In a fascinating experiment, Chinese astronauts from the Shenzhou 16 mission recently struck a match aboard the Tiangong space station. This type of experiment would be nearly impossible on the International Space Station (ISS) due to strict regulations regarding flammable materials and open flames.
A Candle in Space
When you light a candle on Earth, the heat from the flame warms the surrounding air, causing it to become less dense. This creates an upward current of hot air (convection current). Simultaneously, cooler, denser air moves towards the base of the flame to replace the rising warm air, forming a downward current of cold air. This interplay of air currents shapes the characteristic form of a candle flame, with a bright, hot center surrounded by a cooler, more transparent zone.
The hottest part of the flame is often blue or pale blue, while the cooler part is yellow. This color difference results from the varying combustion temperatures within the flame. The blue zone is the hottest, and the yellow zone is slightly cooler.
But how does a naked flame behave in a microgravity environment? To explore this, astronauts Gui Haichao and Zhu Yangzhu lit a candle aboard the Tiangong space station on September 21st. The experiment was conducted live during a conference broadcast to numerous Chinese classrooms.
In the microgravity environment of low Earth orbit, the combustion convection current is weak. This means that flames spread in all directions rather than primarily upwards, resulting in nearly spherical fireballs.
Impossible Aboard the ISS
Such an experiment would be unfeasible on the ISS due to strict fire safety regulations. These measures were largely implemented in response to a significant incident on the Russian space station Mir in 1997, which was caused by an electrical short circuit. The resulting fire caused substantial material damage and raised serious safety concerns for space stations.
To minimize fire risks, space agencies involved with the ISS have established stringent protocols for materials used on board, including fire-resistant materials and waste management procedures for flammable objects.
Despite these precautions, combustion in microgravity remains a field of scientific interest, and many experiments are conducted on the ISS to better understand combustion processes in weightlessness. These experiments are generally carried out in safety devices designed to contain flames, minimizing risks to the station and its crew. Similarly, the Tiangong space station is equipped with a Combustion Experiment Rack (CER) for conducting serious research in this area.
This remarkable experiment not only showcases the innovative spirit of space exploration but also highlights the unique challenges and opportunities of conducting scientific research in microgravity.
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