Russian Rokot launcher to orbit Sentinel-3B Earth-observing satellite
A Russian Rokot launch vehicle is poised to launch the European Sentinel-3B Earth-observing satellite to orbit at 1:57 p.m. EDT (17:57 GMT) April 25, 2018, from Site 133/3 at the Plesetsk Cosmodrome.
The campaign for this mission kicked off on March 17, 2018, when an Antonov aircraft transporting the Sentinel-3B spacecraft from France landed in Archangielsk, Russia. There, it was transported by train to Plesetsk a day later.
“The satellite’s journey from France was hampered slightly by the freezing winter weather here in Russia, but it’s now safe in the milder cleanroom environment,” Kristof Gantois, the European Space Agency’s Sentinel-3 engineering manager said in a March 23 European Space Agency news release.
In late March, engineers were busy conducting initial tests of the spacecraft, together with electrical tests of the Rokot launcher as well as checks of the rocket’s Briz-KM upper stage. The numerous tests included reviewing the GPS units, the onboard time synchronization mechanisms and the payload data-handling unit’s mass memory.
Fueling operations of the spacecraft were carried out between April 11-13. Meanwhile, the teams also filled the Briz-KM upper stage with propellants, which cleared the way for commencing the last phase of pre-launch activities.
After being fueled, the satellite was mated with the Briz-KM upper stage on April 16. This marked the first step of the full integration of the launch vehicle.
Next on the list was the final dress rehearsal, which was conducted two days ahead of liftoff. If everything goes as planned, the State Commission is expected to give the green light for launch operations to get underway.
Wednesday’s flight should last for about 1 hour and 20 minutes in order to deliver the Sentinel-3B satellite into a Sun-synchronous orbit (SSO) at an altitude of some 503 miles (810 kilometers), inclined 98.65 degrees. If everything goes off without a hitch, the satellite will be injected into its proper orbital spot. This final phase of the flight – relies mostly on the Briz-KM upper stage and the two burns its tasked with completing.
Built by Thales Alenia Space, Sentinel-3B is an Earth-observation satellite dedicated to monitoring the world’s oceans as well as Earth’s vegetation. It measures approximately 12.1 by 7.2 by 7.2 feet (3.7 by 2.2 by 2.2 meters). The 2,600-pound (1,200-kilogram) satellite is designed to have an operational of some seven years.
The Sentinel-3B spacecraft combines a multi-spectral optical element with an altimetry component. Instruments on the satellite are designed be used to help produce measurements of sea and ice surface as well as land-based water topography.
To carry out its objectives Sentinel-3B carries four instruments that are meant to work together as a single unit. The medium-resolution Ocean and Land Color Instrument (OLCI) is expected to provide multi-spectral data with a ground resolution of up to 984 feet (300 meters) per pixel with a swath of 790 miles (1,270 kilometers).
Meanwhile, the Sea and Land Surface Temperature Radiometer (SLSTR) is designed to deliver highly accurate temperature readings of the Earth’s surface with a ground resolution of 1,640 to 3,280 feet (500 to 1,000 meters).
The third instrument on Sentinel-3B is designed to use is a dual-frequency (Ku and C band) advanced Synthetic Aperture Radar Altimeter (SRAL) which was developed from the Envisat and CryoSat satellites. If it works as envisioned, it should provide altimeter data with a spatial resolution of approximately 984 feet (300 meters) along the satellite’s track.
Finally, the fourth instrument is a dual-frequency MicroWave Radiometer (MWR) based on heritage technology that was derived from Envisat. The primary purpose of this component is to correct the delay of radar altimeter signals traveling through the atmosphere. The MWR should also serve to measure total column atmospheric water vapor.
If everything goes as planned, Sentinel-3B is expected to join its twin, Sentinel-3A, which was launched on Feb. 16, 2016. A separation of 140 degrees in orbit should help both satellites to measure ocean features such as eddies as accurately as possible.
The Sentinel spacecraft are part of the Copernicus program, which is the result of a close collaboration between ESA, the European Commission, Eumetsat, France’s CNES space agency, industry, service providers, and data users.
Formerly known as Global Monitoring for Environment and Security (GMES), the project aims at achieving an autonomous, multi-level operational Earth observation capability. It uses accurate and timely data to provide key information services to improve the way the environment is managed. It is hoped that this will help mitigate the effects of climate change, and to ensure civil security.
“Sentinel-3 is an extremely complex mission, and I am very proud to say that it’s delivering on its promise,” ESA’s Sentinel-3 mission manager, Susanne Mecklenburg said in July 2017.
ESA is responsible for the development of the space segment component of the Copernicus program and operates the Sentinel-1 and Sentinel-2 satellites. EUMETSAT is responsible for operating the Sentinel-3 spacecraft and delivering the marine elements of the mission and is also expected to operate and deliver the data from the instruments on the Sentinel-4, 5 and 6 satellites.
The Rokot launch vehicle which first took to the skies in November of 1990, is a 95-foot (29-meter) tall liquid-fueled, three-stage rocket manufactured by Eurockot Launch Services. With a total mass of some 107 metric tons, the rocket is capable of delivering up to two metric tons to low-Earth orbit and 1.2 metric tons to SSO. The launch vehicle uses the SS-19/(RS-18) “Stiletto” intercontinental ballistic missile (ICBM) for its first two stages.
The Briz-KM upper stage measures in at about 8.5 feet (2.6 meters) long and 8.2 feet (2.5 meters) in diameter. With a mass of about 6.5 metric tons, this stage uses one S5.98M rocket engine burning for up to 50 minutes in order to deliver its payload into orbit. The stage’s control system includes an onboard computer, a three-axis gyro stabilized platform, as well as a navigational system. The quantity of propellant carried is dependent on specific mission requirements and varies so as to maximize mission performance.
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