Arianespace Soyuz ST-B launches Metop-C

by William Graham

Arianespace launched a new European weather satellite Tuesday, using a Soyuz rocket to deploy the Metop-C spacecraft into orbit around the Earth. Liftoff from the Centre Spatial Guyanais in Kourou, French Guiana, occurred at 21:47:27 local time (00:47 UTC on Wednesday).

The Meteorological Operational (Metop) satellites are operated by the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT), making up the EUMETSAT Polar System (EPS). Operating in near-polar sun-synchronous orbits, Metop satellites carry a suite of instruments to study and monitor the Earth’s weather.

The EUMETSAT Polar System contributes to the Initial Joint Polar System (IJPS), an international partnership between EUMETSAT and the United States National Oceanic and Atmospheric Administration (NOAA). IJPS, which also incorporates the NOAA’s Polar Operational Environmental Satellites (POES), sees the two agencies share data and use each other’s ground stations to control their satellites and downlink data. The NOAA has also provided several of the instruments that fly aboard Metop satellites.

Metop is one of two series of weather satellites operated by EUMETSAT: the organization also operates a fleet of spacecraft in higher geostationary orbits, Meteosat. EUMETSAT also partners with the European Space Agency (ESA) and European Commission on the Sentinel Earth science missions, and with ESA, NOAA and NASA on the Jason ocean research satellites.

MetOp-C during construction – via Airbus

Constructed by Airbus Defence and Space – formerly EADS Astrium – the 4,084-kilogram (9,004 lb) Metop-C is based on the SPOT Mk.3 satellite bus, a platform originally developed for France’s SPOT imaging spacecraft. The satellite is three-axis stabilized and uses a deployable solar array to generate power for its onboard systems.

The sun-synchronous orbit in which Metop satellites operate allows each spacecraft to pass over the Earth’s surface at approximately the same mean solar time in each location. Metop-C will orbit the Earth at an altitude of approximately 811 kilometers (504 miles, 438 nautical miles), inclined at 98.74 degrees. The orbit Metop satellites use is designed so they can observe points on the surface in the mid-morning – about 09:30 – in their local time. NOAA’s satellites use orbits suited to afternoon observations, complementing Metop’s data.

Metop-C will be the third member of the Metop constellation, joining the Metop-A and Metop-B satellites which were launched in 2006 and 2012 respectively. While each Metop satellite is designed to operate for five years, both Metop-A and Metop-B have exceeded their design lives and remain in service. The three spacecraft are of the same design, carrying the same suite of instruments.

Three of these instruments were provided by the NOAA. The Advanced Very High Resolution Radiometer 3 (AVHRR/3), Advanced Microwave Sounding Unit A (AMSU-A) and Space Environment Monitor 2 (SEM-2) are identical to instruments that were flown aboard the NOAA’s fifth-generation POES satellites, that were being launched at the time the Metop spacecraft were developed. All three instruments have previously flown aboard five US weather satellites, beginning with NOAA-15 in 1998, and the two previous Metop spacecraft.

AVHRR/3 is the primary instrument for collecting images of the Earth, to make visual observations such as studying cloud cover. Incorporating a 20.3-centimeter (8-inch) Cassegrainian telescope, AVHRR/3 images the surface in visible light and the infrared. AMSU-A consists of two line-scanning microwave radiometers which will be used to build up temperature profiles for Earth’s atmosphere. SEM-2 is a space weather instrument, consisting of a spectrometer that will be used to monitor the energy and density of charged particles in Earth’s radiation belts and solar radiation.

The Microwave Humidity Sounder (MHS) is another instrument that has previously flown aboard NOAA spacecraft, as part of EUMETSAT’s contribution to those missions. It is a scanning microwave radiometer which collects energy radiated by the Earth and uses it to build up a profile of humidity in the atmosphere as well as liquid water in the form of clouds and precipitation. MHS has flown aboard all three Metop satellites, as well as the NOAA’s NOAA-18 and 19 satellites, launched in 2005 and 2009 respectively.

The Interféromètre Atmosphérique de Sondage (IASI), or Infrared Atmospheric Sounder Interferometer will build a highly-accurate numerical model of temperatures and humidity. IASI consists of a Fourier transform spectrometer which can create a profile of the atmosphere to a resolution of one kilometer (1,094 yards). IASI can also determine surface temperatures and the presence of gases such as carbon dioxide, methane, nitrogen dioxide and ozone in the atmosphere.

