The astronauts of China’s Shenzhou 16 have conducted a surprising experiment in space involving fire aboard the Tiangong space station.
Chinese astronauts lighting a candle on the Tiangong space station. (Image source: CCTV).
Astronauts Gui Haichao and Zhu Yangzhu lit a candle during a live presentation broadcast from the Tiangong space station on September 21, demonstrating how fire behaves in microgravity. Notably, the flame appeared almost spherical, rather than the teardrop shape we are accustomed to on Earth.
On Earth, lit candles produce flames shaped by convection driven by buoyancy, where hot air rises and cool air descends. However, the convection currents that fuel combustion are weak in the low Earth orbit microgravity environment. This means the flame diffuses in all directions, creating spherical fireballs.
The live lecture was the “Tiangong Classroom” series, the fourth session held on China’s space station. The astronauts interacted with students in five classrooms across China, showcasing various microgravity phenomena. Like previous sessions, the astronauts demonstrated that many physical processes operate differently than they do on Earth.
However, the candle experiment – where Gui struck a match to ignite the candle – may surprise participants at the International Space Station (ISS), which has strict regulations regarding flammable materials and open flames.
Strict fire safety measures on the ISS are partly a response to a serious fire incident on Russia’s Mir space station in 1997.
Combustion in microgravity is the subject of many experiments on the ISS, typically using a specialized combustion integrated platform designed to keep the fire isolated and contained. The Tiangong space station also features a Combustion Experiment Rack (CER) for serious research in this field.
