Site selection constraints and options for LILA-Pioneer and LILA-Horizon

Abstract

The Earth's Moon presents a uniquely advantageous environment for detecting astrophysical gravitational waves (GWs), particularly in the scientifically interesting deciHz regime. The Laser Interferometer Lunar Antennae (LILA) project plans to perform GW measurements on the lunar surface, using the Moon's unique seismic quietness to access the deciHz regime. Two mission concepts are considered: the initial LILA-Pioneer L-shaped strainmeter and the more advanced LILA-Horizon triangular interferometer. Because the detection frequency is so low, LILA requires only the Moon's precession around the Earth and Sun to triangulate (unlike Earth-based detectors). Thus, the science return of LILA is site-agnostic; however, significant constraints are imposed by practical considerations. These include the need for isolation from anthropogenic noise, protection from the lunar environment, accessibility for lunar terrain vehicles, and line-of-sight. Candidate sites are shown for both LILA-Pioneer and LILA-Horizon, demonstrating that many options exist for deployment of both tools.

Figures (3)

• Figure 1: Geometry used in calculation of the altitude ($a$) that detector $S_1$ needs to sit above $S_2$. $M$ is the center of the Moon, $R$ is the radius of the Moon, $L$ is the arm length of the detector, $\theta$ is the additional angle of inclination desired above the tangent to give margin, $H$ is the horizon point with no margin, and $h$ is the height of $H$.
• Figure 2: Sites found in the search using the required criteria from Section \ref{['ss:constraints']}. Red circles indicate possible LILA-Pioneer sites while blue indicates possible LILA-Horizon sites. The green lines indicate arm distributions extending from a single vertex. An example demployment using the Monge crater data point is shown in Figure \ref{['fig:MongeExample']}. The list is non-exhaustive.
• Figure 3: Example zoom-in of the Monge site to illustrate a deployment of LILA-Pioneer. The primary instrument lies at the vertex of the triangle, marked with a black box. The retroreflectors are placed via rover 5 km apart at a 55$^{\circ}$ angle. The primary instrument lays about 500m above the two retroreflectors.