Space Sailing
from Gerhard Holtkamp, 21. June 2010, 20:25
For the first time a spacecraft moves across interplanetary space with the help of a sail being propelled by the light of the Sun...
In January I reported on this blog about two space missions being planned this year to use solar sails for propulsion (Sailing to Venus). One of the two, the Japanese IKAROS mission, is successfully on its way.
On May 21, 2010 the Japanese Venus probe AKATSUKI was launched from the Tanegashima space center. This spacecraft has passed its initial tests with flying colors and is heading to Venus. Co-launched with AKATSUKI was the small solar power sail demonstrator IKAROS.
After a few weeks of initial tests the solar sail was deployed. As with every space mission deploying something always bears risks of failure. And a large thin membrane of a solar sail poses its own problems. But all went just as planned. This is a major success for Japanese space engineers and for solar sailing in particular.
To verify the correct deployment of the solar sail pictures were needed. As it would have been difficult to take these pictures by a camera directly attached to the sail the Japanese engineers came up with an ingenious solution: A tiny camera with a small radio transmitter was ejected from the sail and could take pictures of the whole assembly while flying away. 
Now that the solar sail has been deployed the second phase of the mission begins: Verification of the acceleration of the sail by the light of the Sun and the navigation of such a sail.
To control the acceleration and direction of flight of a solar sail you have to orient its attitude in defined ways with regard to the Sun. This can be done in various ways. You could attach small auxilliary sails at the ends or you could change the center of mass with regard to the center of light pressure via a deployable boom. But the Japanese came up with yet another interesting idea: Liquid cristal devices have been added to the sail. They can be switched to change their reflection ratio. Changing this ratio at different sides of the sail will cause a torque and thus a change in attitude.
It will be interesting following this mission over the next few weeks (and maybe months - there is an open end to it!). But we can already congratulate the Japanese to having opened up a new way of space travel: The age of solar sailing has begun!
In January I reported on this blog about two space missions being planned this year to use solar sails for propulsion (Sailing to Venus). One of the two, the Japanese IKAROS mission, is successfully on its way.
On May 21, 2010 the Japanese Venus probe AKATSUKI was launched from the Tanegashima space center. This spacecraft has passed its initial tests with flying colors and is heading to Venus. Co-launched with AKATSUKI was the small solar power sail demonstrator IKAROS.
After a few weeks of initial tests the solar sail was deployed. As with every space mission deploying something always bears risks of failure. And a large thin membrane of a solar sail poses its own problems. But all went just as planned. This is a major success for Japanese space engineers and for solar sailing in particular.
To verify the correct deployment of the solar sail pictures were needed. As it would have been difficult to take these pictures by a camera directly attached to the sail the Japanese engineers came up with an ingenious solution: A tiny camera with a small radio transmitter was ejected from the sail and could take pictures of the whole assembly while flying away. 
Now that the solar sail has been deployed the second phase of the mission begins: Verification of the acceleration of the sail by the light of the Sun and the navigation of such a sail.
To control the acceleration and direction of flight of a solar sail you have to orient its attitude in defined ways with regard to the Sun. This can be done in various ways. You could attach small auxilliary sails at the ends or you could change the center of mass with regard to the center of light pressure via a deployable boom. But the Japanese came up with yet another interesting idea: Liquid cristal devices have been added to the sail. They can be switched to change their reflection ratio. Changing this ratio at different sides of the sail will cause a torque and thus a change in attitude.
It will be interesting following this mission over the next few weeks (and maybe months - there is an open end to it!). But we can already congratulate the Japanese to having opened up a new way of space travel: The age of solar sailing has begun!
If a solar sail becomes an effective method of propelling craft through space, it will greatly decrease the cost of pace travel, since it will not require fuel.