Improved Sensitivity for Space Domain Awareness Observations with the Murchison Widefield Array

TL;DR

This paper presents two novel methods, shift-stacking and near-field refocusing, that significantly enhance the detection sensitivity of the Murchison Widefield Array for space debris and Resident Space Objects, demonstrating a 75% increase in detections.

Contribution

The paper introduces two innovative techniques to improve MWA sensitivity for space object detection, including a shift-stacking method and a post-observation refocusing approach, with validation on real data.

Findings

75% increase in detection count using shift-stacking

Successful near-field refocusing on ISS pass

Discussion of sensitivity gains with upcoming hardware upgrades

Abstract

Our previously reported survey of the Low Earth Orbit (LEO) environment using the Murchison Widefield Array (MWA) detected over 70 unique Resident Space Objects (RSOs) over multiple passes, from 20 hours of observations in passive radar mode. In this paper, we extend this work by demonstrating two methods that improve the detection sensitivity of the system. The first method, called shift-stacking, increases the statistical significance of faint RSO signals through the spatially coherent integration of the reflected signal along the RSO's trajectory across the sky. This method was tested on the observations used during our previous blind survey, and we obtained a $75\%$ increase in the total number of detections. The second method re-focuses the MWA to the near-field RSO's position (post-observation), by applying a complex phase correction to each visibility to account for the curved wave-front. The method was tested successfully on an MWA extended array observation of an ISS pass. However, the method is currently limited by signal de-coherence on the long-baselines (due to the hardware constraints of the current correlator). We discuss the sensitivity improvement for RSO detections we expect from the MWA Phase 3 correlator upgrade. We conclude the paper by briefly commenting on future dedicated Space Domain Awareness (SDA) systems that will incorporate MWA technologies.