Let's get serious here. Light pressure will provide about 3 nanonewtons per watt. Sunlight near the Earth is good for about 1 kilowatt per square meter, so 3 micronewtons per square meter, so a 1 sq. km. sail will produce 3 newtons of thrust. That's a sail 1000 m on a side.
3 newtons would lift about 2/3 lb against Earth gravity. Or accelerate a 1000 kg cargo at .003 m/sec/sec.
Love the lunatic fringe responses, by the way. Always a highlight of comments to articles about space.
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Article ends with "This small cubesat will use a solar sail to visit a near-Earth asteroid to collect data and send it back to Earth." What does the word "it" refer to in this sentence? "data" is a plural noun, so not "data" . Is it sending the asteroid back?
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Thinking about a platform like that with to use as an asteroid hunter.
Why no mention of Bill Nye, The Science Guy, CEO of the Planetary Society since 2010? He shares a better (and more fun) description of the project and process here: https://youtu.be/Gk3K2qr9oiY Nye is one of he main reasons Light Sail 2 is happening and an inspiration. Coolness!
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Some people are confused about the difference between the solar wind, which consists of particles with mass, and solar radiation, which consists of massless photons. The lightsail works by solar radiation, not solar wind. According to Wikipedia, https://en.wikipedia.org/wiki/Solar_sail
the solar wind has a far smaller effect than solar radiation. "Solar wind, the flux of charged particles blown out from the Sun, exerts a nominal dynamic pressure of about 3 to 4 nPa, three orders of magnitude less than solar radiation pressure on a reflective sail."
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This is very exciting that the light sail was able to launch without the technical glitches of the original lightsail. We should be able to expand this technology to help with extend fuel on traditional spaceships.
I don’t completely understand how the funding was possible as the launch of the falcon heavy costs 90 million, far exceeding the 7 million budget. Perhaps SpaceX was generous given the understanding of how this experiment could positively benefit them, but it’s still a lot of money unaccounted for.
Perhaps this launch had other payloads besides this cubesat?
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Oops, the juvenile fiction of Victor Appleton II and Tom Swift Jr's Space Kite was published in 1960 (Tom Swift and the Cosmic Astronauts. I think.) I was a kid when I read it and it stuck with me. Nonetheless it predates Mr. Clark.
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well, have to use "hieroglyphics" for this, regarding the "weight" of a photon.
p=+M(v) & M=0 ergo....
when basic definitions are violated...
The description that Earth gravity will pull the satilite down is incomplete. Drag from the thin extended atmosphere, or sail orientation changes coordinated with the orbit are required. If gravity alone worked, the moon would have crashed into the Earth long ago.
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What an accomplishment. Thank you for sharing. I followed the Dawn Ion Propulsion mission closely, and the Solar Sail is now a huge added accomplishment. Baby steps. I would like to see more of this on the NYTimes.
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Will only function till it reaches radiative equilibrium and emits as much as it receives i.e. zero light sail effect (Thomas Gold)
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@Adrian
As long as the sun is more than a tiny dot, there is no worry that a sail in radiative thermal equilibrium with the 4 degK radiative environment will cease to benefit from solar radiation.
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And what happens when it runs into a micro-meteor shower which completely destroys the sail?
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Spacetime is chock full of wormholes, which are points in the fabric of spacetime which have come together creating momentary transit hubs allowing passage, instantaneous passage, from any point "A" to any point "B".
It is likely that much sooner than we expect, someone, or some group, or some regular users of these transit hubs, will enlighten us, and humankind will finally understand the why of it all.
Solar sails, speed of light travel, ion drives, etc., all such methods of transit will be looked upon as being as slow as our 100,000 plus years trek out of Africa, as we populated the Americas and Eurasia.
Our greatest discoveries are yet to come, and a lot closer than we know.
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@Mel Farrell Have actual wormholes been detected (that is, proven to exist), or are they still theoretical?
Even if actual, do we know that they can be traveled through? Do we know what conditions are like inside a worm hole? Could a spaceship with crew survive such a transit?
I hope the answer to all of these questions is yes, but I have yet to read about the discovery of an actual wormhole.
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@JediProf There is no empirical evidence that wormholes exist, simply some equations that suggest they might.
There is no evidence, and only speculation that individuals or groups use these as "transit hubs". This is entirely speculative.
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I'm hoping to see more information on how a craft powered by a solar sail can go around the Earth. Having done the exercise of sailing a small boat around a buoy a few times I don't see how a lightsail can tack.
