Sentinel-1D: final preparation for flight and a new phase in European Earth observation

At the spaceport on the northeastern coast of South America, a crucial part of the launch campaign for the newest satellite in the Copernicus Sentinel-1 series is being completed. After passing through the final integration steps and detailed functional checks, the spacecraft known as Sentinel-1D has been fueled and is ready for encapsulation in the rocket's fairing. According to the plan, encapsulation is scheduled for Friday, October 24, 2025, and liftoff on the new European heavy-lift launcher is expected on Tuesday, November 4, 2025. This opens a new chapter for radar monitoring of the planet, which does not depend on daylight or weather conditions.

Why Sentinel-1D is important and who benefits from it

The Sentinel-1 family of satellites is an integral part of the European Copernicus program, the backbone of services that provide continuous, reliable, and open data about the Earth. In practice, the images and products from this mission enable a rapid response from civil protection services during floods, landslides, or earthquakes, facilitate the monitoring of maritime traffic and state borders, help foresters and farmers manage resources, and supply climate scientists with data series essential for analyzing long-term trends. From detecting oil spills and tracking ice sheets to assessing dam stability or situational awareness after cyclones – Sentinel's radar "eyes" are often the first source of timely and verifiable information.

With the introduction of the Sentinel-1D satellite, the mission gains greater resilience, a faster revisit rate, and broader capacity to provide data to users. The plan is for Sentinel-1D, once fully commissioned into operational service, to take over the role and relieve Sentinel-1A, which has been orbiting the Earth for eleven years – far beyond its originally planned lifespan. This will maintain the continuity of key data time series, which is crucial for all analyses that rely on the stability and comparability of measurements over time.

Technology at the core: C-band SAR and what makes it irreplaceable

The heart of the Sentinel-1D satellite is a Synthetic Aperture Radar (SAR) operating in the C-band. Unlike optical sensors that depend on sunlight and clear skies, SAR actively transmits microwave signals towards the surface and measures the reflected echo. This approach allows for imaging day and night, through clouds, rain, and even smoke. Precise control of operating modes (e.g., wide-swath maps of large areas, narrowly focused high-resolution scenes, or interferometric pairs for measuring ground deformation) turns SAR data into an extremely versatile tool. Engineers then use advanced signal processing algorithms to reconstruct images and measurement products of high geometric and radiometric quality from the recorded phases and amplitudes.

For practical applications, this means it is possible to monitor: micrometer-level ground displacements on landslide-prone hills, sea surface and ocean currents, calving icebergs that obstruct shipping routes, changes in the urban fabric and infrastructure facilities, vegetation development through the seasons, or the impact of drought on fields and forests. The interferometric technique (InSAR) is particularly valuable, analyzing differences in the radar signal's phase between two flyovers to detect subtle surface deformations – for example, ground subsidence above mines or the swelling of a magma chamber beneath an active volcano.

Faster coverage renewal and higher data frequency with Sentinel-1C and Sentinel-1D

The new satellite will not work alone. The planned constellation relies on Sentinel-1D joining forces with Sentinel-1C. When both spacecraft are simultaneously operational, users will receive more frequent images of the same locations, which is crucial during emergencies when the situation on the ground changes from hour to hour. A higher imaging cadence also shortens the waiting time for an image under cloud cover – SAR "sees" through clouds anyway, but orbital dynamics and task prioritization always set limits, which are pushed by combining platforms.

Both satellites also carry an AIS (Automatic Identification System) receiver, which they use to track ship signals. By combining the radar image of the sea surface and AIS, analysts can more quickly spot suspicious situations: a ship sailing without its transmitter on, a route change in the middle of a storm, unusual circling in an area sensitive for fishing or nature protection. When Sentinel-1C and Sentinel-1D are in play simultaneously, the frequency of AIS observations also increases, providing a denser picture of movement on the seas and oceans.

