Sunday, April 22, 2018

Russian Rokot Launcher to Orbit Sentinel-3B Earth-Observing Satellite on Wednesday

Sentinel-3B being mated with the Rokot adapter. Photo Credit: ESA - S. Corvaja

Russian Rokot launch vehicle is poised to blast off from the Plesetsk Cosmodrome on Wednesday, April 25, tasked with the delivery of European Sentinel-3B Earth-observing satellite. The rocket will blast off from Plesetsk’s Site 133/3 at 17:57 GMT (1:57 p.m. EDT).

Launch campaign for the mission kicked off on March 17, when an Antonov aircraft transporting Sentinel-3B from France landed in Archangielsk, from where it departed by train and arrived at Plesetsk one 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, ESA’s Sentinel-3 engineering manager said back then.

In late March, the engineers were busy conducting initial tests of the spacecraft, together with electrical tests of the Rokot launcher and checks of the rocket’s Briz-KM upper stage. Numerous checks included testing the GPS units, the onboard time synchronization mechanisms and the payload data-handling unit’s mass memory.

On April 11-13 the fueling operations of the spacecraft were carried out. Meanwhile, the teams also filled the Briz-KM upper stage with propellants what cleared the way for commencing the last phase of pre-launch activities.

After the fueling, the satellite was mated with the Briz-KM upper stage on April 16, what marked the first step of the full integration of the launch vehicle. Next on the list is the final dress rehearsal scheduled to be conducted two days ahead of liftoff, and if everything goes as planned, the State Commission will give green light for the start of countdown operations for the launch.

Wednesday’s flight should last some one 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. The injection into the correct orbital spot will rely mostly on the Briz-KM upper stage and its two burns during the ride into space.

Built by Thales Alenia Space, Sentinel-3B is an Earth observation satellite dedicated to monitoring the world’s oceans as well as the world’s vegetation. It measures approximately 12.1 by 7.2 by 7.2 feet (3.7 by 2.2 by 2.2 meters). The satellite, designed to be operational for up to seven years, weighs approximately 2,645 lbs. (1,200 kg), and consumes about 1.1 kW of power.

Sentinel-3B combines a multi-spectral optical element with an altimetry component. Instruments on the satellite will be used to help to produce measurements of the sea surface, ice surface, and in-land water topography. It is hoped Sentinel-3B will deliver data within three hours of making passes high above our home world – 24 hours a day, 365 days a year.

Sentinel-3B carries four instruments that will work together as one. The medium-resolution Ocean and Land Color Instrument (OLCI) will 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).

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 Sentinel-3B will 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 advertised, it will provide altimeter data with a spatial resolution of approximately 984 feet (300 meters) along the satellite’s track.

The fourth instrument is a dual-frequency MicroWave Radiometer (MWR) based on heritage technology that was derived from the Envisat. The primary purpose of this instrument is to correct the delay of radar altimeter signals traveling through the atmosphere. The MWR also serves to measure total column atmospheric water vapor.

If everything goes as planned, in orbit Sentinel-3B will join its twin, Sentinel-3A that was launched February 16, 2016. Separation by 140 degrees in orbit should help the both satellites to measure ocean features such as eddies as accurately as possible.

Sentinel spacecraft are part of the Copernicus program, a result of 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, to 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 satellites and delivering the marine mission and will also operate and deliver products from the Sentinel-4, and -5 instruments, and the Sentinel-6 satellites.

The Rokot launch vehicle is a 95-foot tall (29 meters) liquid-fueled three-stage rocket manufactured by Eurockot Launch Services. With a total mass of 107 metric tons, the booster is capable of delivering up to two metric tons into low-Earth orbit (LEO) and 1.2 metric tons to SSO. The vehicle uses the SS-19/(RS-18) “Stiletto” intercontinental ballistic missile (ICBM) for its first two stages. The first Rokot launch was conducted in November of 1990 and has been selected some 28 times since that inaugural flight.

Briz-KM is 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 engine burning for up to 50 minutes in order to deliver a payload into orbit.

The Briz-KM control system includes an onboard computer, a three-axis gyro stabilized platform, and a navigation system. The quantity of propellant carried is dependent on specific mission requirements and is varied to maximize mission performance.

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