It's been a week, so time to complete the post-mortem.
First of all, I did not meet my goal of completing the prep on all 3 stages before sending them away with Steve. I completed the booster prep, and nearly completed the sustainer prep, but on the 2nd stage I only got as far as making sure I had all the pieces. I rushed the electronics work so that I could get them installed into the rockets to ship out, and I deferred the finalization of the deployment settings, knowing that I could change them via Bluetooth while they were buried in the rocket. However, that approach prevented me from testing all the final settings in a safe configuration without tearing all the stages apart. So lesson #1: Plan to keep a lot of time margin at the end before shipment date.
Why was the lack of testing important? It turned out that the inadequate 2nd stage igniter wasn't the only problem; I also messed up the 2nd stage separation charge setting, by setting it for 0.5 second after motor burnout #1, instead of motor burnout #2. I had always planned to launch on Saturday, and Friday was a prep day. But I was programming the settings on Friday afternoon, after I had already been prepping for hours and was getting a little worn out. I was so focused on the motor ignition settings and thought, "oh, separation charge, that's easy, just set it for motor burnout plus 0.5 second." Which is an understandable mistake to do once, but I hate repeating the same mistake from last year.
So lesson #2: Always run a full simulated flight with the final settings and verify that all the outputs are going off at the intended times. I would have caught the separation charge setting if I had run the simulated flights. For this flight, that would have been 12 outputs between 5 altimeters on 3 stages, which is the kind of thing that makes a class-3 three stage flight so hard. If I had done that before shipping, I could have downloaded and checked all the data in the comfort and quiet of my lab. Doing that under an EZ-up with big rockets going off and customers coming by to ask for troubleshooting help would have been nearly impossible, so the best I could do was just retreat to the relative quiet of the RV, skip any simulated flights and just carefully check the settings. The ignition settings were well-checked, and the deployment settings were well-proven defaults, but the separation charge settings needed attention that I forgot to give them.
I made another critical mistake prepping the second stage on Friday, but it was one I caught at the pad on Saturday. Because of the combination of minimum diameter, head-end ignition, and motor-attached deployments, the motor igniter unavoidably has to be installed early in the assembly process. Because of this, my strategy for safety is to keep the motor grains out of the motor until I get to the pad. This year I learned to attach a guide thread attached to the igniter that I pull on as I insert the motor grains to make sure the igniter goes down the core rather than getting mashed against the top grain, and this worked well during test assembly with no electronics. But when I went to do this for the 2nd stage at the pad, the motor liner didn't fit in quite right. On prep day I added some hot melt glue to the base of the igniter to help keep it straight, and didn't think to re-check the fit. Rather than force the motor grains in, I decided to take apart the 2nd stage to see why the motor wasn't fitting. When I did that, I noticed that I had forgotten to install the forward o-ring on the forward closure. And worse, I couldn't remember installing the forward O-ring on the sustainer motor, either. The 2nd stage I could disassemble and fix in a few minutes because the av-bay is separate from the top of the motor. But disassembling the sustainer is a much bigger deal. I had to reverse all the assembly steps from post #85 and then re-do them all, out on the table in the sun, at the away pad. But I got it done with help from my crew Vic and Steve and James Russell who were incredibly patient. And it turned out that I had installed the O-ring on the sustainer's forward closure, after all. Why? because I did that part of the prep at home.
So lesson #3, which really goes with the other two: Complete all possible prep at home. This is something I have already learned over the years, but apparently I need some periodic reminders.
Other things that went wrong that were new and surprising for me. The second stage ejectable av-bay harness tore through the fiberglass harness attachment bulkhead. This is a brand new one. I had intentionally kept the harness short and without reefing to make sure that the two parts of the chute compartment would fully come apart to expose the chute. I used a small premade cardboard tube charge of a size that I have used before, but I haven't ground tested that recently. I did ground test an aluminum charge holder that I used on the booster, and it was appropriately sized, but because of space limitations in the 2nd stage area, I couldn't use the same approach. Lesson #4: Beef up the harness attachment with 4 threaded holes instead of 2, use a thicker harness, and reef it.
On the sustainer, the nosecone ejection blew, apparently when it was supposed to, but it broke the shock cord. I found the nosecone and the NC ejection piston, and the exploded-looking shock cord by themselves on the playa. This was a setup that I had ground tested the week before, and it worked perfectly. I also flew it at Airfect (though with an electrical short that prevented deployment) and at the NCR August launch. I also ground tested it in July. About the only thing I might do differently would be to use a slightly thicker shock cord, and replace it more often. This one didn't look sketchy, but it had probably taken a fair amount of damage over repeated tests and flights. Maybe stronger reefing, too?
With the nosecone detached, the rocket was descending ballistically with a heavy unburned motor when the main chute blew. So I don't fault the main chute for not surviving that, but it also broke the shock cord. Lesson #5: Go beefier on the recovery gear. It's not a place for finesse.
So, what went right?
The tower got the stack going straight, and the stages were stiff enough and tight enough to stay stable and straight through the boost.
The tower had a little bit of an (unintentional) tilt away from the flight line that you can see in this photo:
but the boost was on track for the second stage to light.
It did fire the 2nd stage igniter, but a later than intended due to the accidental sustainer separation, which messed up the baro altimeter reading:
The separation charge put a big pressure spike on the 2nd stage av-bay, which took some time to recover, and the open front end caused ram air pressurization of the tube also, so it took some time for it to go slow enough for the that effect to be small enough for the baro sensor to detect that it went over the minimum altitude of 2700 feet. Based on the inertial altitude estimate, it got over 2700 feet in about 4 seconds, and the stage igniter lit at 8 seconds when the baro sensor caught up. The tilt hadn't increased much during that time.
The pad checklist I made in June for the class 3 application was pretty much right on the money, and it reduced stress when I was able to get back on it after the disassembly/assembly detour.
