# Development of the Romanian Radar Sensor for Space Surveillance and Tracking Activities +
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* Near-Earth objects (NEO), which is tasked with detecting and monitoring natural space objects passing close to Earth and posing a threat to our planet. Besides satellites and other spacecraft in good operational state, the outer space around Earth is crowded with space debris. Space debris are composed of satellites that have reached end-of-life, space objects intentionally released as part of missions, rocket parts, frozen satellite propellant, and rocket propulsion systems, as well as fragments that have broken off from space objects due to collisions and explosions [2]. As a result, there is a growing risk of collision for operational satellites and other functional space objects, which may either impair their functionality or result in catastrophic failures. According to the US NASA Orbital Debris Program Office, more than 27,000 orbital debris larger than 10 cm are catalogued. The estimated population of particles between 1 and 10 cm in diameter approximates 500,000, while the number of particles larger than 1 mm exceeds 100 million. In 2020, it was estimated that the amount of material orbiting the Earth exceeded 8000 metric tons, with most orbital debris located within the first 2000 km in height above the atmosphere. Extensive studies have concluded that the majority of space debris, operational satellites, and spacecraft are present in the low Earth orbit (LEO), as presented in Figure 1[3,4]. The European Space Agency (ESA) is currently carrying out its Space Safety Programme (S2P), which aims at mitigating and preventing the impact of hazards from space, protecting activities and infrastructures. Starting in 2021, the closely related SSA element of the Space Programme of the European Union has included complimentary activities carried out within the S2P. Decision No. 541/2014/EU of the European Parliament and of the Council establishing a Framework for Space Surveillance and Tracking (EU SST) Support states that the specific objectives of the SST support framework are [5]:  
1. assessing and reducing the risks to in-orbit operations of European spacecraft relating to collisions and enabling spacecraft operators to plan and carry out mitigation measures more efficiently;
2. reducing the risks relating to the launch of European spacecraft;  
Figure 1: Monthly effective number of catalogued objects in Earth orbit by orbital regime, as catalogued by the US Space Surveillance Network. 3. surveying uncontrolled re-entries of spacecraft or space debris into the Earth's atmosphere and providing more accurate and efficient early warnings with the aim of reducing the potential risks to the safety of Union citizens and mitigating potential damage to terrestrial infrastructure; 4. seeking to prevent the proliferation of space debris. The member countries of France, Germany, Italy, Poland, Portugal, Romania, and Spain, in cooperation with the EU Satellite Centre, are gradually combining their sensor, data processing, and service capabilities to support the operations and decisions of owners and operators of space assets, of civil protection authorities, and of other European entities. The EU SST acquires data from a network of sensors from its member states that includes 38 installations: radars, telescopes, and laser ranging stations (Figure 2) [6]. These sensors survey and track space objects in all orbital regimes: LEO, MEO, and GEO. The acquired data are processed and feed a joint database and are used to maintain a catalogue. The important contribution of the EU SST to space industry applications is illustrated by the fact that more than 210 spacecraft of the European Union, its member states, and European owners and operators are currently protected from the risk of collision in all the orbit regimes. The EU SST also provides more than 100 users with free, added-value services in re-entry and fragmentation analysis [7].