Low frequency antenna options for the lunar surface

There are a number of scientific motivations for low frequency radio observations from space. These include the possibility of detecting, and eventually imaging, the spectral line of neutral Hydrogen from the cosmic Dark Ages, before the first stars formed. This is the period between the creation of the cosmic microwave background and the formation of the first stars, massive black holes, and galaxies, a period of large-scale structure formation in the universe. The Hydrogen line from the Dark Ages is redshifted down to frequencies of tens of MHz. In addition, imaging and tracking of emission from solar and interplanetary radio bursts, and detecting electron cyclotron emission from extrasolar gas giant planets, all require observations at and below Earth's ionospheric cutoff. Observations far from Earth can completely eliminate ionospheric absorption and distortion, and greatly reduce terrestrial interference (both natural and human-generated). But efficient antennas at low frequency are physically large. Consequently there has been a lot of work exploring concepts for low mass, wide bandwidth low frequency antennas that can be deployed in space. This paper summarizes recent work on deployable low frequency antennas, including thin film antennas that could be unrolled on the lunar surface and inflatable antennas for both free space and lunar locations.