ar X iv : a st ro - p h / 07 01 77 0 v 1 2 6 Ja n 20 07 Radio Wavelength Observatories within the Exploration Architecture

Observations at radio wavelengths address key problems in astrophysics, astrobiology, and lunar structure including the first light in the Universe (the Epoch of Reionization), the presence of magnetic fields around extrasolar planets, particle acceleration mechanisms, and the structure of the lunar ionosphere. Moreover, achieving the performance needed to address these scientific questions demands observations at wavelengths longer than those that penetrate the Earth's ionosphere, observations in extremely " radio quiet " locations such as the Moon's far side, or both. We describe a series of lunar-based radio wavelength interferometers of increasing capability. The Radio Observatory for Lunar Sortie Science (ROLSS) is an array designed to be deployed during the first lunar sorties (or even before via robotic rovers) and addressing particle acceleration and the lunar ionosphere. Future arrays would be larger, more capable, and deployed as experience is gained in working on the lunar surface. A lunar-based radio wavelength observatory would have two key advantages over ground-based observatories. First, if located on the far side of the Moon, the observatory would be shielded from terrestrial transmissions, both natural and human-generated. Only a small fraction of the radio spectrum is allocated for use by astronomy. Ground-based observatories are often located in remote areas, in an effort to allow them access as much of the spectrum as possible. Nonetheless, many observatories are contending with an increasing fraction of the spectrum being inaccessible. Second, the Earth's ionosphere is opaque at wavelengths longer than about 30 m (frequencies below about 10 MHz). In contrast, without a permanent ionosphere, the surface of the Moon opens a spectral window that is entirely inaccessible from the ground, potentially to wavelengths as much as two orders of magnitude longer than those accessible from the ground. We summarize here key science that would be enabled by a lunar-based radio observatory. In the standard hot Big Bang cosmology, the Universe started in an initially hot, dense ionized state. As it expanded and cooled, it underwent a phase transition to a largely neutral state at the time of recombination. After recombination, baryons began to collapse into overdense regions, eventually leading to the formation of stars and galaxies. Today, the collective action of stars and galaxies maintain the Universe in a largely ionized state. The Epoch of Reionization (EoR) marks this transition from neutral to ionized and is associated with the development of structures in the Universe. As structures began to form …