Solar Sail Navigation
from Gerhard Holtkamp, 06. August 2010, 00:42
The first Japanese solar sail space mission can now be called a full success as the major milestones of the project have been achieved...
Twice this year I reported about the Japanese IKAROS solar sail demonstrator project. After it's successful launch on May 21, 2010 and a few weeks of initial tests the solar sail was deployed as planned. This constituted the first major milestone of the project as deploying large structures in space is not that easy.
In the weeks following the deployment of the solar sail the next major milestones (and the ones defining the full success of the project) were to check whether the light of the Sun does accelerate the sail as predicted and also to check whether the attitude of the sail can be changed by sunlight alone.
The Japanese aerospace agency JAXA has now reported that both the sail's acceleration as well as the attitude control performance tests have been conducted with success.
While the sail's acceleration is important for the sail to gain (or loose) energy and thus change it's trajectory controlling it's attitude determines in which direction the sail will accelerate. This is therefore essential for navigating a solar sail.
The method used by the Japanese to control the attitude is that they put liquid cristal devices around the perimeter of the sail which change their reflection ratio depending on whether there is an electric current running through them or not. To create a torque to change the attitude of the sail the liquid cristal devices on one side of the sail are turned on while they are off on the opposite side. Thus one side of the sail will reflect more sunlight which excerts a stronger force that the other side.
As the IKAROS sail is spinning the attitude-controlling liquid cristal devices had to be turned on and off in sync with the rotation to make sure that the torque always acts in the same direction. This was done for a limited time to check the correct funtioning. (Normally the attitude of the IKAROS sail is controlled by small chemical thrusters as can be found in ordinary satellites. This may sound like a sacrilege by solar sail purists but for a technology demonstrating mission it is prudent to include proven technology as well in case the experimental ones don't work as planned.)
Although the mission objectives of the IKAROS mission have now been achieved the tests will continue. It is important to get more data on the behaviour of the sail in deep space and compare these data with the computer models. This will help designers of future solar sail missions in their work. Without doubt Japan has become the leader in solar sail technology. We can expect interesting missions in the future!
Another development showing Japan's ever increasing determination to be a major space power is the announcement last week that from April next year on space launches from the Japanese facilities at Tanegashima and Uchinora will be able to be conducted year round.
Up to now Japanese space launches were restricted to no more than 190 days per year to periods outside the fishery seasons. This may sound strange to the rest of the world. After all there are plenty of fishing vessels off the Florida coast or off French Guyana. All it takes is to stay clear of a well defined area during the day of a rocket launch to avoid some rocket debris to fall on your boat.
But of course to the Japanese fish is not just another food group but an important element of their culture. Now however an agreement was reached between JAXA and the local fishery organizations. The total number of launches will be limited to 17 per year but this is far less than the Japanese have ever attempted so far and is hardly a restriction.
Opening up launch sites for year round operations is important in two ways: It will improve competitiveness for commercial launches but it also enables more possibilities for interplanetary missions which Japan is very actively involved in and which require highly restricted launch windows.
Space has become an integral part of Japanese culture.
Twice this year I reported about the Japanese IKAROS solar sail demonstrator project. After it's successful launch on May 21, 2010 and a few weeks of initial tests the solar sail was deployed as planned. This constituted the first major milestone of the project as deploying large structures in space is not that easy.
In the weeks following the deployment of the solar sail the next major milestones (and the ones defining the full success of the project) were to check whether the light of the Sun does accelerate the sail as predicted and also to check whether the attitude of the sail can be changed by sunlight alone.
The Japanese aerospace agency JAXA has now reported that both the sail's acceleration as well as the attitude control performance tests have been conducted with success.
While the sail's acceleration is important for the sail to gain (or loose) energy and thus change it's trajectory controlling it's attitude determines in which direction the sail will accelerate. This is therefore essential for navigating a solar sail.
The method used by the Japanese to control the attitude is that they put liquid cristal devices around the perimeter of the sail which change their reflection ratio depending on whether there is an electric current running through them or not. To create a torque to change the attitude of the sail the liquid cristal devices on one side of the sail are turned on while they are off on the opposite side. Thus one side of the sail will reflect more sunlight which excerts a stronger force that the other side.As the IKAROS sail is spinning the attitude-controlling liquid cristal devices had to be turned on and off in sync with the rotation to make sure that the torque always acts in the same direction. This was done for a limited time to check the correct funtioning. (Normally the attitude of the IKAROS sail is controlled by small chemical thrusters as can be found in ordinary satellites. This may sound like a sacrilege by solar sail purists but for a technology demonstrating mission it is prudent to include proven technology as well in case the experimental ones don't work as planned.)
Although the mission objectives of the IKAROS mission have now been achieved the tests will continue. It is important to get more data on the behaviour of the sail in deep space and compare these data with the computer models. This will help designers of future solar sail missions in their work. Without doubt Japan has become the leader in solar sail technology. We can expect interesting missions in the future!
Another development showing Japan's ever increasing determination to be a major space power is the announcement last week that from April next year on space launches from the Japanese facilities at Tanegashima and Uchinora will be able to be conducted year round.
Up to now Japanese space launches were restricted to no more than 190 days per year to periods outside the fishery seasons. This may sound strange to the rest of the world. After all there are plenty of fishing vessels off the Florida coast or off French Guyana. All it takes is to stay clear of a well defined area during the day of a rocket launch to avoid some rocket debris to fall on your boat.
But of course to the Japanese fish is not just another food group but an important element of their culture. Now however an agreement was reached between JAXA and the local fishery organizations. The total number of launches will be limited to 17 per year but this is far less than the Japanese have ever attempted so far and is hardly a restriction.
Opening up launch sites for year round operations is important in two ways: It will improve competitiveness for commercial launches but it also enables more possibilities for interplanetary missions which Japan is very actively involved in and which require highly restricted launch windows.
Space has become an integral part of Japanese culture.
