Sentinel-2B

Sentinel-2B is a European Earth observation satellite developed and operated by the European Space Agency (ESA) as the second component of the Copernicus Sentinel-2 mission, providing high-resolution multispectral imagery to monitor changes in land surface conditions, vegetation, and coastal areas across the globe.^[1] Launched on 7 March 2017 from the Guiana Space Centre in Kourou, French Guiana, aboard a Vega rocket, it operates in a sun-synchronous orbit at an altitude of approximately 786 km. The Sentinel-2 constellation achieves a revisit time of five days or better for most land surfaces.^[1] The satellite carries the Multispectral Instrument (MSI), which captures images in 13 spectral bands ranging from visible and near-infrared to shortwave infrared wavelengths, with spatial resolutions of 10 m, 20 m, and 60 m depending on the band, enabling detailed applications in agriculture, forestry, land-use mapping, disaster management, and water quality assessment.^[2] Its wide swath width of 290 km allows for systematic coverage of Earth's landmasses, inland and coastal waters (excluding main polar regions and small islands), generating up to 1.6 terabytes of data per orbit that is downlinked via X-band and laser communications to ground stations.^[1] Designed for a nominal seven-year mission lifetime, extendable to 12 years, Sentinel-2B features advanced technologies such as push-broom scanning and a three-mirror anastigmat telescope to ensure high radiometric accuracy and geometric fidelity in its observations.^[2] As of November 2025, Sentinel-2B continues to operate nominally within the evolving Sentinel-2 constellation, which now includes the extended operations of Sentinel-2A—repositioned 36 degrees ahead in early 2025—and the newer Sentinel-2C, launched in September 2024 and commissioned in January 2025, enhancing data acquisition frequency to support urgent user needs in environmental monitoring and climate change analysis.^[3][4] This configuration allows for near-daily revisits over key areas, contributing to the Copernicus Land Monitoring Service by delivering open-access data products processed to Level-1C (top-of-atmosphere reflectance) and Level-2A (surface reflectance) for widespread scientific and societal applications.^[1]

Overview

Mission Objectives

Sentinel-2B, as part of the Copernicus program's Earth observation constellation, provides high-resolution optical imagery to support comprehensive land surface monitoring. Its primary objectives include delivering multispectral data for vegetation analysis, enabling the tracking of plant health, growth, and biophysical parameters such as leaf area index and chlorophyll content. Additionally, the mission facilitates land cover classification and change detection to map urban expansion, deforestation, and agricultural patterns, while also focusing on inland water bodies for assessing water quality, pollution levels, and quantity in lakes and rivers. Coastal zones benefit from imagery that monitors ecosystems, bathymetry, and environmental changes like coral reef health.^[5] The data from Sentinel-2B contributes significantly to various Copernicus services by offering frequent, high-quality observations that enhance decision-making processes. In emergency management, it supports rapid disaster response through timely imagery for flood mapping, wildfire assessment, and humanitarian aid coordination. For land management, the mission aids sustainable practices in agriculture, forestry, and urban planning by providing insights into land use changes and resource allocation. Climate change monitoring is bolstered by long-term datasets that track environmental shifts, such as vegetation stress and land degradation, informing global policy and adaptation strategies. These contributions are enabled by the mission's high revisit frequency, ensuring consistent coverage over vast areas.^[6][5] Launched on March 7, 2017, Sentinel-2B represents a phased deployment in the Sentinel-2 constellation, working in tandem with Sentinel-2A to achieve a 5-day global revisit cycle at the equator. This configuration, with satellites phased 180 degrees apart in the same sun-synchronous orbit, doubles the observation frequency compared to a single satellite's 10-day cycle, optimizing coverage for dynamic land processes starting from mid-2017.^[1][7]

Spacecraft Specifications

The Sentinel-2B spacecraft has a launch mass of approximately 1,200 kg, including margins for operational contingencies.^[5] Its stowed dimensions measure 3.4 m in length, 1.8 m in width, and 2.35 m in height, facilitating integration with launch vehicles while accommodating the satellite's modular structure.^[8] Power for the satellite is generated by a deployable solar array spanning about 7.1 m², utilizing gallium arsenide triple-junction cells to deliver up to 1,700 W at end-of-life, supplemented by lithium-ion batteries with 87 Ah capacity for eclipse operations.^[5] The propulsion system employs monopropellant hydrazine with catalytic thrusters and approximately 120 kg of propellant, enabling orbit maintenance, station-keeping, and a nominal mission lifetime of 7.25 years, with potential extensions based on fuel reserves.^[5][8] Sentinel-2B is built on the AstroBus-L platform developed by Airbus Defence and Space, a 3-axis stabilized bus optimized for low Earth orbit environments.^[9] This platform features an aluminum frame divided into a propulsion module and a payload compartment, ensuring structural integrity under launch loads. Attitude control is achieved through a combination of multi-head star trackers for precise pointing (with knowledge accuracy better than 10 µrad), fiber-optic gyroscopes in an inertial measurement unit, four reaction wheels, and magnetic torquers, maintaining stability within 1,200 µrad (3σ) for imaging operations.^[5][8] Thermal management relies on passive radiators, multi-layer insulation, and thermistor-controlled heaters to regulate temperatures across subsystems, including deep-space radiators for heat dissipation in the vacuum of space.^[5]

