powerful tool in investigating the “dark ages” of the universe, before the reionization era, in which highly redshifted 21 cm (1420 MHz) emission from neutral hydrogen would reveal the earliest structures in the universe before the first phase of nuclear enrichment. At redshifts on the order of one hundred, this strong emission line approaches the ~15 MHz plasma frequency of Earth’s ionosphere, below which the opacity is very high and observations from the surface of Earth are not possible. For redshifts below this, the science thrust is for terrestrial efforts (e.g., Low Frequency Array, Square Kilometer Array), although such implementations are handicapped on Earth compared with the lunar farside, because of the severe human-produced and ionospheric radio-frequency noise. These low frequencies, unobservable from Earth, have special relevance also for heliophysical research on solar bursts and particle acceleration processes within them. A low-frequency radio interferometer with simple dipole elements spread out on a kilometer scale of the lunar surface thus has synergistic value to both priority astrophysical and heliophysical research. As a result of this synergy, as well as the usefulness of such low frequencies to understanding particle acceleration mechanisms in active galaxies, a modest nearside array has substantial scientific value both for these bright astronomical sources and also for allowing the refinement of technology and understanding of environmental issues.

An innovative concept recently proposed would have a complete antenna line electrodeposited on a long strip of polyamide film. In this form, a lightweight array could be simply unrolled onto the lunar surface in one of the first lunar return trips (see Figure 6.1). Unlike efforts in the optical, infrared (IR), or ultraviolet (UV) domains,

FIGURE 6.1 An artist’s conception of the Radio Observatory for Lunar Sortie Science farside Mylar dipole radio telescope (shown in yellow); an active Sun is shown on the upper right, and Earth’s magnetosphere is shown at the upper left. SOURCE: Courtesy of J. Lazio, Naval Research Laboratory; R. MacDowall, NASA/Goddard Space Flight Center; J. Burns, University of Colorado; D. Jones, Jet Propulsion Laboratory; K. Weiler, Naval Research Laboratory; and J. Kasper, Massachusetts Institute of Technology.