Gregory L. Matloff

• New York City College of Technology

In 2011, I was invited to participate in a symposium at the London headquarters of the British Interplanetary Society. The subject of the symposium was the contributions of philosopher/science-fiction-author Olaf Stapledon. Instead of concentrating on the many technological projections in Stapledon's masterwork Star Maker, I elected to investigate...

In 2011, I was invited to participate in a symposium at the London headquarters of the British Interplanetary Society. The subject of the symposium was the contributions of philosopher/science-fiction-author Olaf Stapledon. Instead of concentrating on the many technological projections in Stapledon's masterwork Star Maker, I elected to investigate...

Hyperthin solar sails deployed as close to the Sun as possible are the only currently feasible approach to extrasolar solar exploration and interstellar travel. This paper quantifies and investigates the effects of timing errors in the unfurlment (or inflation) of solar sails at the perihelion of parabolic solar orbits upon the spacecraft's traject...

Despite decades of old theoretical foundation and all the efforts of space researchers, until very recently there were surprisingly few attempts to build and fly large solar sails in space. Germany’s Deutschen Zentrum fur Luft-und Raumfahrt (DLR) took particular interest in solar sail technology in the 1990s and fabricated one of the first large-sc...

This chapter describes thoroughly the second sailcraft in these years of efforts for transforming the solar-photon sailing from theory to reality. Once again, NASA is the maker of an historical step in the modern history of Astronautics.

What exactly constitutes a technological breakthrough? A breakthrough is an event that opens unexpected doors and expands horizons. Since JAXA’s IKAROS is the first solar-photon sail deployed in interplanetary space and has demonstrated the sail’s utility in both primary spacecraft propulsion and attitude control, it certainly constitutes a technol...

As these words are composed in 2014, we are in the initial phase of solar-photon-sail operational application. Probably, a good historical analog is the status of the chemical rocket in late 1957. As was then the case with Sputnik 1 and 2 in their relation to the chemical rocket, the utility of small solar sails has been demonstrated by the success...

In 2017, NASA plans to launch the Near Earth Asteroid (NEA) Scout, a solar-photon-sail propelled probe to rendezvous with one or more near-Earth asteroids. According to a publication describing early design parameters, the spacecraft mass is 12 kg and the square sail has an area of 83 square meters. This craft, like many other NASA science missions...

The reality of sunlight-based sailing in space began in May 2010, and solar sail technology and science have continued to evolve rapidly through new space missions. Using the power of the Sun's light for regular travel propulsion will be the next major leap forward in our journey to other worlds. This book is the second edition of the fascinating e...

Hyper-thin, high-speed solar-photon sail space probes exploring the Sun's Oort comet cloud could also be used to set an upper bound to the concentration of WIMPS (weakly interacting massive particles), one of the suggested (but unconfirmed) forms of dark matter within the vicinity of the solar system. Newton's Shell Theorem would be applied to dete...

What was our planet like in years past? How has our civilization affected Earth and its ecology? Harvesting Space for a Greener Planet, the Second Edition of Paradise Regained: The Regreening of the Earth, begins by discussing these questions, and then generates a scenario for the restoration of Earth. It introduces new and innovative ideas on how...

The Sun's gravity focus at >550 AU is if interest to astrophysicists including SETI scientists, researchers seeking to image extra-solar planets and others. One method for an extra-solar probe to reach the Sun's inner gravity focus within a human working lifetime (less than 50 years) is to combine solar and nuclear propulsion techniques. Here, we p...

A review of conceptual interstellar generation ships is followed by a presentation of optical and thermal properties of graphene and a discussion of kinematics/thermal-aspects of the solar-acceleration phase of a starship propelled by a graphene hollow-body solar-photon sail. The spacecraft departs from an initially parabolic solar orbit and the sa...

Intense tempests of celestial origin have blown through the skies of Earth, obliterating landscapes and sending towering tsunami through the oceans. Such events have extinguished vast numbers of living organisms; some of these die-offs have been altered by geological processes into fossils.

Conservation, recycling, more efficient machines, altered lifestyles and new sources of energy are all needed to reduce the growth rate of our greenhouse gas emissions. Unfortunately, the best all of these actions combined can achieve is a reduced rate of emission growth. If humans are truly causing global warming by profligate use of fossil fuels,...

