Sentinel-1B – Second eye of the Earth guardian in orbit
Dual launch for European environmental satellite and MicroSCOPE small satellite mission
Two eyes are better than one; this principle is also true for the two radar satellites that make up the Sentinel-1 mission. On 25 April 2016 at 23:02 CEST, the Sentinel-1B Earth observation satellite lifted off from Europe's spaceport in French Guiana on board a Soyuz launch vehicle. Together with its twin satellite, Sentinel-1A, it will monitor landmasses and oceans, registering even small changes in the environment. The German contribution to this European Union (EU) and European Space Agency (ESA) mission is financed by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) Space Administration using funds provided by the German Federal Government. The French small satellite mission MicroSCOPE – designed to test the equivalence principle underlying the General Theory of Relativity – was also on board.
Strengthening environmental protection from space
Sentinel-1B was injected into orbit at an altitude of 693 kilometres at 23:26 CEST on 25 April. Working together with its identical twin, Sentinel-1A, which was launched in April 2014, it will monitor Earth's terrestrial and marine ecosystems with millimetric precision. The satellites will document the melting of glaciers, changes in land use or the condition of rain forests over an extended period. Each of the satellites will collect data for at least seven years.
One of the mission's tasks is to monitor sea ice. "The radar instruments on the satellites are so accurate that they can be used to produce highly precise ice maps," explains Helmut Staudenrausch from the DLR Space Administration. "The Sentinel-1 satellites will also observe the position of icebergs and enable forecasting of sea ice cover. The data is not only interesting for climate research; it can also be used to increase the safety of ships passing through polar waters."
A map of Earth every six days
The first Sentinel satellite achieved a revisit time of 12 days, meaning it took 12 days to observe every point on Earth. Sentinel-1B will reduce this cycle to just six days. Then, it will be possible to track even short-term environmental damage such as oil slicks at sea with the necessary frequency. The satellites will also provide rapid assistance in the event of disasters; up-to-date maps of regions affected by flooding or earthquakes will help aid organisations deliver effective assistance on the ground. A key factor for this is the capacity of the radar instruments on board the Sentinel-1 satellites to observe Earth's surface day and night, and even through cloud cover. The Laser Communication Terminal (LCT) installed on the satellites uses the European Data Relay System (EDRS) to ensure rapid and secure data transmission to the ground station. Thus, the data may be available in near real time for the user, even if the Sentinel-1 satellite itself has no contact with the ground station.
Sentinel-1B is the fourth satellite in the ESA and EU Copernicus Earth observation programme to be deployed. ESA is responsible for developing and implementing the Sentinel-1B mission, which is financed in cooperation with the EU. An industrial consortium of around 60 companies under the leadership of Thales Alenia Space Italy was responsible for building the satellite. Airbus Defence and Space in Friedrichshafen was the Prime Contractor for the radar instrument, the technical core on board Sentinel-1B. Tesat, a company based in Backnang, 30 kilometres northeast of Stuttgart, developed the LCT. DLR's German Remote Sensing Data Center has been tasked with data processing and archiving. The DLR Microwaves and Radar Institute will be responsible for calibrating the radar system, while the contributions from DLR's Remote Sensing Technology Institute include algorithms for highly accurate data processing. The DLR Space Administration manages the German contribution to the ESA programme, which is mainly financed using funds provided by the German Federal Ministry of Transport and Digital Infrastructure (Bundesministerium für Verkehr und digitale Infrastruktur; BMVI).
MicroSCOPE will check the fundamental principles of our physical world view
The French small satellite mission MicroSCOPE (MicroSatellite à traînée Compensée pour l'Observation du Principe d'Equivalence) is designed to investigate one of the fundamental assumptions underlying Einstein’s theory of relativity – the equivalence principle, which states that all objects located in a vacuum will fall at the same speed, regardless of their mass. "The mystery of the equality of gravitational and inertial mass necessitates ever more precise experiments," explains Hansjörg Dittus, DLR Executive Board Member for Space Research and Technology and a scientist involved in the MicroSCOPE experiment. "Until now, all of the experiments have been conducted on Earth, where we have limited options." MicroSCOPE is the first space mission created to check the equivalence principle – with a precision 100 times greater than has been possible with laboratory experiments on Earth. In this way, the mission will scrutinise one of the fundamental principles of our physical world view. It will also examine whether and where the first discrepancies between experimental data and theoretical predictions become apparent.
Drop test at an altitude of approximately 700 kilometres
The MicroSCOPE spacecraft is built around the experiment payload; this is equipped with two accelerometers, each of which contains two cylindrical test masses. The first measurement device holds different types of cylinder, one made of titanium and the other a platinum-rhodium alloy. The satellite and its experiment will circle Earth in a microgravity environment, in free fall, at an altitude of approximately 700 kilometres. The measurement system will check whether the two masses are accelerated to different degrees in a state of free fall. The validity of the equivalence principle would be limited if this is the case. The second accelerometer – containing two cylinders made of the same material – is used for control purposes. If the experiment is conducted correctly, the identical test masses will move at exactly the same speed.
Franco-German cooperation
MicroSCOPE is a small satellite mission led by the French space agency CNES (Centre National d'Études Spatiales). The French Aerospace Laboratory ONERA (Office National d'Etudes et Recherches Aérospatiales) was responsible for developing the payload and for scientific management. The Center of Applied Space Technology and Microgravity (Zentrum für angewandte Raumfahrttechnologie und Mikrogravitation; ZARM) at the University of Bremen was responsible for verification of the acceleration sensors and has developed a computer simulation for evaluating the mission data; it will also be involved in mission data analysis. The test masses were manufactured at the German National Metrology Institute (Physikalisch-Technische Bundesanstalt; PTB) in Braunschweig. DLR Space Administration is financing the majority of the German contribution to MicroSCOPE using funds provided by the Federal Ministry for Economic Affairs and Energy (Bundesministerium für Wirtschaft und Energie; BMWi).