July Launch of LV2.3
July 31st 2011 we headed to central Oregon to launch our rocket with the same roll control as the previous launch, but this time with much of the full flight computer we have been planning for years in in place and running. This included the PowerPC flight computer, a Hemisphere Crescent GPS receiver board, and our new 2.4 GHz Amateur TV broadcast system with overlay.
Unfortunately the rocket motor failed on ignition, ejecting the fuel (unburnt) from the motor casing. The force of the depressurization lifted the rocket off of the launch rails, to about 30-40 feet into the air. Although the drogue parachute did eject, the rocket came down fairly hard and suffered minor damage to the fin canister and aeroshell.
Loading the rocket on the rail and hoisting the rail to launch position
- Download Original (40.3MB) loading-on-rail-and-hoisting.mp4
- Download Original (23.8MB) tower-flight.mp4
600 FPS High Speed Footage
- Download Original (7MB) lv2-2011-07-31-600fps.mov
View from the flight line
- Download Original (29.4MB) FlightLineView.MP4
- Download Original (6.4MB) Flightline cropped.mp4
- Motor CATO
- The DVR did not record anything on 7/31. The last recording on the SD card was from 2011/07/27 12:32:12 AM PDT, which was when we packed it up for flight in the PSBA. When the payload module was opened for the first time after flight on 2011/08/01 17:20 PM PDT, the slide switch was found to be on (including both blue and red sections of the switch) and the battery was completely discharged. We assume it was never turned off by the recovery team. More disturbingly, the 8 GB SD card had ejected from the slot and was hanging out of the card slot. We assume the card was ejected on CATO or on impact why there was absolutely no video at all is a mystery: the DVR should have recorded until the battery died or the card was ejected. Why there's no files at all from the launch day is strange. The record switch was in the "record" position, the battery was charged the night before, and the camera jack looked plugged in. It's as if it just never ran.
- Did not tape SD card into slot
- The rocket was out of frame in the high speed camera. We could not see the liftoff or any detail of the motor failure.
- The blue tape with the rotary switch markings was left on the rocket for flight.
- The ATV was initially transmitting near enough the same frequency as the LTC WiFi connection and knocked the tower communication out until we switched channels on the LC AP.
Important Airframe Damage
- Main Parachute bag is shredded
- Spin Can got dirt in bearings
- Upper aeroshell is damaged?
We know that the motor stopped almost immediately after ignition. The rocket continued into the air for a short period of time unpowered and came to a rest just behind the tower. When the recovery team reached the rocket we discovered that the aft enclosure and nozzle were missing and most of the fuel had ejected from the motor casing.
Examining the motor casing we found the forward enclosure was also dislodged, though not entirely. Most interestingly the threads on both sides were undamaged. When cleaned and screwed back into the casing the aft enclosure still fit. This suggests that the motor casing expanded under motor pressure enough to disengage the threads of the two enclosures. What remains to be seen is why the pressure was high enough to allow this to happen.
The tower cam had a wide angle lens that captured the event at 30 frames per second. Here we see four consecutive frames around the event:
The motor comes up to pressure in the first and second frame, then the enclosure appears to fail in the third. By the last frame there is little flame left, the motor has already failed and rapid depressurization extinguished the fuel (dP/dt failure).
A fuel grain is seen leaving the end of the motor two frames (0.667 seconds) after the event:
We can see the leftover debris from inside the motor scattered on the ground after the smoke cleared.
There were three fuel grains missing from the motor when we recovered it. The other three were stuck inside the casing with some kind of spacer wedged sideways blocking their escape. Only one grain was seen leaving the motor in the video so the other two must have been ejected in the initial event both so fast -- also suggested because they were found heavily damaged -- and still masked by flame and smoke.