Solar Sailing Moves into the Journals

by Paul Gilster | Mar 13, 2014 | Sail Concepts | 3 comments

I’m just getting started with Chris Impey and Holly Henry’s Dreams of Other Worlds (Princeton University Press, 2013), but glancing through it yesterday reminded me how long it has taken sail hardware to get into space. While Ted Cotter and Carl Wiley hoped for early experiments with sail ideas, we never got them until much later. Interesting mission concepts like JPL’s ‘gyro’ sail to Halley’s Comet did develop (although it never flew), and the Soviet Znamya deployments gave us some experience with thin membranes in space (I’ll talk about those soon), but by and large we left interplanetary exploration for the rockets.

The deep space probes and near-Earth observatories Impey and Henry cover — Viking, Voyager, Stardust, Chandra, Hubble and their ilk — gave us outstanding results but were not, until IKAROS, joined in space by alternative sail technologies. I’ll review this book in some detail as soon as I finish it, but for today let’s go back to the late 1950s, a time when Carl Wiley had already introduced solar sailing to a science fiction audience and Ted Cotter had apprised his colleagues at Los Alamos about the possibilities of a spinning sail.

For sails were about to make their debut in the technical journals. At the IBM Watson laboratory at Columbia University, physicist Richard Garwin, although deeply involved in nuclear weapons issues at a time of serious Cold War tensions, had become taken with the advantages of traveling between planets without propellant, not to mention the continuous acceleration that would allow the minute ‘push’ of photon momentum transfer to build up to high speeds when given enough time. In a March 1958 paper in the journal Jet Propulsion, Garwin published an analysis that ends on a note of genuine optimism: “There are considerable difficulties connected with space travel, but those connected with the sail appear relatively small.”

Image: Physicist Richard Garwin in 1980. Credit: Wikimedia Commons.

Garwin’s paper surely served as the stimulus for the detailed studies that would soon emerge, many of them covered in these pages, from the likes of Robert Forward, who would be talking about not just solar sails but sails propelled by laser in short order. Carl Wiley’s 1951 article in Astounding had been surprisingly technical, showing that sails could be maneuvered by ‘tacking’, thus allowing them to move inward toward the Sun, but it would be Garwin who put the term ‘solar sailing’ into wide use in the scientific community. By 1973, NASA would be funding solar sail studies at Battelle laboratories in Ohio, and Jerome Wright’s work on sail trajectories would lead to the Halley’s Comet mission concept, a spin stabilized heliogyro configuration using twelve 7.5 kilometer long blades of thin film.

Solar-electric propulsion won out over the heliogyro, but sharply rising cost estimates ultimately killed the entire rendezvous mission. It’s worth mentioning, since we’ve been looking at early sail pioneers this week, that the heliogyro concept itself had been developed in the 1960s by Richard MacNeal (Astro Research Corporation). The design was particularly interesting in this timeframe because it seemed to solve the challenging issues of deployment — a heliogyro would simply unroll each individual blade, as Colin McInnes explains in his Solar Sailing: Technology, Dynamics and Mission Applications (Springer, 2004). The work also led to the characterization of a wide range of thin sail films as we began to develop sail expertise.

If you’re interested in the Halley’s Comet mission, Louis Friedman’s Starsailing: Solar Sails and Interstellar Travel should be on your shelf. As to Richard Garwin, something that Enrico Fermi said surely resonates. Working with Garwin at the University of Chicago in the late 1940s, Fermi described him as the only true genius he had ever met, as recalled by fellow Fermi student Marvin Goldberger, who would himself become the head of both Caltech and the Institute for Advanced Study in Princeton. Garwin worked on nuclear arms design and in particular on the world’s first hydrogen bomb.

By 1958, the year of the solar sail paper, he was immersed in his work with IBM but also consulting for Los Alamos as well as Washington and holding down a physics appointment at Columbia. His work on how underground nuclear tests could be detected grew out of Dwight Eisenhower’s proposal of a Comprehensive Test Ban Treaty, one that failed but did lead to a partial ban in 1963.

Garwin’s later efforts on behalf of test ban issues during the Clinton administration are admirably summed up in this 1999 article by William Broad, who refers to him as a ‘onetime boy wonder’ who went on to become a celebrated physicist and passionate advocate of nuclear test bans. By then he had become chairman of the State Department’s advisory board on arms control, taking on the job with a ‘famously sharp tongue’ and bulldog tenacity. Garwin’s interests were wide, and we can be happy that one of them included a then novel way of propelling a spacecraft, a still visionary concept in 1958 but one about which research momentum was beginning to build.

Garwin’s solar sail paper is “Solar sailing — a practical method of propulsion within the solar system,” Jet Propulsion 28.3 (1958): 188-190.

