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Soyuz rocket launches second CSO reconnaissance satellite

A Russian-built vehicle started an encore mission delivering a military reconnaissance spacecraft two years after the launch of its predecessor. After a 24-hour delay due to weather, the liftoff of a Soyuz ST-A/Fregat-M rocket from the ELS facility near Kourou, French Guiana, took place as scheduled on December 29, 2020, with the 3.5-ton CSO-2 imaging satellite for the French military and its allies.


Soyuz ST-A mission (VS25) with the CSO-2 satellite at a glance:

Spacecraft designation
Launch vehicle
Launch site
Launch date and time
2020 December 29, 1:42:07.277 French Guiana Time

The second CSO spacecraft

Marking the 25th mission of the Soyuz-2 rocket series from French Guiana (and the final orbital launch attempt for Russian rockets in 2020), the flight is designated VS25 by Arianespace, a Paris-based launch provider that procured the vehicle for the CSO-2 mission.

The CSO is the French abbreviation of Composante Spatiale Optique (or "optical space component") built for observations of the Earth's surface at very high resolution in the visual and infra-red parts of the spectrum from a Sun-synchronous orbit. The second satellite prepared for launch at the end of 2020 followed the original spacecraft in the series launched in December 2018.

The complete three-spacecraft constellation was designed to work at different altitudes of polar orbit, with CSO-1 and CSO-3 satellites focusing on reconnaissance functions and CSO-2 specializing in the identification of potential targets. According to Arianespace, CSO-2 will be inserted into a Sun-synchronous orbit with an altitude of just 480 kilometers (or around 320 kilometers lower than that of its predecessor) and an inclination 97.3 degrees toward the Equator.

It was to be used to acquire extremely-high-resolution images in the visible and infrared bandwidths, day or night and in fair weather, and using a variety of imaging modes to meet as many operational requirements as possible.

The CSO series was developed by the European consortium Airbus Defense and Space and its main optical imaging instrument was provided by the French division of Thales Alenia Space.

The CSO network is operated by the French space agency, CNES (Centre National d’Etudes Spatiales) via its mission control center in Toulouse, France, and the French defense procurement agency, DGA (Direction générale de l’armement), on behalf of the nation's ministry of defense, but its capabilities are also available to other European countries. In its preview of the CSO-2 launch in December 2020, Arianespace said that Germany, Sweden and Belgium had already joined the CSO community, and that an agreement with Italy was expected shortly.


Known specifications of the CSO satellite:

Spacecraft operator
CNES on behalf of DGA
Spacecraft developer
Airbus Defense and Space (formerly EADS Astrium)
Spacecraft platform
Life span
10 years
Liftoff mass
3,562 kilograms
Total payload mass
3,716 kilograms
Orbit type
Sun-synchronous: 480 kilometers, 97.3 degrees

Preparations for flight

The CSO-2 satellite arrived at Kourou on February 27, 2020 and was moved to the S1A building for pre-launch processing.

Early in 2020, the Fregat upper stage originally intended for the CSO-2 mission had to be transferred to the preceding Falcon Eye-2 mission, whose own Fregat was found to have technical problems. As a result, the launch of CSO-2 had to be postponed from April 10 to the second half of May 2020.

According to the RIA Novosti news agency, the CSO-2 mission was assigned a fresh Fregat upper stage originally intended for the fourth launch of the OneWeb constellation, at the time not expected before the end of 2020.

On March 15, 2020, due to the explosive spread of the coronavirus pandemic, the French space agency, CNES, operating the Guiana Space Center, ordered a stop of ongoing launch campaigns at the site and all unfinished construction. The only exception were the operations to bring the launch vehicles, payloads and facilities in safe condition, and their monitoring.

On March 19, a Nordwind Boeing-777-200 evacuated 250 Russian specialists from French Guiana to Moscow. As of early April, the launch of CSO-1 was tentatively scheduled for October 15, 2020, but by the middle of May 2020, the launch date shifted to November 6, 2020.

By September 14, when officials were able to begin the post-lockdown review of the CSO-2 mission, its launch was not expected before December 14, 2020. In parallel, pneumatic tests of the Fregat stage started inside the Soyuz assembly building. The work was completed on October 23 and three days later, the space tug was moved to the FCube building for fueling.

However, the processing of the satellite did not start until November 17, 2020, by which time, the launch date for the CSO-2 mission had slipped to December 28. Three days later, the electrical and propulsion tests of the three booster stages of the Soyuz ST-A rocket, conducted during most of November, were completed.


The CSO-2 satellite is being integrated with the Fregat upper stage.

In early December, the CSO-2 satellite was moved from the S1A processing building to the S3B building for fueling. The spacecraft was integrated with its launch adapter on December 16, and a day after the arrival of Fregat at S3B on December 17, the two components were bolted together, and the resulting stack was covered with its payload fairing during December 21 and 22.

On December 23, the rocket and the payload section were rolled out to the launch, where the payload was hoisted on top of the rocket for the countdown. The following day was dedicated to on-pad tests of the rocket and payload and, after the Christmas break, personnel was scheduled to conduct a launch rehearsal on December 26. After final checks and preparations for fueling of the booster stages, mission officials planned the launch readiness review before the end of the workday on December 27.

The vehicle was cleared for launch but several hours before its planned liftoff on December 28, at 1:42:07 p.m. local time, the mission had to be postponed for 24 hours due to unacceptable high-altitude winds. Another launch attempt was scheduled for December 29, at 16:42:07 UTC (1:42 p.m. local) Arianespace said.