"Green light" after the Flight Readiness Review

Last week, an extensive Flight Readiness Review was held – a technical review where teams confirm that the spacecraft is ready for the final stages of the launch campaign. This step typically includes checking the results of functional tests, the status of flight software and configuration, the condition of subsystems responsible for power, thermal control, and communications, as well as compliance with safety criteria on the launch pad. The completion of the review opened the way for fueling, followed by the mechanical preparation for encapsulation – placing the satellite in the protective fairing that shields the sensitive equipment during its passage through the atmosphere.

The project team emphasizes that Sentinel-1D is in good technical condition and that the schedule is "to the second" aligned with the launcher preparations. Since its arrival in French Guiana, the spacecraft has undergone final integration procedures, command and telemetry tests, radio frequency behavior checks, and mechanical resistance tests. A special focus was on the launch configuration, which includes locking moving parts, managing and protecting cables, and activating procedures that ensure a stable state of the system until the satellite enters microgravity and separates from the rocket's upper stage.

What specifically follows until liftoff

After fueling and parameter confirmation, technicians perform the encapsulation – a delicate operation where the satellite is placed inside the aerodynamic fairing. This phase is conducted in controlled cleanroom conditions; every dust particle and every change in temperature or humidity is meticulously monitored. Upon completion, the rocket's "nose" is closed, followed by mating with the upper stage and the rest of the launcher. In the days leading up to liftoff, electrical connection checks, final telemetry validation, and a dress rehearsal with numerous "go/no-go" points on the timeline are conducted. In parallel, meteorological conditions, the operation of the launch pad systems, and the flight tracking network are monitored to confirm that all elements of the chain are ready for the T-0 moment.

Ariane 6: a new launcher with large capacity

The launch of Sentinel-1D is entrusted to Ariane 6, the European heavy-lift launcher designed to flexibly transport different types of cargo – from constellations in low Earth orbit to research missions to deep space. The rocket in its full configuration is over 60 meters tall, and its mass at liftoff, with maximum payload and full tanks, can reach almost 900 tons. The modular approach allows for the selection of variants with different numbers of boosters, which directly affects performance, flight profile, and target orbits. For missions in service of Copernicus, accuracy and reliability are key – parameters that determine how precisely the satellite will be inserted into its desired orbit and how much time it will take to assume its operational duties.

Safety protocols during the launch campaign are focused on minimizing risk: from controlled monitoring of fuel, which is chemically reactive, through static tests, to multiple independent checks of telecommands and flight termination systems. Special attention is also paid to contamination – the cleanliness of optical and radar surfaces directly impacts data quality, and any microscopic particle can leave a trace in the measurements or accelerate material degradation in space conditions.

Orbital architecture and operational imaging cadence

The Sentinel-1 mission traditionally relies on a sun-synchronous orbit, which allows for consistent illumination of scenes during the imaging cycle, important for the comparability of measurements over time. Although SAR is not limited by light, stable acquisition geometry facilitates precise interferometric analyses. The arrangement of orbits within the constellation is optimized to shorten the revisit time of the same areas and improve global coverage. During the first weeks after launch, the satellite goes through a commissioning phase: antennas and elements that were locked for flight are deployed, radio links with the network of ground stations are checked, instruments are calibrated, and a series of test scenarios simulating operational conditions are conducted.

Once nominal operation is established, the imaging schedules become increasingly intensive. Priorities are determined by user needs: crisis situations get "emergency slots," while routine scenes for long-term monitoring are scheduled according to a plan that ensures stable time series. Since interests are diverse – from the Arctic and Antarctic, through maritime shipping lanes, to dense urban areas – mission planning resembles a puzzle where coverage, resolution, and limited downlink bandwidth are balanced.

From raw echo to user product

The data SAR collects in orbit is initially raw radar echoes. At ground centers, they go through multiple processing stages: geometry correction, signal power calibration, noise filtering, georeferencing, and conversion into standardized products (e.g., Level-1 GRD and SLC). Thematic products are built on these layers – maps of flooded areas, change maps, deformation rate estimates, detection of ships or ice sheets. The role of the European Union and partner institutions is to ensure that the data is open and accessible to everyone, free of charge, so that a new generation of commercial and public services can be built upon it.

