-reversed containment methods, with the goal of developing fusion power.

Greg and Jim at Tri Alpha Energy, a company doing advanced work in magnetic field-reversed containment methods, with the goal of developing fusion power.

Clarke Center Presents Jon Lomberg

Lomberg at Clarke CenterArtist Jon Lomberg, a speaker at the Starship Century Symposium last May, will return to the Arthur C. Clarke Center for Human Imagination at UCSD for two appearances in December.

Jon Lomberg is one of the foremost artists inspired by astronomy. He did Emmy Award-winning work as Chief Artist for Carl Sagan’s Cosmos series. And he was Design Director of NASA’s Voyager Interstellar Record, the self-portrait of humanity now on its way to the stars.

Lomberg’s December 3 presentation is “Becoming Galactic: Citizens of the Galaxy”:

The word cosmopolitan literally means a citizen of the Cosmos. Our generation is emerging into the Milky Way, and becoming a planetary species. Jon Lomberg shows some ways that an artist can respond to this amazing fact, combining physics and artistry to create the “cosmic perspective” advocated by Lomberg’s friend and long-time collaborator, Carl Sagan. He will feature a description of his unique Galaxy Garden.

The Galaxy Garden models the Milky Way to scale with a garden of living things. By now Lomberg’s plantings have reached full size. galaxygarden2

A fountain in the middle of the garden marks the “gravity well” with a bimodal jet so water is going both directions. Out on the galactic arm corresponding to the position of our solar system, the place where the Sun would be is marked by a tiny jewel on a leaf. Driving home the scale involved, Lomberg says all the stars we can see with the naked eye are either on that same leaf or an adjoining leaf!


At Lomberg’s second appearance, the Galaxy Garden Workshop on December 7, he will explain how the garden is used to encourage science education, and demonstrate hands-on teaching activities that can be done indoors or outdoors using large-scale, explorable model galaxies. 

This event, while open to anyone, is particularly  designed to appeal to teachers in physical sciences grades 4-12, creators of informal science education activities, artists interested in novel art/science collaborations, gardening clubs and astronomy clubs.

The day’s activities will include building a model galaxy with fishing line grid, paper plates, spattered paint, toothpicks, and Play-Dough.


Royal Astronomical Society To Host Starship Century

The UK will host its own Starship Century Symposium next month. The event will gather scientists and sf authors to address the challenge of developing a starship in the next 100 years and opportunities for our long-term future in space.

The Symposium will be at the Royal Astronomical Society, Picadillly, UK on Monday October 21.

On hand will be featured speaker Lord Martin Rees, Royal Astronomer, Ian Crawford, Birkbeck College, University of London, writer/scientist Stephen Baxter, James Benford and Gregory Benford.


10:00 a.m.  Starship Century: James & Gregory Benford

10:30 a.m.  Scientific Benefits of Starships: Ian Crawford

11:30 a.m.  Contact at Alpha Centauri: Stephen Baxter

1:00 p.m. Break for lunch

2:00 p.m.  To the Ends of the Universe  Lord Martin Rees

3:30 p.m.  Panel: Exploring Interstellar Space: Lord Martin Rees, Ian Crawford, Stephen Baxter, Jim & Greg Benford, others TBA

5:00 p.m.  Symposium ends

These authors will also sign Starship Century at Forbidden Planet bookstore on Sunday, October 20, 4:30 p.m.

[Thanks to Gregory Benford for the story.]

Starship Century Symposium – Chris Lewicki

Chris Lewicki

Chris Lewicki

[This post is part of a series about the Starship Century Symposium held May 21-22, 2013.]

Chris Lewicki is President and Chief Engineer of Planetary Resources, leader of its day-to-day operations and responsible for the strategic development of the company’s mission and vision. He was intimately involved with NASA’s Mars Exploration Rovers and the Phoenix Mars Lander, serving as Flight Director for the rovers Spirit and Opportunity, and as Surface Mission Manager for Phoenix. Lewicki even has an asteroid named in his honor: 13609 Lewicki.

Earlier speakers at the Starship Century Symposium warned that humanity will need access to the resources of the entire Solar System to develop the technology and supply the large amounts of energy needed for an interstellar mission.

