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This comparative study deals with the question of whether travelers can terminate an already booked package tour free of charge after the outbreak of COVID-19 ("coronavirus") in EU law and Turkish law. It first provides preliminary information about the regulations related to package tour contracts. It explains afterwards, which package travelers have the right of termination and compares the conditions and legal consequences of termination of the contract, under the perspective of EU and Turkish laws. In this context, the terms such as unavoidable and extraordinary circumstances, force majeure, the situation that cannot be foreseen and prevented and the reason that not caused by consumer are examined in respect of the COVID-19 pandemic. Different results of the cancellation of the package tour or termination of contract are analyzed. Also a recent amendment in the directive about the package tour contracts in the Turkish law is criticized., Çalışma, halihazırda satın alınmış paket turların, COVID-19 salgını (“koronavirüs”) ortaya çıktıktan sonra ücret kesintisi olmadan iade edilebilip edilemeyeceğini araştırmaktadır. Eserde öncelikle paket tur sözleşmeleri hakkındaki kanuni düzenlemeler hakkında ön bilgiler aktarılmıştır. Ardından, salgın sebebiyle hangi paket tur yolcularının sözleşmeyi sona erdirebileceği açıklanmış; sona erdirmenin şartları ve sona ermenin yasal sonuçları AB Hukuku ve Türk hukuku bakımından karşılaştırmalı olarak incelenmiştir. Bu çerçevede, kaçınılmaz ve olağanüstü şartlar, mücbir sebep, öngörülemeyen ve engellenemeyen durum, tüketiciden kaynaklanmayan sebepler gibi terimler COVID-19 pandemisi açısından incelenmiştir. Turun başlangıcından önce ve sonra turun iptali veya sözleşmenin sona erdirilmesi hallerinde ortaya çıkan farklı neticeler analiz edilmiştir. Ayrıca Türk hukukunda konuyla ilgili yakın tarihte yapılan yönetmelik değişikliği eleştirilmiştir.

The two GRACE satellites were launched on March 17, 2002 by a Russian Rockot. GRACE not only was the first dual-satellite mission operated by German Space Operations Center (GSOC), but it also was the first formation flying at an altitude below 500 km. The mission was successful from a scientific point of view and the originally envisaged mission duration of five years finally became almost sixteen. A follow-on mission with the same partners started 2018 and JPL projects a new generation of satellites for gravity measurements in the twenties, so there was a strong incentive to prolong the GRACE mission as long as possible in order to minimize the gap. Infirmity comes with age and several components deteriorated towards the end or even were defunct. The scientific goals were still obtained to a very high level until June 2017, four months before decommissioning. The major challenge for operations was posed by the degradation of the NiH2 batteries. These are comprised of twenty cells packaged in the common pressure vessel (CPV) configuration. Three cells had shorted out on Grace 1 and seven on Grace 2 by the middle of 2017. The charge capacity of the operational cells was severely degraded. The longevity and the occurrence of several anomalies due to power problems depleted fuel ever more rapidly.

Description of End of Life operations on the Grace satellites.

The German Aerospace Center (DLR) launched on 3rd December 2018 the Euglena Combined Regenerative Organic food Production In Space (Eu:CROPIS) mission. Eu:CROPIS is a mission of DLR’s compact satellite class with the objective to test several biological experiments at different levels of artificial gravity. The Eu:CROPIS mission carries experiments and payloads from University of Erlangen, NASA AMES and two DLR Institutes.

TET-1 (a German abbreviation meaning technology experiment carrier) is a small German satellite bringing eleven technical experiments into space. It was built by Kayser-Threde (Munich) and Astro- und Feinwerktechnik Berlin, and will be operated by GSOC for at least one year. Its launch will be piggy-back with Kanopus-Vulkan 1, an Earth observation mini-satellite of the Russian Space Agency, on a Soyuz FG / Fregat rocket from Baikonur/Kazakhstan, which dependency caused a delay of more than a year. The new technologies to be verified cover a wide field – ranging from an infrared camera to e.g. a new type of GPS receiver or solar cells -- requiring a large number of operational modes and a variety of pointing requirements. TET-1 has no orbit control and the finally achieved injection dictates attitude operations to a large extent; several modes require a specific attitude to reach the desired accuracy. Another challenge to the attitude control system is the high degree of autonomy required. TET-1 is monitored in two consecutive orbits every twelve hours, but uplink capability is limited to only once per day.

AOCS operations for two satellites flying at ~514 km altitude with unprecedented small separation of 150 m upwards pose various new challenges and require creative solutions. Several on-ground safety measures were installed, but due to the short reaction times emphasis always lies with the on-board handling of problems. This is achieved by implementation of a data link (one-way) between the satellites, by the design of a new AOCS safe mode that has no effect on the orbit, by the complete re-work of the TerraSAR-X FDIR concept (Fault Detection, Isolation and Recovery) and by autonomous formation control with a dedicated cold gas system on the second satellite TanDEM-X. This paper describes AOCS operations for the TanDEM-X mission in close formation. Most of the tasks are, thanks to extended safety measures and automated control mechanisms, routine. This will be described in the first section, where a short summary of all AOCS related operations will be given. The second section describes some special activities in connection with the cold gas system and the star trackers on TDX. The investigations and the fine tuning of the GPS receivers on both satellites are also described in this section. Although there was never a threat to the formation, close monitoring is required all the time and some mitigation measures were called for. Finally, the influence of the approaching solar maximum in 2013 will also be described in this section. The last part presents the conclusions and contains some suggestions for future missions.

The TanDEM-X project is implemented by a “Public-Private Partnership” between the German Aerospace Centre (DLR) and Astrium GmbH. The primary goal of the TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurement) mission is to generate a global digital elevation model. To achieve this, two satellites – TerraSAR-X (TSX) and TanDEM-X (TDX), satellites of almost identical construction in orbit since June 2007 and June 2010 respectively – form the first configurable SAR (Synthetic Aperture Radar) interferometer in space with a separation of only a few hundred metres. A powerful ground segment, which is interlaced with that of TSX, completes the TanDEM-X system. The satellites fly in close formation since December 2010 and will be operated in parallel for three years to cover the entire surface of the Earth. DLR is responsible for the scientific exploitation of the TSX/TDX data, as well as for planning and implementing the mission, for controlling the two satellites and for generating the digital elevation model. Astrium has built the satellites and shares in the costs of development and exploitation. The responsibility for marketing the data lies in the hands of Infoterra GmbH, a subsidiary of Astrium GmbH. AOCS operations for two spacecraft flying at low altitude with such unprecedented small separations pose several challenges and required creative solutions, mostly stipulated by the fact that the original mission was not designed for formation flight. Several on-ground safety measures were installed, but due to the short reaction times emphasis lies with the on-board handling of problems. This is achieved by implementation of a data link (one-way) between the satellites, by the regular interchange of a “health” signal (two-way), by the design of a new AOCS safe mode that has no effect on the orbit, by the complete re-work of the FDIR concept (Fault Detection, Isolation and Recovery on-board) and by autonomous formation control. Emphasis in this paper is on the implemented safety measures, specifically the FDIR concept which will be presented in Section 1.5.2. and on the routine AOCS operations during close formation flight (Section 2). No major contingencies have occurred in the formation so far – something we don’t want to change in the future either – but some minor operational issues did occur, which will be presented in Section 3. Section 4 finally gives some conclusions and an outlook on the way forward.