IKAROS - solar sail from Japan. Image: JAXA

Japan to Launch Venus Orbiter and Solar Sail Missions

Article Updated: 24 Dec , 2015

Bad weather postponed a scheduled multi-mission launch of an H-IIA rocket from Japan early Tuesday, which includes the first Japanese probe to Venus and an experimental solar sail. The next launch attempt for the “Akatsuki” Venus Climate Orbiter and the solar sail called IKAROS will be Thursday, May 20, at 21:58 UTC (May 20 at 5:58 EDT) – which is May 21 at 6:58 in Japan. Akatsuki is Japan’s first mission to Venus, and it will work closely with the ESA’s Venus Express, already at Venus. Also called Planet C, the box-shaped orbiter should arrive at Venus in December and observe the planet from an elliptical orbit, from a distance of between 300 and 80,000 kilometers (186 to 49,600 miles), looking for — among other things — signs of lightning and active volcanoes.

Another payload is the solar sail, or “space yacht” IKAROS (Interplanetary Kite-craft Accelerated by Radiation of the Sun). This 320kg, 1.8m-wide, disc-shaped spacecraft will deploy an ultra-thin, ultra-light, 14 meter sail that will propel the structure from the radiation pressure from sunlight hitting it.

“The purpose of IKAROS is to demonstrate the technology of the Solar Power Sail,” said Osamu Mori, project leader of IKAROS. “Simply put, the solar sail is a ‘space yacht.’ A yacht moves forward on water, pushed by wind captured in its sails. A solar sail is propelled by sunlight instead of wind, so it’s a dream spaceship – it doesn’t require an engine or fuel. Part of IKAROS’s sail is covered by a solar cell made of an ultra-thin film, which generates electricity from sunlight.”

So far, solar sails have only been tested, but never flown successfully. It is hoped IKAROS will be the world’s first solar-powered sail, and that the structure will sail towards Venus, following Akatsuki.

The experimental sail is thinner than a human hair, is also equipped with thin-film solar cells to generate electricity, creating what JAXA calls “a hybrid technology of electricity and pressure.”

To control the path of IKAROS, engineers will change the angle at which sunlight particles bounce off the sail.

Akatsuki and IKAROS on the launch pad Taken on May 17, 2010, about 24 hours before the planned launch of Akatsuki and IKAROS toward Venus. They are stacked aboard an H-IIA rocket. Credit: Mitsubishi Heavy Industries, Ltd.

If you are a member of The Planetary Society, your name will be heading to Venus on both Akatsuki and IKAROS. The Planetary Society, a long-time proponent of solar sail technology, and Japan’s space exploration center, JSPEC/JAXA, have an agreement to collaborate and cooperate on public outreach and on technical information and results from IKAROS, which will help TPS plan for its upcoming launch of its own solar sail vehicle, LightSail-1, which they hope to launch in early 2011.

Emily Lakdawalla at the Planetary Blog has more details about the two missions and TPS’s involvement.

The H-IIA will also carry four other small satellites, developed by Japanese universities and other institutions. They include:

The 2-pound Negai CubeSat, developed by Soka University of Japan. Negai will test an information processing system during a three-week mission.

The WASEDA-SAT2, developed by Waseda University. The 2.6-pound spacecraft will conduct technology experiments in orbit.

The 3.3-pound KSAT spacecraft developed by Kagoshima University will conduct Earth observation experiments.

The 46-pound UNITEC-1 satellite from the Japanese University Space Engineering Consortium will test computer technologies and broadcast radio waves from deep space for decoding by amateur radio operators.

The rocket will launch from Japan’s Tanegashima Space Center in southern Japan.

For more information on IKAROS, read this interview with the project leader, Osamu Mori

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21 Responses

  1. Spoodle58 says:

    I really hope this solar sail mission gets a chance to test its tech, I am still disappointed over what happened to the Planetary Societys 1st Solar Sail Mission.

    I can’t wait to see the results.

  2. Torbjorn Larsson OM says:

    Nitpick: IIRC several probes such as Hayabusa has been flown successfully in solar sail mode to preserve fuel and/or make up for control failures. What hasn’t been tested is the practicality and acceleration of dedicated solar sails.

    Yeah, hope this is the last leg before test. But one crucial question will remain though: is solar flux powering “green” technology or “yellow”? [/bunny ducks (\_/) ]

  3. Aqua says:

    Good to see JAXA step up to the plate once again. I wish them the same success they enjoyed with the recent HTV flight and the attachment of the Kibo module to the ISS. Great stuff! Hai!

