Report
Dordrecht, 19 February, 2006 - CMT0507, the previous test, was a failure. Instead of taking small steps in our motor development, as we used to do, we now changed three things: the number and therefore the length of the grains, the port size of some of the grains and the throat diameter. Although predicted to be a perfectly fine motor, during the test the pressure inside the motor became to high and the mechanical safety mechanism kicked in. It took place in a very short time span and it bend the safety mechanism. Our conclusion was that we have overcompensated the problems of the motor and thus the next test was going to be a follow-up of the second last test. The only thing we now changed compared to CMT0506 was the smaller throat of 11.5mm. The mechanical safety mechanism was replaced by a brass membrane, which was tested in the weeks before the motor test.
The preparations on the day of the test went very smoothly. Not only the NAVRO motor was to be tested, but NAVRO members Mark Uitendaal and Leon Krancher brought two test motors for their two-stage Spectre II project with them to test. Their first test, a 75mm potassium nitrate and sorbitol based motor, went very well, but after a first glance at the results it didn't produce as much pressure as expected. The smaller 50mm motor (J420-SG), which tested after the NAVRO motor, did perform very good.
The NAVRO motor was quickly assembled and the test itself looked good, but had a long burn time, which was not a good sign. The results confirmed this, as the pressure was 10 bar, which is lower then all the earlier successful tests with bigger throats in this test series. After much speculation the reason of the failure of this test is thought to be a problem with the grains, most likely expired epoxy resin, which smelled badly like ammonia. The next test is going to be a rerun of this one, but with new epoxy resin.
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