With its May 18 launch date fast approaching, Japan’s IKAROS hybrid sail mission is at last getting a bit of press attention, long overdue in my opinion. The Daily Mail, at least, has just run a story on IKAROS, which will combine two mission concepts within a single spacecraft. Its solar sail works conventionally, using the momentum of photons from the Sun to accelerate the craft. But the JAXA designers have added thin film solar cells on the sail membrane. These produce the electricity that could be used in future (and larger) iterations to drive an ion engine.
But IKAROS (Interplanetary Kite-craft Accelerated by Radiation of the Sun) is a demonstrator, not only taking the sail concept into space but pushing it into interplanetary regions. Launched in tandem with the Venus Climate Orbiter AKATSUKI, the spacecraft will deploy its sail a month after launch on the way to Venus, and having swung by the planet, will test out its propulsion and navigation systems. Kelvin Long, head of Project Icarus, was the first to forward me the link to the Daily Mail story, and that reminds me to note that despite the similarity in names, IKAROS bears no relation to the interstellar probe design Kelvin’s team is developing.
Not that the interstellar community doesn’t have high hopes for sail concepts, and it’s safe to say that anyone interested in the problems of deep space propulsion will rejoice at the launch of IKAROS. What we need at this juncture, with reams of theoretical work compiled, is to start gathering data from live missions. Perhaps the most obvious issue for IKAROS and any other design is sail deployment. The IKAROS sail is a square membrane with a diagonal distance of 20 meters, made of polyimide some 7.5 micrometers thick, with the solar cells, steering devices and dust-counter sensors fitted directly to the membrane.
Image: The IKAROS sail, a hybrid design with attached solar cells. Credit: JAXA.
Osamu Mori, project leader for IKAROS, describes the sail membrane in this interview:
Polyimide resin allows us to create a much lighter sail. As well as being extremely strong, it doesn’t need glue, because it can be joined using heat sealing. Polyimide resin is originally yellow, but one side of IKAROS’s sail is silver. This is because aluminum is vapor deposited on one side of the film, in order to reflect sunlight more efficiently. In addition, the film is reinforced in such a way as to prevent it from splitting all the way if it’s ripped. If the solar sail is torn, its performance will decline slightly, but it can still continue its space travels.
One way to deploy a sail is to use conventional mast and boom construction, but you pay a penalty in weight and complexity. The IKAROS team had a different idea. The sail, wrapped and folded around the body of the spacecraft, will be spun up to 20 revolutions per minute. Spinning the spacecraft will allow centrifugal forces to unfurl the sail, and spin-stabilization will likewise keep the weight down due to the lack of a supporting truss. JAXA’s sail team has conducted experiments both on the ground and aboard a balloon, where the sail membrane was spread in a near-vacuum.
Mori adds that sail orientation and navigation is going to prove an interesting issue. IKAROS could change the direction of the sail with an onboard thruster but can also maneuver solely with solar power, changing the reflectivity of various parts of the sail by ‘frosting’ the film. The part of the sail with reduced reflectivity thus generates less acceleration, so the sail’s attitude can be controlled. In addition, IKAROS will carry a dust counter and an instrument to observe gamma ray bursts.
Japan’s plans for the hybrid sail/cell design are quite ambitious. JAXA’s Jupiter and Trojan Asteroids Exploration Program was born in 2003 and chose solar sail technologies for the mission. IKAROS is thus a demonstrator not only for sail concepts in general but for the specific issues that a Jupiter mission will face. At 5 AU, a sail in Jupiter space receives only 4 percent of the amount of sunlight it would in Earth orbit, drastically reducing the effectiveness of a conventional sail. This is the reason for the solar cell experiment, which would drive an ion engine needed for maneuvering a larger Jupiter-bound sail.
But first things first. The IKAROS demonstrator will need to prove itself in terms of deployment, navigation, attitude control and power generating capabilities, teaching us whether future hybrid designs using ion propulsion are indeed feasible. We’ll begin to learn more on May 18, when IKAROS and AKATSUKI blast off from the Tanegashima Space Center.
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Solar sails are the key to cheaply opening up the rest of the solar system for manned and unmanned space travel. If they were launched from the Earth’s Lagrange points (L1, L2, L4, L5), the low delta v requirements would allow multi-kilometer in diameter sails to transport hundreds and even thousands of tonnes of payloads to or from Mars orbit and to the NEO asteroids in less than a year. This would also allow reusable manned interplanetary space craft to be properly shielded from galactic radiation since large light sails would allow us to add the hundreds of tonnes liquid hydrogen or water required to protect astronauts from cosmic radiation.
