Rockot launches Sentinel-3B
A veteran Soviet ballistic missile converted into a space launcher successfully delivered a European Earth-watching spacecraft on April 25, 2018, expanding the Copernicus environment-monitoring satellite constellation. Sentinel-3B is a twin for Sentinel-3A launched more than two years ago from the same launch site in Plesetsk. Together, the duo will be able to deliver remote sensing data to the ground within three hours after scanning a particular region on Earth.
Sentinel-3B mission at a glance:
According to the European Space Agency, ESA, orbiting two identical satellites -- Sentinel-3A and -3B -- provides the best coverage of the Earth's surface for the Copernicus project, which the agency called the largest environmental monitoring program in the world. Sentinel-3B will be the seventh satellite in the constellation.
ESA said that both Sentinel-3 satellites had been equipped with a suite of cutting-edge instruments to supply a new generation of data products, which are particularly useful for marine applications. The agency emphasized monitoring ocean surface temperatures and weather forecasting services, aquatic biological productivity, ocean pollution and sea-level change. The pair was also capable of delivering unique and timely information about changing land cover, vegetation, urban heat islands, and for tracking wildfires.
For the commissioning phase of the mission, ESA planned to insert Sentinel-3B into orbit just 223 kilometers or 30 seconds behind the 3A satellite, in order to identify expected discrepancies in the data from identical instruments on the two spacecraft. But after around four-month calibration of the fresh satellite, the pair would be allowed to drift 140 degrees apart instead of the traditional 180-degree split used by identical remote-sensing satellites. According to ESA, that unusual arrangement will provide the most accurate continuous coverage of oceanic phenomena, such as eddies.
Preparing for flight
As of January 2014, the Rockot vehicle, which would be ultimately assigned for the Sentinel-3B mission, was expected to launch Sentinel-2B satellite in April 2016.
However, in 2016, technical problems were found in five OLCI-B cameras intended for Sentinel-3B, which required their refurbishment. There were also problems with the delivery of the Ukrainian-built flight control system for the Rockot.
In any case, Sentinel-2B swapped places with Sentinel-3B, which was originally slated to go up on the European Vega rocket. Vega successfully delivered Sentinel-2B on March 7, 2017.
In the meantime, the Rockot launch with Sentinel-3B was postponed from 2017 to March 2018 and then delayed again to around April 6, 2018.
Thales Alenia Space, the prime contractor in the Sentinel-3B project, completed assembly of the satellite in 2017 at its facility in Cannes, France, and conducted testing of the spacecraft for the remainder of the year. By mid-February 2018, the launch was set for April 25, after a delay in the planned delivery of the satellite to Russia.
On February 2, ESA announced that all tests of the Sentinel-3B had been completed and it was ready for shipment to the Plesetsk launch site.
An Antonov-124 transport plane carrying the satellite flew from Nice, France, to the Talagi airfield near Arkhangelsk, via Moscow, Russia, on March 16, 2018, after a two-day delay caused by an ice-covered runway in Arkhangelsk.
The container with the Sentinel-3B satellite is being unloaded from an An-124 transport plane at Talagi airport near Arkhangelsk on March 16, 2018, before a day-long trip by rail to Plesetsk.
On March 18, the container with the spacecraft made an overnight train ride to Plesetsk. Between March 21 and 23, the container was opened inside the clean-room facility, the spacecraft was rotated into a vertical position and powered up for tests. Also on March 23, the European Spacecraft Operations Center in Germany completed the Operations Readiness Review for the upcoming launch.
On March 24, the processing team in Plesetsk conducted testing of the satellite’s S-band communication system, while the propulsion specialists inspected the "fill and drain" valve for leaks before the planned fueling of the satellite.
In the following days, engineers tested the GPS units, the onboard time synchronization mechanisms and the payload data-handling unit’s mass memory on the spacecraft. The satellite’s radar altimeter, the ocean and land color instrument, and the sea and land surface temperature radiometer had their ‘nominal and redundant chains with science data’ checked, ESA said.
The propulsion team checked the fuel tank by putting it under pressure to make sure that the ‘latch valve’ doesn’t leak. Since the pressure of the tank was taken to 23 bar, which is considered hazardous, the clean room in Plesetsk was restricted to essential personnel only. Once this was done, the team brought the pressure back down to 2 bar for another important test to check that the satellite’s eight thrusters were also leak-tight. All tests were successful.
Around the same time, the rocket's upper composite, including the Briz-KM stage and the payload fairing, were rolled out to the launch pad at Site 133 and fitted onto the Rockot booster to test the electrics on the complete launch vehicle.
