Interstellar Missions: Why was the clover-shaped sail and fan-shaped sail chosen over other designs? Has there been any indication that one performed better than the other?
ISAS/JAXA: There are two types of tension directions that expand the fold lines. One idea is to make the centrifugal force aligned to radial direction. The fan type sail comes from this configuration. The other type of sail utilizes the centrifugal force aligned perpendicular to the fold lines so that they are expanded. This idea leads to the clover-leaf sail. The primary purpose of the experiment is to obtain how the tension contributes to expanding the membrane from distinct aspects.
Interstellar Missions:
What basic materials were chosen for the sail and frame/structure?
ISAS/JAXA: There are neither rib nor frame that expand the membrane. This is the most important point in the sails we devised and tested. Our idea is to use spacecraft spin whose centrifugal force is made use of to span the sail. The sail membrane is made of 7.5 micron aluminized polyamide thin film.
Interstellar Missions: Does the sail itself relay data? If so, how?
ISAS/JAXA: The rocket instruments sent the attitude and the sail shape information. No mission payload was aboard it. [the sail]
Until recently previous attempts to deploy a solar sail have been unsuccessful, as was the case when the Planetary Society attempted to do so in July 20, 2001. Solar sail technology is currently the only known technology with the potential to approach the speeds necessary to reach other solar systems in a human life time. Theoretically a solar sail should be capable of .1c, or 10% of the speed of light, assisted by beamed energy from a laser in addition to energy by the sun.
For further reading go to the ISAS/JAXA web site at: www.isas.jaxa.jp/e/snews/2004/0809.shtml