An ESA Cluster II satellite re-enters Earth's atmosphere over the South Pacific (uninhabited area) (artist's rendering). ©

ROSIE: University of Stuttgart Observes the Re-entry of Samba and Tango

September 4, 2026 /

On August 31 and September 1, 2026, the last two satellites of the ESA Cluster II mission deliberately re-entered Earth’s atmosphere over the South Pacific. Researchers from the Institute for Space Systems (IRS) at the University of Stuttgart were part of the mission. As part of the international ROSIE mission, they observed the satellites’ disintegration from a specially equipped aircraft. Among other things, they recorded when and how various materials melted and vaporized.

An ESA Cluster II satellite re-enters Earth's atmosphere over the South Pacific (uninhabited area) (artist's rendering). ©
An ESA Cluster II satellite re-enters Earth's atmosphere over the South Pacific (uninhabited area) (artist's rendering).

Observation from an Airplane

How does a satellite break up upon re-entry into Earth’s atmosphere? And how accurately can these processes be predicted? The international ROSIE mission (Re-entry Observation Setup and International Execution) sought to answer these questions.
To find answers, on August 31 and September 1, 2026, the ESA deliberately guided the two Cluster-II satellites, “Samba” and “Tango,” to re-enter the atmosphere over the South Pacific. The international ROSIE team, which included Stuttgart-based scientists Stefan Löhle, David Leiser, and Martin Eberhart, observed the re-entries from a specially equipped aircraft.

Stefan Löhle (left) and David Leiser (right) from the IRS are installing, calibrating, and testing their measuring instrument. ©
Stefan Löhle (left) and David Leiser (right) from the IRS are installing, calibrating, and testing their measuring instrument.

Stefan Löhle heads the High Enthalpy Flow Diagnostics Group (HEFDiG) at the IRS and serves as the scientific director of the ROSIE mission. Astros Solutions in Bratislava is responsible for project management, while Zafiro Systems coordinated the space mission. ROSIE is a joint project of the IRS/HEFDiG and Comenius University in Bratislava, in collaboration with industry partners Hypersonic Technology Göttingen, Zafiro Systems, and Astros Solutions—in close cooperation with the European Space Agency (ESA). “For us, the particular scientific value of ROSIE lies in the fact that we can observe the re-entry of several satellites of identical design. This allows us to compare whether the observed disintegration processes repeat themselves or whether there are differences,” explains Löhle. 

The Samba-Tango team with the Falcon 900 aircraft modified for the ROSIE mission, prior to the transfer flight to Tonga: J. Vaubaillon, T. Paulech, D. Buttsworth, J. Silha, M. Zigo, T. Voros, S. Löhle, D. Leiser, M. Eberhart, I. Tucker, L. Younes, F. Zander. ©
The Samba-Tango team with the Falcon 900 aircraft modified for the ROSIE mission, prior to the transfer flight to Tonga: J. Vaubaillon, T. Paulech, D. Buttsworth, J. Silha, M. Zigo, T. Voros, S. Löhle, D. Leiser, M. Eberhart, I. Tucker, L. Younes, F. Zander.

Specialized Measurement Technology from Stuttgart

For the ROSIE mission, the IRS had specifically developed special instruments and tested them in the institute's plasma wind tunnels at the University of Stuttgart: On the one hand, it recorded the re-entry; on the other hand, it broke down the light emitted during the process into different spectral regions.
A total of 30 cameras were used at six observation stations during the campaign. In addition to imaging cameras, numerous instruments detected individual atomic lines. The spectral data is intended to reveal characteristic signatures of the melting and vaporizing materials, thereby providing insight into which materials melt or vaporize at what point in time. The spectroscopic measurement technology was supplemented by visual and infrared cameras.

The devices, which the IRS's HEDFIG group developed specifically for the ROSIE mission, are integrated into the Falcon 900. ©
The devices, which the IRS's HEDFIG group developed specifically for the ROSIE mission, are integrated into the Falcon 900.

“Salsa” Provided Initial Key Insights

ROSIE built on an initial observation from 2024. On September 8, 2024, the Cluster II satellite “Salsa” was observed during its re-entry. This observation already revealed interesting deviations from the expectations at that time.
For example, a deviation of up to 20 percent from the expected atmospheric density was detected. This highlighted the impact that uncertainties in the upper atmosphere can have on re-entry predictions.

“Samba” and “Tango” now offered the opportunity to repeat these observations under similar conditions. This allows for a better assessment of whether the effects observed with “Salsa” were an anomaly or indicate a process that is not yet fully understood.
Since the “Salsa” observation, the theoretical models had been further refined and now provided a more realistic representation of the decay. In addition, a different route had been chosen for the observation aircraft to monitor “Samba” and “Tango” in order to better detect and resolve the decay processes.es.