Chris Lewicki advised that the practical first step is commercializing space, prospecting and claiming the most valuable Near-Earth Asteroids.

Astronomers have discovered more than half-a-million new asteroids since 1997. Most asteroids are in the Main Belt.

There were 9,833 known Near-Earth Asteroids as of May 21. Near-Earth Asteroids (NEA) are generally defined as that population of asteroids which spends at least part of each orbit between 0.983 and 1.3 Astronomical Units from the Sun (1 Astronomical Unit is the Earth’s distance from the Sun).

Throughout the Solar System are over 1.5 million asteroids larger than one kilometer in diameter. Of these, 981 are Near-Earth Asteroids, and 17% of NEAs are energetically closer than the Moon. Several dozen asteroids could be reached with less energy than is required to put a television satellite into geostationary orbit.

Two NEAs have been visited by robotic spacecraft: 433 Eros by NASA’s NEAR mission, and 25143 Itokawa by Japan’s Hayabusa mission. NASA is currently working on the OSIRIS-REx mission to visit the carbonaceous asteroid 1999 RQ36 in 2019. (Asteroids are generally classified as C-type, carbonaceous, S-type, silicaceous,  or M-type, metallic.)

Asteroids contain platinum group metals — ruthenium, rhodium, palladium, osmium, iridium, and platinum (PGM). One in four manufactured goods requires PGM.

Some near-Earth asteroids contain PGM in much higher concentrations than the richest Earth mines. In space, a single platinum-rich 500 meter wide asteroid contains about 174 times the yearly world output of platinum, and 1.5 times the known world-reserves.

Asteroids also contain common metallic elements such as iron, nickel, and cobalt, sometimes in incredible quantities. In addition to water, other volatiles, such as nitrogen, CO, CO2, and methane, exist in quantities sufficient to warrant extraction and utilization.

Low cost commercial robotic spacecraft will explore asteroids and determine their position, composition, and accessibility of resources. Planetary Resources is creating robotic explorers to visit the best asteroid candidates, then access and process their resources during subsequent campaigns using a solar concentrator.

Water from asteroids can be both converted to and used directly as propellant, then shipped and stored at strategic locations set up as fuel depots. This fuel – supplied and sold to NASA or other in-space customers – will accelerate the pace of human spaceflight.

In Earth orbit, water from asteroids can also be converted and used to refuel satellites, increase the payload capacity of rockets by refueling their upper stages, reboost space stations, supply propellant needed to boost satellites from Low Earth Orbit to Geostationary Orbit, provide radiation shielding for spaceships, and provide fuel to space tugs that could clean up space debris.

The Starship Century anthology, Symposium edition, is currently available in paperback for $28 — click here.  

Arkyd series 200 Interceptor.

Arkyd series 200 Interceptor.

Starship Century Symposium: Geoffrey Landis

Geoffrey Landis

Geoffrey Landis

[This post is part of a series about the Starship Century Symposium held May 21-22, 2013.]

Geoffrey Landis is a scientist at the NASA John Glenn Research Center working on Mars missions and on developing advanced concepts and technology for future space missions — interstellar propulsion, solar power and photovoltaics. Landis, supported by his scientific background, also writes hard sf and is the winner of a Nebula Award, two Hugo Awards – plus two Rhysling Awards for his poetry.

Landis opened by echoing a mantra of earlier speakers — Starflight requires producing and controlling vast levels of energy resources – ice and 3He harvested from the outer Solar System.

“The Moon was easy,” he teased, then said seriously, “It was the hardest technical project ever accomplished.” But the chemical rockets that took us there aren’t good enough for missions to the farther reaches of the Solar System, and certainly not for starflight.

Landis argued that the next thing we need is the spaceship equivalent of a pickup truck capable of hauling cargo for a wide variety of jobs – thus the title of his presentation, “Workhorse of the Solar System – The Nuclear Rocket and Beyond.”

Chemical fuels run up against the “rocket equation,” which dictates that as you go faster, it takes exponentially more fuel.  Missions to the distant reaches of the Solar System really need an energy source that is more energetic per unit of mass like nuclear, or an energy source you don’t have to carry on board (microwave, laser).