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@Thomas I fail to see how this contraption can do anything other than sail off directly downwind. A yacht makes progress in all directions, except dead to windward, because of the interface between the sails, in the air, and the hull in the water. A sideways force on the sail is resisted by the keel and hull in the water and the boat therefore must go forward, with a bit of leeway. It's rather like squeezing a watermelon seed between the fingers. A solar sail has neither keel nor lateral resistance.
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@Thomas there are people with sailboats and there are people who know how to sail. I imagine the engineers piloting this vessel are the latter.
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@Thomas
Even without supplement, a sailcraft can gain orbital energy from solar radiation (thus improving flight time to an outer planet0. However, the article implies that the craft uses an internal gyroscopic rotor to counteract torque from a tacking position of the sail. This is possible, but only by expending stored energy on the rotor. In other words, a solar sail can never be the sole source of energy for a space journey.
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https://en.wikipedia.org/wiki/Sunjammer
I remember reading the story in "Boy's Life". I suppose some future astrophysicists were created by it. For me it was only the birth of a taste for good, intelligent speculative fiction.
And who could pass up a story with such imagery?
https://superretro.com/wp-content/uploads/2017/02/R9c6hRI.jpg
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@Steve Paradis. As a young boy, hunched over the dining room table, I also remember reading the Arthur C Clarke story, Sunjammer,in Boys Life.
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Oh, great. Now we have another piece of space junk floating around, getting in front of ground-based observatories.
The Iridium flares were bad enough. This is an experiment, and should have self destructed after some time, like a few weeks or months at most.
Yes, it is interesting. But when Cassini and other more distant probes like New Horizons which need a plutonium decay battery since the sunlight farther out than say Mars is so weak as to be of no use generating power, what's going to happen to the solar push after a few planets outward have exhausted the energy?
I'm surprised with the space and dark-sky aware organization such as the Planetary Society making such a smuck of themselves with this night polluter.
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@reid
did you not read the story? It will burn up in the atmosphere before terribly long. And yes, even out by Mars there will still be a gentle push from the sun. Read up on the concept of frictionless momentum.
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@reid And here I was, naive as ever, thinking that nobody could POSSIBLY object to such a fascinating experiment.
The human capacity for creativity and exploration is dwarfed only by the capacity to irrationally complain about the same.
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@reid it’s going to fall to earth rather quickly, did you bother to read the article?
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As long as chemical rockets are the primary means of himan space exploration and travel most of what we are trying to get into space is fuel.
Human dependency on gravity, liquid water, oxygen and protection from radiation requires that we be able to get places in space cheaper and faster.
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Congratulations to all of us that find the exploration of outer space important. Another effort to enrich our knowledge by these creative endeavors.
I wish I could see into the future the day we land on an alien planet outside our solar system. It may or may not ever happen but it sure is fun trying give or take a billion years.
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I am very surprised at the size of the research funds for this unbelievable project - only $7 million. It is also amazing that just 10 years of research can make this happen. This should be a great research project for future scientists. I hope many people who cannot afford millions and millions of dollars to pay Amazon, Space X or Galactic would be able to watch the great blue planet once in a lifetime.
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Behold the wondrous power of sunshine!
Finally, some 400 years after Kepler and 50+ years after Clarke, we're making their imaginations a solar-sailing reality. The solar ocean awaits us!
This recalls Dennis Overby's 2009 NYT article and reader comments re LightSail 1 (NYTimes, please keep us updated soon on LightSail 2's unprecedented voyage.)
Technical correction: Since sunshine propelled spaceships operate in a near-vacuum, they cannot add the second force vector provided by an earthly sailboat's keel pressing on water. Thus, (other than a few special going-toward-the-sun maneuvers requiring planetary-flyby gravity-slingshot turns), they can't really "tack" upwind. A more accurate sailing ship analog is the (downwind only) "jibe" or "gybe".
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@G Strand ah, a thoughtful comment, thank you. You must be a sailor, not just some person with a sailboat!
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@Paulie Ahoy back.
Imagination. Reality. It's all one limitless ocean.
And we all can be sailors there.
See also "Solar Journeys (two letters)" from Nov. 16, 2009 NYTimes:
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Science-fiction stories.
"The Wind from the Sun" - Arthur C. Clarke
"Sunjammer" - Poul Anderson
Both from 1964.
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@Alan Dean Foster
"Explorers" - Star Trek: Deep Space Nine Season 3, Episode 22
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@Alan Dean Foster “"Sunjammer"… has also been published under the title "The Wind from the Sun" in Clarke's 1972 collection of short stories with this title.”
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@Alan Dean Foster Honorable mention to "The Mote in God's Eye" - Larry Niven & Jerry Pournelle
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Maybe for a month or two the New York Times can take the space they use to cover Trump and the Congress and shrink it to 10% and use the remaining 90% for a thorough appraisal of our Space programs and current progress.
