Lunar Far-Side Radio Arrays: A Preliminary Site Survey

The Dark Ages is an unobserved period of the early universe, which was permeated by neutral hydrogen atoms, before the first stars formed. The Dark Ages can be used to test Inflationary models from the multipole spectrum of HI at z~40-80, i.e. at low radio frequencies unobservable from Earth. A telescope on the radio-quiet lunar far-side could allow these tests of inflation. Robust inflation tests are achieved by increasing the number of spatial modes through hydrogen cloud mapping against the CMB with angular resolution ultimately reaching ~10 arcsec. Preliminary studies of the Lunar Crater Radio Telescope (LCRT) by NASA and the Far-Side Explorer by ESA demonstrate a resurgent interest in lunar-based astronomy. LCRT and Far-side Explorer are relatively small-scale infrastructure, however a high angular resolution instrument (~10 arcseconds) is needed to explore the full information content of this spectrum. That resolution at 20 MHz requires a 200 km diameter array. As the array consists of 100s of cable-linked dipole antennas, the optimum region on the moon needs to be relatively flat and smooth for ease of deployment. Wheeled vehicles are limited to inclines <30 degrees and require minimal roughness from rocks and boulders to ensure ease of manoeuvre around the site. Unlike the near-side of the Moon, the far-side is very mountainous, with only a handful of promising sites. In this poster we have used Lunar Orbiter Laser Altimeter (LOLA) data from the Lunar Reconnaissance Orbiter (LRO) to construct digital terrain maps (DTM) of feasible preliminary sites, starting with Mare Moscoviense. From DTM, slope and roughness parameters were derived and analysed as the first steps in a site survey. Astronomers will need to urgently protect the most promising sites as competition for use of lunar sites increases.