IKAROS - how does it tack against the solar wind?

[Valamir]

I have a question about Japan's IKAROS solar sail craft that I hope someone can answer.

When a sail boat sails into the wind it is the boat's rudder that makes it possible to make headway by tacking; the reaction force of the rudder against the water provides the force to keep the boat from being driven backwards. The IKAROS solar sail is sailing towards Venus in the inner solar system. How does a solar sail make progress against the solar wind when moving towards the inner solar system when there isn't a rudder or a medium for a rudder to work against?

 

[MeteorWayne]

It's a good question, but probably belongs in the mission thread in the Mission and Launches forum. So keep an eye out to see if it's been moved.

MW

 

[mental_avenger]

The answer is that IKAROS cannot and will not tack against the solar wind.

 

[EarthlingX]

I have a question about Japan's IKAROS solar sail craft that I hope someone can answer.

When a sail boat sails into the wind it is the boat's rudder that makes it possible to make headway by tacking; the reaction force of the rudder against the water provides the force to keep the boat from being driven backwards. The IKAROS solar sail is sailing towards Venus in the inner solar system. How does a solar sail make progress against the solar wind when moving towards the inner solar system when there isn't a rudder or a medium for a rudder to work against?

I will try this, and let somebody correct me.

I think about the curve which spacecraft would take only from launch as a keel, if you want. Trick is, to make tiny adjustments to that curve, at the part of the curve, where adjustments have most influence. Similar to Tao yin.

It doesn't use solar wind, just light radiation, photons, through radiation pressure.
Solar sail can also save on propulsion mass used for spacecraft orientation, among other things.

 

[orionrider]

Obviously, additional propulsion or gravitational influence is required:
http://en.wikipedia.org/wiki/Solar_sail ... ht_example

 

[mental_avenger]

It doesn't use solar wind, just light radiation, photons, through radiation pressure.

At least someone was paying attention. +1 for EarthlingX.

Solar sail can also save on propulsion mass used for spacecraft orientation, among other things.

Correct. In some cases a solar sail could assist in the acceleration or deceleration of a spacecraft. Because of the velocity of the solar radiation, a solar sail can assist propulsion regardless of how much thrust is being produced by the main engine.

 

[mental_avenger]

I will try this, and let somebody correct me.

I think about the curve which spacecraft would take only from launch as a keel, if you want. Trick is, to make tiny adjustments to that curve, at the part of the curve, where adjustments have most influence. Similar to Tao yin.

I have studied the physics of solar sails in detail. I determined that a totally flat solar sail cannot tack in space against the Solar Radiation (or the solar wind ) In order to tack, the spacecraft has to have something that will function similar to a keel on a watercraft. There is nothing to keep the sail at a 45º angle to the direction of Light. Without some rotational “anchor”, the sail will rotate around and orient edge on to the direction of the solar light.

My solution is what I called a “Tail Sail”. That is a small solar sail out to the side on a boom, which can be used to counteract the normal rotational effect of radiation pressure on the sail.

The procedure is more like jibing, than tacking, but it is really neither of those. The solar sail is used to slow down the craft or speed up the craft in orbit. It is the change in orbital velocity that moves the craft closer to, or further from, the Sun, in a spiral orbital path.

If a solar sail was stationary, not in orbit about the Sun, the only direction it could move is directly away from the Sun.

 

[silylene]

I think it is possible, although not on IKAROS, but on my imaginary solar sail spacecraft.

Imagine a spacecraft in which there is a very efficient thermal conductor built into the solar sails...for example, fluid filled and circulating nanochannels which draw heat from the sails (such very thin membranes designed for RO water purification by some high tech extrusion processes exist - I have seen them made, and held them in my hands). The sails are not 100% reflective of course, perhaps 90%, and the other 10% of the light radiation impinging on these nanochanneled sails is absorbed as heat, and then transferred to another part of the spacecraft via my hypothetical heat fluid transfer mechanism. If the heat is then transferred into a special vane which functions as a rudder, this vane being shadowed behind the sail, and the vane then sheds heat (infrared light), this will give a slight acceleration in the direction the flat area of the vane is pointing. This will give a lateral acceleration component. Hence the craft will slowly alter direction.

I should patent this. But the patent would expire before it is commercially useful.

 

[mental_avenger]

First, I am unable to visualize your concept as you described it. Perhaps a diagram would help.

I see two problems with your design. A solar sail must be very thin and very light. I don’t think it would be possible to have a multi-layer sail with fluid in between the layers, regardless of how nano it is. The fact is that the light pressure on a solar sail would be so slight, that it would only be practical on very low mass vehicles. Anything that would add mass would work against the system.

Also, impact by extremely small particles would perforate the membrane and the fluid would leak out.

 

[orionrider]

No need for a 'rudder'. The solar sail must be doubling as a solar panel, generating electricity for attitude control via reaction wheels. Enough to counter the tiny photon pressure and keep the craft at an angle to the sun, thereby slowly reducing orbital velocity and coming closer to the sun.

Contrary to the above path, which is designed to get the best acceleration out via a gravity assist around the sun, the Ikaros would be spiraling in, then it needs to stop. At the end of its journey, Venus captures the craft and the sail can be used for aerobraking to a circular orbit.

 

[silylene]

First, I am unable to visualize your concept as you described it. Perhaps a diagram would help.

I see two problems with your design. A solar sail must be very thin and very light. I don’t think it would be possible to have a multi-layer sail with fluid in between the layers, regardless of how nano it is. The fact is that the light pressure on a solar sail would be so slight, that it would only be practical on very low mass vehicles. Anything that would add mass would work against the system.

Also, impact by extremely small particles would perforate the membrane and the fluid would leak out.

MA, the sheets we have made are about 10 micrometers thick, and the channels within are about 5 microns in diameter. In comparison a human head hair is about 80 micrometers in diameter. The mass of the sheets would be the same, as the fluid in the channels would have about the same density as the sheet. The sheet mass/area are comparable or better to what IKAROS has now.

Micrometeors is a problem. Perhaps we could use self-healing plastics. This is also known technology.

 

[Valamir]

Thanks guys for the answers.

The H-reversal trajectory explained it. It appears that the sail is oriented so that the sail decelerates the craft's velocity vector component that is tangential to its solar orbit. That means that even though it is also being pushed away from the sun at a direction that is normal to its solar orbit, as the tangential velocity decreases the greater solar gravitational force causes it to fall inwards toward the sun.

 

[SpaceTas]

Have a look at the wiki article. The orientation of the sail is dome with variable reflectance liquid crystal panels around edge.
Make one side darker than other, less reflection on that side, less force on that side, so craft will turn; dark side moving toward sun .... switch off and will keep that orientation (same reflection everywhere so no net turning moment)

very neat.

Orientate craft so light force is opposite orbital velocity craft slows down and "falls" inward.



Read Sunjammer by Arthur C Clarke

 

[bdewoody]

On a water bound sailboat it is not exactly the rudder so much as the keel that allows the boat to sail upwind. Note that only a fore and aft rigged boat can sail efficiently upwind. A square rigged vessel can just barely make headway upwind. On a fore and aft rigged sailboat or ship when the sails are sheeted in as close to parallel to the keel as possible the sails act as an air foil providing lift which is tranlated through the keel as forward motion. A sailboat going upwind can actually sail faster than the windspeed. Going downwind with the sails perpendicular to the keel a sailboat an only go as fast as the wind, less a little due to friction in the water. It will be interesting to see whether science can figure a way for solar sails to function in a similar manner.