He added that ion thrusters have been successful for some missions, but electronic propulsion scales poorly to high thrust, requiring large amounts of power.

NASA tested a NERVA (Nuclear Energy for Rocket Vehicle Applications) NTR engine in the 1960s. All the requirements for a human mission to Mars were demonstrated, but it wasn’t pursued at that time.

Landis extolled the simplicity of nuclear rockets. The nuclear reactor produces heat. If you pass a gas over that heated reactor core, the gas heats up – and you can expand heated gas out a nozzle to produce thrust. A nuclear thermal rocket (NTR) is far simpler than nuclear generators used to generate electricity.

Hydrogen has been used because its atoms are the lightest and move the fastest when heated. But because of its low density large tanks are required to hold hydrogen fuel.

Another advantage of choosing hydrogen is that water is abundant in the outer Solar System. “Water is rocket fuel ore,” he noted. And once you get far from the Sun, “Water is just another type of rock.” So a nuclear rocket could be refueled using hydrogen generated from rocks harvested among the Trojan Asteroids or short period comets.

Landis devoted some time to the limits on NERVA’s efficiency inherent in the high-temperature sensitivity of the materials available to build the rocket. He mentioned several hypothetical ways to get higher temps without melting the reactor, suggesting “it’s an engineering problem,” so may eventually be overcome.

Lastly he outlined a manned mission to Callisto, a moon of Jupiter, that was studied in NASA’s Revolution Concepts for Human Outer Planet Exploration (HOPE). Two reasons for choosing Callisto are that it is believed to have water ice, and is far enough from Jupiter to be subject to only 0.01 rem a day. A surface base might be built there that would produce fuel for further exploration of the Solar System.

These developments are prerequisites to creating the energy economy needed to support interstellar missions.

[Note: Landis acknowledged Stanley Borowski of NASA for some material used in the presentation.

[The Starship Century anthology, Symposium edition, is currently available in paperback for $28 — click here.]  

How To Buy the Starship Century Anthology

Starship CenturyThe Starship Century anthology, Symposium edition, is currently available in paperback for $28 — click here.  (The ebook edition is coming in August.)

Starship Century: Toward the Grandest Horizon is a 340-page partnership between authors from both science and fiction writing backgrounds to illustrate what it will take to travel to another star within the next century.

Edited by Gregory Benford, New York Times bestselling science fiction author, and James Benford, leading expert on space propulsion, Starship Century includes science fiction by Neal Stephenson, David Brin, Joe Haldeman, Nancy Kress, Stephen Baxter, Gregory Benford, John Cramer, Richard A. Lovett, and Allen Steele, as well as scientific articles by Stephen Hawking, Freeman Dyson, Robert Zubrin, Peter Schwartz, Martin Rees, Ian Crawford, James Benford, Geoffrey Landis, Paul Davies and Adam Crowl.
This groundbreaking anthology of science and science fiction is based on findings and discussions of the 100-Year Starship Symposium held in 2011. In it, top scientists tackle the opportunities for our long-term future in space. Alongside them, science fiction authors explore the dream and the possibilities.

Starship Century Symposium: Patti Grace Smith

[This post is part of a series about the Starship Century Symposium held May 21-22, 2013.]

Patti Grace Smith

Patti Grace Smith

Patti Grace Smith formerly served as Associate Administrator for Commercial Space Transportation for the Federal Aviation Administration, U.S. Department of Transportation. For eleven years she headed the area responsible for licensing, regulating, and promoting U.S. commercial space transportation.

Speakers at the Starship Century Symposium generally dealt with a yet-to-be created future they have extrapolated from current science, whereas Smith, a former Department of Transportation official, focused on today’s commercial space industry. If the others gave us storyboards, Patti Grace Smith gave us high definition photos.

“Space is an attitude,” said Smith, who credited Elizabeth Dole for getting the commercial space office placed in the Department of Transportation.

The FAA forecasts there will be 291 commercial space launches in the global market from 2012-2021.
Reusable suborbital

Builders of Suborbital Reusable Vehicles (SRV) are taking reservations – Virgin Galactic wants to start flying its 6-seater SpaceShipTwo before the end of the year.

