Every now and then, someone writes to point out that when I write about the ‘nearest star,’ I am actually talking about the Sun. True enough, and despite our interstellar focus in these pages, I don’t want to neglect the contribution of missions like SOHO, Ulysses, Hinode, STEREO and others to our understanding of how stars work. What we now need to deepen that knowledge further is a polar mission like POLARIS, which is being designed to make high-latitude studies of the Sun.

For we have no extended studies of these regions, which will set up observations impossible to make from the ecliptic. Nor does the proposed Solar Orbiter mission offer a wide enough view of the polar regions. A new study of the POLARIS mission notes its purpose: to “determine the relation between the magnetism and dynamics of the Sun’s polar regions and the solar cycle.” Indeed, the spacecraft would map the solar magnetic field in 3-D as well as helping us understand its origins.

But you knew there had to be more of an interstellar hook here. POLARIS (Polar Investigation of the Sun) would use a combination of a Venus gravity assist and solar sail propulsion to reach its 0.48 AU orbit around the Sun, with an inclination to the solar equator of 75 degrees. Two reference studies depict a sail varying in weight from 195 to 408 kilograms, with sail side length of, respectively, 153 meters or 179. Significant issues arise in considering these studies, one being the question of whether the sail should be deployed before or after the Venus gravity assist (if after, stowing the sail for six months could cause later problems).

Paulette Liewer (JPL), Thierry Appourchaux (Institut d’Astrophysique Spatiale) and colleagues run through the options in a recent paper, with the significant note that the major challenge for the entire mission is the development and use of the sail. We need advancements in sail material, deployment, attitude and orbit control, the sail jettisoning mechanism and communications, which is why this mission catches the eye. Can an earlier GeoSail mission, a small 250-kg spacecraft with a 50 X 50 meter sail provide the essential shakedown to move some of these technologies forward?

Image: A view of the spacecraft with the sail deployed on its mast. The sail size is a square of 180 m while the spacecraft fits into a 2-m on a side cube. Credit: J.-C.Leclec’h.

Ultimately, of course, those of us who believe in sail technology hope to see sails taking us throughout the inner Solar System and used as an early boost for fast missions to the outer planets as well. Take the engineering to an extreme and we might someday envision ‘sundiver’ missions deploying a sail at close approach to the Sun for the kind of accelerations we can today only dream about. And there are, of course, those ‘lightsail’ ideas using beamed propulsion to get us to the stars.

All of which depends upon getting a sail, any kind of sail, operational in space for further study. No insurmountable difficulties stand between us and implementation of early sail missions, if we have the will to proceed with the necessary funding. So keep an eye on mission concepts like POLARIS, discussed in Appourchaux et al., “POLAR Investigation of the Sun – POLARIS,” accepted by Experimental Astronomy and now available online. Nor are we through with the Sun — I want to discuss Solar Probe+, a mission that will reach into the Sun’s corona, next week.