Earth-Observation Satellite and Einstein-Challenging Physics Experiment Launch Into Space

PARIS—A Europeanized Russian Soyuz rocket on April 25 successfully placed a European radar Earth observation satellite, a French fundamental-physics experiment and three European university-built cubesats into low-Earth orbit.

The operators of all five satellites confirmed that their spacecraft were in the correct orbit and sending signals of good health.

Operating its 14th mission from Europe's Guiana Space Center spaceport, on the northeast coast of South America, the four-stage Soyuz's Fregat restartable upper stage conducted four burns to distribute its payloads into three separate orbits over a four-hour period.

The launch, originally scheduled for April 22, was delayed by three days — two successive scrubs due to high upper-atmospheric winds, and a third to change out a defective inertial measurement unit.

The first to be deployed was the principal payload, the Sentinel-1A satellite radar Earth observation satellite. It is part of the European Commission-owned Copernicus environment-monitoring program, which includes multiple Sentinel spacecraft carrying different sensors.

The 22-nation European Space Agency is a co-investor with the European Commission in the multibillion-dollar Copernicus program and manages the satellite construction contracts.

Sentinel-1B is a twin of the Sentinel-1A satellite launched in April 2014. The two satellites, operating in tandem at 686 kilometers in altitude, will reduce the time between revisits over a given point at the equator from 12 days now to six days with the two spacecraft spaced 180 degrees apart.

Imaging frequency over Europe will also be cut in half, from four days to two days, substantially improving the system's value to European maritime and coastal authorities. Copernicus officials say that if satellite data one data wipes out the practice of ships illegally emptying their bilge tanks, often with oil, in the open ocean, it is the Sentinel-1 system that will do it.

The 2,164-kilogram Sentinel-1B is designed to operate for at least seven years but carries sufficient fuel for 12 years. To guarantee continuity to Copernicus users, ESA and the European Commission have financed "C" and "D" units for the three main Sentinel families.

These satellites plus individual Sentinel payloads will assure an unbroken Copernicus data flow well beyond 2030, said Volker Liebig, ESA's director of Earth observation.

Thales Alenia Space of France and Italy is prime contractor for all four Sentinel-1 satellites. The two remain spacecraft, also designed to operate in tandem, will be launched in 2021 or later, depending on the health of the first pair now in orbit.

Liebig said the Sentinel-1C and 1D satellites are substantially identical to the first two, with the exception of an Automatic Identification terminal on each one. The two in orbit now do not have AIS payloads, which track maritime traffic by capturing signals sent from shipboard transmitters.

Coupling an AIS terminal to a radar imager will allow maritime authorities to more quickly identify the ships captured in the radar images.

With the Sentinel satellites now entering service and more on the way, ESA and the European Commission are focusing on the Big Data challenge posed by the Copernicus system.

Copernicus data is distributed freely and openly to users who registered at the Sentinel Scientific Data Hub. In a taste of what may be to come when the entire Sentinel fleet is in service, the hub has already registered nearly 30,000 users, Liebig said.

In the two years since Sentinel-1A was launched, the Copernicus data-processing center has catalogued and made available for download some 482,000 Sentinel-1 products and registered about 4 million downloads – a transmission of 4.71 petabytes of data from just one spacecraft.

"For those of you not used to working with radar data, I can tell you: You don't download a radar image if you don't need it," Liebig said in a prelaunch briefing. "It’s not like an optical image, which is easier to understand."

The scale of the Copernicus endeavor has begun to attract governments outside of Europe. The U.S. State Department and the European Commission recently concluded an agreement under which U.S. government agencies would receive Copernicus data free of charge.

"We have imported data from the United States for many years," Liebig said, referring to U.S. Landsat and other satellite imagery. "Now we can pay that back."

The main secondary passenger launched with Sentinel-1A was the 303-kilogram Microscope satellite, an ambitious test of Einstein's general theory of relatively, and specifically the equivalence principle.

Developed by the French space agency, CNES, Microscope will test the behavior in free fall of two objects – one titanium, one platinum — of the same mass but of different composition.

The goal: Test, to limits beyond what can be done on Earth, whether the equivalence principle is violated when tested to a precision of 10 to power of minus 15 – 100 times more precise than ground-based tests. The results will come from measuring the slightest difference in acceleration between the two masses.

The mission, budgeted at 130 million euros ($147 million), has taken more than 15 years to produce at CNES. The French aerospace research institute, ONERA, developed the instrument payload, called T-SAGE, or Twin Space Accelerometer for Space Gravity Experiment.

To get as close to possible to true free-fall, the satellite is equipped with eight high-pressure-nitrogen micro-thrusters that will compensate for the slight atmospheric drag the satellite will encounter at its 700-kilometer altitude.

The mission is designed to last two years.

Originally published on Space News.