Drawing on DOT’s 2012 report Suborbital Reusable Vehicles: A 10-Year Forecast of Market Demand [PDF file], Smith said the average price per seat for a ride to the threshold of space is estimated at $123,000. Armadillo, Virgin Galactic and XCOR reported 925 total reservations as of June 2012.

A survey of high-wealth individuals suggests there are enough customers willing to pay current prices (between $95,000 and $200,000) to keep up a sustained demand for suborbital flight.

No cargo prices (other than satellite deployment costs on an XCOR Lynx Mark III) have been announced, though some providers say cargo costs align with seat costs for their vehicles.


Smith, noting that when in government service she was especially concerned with domestic business opportunities, said U.S. launch providers will need to remain competitive to win a significant portion of the future launch contracts over foreign competitors.

The government supports domestic launch providers through its policy toward risk. A launch provider is required to obtain the maximum possible liability insurance. Then, in the event of a mishap that leads to successful third-party claims in excess of the insurance requirement, the U.S. government is authorized to pay up to an additional $1.5 billion (adjusted for post-1988 inflation – approximately $2.7 billion today). The payment is not automatic and subject to Congressional appropriations. The commercial space launch provider (or other legally liable party) is responsible for any claims beyond that.

The supporting law has been extended by Congress several times since its original passage in 1988. The U.S. industry views the arrangement as a key element in its commercial competitiveness. While Smith had advocated for another 5-year extension, with the current political climate and budget constraints it has kept going with a year-to-year renewal.

Starship Century Symposium: Neal Stephenson

SCS Thinking Big[This post is part of a series about the Starship Century Symposium held May 21-22, 2013.]

Neal Stephenson

Neal Stephenson

The words “THINKING BIG” covered the screen at the beginning of Neal Stephenson’s segment, where he was joined on stage by four scientists and engineers.

Lately Stephenson has been active in the Hieroglyph, a collaboration with Arizona State University’s Center for Science and the Imagination, working to make it a place where authors and scientists Think Big.

Stephenson told the audience he had made a soapbox speech at a conference about the decline of the space program, then pivoted to the gulf oil spill as a way of indicating the real issue isn’t about space launch. It’s our inability as a society to do big things, to execute big plans. The theory of the Hieroglyph is that good science fiction can help change that. Sf supplies a plausible, fully thought-out picture of an alternate reality in which some sort of compelling innovation has taken place, presented in a way that makes sense to a scientist or engineer, and around which they can organize their work. The ideal subject matter is an innovation that a young, modern-day engineer can make substantial progress on during his or her career.

Stephenson’s contribution is The Tall Tower. Inspired by Geoffrey Landis’ papers on the subject, Stephenson began wondering how tall we could build a structure using mundane materials – things available now, because if you have to develop special new materials then people push you off into the future, saying go play in the sandbox and come back in 15 years.

Stephenson discussed the question with Dr. Keith Hjelmstad, a professor of structural engineering at Arizona State University, and learned it might be possible to build a very large structure using high-grade steel.

Hjelmstad proceeded to take up the story about how the two now envision a 20km tall steel tower able to cope with cold temperatures and 480 mph jetstream winds.

Hjelmstad says what interested him in the project was the need to design from first principles — like back in the days before lawyers dominated the conversation. Lots of geometry of structure. A base covering 11 square miles. Using 430 million tons of steel, a significant portion of the world’s production.

Jenny Hu and Daniel MacDonald followed with a media presentation, “Accessible Tower Model,” exploring the structural requirements of such a tower. One of the recurring challenges is that solutions to recognized engineering problems end up adding weight to the tower. One CAD display footed to 985 million tons of steel and a budget of nearly a trillion dollars

The final presenter, Kevin Finke of the Furlong/Fortnight Bureau, presented the fascinating challenge of wind forces — the drag equation.

The density of the air falls off with altitude, but the velocity of the wind increases with altitude. In the worst case, winds will be greater than 300 mph in the jetstream.

