Soyuz ST

The Soyuz-ST-A and ST-B were modified versions of the Soyuz-2 rocket, designed to launch from the Guiana Space Centre (CSG) in French Guiana. Developed as part of a European Space Agency (ESA) programme to add a medium-lift launch vehicle to complement the light-lift Vega and heavy-lift Ariane 5 rockets.

A collaborative effort between Russia and Europe, the project involved constructing the Ensemble de Lancement Soyouz (ELS; ) at the CSG and adapting the Soyuz 2 to the tropical climate. The first launch of a Soyuz ST-B occurred on 21 October 2011, while the first ST-A launch occurred on 17 December 2011.

The Soyuz-ST-A and ST-B were four-stage rockets designed for low Earth orbit missions. Notably, their stage numbering differs from that of some rockets, with the boosters considered the first stage and the central core the second. Unlike the standard Soyuz-2, the Fregat upper stage was mandatory for the ST variants.

Between 2011 and 2022, 27 Soyuz-ST rockets were launched from the CSG, with 26 successful missions. Most of these launches utilized the more powerful ST-B variant, while nine employed the ST-A.

However, the Russian invasion of Ukraine in 2022 created diplomatic tensions between Russia and Europe, ending Soyuz launches from the CSG. Additionally, the introduction of the Vega C and Ariane 6 launchers, both offering medium-lift capabilities, rendered the role of Soyuz largely redundant.

Soyuz modifications for the Guiana Space Centre

To accommodate the conditions and requirements of the CSG, Soyuz rockets underwent several key modifications. These adaptations ensure the vehicle's optimal performance and safety within the tropical environment.

Launch Infrastructure and Payload Integration

* Mobile Service Tower: Unlike other Soyuz launch complexes, the ELS employed a mobile service tower that enabled vertical payload integration directly on the launchpad.
* European Payload Adapters: Launch vehicles used European-supplied payload adapters, enhancing compatibility with a broader range of spacecraft.
* Engine Ignition: At the ELS, the engines of the boosters and first stage were pyrotechnically ignited. At other Soyuz launch complexes, engines are chemically ignited.

Enhanced Safety Systems

* European Safeguard Kit (): This system can locate the rocket in real-time and, if necessary, transmit a flight termination signal, ensuring the safe destruction of the vehicle in the event of an anomaly.
* Destruct System for Boosters and Core Stage: Boosters and core stage are equipped with pyrotechnic devices to ensure they sink in the ocean for disposal after flight.
* S-Band Telemetry System Adaptation: The S band telemetry system is modified to operate on the Inter-Range Instrumentation Group standard used at the CSG.

Environmental Adaptation

* Tropical Climate Adaptation: The air conditioning system is adapted to keep the payload cool inside the faring, and protective measures are added to reduce icing when loading cryogenic fluids in the humid environment.
* Pest Control: To avoid potential wildlife intrusions, all cavities and openings within the rocket were studied and certified to be adequately sealed against insects and rodents.

Vehicle processing

Soyuz rockets arrive at the CSG by ship, where components are offloaded and stored for assembly. In preparation for launch, these components are transferred to the temperature-controlled Launch Vehicle Integration (LVI) Building. Here, in a horizontal orientation, the four strap-on boosters are attached to the core stage, followed by the third stage. Several days before launch, a dedicated transporter moves the assembled Soyuz stages from the LVI Building to the launchpad. At the pad, the launch vehicle is erected into a vertical position, and the mobile service tower is moved into place.

Concurrently, within the Payload Processing Facility (PPF) clean room, customer teams prepare their spacecraft. The day before leaving the PPF, the spacecraft is integrated with an adapter/dispenser. This assembly is then transferred to the S3B building, where the fueled Fregat upper stage awaits. Here, the spacecraft and Fregat are integrated and encapsulated within the payload fairing.

Everything comes together on the third day prior to launch when the mobile service tower lifts the encapsulated spacecraft and Fregat upper stage, positioning them atop the Soyuz launch vehicle. Finally, approximately one hour before launch commences, the mobile service tower is meticulously retracted, readying the Soyuz for its mission.

Launch history

Inaugural flight

The first contract for the launch of Soyuz the CSG was signed at the 2009 Paris Air Show by the Director of the Galileo Programme and Navigation-related Activities René Oosterlinck and a CEO of Arianespace Jean-Yves Le Gall. This contract covered 2 launches of two Galileo satellites each. The contract for the satellites themselves had already been signed by ESA and Galileo Industries in 2006.