On the morning of December 29, Arianespace announced that "based on predicted meteorological conditions over Europe’s Spaceport, our teams just gave a go to resume launch operations, fueling of the launcher ongoing."

Countdown milestones for the VS-25 mission on December 29, 2020:

Time (h:min:sec)
Beginning of the meeting for launcher fueling authorization (BTR)
Beginning of launch vehicle fueling with propellant components
Completion of launch vehicle fueling
Mobile gantry withdrawal
"Key-to-launch" command (beginning of Soyuz synchronized sequence)
Fregat transfer to onboard power supply
Upper Composite umbilical drop off command
Ground-board power transfer
Lower stage mast retraction
Preliminary thrust level
Full thrust level

CSO-2 launch profile


A Soyuz ST-A rocket with the CSO-2 satellite lifted off on December 29, 2020, at 1:42:07 p.m. local time (11:42 a.m. EST; 16:42 GMT) from the ELS facility near Kourou, French Guiana.

After eight seconds of vertical ascent, the rocket headed north over the Atlantic Ocean. The four strap-on boosters of the first stage finished firing and separated one minute 58 seconds into the flight.

As the rocket continued to climb under the thrust of the second (core) stage booster, the payload fairing split into two halves and dropped off four minutes and 15 seconds into the flight. Just 32 seconds later, the second stage also completed its work and separated. Moments earlier, the main engine of the third stage ignited and fired through the lattice structure connecting the two stages until their separation. Around five seconds after the separation of the second stage, the aft adapter ring on the third stage split in three sections and separated as well.

The powered phase of the ascent for the first three stages of the launch vehicle lasted 8 minutes and 49 seconds. The payload section, consisting of the Fregat upper stage and the satellite, then separated from the third stage into a suborbital trajectory just short of orbital velocity. A minute later, Fregat will fired its propulsion system for around nine minutes to enter a highly elliptical orbit with an apogee close to the planned orbital altitude of the CSO-2 satellite.

The stack then climbed passively toward the apogee for around 35 minutes, before Fregat initiated its second engine firing, this time for 30 seconds, to make the orbit circular. Another five minutes later, the spacecraft was released into its 480-kilometer orbit, completing the mission 59 minutes and 37 seconds after liftoff from French Guiana.

After the separation of its payload, the Fregat upper stage was programmed to make another engine firing, entering a burial orbit safely below the CSO satellite and one more burn to put the spent booster on a destructive reentry into the Earth's atmosphere.


The VS-20 mission timeline:

Scheduled elapsed time
Stage I separation
1 minutes 58 seconds
Payload fairing separation
4 minutes 15 seconds
Stage II separation
4 minutes 47 seconds
Stage III separation
8 minutes 49 seconds
Fregat engine firing 1 begins
9 minutes 49 seconds
Fregat engine firing 1 ends
18 minutes 29 seconds
Fregat engine firing 2 begins
54 minutes 15 seconds
Fregat engine firing 2 ends
54 minutes 07 seconds
CSO-1 satellite separation
59 minutes 37 seconds
Fregat engine firing 3 begins
1 hour 36 minutes 40 seconds
Fregat engine firing 3 ends
1 hour 37 minutes 30 seconds
Fregat engine firing 4 begins (to deorbit)
1 hour 51 minutes 40 seconds
Fregat engine firing 4 ends
1 hour 52 minutes 35 seconds
Mission end
1 hour 53 minutes 15 seconds

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Page author: Anatoly Zak; Last update: April 19, 2023

Page editor: Alain Chabot; Last edit: December 26, 2020

All rights reserved


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The payload section of the Soyuz rocket with the CSO satellite. Credit: Arianespace


Payload section with CSO-2 satellite is being prepared for integration with the launch vehicle. Click to enlarge. Credit: Arianespace


A Soyuz rocket for the CSO-2 mission leaves the vehicle assembly building. Click to enlarge. Credit: Arianespace


Soyuz rocket lifts off with CSO-2 satellite on December 29, 2020. Click to enlarge. Credit: Arianespace


Tracking cameras captured separation of the first stage two minutes after the liftoff. Credit: Arianespace


Fregat initiated its 1st burn lasting 510 seconds at an altitude of around 268 kilometers, distance from launch site of more than 2,000 kilometers and a velocity of around 6.7 kilometers per second. Click to enlarge. Credit: Arianespace


After crossing into the Southern Hemisphere, Fregat flew out of range of communications until reaching Australia. Click to enlarge. Credit: Arianespace


Fregat's 2nd burn lasted for 29 seconds. Click to enlarge. Credit: Arianespace


Separation of the CSO-2 satellite took place 59 minutes into the flight in view of New Norcia ground station in Australia. Click to enlarge. Credit: Arianespace


After releasing its payload, Fregat began orienting itself for deorbiting maneuvers. Click to enlarge. Credit: Arianespace


A telemetry hole took place during the passive phase of the flight after the 2nd Fregat maneuver. Click to enlarge. Credit: Arianespace


The 3rd Fregat maneuver using attitude control thrusters was designed to increase the distance between the space tug and its former passenger. Click to enlarge. Credit: Arianespace


A short telemetry hole took place at the end of the first orbit. Click to enlarge. Credit: Arianespace


The 4th Fregat maneuver lasting 30 seconds was designed to deorbit the stage. Click to enlarge. Credit: Arianespace


At the start of its second orbit, Fregat would downlink telemetry to ground control. Click to enlarge. Credit: Arianespace