# ATLAS: Latest Advancements and First Observations
## 1 Introduction  
Since the beginning of the Space Age in the 1950s, humanity has launched an increasing amount of objects into the Earth's orbit [1]. A consequence of the unregulated launch of objects into orbit is the increasing amount of space debris--defunct, non-operational man-made objects and fragments that orbit the Earth. Many space-based assets are the backbone of an array of services essential for the progress and safety of economies and societies, such as communication, navigation, and Earth observation. Space debris poses a significant threat to these assets, as their presence can lead to collisions with active satellites.  
To mitigate the risk of collision and ensure the long-term operation of current satellites, many organizations have created sensor networks comprising telescopes, radars, and lasers to monitor the orbits of space objects and warm satellite operators. This proactive approach is central to the field of Space Situational Awareness (SSA) and Space Surveillance and Tracking (SST) and is vital for safeguarding the interests of nations and upholding international agreements set forth by the United Nations for the peaceful use of outer space [2]. In this context, understanding and addressing the issue of space debris has become imperative for the safe and sustainable utilization of Earth's near-space environment.  
In the European effort, there are mainly two initiatives: the ESA SSA Programme and European Space Surveillance and Tracking (EUSST). The ESA SSA Programme is a multifaceted initiative with many objectives, including monitoring space weather, tracking near-Earth objects, cataloging space debris, and providing essential services like satellite collision avoidance [3]. EUSST is a support framework designed to establish an independent monitoring network dedicated to detecting and tracking space debris, as well asissuing alerts when preventative maneuvers may be required [4]. The primary objective of EUSST is to create an SST capability at the European level, ensuring a suitable degree of European self-sufficiency. Portugal is a participant in the EUSST program, actively developing expertise and capabilities in both optical and radar sensors to contribute to this initiative [5; 6].  
This paper updates the community on the current status of the development of ATLAS (rAdio TeLescope pAmpilhosa Serra), a monostatic tracking radar that is part of the EUSST network. Section 1 briefly explains the problem of space debris. Section 2.1 introduces ATLAS, explains how it has evolved since its infancy in 2020, and outlines its current operational status. Section 2.2 provides a technical summary of the transmitting and receiving chains. Section 2.3 explores the task of tracking space objects with ground-based radar, the main constraints and problems that arise, and how to approach them to perform successful observations. Section 2.4 is dedicated to explaining the procedure used in ATLAS to calibrate the pointing system. Section 2.5 explains the signal model assumed and used to develop the signal processing chain. Section 2.6 is dedicated to the signal processing chain: echo processing and detection. Section 3 showcases the results obtained during the calibration and first space object observations. Section 4 is dedicated to discussing the results and drawing conclusions from them. Section 5 concludes this article and reveals the next steps in the development of ATLAS.