Launch vehicle components shipped from Saint Petersburg first arrived in French Guiana by ship in November 2009. The Soyuz Launch Site acceptance review took place during the last week of March 2011, leading to the first simulated launch campaign between 29 April and 4 May 2011. The launch site was officially handed over from ESA to the Arianespace on 7 May 2011.

Assembly of the Soyuz ST-B begun on 12 September 2011 in the Assembly and Testing building, while two Galileo satellites underwent final tests after their arrival from Thales Alenia Space facilities in Italy on 7 and 14 September 2011. The launch was planned for 20 October 2011, however an anomaly was detected in the pneumatic system responsible for disconnecting the fuel lines from Soyuz third stage, forcing the mission to be postponed for 24 hours. On 21 October 2011, at 10:30 UTC, Soyuz ST-B took off for its inaugural, 3 hour 49 minute, flight, making it the first time Soyuz was launched outside of the former Soviet Union territory.

Flight VS09

On 22 August 2014, Arianespace launched the first two Full Operational Capability satellites for the Galileo satellite navigation constellation into medium Earth orbit. The mission appeared to proceed normally and Arianespace reported the launch to be a success, however analysis of telemetry data provided by ESA and CNES tracking stations showed that the satellites were injected into an incorrect orbit.

The orbit was determined by the European Space Operations Centre within 3 hours after the separation from launcher, and the satellites were operating normally and under control. Both satellites were switched to safe mode, pointing at the sun while both ESA/CNES and OHB teams investigated the failure and options for the satellites.

On 25 August 2014, Arianespace announced the creation of an independent inquiry commission to investigate the anomaly. On 28 August 2014, details emerged on the events that most likely led to a failure of the Fregat upper stage. At the end of the re-orientation phase the flight control system detected an incorrect angular speed and unsuccessfully attempted to use thrusters to correct the situation. The flight control system did not detect the thruster issue and continued the flight plan with the upper stage oriented in a wrong direction, leaving the satellites in an incorrect orbit.

In late September 2014, the Roscosmos commission report, quoted by ''Izvestia'', indicated that the Fregat failure was due to a design flaw leading to freezing in one of the hydrazine propellant lines, which was placed alongside a line carrying cold helium used for pressurization of the main propellant tanks. During the long first burn required for Galileo orbital insertion the propellant line was cooled to below the freezing point of hydrazine. Further investigations were focused on the software error and a means to prevent similar failures in future. Izvestia also reported that the failure of flight VS09 caused a serious reaction in Russian government. Oleg Ostapenko, head of Roscosmos, had a "difficult conversation in the (Moscow) White House".

On 7 October 2014, the Independent Inquiry Board announced the conclusions of its investigation, revealing that a proximity of helium and hydrazine feed lines resulted in a thermal bridge that caused an interruption of propellant supply to the thrusters. Ambiguities in the design documents allowing this to happen were a result of not taking into account thermal transfers in the thermal analyses of the stage system design. The Board recommended 3 corrective actions: Revamping thermal analysis, correcting design documents and modification of manufacture, assembly, integration and inspection procedures of the supply lines.

In November 2014, ESA announced the satellites would perform a total of 15 orbital maneuvers to raise their perigee to 17,339 km. This would reduce the satellites' exposure to the Van Allen radiation belt, reduce the doppler effect, increase satellite visibility from the ground, and allow the satellites to keep their antennas pointed at Earth during perigee. These orbits would repeat the same ground track every 20 days, allowing synchronization with other Galileo satellites which repeat the same ground track every 10 days. Once in their new orbits the satellites could begin in-orbit testing.

Recovery of the satellites concluded in March 2015, when Galileo-FOC FM2 entered a new orbit, mirrored to the orbit of Galileo-FOC FM1, which concluded its manoeuvres on the end of November 2014 and successfully passed testing. Currently satellites overfly the same location on the ground every 20 days, comparing to 10 days of standard Galileo satellites.

Missions

Launch sequence

Typically, operations 3 days before launch include countdown rehearsal for all stages as well as final preparations and verification of the Fregat upper stage. Two days before launch preparations for fueling begin. This is also the last day when pre-launch activity with the payload can occur. The launch sequence is optimized for each mission, the sequence described here is based on flight VS07 which lifted the Sentinel-1A satellite:

Notes

References

External links

European Space Agency about Soyuz-ST (Russian name Soyuz-STK)

{{Arianespace launches

R-7 (rocket family)
Space launch vehicles of Europe
European Space Agency
France–Russia relations
Roscosmos
Guiana Space Centre
Arianespace