First rays of the sun for the balloon-mounted solar observatory Sunrise III

(ORDO NEWS) — About a month before the start of the exploratory flight into the stratosphere in a balloon, the Sunrise III solar observatory looked at the Sun for the first time from its launch pad above the Arctic Circle.

In June, the Sunrise III will take off from the Esrange Space Center, the Swedish Space Agency’s (SSC) balloon and rocket base in Kiruna, Sweden, to an altitude of about 35 kilometers. During the flight, which will last several days, she will make unique measurements of the Sun.

Thus, processes in the chromosphere, the highly dynamic layer between the visible surface and the outer atmosphere of the Sun, will be seen more accurately than ever before.

In the weeks remaining before launch, technical and scientific teams from Germany, Spain, Japan and the United States will prepare all systems and scientific instruments for flight and practice flight procedures and operations.

Since the beginning of April, the final preparations for the Sunrise III flight have been underway at the Esrange Space Center in Kiruna (Sweden).

All equipment, including the gondola, solar telescope and scientific instruments, was delivered disassembled from the Max Planck Institute for Solar System Research (MPS) in Göttingen (Germany) by truck. MPS leads the mission.

Since then, temperatures as low as -15 degrees Celsius and the snow that prevailed upon arrival have given way to more tolerable conditions. The so-called “First Light”, Sunrise III’s first sight of the Sun, occurred at temperatures near freezing.

“Launching from the Arctic Circle requires a significant logistical effort,” says Sunrise III project leader and MPS scientist Andreas Korpi-Lagg, looking back over the past few months. But for the scientific success of the mission, a remote launch site in the far north is critical.

Beyond the Arctic Circle, the Sunrise III can record observations around the clock while in flight. On the ground, solar researchers find the best viewing conditions in places like Hawaii, the Canary Islands, and the US Southwest.But even during the most favorable observing season, usually in early summer, measurements are usually limited to a few hours a day.

Another advantage of the Sunrise III is the height of observation. When launched, a huge balloon filled with helium lifts the six-meter observatory into the stratosphere to a height of about 35 kilometers. Then the wind will blow it to the west.

At this altitude, which almost marks the passage into space, the atmosphere is so thin that air turbulence doesn’t obscure the view.

In addition, Sunrise III will have access to the sun’s ultraviolet radiation, most of which is absorbed by the Earth’s atmosphere. “Only space probes offer the best observational conditions,” says Sunrise III principal investigator Sami Solanki, MPS director.

During the “First Light” in Kiruna, Sunrise III remained on the ground. This milestone does not so much provide scientifically relevant data from the Sun as it provides an opportunity to test and calibrate all systems in natural sunlight.

For the first time, the gondola was automatically aligned with the sun – just like during a research flight. Rays of sunlight fall into a telescope and from there fall on scientific instruments and an image stabilization system. In front of their computer screens at the back of the room, the science and engineering teams monitor the response of the systems.

Sunrise III is equipped with three scientific instruments. Together they provide comprehensive observational data from just below the visible surface of the Sun to the upper chromosphere at an altitude of about 2,000 kilometers.

They capture infrared, visible and ultraviolet light from this region, which allows visualization of dynamic processes and magnetic fields. In addition, Sunrise III contains a sophisticated image stabilization system. Thanks to it, the observatory records highly accurate data even in a swaying balloon.

If a target shooter wanted to shoot the same way “without hesitation”, he would have to hold his equipment so steady that the shot would deviate no more than a hair’s breadth at a distance of seven kilometers.

The Sun’s chromosphere lies between the visible surface and the outer atmosphere, the corona. There is a huge temperature jump in this connecting layer, from a relatively mild 6,000 degrees Celsius at the surface to 20,000 degrees Celsius.

In the higher layers, the temperature rises to a million degrees Celsius. “Even after decades of modern exploration of the Sun, the chromosphere remains a mystery,” says Solanki. “There are a lot of processes going on in the chromosphere that we don’t fully understand yet that power the corona,” he adds.

Combined, these processes not only create incredibly high coronal temperatures, but also contribute to violent eruptions, during which the Sun repeatedly ejects into cosmos particles and radiation”.

Observational data from Sunrise III will provide the best possible height resolution of the chromosphere: more precisely than ever before, it will be possible to determine the exact height of individual processes above the solar surface. “With Sunrise III, we will be able to track processes in the chromosphere better than ever before,” says Sunrise III project scientist Achim Gandorfer.

It will be several weeks before the adventurous Sunrise III flight begins and the observatory collects its first data. During this time, all systems will be put into operation and in-flight procedures will be worked out.

“The flight will only last a few days. Everything should work smoothly from the start,” says Korpi-Lagg. Depending on wind speed, Sunrise III will reach the uninhabited regions of northeastern Canada in about five to seven days. There the observatory will land by parachute.

However, the exact launch date is determined by the weather. If precipitation falls, the Sunrise III will not be able to take off; a gentle breeze is also needed. “Our preparations are going according to plan. We will be ready for launch in early June,” says Korpi-Lagg. The last phase of the adventure has begun.

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