In the main control room of the European Space Operations Centre in Darmstadt, a few minutes after the nominal separation of the spacecraft from the launch vehicle, a hiss was heard in the headsets. Instead of the expected telemetry frames, an intermittent signal arrived with traces of receiver saturation. The scenario was fictional, but the consequences were realistic down to the last detail: an extreme solar storm that, in a minute, takes down navigation, chokes communications, and confuses the instruments on the satellite. It is precisely such situations that the Sentinel-1D mission operators have been rehearsing in recent weeks, preparing for everything that might await them in the first hour, the first day, and the first weeks in orbit.

Why even create “nightmares”? From a laboratory exercise to operational resilience

Before every launch, operations teams go through a rigorous simulation phase that reproduces the first hours and days of the satellite in orbit and prepares the control center for anomalies. In this process, the most valuable experiences are those from earlier missions, but also the practice of scenarios that rarely occur and for which there are no “ready-made” procedures. Since mid-September 2025, an extended simulation campaign for Sentinel-1D has been underway at ESOC: through a series of realistic failures, deliberately degraded communication links, and “lost” navigation signals, the limits of procedures, crew endurance, and the ability to make timely decisions are being tested. The idea is simple – to go through the worst-case scenario in controlled conditions so that everything seems easier during the actual flight.

Inspiration from history: in the footsteps of the Carrington Event

History offers a comparison that still inspires awe today. In early September 1859, the world was hit by an extremely powerful geomagnetic storm, later named the Carrington Event. Telegraph lines sparked, and auroras were seen far to the south, much further south than their usual latitudes. At a time when telegraph wires were the “nerves” of the modern world, this was a sufficient demonstration of the fragility of infrastructure. Today, 166 years later, our dependence on space infrastructure—from satellite navigation to geographically dispersed power systems—is incomparably greater. That is why the simulation instructors for Sentinel-1D are drawing on precisely that: to practice the procedure for an event that may not happen tomorrow, but which, statistically, will happen again one day.

Three waves of one storm: how an extreme event breaks down routine

The modeled “perfect” solar storm is structured in three separate phases that follow the physics of solar eruptions and their echo in the Earth's ionosphere and magnetosphere. In each of these phases, the emphasis is on a different type of risk and a different way of reacting. The goal was to force the team, even without a solid reliance on global navigation systems, with intermittent telemetry and potential electronics failures, to make decisions that keep the satellite safe, stable, and in orbit.

1) The fast strike: light arrives first

In the first phase, a powerful solar flare arrives. The electromagnetic wave—from X-ray to ultraviolet radiation—reshapes the ionosphere almost instantly, reaching Earth in about eight minutes. In the control room, this means: interference in radar and communication systems, message distortion, a drop in telemetry quality, and delayed or difficult acquisition of flight parameters. The procedure is therefore clear and measured: slow down the pace, confirm the status of critical subsystems, check the safe mode configuration, temporarily reduce the load on the instruments, and prepare for the next wave. It is crucial to distinguish what is a real anomaly and what is a consequence of a “saturated” ionospheric medium.

2) The particle shower: electronics under fire

Ten to twenty minutes after the flash, a new problem arises—high-energy particles. Protons, electrons, and alpha particles take a little longer, but when they arrive, they hit sensitive parts of the electronics and cause so-called single-event upsets: random bit flips in memory, software glitches, and occasional, sometimes permanent, damage. In this phase of the simulation, the team follows a strict protocol: limiting the load on batteries and thermal circuits, selectively switching off non-essential consumers, switching to redundant lines, and performing memory “scrubbing” to minimize the risk of cumulative errors. The emphasis is on a calm pace and precise documentation: every decision, every configuration change, and every unexpected reset is recorded so that lessons can be learned later and procedures improved.

3) The slow but heaviest round: coronal mass ejection and geomagnetic storm

After several hours—often as many as fifteen—the most challenging phase arrives: a massive coronal mass ejection (CME). This is a cloud of hot plasma with a “frozen-in” magnetic field that collides with the magnetosphere and causes a geomagnetic storm. On the ground, this means possible auroral displays far from the polar regions and additional currents induced in power lines and pipelines. In orbit, however, the atmosphere at altitudes typical for low Earth orbit “puffs up,” which increases aerodynamic drag and accelerates orbital decay. Under these conditions, the risks of close encounters with other objects also increase: data on the position of satellites and debris become temporarily less reliable, and collision probability estimates change more quickly. The key skill is to distinguish when an avoidance maneuver is necessary and useful, and when it might inadvertently increase the risk with another object in the vicinity.