For users in the field, the key is latency – the time that passes from the moment of imaging to the moment the product arrives in their systems. A constellation with two active radar satellites makes it easier to achieve target latencies precisely when pressure mounts, for example, during major floods or after a strong earthquake. Using distributed processing centers and modern data transmission networks further reduces bottlenecks, and standardized formats and APIs help integration into existing workflows.

Maritime safety and sea surveillance: the synergy of SAR and AIS

The maritime sector profits greatly from the combination of radar scenes and AIS signals. While AIS provides the identity, position, course, and speed of ships that transmit it, SAR detects physical objects on the sea surface regardless of whether they have their transponders turned on. This way, "dark ships" can be spotted, sudden route changes detected, or movements typical of illegal fishing recognized. The increased frequency of observations when Sentinel-1C and Sentinel-1D work in tandem allows operational centers a more realistic view of the situation, especially in areas with heavy traffic or challenging weather conditions.

For administrations responsible for environmental protection, radar images also serve as a tool for early detection of marine pollution. Oil spills have a specific radar signature because they dampen the short waves on the surface, so in SAR images, they appear as dark areas of various geometries. With proper processing and validation from satellites and the air, services can direct resources more quickly and organize interventions.

Climate and geoscience applications: from glaciers to urban heat islands

In the context of climate change, a continuous radar archive is key to monitoring glacier movement, permafrost deformation, changes in seasonal soil moisture, and the impact of extreme weather events on infrastructure. SAR is particularly powerful in assessing structural changes – for example, how the ground moves after a drought or how a dam reacts to changes in water level. In urban areas, interferometric series help assess the stability of embankments, tunnels, and tall buildings, while combining them with other data (e.g., temperatures, topography, and traffic flows) provides a better understanding of the formation and spread of urban heat islands.

Teams and partners: industry, agencies, and the user community

Behind every space mission stands a wide network of experts. In the case of Sentinel-1D, industrial partners developed the platform and instruments, agencies led the systematic validation, certification, and integration, and user communities have already prepared scenarios and software tools that will utilize the new data as soon as possible. The mission's project manager highlights the perseverance and dedication of the teams – from those who worked on assembling the antenna and RF chains, through specialists in the radiation resistance of electronics, to experts in ground segmentation and data distribution. This coordination made it possible for all overlapping tasks to be completed on time and for the satellite to be "in good shape" to meet the demanding environment of launch and flight.

Logistics on the ground: from the cleanroom to the launch pad

Preparing the satellite in French Guiana begins with its transport in special containers with controlled temperature and humidity. Upon arrival, teams conduct visual inspections, check shock indicators and vibration sensors, followed by careful unpacking in a cleanroom. Integration steps include connecting the solar array, RF assemblies, and cabling, after which functional tests follow. Before fueling, the hermeticity of the tanks and the calibration of valves and sensors are also checked. Every step has detailed checklists, and any deviation from nominal values opens "non-conformance" records that are resolved immediately or, if necessary, escalated.

What the first weeks after separation from the rocket will look like

Upon entering the target orbit, the satellite undergoes the early operations phase (LEOP), where the priority is stabilization, establishing communication, and the basic health of the system. This is followed by deployment and unlocking procedures, after which the gradual power-on of the instrument begins. The first "engineering" images are used to check calibration coefficients and the radar's behavior in different operating modes. In parallel, the antenna's orientation is adjusted, clock sources are synchronized, and the performance of space-exposed components under the influence of the orbit's thermal cycle is verified. Only after all criteria are met do the images start regular distribution to users.