Development and Launch

Design and Construction

The development of Sentinel-2B was initiated under the Copernicus programme framework in 2008, building on the Global Monitoring for Environment and Security (GMES) initiative, with the implementation phase for the Sentinel-2 mission starting in October 2007.^[10] The prime contract for the overall Sentinel-2 satellites, awarded to EADS Astrium (now Airbus Defence and Space) in April 2008, covered the design, development, and integration of the first satellite, while a dedicated contract for the duplicate Sentinel-2B was signed in December 2009.^[5][11] Airbus Defence and Space led the project from facilities in France and the UK, completing the satellite's manufacture by June 2016.^[12] The spacecraft's integrated platform was developed by Airbus Defence and Space, incorporating contributions from multiple European partners for specialized components and expertise. EADS Astrium handled the primary assembly and system integration, while the French space agency CNES provided key support for calibration systems and image processing algorithms.^[5] Additional subcontractors included Boostec for the silicon carbide telescope elements and Sener for calibration mechanisms, ensuring the satellite's robust design as an identical twin to Sentinel-2A for enhanced mission redundancy.^[11] Following assembly, Sentinel-2B underwent rigorous environmental testing at ESA's European Space Research and Technology Centre (ESTEC) in Noordwijk, Netherlands, starting in June 2016. The test campaign included vibration simulations to replicate launch stresses, thermal vacuum trials exposing the satellite to space-like temperature extremes (as low as -190°C during a "chilly summer" phase), and electromagnetic compatibility assessments to verify signal integrity.^[13][5] These phases were successfully completed by November 2016, confirming the satellite's readiness for deployment.^[12]

Launch Sequence

Sentinel-2B was launched on March 7, 2017, at 01:49 UTC from the Guiana Space Centre in Kourou, French Guiana, aboard a Vega rocket designated as flight VV09 by Arianespace.^[14] The mission marked the ninth flight of the Vega launcher and the second deployment in the Sentinel-2 constellation for the Copernicus program.^[15] The launch sequence began with liftoff from the ELV launch pad, powered by the P80 first-stage solid rocket motor, followed by separations of the first stage at T+1:55, second stage at T+3:39, and third stage at T+6:32.^[16] The AVUM upper stage ignited twice—first for a 7-minute burn reaching T+15:27 and second at T+55:07 for a 2-minute burn—to insert the payload into a sun-synchronous orbit at 786 km altitude with a 98.57° inclination.^[16] Sentinel-2B separated from the AVUM stage at T+57:57, approximately 58 minutes after liftoff, achieving the targeted orbit parameters successfully.^[16][14] Following separation, the Launch and Early Orbit Phase (LEOP) commenced under control of ESA's operations team, with the satellite's solar arrays deploying autonomously within hours to provide power.^[17] The LEOP proceeded nominally, with no major anomalies reported; minor attitude adjustments were performed using the satellite's reaction control system to establish stable pointing.^[18] Arianespace confirmed the overall mission success, enabling the transition to commissioning activities.

Instruments

Multi-Spectral Instrument

The Multi-Spectral Instrument (MSI) serves as the core payload on Sentinel-2B, functioning as a 13-channel push-broom imager engineered by Airbus Defence and Space to deliver high-resolution multispectral imagery for Earth observation. This design leverages a Three Mirror Anastigmat (TMA) telescope with a 150 mm pupil diameter, constructed from silicon carbide for thermal stability, which directs incoming light onto two distinct focal plane modules. The visible and near-infrared (VNIR) module employs 12 monolithic CMOS detectors based on silicon technology, while the short-wave infrared (SWIR) module utilizes 12 hybrid HgCdTe CMOS detectors cooled to below 210 K to minimize noise and enhance sensitivity. Overall, these components form a detector array exceeding 450,000 pixels, with built-in redundancy to mitigate potential failures over the mission lifespan.^[19][5] Calibration of the MSI relies on an integrated Calibration and Shutter Mechanism (CSM), a single deployable unit that combines protective and calibration functions to optimize mass and reliability. For radiometric calibration, the CSM positions a full-aperture Spectralon diffuser—composed of polytetrafluoroethylene for high diffuse reflectance—into the optical path, allowing the instrument to measure solar-illuminated reference signals for absolute gain determination and relative detector uniformity. This process occurs periodically during orbit to track degradation and maintain radiometric accuracy within 3-5%. The CSM also supports geometric calibration by ensuring precise deployment angles (with errors below 0.1°) and shielding the telescope entrance from stray light and contaminants, thereby preserving the instrument's alignment and focus stability essential for accurate geolocation.^[20][5][21] The MSI achieves a swath width of 290 km through its wide 20.6° field of view, enabling broad contiguous coverage along the satellite's orbital path for systematic land surface monitoring. To facilitate targeted observations, the instrument incorporates a ±43° field of regard for cross-track off-nadir pointing, adjustable via the spacecraft's attitude control system, which shortens effective revisit times to as low as five days when combined with the twin-satellite constellation.^[19][5]

