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Romanian InSpace Engineering (RISE), supported by the European Space Agency (ESA), developed DropCoal, Romania’s first experiment to operate on the International Space Station. It was designed to perform fluidic experiments proposed by a group of scientists from Romania, Germany and the USA.
Hosted inside the ICE Cubes Facility (ICF) in ESA’s Columbus module, DropCoal investigated how droplets collide, merge, and mix in microgravity, revealing fluid dynamic behaviours normally hidden by Earth’s gravity.
Why it matters
DropCoal focused on the physics of droplet coalescence, a process that is central to combustion and rocket engine performance, microbiology, and the transport and absorption of medicines. These insights have direct relevance for astronaut health, life support systems, fuel handling, and key technologies required for space exploration. The microgravity environment allowed scientists to isolate surface‑tension ‑dominated dynamics, providing a clearer view of early stage droplet interactions.
A miniature laboratory in orbit
The compact DropCoal instrument generated 2–5 mm droplets of water and ethanol at controlled approach velocities and recorded their interactions at up to 8000 frames per second. The payload integrated precision pumps, motors, sensors, and custom software, all engineered and qualified to ESA and NASA standards.
During the operational phase, the ICE Cubes Facility enabled continuous remote monitoring and control of the payload from the ground. This allowed RISE operators to command experiments, adjust and fine-tune parameters, and retrieve data without crew involvement beyond installation and de-installation. Following installation by NASA astronaut Don Pettit, DropCoal successfully generated its first droplets and conducted controlled collision experiments in microgravity.
Key findings from the recent publication
A recently published peer‑reviewed study documents the experiment’s design, development and commissioning, along with the first results obtained during the orbital phase. Highlights include:
- Reliable droplet generation and precisely controlled approach and impact speeds during the commissioning phase.
- Clear observation of capillary‑wave propagation, bridge‑oscillation dynamics, and delayed mixing, confirming the isolation of interfacial physics in microgravity and gravity-free coalescence
- Validation of the payload’s performance and experimental concept, as well as readiness for extended scientific operations.
After the space mission concluded, analysis and interpretation of the datasets collected by DropCoal continued, with further insights expected as detailed modelling and comparisons with capillary-driven fluid behaviour theory continue.
Applications on Earth and in Space
Insights and knowledge gained from DropCoal support advances in:
- Rocket propulsion and spacecraft fuel handling,
- Medical delivery and drug formulation, particularly for microgravity environments,
- Biotechnology and microfluidics,
- Thermal control and water recycling systems,
- Earth‑based studies of combustion, atmospheric processes and weather phenomena.
2-5 mm
water & ethanol droplets
Image credits: ESA / NASA / RISE
Further reading
The recent scientific publication provides an in‑depth look into the physical factors governing droplet coalescence and mixing, the control strategies implemented in DropCoal, the experimental scientific requirements, the payload development and validation campaign, and the preliminary results derived from ISS mission data, a valuable resource for readers seeking more technical detail. Read the full publication here.
Launch to the ISS
DropCoal was launched to the International Space Station in November 2024 aboard the SpaceX CRS‑31 cargo resupply mission, marking a major milestone for Romania’s participation in ESA‑supported orbital research and presence in the microgravity investigations arena.
A milestone for Romania and ESA
DropCoal showcases RISE’s capability to design, build, and operate an ISS‑qualified experiment, strengthening Europe’s role and leadership in microgravity research and expanding Romania’s footprint within ESA’s scientific programmes. The results were analysed by an international science team led by experts at the National Institute for the Physics of Lasers, Plasma and Radiation in Romania, in collaboration with the Technical University of Darmstadt, Germany, and Carnegie Mellon University in the USA.
Readers are invited to watch Don Pettit’s message to the Romanian public, recorded during the installation of DropCoal inside the ICF, and also to explore the resources and related articles below to learn more about the project and similar investigations.
8000
frames per second