  By volume, more than 99% of the solar system has not been imaged at radio
frequencies. Almost all of this space (the solar wind) can be traversed by fast
electrons producing radio emissions at frequencies lower than the terrestrial
ionospheric cutoff, which prevents observation from the ground. To date, radio
astronomy-capable space missions consist of one or a few satellites, typically
far from each other, which measure total power from the radio sources, but
cannot produce images with useful angular resolution. To produce such images,
we require arrays of antennas distributed over many wavelengths (hundreds of
meters to kilometers) to permit aperture synthesis imaging. Such arrays could
be free-flying arrays of microsatellites or antennas laid out on the lunar
surface. In this white paper, we present the lunar option. If such an array
were in place by 2020, it would provide context for observations during Solar
Probe Plus perihelion passes. Studies of the lunar ionosphere's density and
time variability are also important goals. This white paper applies to the
Solar and Heliospheric Physics study panel.