Spectral Bands and Resolution

The Multi-Spectral Instrument (MSI) on Sentinel-2B captures imagery across 13 spectral bands, configured to support diverse Earth observation applications. These include four bands in the visible and near-infrared (VNIR) spectrum at 10 m spatial resolution, six bands in the red-edge and shortwave infrared (SWIR) regions at 20 m spatial resolution, and three bands dedicated to atmospheric correction at 60 m spatial resolution.^[19] The bands span a wavelength range from 443 nm to 2190 nm, enabling detection of features from coastal aerosols to vegetation moisture content.^[5] Spatial resolutions are optimized for specific observational needs: the 10 m bands provide high detail for land cover mapping in VNIR wavelengths, the 20 m bands balance detail and coverage for vegetation and soil analysis in red-edge and SWIR, while the 60 m bands facilitate broad-scale atmospheric adjustments with lower detail requirements.^[19] The instrument achieves a radiometric resolution of 12 bits per pixel, allowing for 4096 discrete intensity levels to capture subtle variations in surface reflectance.^[22] These spectral bands support the computation of key vegetation indices, such as the Normalized Difference Vegetation Index (NDVI), which quantifies vegetation health and density by contrasting chlorophyll absorption in the red band with scattering in the near-infrared band. The NDVI is calculated using the formula: $$\text{NDVI} = \frac{\text{NIR} - \text{Red}}{\text{NIR} + \text{Red}}$$NDVI=NIR+RedNIR−Red​ where NIR corresponds to the 842 nm band (B8) and Red to the 665 nm band (B4), both at 10 m resolution; values range from -1 (indicating water or bare soil) to +1 (dense, healthy vegetation).^[23] This index, derived directly from Sentinel-2B's high-resolution bands, aids in monitoring crop vigor, forest cover changes, and land degradation.^[23]

Operations

Orbital Configuration

Sentinel-2B operates in a sun-synchronous orbit at a mean altitude of 786 km, with an inclination of 98.62° and a mean local solar time of 10:30 a.m. at the descending node.^[24] This configuration ensures consistent lighting conditions for imaging across its 14.3 orbits per day, supporting the mission's land monitoring objectives.^[5] To complement Sentinel-2A, Sentinel-2B was initially positioned in 180° orbital opposition following its launch, achieved through post-launch delta-V maneuvers using the satellite's propulsion system.^[5] This initial phasing enabled a combined 5-day global revisit time at the equator, doubling the temporal resolution compared to a single satellite's 10-day cycle.^[7] As of November 2025, the Sentinel-2 constellation includes Sentinel-2C operating 180° from Sentinel-2B in the former Sentinel-2A position, with Sentinel-2A repositioned 36° ahead of Sentinel-2B, allowing for near-daily revisits over key areas.^[3][4] Orbital maintenance for Sentinel-2B involves periodic station-keeping maneuvers performed with a monopropellant hydrazine-based reaction control system featuring 1 N thrusters, which apply in-plane and out-of-plane delta-V adjustments.^[5] The spacecraft carries 80 kg of hydrazine fuel, sufficient for 12 years of operations including routine adjustments and end-of-life deorbiting.^[5]

