After three postponements due to weather and technical issues, Sentinel-1B finally lifted off on a Soyuz rocket from Europe’s Spaceport in Kourou, French Guiana, on 25th April at 21:02 GMT, separating from the rocket’s Fregat upper stage 23 min 35 sec later.

Sentinel-1B will orbit 180° apart from its identical twin, Sentinel-1A, which was launched two years ago. The satellites — part of Europe’s Copernicus programme — carry a high-resolution radar that images Earth’s surface through cloud and rain, day and night.

Also hitching a ride on the Soyuz was the Microscope satellite from the French space agency, CNES. Microscope carries an experiment designed to verify the universality of free fall or the equality of gravitational and inertial mass — Einstein’s equivalence principle, the basis of the theory of general relativity. Using two masses in almost perfect and permanent free fall, the experiment will verify the principle with a degree of precision unobtainable on Earth.

Three CubeSats also took advantage of the launch. These mini-satellites, each measuring 10×10×11 cm, were developed by teams of university students through the ‘Fly Your Satellite!’ programme, run by ESA’s Education & Knowledge Management Office in collaboration with European universities. The three CubeSats are: OUFTI-1 from the University of Liege, Belgium, e-st@r-II from the Polytechnic of Turin, Italy, and AAUSat-4 from Aalborg University, Denmark.