Project Solar Sail

by Arther C. Clarke

  The book opened with a creak. Rachel’s eyes grew wide. On the title page, in Old English lettering, were the words Goodnight, Children. Below it, in a more common type style, was Preservation Press. New York, London, Burroughs City.

  “Tell how it was written, Dad.”

  He smiled at Benjamin. It wasn’t the story itself that the boy was still interested in. It was the history.

  “All right.” He closed the book. “Almost a hundred years ago, the first colony ship came to Mars. The job of those on board was to select and clear a site in preparation for the arrival of the Great Silver Fleet, which was bringing more colonists and supplies. They came down at Viking 1, built the monument there, and set up the biosphere that they would live in while doing their work.

  “The place would eventually become Burroughs City, but back then it was just a little frontier outpost. The people worked at clearing landing sites for the incoming fleet, made studies of the soil so they could start terraforming, and did all sorts of research on what natural resources were here.”

  “What about kids?” Rachel asked.

  “There were children,” Father continued. “They went to school and helped their mothers and fathers, just as you do. The difference was, things weren’t as nice as they are now. They didn’t have the masterdome complexes or parks full of scrubgreens. Each family had their own dome and the domes were connected by tunnels, so there wasn’t an outside to play in. They hadn’t even tapped the icecaps yet, so water was strictly rationed and they used bottled or recycled air. But they were all very brave and grew up wanting to make this planet a good place to live. And when they grew up, most of them stayed here and did just that.”

  “Tell about the story,” Benjamin said.

  “One of the men who came to Mars had the job of figuring out the best way to free the water trapped in the permafrost while others set up the polar-ice network. He had two children, a girl and a boy, who were both just a little younger than the two of you.”

  “The girl was older than the boy,” Rachel said, glaring at her brother.

  “The children had been born on Terra and had slept on the trip out, so this was their first year on Mars. And as Christmas got closer, they started to worry about whether or not their presents were going to arrive because they were so far away from the home world.

  “This bothered the father, and he tried to explain that everything would arrive on Christmas Eve, just as it did back home. But his children kept asking questions about how everything was going to get here, so one night he sat down and wrote them this story. And he read it to them every Christmas Eve.”

  “Like you do,” Benjamin said.

  Rachel opened the book to the title page. “G’nite, children,” she read, pointing at the words.

  “Goodnight, children,” Father repeated. He turned the page to the first illustration, one of an unlikely looking vehicle passing through deep space. He cleared his throat and began to read.

  “For the longest of times we have all heard the tales,

  That through space he will come pushed by bright silver sails,

  And how what he brings puts a smile on the face,

  And brings a warm glow to this desolate place.”

  Benjamin pointed at the vehicle’s driver. “There he is, sis.” Rachel mimicked her older brother. “That’s him.” Father turned the page and continued reading.

  “But it’s not been too long since his travel was slow,

  And his coming this far has not always been so,

  His business has been all on Terra, you see—

  Till at last humankind from old Terra broke free.

  “And he always assumed (in his kindly old way)

  That all children remained while their folks were away,

  But leave here they did in a glorious ascent!

  And on outsystem ships to the planets they went!”

  “Is that what the Great Silver Fleet looked like?” Benjamin asked. They had been studying it in school and he hadn’t been able to learn enough about it.

  “Yes and no.” Father pointed to the lead ship in the illustration. “This one was the first colony ship, the Utopia Bound. Behind it is the wave of ships that followed, although they didn’t arrive for another three years.”

  “That’s because the sailers are slow,” Benjamin said.

  Father put his finger to his lips and gestured at Rachel. The boy nodded.

  “Most of them are slow,” he amended.

  “The first fleet had about a dozen ships,” Father continued. “And while the later ones were bigger, everyone was so excited over that first one that it became known as Great.”

  “Great Silver Fleet,” Rachel said.

  He turned the page.

  “And one day he said as he gazed at the stars,

  Look at all of the children on Luna and Mars,

  How can I reach them for one night a year?

  My promise was made to the far and the near!”

  “Far away,” Rachel said, waving at the forlorn figure on the page.

  “Far away,” Benjamin echoed.

  “So he sat and researched and the experts he called,

  Until one gave him blueprints that left him enthralled,

  To the workshop he went! And he called up his crew!

  And he gave them the task to build something brand new!

  “Oh, the clang and the clatter! The noise and the din!

  They worked through the year on a Something so thin—

  Till that Something was ready they worked night and day,

  And with minutes to spare it attached to his sleigh . . .”

  Father paused. This was the problem spot. Last year, Benjamin, who had been near the end of believing in the overnight delivery of specialized payloads from Terra to Mars, began to question how a sleigh could lift off with such a big Something attached to the back. For Rachel’s sake, Father had insisted that if it could haul all of those toys, it could certainly haul the Something. The rest of the reading had been interrupted with all sorts of technical questions brought on by a ballistics study in his science class.

