I was wrong. IKAROS is in a true vacuum and uses sunlight pressure, while the Crookes radiometer is using the movement of air molecules around the paddles in a partial vacuum. Learn something new everyday.
- LRK -
-------------------------------------
http://www.jaxa.jp/press/2010/
Small Solar Power Sail Demonstrator 'IKAROS' Successful Attitude Control by Liquid Crystal Device
July 23, 2010 (JST)
Japan Aerospace Exploration Agency (JAXA)
The Japan Aerospace Exploration Agency (JAXA) performed an attitude control experiment (*1) of the solar sail of the Small Solar Power Sail Demonstrator "IKAROS," after its deployment, using an attitude control device, or the liquid crystal device, on July 13, 2010 (Japan Standard Time, the following dates and time are JST, unless otherwise noted. ) We have since confirmed that the attitude control performance was successfully accomplished as planned through post-experiment data verification and analysis. The IKAROS was launched from the Tanegahima Space Center on May 21, 2010.
The liquid crystal device is a thin-film instrument to change the surface reflection characteristics of sunlight by turning on and off the power of the device. It is an engineering test device to control attitude using only sunlight pressure without any additional propellant.
Two kinds of technologies are extremely important for a spin solar sail, like the IKAROS's sail: one is technology to generate small attitude control torque (*2) constantly without causing oscillation on the large flexible sail, and the other is technology to control the direction (attitude) of large angular momentum generated by the spinning membrane without consuming propellant. The attitude control method using sunlight pressure is one of the most feasible methods for satisfying the above two technological requirements, and JAXA has been a global leader in developing this original method.
JAXA will continue the attitude control experiment by the IKAROS to evaluate the details of the attitude control performance while continuing to conduct research on attitude control technology using sunlight pressure as a technology that enables navigation for longer in time and further in distance by a solar sail.
*1 The IKAROS usually uses its onboard thrusters attached to its main body, not the liquid crystal device, for attitude control during normal operations.
*2 Torque is a moment of force to rotate an object about an axis or pivot. For the attitude control experiment using the liquid crystal device this time, the attitude control torque was minimal as sunlight pressure was used for attitude control, thus, by generating torque constantly, it was possible to control attitude without causing vibration on the membrane.
snip
------------------------------
http://www.jaxa.jp/projects/
------------------------------
Some on the Crookes radiometer.
- LRK -
------------------------------
http://en.wikipedia.org/wiki/
The Crookes radiometer, also known as the light mill, consists of an airtight glass bulb, containing a partial vacuum. Inside are a set of vanes which are mounted on a spindle. The vanes rotate when exposed to light, with faster rotation for more intense light, providing a quantitative measurement of electromagnetic radiation intensity. The reason for the rotation has historically been a cause of much scientific debate.[1][2]
It was invented in 1873 by the chemist Sir William Crookes as the by-product of some chemical research. In the course of very accurate quantitative chemical work, he was weighing samples in a partially evacuated chamber to reduce the effect of air currents, and noticed the weighings were disturbed when sunlight shone on the balance. Investigating this effect, he created the device named after him. It is still manufactured and sold as a novelty item.
snip
------------------------------
http://www.howstuffworks.com/
------------------------------
Thanks for looking up with me.
- LRK -
Web Site: http://lkellogg.vttoth.com/
BlogSpot: http://kelloggserialreports.
Comments accepted here - http://lunar-update.blogspot.
RSS link: http://kelloggserialreports.
Newsletter: https://news.altair.com/
==============================
http://www.howstuffworks.com/
How does a Crookes' radiometer work?
A Crookes' radiometer has four vanes suspended inside a glass bulb as you've described. Inside the bulb, there is a good vacuum. When you shine a light on the vanes in the radiometer, they spin -- in bright sunlight, they can spin at several thousand rotations per minute!
The vacuum is important to the radiometer's success. If there is no vacuum (that is, if the bulb is full of air), the vanes do not spin because there is too much drag. If there is a near-perfect vacuum, the vanes do not spin unless they are held in a frictionless way. If the vanes have a frictionless support and the vacuum is complete, then photons bouncing off the silver side of the vanes push the vanes, causing them to rotate. However, this force is exceedingly small. If there is a good but incomplete vacuum, then a different effect called thermal transpiration occurs along the edges of the vanes, as described on this page. The effect looks as though the light is pushing against the black faces. The black side of the vane moves away from the light.
snip
==============================
http://www.xs4all.nl/~johanw/
How does a light-mill work?
