From Diana to LightSail 2 – TTG


The Sunjammer

By Arthur C. Clarke | Illustrations by Robert McCall

“T minus two minutes,” said the cabin radio. “Please confirm your readiness.”

One by one, the other skippers answered. Merton recognized all the voices—some tense, some calm—for they were the voices of his friends and rivals. On the four inhabited worlds, there were scarcely twenty men who could sail a sun yacht; and they were all here, on the starting line or aboard the escort vessels, orbiting twenty-two thousand miles above the equator.

“Number One, Gossamer—ready to go.”

“Number Two, Santa Maria—all O.K.”

“Number Three, Sunbeam—O.K.”

“Number Four, Woomera—all systems go.”

Merton smiled at that last echo from the early, primitive days of astronautics. But it had become part of the tradition of space; and there were times when a man needed to evoke the shades of those who had gone before him to the stars.

“Number Five, Lebedev—we’re ready.”

“Number Six, Arachne—O.K.”

Now it was his turn, at the end of the line; strange to think that the words he was speaking in this tiny cabin were being heard by at least five billion people.

“Number Seven, Diana—ready to start.”

“One through Seven acknowledged.” The voice from the judge’s launch was impersonal. “Now T minus one minute.”

Merton scarcely heard it; for the last time, he was checking the tension in the rigging. The needles of all the dynamometers were steady; the immense sail was taut, its mirror surface sparkling and glittering gloriously in the sun.

To Merton, floating weightless at the periscope, it seemed to fill the sky. As it well might—for out there were fifty million square feet of sail, linked to his capsule by almost a hundred miles of rigging. All the canvas of all the tea-clippers that had once raced like clouds across the China seas, sewn into one gigantic sheet, could not match the single sail that Diana had spread beneath the sun. Yet it was little more substantial than a soap bubble; that two square miles of aluminized plastic was only a few millionths of an inch thick.

“T minus ten seconds. All recording cameras on.”

Something so huge, yet so frail, was hard for the mind to grasp. And it was harder still to realize that this fragile mirror could tow them free of Earth, merely by the power of the sunlight it would trap.

“. . . five, four, three, two, one, cut!”

Seven knife blades sliced through the seven thin lines tethering the yachts to the mother ships that had assembled and serviced them.

Until this moment, all had been circling Earth together in a rigidly held formation, but now the yachts would begin to disperse, like dandelion seeds drifting before the breeze. And the winner would be the one that first drifted past the moon.

(The story continues here.)


I read this short story by Arthur C. Clarke in 1964 when it came out in Boys’ Life. Our manned space program was still young. Shepard and Glenn have done their things, but there was so much before us. There was plenty of literature for young readers who wanted to keep up with the space race. Reading “The Sunjammer” struck a chord. The idea of sailing across the universe riding the solar winds thrilled me. Even at that young age, I was occasionally scooting an old wooden dinghy around Long Island Sound with a scrap canvas sail. I knew the freedom of the wind and the water. The idea of scooting across the solar system in a single handed “space dinghy” tethered to a massive gossamer sail was exhilarating. 


In a few days, The Planetary Society’s LightSail 2 is scheduled to unfurl its solar sail. It launched into orbit on 25 June aboard SpaceX’s Falcon Heavy rocket and has undergone extensive testing and tweaking of its navigation and flight control systems. In another month LightSail 2 will maneuver into a higher orbit under solar sailpower. The purpose of this craft is to demonstrate a viable propulsion system for other CubeSats. This could be a very cost effective propulsion system for these CubeSats. Not only is there no need to carry fuel, but acceleration is cumulative. Although initial velocity is slow, the longer a solar sail flies, the faster it goes…. far faster than a conventional rocket engine can go if the voyage is long enough. All this was explained clearly in Clarke’s “Sunjammer” over fifty years ago.


This is not theoretical and certainly not just a science fiction story. In 2010 the Japanese Aerospace Exploration Agency launched IKAROS (Small Solar Power Sail Demonstrator). This craft sailed past Venus in six months. In 2013 it reached a velocity of 400 meters per second. By 2014 it was in a ten month orbit of the Sun. The last signal received from IKAROS was in 2015. 