Two re-entries within 24 hours

The observation campaign also posed a significant logistical challenge. The aircraft took off from Tonga and flew for several hours over the South Pacific to “Samba’s” calculated re-entry location. It had to be in the right place at the right time to observe the events. In the case of “Samba,” the calculations were spot on: The predicted re-entry time matched the actual event closely, and the ROSIE team was able to thoroughly document the disintegration. “The combination of precise reentry prediction, our measurement technology, and the work of the entire team worked exceptionally well. We were able to observe the satellite very well and collect data using nearly all of our instruments. Absolutely fantastic—teamwork at its best!” says Stefan Löhle, summarizing the successful observation.
The observation of “Tango,” which took place about 24 hours later, was also successful. This meant that both cluster satellites designated for the campaign could be comprehensively observed.

Left: ESA’s Samba during its controlled re-entry over the South Pacific on 31 August 2026; right: ESA’s Tango during its controlled re-entry on 1 September 2026 — both re-entries were observed at Station 3 by the HEFDIG group at the Institute of Space Systems (IRS), University of Stuttgart, as part of the ROSIE mission, using a Nikon Z8. ©
Left: ESA’s Samba during its controlled re-entry over the South Pacific on 31 August 2026; right: ESA’s Tango during its controlled re-entry on 1 September 2026 — both re-entries were observed at Station 3 by the HEFDIG group at the Institute of Space Systems (IRS), University of Stuttgart, as part of the ROSIE mission, using a Nikon Z8.

Preparations for the mission had already begun days earlier. On August 22, the IRS team traveled to Sydney. There, together with the project partners, they integrated the instruments into the Falcon 900 aircraft, calibrated the equipment, and conducted extensive tests. On August 28, the transfer flight to Tonga took place.

Targeted Re-entry in the South Pacific

The ability to track the two satellites with such precision was a unique feature of the Cluster mission. The four Cluster spacecraft were in highly elliptical orbits. Their return to Earth was determined not primarily by air resistance, but by long-term gravitational interactions with Earth, the Sun, and the Moon.
This allowed “Samba” and “Tango” to be placed on specific trajectories that enabled a controlled re-entry at a remote location that was still accessible to the observation aircraft. For “Samba,” the re-entry trajectory had already been adjusted accordingly in 2024 and was further slightly optimized in early 2026 for observation from the aircraft. The combination of satellite data and telescope observations ultimately enabled a very precise prediction of the time and location of re-entry.

Of the four identical satellites, three were thus relevant for ROSIE observations: “Salsa” was observed in 2024, followed by “Samba” and “Tango” in 2026. The fourth satellite, “Rumba,” reentered on October 22, 2025, but could not be observed.

The trajectories of “Samba” and “Tango” were calculated to precisely position the ROSIE team aboard the Falcon 900 for re-entry. ©
The trajectories of “Samba” and “Tango” were calculated to precisely position the ROSIE team aboard the Falcon 900 for reentry.

Contribution to Sustainable Space Exploration

Since 2000, the Cluster satellites have been studying the Earth’s magnetic field and its electrical environment in three dimensions. In particular, the mission investigated the interaction between the solar wind and the magnetosphere. With the re-entry of “Samba” and “Tango,” the story of the Cluster quartet has now come to an end.
The data collected by ROSIE are also significant for future space missions. For example, the complete observation of “Samba’s” disintegration provides important insights into when and how satellites heat up and break apart during re-entry, as well as which materials survive re-entry. They help improve re-entry and disintegration models and enable the development of satellites in the future that will burn up as completely as possible upon re-entry. Given the growing number of spacecraft, ROSIE thus contributes in the long term to the safe and sustainable use of space.

The campaign thus makes a direct contribution to ESA’s “Zero Debris” approach, which aims to ensure the sustainable use of space for future generations. The University of Stuttgart joined this initiative in October 2025.

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Samba re-entry recorded

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Following its targeted reentry on 31 August, Samba (Cluster II FM-7), the third of ESA's four Cluster satellites, was successfully observed by the ROSIE airborne mission 2026. The ROSIE reentry observation team acquired the image with a Nikon Z8 camera operated by University of Stuttgart (HEFDiG). 

Aerospace research at the University of Stuttgart
Aerospace studies in Stuttgart form a unique interdisciplinary think tank for key technologies in space and on Earth. Researchers at the University of Stuttgart bring together expertise from the fields of climate and energy research, communications technology, propulsion technology, and AI-assisted flight. A central focus is the exploration of sustainable technological solutions aimed at minimizing the environmental impact of aerospace. Research is conducted in an interdisciplinary manner and in close collaboration with regional and international partners from academia and industry, for example within the framework of the Collaborative Research Centers ATLAS (SFB 1667) and SynTrac (SFB-TRR 364). As a partner of THE Aerospace LÄND, the University of Stuttgart contributes to the implementation of Baden-Württemberg’s state strategy to shape aerospace in a sustainable, digital, and collaborative manner by 2050. The University offers its students a solid engineering and application-oriented education. In promoting young talent, it cooperates with the “Future Initiative for Young Talent in Aerospace,” an initiative of the state of Baden-Württemberg dedicated to strengthening the promotion of young talent in STEM fields.

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