The Lunar Reflective Interferometer: Mapping the low-frequency Radio Universe from Lunar Orbit

Speaker: Prof. Peter Gorham (UHM)

Radio interferometry has provided remarkable improvements in angular resolution over a very wide spectrum of the radio sky: from a few tens of MHz, just above Earth’s ionospheric cutoff, up to nearly 1 TeraHertz. Very long baseline interferometry has enabled imaging resolution approaching 10 microarcseconds, and most radio interferometers match or exceed the angular resolution of optical and infrared telescopes. However, below the ionospheric cutoff at around 10 MHz, radio imaging resolution remains hundreds or thousands of times worse due to the lack of space-based interferometers. This regime is thus the last frontier for radio astronomical imaging. 
To address this we present the novel method of lunar reflection interferometry (LRI) in which a virtual interferometer can be formed by using a spacecraft-borne antenna in lunar orbit that receives both direct rays and those reflected from the lunar surface. The technique exploits the method of images and is akin to the classic “sea cliff” interferometer, with the Moon’s surface, primarily the lunar Maria, replacing the ocean surface. We describe the method in detail, demonstrate that significant portions of the Moon’s surface are sufficiently smooth at low radio frequencies (below ~10 MHz) for the technique to work, and outline a spacecraft instrument implementation. We describe potential systematic errors and how they could be mitigated. We present several astrophysics applications of the method. An LRI mission, led by UH investigators, is currently under review for NASA’s Astrophysics Pioneers program.

https://indico.phys.hawaii.edu/event/2871