In 1873, while investigating infrared radiation and the element thallium, the eminent Victorian experimenter Sir William Crookes developed a special kind of radiometer, an instrument for measuring radiant energy of heat and light. Crookes's Radiometer is today marketed as a conversation piece called a light-mill or solar engine. It consists of four vanes, each of which is blackened on one side and silvered on the other. These are attached to the arms of a rotor which is balanced on a vertical support in such a way that it can turn with very little friction. The mechanism is encased inside a clear glass bulb that has been pumped out to a high, but not perfect, vacuum.
When sunlight falls on the light-mill, the vanes turn with the black surfaces apparently being pushed away by the light. Crookes at first believed this demonstrated that light radiation pressure on the black vanes was turning it around, just like water in a water mill. His paper reporting the device was refereed by James Clerk Maxwell, who accepted the explanation Crookes gave. It seems that Maxwell was delighted to see a demonstration of the effect of radiation pressure as predicted by his theory of electromagnetism. But there is a problem with this explanation. Light falling on the black side should be absorbed, while light falling on the silver side of the vanes should be reflected. The net result is that there is twice as much radiation pressure on the metal side as on the black. In that case the mill is turning the wrong way.
When this was realised, other explanations for the radiometer effect were sought and some that people came up with are still mistakenly quoted as correct. It was clear that the black side of each vane would absorb heat from infrared radiation more than the silver side. This would cause the rarefied gas to be heated on the black side. In that case, the obvious explanation is that the pressure of the gas on the darker side increases with its temperature, creating a higher force on the dark side of the vane which thus pushes the rotor around. Maxwell analysed this theory carefully — presumably being wary about making a second mistake. He discovered that, in fact, the warmer gas would simply expand in such a way that there would be no net force from this effect, just a steady flow of heat across the vanes. So this explanation in terms of warm gas is wrong, but even the Encyclopaedia Britannica gives this false explanation today. A variation on this theme is that the motion of the hot molecules on the black side of the vane provide the push. Again this is not correct, and could only work if the mean free path between molecular collisions were as large as the container, instead of its actual value of typically less than a millimetre.
snip
The correct solution to the problem was provided qualitatively by Osborne Reynolds, better remembered for the "Reynolds number". Early in 1879 Reynolds submitted a paper to the Royal Society in which he considered what he called "thermal transpiration", and also discussed the theory of the radiometer. By "thermal transpiration", Reynolds meant the flow of gas through porous plates caused by a temperature difference on the two sides of the plates. If the gas is initially at the same pressure on the two sides, it flows from the colder to the hotter side, resulting in a higher pressure on the hotter side if the plates cannot move. Equilibrium is reached when the ratio of pressures on either side is the square root of the ratio of absolute temperatures. This counterintuitive result is due to tangential forces between the gas molecules and the sides of the narrow pores in the plates. The effect of these thermomolecular forces is very similar to the thermomechanical effects of superfluid liquid helium. This liquid, which lacks all viscosity, will climb the sides of its container towards a warmer region. In fact, this form of liquid helium climbs so quickly up the sides of a thin capillary tube dipped into it, that a fountain is produced at the tube's other end.
The vanes of a radiometer are not porous. To explain the radiometer, therefore, one must focus attention not on the faces of the vanes, but on their edges. The faster molecules from the warmer side strike the edges obliquely and impart a higher force than the colder molecules. Again, these are the same thermomolecular forces responsible for Reynolds' thermal transpiration. The effect is also known as thermal creep, since it causes gases to creep along a surface that has a temperature gradient. The net movement of the vane due to the tangential forces around the edges is away from the warmer gas and towards the cooler gas, with the gas passing around the edge in the opposite direction. The behaviour is just as if there were a greater force on the blackened side of the vane (which as Maxwell showed is not the case); but the explanation must be in terms of what happens not at the faces of the vanes, but near their edges.
snip
==============================
http://trs-new.jpl.nasa.gov/
Thermal Transpiration in Microsphere Membranes
Marcus Young, Yen Lin Han, E.P. Muntz, G. Shiflett
USC AME Department
Andrew Ketsdever
Air Force Research Laboratory
Amanda Green
Jet Propulsion Laboratory
Abstract. Self-assembled glass microsphere membranes as an alternative transpiration membrane for application in a Knudsen Compressor are discussed. A performance model is constructed and used to compare the performance of glass microsphere membranes to silicon aerogel membranes for this application. An initial experimental Knudsen Compressor stage based on glass microsphere membranes has been designed and experimentally tested. Preliminary performance results show a discrepancy between the predicted and observed pressure differences produced by the single stage. Several possible explanations for the discrepancy are discussed. Two variations of a proposed design for a Knudsen Compressor employing a microsphere transpiration membrane are discussed. It is concluded that beds of glass microspheres may be attractive candidates for transpiration membrane materials over the entire pressure range of operation for a micro-scale vacuum pump, lOmTorr to 760 Torr.