Connecting with the community and developing new services

The ecosystem around Copernicus data grows year by year: startups, scientific institutes, public services, and the media are developing applications that turn satellite pixels into understandable stories and operational tools. The arrival of Sentinel-1D will spur a new generation of solutions – from tools for flood risk assessment at the municipal level, through monitoring of construction sites and land-use change, to services for insurers who want to more accurately quantify the exposure of infrastructure facilities. Since the data is open, the barriers to entry are lower, and the key is the ability to extract what makes a difference to the user's daily work from the multitude of information.

What this step means for mission continuity

The stability of radar time series is the foundation of the quality of many analyses. Replacing or relieving the oldest member of the constellation – Sentinel-1A – with a new spacecraft means there is no interruption in data availability and that high-quality comparisons can continue without jumps or gaps. From an engineering perspective, this requires careful cross-calibration between platforms, checking the consistency of geolocation and radiometry, and transparently documenting all changes in operating modes, so that users can account for any nuances in their models.

Where to follow the story's development and find additional information

As November 4, 2025, approaches, public and expert interest is growing. Our portal, in line with its policy of openness and accurate information, will regularly follow all steps – from the encapsulation on October 24, through the mating with the launcher, to launch day and the first signals from orbit. For more detailed thematic records and explanations of key terms, readers can also visit our thematic pages: Copernicus, Sentinel-1, Ariane 6, and SAR technology, where we will regularly publish guides, visualizations, and examples of data applications in practice.

Glossary of terms for quicker reference

• SAR (Synthetic Aperture Radar): an active sensor that transmits a microwave signal and measures the echo, enabling imaging regardless of clouds and lighting.


• C-band: a portion of the microwave spectrum (around 4–8 GHz) suitable for observing surface structures, vegetation, and the sea.


• Interferometry (InSAR): a technique that calculates surface deformations and other parameters by comparing the phase information of two or more SAR images.


• AIS (Automatic Identification System): a system for the automatic identification of ships, which transmit data about their position, course, and speed.


• Encapsulation: placing the satellite in the rocket's aerodynamic fairing, which protects it during launch.


• Flight Readiness Review: a formal review of the readiness of the spacecraft and associated systems for the final stages of the campaign and launch.


• Commissioning: the post-launch phase in which instruments are calibrated and systems are tested before full operational use.

Key timelines and what they mean for data users

October 21, 2025 – today brings confirmation that the satellite is fueled and ready for the next step. October 24, 2025 – planned encapsulation, after which mating with the launcher and a series of final checks will follow. November 4, 2025 – planned launch of Ariane 6 with Sentinel-1D on top. With the successful completion of these steps, users can expect a shortening of the revisit interval and faster delivery of products at the most critical moments, especially during emergencies when fresh data is most needed.

How the community will prepare for the arrival of new data

Organizations that work with radar images daily are already updating their protocols to "catch" the first data streams from Sentinel-1D. This includes adapting automated processing workflows, matching new images with existing archives, establishing reference datasets for validation and performance testing, and recalibrating thresholds in change detection systems. Developers are integrating support for new scene identifiers and metadata, and operational services are checking that alarm systems, dashboards, and reporting procedures are ready for the increased volume and rhythm of data.

Upgrading the value chain: from academia to industry

The success of a mission is not measured solely by the quality of the hardware or the precision of the orbit, but also by the degree of data adoption in real processes. Academic communities expect better conditions for comparing models and developing new methodologies in geosciences, while industry seeks a robust and predictable source of information for operational decisions. From the energy sector monitoring power line corridors and landslide risks, to transport and logistics needing up-to-date maps of sea and land conditions – expanding Sentinel-1's capacity translates directly into measurable operational benefits.

The bigger picture: independent access to space and European technological sovereignty

Ariane 6 and missions like Sentinel-1 together form the backbone of Europe's approach to space, which simultaneously strives for technological sovereignty, sustainability, and open science. A reliable launcher reduces dependence on external launch service providers, while open data access fosters innovation and market competition. At a time when information is the most valuable currency, a stable and predictable Earth observation program is one of the most important investments in security, the economy, and science.