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From the stratosphere, the balloon-borne solar observatory has a clear view of the sun

After a series of weather-related aborts since the end of May, the Sunrise III balloon-borne solar observatory has now begun its research flight. On July 10th at 6.24 AM (CEST), the observatory lifted off safely from Esrange Space Center near the small town of Kiruna in northern Sweden. Carried by a giant helium balloon, the stratospheric flight of several days now leads westwards along the Arctic Circle across the Atlantic to Canada. During its journey, Sunrise III will study the outer layer of the sun, where solar storms originate. The data should be promising, as the sun is currently particularly active.

Sunrise III will observe processes in a layer of the Sun that is more than 2000 kilometers thick, extending from just below the surface to the upper chromosphere. The interplay of dynamic magnetic fields and hot plasma flows in this region drives the Sun’s activity. Sunrise III makes the processes and structures visible with extremely high spatial resolution and without interruption. Several large groups of sunspots can currently be seen on the solar surface. Such areas can be the starting points of solar eruptions and are therefore of particular interest to the scientists. The launch of Sunrise III also marks the start of a worldwide observation campaign: in coordination with Sunrise III, four space probes and ten ground-based solar telescopes will be looking at our central star at the same time over the next few days.

“We are incredibly relieved that the launch was successful today and that everything has gone smoothly so far,” says Sunrise III project manager Andreas Korpi-Lagg, who followed the launch at the Göttingen Operations Center, the mission’s control center at the Max Planck Institute for Solar System Research in Göttingen. At the end of May and beginning of June, several launch attempts had to be called off or canceled due to unfavorable wind and weather conditions; only now did another launch opportunity present itself. The launch could not have been delayed much longer; the stratospheric winds that are supposed to carry Sunrise III to Canada are already showing the first signs of instability. However, according to the NASA meteorologists involved, there should still be enough time for Sunrise III to fly safely.

By now, Sunrise III has already reached its final altitude and so far all systems and instruments are functioning as expected. The observatory should soon be collecting its first scientific data.

Sunrise meets Hercules

Preparations for the launch began the day before at 9 PM (CEST), both at Esrange Space Center in Sweden and at the control centers at the Max Planck Institute for Solar System Research and at the Applied Physics Laboratory of Johns Hopkins University in Maryland, USA. First, the gate of the balloon hall where the international Sunrise III team has been preparing the observatory for its flight since April opened. Around 10.30 PM (CEST), the huge crane and launch vehicle, called Hercules, took over the three and a half ton load and carefully maneuvered it through the gate. Once outside, members of the Sunrise III team assembled the final solar panels that ensure the power supply during the flight. Damping elements made of corrugated cardboard, which are intended to soften the impact of the subsequent landing, and containers with ballast, which can be dropped during the flight to regulate the height, were being mounted.

Hercules then transported its gently rocking cargo onto the launch pad. At first, weather conditions call for substantial waiting time; finally the colleagues from the Columbia Scientific Balloon Facility, a department of the American space agency NASA, which is responsible for the launch, flight and landing of the observatory, gave green light for the final phase of preparations. Via two side tubes, a total of 1050 kilograms of helium streamed into the balloon, which had been laid out on the launch pad earlier. It still looks a little flabby, but will expand as it rises into the stratosphere until it measures around 130 meters in diameter.

Around 6.20 AM (CEST) everything was ready. At a command, the balloon’s anchoring was released and it rose slowly. To make sure that it doesn’t tug sideways at the observatory, Hercules started to move. Only when the balloon was exactly above the observatory did the launch vehicle release its load. To the applause of the bystanders on site and the relieved cheered in the control center, the observatory and balloon disappear into the sky.

Unique look into the Sun’s atmosphere

The Sunrise III’s research journey offers a unique view of our star. As the Sun does not set at the Arctic Circle at this time of year, Sunrise III can optimally collect scientific data around the clock. At an altitude of more than 35 kilometers, air turbulence hardly affects the view. In addition, at this altitude Sunrise III has access to the ultraviolet radiation from the Sun. This part of the solar radiation is largely absorbed by the layers of air in the Earth’s atmosphere and is therefore not available to solar telescopes on Earth.

The ultraviolet radiation that Sunrise III analyzes is primarily generated in the Sun’s chromosphere, which is up to 10,000 degrees Kelvin hot. In the corona, which lies further out, even temperatures of more than one million degrees prevail in some places. It is still not fully understood how our star manages to heat its outermost layer to such unimaginably high temperatures and to hurl particles and radiation from there into space in sometimes violent eruptions. Various wave phenomena, changes in the Sun’s magnetic field and smaller bursts of radiation are just some of the processes that could play a role. The task of Sunrise III is to make the associated processes in the region from just below the solar surface to the upper chromosphere visible and to investigate them in detail. It will be possible to assign individual processes and structures to a precise height above the solar surface better than ever before. “Sunrise III will help us to understand the dynamic processes in the solar atmosphere better than ever before,” says Sami Solanki, Sunrise III Principal Investigator and director at the Max Planck Institute for Solar System Research.

In this endeavor, Sunrise III will receive support over the next few days: ten ground-based solar telescopes around the world, including the Daniel K. Inouye Solar Telescope (DKIST) in Hawaii and GREGOR in Tenerife, as well as the space probes and satellites IRIS, Hinode, CHASE and Aditya-L1 from the USA, Japan, China and India will be looking at the Sun at the same time as part of a coordinated observation campaign.

Across the Atlantic without propulsion

Over the next few days, the last stable easterly stratospheric winds of the season will drive the Sunrise III solar observatory, which has no propulsion system of its own, westwards across the Atlantic. Depending on the wind speed, the flight may take five to seven days. Sunrise III then reaches northern Canada where it is to land. The exact landing site is determined by the flight path, topography, and local weather conditions. However, it is certain to be far enough north that Sunrise III can safely descend by parachute over uninhabited areas. Members of the Sunrise III team will recover the observatory and its treasure trove of data there.

The adventurous concept has already been successful twice. In 2009 and 2013, the flights of Sunrise I and Sunrise II provided valuable scientific data. The flight of Sunrise III in 2022 had to be terminated a few hours after take-off due to technical difficulties.

About the mission

The balloon-borne solar observatory Sunrise III is a mission of the Max Planck Institute for Solar System Research (MPS, Germany) and the Johns Hopkins Applied Physics Laboratory (APL, USA). Sunrise III looks at the Sun from the stratosphere using a 1-meter telescope, three scientific instruments, and an image stabilization system.

The three scientific instruments SUSI (ultraviolet spectropolarimeter), TuMag (spectropolarimeter in the visible range) and SCIP (infrared spectropolarimeter) as well as a sophisticated image stabilization system (CWS) together offer the best height resolution of this region to date.

Significant contributors to the mission are a Spanish consortium, the ³Ô¹ÏÍøÕ¾ Astronomical Observatory of Japan (NAOJ, Japan), and the Leibniz Institute for Solar Physics (KIS, Germany). The Spanish consortium is led by the Instituto de Astrofísica de Andalucía (IAA, Spain) and includes the Instituto Nacional de Técnica Aeroespacial (INTA), Universitat de València (UV), Universidad Politécnica de Madrid (UPM) and the Instituto de Astrofísica de Canarias (IAC). Other partners include NASA’s Wallops Flight Facility Balloon Program Office (WFF-BPO) and the Swedish Space Corporation (SSC).