Both IKAROS and LightSail 2 are a far cry from Clarke’s sun yachts, but give it time.


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26 Responses to From Diana to LightSail 2 – TTG

  1. blue peacock says:

    Thanks TTG for this post. I too remember reading Sunjammer as a kid. Clarke was an amazing person. Living in Sri Lanka and conjuring up visions of the future.
    Light sails are truly fascinating. Using thrust provided by photons. I’m curious how long before they have serious maneuver capability and when they’ll have the ability to provide continuous power for radio transmission and instruments?
    Lightsail 2 was just a $7 million project. Wouldn’t it be amazing if we shaved the DoD budget by 10% (the DoD would still have a larger budget than the next 10 countries defense budgets combined) to do more space exploration by sending more sophisticated robots deeper into space?
    What about the Voyager spacecraft who are now in interstellar space?

  2. GeneO says:

    Thanks TTG! It is citizen funded! I did a small donation and entered the LightSail sweepstakes. Hoping I can win some of Bill Nye’s swag:
    But just in case my tickey is a loser I bought an LightSail lapel pin and a Chicxulub T-shirt.

  3. Larger and more maneuverable solar sails will be a boon to interplanetary and interstellar travel. A solar propelled Voyager with autonomous control could be at the vanguard of our space exploration in the future.
    On the manned exploration front, I watched a PBS show this week entitled “8 Days: To the Moon and Back” and found it to be almost as exciting as the original landing. This documentary used NASA recorder conversations among the astronauts coupled with actual footage, CGI and reenacted scenes to create a feeling of being side by side with them during their voyage. I heartedly recommend it.
    I braved the heat last night to sit outside and gaze at the Moon just as I did 50 years ago. Rather than sitting in front of a TV, I went stealth camping with 2 friends to a pine covered hilltop above a posted reservoir. We listed to Walter Cronkite narrate the landing as we laid on the deep pine needles and stared at the Moon. It was a far better experience than sitting in front of the TV.

  4. GeneO says:

    I am trying to find info on the web about the spars and rigging. No luck so far. Do any of the more science minded here know of what type of material those would be made? Or what is their mass?
    I did find the link below from NASA about their research on diffractive lightsails. They push instead of pull, and might do away with much of the rigging – in principal at least.
    BTW, SWMBO chewed me out about buying for myself and forgetting the great-grandkid whose birthday is around the corner. So I changed the size on the Chicxulub shirt to Kids XS, added some posters, and lots of stickers. His Mom & Dad are going to give me the evil eye about the stickers.

  5. Mark Logan says:

    Not that I am claiming to be better versed in science than yourself, or anything…but after viewing the Jules of energy they are dealing with from their site, there appears to be no need for the sort of rigging that sailboats have on earth.
    The forces involved vastly smaller, so the “yards” could be 1/8″ diameter hollow carbon fiber tubes, which could support cubic miles of sail. A single 18ga copper wire could handle the pull from that large a sail. I suspect they may need more than that to handle the wattage.
    A heck of a lot of the total thrust appears to be produced by electrically driven ion drives. I suspect Bernoulli becomes irrelevant in the absence of gases, but I’m not 100% sure of that. Do photons behave like a gas? I really don’t know, but it seems they are using electrically fueled ion drives for all maneuvering on this model. They are “motor sailing” up there, which yachts do too. When conditions are right you can get something from both the sails and the engine.

  6. GeneO says:

    Thanks Mark! Found these two sites.
    First is a five-year old update on boom deployment. It contains a video of an early deployment test. Author says boom consists of an alloy called elgiloy. It deploys by unrolling like a tape measure (or four of them):
    Second is an overview schematic, six sheets, but four years old. I’m assuming (bad I know) it is for both the -1 or -2, at least at the overview level. Sheets five and six are interesting.
    Seems to me one of the weak points in addition to the sail deployment mechanism itself, would be where the boom tips attach to the sail, you think?