“At 5 AU, a sail in Jupiter space receives only 4 percent of the amount of sunlight it would in Earth orbit…”
Clear glass reflects four percent of incident light. It appears to be considerable when the sun is reflected into our eyes from a window on a building, or from the glazed truck cap rear door ahead of us on the road. Herschel wedge prisms use this reflection property for white-light viewing of the sun.
The environment nearer Venus offers something for the small IKAROS sail. MESSENGER has proved the utility of orienting its panel arrays to maneuver by light pressure alone with a saving on propellant. It has worked to be reliable with predictable results for course corrections.
Solar sails look like the only technology that can get a probe to near-interstellar space in my lifetime, even if it takes 20 years to get it launched. So besides all the rational reasons for them I have a completely selfish one.
There use to be a phrase used in Cristopher Columbus’ time for deep sea voyages “Sailing the ocean, blue”.
Well now thanks to JAXA, and also the Planetary Society, we are purched on the beginnnng edge of “Sailing the universe, black”.
With the development of ambient sun-light thrusted sails, we can eventually move on to solar dive and fry missions, and artificially columated beam driven missions.
Now if we can develop large scale zero point energy field extractors that reifiy or extract zero point electromagnetic energy fluctuations, the potential for velocities of C – e, may present itself, where e can be made arbitrarilly small. I use this longhand notation to express the concept of simply as close to C as desired, simply because of its symbolic significance on the psyche. The term epsilon, which I write here as the letter “e” is often used for vanishingly small numerical values.
Of course we could use concentrated sunlight, fusion reactor generated beam light, or perhaps solar PV space station generated beam light for similar end effects, but the point is that a real world technology that can enable us to reach the stars, in principle is poised to be tested soon, even if only on a relatively rudimentary level.
HMMMmmm! Riding along on a beam of light. Sounds like something Einstein would have enjoyed as a youth and something that the global citizen of all levels of intellegence, socio-economic status, ethnicity, and state of life would enjoy.
I like to muse that EM beam sailing is somewhere between rockets, be they chemical, nuclear, or matter antimatter rockets, and still speculative forms of travel such as superliminal warp drive, wormhole production, gravatic or antigravatic propulsion and the like, in terms of exotic-ness.
The beautiful thing is that solar sailing and EM beam sailing in general, at least as far as the sail is concerned has lots of room for improvement, as far as the effective mass specific sail capture area is concerned. We know how in principle to do solar sailing, but as many folks like to say, “The devil is in the details”. As polymeric materials science and manufactures develop better and thiner materials, and perhaps eventually, metalized carbon nanotube, graphene, or metalized boron-nitride forms of materials, expect to see big strides being made in solar sail technology.
We finally have a technology in its infancy by which we can set sail for distant Suns and destinations now only dreamed of.
Essig … “now if we can invent a way to extract zero-point energy…”
My dear colleague, please refrain from throwing around the impossible. I’m not going to get into a Casimir force discussion, or any of the limitless musings of the zero-point energy fellows, but it rests: no one has extracted any such energy in excess to whatever energies and methods were used … ever. It may, but most likely will not happen.
We humans have an all-too-ready belief in “eventually the impossible becomes possible”. Over and over we view the rather hard limits of space-time as things that can be overcome. They cannot any more than two blocks of steel can be made to pass through each other without friction. From quantum first principles, the blocks of steel COULD pass through each other – there’s a probability, finite, for it. But … in our all-too-human perception, we know that it is absurdly improbable. Same too for quantum limits to the nature of space, spacetime and astrophysics. No stellar process theory has yet to pull in the zero-point function for a predictive result. Doesn’t happen, and is unlikely going to.
Same goes to the people who rail endlessly about “if we just get a nice big chunk of antimatter”. Stop it! It is just as likely as the two steel cubes passing through each other without friction.
Solar “sails” are an excellent idea. Crack open your basic “Calculus 1” text book, and integrate over time the amount of net-force that a sail would receive if its orbit were to pass within 0.25AU of the Sun. Yet, it is a double integration, but not that hard.
This is the way to go, whether or not it works. The fastest way to another solar system is not to build a ship that goes there, but to build ships that travel our solar system first using many of the technologies necessary to go to other solar systems. Otherwise it’s like building a plane to fly across the ocean before you’ve built a plane that can fly to the next town.
Maiden voyage for first true space sail
New Scientist Space May 12, 2010
Japan’s aerospace exploration
agency (JAXA) plans to launch the
first spacecraft fully propelled by
sunlight on May 18, piggybacking on
Japan’s Venus Climate Orbiter,…