Sunrise III: Next research flight this year

First icy cold, then midnight sun: at the Arctic Circle, the team will prepare the next flight of the balloon-borne solar observatory - and hopes for solar fireworks.

The next stratospheric flight of the balloon-borne solar observatory Sunrise III is planned for early summer this year. Today's departure of the flight hardware from the Max Planck Institute for Solar System Research (MPS) in Germany to the launch site beyond the Arctic Circle marks the beginning of the final and decisive phase of the mission. On site at the Swedish Space Agency's Esrange Space Center near the city of Kiruna, the Sunrise team will spend the next two months preparing the telescope, scientific instruments, and gondola for their mission at an altitude of 35 kilometers. All work before and during the flight will be controlled from the Göttingen Operations Center at the MPS. Sunrise has already captured unique data from the Sun on two previous flights. The third flight in July 2022 had to be terminated due to technical difficulties. This year’s flight should be particularly exciting: the Sun’s activity cycle is currently heading towards solar maximum.

Preparations for this year's flight of Sunrise III have been in full swing at the MPS and its partner facilities for months: the 376 kilogram telescope, the heart of the solar observatory, and the gondola have been completely overhauled; the scientific instruments and other systems have been tested and calibrated and the software has been brought up to date. The last few weeks before the launch will now take the team into the cold - at least at first. Kiruna is currently experiencing bitter permafrost with temperatures as low as -20 degrees Celsius. By the time Sunrise III is ready for launch at the end of May, the weather should be much milder. The Sun will then no longer set north of the Arctic Circle - ideal conditions for solar researchers.

"The flight of Sunrise usually takes around five to seven days, depending on the wind speed. To make the most of this time, we want to be able to look at the Sun without interruption. This is only possible beyond the Arctic Circle," Sunrise III Principal Investigator and MPS Director Prof. Dr. Sami Solanki explains the choice of launch site in the far north. At a cruising altitude of around 35 kilometers, even clouds do not impair visibility. The long series of observations make it possible to follow processes and events on the Sun, which extend over several days, undisturbed.

The solar observatory will now take shape over the next eight weeks in a large, rather unadorned hall at the Esrange Space Center with a view of the extensive balloon launch field. In addition to the solar telescope with a main mirror diameter of one meter, the seven-meter-high gondola will also house the instruments SUSI (Sunrise UV Spectropolarimeter and Imager), SCIP (Sunrise Chromospheric Infrared Spectro-Polarimeter), and TuMaG (Tunable Magnetograph), which were developed and built by the MPS, the National Astronomical Observatory of Japan (NAOJ), and the Spanish Space Solar Physics Consortium (S3PC) under the leadership of the Instituto de Astrofísica de Andalucía. The image stabilization system is provided by the Institute of Solar Physics in Freiburg. The gondola itself is provided by the Applied Physics Laboratory at Johns Hopkins University in the USA. 

Operations Center in Göttingen

Sunrise III will be ready for launch at the end of May. The weather will then determine the further schedule. At the time of launch, there may be neither precipitation nor wind in the air layers close to the ground. "We very much hope that we won't have to wait until the beginning of July for the launch, as we did two years ago," says Sunrise III Project Manager Dr. Andreas Korpi-Lagg. In the event of a late launch, however, the team is prepared. This year, all work will be coordinated from Göttingen; only a few team members will be on site at the Arctic Circle. "The Göttingen Operations Center offers a better technical infrastructure and simplifies many logistical processes," says Korpi-Lagg.

Telescope and instruments as good as new

The upcoming flight is the fourth of the Sunrise mission. The flights of Sunrise I and II in 2009 and 2013 provided unique measurement data. Sunrise was able to determine the strength of the magnetic field in the Sun's magnetic building blocks and show structures in the lower atmosphere of the Sun, which is 150 million kilometers away, for the first time with a resolution of 50 kilometers in ultraviolet light. The flight of Sunrise III in July 2022 had to be terminated prematurely because the telescope could not be aligned with the Sun. A few hours after take-off, the observatory landed by parachute in the far north of Sweden. The technical difficulties have now been resolved. 

"Fortunately, the landing two years ago was picture-perfect. The telescope and instruments survived everything perfectly," says Korpi-Lagg. Nevertheless, the flight, landing and, above all, the several days of waiting in rough terrain for the recovery team had left their mark. Accordingly, over the past months all of the telescope's mirrors had to be coated with a new, reflective layer of aluminum. The instruments were cleaned and all cables replaced. The effort was worth it. "The telescope and instruments are in great condition," says Sunrise III project scientist Dr. Achim Gandorfer happily. "The telescope's optics are even more precisely aligned than they were two years ago," adds Sunrise III engineer Bianca Grauf.

View of the origin of solar storms

These are perfect conditions for studying the Sun again this summer. At an altitude of 35 kilometers, Sunrise leaves most of Earth's atmosphere behind. The instruments thus have access to the ultraviolet radiation from the Sun, which is otherwise absorbed by the Earth's atmosphere. "The Sun's ultraviolet radiation primarily contains information about the hot layers above the Sun’s visible surface," says Solanki. Sunrise III offers the opportunity to chart the structures and processes in the Sun's lower atmosphere more closely than ever before.

The launch time could hardly be better for this. The Sun is currently approaching its next solar maximum. Processes in the Sun's lower atmosphere drive, among other things, the numerous solar flares and eruptions that have in recent weeks and months led to auroras at comparatively low latitudes.

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. Significant contributors to the mission are a Spanish consortium, the National 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).

Sunrise III is supported by funding from the Max Planck Foundation, NASA under Grant #80NSSC18K0934 and #80NSSC24M0024 (“Heliophysics Low Cost Access to Space” program), and the ISAS/JAXA Small Mission-of-Opportunity program and JSPS KAKENHI JP18H05234. The Spanish contributions have been funded by the Spanish MCIN/AEI under projects RTI2018-096886-B-C5, and PID2021-125325OB-C5, and from ”Center of Excellence Severo Ochoa” awards to IAA-CSIC (SEV-2017-0709, CEX2021-001131-S), all co-funded by European REDEF funds, “A way of making Europe”.