A Sail Mission Emerges

by Paul Gilster | Mar 12, 2014 | Sail Concepts | 7 comments

Carl Wiley, the prescient engineer who offered an early description of solar sails in “Clipper Ships of Space” (Astounding Science Fiction (May, 1951), was not the first to look into sail propulsion, but he was one of the more visible. Konstantin Tsiolkovsky’s thinking on the matter in the 1920s was not widely circulated, and it may be that John Desmond Bernal, a political activist and professor at Cambridge and, later, the University of London, was Wiley’s primary forerunner as far as public awareness of sail ideas is concerned. In The World, the Flesh & the Devil (1929), Bernal looked at the propulsive possibilities in light:

However it is effected, the first leaving of the earth will have provided its with the means of traveling through space with considerable acceleration and, therefore, the possibility of obtaining great velocities – even if the acceleration can only be maintained for a short time. If the problem of the utilization of solar energy has by that time been solved, the movement of these space vessels can he maintained indefinitely. Failing this, a form of space sailing might be developed which used the repulsive effect of the sun’s rays instead of wind. A space vessel spreading its large, metallic wings, acres in extent, to the full, might be blown to the limit of Neptune’s orbit. Then, to increase its speed, it would tack, close-hauled, down the gravitational field, spreading full sail again as it rushed past the sun.

Image: Artwork for Carl Wiley’s article “Clipper Ships of Space,” which ran in the May, 1951 issue of Astounding Science Fiction. Credit: Orban.

My friend Adam Crowl, whose research skills are all but preternatural, has also called my attention to J. B. S. Haldane’s “The Last Judgement,” a look at future human history that was an influence on Olaf Stapledon’s Last and First Men. Haldane, a well-known British biologist and geneticist, has solar sails worked into an interplanetary infrastructure that eventually is considered for an interstellar crossing. The essay covers a Clarke-ian 40 million years, and it’s interesting to note the exchange of letters between Arthur C. Clarke and Haldane. Clarke would go on to edit The Coming of the Space Age: Famous Accounts of Man’s Probing of the Universe (London, 1970), in which “The Last Judgement” was reprinted.

I could spend a lot of time on Haldane and his relation to Clarke, and especially on his paper “Daedalus, or Science and the Future, delivered at Cambridge in 1923, but I’d quickly be digressing to the point of absurdity. So back to sails: We can say that by 1951, when Carl Wiley wrote his essay on the matter for John Campbell’s magazine, he was probably introducing the subject to most of his readers, and certainly looking at it with a level of detail that no previous writer had offered to the public. Its influence would be felt later in the decade.

A Sail Mission Design

For it was in 1958 that Ted Cotter, then working at Los Alamos and later himself an influence on ‘Medusa’ creator Johndale Solem, put together “An Encomium on Solar Sailing.” The memo — and it was little more than that, assembled for internal circulation at Los Alamos — set about to flesh out details of solar sail ideas by describing a design for an unmanned sail mission to Mars. ‘Russell Saunders,’ who as we saw yesterday was Wiley’s pseudonym for the “Clipper Ships of Space” article, appears in one of two footnotes, the other name being that of Richard Garwin, the third of our 1950’s engineers with a sail bent, about whom I’ll be speaking tomorrow.

Cotter’s memorandum was influential only within the realm of Los Alamos, but it makes for absorbing reading nonetheless, and it offers at least one new wrinkle:

The present note contains little new beyond the observations of the previous authors, except the notion of spinning the sail. Its intent is to advertise the considerable merits of solar sailing by filling in more details of the scheme. In order to expose the problems and indicate some technical possibilities for their solution, I will presently describe the construction, operation and flight of an unmanned instrumented solar sailing vehicle on a round trip of exploration to the neighborhood of Mars under command guidance from the earth. Before presenting this particular body of circumstantial evidence in favor of feasibility it seems worthwhile to provide some incentive for the task by emphasizing some of the implications of the properties of solar-sailing vehicles in general.

What follows is a backgrounder on the advantages of using solar photon momentum and the issues sails raise in relation to conventional rocketry. Remember that this was being written just as the first satellites had reached orbit, and Cotter speculates that now that placing objects in orbit had been accomplished, it should be possible to experiment with solar sail designs (it’s probably a good thing he didn’t know just how long it would be before the IKAROS deployment). He is at pains to stress the key advantage of all sails — they require no propellant. No wonder he assumed we’d have a working sail in orbital testing within a few years of his writing.

The Cotter design is a circular disk 500 meters in diameter and 10^-4 centimeters thick, made out of a plastic film coated on one side with 20-30 micrograms per square centimeter of aluminum. Cotter envisioned reinforcing the sail panel seams to prevent tears. He assumed a 250 kilogram payload and introduced the idea of spinning the sail, which aids deployment and holds the sail flat, with stress nowhere exceeding 0.1 percent of the breaking strength of the plastic film. Here’s an essential part of the description:

The capsule consists of two parts connected through a universal joint, and provided with a motor which now causes the sail package and the main part of the load to start counter-rotating. At the appropriate times the collapsed structural backbone is extended, the capsule cases are jettisoned and the vehicle blossoms forth under centrifugal force… The sail is spinning at the rate of one revolution in two minutes. The load, two-thirds of which is suspended in three pods by wires at 50 meters from the axis of spin, is counter-rotating at a rate of 10 revolutions per minute. The vehicle as a whole has zero net angular momentum.