Data Acquisition Process

The Multi-Spectral Instrument (MSI) aboard Sentinel-2B acquires Earth observation data across 13 spectral bands ranging from visible to shortwave infrared wavelengths.^[24] The instrument operates primarily in three acquisition modes to ensure flexible and prioritized data collection. In nominal mode, the satellite conducts systematic imaging of land surfaces and coastal zones between 56°S and 84°N latitudes, enabling routine monitoring with a 290 km swath width.^[7] Emergency mode provides higher priority tasking for urgent scenarios, such as natural disasters, allowing near-real-time data capture and downlink to support rapid response efforts.^[24] Calibration mode facilitates periodic instrument health checks, including dark signal measurements twice per month, sun diffuser observations once per month, and vicarious validation over dedicated sites 2-3 times annually.^[7] These modes collectively generate up to 1.5 TB of data per day per satellite.^[17] Onboard the spacecraft, raw MSI data undergoes immediate processing to optimize storage and transmission efficiency. The instrument's focal planes convert optical signals into digital counts, which are then compressed using lossless and lossy algorithms to achieve ratios of up to 2.5:1 for visible-near infrared bands and 3.5:1 for shortwave infrared bands, reducing the data volume while preserving radiometric fidelity.^[24] Compressed data is formatted into standardized Level-0 packets compliant with the Consultative Committee for Space Data Systems (CCSDS) protocols and stored on redundant solid-state mass memory units with a capacity of 2.5 Tbit each.^[5] These packets are subsequently downlinked via a high-rate X-band transmitter operating at up to 520 Mbps to a network of core ground stations, including those in Svalbard, Kiruna, and Matera, ensuring global coverage with minimal latency.^[7] Upon reception, the data integrates into the Copernicus Payload Data Ground Segment (PDGS), a distributed system managed by the European Space Agency at ESRIN in Italy. The PDGS handles payload planning, acquisition scheduling, and initial processing to produce Level-1B (top-of-atmosphere radiometrically corrected) and Level-1C (orthorectified) products systematically within 3 to 24 hours for nominal acquisitions.^[17] For higher-level analysis, Level-2A (bottom-of-atmosphere surface reflectance) products are generated through atmospheric correction algorithms applied to Level-1C data, either systematically via PDGS processors or on-demand using tools like the Sentinel-2 Toolbox.^[24] This ground segment workflow ensures the delivery of geolocated, cloud-screened imagery ready for user applications, with all products archived and disseminated through the Copernicus Data Space Ecosystem.^[7]

Status and Legacy

Operational History

Following its launch on 7 March 2017, Sentinel-2B entered a commissioning phase that involved in-orbit verification, calibration, and testing of its systems from March through June 2017.^[25] Initial test images were acquired within days of launch, but the primary commissioning activities, including multispectral imager calibration, occurred primarily in April and May 2017.^[26] The first set of operational images was released to users in June 2017, demonstrating the satellite's ability to capture high-resolution multispectral data over land and coastal areas.^[27] Commissioning concluded on 15 June 2017, paving the way for full operations to commence in July 2017.^[26] With Sentinel-2B operational alongside Sentinel-2A, the Sentinel-2 constellation achieved its designed full capability in 2017, enabling routine global imaging of vegetation, land cover, and inland/coastal waters every five days at the equator.^[28] The satellites' complementary orbits ensured comprehensive coverage, supporting applications in agriculture, forestry, and environmental monitoring under the Copernicus program.^[5] The nominal mission duration for Sentinel-2B was seven years, projected to end in 2024, but extensions were approved based on the satellite's performance and remaining fuel reserves, allowing continued operations into 2025 and beyond.^[17] The arrival of Sentinel-2C, launched on 5 September 2024, bolstered the constellation's redundancy while Sentinel-2B maintained its core role in data acquisition through 2025.^[28] Throughout its operational history, Sentinel-2B has contributed to over a petabyte of archived imagery, aiding in disaster response and climate studies, with no major disruptions reported to date.^[7]

Future Decommissioning

The operations of Sentinel-2B, launched in March 2017, were initially planned for a nominal seven-year duration but have been extended based on the satellite's onboard resources, with potential continuation until 2030 or beyond depending on remaining fuel levels. Each Sentinel-2 satellite, including 2B, carries 123 kg of hydrazine propellant, sufficient for up to 12 years of operations including end-of-life maneuvers.^[17][24] To ensure seamless data continuity, Sentinel-2D is scheduled for launch in June 2028, allowing it to phase in as the successor to Sentinel-2B while maintaining the mission's five-day revisit cycle over land surfaces.^[29] Upon depletion of operational fuel, Sentinel-2B's end-of-mission activities will involve a controlled deorbit using its remaining propellant to lower the orbit from its sun-synchronous altitude of approximately 786 km, facilitating atmospheric re-entry. This strategy complies with European Space Agency (ESA) guidelines for space debris mitigation, directing the re-entry toward a remote, uninhabited ocean area—typically the South Pacific—to minimize risks to populated regions and aviation.^[17][24] The decommissioning of Sentinel-2B will support the broader legacy of the Copernicus Sentinel-2 program by transitioning responsibilities to newer satellites, ensuring uninterrupted high-resolution optical imagery for land monitoring, agriculture, and environmental applications. Specifically, Sentinel-2C, launched on September 5, 2024, has already assumed primary duties from Sentinel-2A as of January 2025, while Sentinel-2D will similarly take over from 2B, extending the constellation's capabilities into the 2030s.^[7][30]