snip
==============================
WHAT THE MIND CAN CONCEIVE, AND BELIEVE, IT WILL ACHIEVE - LRK
==============================
Small Solar Power Sail Demonstrator 'IKAROS' Successful Attitude Control by Liquid Crystal Device
July 23, 2010 (JST)
Japan Aerospace Exploration Agency (JAXA)
The Japan Aerospace Exploration Agency (JAXA) performed an attitude control experiment (*1) of the solar sail of the Small Solar Power Sail Demonstrator "IKAROS," after its deployment, using an attitude control device, or the liquid crystal device, on July 13, 2010 (Japan Standard Time, the following dates and time are JST, unless otherwise noted. ) We have since confirmed that the attitude control performance was successfully accomplished as planned through post-experiment data verification and analysis. The IKAROS was launched from the Tanegahima Space Center on May 21, 2010.
The liquid crystal device is a thin-film instrument to change the surface reflection characteristics of sunlight by turning on and off the power of the device. It is an engineering test device to control attitude using only sunlight pressure without any additional propellant.
Two kinds of technologies are extremely important for a spin solar sail, like the IKAROS's sail: one is technology to generate small attitude control torque (*2) constantly without causing oscillation on the large flexible sail, and the other is technology to control the direction (attitude) of large angular momentum generated by the spinning membrane without consuming propellant. The attitude control method using sunlight pressure is one of the most feasible methods for satisfying the above two technological requirements, and JAXA has been a global leader in developing this original method.
JAXA will continue the attitude control experiment by the IKAROS to evaluate the details of the attitude control performance while continuing to conduct research on attitude control technology using sunlight pressure as a technology that enables navigation for longer in time and further in distance by a solar sail.
*1 The IKAROS usually uses its onboard thrusters attached to its main body, not the liquid crystal device, for attitude control during normal operations.
*2 Torque is a moment of force to rotate an object about an axis or pivot. For the attitude control experiment using the liquid crystal device this time, the attitude control torque was minimal as sunlight pressure was used for attitude control, thus, by generating torque constantly, it was possible to control attitude without causing vibration on the membrane.
snip
------------------------------
http://www.jaxa.jp/projects/
------------------------------
Some on the Crookes radiometer.
- LRK -
------------------------------
http://en.wikipedia.org/wiki/
The Crookes radiometer, also known as the light mill, consists of an airtight glass bulb, containing a partial vacuum. Inside are a set of vanes which are mounted on a spindle. The vanes rotate when exposed to light, with faster rotation for more intense light, providing a quantitative measurement of electromagnetic radiation intensity. The reason for the rotation has historically been a cause of much scientific debate.[1][2]
It was invented in 1873 by the chemist Sir William Crookes as the by-product of some chemical research. In the course of very accurate quantitative chemical work, he was weighing samples in a partially evacuated chamber to reduce the effect of air currents, and noticed the weighings were disturbed when sunlight shone on the balance. Investigating this effect, he created the device named after him. It is still manufactured and sold as a novelty item.
snip
------------------------------
http://www.howstuffworks.com/
------------------------------
Thanks for looking up with me.
- LRK -
Web Site: http://lkellogg.vttoth.com/
BlogSpot: http://kelloggserialreports.
Comments accepted here - http://lunar-update.blogspot.
RSS link: http://kelloggserialreports.
Newsletter: https://news.altair.com/
==============================
http://www.howstuffworks.com/
How does a Crookes' radiometer work?
A Crookes' radiometer has four vanes suspended inside a glass bulb as you've described. Inside the bulb, there is a good vacuum. When you shine a light on the vanes in the radiometer, they spin -- in bright sunlight, they can spin at several thousand rotations per minute!
The vacuum is important to the radiometer's success. If there is no vacuum (that is, if the bulb is full of air), the vanes do not spin because there is too much drag. If there is a near-perfect vacuum, the vanes do not spin unless they are held in a frictionless way. If the vanes have a frictionless support and the vacuum is complete, then photons bouncing off the silver side of the vanes push the vanes, causing them to rotate. However, this force is exceedingly small. If there is a good but incomplete vacuum, then a different effect called thermal transpiration occurs along the edges of the vanes, as described on this page. The effect looks as though the light is pushing against the black faces. The black side of the vane moves away from the light.
snip
==============================
http://www.xs4all.nl/~johanw/
How does a light-mill work?
In 1873, while investigating infrared radiation and the element thallium, the eminent Victorian experimenter Sir William Crookes developed a special kind of radiometer, an instrument for measuring radiant energy of heat and light. Crookes's Radiometer is today marketed as a conversation piece called a light-mill or solar engine. It consists of four vanes, each of which is blackened on one side and silvered on the other. These are attached to the arms of a rotor which is balanced on a vertical support in such a way that it can turn with very little friction. The mechanism is encased inside a clear glass bulb that has been pumped out to a high, but not perfect, vacuum.
