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Mission Phases: getting to know a spacecraft and its instruments

After a spacecraft launch, you cannot just switch it on and start doing science. It is far more complicated than that. A mission typically has different phases during which the operators on Earth slowly get to know the spacecraft and its instruments.


It is a bit like flying a kite. Even if you designed it and built it yourself, with a lot of experience on how it should behave in flight, its first flight will not be a success first time around. You have to get to know your kite, learn about its behaviour in different wind conditions, practice much, and teach yourself how to fly it best.


Satellites are a bit similar. Even if engineers have run all kinds of tests on ground to predict how it will behave in space, you still have to try it out before you know for sure.

Therefore space missions have different phases, during which the satellite systems get tested out one by one, and we learn how to operate it best.


The first days are reserved to make sure the satellite gets launched into the correct orbit, and can deploy all the crucial systems like solar panels, antenna to communicate with Earth, etc. This phase is called Launch and Early Operations Phase. People make sure that the satellite is stable enough so they can try to switch on the other systems onboard: Do we get enough power from the solar panels? Has the onboard computer been switched ON without problems? Can we steer the antenna to Earth and send and receive messages? Is the spacecraft following the correct orbit?


Near Earth Commissioning Phase: The next 4 months of the Solar Orbiter mission were used to try out the other systems on board the spacecraft, for example the systems that have to keep it pointing exactly at the Sun at all times. And then all instruments were switched on one by one and checked whether they worked as planned.

Often we did not open the little doors yet, but we made some test images in dark to make sure the cameras worked before exposing them to the heat and light of the Sun. For Solar Orbiter this phase finished mid June 2020 and then we started the so-called Cruise Phase. During 1,5 years we can try to take good-quality data with the instruments and prepare them for the real scientific phase that will start in Nov 2021.


From then on, the mission will officially be in its Nominal Mission Phase during which we will take the most exciting pictures of the Sun and measurements of the Solar Wind. With these data we hope to resolve several of the questions we still have about our star and how it affects the Earth. This phase will take about 5 years. During that time, Solar Orbiter will follow an orbit in the form of an ellipse that will bring the spacecraft at times very close to the Sun (closer than the closest planet Mercury) and at other times as far as the Earth. This changing distance to the Sun is plotted in the first plot in the figure below.


If everything is still working fine at the end of 2026, we hope Solar Orbiter can enter its Extended Mission Phase. During these extra 3-4 years we hope to take very cool images from the north and the south pole of the Sun. In the second plot in the figure below you can see how far above and below the equator of the Sun the spacecraft will fly.


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