ASCAT, or Advanced Scatterometer, will be used to study the speed and direction of wind over the planet’s oceans. ASCAT uses a C-band microwave radar system, sending pulses towards the surface and recording how the signals are scattered back towards the satellite. Over water, scientists will be able to infer the wind speed and direction by how the signals were affected, while over land the radar will help to identify the properties and water content of the ground.

The Global Ozone Monitoring Experiment 2, GOME-2, is a spectrometer which optically measure the atmospheric levels of ozone, aerosols and greenhouse gases. The GNSS Receiver for Atmospheric Sounding (GRAS) will use a technique called limb sounding, studying the occultation – or distortion – of signals from navigation satellites as they pass behind the planet and their signals travel through the atmosphere to reach Metop-C. By studying how the signal has shifted in phase, the atmospheric conditions in the region of the atmosphere it passed through – such as the temperature, pressure and humidity – can be determined.

In addition to its meteorological payloads, Metop-C also carries the Argos Advanced Data Collection System (A-DCS, or Argos-3), consisting of a receiver-processor and a transmitter. This collects data from remote research buoys, stations and wildlife tracking beacons and relays it back to central stations for analysis and dissemination. A-DCS was provided by NOAA and is based on a similar data collection system flown aboard their satellites.
Metop-C is the final first-generation Metop satellite to be launched. The Metop Second Generation (Metop-SG or MSG) satellites are scheduled to begin launching in the early 2020s. Metop-SG will use two satellites equipped with different instruments to collect complimentary data, with three satellites of each type launching sequentially to continue data collection for almost another thirty years.

Arianespace used a Soyuz ST-B rocket with a Fregat-M upper stage to place Metop-C into orbit. The Soyuz ST-B is a version of the Soyuz-2-1b vehicle, optimized for launch from Arianespace’s Centre Spatial Guyanais launch site in French Guiana.

Both previous Metop satellites also launched aboard Soyuz-2 rockets. Metop-A was the first payload to be launched aboard a Soyuz-2, flying on the second Soyuz-2-1a in October 2006, after the rocket’s maiden flight had carried an inert, obsolete, spacecraft. This was also the first Soyuz-2 launch with a Fregat upper stage.

Metop-B was launched atop a Soyuz-2-1a/Fregat-M in September 2012. Both launches were conducted by Arianespace’s subsidiary Starsem, with the rockets flying from the Baikonur Cosmodrome in Kazakhstan.

Soyuz ST-B rolled out head of payload mate – via Arianespace

Soyuz-2 is a modernized version of Russia’s Soyuz family of rockets. First flown in 1966, Soyuz was an upgraded version of the earlier Voskhod rocket, itself developed from Sergei Korolev’s R-7 missile. Soyuz-2 introduced upgraded first and second stage engines and a new digital flight control system.

Three different versions of the Soyuz-2 have been flown: The Soyuz-2-1a is the basic version, modernizing the previous-generation Soyuz-U, while the Soyuz-2-1b also upgrades the upper stage with an RD-0124 engine. The Soyuz-STA and STB configurations incorporate additional modifications, including flight termination packages, necessary for operation from French Guiana.

The third configuration, Soyuz-2-1v, is a smaller vehicle without the first stage boosters used on the Soyuz-2-1b. However, it is only launched from Russia.

The Soyuz-STB/Fregat-M is a four-stage rocket, consisting of the three-stage Soyuz and the Fregat upper stage. All three stages of the Soyuz burn RG-1 fuel – a refined petroleum product – oxidized by liquid oxygen, while Fregat uses storable propellant. Designated VS19 under Arianespace’s numbering scheme for its missions, Soyuz will take just over an hour to place Metop-C into orbit.

Fuelling of the Soyuz rocket began four and a half hours before the planned liftoff, continuing until 95 minutes before launch. Shortly afterwards – about seventy minutes before liftoff – the launch pad’s mobile service tower was moved away from Soyuz. Tuesday’s launch was targeting an instantaneous opportunity, so any hold in the countdown would have resulted in a scrub and a delay of at least 24 hours.