When sunlight falls on the light-mill, the vanes turn with the black surfaces apparently being pushed away by the light. Crookes at first believed this demonstrated that light radiation pressure on the black vanes was turning it around, just like water in a water mill. His paper reporting the device was refereed by James Clerk Maxwell, who accepted the explanation Crookes gave. It seems that Maxwell was delighted to see a demonstration of the effect of radiation pressure as predicted by his theory of electromagnetism. But there is a problem with this explanation. Light falling on the black side should be absorbed, while light falling on the silver side of the vanes should be reflected. The net result is that there is twice as much radiation pressure on the metal side as on the black. In that case the mill is turning the wrong way.
When this was realised, other explanations for the radiometer effect were sought and some that people came up with are still mistakenly quoted as correct. It was clear that the black side of each vane would absorb heat from infrared radiation more than the silver side. This would cause the rarefied gas to be heated on the black side. In that case, the obvious explanation is that the pressure of the gas on the darker side increases with its temperature, creating a higher force on the dark side of the vane which thus pushes the rotor around. Maxwell analysed this theory carefully — presumably being wary about making a second mistake. He discovered that, in fact, the warmer gas would simply expand in such a way that there would be no net force from this effect, just a steady flow of heat across the vanes. So this explanation in terms of warm gas is wrong, but even the Encyclopaedia Britannica gives this false explanation today. A variation on this theme is that the motion of the hot molecules on the black side of the vane provide the push. Again this is not correct, and could only work if the mean free path between molecular collisions were as large as the container, instead of its actual value of typically less than a millimetre.
snip
The correct solution to the problem was provided qualitatively by Osborne Reynolds, better remembered for the "Reynolds number". Early in 1879 Reynolds submitted a paper to the Royal Society in which he considered what he called "thermal transpiration", and also discussed the theory of the radiometer. By "thermal transpiration", Reynolds meant the flow of gas through porous plates caused by a temperature difference on the two sides of the plates. If the gas is initially at the same pressure on the two sides, it flows from the colder to the hotter side, resulting in a higher pressure on the hotter side if the plates cannot move. Equilibrium is reached when the ratio of pressures on either side is the square root of the ratio of absolute temperatures. This counterintuitive result is due to tangential forces between the gas molecules and the sides of the narrow pores in the plates. The effect of these thermomolecular forces is very similar to the thermomechanical effects of superfluid liquid helium. This liquid, which lacks all viscosity, will climb the sides of its container towards a warmer region. In fact, this form of liquid helium climbs so quickly up the sides of a thin capillary tube dipped into it, that a fountain is produced at the tube's other end.
The vanes of a radiometer are not porous. To explain the radiometer, therefore, one must focus attention not on the faces of the vanes, but on their edges. The faster molecules from the warmer side strike the edges obliquely and impart a higher force than the colder molecules. Again, these are the same thermomolecular forces responsible for Reynolds' thermal transpiration. The effect is also known as thermal creep, since it causes gases to creep along a surface that has a temperature gradient. The net movement of the vane due to the tangential forces around the edges is away from the warmer gas and towards the cooler gas, with the gas passing around the edge in the opposite direction. The behaviour is just as if there were a greater force on the blackened side of the vane (which as Maxwell showed is not the case); but the explanation must be in terms of what happens not at the faces of the vanes, but near their edges.
snip
==============================
http://trs-new.jpl.nasa.gov/
Thermal Transpiration in Microsphere Membranes
Marcus Young, Yen Lin Han, E.P. Muntz, G. Shiflett
USC AME Department
Andrew Ketsdever
Air Force Research Laboratory
Amanda Green
Jet Propulsion Laboratory
Abstract. Self-assembled glass microsphere membranes as an alternative transpiration membrane for application in a Knudsen Compressor are discussed. A performance model is constructed and used to compare the performance of glass microsphere membranes to silicon aerogel membranes for this application. An initial experimental Knudsen Compressor stage based on glass microsphere membranes has been designed and experimentally tested. Preliminary performance results show a discrepancy between the predicted and observed pressure differences produced by the single stage. Several possible explanations for the discrepancy are discussed. Two variations of a proposed design for a Knudsen Compressor employing a microsphere transpiration membrane are discussed. It is concluded that beds of glass microspheres may be attractive candidates for transpiration membrane materials over the entire pressure range of operation for a micro-scale vacuum pump, lOmTorr to 760 Torr.
snip
==============================
WHAT THE MIND CAN CONCEIVE, AND BELIEVE, IT WILL ACHIEVE - LRK
==============================
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