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Sentinel-2C, the third Sentinel-2 satellite of the Copernicus program, is planned to be launched in 2024.

Currently, the Copernicus SENTINEL-2 mission "comprises a constellation of two polar-orbiting satellites placed in the same sun-synchronous orbit, phased at 180° to each other".

Whilst this pattern leads to an interesting revisit window of 5 days, it is not clear how Sentinel-2C will be integrated into this current system.

Will Sentinel-2C replace an existing Sentinel-2 satellite? Or will Sentinel-2C be orbiting in a similar sun-synchronous orbit, but phased at +/-90° from the two other systems?

EDIT 12/05/2023 : The same question holds for Sentinel-2D.


Per https://space.skyrocket.de/doc_sdat/sentinel-2.htm

  • Sentinel-2A: 2015-028A
  • Sentinel-2B: 2017-013A
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Yes, 2c replaces a, d replaces b

The mission is based on a constellation of two identical satellites in the same orbit, 180° apart for optimal coverage and data delivery. So, when Sentinel-2A retires, Sentinel-2C will be there to take its place, and eventually Sentinel-2D will replace Sentinel-2B.

https://www.esa.int/Applications/Observing_the_Earth/Copernicus/Sentinel-2/Gearing_up_for_third_Sentinel-2_satellite

Further:

D. END-OF-LIFE DISPOSAL

Since uncontrolled re-entry is sufficient, end-of-life disposal for the Sentinel-2 satellite was found to be uncritical with limited impact on the satellite design. As outcome of a trade study, the following scenario was defined for disposal operations with minimum impact on the satellite's power and thermal state.

  1. Controlled descent from nominal 786 km altitude orbit to a circular 653 km altitude disposal orbit to leave the highly populated 800 km region quickly. Due to the low thruster capacity at end of life the descent is performed by 116 delta-v manoeuvres of 10 min each. The total delta-v is 73 m/s consuming 47 kg of fuel. One manoeuvre per orbit is performed;

  2. Satellite passivation and un-controlled re-entry within 25 years.

https://www.researchgate.net/publication/271584776_THE_SENTINEL-2_SATELLITE_ATTITUDE_CONTROL_SYSTEM_-_CHALLENGES_AND_SOLUTIONS/link/54ccb6930cf298d6565ac14f/download

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    $\begingroup$ suggested followup question "Where to Sentinels go to retire?" $\endgroup$
    – uhoh
    May 12, 2023 at 13:34
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    $\begingroup$ @uhoh added another part that covers that :) $\endgroup$ May 12, 2023 at 13:47
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    $\begingroup$ Nice, thanks! Suggested followup question "Is it still called the Oberth effect when perigee burns are retrograde used to decelerate and circularize rather than prograde for raising apogee?" $\endgroup$
    – uhoh
    May 12, 2023 at 21:02
  • $\begingroup$ Thanks. It makes sense to have Sentinel-2C replace Sentinel-2A. But will we have both satellites being operational at the same time until Sentinel-2A retires? Or will Sentinel-2C replace Sentinel-2A as soon as operational? In other words, whilst Sentinel-2A theoretical lifetime is reaching an end, how many months/years can it still be useful in practice? $\endgroup$
    – AlixL
    May 13, 2023 at 23:43
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    $\begingroup$ Design lifespan was 7 years. Maximum designed fuel capacity was for 12 years assuming normal operations. 47kg of the 117kg total monopropellant onboard is set aside for de-orbit manoeuvers. So, in practice it can still be useful up to 2026-7. In reality, what is left of the fuel is not currently stated (thrusters are used for initial attitude acquisition and safe modes, reaction wheels are used for normal ops) so the situation (unknown to us) might be dictating the replacement of 2a sooner rather than later. $\endgroup$ May 14, 2023 at 2:53

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