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Weekly Activity Report - April 30-May 6, 2012

Highlights of recent developments on the DoubleSShot project
The DSS BPS rocket motor was test fired on Saturday, May 5th, 2012 at 3:44 PM PDT at the FAR test site in the Mojave Desert. Members of the SS2S Motor Team arrived at the site around 9 PM then began assembly the propellant grain and rocket motor. Ground Team members were Paul Avery, Randy Dormans, Chris King and Rick Maschek. Assembly of the six grain segments into a single grain went well with only minor glitches. Motor assembly proceeded well with no issues. Chris reported that the measurement instrumentation setup went very smoothly with only one minor issue relating to a pressure sensor reading. The motor was loaded onto the test stand, which also went smoothly. Cameras were set up to record the event, and Chris started data acquisition. The Team retreated to the safety bunkers and began the countdown.

When the count reached zero, Paul pressed the firing button. A puff of smoke signaled successful ignition of the pyrogen unit, quickly followed by smoke billowing from the nozzle. The pyrogen canister was seen ejecting at this time. The motor rapidly built up pressure and within one second, the motor CATO’ed. The casing and nozzle flew straight off the test stand, as the casing ripped open at the Midbulkhead joint. The two bulkheads and severed section of casing fell below the test stand, as did the apparently intact Delay Plug, which continued to burn for over a minute.

Despite damage to the data acquisition equipment, including Chris’s laptop, excellent thrust and chamber pressure data was collected. The pressure reached just under 2000 psi (13.8 MPa) at the moment of rupture, with a corresponding thrust of 5750 lb. (25.5 kN) (giving a Thrust Coefficient of 1.45).

The Nozzle, Midbulkhead and Forward Bulkhead were all recovered and appear to be in reasonably good, reworkable condition. The test stand was damaged and is in need of major repair.

Photos and video of the event are currently being processed and will be posted later this week.

A huge “Thank-You” goes out to the SS2S Motor Team for their tremendous effort and tireless devotion over the past months meticulously preparing for this test firing, taking every precaution to maximize the chance for a successful firing. Experimental Rocketry lived up to its name, and this time around, a“yet to be discovered” factor ruled the day. This was despite our best efforts that we should all be proud of. A big thank-you also goes out to Paul Breed, Ed LeBouthillier and Theo Dormans for their generous assistance provided to the SS2S Motor Team in setting up this test firing.

The day following the firing event, a de-briefing telecon was held. Participants were Randy Dormans, Chris King, Rick Maschek and Richard Nakka (Paul will be have a debriefing session early this week). The consensus was that this result was essentially a repeat of the September firing of the DSS BP motor and that the cause of the anomaly may be one and the same. It was agreed that nozzle blockage would likely be ruled out, based on the thrust and pressure curves, exhibiting closely matched profiles as expected for a nominal burn, however being more than double that of design. As such, the overpressure must have resulted from a large increase in burning area. Rick felt confident that the grains did not have any cracks, prior to loading in the motor, and the “tap test” performed on all grains showed no indication of disbonding. The overall thought was that the propellant likely fractured upon pressurization. This has always been a concern with sugar propellants, which are known for their brittle and high-modulus nature.

SS2S Motor Team members +1, left to right: Chris King, Rick Maschek, Randy Dormans and son, and Paul Avery:


Thrust and Chamber pressure curves:


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