The mission slipped from 2011 for an unusual reason. IRIS uses the same momentum wheels, from Goodrich Aerospace, as NASA's 2011 Grail (Gravity Recovery and Interior Laboratory) mission. Grail's wheels have performed without incident. But when pushed to extremes in IRIS testing, the wheels blew a fuse. An investigation revealed that their logic control can draw excess current if they are accelerated too quickly. Lockheed Martin verified that if they are started “gently,” they will operate nominally, Title says. The issue mainly pertains to an unanticipated spacecraft shutdown and restart, he notes.
The dynamics of solar energy have been studied for decades, but the interface between the Sun's photosphere and corona remain a challenge in solar and heliospheric science. Where past instruments, such as the Atmospheric Imaging Assembly (AIA) on the SDO, view the solar surface and atmosphere broadly (2,000 arcsec.), IRIS must take a narrow view of just 50 arcsec, as if it were a P-3 Hurricane Hunter flying into a hurricane's eye instead of a weather satellite viewing the whole storm, as AIA does.
The big leap that distinguishes IRIS is advances in supercomputing. “We've finally reached the state where we can interpret the data that [IRIS's spectrograph] will capture,” Title says. “The region of the Sun that we're looking at is where temperatures go from 6,000K to several million degrees. There's a lot of complex physics and until quite recently the data were hard to interpret.”
The spacecraft will transmit enormous data sets—0.7 Mbps.—in X-band to Norway's Svalbard ground station. Number-crunching, chiefly by NASA Ames Research Center's Pleiades supercomputer, is so important to the mission's success that “Ames has had a presence from the beginning of the design,” Title says.
Understanding the energy transfers that take place in the corona may play a role for energy projects on Earth. The Sun is an excellent laboratory for understanding the electro-mechanical processes necessary to make fusion reactors practical, and for that reason IRIS's science collaborators include physicists at the Princeton University Plasma Physics Laboratory.