Why would anyone want to light a fire in space?
Figure 1: An illustration of a drop tower. Drop towers consist of a vacuum (to reduce friction) through which a cylindrical container is dropped from the top. They are used to produce microgravity conditions within Earth’s atmosphere.
For starters, sometimes gravity isn’t all that helpful. For example, when studying the process of combustion, gravity actually introduces a number of complications. Most numerical and analytical models used in combustion research rely upon the simplifying assumption that buoyancy forces acting on fuel droplets are negligible (Space et al., 2011). Consequently, Earth’s gravitational field renders this assumption invalid for many experiments done in terrestrial facilities. There are methods of producing microgravity conditions (ie. weightlessness) on Earth, such as through the use of drop towers (Figure 1), but these have complications of their own (ESA, n.d.). Namely, researchers are temporally limited when using drop towers because microgravity is only generated during the short dropping periods (ESA, n.d.). That is why many scientists have relocated their combustion experiments to the International Space Station (ISS; Beysens et al., 2011).
Figure 2: Fire in space. Left: Flame under normal gravity conditions. Right: Flame under microgravity conditions. The difference arises from the fact that convection currents carry hot air upwards on earth, but this does not occur in space (NASA, 2010).
Orbiting the Earth at a height of 400 km and velocity of 28,000 km/h, the ISS is in a constant state of microgravity (Beysens et al., 2011). Under these conditions, buoyancy-induced flows are greatly reduced, allowing for the isolation and observation of weaker forces and mass or energy transport processes (Ross, 2001). In addition, under microgravity conditions, flame flickering does not occur, allowing for the production of steady and symmetrical flames that are easier to study (Ross, 2001). In fact, flames assume a spherical shape under microgravity conditions, and so do the fuel droplets they ignite (Figure 2; Beysens et al., 2011). This allows for researchers to create idealized experiments, where homogeneously sized, equidistant, stationary fuel droplets can be arranged in series, allowing for the use of relatively uncomplicated theoretical models (Ross, 2001).
By this point, if you’re wondering, “OK, I get it, combustion seems a lot easier to study in space, but why waste a whole lot of time, effort, and money to study something as silly as fire?”, I’ve got some news for you: understanding combustion is of the utmost importance. Almost all of human transport in contemporary Western society occurs with the aid of combustion engines. In addition, combustion is a key element in many industrial processes, and in the production of energy – global energy as of 2010 was 80% fossil fuel based (Government of Canada, 2010)! In addition, understanding how flames travel in space helps researchers develop better means of containing and extinguishing fires that could occur in space stations. This is a very real concern, as just 16 years ago, an oxygen canister ruptured and ignited aboard the Mir space station. Luckily no one was injured, but the event highlighted the shortcomings of the scientific community in terms of its understanding of combustion in space. I hope you can now appreciate the importance of lighting fires in space. Not only is space combustion research necessary to protect our astronauts, but it also translates into real-world benefits down here on the surface.
Works Cited:
Beysens, D., Carotenuto, L., van Loon, J., Zell, M., 2011. Laboratory Science with Space Data: Accessing and Using Space-Experiment Data. Springer, New York.
European Space Agency (ESA), n.d. How to Make Microgravity. Available from: http://www.spaceflight.esa.int/impress/text/education/Microgravity/Producing_Microgravity.html. Accessed 11.4.13.
Government of Canada, N.R.C., 2010. Canada’s Fossil Energy Future: The Way Forward on Carbon Capture and Storage | Natural Resources Canada. Available from: http://www.nrcan.gc.ca/publications/fossil-energy-future/261. Accessed 10.30.13.
NASA, 2010. A comparison between a flame on Earth and a flame in a microgravity environment. Available from: http://commons.wikimedia.org/wiki/File:Space_Fire.jpg. Accessed 10.30.13.
Ross, H.D., 2001. Microgravity Combustion: Fire in Free Fall. Academic Press.
Space, C. for the D.S. on B. and P.S. in, Board, S.S., Board, A. and S.E., Sciences, D. on E. and P., Council, N.R., 2011. Recapturing a Future for Space Exploration: Life and Physical Sciences Research for a New Era. National Academies Press.