  7. dilbert dogbert says:

    Sails are fine. I have been a small boat sailor since 1967 and enjoy going slow. If one wants to go faster I recommend this: I think Ted Talyor was part of this project.

  8. dilbert, if you haven’t already read “The Starship and the Canoe” by Kenneth Brower, you should. It’s about Freeman Dyson’s Project Orion and his son’s experiences in the wilds of the Pacific Northwest including his huge aluminum framed kayaks for sail and paddle.

  9. Lars says:

    I have now lived on Florida’s Space Coast for 21 years and have become familiar with the reality of the space program. The early pioneers, many who have now passed away, were visionaries, in the manner of what depicted in the important stories already provided. They were fearless and a swashbuckling bunch.
    Now they have been replaced with bureaucrats that have none of the attributes once found around here. I got to meet a lot of the old crowd, since my wife’s late husband was a high ranking functionary at NASA, after a stellar career in the US Navy. I was also neighbor with the Director of the KSC and got to see a lot of launches.
    Now, many of my neighbors are still in the space program and while very nice, educated people, they just do not have the same qualities required to take “giant leaps”. In addition, politicians are now in charge of the effort and that does not give me much confidence either.
    But Mr. Clarke did much to expand the horizon and for that we are grateful. There are a lot of local celebrations of the incredible feats 50 years ago and it is pleasant to look back. Looking forward, not so much.

  10. blue peacock says:

    “The early pioneers, many who have now passed away, were visionaries, in the manner of what depicted in the important stories already provided. They were fearless and a swashbuckling bunch.”
    This is the general state of our country as the financiers and bureaucrats have taken over. With the few exceptions at the margins in Silicon Valley & biotech, we’re now focused more on milking the cow. I can see how the current generation of NASA bureaucrats are motivated more by not being blamed for failure.

  11. Lars, I see that in all the retrospectives about the Moon shot being shown lately. There’s an inner drive and sense of honor in those early pioneers that is quite uncommon today. They lived with a great fear of having to live with the shame of letting down the team if they didn’t give their best to the mission and job at hand.
    Although not one of the earliest pioneers, John Muratore put this attitude to words when he wrote his NASA Pirates Code.
    – Pirates have to know what they’re doing.
    – If we fail, there is no mercy.
    – You’re operating outside the normal support structure of society. It’s all about knowing all the details.
    – You hit hard and fast. Pirates don’t spend months wandering around.
    – Pirates live on the edge or just in front of the wave that is about to catch them.
    – Piracy is about taking risks. Occasionally we’re going to fail and you’ll get some holes blown in you.
    – Pirates don’t have resources to waste. You’re always operating on a thin margin, not in fat city.
    – We’re all banded together.
    Definitely words to live by. I understand Muratore is now part of SpaceX.

  12. Lars says:

    That is a good analogy. One of my favorite tales from the early days was my friend Andy, who has since left us, going out to a rocket that failed to launch when the button was pushed and hit it in a few places with a hammer. Don’t try that today. The good news was that he lived to tell it.
    One of the problems today is that NASA has decided to use old technology from the Apollo days, when more effective and cheaper services are available from reusable rockets from SpaceX that could cut years off the schedule and a lot off the budget. But it is what they call “the project of record” and a lot of big players are dependent on soaking the tax payers and provide as little as possible for as long as possible.
    Mike Pence providing “thoughts and prayers” will not make much difference, unless the revolutionaries take over. They are there, but so far ignored.

  13. dilbert dogbert says:

    I have his son’s book, Badarka.
    I also have John McPhee’s book Curve of Binding Energy. Also met the man described in The Deltoid Pumpkin Seed.
    I have built only 5 small boats and getting too old for more. I liked to go from a table of offsets, lofting full scale to building.

  14. elkern says:

    Thanks, TTG. I thought I recognized the illustration at the top – I, too, read this story in Boys’ Life, “back in the day”. (My Dad worked for Boys’ Life, so I had free “subscription”, including decades of back-issues).