1. This will really motivate Americans of all ages, races, income levels to unite towards common goals, challenges and successes.
2. It will provide some sanity, a break from the nonstop blitzkrieg of nonsense and rancor that has been bombarding us these past years.
Blame it on the 50th Anniversary of the Moon Landing, or just blame it on me. You will not lose readers, you might actually gain some, and for a couple of months we will see what it is when America is Great Again.
Please link the SpaceX clip of launching the Falcon Heavy as an introduction. Watching those boosters land back on Earth, even the one that fell off the drone ship into the water, is a joy and celebration of life.
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In the future... the Americas Cup of Light Sail Yacht Racing? Who knows?
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@Joe G. The America’s Cup is boring enough, watching millionaire play. Imagine it slowed down a few thousand times. The solar sailors may be moving quickly but the maneuvers would take weeks if not months.
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The article is using inconsistent language and confusing things. The title refers to the solar wind which is never mentioned in the article. The solar wind is distinct from the photons emitted by the sun. It consists of particles with mass, mainly hydrogen. These also contribute to the thrust generated.
is the sail really kept perpendicular to the sun? That would make the thrust for half the orbit negate the thrust in the other half. It would make more sense of the sail to be held at an angle that the creates thrust in the direction the craft is moving, thus always accelerating it. That's how you increase the apogee. This has nothing to do with tacking, which is the technique that sailing ships use to sail into the wind.
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@feanole not mentioned is if both sides of the sail are capable of capturing the solar wind. I would suppose there is a coating that would optimize the wind’s effect.
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@feanoleI agree that the part about the direction should be clarified. assuming the orbit is roughly equatorial, the satellite is moving roughly away from the sun half the time. If the sail were facing the sun for that time, the satellite would gain orbital energy. However, on the other. Half of the orbit it travels toward the sun, so a sail facing the sun would slow it down. The description in the article must be wrong. I would maneuver the satellite so the sail faced forward (along the orbit) while moving away from the sun, and edge-on to the sunlight while moving away. It would have to start a slow rotation when the sun was directly overhead, and stop it while passing through the earths shadow.
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Silly question....is Lightsail2 visible to our unaided eyes?
I've often seen transits by the space station, using NASA's great site..."spot the space station"
Number of transits visible around sunup, or sundown.
Satellites also visible. I live in an area away from city lights. Its amazing to gaze upward on a clear night and see all that's zipping 'round us.
Fascinating experiment...the elusive perpetual motion machine coming to mind.
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I’m totally willing to take a one-way space voyage but “sailing” anywhere of note stretches even the optimism I might bring to “casting off”. Sail on!
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Fascinating. I get the propulsion part but how do you stop a sail in space?
@JB - hit something!
Once you get something moving out there, it's just gravity, inertia and whatever tiny energy from particle collisions.
A fun bit of reading a few years ago concerned the extremely slight drift of Voyager I from its predicted trajectory out near the edge of the solar envelope. So some of the engineers started thinking about it and concluded that the very slight heating on one part of the exterior, from the radioactive fuel unit, was creating a very tiny bit of thrust from the infrared photons being emitted. A really tiny amount, but over the millions of miles it added up enough to be noticed.
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@JB Altering the orientation of the spacecraft and sail so that the flow of photons is edge-on to the sail's plane will effectively stop further addition to whatever momentum the craft has attained, as the steerable sail can also be used for some degree of directional guidance. "Stopping" is really not something which would be a viable outcome if in Earth orbit, as it would mean the craft would immediately begin de-orbiting. If a lightsail craft were to approach another body in solar orbit, the objective would likely involve orbital capture for extended study or perhaps merely adjustment of its orbital trajectory without capture. If it was some future interstellar mission, the craft would midway between literally flip so that the photons from the destination's sun would be pushing against the direction of its built-up momentum, slowing it gradually to enter that solar system with lower speed to become another orbiting body around it.
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All incredible good news on space - in this 50th year anniversary of Apollo 11 moon landing.
I read somewhere that Elon just announced his space craft will be ready in 6 months - before this golden year is out - to ferry Americans back in space.
And then if NASA meets goals of landing back on the moon in 2024 - why we may yet see three decades of great accomplishments like we did in 60's, 70's and 80's of the last century.
All in all - Mr. Armstrong would have been might pleased.
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@Neil because the present administration thinks it’s a better idea to give those that have too much more. Also they don’t believe science for science’s sake is worth anything. Although this is a technology project, not necessarily science, there is a difference. Solar wind has been known of for quite a long time.
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