Arianespace Soyuz ST-A launches with CSO-1

by William Graham

Arianespace conducted its final launch of 2018 on Wednesday, following a scrub – due to strong winds at the launch site – on Tuesday. The launch used a Soyuz rocket to deploy a high-resolution imaging satellite for the French military. Soyuz lifted off from the Centre Spatial Guyanais – near Kourou, French Guiana.

Wednesday launch deployed CSO-1, the first of three satellites that will form the Composante Spatiale Optique (CSO), or Optical Space Component. These spacecraft will serve the French military, replacing the earlier Helios reconnaissance satellites. To develop the constellation, France’s Direction Générale de l’Armement (DGA – Directorate General of Armaments) has entered into a partnership with the national space agency, CNES.

Airbus Defence and Space is the prime contractor for the three CSO satellites, which are based around its AstroSat-1000 platform. Each satellite has a mass of 3,565 kilograms (7,859 pounds) and is expected to operate for at least ten years. The imaging systems were produced by Thales Alenia Space. From sun-synchronous orbit at an altitude of about 800 kilometers (497 miles, 432 nautical miles), CSO-1 is expected to be able to image the Earth at resolutions of about 35 centimeters (14 inches).

CSO-1 is the first satellite in France’s third generation of reconnaissance satellites, following on from two pairs of Helios spacecraft. The first dedicated French military reconnaissance satellite was Helios-1A, launched atop an Ariane 4 rocket in July 1995.

The near-identical Helios-1B was deployed in December 1999 to replace it. A second generation of Helios spacecraft with higher-resolution imaging systems followed: Helios-2A was deployed by an Ariane 5G+ on 18 December 2004 and Helios-2B launched aboard an Ariane 5GS five years later, to the minute. Remarkably, CSO-1 was scheduled to lift off on the anniversary of both of these launches, although the launch time for Tuesday’s mission was eleven minutes later than for the two Helios launches. The scrub to Wednesday extends that by a day.

CSO-1 – via Arianespace

Once all three satellites have been launched, CSO will operate with two satellites in the 800-kilometer orbit, while CSO-2 will use a lower orbit for higher-resolution imaging. CSO-2’s mission has been described as one of identification – distinguishing features observed by its sister satellites in the higher orbit. CSO-2 is currently slated for launch in 2020 or 2021, with CSO-3 joining the constellation a year or two later.

CSO-1 was launched by Paris-based Arianespace, who have deployed all of France’s previous reconnaissance satellites. Arianespace operates a fleet of three different types of rockets: Vega is used to launch smaller satellites, Ariane 5 carries the heaviest payloads – typically pairs of geostationary communications satellites – and the Russian Soyuz rocket fills the gap in capacity between these two vehicles. The mission used Soyuz, in its Soyuz ST-A configuration with a Fregat-M upper stage.

The Soyuz ST-A is based on the Soyuz-2-1a rocket, incorporating modifications specific to using Arianespace’s launch site, the Centre Spatial Guyanais (CSG), located near Kourou in French Guiana. Soyuz-2-1a is itself one of three modernized versions of earlier Soyuz rockets, derivatives of Sergei Korolev’s R-7 missile that have been used for Russian (and formerly Soviet) satellite and crewed spaceflight launches since the 1960s.

Soyuz ST-A during pre-payload integration – via Arianespace

Soyuz-2-1a made its first suborbital test flight in 2004 and its first orbital launch two years later. It introduced upgraded first and second stage engines over the previous-generation Soyuz-U, as well as a digital flight control system and other enhancements. A second Soyuz-2 configuration, the Soyuz-2-1b (operated by Arianespace as the Soyuz ST-B) also has an upgraded third stage engine. The smaller Soyuz-2-1v is designed to carry lighter payloads, but this version of the rocket is not used by Arianespace.

Soyuz is a three-stage rocket, although the first and second stages fire together at liftoff. To reach higher orbits or perform more complex missions, Soyuz can be used in conjunction with an upper stage. For this mission a Fregat-M will be used to insert CSO-1 into its planned sun-synchronous orbit. Fregat is the most common type of upper stage flown on Soyuz; it is based on the propulsion systems of the Soviet Union’s late interplanetary probes and can restart its engine multiple times over a lengthy extended mission to ensure delivery of its payload into the required orbit.

The launch was the twentieth flight of a Soyuz from French Guiana. The Soyuz launch pad, Ensemble de Lancement Soyouz (ELS), was first used in October 2011 for the deployment of a pair of Galileo navigation satellites. Including the vehicle that is performing the CSO-1 mission, six Soyuz ST-A and fourteen Soyuz ST-B rockets have departed Kourou. All but one of the Soyuz launched from Kourou – a Soyuz ST-B whose Fregat upper stage malfunctioned – have completed their missions successfully.

Arianespace’s Soyuz launch pad – via Arianespace

Soyuz launches also take place from the Baikonur Cosmodrome in Kazakhstan and the Plesetsk and Vostochny Cosmodromes in Russia.

Arianespace’s designation for this mission was VS20. The launch began with ignition of the first and second stage engines about sixteen seconds before liftoff. The first stage of the Soyuz ST-A vehicle consists of four boosters with RD-107A engines, clustered around the second stage which is powered by a single RD-108A.

The rocket’s engines built up thrust while the rocket was held down, reaching full power at the T-1 second mark in the countdown. At zero, the launch pad’s swing arms open, and Soyuz began its climb towards space.

Soyuz ST-A during a previous launch – via ESA

The rocket’s first and second stages burned together for the first minute and fifty-eight seconds of ascent. At this point the four first-stage boosters shut down, venting excess oxygen to push their noses away from the rocket as they separate. The pattern made by the separating boosters is known as the Korolev Cross after the rocket’s chief designer.

After the first stage separated, Soyuz continued to fly under the power of its second stage for another two minutes and 49 seconds. About thirty-two seconds before the end of second stage flight the payload fairing separated from the nose of the rocket.

The second and third stages are designed to separate while the second stage is still firing. The third stage ignited its RD-0110 engine while the RD-108A is still burning to ensure the propellant remains settled in the third stage tanks. The third stage fired for four minutes and two seconds before deploying Fregat to continue CSO-1’s journey to orbit.

Sixty seconds after separating from the third stage, Fregat ignited its S5.98M engine for the first of three planned burns. This lasted eight minutes and fifty-two seconds, setting up an initial parking orbit. After a 35-minute, 34-second coast phase Fregat fired again for another 89 seconds, circularising the orbit.

CSO-1 separated from Fregat five minutes after its second burn concluded – about one hour and 44 seconds after liftoff. Fregat will make its third and final burn four seconds short of 51 minutes later, with this 55-second maneuver serving to deorbit the stage so as not to leave unnecessary debris in orbit.

The CSO-1 launch was the eleventh and last for Arianespace in 2018, following two previous Soyuz missions, two Vega launches and six Ariane 5s. Arianespace’s next launch is scheduled for late January with the HS4-SGS1 and GSAT-31 communications satellites aboard and Ariane 5, while the next Soyuz launch from Kourou is expected to carry four O3b satellites in the first quarter of the new year.

One more Soyuz launch is expected from Russia before the end of the year: a Soyuz-2-1a/Fregat-M vehicle is scheduled to lift off from the Vostochny Cosmodrome on 27 December, with its primary payload a pair of Kanopus-V remote sensing satellites.

Related Articles