On April 4, 2018, specialists completed electric (dry) tests of the assembled Rockot/Briz-KM vehicle on the launch pad. According to Roskosmos, the launch campaign sequence then called for the removal of the payload section and its return to the processing building on the same night, while the two booster stages of the launch vehicle were to remain on the launch pad.
Once inside the processing building, the payload fairing was removed, so the Briz-KM upper stage could be prepared for fueling. After loading of propellant components, Briz-KM was to be returned to the processing building for the final assembly of the payload section.
On April 9, personnel from ESA and GKNPTs Khrunichev used a heavy truck to transport a large power supply unit to Site 133, where it was installed into a bunker below the launch pad. On the same day, the clean room facility at Hall 101B was cleared of all the equipment except for hardware needed for fueling the satellite with 130 kilograms of hydrazine. Inside Hall 101A, the satellite's solar array deployment arms were armed in preparation for fueling.
The fueling operations on Sentinel-3B and Briz-KM began on April 11 at two separate facilities and were completed by April 13, clearing the way for the final assembly.
On April 14, the fueled satellite was mated with its launch vehicle adapter and electrical checks the next day confirmed a proper interface. The satellite was then transferred to Hall 101B for the integration with the Briz-KM stage.
On April 16, the satellite was integrated with Briz-KM and covered with its payload fairing the next day. Roskosmos declared the assembly operations completed on April 19, 2018. Covered with thermal insulation, the upper composite was installed on the rail transporter on the evening of April 20 and rolled out to the launch pad the next morning. By the end of the day on April 21, the upper composite was lifted by the crane of the service tower and connected to the second stage of the Rockot launcher.
A Rockot/Briz-KM booster with Sentinel-3B lifted off as scheduled from Site 133 in Plesetsk on April 25, 2018, at 20:57:52.016 Moscow Time (1:57 p.m. EDT, 17:57 GMT). The ascent proceeded according to the following timeline:
After few seconds of a vertical ascent, the rocket headed north-northwest on a so-called retrograde trajectory, which will take the vehicle westward, unlike most orbital missions, which fly east with the rotation of the Earth. The ascent profile was designed to insert the satellite into an orbit extending from the North Pole to the South Pole of our planet. It enables remote-sensing satellites to observe the entire planet, as the globe makes a full rotation from west to east under the spacecraft's flight path every 24 hours.
The first stage of the Rockot booster separated two minutes 16 seconds into the flight at an altitude of more than 68 kilometers in the upper atmosphere. Then, more than three minutes into the flight, the payload fairing protecting Sentinel-3B split into two halves and fell off. Both the first stage and the fragments of the payload fairing were expected to fall into the Arctic Ocean between the coast of Norway and Spitsbergen.
The second stage continued firing until 5.3 minutes into the flight, followed by the separation of the Briz-KM upper stage along with the satellite. The Briz-KM then immediately fired its engine for more than nine minutes to insert the stack into a 785 by 153-kilometer initial orbit over the Arctic Canada. The spent second stage was expected to fall into the Northern Atlantic between Greenland and Canada.
The Briz-KM/Sentinel-3B stack continued an unpowered climb along its initial elliptical orbit for slightly more than one hour, interrupted only be a pair of short bursts of attitude control thrusters on Briz-KM to keep the vehicle in a desirable attitude.
The third low-thrust firing of Briz-KM oriented the stage for the second and final major maneuver of the mission. By that time, the vehicle was near the highest point (apogee) of its elliptical orbit, where the main engine fired to circularize the orbit at an altitude of around 817 kilometers. Minutes later, the stage oriented itself for the separation of Sentinel-3B around one hour 20 minutes after the liftoff.
Following the separation of its payload, the Briz-KM stage was programmed to perform two maneuvers to enter a burial orbit, where it will not represent a collision threat for other spacecraft.
Following the scheduled separation, Sentinel-3B successfully established contact with the European ground station in Kiruna, Sweden, which confirmed that activation process aboard the satellite had been going according to schedule.
The control of the satellite was taken over by ground teams at ESOC, ESA's mission control center in Darmstadt, Germany.
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The final assembly of the Sentinel-3B satellite. Credit: ESA
Sentinel-3B is rotated into a vertical position shortly after delivery to Plesetsk in March 2018. Click to enlarge. Credit: ESA
Sentinel-3B is being prepared for installation of the payload fairing on April 17, 2018. Click to enlarge. Credit: ESA
The upper composite with Sentinel-3B is being prepared for transportation to the launch pad. Click to enlarge. Credit: ESA
The upper composite with Sentinel-3B is integrated with the Rockot booster on April 21, 2018. Click to enlarge. Credit: ESA
Click to enlarge. Credit: ESA
Rockot with Sentinel-3B lifts off on April 25, 2018. Click to enlarge. Credit: ESA