Associate Professor Grunde Jomaas from DTU Civil Engineering is coordinating an international research programme targeted at fire safety in space. It includes what are known as ‘parabolic flights’, which create a 22-second period of weightlessness—31 times in a row.
Fire and flames behave differently on Earth and in space where weightlessness drastically alters the progression of a fire. This means that if you want to test the flammability of materials in space, you must either transport them up to space stations or find other ways to create weightless conditions. What are known as ‘Parabolic flights’ are one of the options, and Associate Professor Grunde Jomaas from DTU Civil Engineering has participated in a couple of missions of this kind.
He is a fire safety expert and joined a ‘topical team’ at the European Space Agency (ESA) a few years ago. He was appointed coordinator of the ‘Safe Cosmos’ project, and in this context—in partnership with NASA—he has been involved in developing, designing and carrying out experiments centred on the flammability of materials in weightless conditions.
“Fires are generally powered by buoyancy, so when this aspect is absent, the flames behave very differently. For example, in weightless conditions candles burn with a blue, semi-circular flame. As the flame is powered exclusively by radiation, it makes no difference in which direction the light is turned. Because the ventilation system is always running in a space station, however, there will always be flows of air that may result in the flames spreading. And it is precisely this aspect we are examining,” relates Grunde Jomaas.
It is actually possible to achieve weightlessness within the sphere of the Earth’s gravity, but only for very short periods of time. For example, in a so-called ‘drop tower’, four or five seconds of weightlessness will occur when a material is in free fall, but this is not sufficient time to study how a fire spreads. It therefore makes more sense to take an experiment on a parabolic flight, where the aircraft climbs 47-degree angle—as opposed to the usual 20 degrees—turns at the apex and then descends again at the same angle. This generates 22 seconds of weightlessness, which is enough to produce usable evidence of whether a material is sufficiently fireproof to be used in a space flight.
Climbing and descending at such a sharp angle sounds demanding enough in itself, but each flight comprises 31 incidences of weightlessness—and the flights are flown three days in a row. It takes a very special person to stay the course, and only a select few people have the right stuff for these extreme experiments.
“I’m not normally a good sailor, but as long as I get a shot of sea-sickness medicine before we take off, I make it through without any real problems,” says Grunde Jomaas, who has already completed two missions and will be embarking on a third this autumn.
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If the fire in a material sample measuring 30 x 5 cm does not spread more than 15 cm during three experiments, the material is approved for use in space.
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Every flight is preceded by a long development phase, during which the experiments are timed and prepared down to the tiniest detail; a complete experiment design can easily fill 100 pages. It is incredibly costly to send a team on a parabolic flight, so the researchers cannot afford to risk something going wrong and ruining their hard-earned data, or preventing them from gaining the results from the experiment they had been counting on. That is why the sponsors (ESA or the Centre National d’Etudes Spatiales) are extremely careful to run safety checks on the experiments all the way up to take-off.
The whole team, which comprises experts from several countries, meets up in Bordeaux a week before the Airbus takes to the skies to set up the experiment and perform a series of ‘dry runs’. During the flight, the pilots relay messages such as ‘next climb in 20 seconds’ and ‘we’re now at 40 degrees’, and the entire experiment is timed in relation to these announcements. During the 22 seconds of weightlessness, the team uses a short circuit to ignite the material, so they can see how the fire develops.
“You’re at 100 per cent for the entire two hours the flight lasts, and afterwards you feel like you’ve just played a full 90 minutes of football. Three days later, you’re absolutely exhausted,” relates Grunde Jomaas.
Article in DTUavisen no. 4, April 2015.
31 times in the course of a single flight, the ESA Airbus climbs and descends to simulate conditions in space. Illustration: Novespace.