Purpose of the flight and payload description
Keystone TV BALLET (Terahertz/Visible BALLoon ExperimenT) was a balloon mission conducted in preparation for the proposed ESA Keystone satellite mission, part of the Earth Explorer programme. The experiment investigated atomic oxygen in the mesosphere and lower thermosphere and evaluated measurement techniques for future satellite observations. Atomic oxygen is the predominant species in the upper atmosphere between approximately 80 and 600 km. Its concentration and distribution are important for modeling the mesosphere and lower thermosphere and for predicting atmospheric drag on satellites and space debris in low Earth orbit.
The payload included the OSAS-B (Oxygen Spectrometer for Atmospheric Science on a Balloon) heterodyne spectrometer, developed and provided by the German Aerospace Center (DLR). The instrument measured atomic oxygen through its spectral emissions at 2.1 and 4.7 THz, the only atomic oxygen transitions in the atmosphere that are thermally excited. These emissions provided information on the local temperature and atomic oxygen concentration. OSAS-B observed the atmosphere from the side while scanning different atmospheric layers and recorded high-resolution spectra of the atomic oxygen emission.
The OSAS-B measurements were conducted in parallel with observations by the OSIRIS (Optical Spectrograph and InfraRed Imaging System) instrument, a UV/VIS spectrometer provided by the University of Saskatchewan in Canada. OSIRIS measured the green 577 nm emission of atomic oxygen, which is observable shortly after sunset and is also associated with auroral emissions. The simultaneous observations in the terahertz, infrared and ultraviolet-visible spectral ranges allowed different measurement techniques to be compared and combined to improve the characterization of atomic oxygen and related atmospheric processes.
Video footage of preparations and launch
Details of the balloon flight
Balloon launched on: 8/26/2026 at 18:34 UTC
Launch site: European Space Range, Kiruna, Sweden
Balloon launched by: Swedish Space Corporation (SSC)
Balloon manufacturer/size/composition: Zero Pressure Balloon 334.000 m3
End of flight (L for landing time, W for last contact, otherwise termination time): 8/27/2026 at 16:50 UTC
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): 22 h 16 m
Landing site: 7 km SW of Raistakka, Lapland, Finland
External references
- Keystone mission ESA website
- OSAS-B: A Balloon-Borne Terahertz Spectrometer for Atomic Oxygen in the Upper Atmosphere IEEE Transactions on Terahertz Science and Technology, vol. 14, no. 3, pp. 327-335, May 2024
Images of the mission
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