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On board the European module of the International Space Station (ISS), January 26, 2021, will mark the end of two RUBI experiment sessions inside the Fluid Science Laboratory (FSL) rack. The FSL rack can host experiments for the study of the dynamics of fluids in space and RUBI — the Reference mUltiscale Boiling Investigation — is expanding our knowledge on the boiling process. At B.USOC (Belgian User Support and Operation Centre), the operators were in charge of this complex ESA instrument.

After the first successful RUBI session, ESA decided to initiate a second session to increase the science output, completing set points that had been left out in the first session, and attempting new conditions closer to the very limits of what the instrument could do. As X marks the spot for success, RUBI-X was a fact. The complete mission hosted 622 science runs (with 3 repetitions for each run), creating a huge amount of nucleate boiling bubbles and recording 12,5 TB of imagery and science measurements recorded on-board. Providing the scientists with plenty of data for analysis.

FSL rack
The Fluid Science Laboratory rack in the Columbus module of the ISS. Credit: ESA

On Tuesday, NASA Astronaut Shannon Walker will remove the RUBI container from the FSL rack and install the SMD container for the upcoming Soft Matter Dynamics mission that will also initiate additional science sessions studying the evolution of granular matter and foams in microgravity. This complex crew activity is also coordinated and real-time supported by the operators at B.USOC.

Background information

The Belgian User Support and Operations Centre (B.USOC) is responsible for the implementation of European payloads on board the International Space Station on behalf of the European Space Agency (ESA). It acts as the link between the scientists and the ISS environment and is responsible for preparing and operating those experiments. B.USOC operators are in contact with other ground control stations across Europe in order to make sure that these experiments are executed as expected and according to the needs of the scientists. Experiments start with a commissioning phase that requires a 24/7 based console coverage to perform a functional checkout. Later throughout the mission, this can be reduced.

B.USOC has been responsible for quite an extensive list of payloads since the launch of the Columbus module in 2008. The external platforms SOLAR and ASIM, the PCDF rack, the METERON robotics project, and the Fluid Science Laboratory that can host a multitude of experiments. The latter is RUBI (Reference mUltiscale Boiling Investigation), soon to be replaced by CompGran-2 in the Soft Matter Dynamics (SMD) Experiment Container.

The main goal of the RUBI experiment was to expand our knowledge about the boiling process within a fluid. In your everyday kitchen on Earth, gravity plays an important role in this process through buoyancy of the created bubbles. The ISS microgravity environment is therefore ideal to study the fundamental physics that would otherwise be hidden by gravity effects. RUBI’s main component is the fluid cell that is surrounded by heaters to reach near-boiling temperatures. Instruments to accurately control and monitor the boiling process include the Substrate Heater with a nucleation site where the boiling is initiated by a laser, a high-speed Black&White camera and a high speed infrared camera to capture images of the generated bubbles. An electrode within the fluid cell gives the scientists the possibility to observe the effects of an electric field on the bubbles, a pump can produce a flow to study how bubbles can be carried away by it and accurate temperature sensors are able to pinch through the bubbles like a needle.

With RUBI and RUBI-X, 847 + 622 scientific runs were performed producing more than 12.5 TB of data that is being analyzed by the scientists. Besides telemetered values from each science run, the largest share of this data is coming from the High Speed Black&White and infrared cameras to monitor the boiling process. Having real-time access to the downlinked images to assess the progress and success of each run is producing the most delightful images of bubbles in microgravity providing that extra touch of joy for the operator on console. In order for the scientists to cope with that amount of data, automation was key to extract valuable data and process it.

At the end of January 2021, the next FSL experiment, CompGran-2, will take place, starting with a commissioning phase during which the operator is on console 24/7 to test extensively every sub-systems of the experiment before proceeding with the science runs. CompGran-2 is a re-flight of the Compact Granular experiment operated for the first time in 2018.

Belgian Contribution

Belgian contribution goes beyond the space operations:

  • Université Libre de Bruxelles is part of the research team (ULB- Transfers Interfaces and Processes, Prof. P. Colinet).
  • Lambda-X, in Nivelles, took part of the optics development.
  • Space Applications Services, in Zaventem, developed the new Video Management Unit of FSL.
News image 1
News image legend 1
Bubble resulting from the boiling process in microgravity inside the RUBI experiment on the ISS. Real size ~4mm.
Credit: B.USOC/ESA
News image 2
News image legend 2
Inside the Columbus module.
Credit: ESA
News image 3
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Operations from the B.USOC control center.
Credit: B.USOC