386,000,000,000,000,000,000,000,000 W. By any measure, that is a lot of power, and that is the Sun’s power output every second of every day (Fig. 12.1). To make this number easier to work with, scientists write it as 3.86 × 1026 W, or 386 followed by 24 zeros. The amount of solar energy per second reaching Earth, which is 93 million miles from the...

In this chapter, we review the evolution of life on Earth and attempt to address the issue of how pleasant our planet’s pre-human environment was. But before we begin, it might be helpful to investigate how benign or special early Earth was for the origin and evolution of life. We have learned a lot in the past few decades indicating that just havi...

If you are reading this book, you are most likely a member of the most privileged generation in humanity’s experience. You have a roof over your head—a vast improvement over the lot of many of our ancestors and a significant number of humans today. You have access to good health-care facilities and can count on between 70 and 80 good years.

It is a strange time on Planet Earth. For the first time in humanity’s recorded history, we no longer can feel totally secure in Mother Nature’s “balmy nest.” There are simply too many of us, and we all desire to live well. As far as we know, humanity is the first terrestrial species with the technological power to alter Earth’s global environment...

Gloom and doom is easy to sell. Simply watching the evening news fills one with a sense of what is bad in the world: murder, child abuse, increases in the price of gasoline, water rationing due to drought, tension among nation states arising over a religious or economic disagreement, and so on. Listening to the prognostication of the coming age of...

Solar-photon sails have been proposed for decades-duration missions to the heliopause (~200 AU) and the Sun’s inner gravitational focus (~550 AU). A more advanced goal for space-manufactured sails capable of ~500 km/s interstellar cruise velocities is a search for weakly interacting massive particles (WIMPS), a suggested form of dark matter, within...

Graphene, a two-dimensional carbon molecular monolayer, has properties that may render it very useful for application to interstellar solar photon sailing. These include very low areal mass thickness, high melting point, high impermeability to fill gas in a hollow-body sail configuration, and high tensile strength. With appropriate "additives," gra...

The solar collector (SC) is a proposed method of altering the solar orbits of Earth-threatening asteroids. A jet of material, energized by concentrated sunlight, would alter the asteroid's trajectory as a consequence of Newton's Third Law. A model, first applied during a 2007 NASA study, is further developed and applied to various classes of astero...

Solar photon sailing, spacecraft propulsion by the pressure of sunlight, has long been a theoretical concept. During 2010, two successful missions - one in Earth orbit and one in deep space - demonstrated the utility of the concept and advanced its technological readiness level. This paper reviews the history of the solar sail, near term mission po...

The light sail, which is pushed through space by momentum exchange from impacting and reflected photons, is the only suggested method of interstellar propulsion that has thus far been successfully tested in space. The solar photon sail, unfurled as close to the Sun as possible, offers the possibility of ~2,000-year duration voyages to Alpha Centaur...

Sixty-five million years ago, a Manhattan-size meteorite traveling through space at about 11 kilometers per second punched through the sky before hitting the ground near what is now Mexico's Yucatán Peninsula. The energy released by the impact poured into the atmosphere, heating Earth's surface. Then the dust lofted by this impact blocked out the s...

The World Ship, a spacecraft large enough to simulate a small-scale terrestrial internal environment, may be the best feasible option to transfer members of a technological civilization between neighboring stars. Because of the projected size of these spacecraft, journey durations of ~1,000 years seem likely. One of the propulsion options for World...

Graphene (a carbon molecular monolayer) is a wonder material of great interest to materials researchers. Its molecular-layer thickness, finite fractional absorption, high melting point, and impermeability to gases coupled with the fact that doped materials, additives and multiple layers increase both fractional absorption and reflectivity indicates...

A significant fraction of the Near-Earth Object (NEO) population may be objects that originated as comets. Kinetic or nuclear defection schemes may result in the fragmentation of an extinct comet, rather than its deflection. The Solar Collector (SC) has been proposed as a method of deflecting water-ice-rich NEOs on Earth-threatening trajectories. T...

The next extrasolar destination after the heliopause at 200 AU is likely to be the Sun's inner gravity focus at 550 AU. At solar distances beyond this point, electromagnetic radiation from celestial objects occulted by the Sun will be concentrated in a highly amplified narrow beam. This effect of general relativity will be of interest to SETI resea...

