![]() ![]() However, due to the vastly increasing number of satellites in mega constellations such obligations are being discussed in the space agencies of several space faring countries. Today, there is no commitment to carry a propulsion system for spacecraft. Thus, this experiment is a concept demonstration of a de-orbiting manoeuvre shown at the smallest class of spacecraft in LEO. ![]() Lowering the altitude of a spacecraft in low earth orbit (LEO) is equivalent to a reduction of its lifetime, since satellites in LEO usually burn up during re-entry due to the friction with the Earth’s atmosphere. The Figure shows the altitude of UWE-4 since launch on December 27th 2018 based on Two-Line Elements published online by the North American Aerospace Defence Command (NORAD). An analysis of the orbit of the two spacecraft after July 5th 2020 results in a closest approach of more than 6000 m. No further CDMs have been issued regarding this possible conjunction. Thus the on-going altitude lowering manoeuvre could only improve the situation and can be considered as a collision avoidance manoeuvre. An analysis has shown that the altitude of UWE-4 would already be below the Iridium satellite at the time of conjunction. A conjunction of UWE-4 with a non-operational Iridium satellite (ID: 34147) in the morning of July 5th 2020 with a minimum range of about 800 m was a threat to the safety of UWE-4. As chance would have it, the team of UWE-4 received a conjunction data message (CDM) in the morning of July 2nd 2020 from the United Air Force’s 18th Space Control Squadron. This marks the first time in CubeSat history that a 1U CubeSat changed its orbit using an on-board propulsion system. Several manoeuvres have been performed within 11 days between June 23rd – July 3rd 2020 such that the altitude of the CubeSat was reduced by more than 100 m, compared to an average of 21 m with natural decay. The 1U CubeSat, developed and built at the Chair for Robotics and Telematics, is equipped with the electric propulsion system NanoFEEP which has been developed by TU Dresden. ![]() The University Wuerzburg Experimental Satellite 4 (UWE-4) successfully used its propulsion system in order to conduct orbit control. ![]()
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