What a day in flight control looks like when navigation goes silent

If GNSS signals temporarily weaken or become unreliable, the error in orbital solutions increases. Star trackers occasionally go “blind” because the detectors register bursts of charged particles instead of stars. The spacecraft then switches to alternative orientation references, and power consumption is strictly controlled to avoid deep battery charge and discharge cycles. Communication links to polar stations may weaken or close completely, so telemetry is acquired in visibility windows that are no longer as reliable as usual. The team in the background is constantly recalculating: how much fuel is needed to counteract atmospheric drag, which instruments are most sensitive under the given conditions, which planned actions should be postponed, and when is it safe to reactivate them.

The wider team and the bigger picture: the Space Safety room and common procedures

This cycle of exercises has fully activated the specialized structure responsible for coordinating responses to threats from space. In the control building in Darmstadt, experts on space weather, orbital traffic, and space debris, as well as managers of other European missions in orbit, are brought together in one room. The purpose is clear: when something extreme happens, everyone looks at the same set of data, uses harmonized thresholds for issuing warnings, and speaks a common operational language. Such an approach reduces the number of “false alarms,” shortens decision-making time, and allows resources to be directed where they are most needed—whether it's changing the imaging schedule, securing additional communication windows, or preparing avoidance maneuvers.

Why Sentinel-1D is important for both science and the economy

Sentinel-1D is part of the European radar constellation that delivers images of land and sea day after day, regardless of clouds and lighting. These images are used for monitoring the sea and ice, tracking landslides and ground subsidence, controlling maritime traffic, planning infrastructure, and for emergency response after earthquakes or floods. Continuity is key here: if the data series is disrupted, it becomes difficult to make comparisons over time and the accuracy of estimates decreases. That is why the simulation scenario for Sentinel-1D is strictly defined—the goal is to build resilience, not to perform a formality. Radar instruments, such as synthetic aperture radar (SAR) technology, have additional value in crisis situations because they can observe even when it is cloudy and at night; their protection during extreme events is therefore a priority.

Historical lessons: from the telegraph to the global satellite economy

Past cases well illustrate the scale of the risk. In the 19th century, when the only widespread infrastructure was the telegraph network, a powerful storm was enough to cause sparks in the wires, “phantom” currents, and service interruptions. In our century, storms have been recorded that have temporarily degraded navigation, hampered radio communications on transpolar routes, and caused problems for individual satellites. The difference is that today, almost every branch of the economy—from finance and logistics to agriculture—begins and ends with data that is created or synchronized in space. Every extra minute of resilience means fewer disruptions, lower costs, and a faster recovery.

Space weather forecast: a view from the side and a network of sensors

Another important lesson is that not every coronal mass ejection is the same. The orientation of the magnetic field and the speed of the plasma are crucial—only certain combinations lead to strong geomagnetic storms on Earth. To improve forecasting and enhance early warning, Europe is developing a dual approach. The first is to build a distributed system of sensors that monitor the electric and magnetic environment around Earth and near the Lagrange points from multiple locations. The second is to plan a mission that will observe the Sun from a “side” position, from the L5 Lagrange point, which provides insight into active regions several days before they “turn” towards Earth. This additional warning horizon can be the difference between a neatly prepared maneuver and improvisation under pressure.

From scenario to practice: what specifically changes after the exercise

Exercises of this type do not end with a report that gathers dust. The results are translated into changes: procedures for entering and exiting safe mode are updated, algorithms for autonomous switching to redundant lines are improved, and fuel consumption calculations are calibrated based on more conservative estimates of drag and atmospheric density. At the same time, collision risk assessment models are adapted for regimes where input data is less reliable. This requires more professional experience and “muscle memory” from the operators: the ability to correctly interpret changes in probabilities and to choose a maneuver that reduces the overall risk, not just the most visible one.

Communication with the public: what people see and what remains in the background

The general public usually notices auroras in unusual places in the sky and the occasional signal interruption. But behind the scenes, a coordination marathon is taking place. Control centers arrange overlapping visibility windows, prioritize telemetry packages, exchange expert briefings with the space weather community, and, if necessary, change imaging plans to protect the instruments. Every such hour teaches the team how to filter noise from the signal faster, when to persist in waiting for better reception, and when to switch the satellite to a simpler, safer state. This is perhaps the greatest value of simulations: to practice a cool head when it is easiest to raise the temperature.

What remains after October 16, 2025: a practiced routine for an uncertain space

As Europe prepares for new launches at the end of the year, the current simulations serve as a dress rehearsal for the unpredictable. The solar cycle is in a period of heightened activity, so the “stress tests” are also becoming more ambitious. In parallel, tools are being developed that allow for earlier and more accurate risk assessment, and operational procedures are becoming more complex, but also more robust. In this interplay of technology, experience, and practice, Sentinel-1D occupies an important place: as a platform that must be ready for anything, from loss of navigation and blinded star trackers to temporary communication interruptions and increased orbital drag. If there is a “secret” to success, it is simple: to practice difficult scenarios long enough for them to become routine, and then to adapt the routine to new knowledge about the Sun and the space environment.