Ultra-Low-Frequency Radio Astronomy Observations from a Selenocentric Orbit: first results of the Longjiang-2 experiment

TL;DR

This paper reports the first results of ultra-low-frequency radio observations from the Longjiang-2 satellite at the Moon, demonstrating the instrument's operational reliability and initial measurements of radio interference levels.

Contribution

It presents the first in-orbit results of a selenocentric ultra-long-wavelength radio interferometer, including RFI analysis and operational validation.

Findings

RFI suppression of about 80 dB is necessary for lunar radio astronomy.

RFI levels below a few MHz are below the receiver noise floor.

The LFIS payload operated reliably during initial observations.

Abstract

This paper introduces the first results of observations with the Ultra-Long-Wavelength (ULW) -- Low Frequency Interferometer and Spectrometer (LFIS) on board the selenocentric satellite Longjiang-2. We present a brief description of the satellite and focus on the LFIS payload. The in-orbit commissioning confirmed a reliable operational status of the instrumentation. We also present results of a transition observation, which offers unique measurements on several novel aspects. We estimate the RFI suppression required for such a radio astronomy instrumentation at the Moon distances from Earth to be of the order of 80 dB. We analyse a method of separating Earth- and satellite-originated radio frequency interference (RFI). It is found that the RFI level at frequencies lower than a few MHz is smaller than the receiver noise floor.