18th January 2012 - On Monday the European Space Agency approved the first experiments with open fire in a spacecraft. An international team from Europe, Japan, Russia and the United States wants to use the return flight of the ATV (Automated Transfer Vehicle) for their research improving fire safety in manned spaceflight. Included is a team from the Center of Applied Space Technology and Microgravity (ZARM) at Bremen University.
The regular purpose of the ATV, an unmanned space freighter, is to transport supplies such as food, water, equipment, nitrogen, oxygen and fuel to the International Space Station. As soon as the spacecraft has fulfilled this purpose, it is designated to burn up on the way back, while enter Earth’s atmosphere. Now for the first time the return flight is used for an experiment. Instead of designing and financing an autonomous space mission, a waste product is used to perform experiments under conditions of weightlessness – a big space experiment for free.
The experiments planned for the return flight of the ATV will test the assumption that materials used in aerospace, really do extinguish automatically in weightlessness. For this purpose it is necessary to kindle an open fire on a spacecraft for the first time and at the same time keep an eye on a significant criterion: After the combustion experiment the thrusters of the ATV still have to work properly in order to guarantee a correct entry into the atmosphere and a safe burn up of the vehicle. A feasibility study by ESA has now classified this project as practicable.
The proposed experimental setup is a test of one of the current fire regulations. Basically combustible organic materials used in manned space flight, e.g. for astronaut clothing, wall coverings, thermal insulation of walls and electrical insulation of cables, are considered non-combustible if they pass the NASA Test 1. This test, borrowed from the aeronautics, examines the extension of a fire lit at the bottom of a vertical disk of the test material. The sample has passed the test if the flame extinguishes after switching off the ignition source within a length of 150 mm. If the fire spreads over a longer distance, the sample drips down in flames or burning parts fly away from the sample, the material is considered unsuitable. The question whether this test is really relevant for the actual behavior under conditions of weightlessness can only be answered by the experiment results.
The additional question of the Bremen team applies to the combustion behavior of materials that are built into space vehicles with a heavily textured surface and thus differ from the set-up of the NASA test. It is known from the ground test that grooved surfaces can promote the spreading of flames just as well as ribs, where heat is stowed. Because NASA's standard test normally checks smooth surfaces, the ZARM team regards significant deviations in weightlessness as likely.
The project around the first ATV experiment gains additional tension by the fact that the period from the idea to the first flight should take only a maximum of two and a half years. Such a short period of time is reminiscent of the pragmatism of the Russian space program of past days and it is at least unusual in the current aerospace. Because there are only a three more ATV missions scheduled, of which only two are suitable for the project, time is of the essence.But to use the missions ATV 4 (2013) and ATV 5 (2014) for the experiments the research team still searches for the equipment necessary to install an independent broadband data connection between the ATV and the ground stations in order to transfer the experiment data.In addition, it will be tested already on the ATV 3 before undocking from the ISS, if the pressure can be lowered to 950 hPa. Only if this is possible, all planned experiments can be performed on ATV 4 and 5, without the pressure exceeding the upper limit in the worst case scenario of the entire burning of all samples.
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