Human interplanetary missions are constrained by the problem of astronaut exposure to galactic cosmic radiation. This paper surveys the existing on-line near-Earth object (NEO) data base in an effort to identify NEOs that cross both Earth's ad Mars’ orbits and could be used as cosmic ray shields by interplanetary voyagers. The search concentrated o...

Solar sails can play a critical role in enabling solar and heliophysics missions. Solar sail technology within NASA is currently at 80% of TRL-6, suitable for an in-flight technology demonstration. It is conceivable that an initial demonstration could carry scientific payloads that, depending on the type of mission, are commensurate with the goals...

There can be no question that today, one species, Homo sapiens, bestrides the world. In some circles, it is fashionable to lament this situation. Has a Golden Age been lost; has Eden been transformed into an omnipresent global civilization of commerce, popular culture, consumerism, and accumulation? Perhaps, according to some, Earth’s prime is past...

“Gloom and doom” is easy to sell. Simply watching the evening news fills one with a sense of what is bad in the world: murder, child abuse, an increase in the price of gasoline, water rationing due to drought, tension among nation states arising over a religious or economic disagreement, and so on. Listening to the prognostication of the coming age...

As Walt Whitman watched the multitudes commuting between Brooklyn and Manhattan in the days before the construction of the Brooklyn Bridge, he dreamt of the multitude that would make that crossing in the future. He could not have imagined the much larger population that has been born in recent years to challenge the future of Earth.

When people think of the issue of decreasing biodiversity, they generally consider pets, domestic animals, majestic beasts, and useful plants. Although many beasts and plants are threatened (pets and domestic animals are not threatened), the problem runs far deeper.

Walt Whitman was right: Earth is not a closed system. The road to the riches of the solar system lies open. Nature has provided humanity with a virtually unlimited supply of raw materials, and that supply is right above our heads. The asteroids, comets, planets, and moons of the solar system contain enough of the soon-to-be-scarce raw materials req...

Philosophers and theologians have debated what constitutes morality since there have been people around to consider the notion. The word morality comes from Latin and refers to our notion of what constitutes right and wrong or good and evil. What constitutes a moral action varies dramatically from culture to culture, though many cultures share some...

Conservation, recycling, more efficient machines, altered lifestyles, and new sources of energy are all needed to reduce the growth rate of our greenhouse gas emissions. Unfortunately, the best that all of these actions combined can achieve is a reduced rate of emission growth. If humans are truly causing global warming by profligate use of fossil...

In the late 1990s, the author Frank White visted Huntsville, Alabama, and lectured at the local university on what he called the “overview effect.” White had just authored a book by that title and was touring the country speaking on the subject and promoting his book. According to White, most of the world’s astronauts experience an epiphany when th...

All of us have experienced the darkness and felt despair. Our civilization’s problems seem beyond measure—an exploding population, pollution, energy shortages, climate change, terrorism, and nuclear proliferation are among those threats. There is nowhere in space to flee to; Earth is filled up, the moon may be waterless, Mars is a lifeless desert,...

Our Sun will eventually leave the main sequence and expand in size and luminosity to become a giant star. For much of its ~108 year career as a giant, the Sun will reside on the horizontal branch of the Hertzsprung-Russell diagram, with a surface temperature of ~5000 K, a radius about 10x its present-day radius, and about 50x its current luminosity...

In the beginning, a cloud composed mainly of hydrogen and helium gas drifted through the interstellar void. Near or within this immense nebula (it must have been trillions of miles across), a bright star blazed. Much larger and more massive than our present-day sun, this nameless star approached the end of its life cycle about 5 billion years ago....

As we have seen, the distant past was difficult for the ancestors of man. But where have the development of civilization, the agricultural revolution, the art of metallurgy, and the scientific revolution left us? We seem to be suspended from an environmental cliff. We cannot hang on, but we are doomed if we let go!KeywordsHeat EngineGlobal Civiliza...

The thought is not new, but it is profound and it can help guide humanity as we deal with the myriad environmental challenges facing us at the beginning of the 21st century: we all inhabit one giant spaceship on a voyage together through the dark emptiness of space. We call it “Spaceship Earth.”

As mentioned in Chapter 3, the immutable laws of thermodynamics appear to place a limit on how well we can be stewards of our planet. To recap, the first law states that all energy is conserved. This means that no matter what you do, you cannot get more energy out of a system than you put into it. And some of that energy is inevitably wasted, which...