He has considered various solutions. One is mounting airfoils and essentially flying The Tower through the wind. Alternatively, they might counter the drag with the thrust of attached jet engines. Adhering to the vision of using off-the-shelf technology, he calculated that would require about 22,300 of the most powerful jet engines made. Alternatively, Finke looked at the specifications for Pratt & Whitney F-1 engine used by the Saturn V — he would still need 700 of those.

Finke assured listeners they are serious about building the Tall Tower. In any case it is a great thought experiment that allows people to practice visualizing huge projects that will be the necessary forerunners of a starship. If actually built, the tower might facilitate the launching of spacecraft. However, in Stephenson’s story “Atmosphæra Incognita” for Starship Century (click to read an excerpt), by the time the tower is finished it is being used for technologies as yet unimagined or undeveloped when the project was first conceived.

Gregory Benford closed the presentation on a light note saying the Clarke Center is trying to get people to think big again because too many have become limited to ideas the size of their phone.

Starship Century Symposium: Robert Zubrin

Robert Zubrin

Robert Zubrin

[This post is part of a series about the Starship Century Symposium held May 21-22, 2013.]

Robert Zubrin is President of Pioneer Astronautics and the founder and President of the Mars Society, and was responsible for developing the Mars Direct mission plan.

With the zeal of a prophet, Zubrin made fiercely anti-Malthusian arguments that the goal of building a starship in the coming century is attainable.

What are the requirements for a starship? He postulates a 1000-ton ship that travels at 10% light speed. What resources will society need for the mission? Zubrin said that to keep the cost from exceeding Apollo levels in proportion to society’s wealth, humanity will need a gross global domestic product (GDP) of 1000 times greater than existed in 1968, or 200 times greater than exists today.

To achieve a 200-times increase over today’s GDP, we will need a population of 54 billion. We will need energy of 2500 terawatts by the year 2200.

Pounding away at the opposite conclusions reached in Paul Ehrlich’s famous book The Population Bomb, Zubrin said, “If humans destroyed more than they made, the earth would be barren already. The real resource is human creativity.” Every mouth comes with a pair of hands and a brain. If we accept Malthusian advice, and act to reduce the world’s population, we will impoverish the future by denying it the contributions the missing people could have made.

For one thing, the more people, the larger the market, the easier to justify investments. For another, technological progress is cumulative.

Zubrin’s historical graph showed that GDP/per capita has increased with total global population over the years. This is because productivity depends upon technology, which is the cumulative result of human effort. For example, he pointed to the jump in worldwide wealth in the 1500s, something he credited to the development of sailing ships which unified the world and allowed inventions to be disseminated more rapidly than ever before.

Humanity’s escape from poverty depends upon energy use – GDP/per capita is a function of carbon use. Rising levels of energy consumption have correlated directly with rising living standards. Zubrin does not consider that this has been accomplished at the cost of a climate catastrophe. “The weather is about the same as when I was a boy,” he said dismissively.

In the future our energy resources will be (1) The sum of known and unknown Terrestrial fossil fuels, plus (2) local planetary He3.

He speculated that a winged transatmospheric vehicle that can use a gas giant’s atmosphere for propellant, heating it in a nuclear reactor to produce thrust (Nuclear Indigenous Fueled Thermal rockets) could be used to transport He3 from the planet to an orbiting tanker, which would deliver it to Earth orbit.

This would provide fuel for fusion reactors. A fusion configuration could theoretically yield exhaust velocities of 5% the speed of light. The thrust level would be too low for in-system travel, but would make possible voyages to a nearby star with trip times of less than a century.

Zubrin is counting on human wanderlust as the motive for colonizing the nearby planets, and in time the Kuiper Belt and the Oort Cloud. “Why go? Why stay? Why live on a planet whose laws and social possibilities were defined by generations long dead, when you can be a pioneer and help shape a new world according to reason as you see it?” The need to create is fundamental. “Once outward move begins, it will not stop,” Zubrin promised, “We can make it to the stars provided we remain free.”

