Even though the average temperature outside was far below the freezing point the Dawn team of DARE pushed on with the planned igniter test last Tuesday the 7th of February. This was needed as since the recent project, which was part of the Spacecraft Engineering Minor of the TU Delft, it was found that the igniter that was in use by the team was not as reliable as once thought.
The old igniter, which consisted of a NiChrome wire with magnesium strips, had worked consistently during all Dawn tests during 2010 and 2011. However, during the tests of the minor project the igniter failed to work more than 50% of the time. The cause of this might be due to the change from a horizontal to vertical orientation of the engine, because of the use of a different valve, because of higher oxidizer tank pressures or maybe simply because of environmental reasons: All Dawn test were conducted in warmer times of the year. Most likely is that it is a combination of the mentioned factors but either way, a new ignition system needed to be designed.
The eventual system tested consisted of a small igniter made of a mix of nitrocellulose and graphite, surrounded by a larger amount of steel wool. This igniter has now proven that it can light the engine, even at the low temperatures of last Tuesday. Compared with the old NiChrome igniter this system also has the added benefit that it requires only a small amount of electrical power to ignite, whereas the old system needed a very high current to function.
The test of Tuesday was conducted on a snow-white Architecture field on the TU Campus. The temperatures started of around -10°C to -8°C in the morning but rising to around a comfortable -5°C in the afternoon. Next to the difficulties that such cold weather brings to the human body, it also influenced some of the test equipment. For example, one of the valves was found to be leaking very slowly, probably due to shrinking of the sealing rings because of the temperature. This problem was however solved by greasing the valve with Krytox. Furthermore the leak detection spray that is frequently used by the team was found to be frozen and could unfortunately not be used.
In conclusion, it was a rough environment to do an engine test, but the Dawn team can now celebrate that they have found an igniter that looks very promising, even at these low temperatures.
Slow motion videos of the tests can be found here. There is unfortunately no other footage of the tests as the camera regularly used for this did not work because of the low temperatures.