Subject: [SLR-Mail] No.2899: Successful launch of the Sentinel-6B/Jason CSB mission From: Carabajal, Claudia C. (GSFC-61A.0)[SCIENCE SYSTEMS AND APPLICATIONS INC] Dear ILRS Station colleagues, ILRS CB, ILRS GB, ILRS QCB and associates, We are happy to announce the successful launch of the Sentinel-6B/Jason CS-B mission. The Sentinel-6B satellite was launched on November 16, 2025, at 9:21 p.m. PST from Vandenberg Space Force Base in California, using a SpaceX Falcon 9 rocket. You can view the launch in the mission page at https://science.nasa.gov/mission/sentinel-6B/. The ILRS GB approved SLR tracking support for this mission. The Sentinel-6/Jason-CS mission is a joint oceanography mission to monitor global ocean circulation and sea-level. The Sentinel-6B/Jason-CSB satellite is the follow-on to the TOPEX/POSEIDON, Jason-1, Jason-2, Jason-3 and Sentinel-6A/Jason-CSA satellites. The Jason-CS Program constitutes EUMETSAT`s direct contribution to the funding, development and implementation of the Sentinel-6/Jason-CS mission, which also involves ESA, the EU, NOAA, NASA, and CNES. Sentinel-6/Jason-CS aims to continue the high-precision ocean altimetry measurements of the TOPEX/POSEIDON and Jason satellites. A secondary objective of Sentinel-6/Jason-CS is to collect high-resolution vertical temperature profiles, using the GNSS Radio-Occultation sounding technique, to assess temperature changes in the troposphere and stratosphere and support Numerical Weather Prediction. The Sentinel-6/Jason-CS satellites are planned to have 5.5 years lifetime each (plus 2 years consumables). The Sentinel-6B/Jason-CS-B satellite will guarantee adequate overlap with Sentinel-6A/Jason-CS-A and provide full continuity of service until 2030 and beyond. Sentinel-6B is a clone of Sentinel-6A. It is the same satellite. There may be minor changes to the tracking point offsets, or CofM, but otherwise, the mission and the platform will be the same as Sentinel-6A. The satellite will first fly tandem with Sentinel-6A for calibration/validation purposes. Then Sentinel-6A will be moved to another orbit, probably an interleaved orbit. Then Sentinel-6B will become the official satellite providing altimeter sea surface height measurements on the TOPEX ground track. Regarding the role of Satellite Laser Ranging for the Sentinel-6/Jason-CS mission, accurate orbit determination is a fundamental requirement for achieving the Jason-CS mission objectives. The SLR data play such an important role in two ways: (1) by providing robust tracking information to complement GNSS and DORIS; (2) by providing a unique and unambiguous verification of the absolute radial orbit accuracy Mission Parameters: Satellite name: Sentinel-6B/Jason CS (sentinel6b) Sponsor: NASA/ESA/EUMETSAT/NOAA/CNES Expected Life: 5.5 years Primary Applications: Ocean altimetry, vertical temperature profiles COSPAR ID: 2025-264A/ILRS ID 2526401 SIC Code: 4382 NORAD SSC Code: 66514 Launch Date: 16 November 2025 RRA Size: RRA Shape: spherical surface Reflectors: 9 cubes Size of Reflector: ∼ 32mm diameter Orbit: slightly elliptical Orbital period: 6745.7605 seconds Inclination: 66.042 degrees Altitude: Min. 1339.4 km / Max. 1355.9 km (When science orbit is achieved, on December 16th, 2025) Eccentricity: 0.000098 degrees SP3c Code: L77 The ILRS will be assigning a tracking priority to the mission closer to the time when the mission is to achieve its science orbit, on December 16th, 2025. Predictions have become available at CDDIS and EDC. Stations may choose to track earlier if they can accommodate. The success of the mission will greatly be facilitated by our ILRS support. This support is very much appreciated by the mission. For more information you can go to the Sentinel-3B/CSB Mission page: https://science.nasa.gov/mission/sentinel-6b/ Regards, Claudia, ILRS CB Secretary.