Wednesday, April 25, 2018

Rokot Sends Europe’s Sentinel-3B Earth-Observing Satellite to Orbit

Rokot lifts off with Sentinel-3B. Credit: ESA

A Russian Rokot booster took to the skies on Wednesday, April 25, on a mission to orbit Sentinel-3B - the latest satellite of Europe’s Copernicus Earth observation program. The launch vehicle blasted off at 1:57 p.m. EDT (17:57 GMT) April 25, 2018, from Site 133/3 at the Plesetsk Cosmodrome in northern Russia.

Powered by a cluster of three RD-0233 engines and one RD-0234 engine, Rokot thundered off the pad to complete a brief vertical climb after which it started into northwesterly direction. The first stage was accelerating the launch vehicle for the first one minute and 19 seconds of the mission until it was separated and the second stage took control over the flight.

The second stage was powering the rocket for about three minutes. During this phase of the flight, the protective payload fairing was jettisoned, what uncovered the mission’s sole passenger. Separation of the second stage occurred around five and a half minutes after liftoff.

Afterward, the longest phase of the flight commenced, when the Briz-KM upper stage fired its S5.98M engine. Lasting about one hour and 15 minutes, this part of the mission is planned to conclude with an injection of the Sentinel-3B satellite into a Sun-synchronous orbit (SSO) at an altitude of some 503 miles (810 kilometers), inclined 98.65 degrees. In order to complete this task, Briz-KM is scheduled to conduct to engine burns.

If the deployment of Sentinel-3B is successful, ground stations of the European Space Operations Centre (ESOC) will seek to establish contact with the satellite in orbit.

“Following separation from the upper stage, we have to wait about 13 minutes until we receive the first signals from Sentinel-3B via our Kiruna ground station in Sweden, while the satellite uses its sensors and actuators to stabilize itself toward a Sun-pointing attitude,” said Pier-Paolo Emanuelli, Flight Director at ESOC.

Wednesday’s launch of Rokot ends a five-week long mission campaign, which started with the arrival of the Sentinel-3B satellite in Russia.

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). Built by Thales Alenia Space, the 2,600-pound (1,200-kilogram) satellite is designed to have an operational of some seven years.

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.

“Once Sentinel-3B is launched, the end user will have twice as much data, with hopefully twice as much value. But one has to see this constellation of Sentinel-3A and -3B as a single source of measurements, not two different satellites. This is why, during the commissioning phase, where the satellites fly in a tandem configuration, we will intercalibrate the instruments to understand more accurately their response to the same signal,” said François Montagner, Marine Applications Manager at Eumetsat.

“Later, during regular operations, we will keep the satellites apart, to ensure that there is minimum redundancy between the two datasets. There should be no surprises – apart from what we will learn from the additional information,” he added.

In order to achieve 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.

Formerly known as Global Monitoring for Environment and Security (GMES), the Copernicus 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.

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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