Many of the critical events in the countdown occur in the last five minutes before launch. About five minutes and ten seconds before liftoff, flight controllers turned the launch key to enable startup of the rocket. Shortly afterwards the upper stage moved onto internal power.

The first of two umbilical towers at the launch pad, which provides connections to the spacecraft and Fregat, retracted two minutes and 25 seconds before liftoff. The second umbilical retracted about 28 seconds before launch following the transfer of Soyuz to internal power at the H-40 second mark in the countdown.

Sixteen seconds before liftoff the first stage’s four RD-107A engines, and the RD-108A engine of the second stage, ignited. The engines took fifteen seconds to build up to full thrust.

Once the countdown reached zero, Soyuz was released to begin its ascent towards space. For the first minute and fifty-eight seconds of the mission, the first and second stages burned together to push the rocket through the dense lower regions of Earth’s atmosphere. The first stage then separated, leaving the second stage to continue powering the rocket’s ascent.
The first stage of a Soyuz rocket consists of four boosters, clustered around the second stage. When these separate, valves in the nose of each booster open to vent remaining oxygen, which pushes the boosters away from the core vehicle. The separation of the four boosters makes a pattern known as the Korolev Cross, after the rocket’s chief designer. This occurred without incident.

About ninety-eight seconds after first stage separation, the payload fairing separated from around Metop-C at the nose of the rocket. The fairing, which protects the satellite and upper stage from Earth’s atmosphere during the early stages of flight, was no longer needed once Soyuz reached space and was discarded to save weight.

Two minutes and fifty seconds after first stage separation, Soyuz reached the end of second stage flight. At this point, the third stage fired its RD-0124 engine while the second stage was still burning, allowing the acceleration from the second stage engine to keep propellants settled in the third stage tanks. The third stage burned for four minutes and thirty-six seconds during Tuesday’s mission.

At the end of the third stage burn, Fregat was released to begin its role in the launch. About one minute after separating from the third stage of the Soyuz rocket, Fregat’s S5.98M engine ignited for the first of three planned burns. The S5.98M consumes unsymmetrical dimethylhydrazine propellant and dinitrogen tetroxide oxidizer and can make multiple burns to ensure precise injection of Fregat’s payloads into orbit.

During Tuesday’s launch, Fregat’s first burn lasted three minutes and 16 seconds. Afterwards, the ascent entered a coast phase for forty-eight minutes and forty-three seconds before a second burn took place to circularise the orbit. The second burn lasted 75 seconds.

Fregat Upper Stage – via ESA

Six minutes and forty seconds after the end of the second burn – at one hour and eighteen seconds mission elapsed time – Metop-C separated from Fregat to begin its mission. Fifty-two minutes later, Fregat made a final, twenty-second burn to remove itself from orbit, concluding Tuesday’s launch.

The Metop-C mission was Arianespace’s eighth launch of 2018. It is also the twelfth flight of Soyuz this year, although only one of the year’s previous launches was conducted by Arianespace. Tuesday’s launch took place less than a month after the failure of a Soyuz-FG launch, in a mission out of the Baikonur Cosmodrome that was to carry a crew of two to the International Space Station aboard the Soyuz MS-10 spacecraft. Soyuz has since returned to flight with two successful launches for the Russian military in the last fortnight. This was the third success.

Up to five more Soyuz launches could take place before the end of the year. The next of these is scheduled for 18 November, with a Soyuz-FG launching the Progress MS-10 resupply mission to the International Space Station. If this goes to plan, another Soyuz-FG will launch at the start of December with Soyuz MS-11 and a crew of three bound for the station.

Arianespace has one more Soyuz launch on their books for 2018, planned for mid-December with France’s CSO-1 reconnaissance satellite aboard. Two more launches at the end of the year – from the Vostochny and Baikonur Cosmodromes respectively – will deploy a pair of Kanopus-V spacecraft and the EgyptSat-A remote sensing mission.

Before next month’s Soyuz launch, Arianespace will fly missions with both of the other rockets in their fleet. Around 20 November a Vega rocket will launch Mohammed VI-B for Morocco, while an Ariane 5ECA is expected to lift off in early December with India’s GSAT-11 communications satellite and South Korea’s geostationary Cheollian-2A weather satellite. An additional Ariane 5 launch could also take place later in December.

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