Tuesday, February 16, 2016

Sentinel-3A Earth-observing Satellite Successfully Launches from Plesetsk

Sentinel-3A liftoff. Credit: ESA

Europe saw the successful launch of its Sentinel-3A satellite on Tuesday, Feb. 16, expanding its fleet of Earth observation spacecraft. The satellite lifted off from Site 133/3 at the Plesetsk Cosmodrome in northern Russia at 12:57 p.m. EST (17:57 GMT) atop a Russian Rokot launch vehicle (also known as “Rockot”).

At liftoff, Rokot started its short vertical ascent before pitching over and heading in a north-west direction. About two minutes and 19 seconds into the flight, the first stage shut down and separated from the launch vehicle. Approximately 47 seconds later, the payload fairing was jettisoned, unveiling the Sentinel-3A spacecraft. The launch vehicle continued its flight for the next two minutes and 16 seconds until separation of the second stage occurred.

The Briz-M upper stage, stacked together with the satellite, fired its engine six seconds later. The mission, from this moment on, relied on the thrust provided by the upper stage. Sentinel-3A was pushed forward by two engine burns from the upper stage. These burns were conducted to fulfill the task of injecting the spacecraft into a targeted near-polar, Sun-synchronous orbit (SSO) at an altitude of some 506 miles (815 kilometers), inclined 98.65 degrees. The satellite’s deployment occurred about one hour and 20 minutes after liftoff.

The spacecraft was shipped to Plesetsk in December of last year (2015). The launch of the Sentinel-3A mission, was initially scheduled for late January. It was postponed due to a ‘re-certification’ process of the launch pad.

During the first week of February, the so-called ‘combined operations’ started with the mating of the satellite with the launch vehicle adapter and to put this stack on top of the upper stage. The teams also carried out electrical checkouts on the adapter system. Finally, the spacecraft was encapsulated in the payload fairing.

The Rokot booster was rolled out to the launch pad on Friday, Feb. 12. Two days before liftoff, on Feb. 14, the final dress rehearsal took place at the Mission Control Center (MCC) to simulate completely all activities of the launch day.

“We’ve practiced all phases of the flight during more than 25 ‘sim’ sessions, including when everything goes according to plan, and when anomalies or system failures occur,” said European Space Agency’s (ESA) satellite operations manager José Morales.

On the same day, the State Commission gave the mission a green light, allowing fueling of the launch vehicle to begin.

Countdown operations started seven hours ahead of the planned liftoff time. During this phase, the spacecraft was configured for launch. Final checkouts were made, including data flow checks with the various ground stations that supported the mission.

Sentinel-3A, roughly the size of a car, 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 weighs approximately 2,645 lbs. (1,200 kg), and consumes about 1.1 kW of power. Sentinel-3A was built by Thales Alenia Space, and it is expected to be operational for up to seven years.

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

Artist's rendering of the Sentinel-3A satellite in space. Credit: ESA–Pierre Carril
Artist's rendering of the Sentinel-3A satellite in space. Credit: ESA–Pierre Carril

Sentinel-3A 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).

“SLSTR also includes dedicated channels for active fire monitoring. It is a dual view scanner, with a swath of 1,420 kilometers (Nadir) and 750 kilometer (backwards). The OLCI and SLSTR swaths fully overlap for synoptic views of the same area and production of specific synergy products,” Bruno Berruti, European Space Agency’s (ESA) Sentinel-3 Project Manager, told SpaceFlight Insider.

The third instrument Sentinel-3A 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.

Sentinel-3 is part of a constellation of two satellites operating at the same altitude which should optimize coverage. Sentinel-3A and Sentinel-3B (scheduled to be launched in 2017) should provide global coverage every two days.

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.

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 that was used to lift the Sentinel-3A satellite is a 95-feet 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-M is a liquid-propellant fueled upper stage designed to boost payloads into orbit (manufactured by Khrunichev State Research and Production Space Center). It is composed of a central core and an auxiliary propellant tank that is jettisoned in flight following the depletion of the stage’s propellant. The Briz-M 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.

Tuesday’s mission is the first use of the Rokot system since Sept. 23, 2015, when it launched three Strela communications satellites into orbit. The launch of Sentinel-3A marks the second mission conducted from Plesetsk in 2016.

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