Cotter was already anticipating the many issues that sails would raise, including the deterioration of plastic films in strong ultraviolet radiation, and the problem of sail damage due to micro-meteorites — on the latter point, basing his thoughts on estimates of interplanetary dust and particles current at the time, he concluded that the half-life for decay of the sail’s reflectivity would be measured in thousands of years. Of course, as we look ahead to interstellar applications and vastly ramped up speeds, these issues become much more acute.

And I love this statement, which concludes the piece:

Any remarks on the effects of interplanetary electromagnetic fields would be purely conjectural. These are typical of questions which are perhaps best answered by sending out a solar sail to see.

Indeed. And we are finally in the process of deploying our early sails to make such measurements, long after the first speculations about actual missions were produced. But it’s fascinating to see how space technologies develop in our thinking, particularly when we trace them back to the first engineering concepts. If you’d like to see Cotter’s text, it’s now available online, a restricted access paper long since declassified and made available through the website of the Federation of American Scientists. Tomorrow: Sails get into the scientific literature, and the man who made it happen.

Solar Sails: Remembering Carl Wiley

by Paul Gilster | Mar 11, 2014 | Sail Concepts | 14 comments

If you’re interested in solar sails and find yourself in California, a stop by UC Riverside’s Tomás Rivera Library should be worth your time. There you will find the Carl A. Wiley collection on solar sails, containing books, manuscripts and various other materials related to sail technologies. Wiley was an aeronautical engineer who wrote the first detailed article on solar sails to reach a wide audience. Evidently concerned about the venue — Wiley’s article had been accepted by John Campbell’s Astounding Science Fiction, which some of his colleagues might not have taken seriously — he chose to write under the pseudonym ‘Russell Saunders.’

Finding Wiley’s papers at Riverside is perhaps no surprise, given that this is the home of the Eaton Collection of Science Fiction & Fantasy, ‘the largest publicly-accessible collection of science fiction, fantasy, horror and utopian literature in the world.’ Pulp magazine enthusiasts like myself will note that the archive houses full runs of many pulp titles, along with movie scripts, almost 100,000 science fiction fanzines and over 100,000 hardback and paperback books, along with a growing list of manuscripts and papers from authors in the field.

Wiley’s connection with science fiction may have been tenuous, though I suspect he was a regular reader. But editor Campbell loved the sail concept, and “Clipper Ships of Space” appeared in Astounding’s May, 1951 issue. Wiley wrote with a straightforward style for an audience accustomed to much wilder ideas than the momentum of photons pushing a sail up to speeds suitable for interplanetary missions. He notes in his first paragraph that while science fiction had been full of ‘warp drives’ and other exotica, few writers had really explored near-term alternatives to rockets. It seemed time to do so, and as Wiley had been studying these matters throughout the 1940s, he was the right man for the job. His second paragraph reads as follows:

I intend to propose another method of propulsion in a vacuum which is based on present day physics. I will show that in many ways this drive is more practical than the rocket. In order to prove my point I will have to use a certain amount of mathematics. This will permit those who wish to, a chance to check my assertions. The rest may follow my verbal argument which I hope will be fairly coherent without the mathematics.

Wiley had a lot more on his plate in 1951 than solar sails, and we can get a bit of insight into his use of a pseudonym when we put his life at that time into context. He was working at Goodyear Aircraft Corporation (later Lockheed Martin), which despite its history with airships like the USS Akron, had turned to aircraft production during World War II, building the tail assembly for the B-26 Marauder bomber. As the war ended and the Cold War emerged, Wiley led the effort to improve aerial reconnaissance through the development of Synthetic Aperture Radar (SAR), his breakthrough coming at just about the time his solar sail article appeared in Astounding.

Wiley’s work would result in the first synthetic aperture patent just three years later. It was a real breakthrough for aerial reconnaissance considering that higher-resolution radar was needed to see smaller objects at higher altitudes, and Wiley’s relatively detailed imagery could be created with an antenna that was 1/100th the size of the more traditional antennae such details would demand. He called his method Simultaneous Buildup Doppler and saw it lead to decades of further development including live SAR technologies in the cockpit — the imaging radar for the SR-71 Blackbird grew out of all this, capable of identifying objects 30 feet in diameter up to 100 miles away from a height of more than 80,000 feet while traveling at Mach 3.

This Lockheed Martin overview of Synthetic Aperture Radar remembers Wiley as ‘a brilliant if eccentric engineer,’ a term evidently chosen because of his enthusiasm for space technologies like the sail, considering that the following sentence refers to Wiley’s article in Astounding. But over the years we’ve seen Wiley become a part of deep space lore, particularly now that solar sails have become an operational reality. It’s certainly true that he was not the first to discuss solar sails openly — J. D. Bernal had written about space sailing, and Konstantin Tsiolkovsky worked on it in the 1920s. Thinking about their possibilities goes back to Kepler’s day. But few engineers in the 1950s were serious about flying without propellant, which is why I’ll turn tomorrow to the work of two others who deserve our thanks.