  “Go on,” Rachel said.

  Father studied Benjamin’s face. “Any questions?”

  “Nope.” He smiled.

  “You’re sure?”

  “Please,” said Rachel. “Read it, Daddy.”

  “Then his crew watched him leave—and not one of them knew,

  What that big Something was—or just what it would do.

  Nor would they believe, as he went on his rounds,

  That the Something would take him beyond Terra’s bounds!”

  His reading began to slow. The next few lines had produced a myriad of questions about escape velocities.

  “He was done in a flash (as he had been for years),

  And then upward he flew into thin atmospheres.

  With his reindeer cut free a new helmet he donned,

  And his upward trajectory took him beyond . . .”

  He trailed to a stop.

  “Terry Below,” Rachel urged. “Poor old Terry Below.” Father looked at Benjamin and smiled, then turned back to the page.

  “. . . poor old Terra below, and out of the blue—

  And in blackness of space that old sleigh became new . . .

  The bells were all silenced by the vacuum of space,

  So bright red and green lasers were put in their place!

  “From the back of the sleigh, robot arms did deploy

  And they shook out a sail of metal alloy—

  It was bright, shining Mylar that caught the sun’s light—

  And it gave him a push for a Luna-bound flight!”

  “Not slow,” Rachel said, gesturing at the restructured sleigh. “Not slow, Benjamin.”

  Benjamin shrugged. “You’re right, sis.”

  He hadn’t believed that his sister doted on every word that he said. He’d believe it now.

  “And when Luna was finished he headed to Mars,
<
br />   Guided by maps he had made of the stars,

  Then when in Mars orbit this sailer arrives,

  He makes planetfall and a Sandcrab he drives.”

  The picture was of an ancient-model Sandcrab topping a dune, great clouds of rust billowing behind it.

  “Is this Daddy’s ’crab?” Rachel asked.

  “No,” Father said.

  “Is Daddy’s ’crab better?”

  “Dad’s ’crab is different.” Benjamin said. He winked at his father. The kid’s learning, Father thought.

  “Then across all of Mars with a great sack he roams,

  Till he finds sleeping children inside of the domes,

  And because there’s no chimney (no entrance, it seems),

  He steps through their holo of soft Winter Scenes.

  “With a twitch of his nose the great sack will unfold,

  And he lays out the presents for young and for old,

  Then he’s off to see others, and when he is done,

  It is up to his sleigh that is powered by sun—

  “To return him to Terra through the vacuum’s travails,

  Riding home on the solar wind trapped in its sails.

  And he says, ‘Goodnight, children—sleep in freedom from fear—

  Be good little Martians—I’ll see you next year.”

  He sat with them for a moment, leaving the book open.

  “G’nite, children,” Rachel said, waving. “G’nite, g’nite.”

  Benjamin smiled at his father. “I liked it better this year.”

  “For a different reason?”

  The boy nodded.

  Father closed the book and returned it to the box, sealing it tight and hooking the latch. As he did, his wife appeared in the living room.

  “Did you get it all read?” she asked.

  “Made it all the way through.”

  Benjamin made a point to say, “It’s a pretty good story, really.”

  “Fantastic.” She clapped her hands. “Now it’s time for the two of you to get to bed.”

  “But I didn’t find him,” Rachel stressed.

  Father plucked her up from his lap and dangled her overhead. “That’s a good thing. If you had, he wouldn’t come.”

  “Why won’t he come till we’re asleep?”

  “Because if he stopped to answer all of the questions that all of the boys and girls want to ask him, he wouldn’t make it back to Terra in time for next year.” He flexed his arm and brought her down for a kiss. “Goodnight, Rachel.”

  She gave him a wet smack on the cheek. “G’nite, Daddy.”

  He turned Rachel to her mother and gave a gentle heave. Squealing with delight, she flew across the room, arms outstretched, through winter birches and swirling flakes until she landed in her mother’s arms.

  Benjamin kissed them both, and they went to the bedroom.

  Father rose slowly from the couch and patted his son’s shoulder. “That goes for you, too.”

  “Can’t I go see if I can spot the incoming fleet?”

  He shook his head. “They won’t be visible until after New Year’s.”

  They walked to Benjamin’s bedroom, which was lined with posters of popular sail jockeys and the latest designs of sporting sailers. The boy folded back the simulated Mylar comforter and climbed between the sheets.

  “By the way,” Father said, turning off the lights, “there’s something I wanted to tell you.”

  Benjamin rolled onto his side. “Yeah?”

  “Thanks for not spoiling the story for Rachel. She won’t be able to enjoy it like that for much longer.”

  “No problem,” he answered. “Everyone’s got to have something to dream about, you know?”