  15. Fred says:

    So tens of millions of new immigrants have not been our strength? All that Great Society spending didn’t create a new and more robust economy? My, who knew such policy choices might not achieve the results promoted.

  16. Fred, the space industry never had an influx of foreign talent beyond the limited H1-B visas and the likes of Elon Musk. It’s faced ITAR restrictions since 1976. The current problems of NASA are American grown and raised.

  17. Fred says:

    Lars mentioned “many of my neighbors are still in the space program and while very nice, educated people, they just do not have the same qualities required to take “giant leaps”.” I don’t think he is refering to Elon Musk.

  18. Lars says:

    The more inventive and daring people in the space program are working for Elon Musk. The people working for NASA, ULA, Boeing, et al, are not nearly as ambitious and are more concerned about having the tax payers support their life style. They have an army of lobbyists making sure it stays that way.

  19. Fred says:

    And we got that way because of the political leadership of the Republic in the 1960s and 1970s. Reagan, for all his faults, tried to change that direction but was opposed by the institutional left and much of the emerging ‘conservative’ right. To quote Daniel Greenfield “The whole mess of bureaucrats, contractors, lobbyists, policy experts, consultants, congressmen, aides, crooks, creeps, thieves and agents is no longer a necessary evil that we put up with in order to accomplish great things. It is the great thing that we accomplish. ”
    I think he articulates that rather well. That insitutional bureaucracy, from education to nasa, is opposed to what has emerged in opposition: Trump and all his non-left support. They stand to lose a great deal of gravy along with big sliced of overstuff, overcooked goose they’ve been feeding on for decades.

  20. LightSail 2 has successfully deployed her solar sail. The “mission control” consisted of a half dozen people sitting in front of their laptops around a folding table. One woman even had her child with her. Should be getting some photos later today. Not bad for a crowd funded project… so far.

  21. Fred, the 1960s to mid 1970s was the heyday of NASA space exploration with Apollo, SkyLab and the Voyager missions. Seems you and Greenfield long for a time when we work together to accomplish a shared mission without the “what’s in it for me” grifters gumming up the works. That’s a pretty socialist notion. Too bad it’s spoiled by the spreading cancer of a “greed is good” brand of capitalism. You’re right about Reagan cheerleading for a greater and shared sense of national purpose. He spoke loftily about us being a nation of immigrants coming together as Americans through that shared purpose.

  22. GeneO says:

    Dang! I missed the LiveStream. When will they download the imagery?

  23. Fred says:

    I don’t think Elon Musk is running SpaceX out of the goodness of his heart.
    “loftily about us being a nation” He was speaking of a nation where everyone was, to use the term, consubstantial, with every other citizen. That is not what the term ‘immigration’ means today.

  24. GeneO, seems the LightSail 2 mission has limited bandwidth and limited time to receive signal from the craft during each orbit. They hoped to download images during the last pass over Cal Poly yesterday, but were unable to do so. They plan to get the images today. Don’t worry about missing the livestream. It’s not near as impressive as a NASA or JPL mission control livestream. It’s was just half a dozen people around their laptops. I imagine most of their screens were just open terminal windows with command line input without fancy graphics. For the most part, it was like watching paint dry. But then again I was once excited by a CLI at a 300 baud rate over an acoustic coupler. The Planetary Society twitter feed is a handy source for news updates.

  25. GeneO says:

    Got it, thanks.
    Looks like from one of the tweets on your link that comms were suboptimal maybe because of the solar sail orientation. But then the comms were strong enough to clearly send telemetry on mission info, instrumentation, and results of checkout tests. They were just not able to download the photos, which were presumably sent via a different communications process than telemetry that needed a stronger signal.
    That makes sense to me given the aluminized mylar of the sail. It could easily have blocked or given interference to the antenna. And perhaps the signal may have been further compromised by amteur radio, which also is allowed to use the 433 MHz frequency.
    But then I’m no RF Engineer. I’ll be interested in any after action reports.

  26. GeneO says:

    partially blocked

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