These articles are alarming. They warn that Earth is getting warmer and changes in the global climate are inevitable. The evidence of a global change in climate is mounting and the consensus is that humans are responsible through our profligate emission of so-called greenhouse gases. The authors of this book are not climatologists and are therefore...

If technologically advanced civilizations migrate from the vicinities of their dying stars, the solar-photon sail is a very viable propulsion system. Interstellar crossings that might require 2,000 years for departure from a Sun-like star might require only a few centuries if sail craft depart from larger and more luminous red giant stars. Unless s...

What was our planet like before the advent of our modern civilization? What effect has our civilization had on the planet and its ecology? Paradise Regained begins by discussing these questions and then generates a scenario for the re-greening of Earth. It introduces new and innovative ideas on how humankind could use the resources of the Solar Sys...

This paper has been prepared in the frame of IAA Advanced Propulsion Working Group (IAA Study Group #3.1) and is focused on non-chemical, non-nuclear propulsion concepts for space application, excluding Breakthrough-Propulsion Physics concepts. Three main families of propulsion are considered in this: launch-assist catapult systems using Lorentz Ra...

Future lunar inhabitants could orbit payloads using a maglev-type rail system that could match velocities with the lower terminus of a non-stationary lunar space elevator. Lower elevator terminus velocities of about 90–170 m/s can be achieved with the elevator center-of-mass 6000–10,000 km above the lunar surface. Advantages of this approach over a...

Previous analysis has concentrated on two modes of thrustless interstellar deceleration. These are electromagnetic (EM) reflection of interstellar ions before arrival in the destination planetary system and solar sail deceleration to planetary velocities. The former approach is less effective for low starship velocities. The latter requires a close...

Sailcraft offer unique opportunities to space-mission planners. Some of these possibilities will be exploited in the near future, others within a few decades, and some in the more distant future. We consider near-term mission possibilities first.

At this point in its development, the solar sail can be characterized as fairly late in its theoretical phase and fairly early in its developmental phase. It is probably equivalent to the chemical rocket in 1930, the automobile in 1900, and the heavier-than-air aircraft in 1910.

We are nearing the end of this introductory book on solar sailing. We saved one of the most intriguing topics—trajectory design—for last. However, it is beyond the scope of this book to delve deeply into mathematics and the related physical aspects. So after a very short presentation of the sailcraft motion equations, we discuss the class of trajec...

Many astrophysicists consider that α Centauri B has a high probability of possessing one or more planetary companions within the habitable zone. The higher luminosity of its companion star α Centauri B as compared with the Sun could be applied to the deceleration of solar-sail starships. The theory of decelerating to parabolic velocity or rest usin...

Despite its decades old theoretical foundation and all the efforts of space researchers, there have been surprisingly few attempts to build and fly large solar sails in space. Germany’s DLR took particular interest in solar sail technology in the 1990s and fabricated one of the first large-scale ground-based engineering model sails. The Russians de...

Near-sun space-environment effects on metallic thin films solar sails as well as hollow-body sails with inflation fill gas are considered. Analysis of the interaction of the solar radiation with the solar-sail materials is presented. This analysis evaluates worst-case solar radiation effects during solar-radiation-pressure acceleration. The depende...

Near-sun space-environment effects on metallic thin films solar sails as well as hollow-body sails with inflation fill gas are considered. Analysis of interaction of the solar radiation with the solar sail materials is presented. This analysis evaluates worst-case solar radiation effects during solar-radiation-pressure acceleration. The dependence...

Spacecraft kinematics, peak perihelion temperature and space environment effects during solar-radiation-pressure acceleration for a beryllium hollow-body interstellar solar sail inflated with hydrogen fill gas are investigated. We demonstrate that diffusion is alleviated by an on-board fill gas reserve and electrostatic pressure can be alleviated b...

In this era of designer materials, a reasonably accurate formalism of the efficiency of various candidate solar-photon-sail materials is a worthy goal. A review of previous research on partially transmissive metallic sail films for interstellar application reveals that various parameters influence maximum interstellar cruise velocity for given sail...

This paper continues our study of space-environment effects upon a beryllium hollow-body solar-photon sail unfurled at a 0.05 AU perihelion from an initially parabolic solar orbit. Effects considered include hydrogen diffusion through the beryllium sail walls, recombination of UV-ionized sail beryllium ions, possible application of the two sail con...