  “I know.” He kissed his forehead. “Goodnight, Benjamin.”

  “Goodnight, Dad.”

  He started out the door.

  “Dad?”

  “Yes, son.”

  “The solar wind—technically, it’s not really wind, is it?”

  “Not like we have here. It’s more like a stream of light energy.”

  “Thanks,” he said.

  “Goodnight.”

  The voice of his wife singing a carol filled the hall. Slowly, he returned to the living room and settled down in the middle of the snow-covered forest, nose filling with the scent from the small house’s chimney. In a little while, when the children were asleep, he would go to his bedroom closet and step back through the soft Winter scenes, laying out disks and fruit and nuts for them both, the Jenny Astro doll that Rachel had wanted, and the scale model of the Great Silver Fleet’s flagship that Benjamin had been hinting about since the week after his birthday. And early tomorrow morning, whether they really believed or not, their dreams would come true.

  As his son had said, everyone had to have something to dream about.

  They were living proof of that.

  ###

  Joe Clifford Faust is the author of five science fiction novels and a very strange play called Old Loves Die Hard. He also scripts stories for Open Space, a science fiction title for Marvel Comics, and advertisements for a top-rated FM station in northeast Ohio. He currently lives in Ohio with his wife and two children, and is at work on a new novel.

  Solar Sails in an Interplanetary Economy

  By Robert L. Staehle and Louis Friedman

  Liverpool . . . Bombay . . . New York . . . Rio . . . Perth . . . Shanghai . . . Rotterdam. Do your grandparents remember these ports of call for the great ocean liners of the past? They remain focal points of international commerce. Where will the ports of call be in an interplanetary economy? The moon? Phobos? The icy plains of Callisto? Will these and other exotic destinations be served by the new generations of clipper ships? Moreover, might these ships ride a network of powerful, pencil-thin beams, or be gently pushed by natural sunlight?

  We must, of course, walk before we can run. In order to locate the ports, much less name them, we will have to explore our solar system in much greater detail, discover the resources, and create the demands which will drive the commerce. And before majestic, city-size sails fill the heavens, playing a part in this great drama, we must develop the rudimentary skills of interplanetary sailing.

  Our first tentative steps will be with the smallest sails, no bigger than a football field or two. We will hold a collective “school for solar sailing,” where everyone starts as a freshman. Theoretical studies and computer simulations already model basic control laws, but only real flight can teach us the techniques and refinements needed to harness and best use our sun-driven spacecraft.

  The Interplanetary Shuttle

  Just as with the shores of the seven seas from the sixteenth through the nineteenth centuries, the planets, natural satellites, comets, and asteroids of the solar system are the targets for exploration and, at least for some of them, development in the twenty-first century and beyond.

  For a single mission it rarely makes sense to develop a whole new technology. This reasoning has thus far prevented the use of low-thrust (electric- or sail-derived) primary propulsion. But now that we are beyond the initial reconnaissance of the solar system, solar sailing will become really useful for the more intensive exploration and later development, which will follow.

  The chief advantage of a solar sail interplanetary vehicle we could build over the next decade is not the amount of speed it gains over ordinary spacecraft. In fact, the minimum energy ballistic trajectories used by chemical rockets take somewhat less time than first-generation sails. (But advanced, metal-only sails built in space can cut trip times far below those using the best chemical rockets.) Nevertheless if we can accept a typical trip time from Earth to Mars of 400 days, or 600 days to Mercury, or 270 days to Venus, then we can reap the benefits of launching a smaller mass from Earth for a given mission, or placing more scientific instruments on a spacecraft for a given launch weight. At $3,000 per kilogram (over $6,500 per pound) for launch costs, the cost savings can be dramatic.

  Where the
sail really becomes advantageous, because it requires no fuel or other propellant, is for roundtrip missions, such as sample returns. Rocket-driven missions must not only carry the propellant required to get to the destination, but also fuel and oxidizer for the return journey. All of this along with the useful payload. This results in much more than a doubling of the weight burden. Propellant masses multiply exponentially, even for highly efficient schemes such as electric propulsion. A sail, on the other hand, needn’t weigh a single pound more to bring samples back from Mars than if it were simply carrying a scientific orbiter on the one-way trip to the Red Planet. Controlled from Earth, the sail can just turn around and come home.

  Sails offer the added option, if you’re not in a hurry, of trading trip time for added payload. For example, using the kind of sail designed at Jet Propulsion Laboratory (JPL) during the mid-1970s, over a ton can be delivered to Mars in a 400-day mission; but if we can accept a 500-day trip time, the sail can deliver 2.5 tons! For Mercury, nearly four tons can be delivered in 600 days, but this goes to eight tons for a 900-day mission. Even out to the main belt asteroids, over a ton can be delivered in 600 days. And of course, with the sail each of these journeys comes with a return-trip option.