  4. Maxwell says:

    Solar sails are bad luck.

  5. Dark Gnat says:

    If I understand correctly, the solar sail craft will be heading toward Venus, which is closer to the Sun than Earth.

    I thought solar sails used solar wind to gently push the craft away from the Sun. Am I misunderstanding something?

  6. Maxwell says:

    I don’t know how “Steerable” any of these sails were meant to be, but I’d think its kind of like a boat in the wind. The direction of push is not always the direction of travel.

    So say you’re in an orbit around the sun and you tilt to catch the light (solar wind) while on the downward slope from apogee. I’m thinking you would slow down and, as a result, reduce your orbital distance and cut closer on perigee.

    I’ve got no idea if that is how its meant to work, but if so then you could use it to bop around the solar system.
    This sail is too small to have much of an effect, but any change in velocity would produce good science.

  7. Lawrence B. Crowell says:

    The solar craft is not going to Venus. To sail into the sun one would have to tack the solar irradiance. I am not sure how that could be done. Some other force is required to act on the craft. For sailboats tacking accomplished through the normal force on the craft. In space you need to have some other force. Maybe some magnetic interaction with the solar wind?


  8. tek_604 says:


    Hayabusa was powered by ion engines, as is Dawn. Hayabusa suffered problems with its engines on the return leg, and so has been coasting back to Earth.

  9. SteveZodiac says:

    Dark Gnat has a point, you need a keel to sail against the wind, a bit difficult in space. If the solar cells could accelerate ions then could a thrust vector replace a keel so that a sail could tack towards the sun?

  10. pfon71361 says:

    “The next launch attempt for the “Akatsuki” Venus Climate Orbiter and an the solar sail called IKAROS will be Thursday, May 20, at 21:58 UTC (May 20 at 5:58 EDT) – which is May 21 at 6:58 in Japan.” If May 20 at 5:58 EDT means May 20 at 5:58 AM then the launch in Japan would be May 20 at 18:58 PM (6:58 PM) since Japan is 13 hours ahead of EDT.

  11. Maxwell says:

    Sailboats work on three main factors. The resistance of the water, the force of the wind, and their momentum to carry them through the turns.

    In this case I’m thinking you have gravity (the water) orbital velocity (the momentum) and solar wind (the …uh, wind).

    I suspect you would tack by turning the sail relative to the source of your energy.
    If your in orbit around earth that means turning to the sun on the uphill and turning edge on for the downhill to raise your orbit.

    Now the real sails are supposed to be miles wide. So I don’t have a clue how they would actually turn a flimsy structure of that scale.

  12. Tony says:

    I really hope this Solar Sail Missions will be sended succeed! Good luck to Jap

  13. solrey says:

    The solar sail mission is not using the sail to get to Venus. It’s going to coast there on a similar trajectory as the Venus probe. Once it’s “on station” near Venus the solar sail will then be deployed. You can’t tack without a keel in a denser medium than what the sail is in. The keel keeps it from capsizing. You also need a sail that’s pliable enough to form the shape of an airfoil because it’s that airfoil shape that produces the horizontal “lift”, or thrust to propel the vessel against the wind. That’s what all that rigging is for, to fine tune the shape of the airfoil in any direction so you can zig-zag into the wind.

    The solar sail is designed more like a parachute than a sail. Now it might be possible to have some directional control of lateral movement if the length of each cable between the probe and the sail could be adjusted as is done with a parachute. I believe the solar sail concept also uses a VASIMR for a maneuvering thruster. But with the sail deployed it’s still going to be limited to moving in the direction of the solar wind away from the sun. The only option for moving toward the sun against the solar wind would be to haul the sail in and slingshot around a planet.

    Since the solar “wind” is really plasma a solar sail might not survive in that dynamic electromagnetic environment. I think they’ll discover a few surprises as a result. 😉

  14. xrayexplorer says:

    I do not think the Solar Sail actually uses the Solar Wind but rather the pressure exerted by light which is substantially greater in force than any force exerted by the charged particles forming the solar wind.

  15. solrey says:

    Actually “tacking” into the solar wind could be done if the sails were deployed out like tail fins. A “clamshell” design with four isosceles triangles might work. The frame would be similar to a box kite. Spread the tips of the triangles out for fins or pull the tips together for a parachute. In the fin configuration, moving toward the sun against the solar wind after a slingshot, each tip could be adjusted individually to change the angles of the fins for some maneuverability. The probe would be like the tip of a dart.

