2013.06.23 NEWS *A Motor Team telecon was held this weekend to discuss the DSS TM-2 motor test and to come up with a recovery plan. Attendees were Rick Maschek, Paul Avery and Richard Nakka. Details of the TM-2 motor preparation, assembly, test firing and post-burn inspection of the motor were presented and discussed; in particular, any deviations were noted from the test plan. As well, differences between the TM-2 motor and the earlier successful TM-1 motor were noted and assessed. Test data such as chamber pressure gauge readings were carefully reviewed in an attempt to come up with an explanation for the anomaly. A failure of the Chamber Separation Disc (CSD) was discounted as the cause, as there was no evidence to suggest an off-nominal performance of this component. A comparison was made of the pressure readings of TM-2 with the earlier successful TM-1, and with the BPS motor, which also CATO’d. It had been concluded earlier that BPS failed due to catastrophic propellant fracturing during motor startup. The comparison proved enlightening. The chamber pressure rise for TM-2 was much more rapid than TM-1, and was similar to that of BPS. It was agreed that propellant fracturing upon startup was therefore the likely cause of the TM-2 CATO. A conclusion could not be reached as to why the two nearly identical motors (TM-1 and TM-2 ‘first burn’) behave differently at startup. There were no significant differences in the two designs, assemblies or ambient conditions. Based on the negative experiences with “cored” grains (e.g. BATES, Star) which can be subjected to significant tensile stress upon motor startup, it was concluded that scaling up of sugar propellant motors has its challenges. In particular, cored grains are best avoided, and a non-cored grain configuration is the most promising way to go. A grain configuration that is subjected solely to compressive loading on startup will be tested next. Rick suggested that a “success” criterion of three successful firings, in succession, be set. This was agreed upon and work is already underway to repair the TM-2 motor (as a single burn configuration). Test firings will take place in the near future at our alternate test site in the Mojave Desert (since FAR is currently unavailable to SS2S). These motor tests will be designated DSS TM-4A, TM-4B and TM-4C. Upon successful completion of these tests, the ‘six-grain’ DSS TM-3 motor (currently being worked on) will be test fired. *Blair and Richard Nakka have nearly completed the machining of the DSS TM-3 “nozzle adapter”. This component will be used to adapt the BPS nozzle to the 7 inch (178 mm) casing. The part still needs to have the 20 radial holes tapped, and then a chamfering of all cut edges.
Posted on: Wed, 03 Jul 2013 13:11:34 +0000
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