Saptarshi Bandyopadhyay
NASA Jet Propulsion Laboratory
An ultra-long-wavelength radio telescope on the far side of the Moon has significant advantages compared to Earth-based and Earthorbiting telescopes, including (1) Conducting observations of the Universe at wavelengths longer than 10 meters (i.e., frequencies below 30 MHz), wavelengths at which critical cosmological or extrasolar planetary signatures are predicted to appear, yet cannot be observed from the ground due to absorption from the Earth’s ionosphere; and (2) The Moon acts as a physical shield that isolates a far-side lunar-surface telescope from radio interference from sources on the Earth’s surface, the ionosphere, Earth-orbiting satellites, and the Sun’s radio emission during the lunar night. We propose the design of a Lunar Crater Radio Telescope (LCRT) on the far side of the Moon. We propose to deploy a wire mesh using wall-climbing DuAxel robots in a 3-5 km diameter crater, with a suitable depth-to-diameter ratio, to form a parabolic reflector with a 1 km diameter. LCRT will be the largest filled-aperture radio telescope in the Solar System; larger than the former Arecibo telescope (300 m diameter, 3 cm – 1 m wavelength band, 0.3-10 GHz frequency band) and the Five-hundred-meter Aperture Spherical radio Telescope (FAST) (500 m diameter, 0.1-4.3 m wavelength band, 60-3000 MHz frequency band). LCRT’s science objective is to track the evolution of the neutral intergalactic medium before and during the formation of the first stars, which is consistent with priorities identified in the Astrophysics decadal survey. In this NIAC Phase 2 proposal, we will address the following topics: (1) In Phase 1, we explored the fundamental physics and cosmology underlying the scientific objective of LCRT, towards understanding the evolution of the early universe. We generated technical requirements for LCRT to measure signals from the “Dark Ages” phase of the early universe, separating them from the galactic foreground noise which is five orders of magnitude stronger. We also selected suitable lunar craters that shield LCRT from the strongest noise sources in the galactic center. In Phase 2, we propose to build a forward model simulation to study and refine the entire scientific measurement pipeline. (2) The LCRT reflector has a very complex design, since its key component dimensions span six orders of magnitude, i.e the reflector is 1km in diameter while the wires used in the mesh are 1mm in diameter. In Phase 1, we conducted multiple studies to understand the following factors: (i) Storage and deployment of such a large mesh from a lunar lander, (ii) Structural and thermal loading on the mesh during deployment and nominal operations on the Moon, (iii) Radio performance of the mesh. We separately proved the feasibility of each individual mesh design concept in these studies. Phase 2 will now focus on the design of a mesh that simultaneously satisfies inter-disciplinary constraints combining all the factors discussed above. (3) In Phase 1, we studied different deployment options and mission concept-of-operations (ConOPs) that could potentially be used to deploy LCRT on the Moon. We made some important conclusions that narrowed the list of possible options down to 4 alternatives. These range from an option that costs below $1 Billion but has moderate risks, to an option that costs $4-5 Billion and could potentially be launched with existing present-day technology. In Phase 2, we will perform detailed studies on each option, to find the best and most cost-effective approach for deploying LCRT on the Moon. In addition, the Phase 2 proposal will cover other relevant secondary technologies, programmatic issues like work plan, team strengths, risk and mitigation, and future plans beyond NIAC Phase 2. We envision that the work in Phase 2 will set the stage for LCRT to become a real NASA mission.
2021 Phase I, II, and III Selections