  16. Trippy says:

    You’re all (well, maybe not all) forgetting about the fact that we’re dealing with Vectors, three of them to be precise.

    The force exerted by the sunlight on the solar sail. This force is away from the sun.
    Gravity – This forces is towards the sun.
    Momentum – this is in the direction of travel.

    Given that an orbit is (essentially) a balance between gravity and inertia, getting closer to the sun is easy-peasey lemon squeezy. There are two requirements, and two requirements only to doing this with a solar sail:
    1. The outward radiation force is less than the inwards gravitational force.
    2. The sunlight does work to overcome the inertia of the craft.

    Consider this grossly over simplified ASCII diagram which I will now attempt.


    Consider the scenario where the ‘\’ represents the solar sail propelled probe, and the ‘(‘ represents the direction of motion.

    If the sun is ‘below’ the solar sail, and the solar sail is at an angle of 45° to the sunlight, then the sunlight will have an incident angle of 45° to the surface of the probe, and be reflected by the probe at an angle of 45° to the probe. This will ’cause’ a force normal to the surface of the probe, which will be at an angle of 45° to the direction of motion, but opposing the direction of motion.

    This force can be considered then to have two components, one opposing the direction of motion, and one opposing gravity.

    The force opposing the direction of motion will cause the craft to deccelerate, and as long as the component of the force opposing gravity is less than the force of gravity acting on the probe, then the probe will ‘fall’ towards the sun at some reduced rate.

    Venus with no fuel.

    Easy Peasey Lemon Squeezey.

  17. Trippy says:

    I think there’s a couple of places in the last post where I said Inertia, but meant momentum.


  18. Trippy says:

    It has occured to me that there is a second, equally easy way of doing it.

    The first step is to launch the solar sail propelled vehicle into an orbit that’s “eliptical enough” so that it has ‘distinct’ sunbound and outward bound legs.

    On the sunbound leg, the direction of motion and the direction of the force applied by the solar sail can be easily opposed, and so decceleration is pretty straight forward.

    The trick then comes in the outward bound leg where the direction of force applied by the sunlight and the direction of motion of the spacecraft are aligned, you have a couple of options here. First you could use the method outlined above to provide decceleration on the outward leg, or, you could simply angle the space craft so that the acceleration provided on the outward leg is less than the deceleration on the sunbound leg (increasing the angle of incidence as well as changing the direction of the vector, reduces the size of the vector by reducing the effective cross section of the sail (and therefore the number of photons per square meter).

    And so we now have two methods of using a solar sail to travel inwards.

  19. Olaf says:

    I think your explanation makes sense Trippy. We always fail to think in orbits and ellipses.

    The spacecraft has no direct Earth Sun movement , but an elliptical orbit.

  20. Torbjorn Larsson OM says:

    @ tek_604:

    Here is a reference:

    “For three-axis control, you need to be able to control the spacecraft’s spin around three perpendicular axes. Pilots (or anyone who’s ever tried a flight simulator) will recognize the terms pitch, yaw, and roll. Hayabusa’s one remaining reaction wheel can control the spacecraft’s yaw. The ion engines are gimbaled, and could be used to control yaw and pitch. There’s two directions there, but one is redundant with the remaining reaction wheel. So that leaves the roll direction uncontrolled. How the heck did the Hayabusa team reestablish three-axis control then?

    Any guesses? Hint: longtime supporters of The Planetary Society will be happy to see yet another application of this principle!

    The answer: the Hayabusa team is using photon pressure off of slightly tilted solar panels to control the roll axis. In other words, they’re doing attitude control by solar sailing. And they’re not just doing it as a neat trick to save fuel; solar sailing is what’s enabling them to bring the plucky spacecraft back home, because without it, they wouldn’t be able to control their spacecraft. [With thanks to Emily Lakdawalla.]”

    I’m also fairly certain that Messenger tries out some of the same, but for fuel savings.

  21. Aodhhan says:

    The craft will not be going directly towards the Sun, therefore it can tack slightly to gain energy.
    Visualize a clock. The Sun is in the center; the Earth is at the 5:00 marker on the edge of the clock, and the craft is shooting towards 2:00 marker (where Venus will be) although it is a bit closer to the center of the clock than Earth. Perhaps even look at Earth being at the 6 or 7:00 position.

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