The solar collector (SC), a two-sail solar-photon thruster utilized to concentrate solar energy, is a possible method to deflect Earth-threatening near-Earth objects (NEOs). This paper expands an existing SC model to categorize SC performance as a function of parameters including NEO composition, solar distance and rotation.

Gossamer structures like solar sails are very fragile. First-generation solar sails will be manufactured and tested on Earth and, consequently, be required to sustain their own weight in our 1 g environment. In space they will experience what is perhaps the most hostile environment known to man—space itself. The operating “space” for a solar sail i...

In the previous chapters, we described the space rocket engines, how they work, their role in past and current spaceflight, and their limitations. We have also shown that the rocket is not the only propulsion type that could be employed in space. Among the types of space propulsion currently under investigation, one is particularly promising: the s...

Although the rockets described in the previous chapter have opened the solar system to preliminary human reconnaissance and exploration, there are severe limitations on rocket performance. This chapter focuses on these limits and what we may ultimately expect from rocket-propelled space travel.

We have lingered for too long on the shores of the cosmic ocean; it’s time to set sail for the stars.

The romantic-sounding term solar sail evokes an image of a majestic vessel (similar to the great sailing ships of the 18th century) cruising the depths of interplanetary space (Fig. 6.1). In a very literal sense, this imagery is very close to the anticipated reality of solar sails. Very large and diaphanous sail-propelled ships will traverse our so...

Now that we’ve examined rocket theory, potential, and limitations, we are ready to consider some of the alternatives to this mode of propulsion. If our spacecraft is ground-launched, we might consider a jet as the first stage, where oxygen is ingested from the air instead of carried on board. Other launch alternatives include igniting the rocket wh...

Rockets move spacecraft around in space from one destination to another. Solar sails also move spacecraft around in space from one destination to another. That is just about the only similarity between these two methods of spacecraft propulsion—commonality of function. Once you get to the next level and begin to describe how they work, their proces...

In Chapter 5, we addressed the problems of light and its amazing nature. We discussed the twofold nature of light: wave and particle. As this book regards solar sailing as a non-rocket photon-driven propulsion mode, we shall primarily focus on the properties of solar light and, secondarily, on the light from planets.

The single most important characteristic of a solar sail is its power source— the Sun. The Sun supplies a continuous source of sunlight, providing the gentle push that makes a solar sail such a useful propulsion system. Unfortunately, the Sun is also the limiting factor in the overall usefulness of a solar sail. When a spacecraft gets far from the...

We’ll never know when the dream of spaceflight first appeared in human consciousness, or to whom it first appeared. Perhaps it was in the sun-baked plains of Africa or on a high mountain pass in alpine Europe. One of our nameless ancestors looked up at the night sky and wondered at the moving lights in the heavens.

For solar sails, as with most engineering challenges, there is no single, “best” design solution that will meet all potential needs and mission scenarios. This chapter discusses the most viable solar-sail design options and the pros and cons of each, and the problem of controlling the orientation of a sail in space.

The rocket is a most remarkable device. Its early inventors could not have guessed that it would ultimately evolve into a device capable of propelling robotic and human payloads through the vacuum of space. In fact, the rocket actually works better in a vacuum than in air!

Chapters 1 to 4 discussed the importance of the rocket propulsion in the first 50 years of spaceflight, and its limitations with respect to what space-faring nations (augmenting in number and quality) would want to accomplish in the solar system and beyond. Chapter 5 discussed the concept of sailing, first on Earth seas with conventional sailboats...

In Chapter 15, we saw what type of light the Sun and Earth cast into space, each body with its own characteristics. In particular, we emphasized that 30 years of high-precision measurements from satellites have revealed that the total solar irradiance fluctuates, and which parts of its spectrum can affect a solar sail significantly. In practice, th...

The "space elevator," "orbital tower," or "beanstalk" is a venerable idea in which people or payloads ride an elevator to equatorial geosynchronous Earth orbit from Earth's surface. Because orbital debris is a major limiting factor, some have considered use of a partial beanstalk with the low station hundreds of kilometers above Earth's surface. Th...

A 2-3 decade mission is proposed with a solar-sail spacecraft approaching the Sun within 0.2 AU. After sail unfurlment at the perihelion of an initially elliptical solar orbit and the completion of acceleration, the spacecraft splits into two components. One part is a scientific payload bound for the heliopause; the second is designed to rendezvous...

