A Lunar Array Precursor Station to monitor the lunar ionosphere

The lunar surface offers several advantages for astronomical observations at low radio frequencies. These include shielding from terrestrial interference on the farside, shielding from solar emission half the time, and stable, easily calibrated array baselines. Low frequency radio astronomy offers compelling science in multiple areas, from cosmology to extrasolar planets. It is likely to be one of the first large-scale scientific deployments on the lunar surface. But the lunar ionosphere could limit observations at the lowest frequencies during lunar daytime. This has serious implications for observations of solar and heliospheric radio bursts, whose radio emission occurs below 1 MHz except when the emitting regions are very close to the Sun. The objective of the LAPS (Lunar Array Precursor Station) instrument described here is to measure the absorption of low frequency radio signals by the lunar ionosphere as a function of time and frequency. These measurements will greatly increase our understanding of the magnitude and evolution of electron density near the lunar surface during all phases of the lunar day-night cycle. They will directly determine the minimum usable observing frequency as a function of time.