Ultra-Long Wavelength Radio Astronomy using the Lunar Crater Radio Telescope (LCRT) on the Farside of the Moon

Abstract:

A radio telescope on the far side of the Moon can have a revolutionary impact in the field of cosmology. It can measure signals at frequencies below 30 MHz, which represent some of the earliest signals in the cosmological history of the universe, but are blocked from reaching terrestrial radio telescopes by the Earth’s ionosphere. Measuring radio signals in the 6-30 MHz band allows us to track the evolution of the neutral intergalactic medium (IGM) before and during the formation of the first stars by measuring the signal associated with the highly red-shifted hyperfine transition of neutral hydrogen. In addition, being on the far side of the Moon, it is shielded from terrestrial sources of radio frequency interference. We propose to build a ~1 km aperture radio telescope on the far side of the Moon, by robotically suspending a wire mesh into an appropriately-sized crater.

The concept of operations requires two landers, one of which lands near the center of the crater, carrying the wire mesh. The other lander lands on the rim, carrying DuAxel robots. These are four-wheeled rovers with an ability to split and rappel their front wheels and axles down crater walls while remaining tethered to the rest of the system that serves as an anchor and provides power and communication to the rappelling two-wheeled rover. Upon reaching the lander at the center of the crater, it helps deploy the mesh by carrying its ends up the crater walls to different points on the rim. The DuAxel rovers also help in the deployment of guy-wires for hoisting the receiver.

Suspending a wire mesh by anchoring its ends will lead to a catenary shape, which is not ideal for focusing the signal at the receiver. This can be compensated for by using wires with variable linear mass density. The density of the wire mesh, thickness and material of the wire, and tolerance for non-parabolic shape of the telescope are all parameters that dictate the RF performance of the telescope and also dictate the complexity and cost of the robotic operations that need to be carried out. We describe the results obtained by simulating the electromagnetic performance of different antenna configurations generated by varying the aforementioned parameters. These simulations help us optimize the engineering design of the telescope for meeting our science objectives.