Space-environment effects on beryllium hollow-body sails with hydrogen fill gas unfurled at a 0.05 AU perihelion from initially parabolic solar orbits are considered. The study of the effects of interaction of the solar radiation with the Be sail and the hydrogen fill gas is presented. The diversity of physical processes of the interaction of photo...

The photon sail is the current leading propulsion option for interstellar travel. We currently do not have the capability to conduct centuries‐duration robotic interstellar‐probe missions and millennial journeys aboard human‐occupied worldships. This paper considers various mission options for the solar photon sail that are under consideration by N...

On-orbit deployment tests and operational missions for first-generation solar-photon sails may require a method of monitoring post-deployment sail health. A low-technology device capable of performing this function is the pinhole camera, combined with an inflatable hydrostatic beam mounted at the sail's center of mass.

The NASA Heliopause sail and other early extrasolar probes will be mass limited and probably not equipped with imaging equipment. However, trajectory deflections during close approaches to Kuiper Belt objects (KBOs) can yield information regarding KBO mass. When combined with KBO size estimates derived from terrestrial telescopic observations, appr...

It should not be surprising that chemical rockets derive their thrust from chemical reactions. The reaction between a rocket fuel and an oxidizer (a chemical compound containing oxygen) releases a tremendous amount of energy. The energy is released as new chemical bonds are formed in the “burning” process. Channeling the energetic reaction products...

Civilization began with the birth of metallurgy and the first application of the mine to tap the hidden wealth of Planet Earth. Since the Egyptian Bronze Age, every temple and cathedral, every castle, every public building has depended upon stone from the quarries and tools constructed from mined metal.

The Interstellar Message Plaques, affixed to our tiny Pioneers and Voyagers as they cruise toward the boundaries of nearby interstellar space, are messages to the far future. They have been compared to letters sealed in bottles and dropped in the ocean, in the hope that they might be retrieved and read in distant climes, on far shores.

For countless generations, humans have peered up into the evening sky and wondered about those strange lights yonder. Could we touch them? For most of human history, such speculations were the province of the poet or the writer of visionary fiction.

Shorthly after the beginning of the Space Age, in the late 1950s, rocketeers in the USA and the USSR realized that their primitive, military-derived rockets could escape the gravitational field of the Earth, navigate by the stars to cruise the depths of interplantety space, and begin the preliminary reconnaissance of the solar system. This was a ve...

The development of the American west, to a very large extent, depended upon the steam locomotive. Not only did the coal-driven trains of the transcontinental railroad transport the mail but such items as tools, produce, and people were carried by this service.

Imagine catching a plane to a Pacific island located on the equator, walking from the airplane to an elevator that goes strainght up—into space—talking you from the ground to any altitude up to or below geosynchronous orbit (that is, approximately 35,786 kilometers—the altitude at which an Earth-orbiting satellite travels with a velocity that maint...

Some day there will be deep-space ships that we can enter and live within, ships that can support us on millennial journeys and sail the dark seas of the interstellar void. And even if we utilize the resources of Sol’s system wisely, husbanding rather than blindly consuming, we will some day need such ships. For the Sun’s lifetime is finite.

Far above the emerald green seas that served as passageways through the Mediterranena, the Polynesian Pacific and to the New World, far aboves the tremulous canopies of elm forest and beyond the finest wisps of Earth’s life-giving atmosphere sits the Interplanetary Frontier. In crystal clarity, telescopes and space probes have returned photos of th...

How does the manager of multimillion-dollar space mission know that the technologies required for it are “ready to go”? Often, the technologies required for space exploration are audacious, complex, and very expensive.

In 2004, United States President George Bush announced that American astronauts will be returning to the Moon before the year 2020, and then setting their sights upon the planet Mars. When this was announced, the advanced space technology community was energized. After all, it has been many years since Neil Amrstrong first placed his footprint in t...

Early in the Space Age, as thunder fell earthward from the rising rockets as they pierced the firmament, researcher realize the necessity of developing space technologies to exploit the Near-Earth environment. To get into space astronauts and cosmonauts would use the high-technology rocket. But to return from orbital journeys, spacefarers would use...

It was before the dawn of recorded history that the first great Age of Sail began. Perhaps along the Nile River, a genius lived who observed the ways of swans and reached a brilliant conclusion. If birds could fluff out their feathers to catch the wind, and drift effortlessly against the current, why couldn’t humans learn the same trick?