Here's the shipping forecast for space
Not so much an armada, more like a flotilla.
We're going to see a series of spacecraft launch in the next year or so that try to demonstrate the principle of solar sailing.
These craft will deploy very large, ultra-thin membranes to catch the light of our star to push them through space.
The idea has long been discussed and now a few groups are very close to showing us the reality. Or so we hope.
First out of the space marina is , which will be launched on the same rocket as the nation's (just as soon as the ).
In the coming weeks, this 1.6m-diameter spacecraft will run out an almost 200-square-metre solar sail.
Photons, or particles of light, falling on this highly reflective, ultra-thin (7.5 microns) surface will exert a pressure.
This force will be tiny...but it'll be continuous and it'll be free; and over time, the acceleration gained should amount to quite a kick.
Ikaros will chase after the main probe to Venus.
Solar sails will never replace conventional propulsion systems like chemical thrusters, but they do have the potential to play a much greater role in certain types of space mission.
Louis Friedman, from the space advocacy group The Planetary Society, is a big fan of the technology. The society's , a much smaller venture than Ikaros, could launch by the year's end. Louis told me:
"The potential that we all seek is the ultra-lightweight, very fast spacecraft that doesn't use fuel. That's the future of interstellar travel; that's the long-term goal. The intermediate goals are to be able to use this technology to 'hover' in interplanetary space at particular points for monitoring, say, the Sun or monitoring the Earth's geomagnetic poles or magneto-tail; and then also to fly between the planets without using fuel."
Already some satellites in geostationary orbit above the Earth use flaps on the ends of their solar panels to catch the pressure of sunlight to maintain their correct attitude.
This leads to a considerable saving on the fuel that would otherwise have to be sent surging through the satellites' thrusters, and operators have found this strategy can extend the longevity of some missions by many months.
British forces in Afghanistan are talking through communications spacecraft right now () that use precisely this technique.
Helping a satellite to point in the right direction is one thing, however; using sunlight to drive an interplanetary probe is a very different kind of challenge.
Just deploying these sails is a big ask. In order for sunlight to provide sufficient pressure to propel a spacecraft forward, a solar sail must capture as much sunlight as possible. This means that the surface of the sail must be big - very big.
And packing up that enormous structure for launch and then getting it out again in space is tricky. Ikaros is going to use a spin technique.
The disc-shaped craft will be despatched with the sail wrapped around it. The plan is to unbutton the four weighted corners of the membrane and allow them to fly outwards as the central module turns. This should pull the sail taught.
Dr Vaios Lappas is working on a British project called which should launch next year. The UK mission will be slightly smaller than LightSail-1 but both experiments will use booms, or ribs, to unfurl their membranes and keep them flat.
Dr Lappas is excited to see how the Japanese approach works.
"We thought about doing it the same way but decided in the end it was higher risk. Ikaros relies on gyroscopic stiffness. This satellite will need to be continuously spinning and when you've got large structures spinning, things can go wrong. Think of a fishing line with a mass at the tip of it and you're rotating it with your hand. That whole structure looks like a disc but just a tiny little movement from your hand can introduce a wobble. It's an interesting concept and I wish them well. I really hope it works."
Nasa did a a few years back in which they worked out that a 200kg spacecraft with a solar sail 400 metres across could get to 200 times the Sun-Earth distance in about 15 years. By comparison, the, which is the most distant man-made object, left our planet 32 years ago and is still only 113 times the Sun-Earth distance.
The futurologists envision solar sail spacecraft being driven out of the Solar System by the additional impetus of a powerful laser beam directed at them from Earth.
We're some way away from that. Let's see first if Ikaros gets a fair wind.
The Japanese space agency (Jaxa) is being cautious about its milestones. Just getting Ikaros to deploy properly will be some achievement. But the sail then has some added extras which will be fascinating to see if they work.
Embedded in the sail are LCDs to change the reflectivity of the membrane. The idea is that by introducing some asymmetry, the sail can be trimmed and the direction of the spacecraft changed.
Also embedded in the sail are some solar cells. The idea here is to prove the principle of generating power from a solar sail.
Jaxa's thinking is that future craft could be equipped not only with a solar membrane but with an ion propulsion engine as well.
Under this scenario, sunlight would push on the sail whilst at the same time providing the electricity to accelerate a charged gas, thus providing additional thrust. Neat.
Watch this space.
±õ’m 
Comments
or to comment.