A question session followed which might have veered onto unpacking the speaker’s data and endlessly processing his analysis, except that Zubrin, with a verbal flourish, used the first question to point to the fuller support in his book Merchants of Despair: Radical Environmentalists, Criminal Pseudo-Scientists, and the Fatal Cult of Antihumanism (2011) – a bit of verbal judo that gained applause from the many authors in the audience. Remember: Always Be Closing…

Starship Century Symposium: Freeman Dyson,
“Noah’s Ark Eggs and Warm-Blooded Plants”

Freeman Dyson in 2005.

Freeman Dyson in 2005.

Freeman Dyson has been a household name in Los Angeles sf fandom since he provided the inspiration for Larry Niven’s Ringworld, but that represents only a narrow slice of his life’s work. Dyson, born in England in 1923, began his career as a mathematician before turning to physics in the 1940s. His papers on the foundations of quantum electrodynamics have had a lasting influence on many branches of modern physics. He went on to work in condensed-matter physics, statistical mechanics, nuclear engineering, climate studies, astrophysics and biology. He even received the Templeton Prize for Progress in Religion (2000).

Standing at the lectern, Dyson appeared a coil of energy with mischievous eyes.

“Saving society through engineering – I’ve always believed in that,” he said to someone aside. Then he launched into his presentation, rapid-firing ideas at a rate that hardly slowed for the next 45 minutes.

Dyson proclaimed we are now at the beginning of a revolution in space technology, when for the first time cheapness will be mandatory. “This is bad news for something that requires the investment of the Apollo Program. It is good news for people who will develop these technologies…. Cheapness now has a chance.”

Cheap manned missions will require new biotechnology, to survive after we get there. (“There is no future for humans tramping around in clumsy spacesuits on lifeless landscapes of dust and ice,” says Dyson in his Starship Century article.)

“My guess is that the era of cheap unmanned missions will be the next fifty years, and the era of cheap manned missions will start sometime late in the twenty-first century.” Dyson picks 2085 as the year humans will settle multiple sites in the solar system, 120 years after Apollo, using an estimate based on the elapsed time between Columbus and Plymouth Rock.

“It turns out scientific data is a lot cheaper than beautiful pictures,” he in a wry tone. “Missions to the planets have been few and far between in the past ten years because they became inordinately expensive. They were expensive because it was easier politically to obtain ten dollars for a space-science mission than to obtain one dollar for astronomy on the ground.”

Once the barrier of high cost is broken, missions will be more frequent and the pace of discovery will be faster. The next missions will explore the planets and asteroids in detail.

Eventually most of the population will be living in the Kuiper Belt where they will utilize light energy captured by mirrors requiring only a few thousand tons of metal and plastic to construct.

We shall not jump in one huge step from planetary to interstellar voyages. There is no reason to believe that the space between stars is empty. The universe probably contains more unattached planets than planets attached to stars. During the evolution of starships unattached planets will be like the islands of Polynesia where travelers can stop and collect fresh supplies.

We will prepare the way for human habitats by establishing robust ecologies in space consisting of many kinds of life. The speed of sequencing genomes is increasing and the costs decreasing. At that rate it may take only 20 years to sequence the genomes of all the species on our planet. So, as we learn more about the conditions in various locations of space, that information can be used to design a biosphere genome tailored to the place it is to be sent.

The first species to emerge from a Noah’s Ark egg will be warm-blooded plants designed to collect energy from sunlight and keep themselves warm in a cold environment. “Plants could be engineered to grow greenhouses the way turtles grow shells” The greenhouse would consist of a thick skin providing thermal insulation, with small windows to admit sunlight. Outside the skin would be an array of simple lenses, focusing sunlight through the windows into the interior. Groups of greenhouses could grow together to form extended habitats for other species of plants and animals. In that way, “We will be the machines getting life to grow all over the universe.”

Dyson speculates there will be “superhighways” in space. Sunlight will be the source of energy powering laser or microwave beams that propel small, light spacecraft. Unlike chemical rockets, these will not be carrying their own fuel. The beams may push against wire mesh sails.

Because voyages to stars will take longer than a human lifetime, we cannot expect humans to travel with them. Ships will carry eggs that grow into humans at destination. In the end we would populate the galaxy by sending the information for growing humans rather than sending human bodies in storage.

[This post is part of a series about the Starship Century Symposium held May 21-22, 2013.]