Basic Information
Name	Xi-31
Launch date:	19 November 2022
Rocket description	- 3”/ 76.2 aluminum airframe (0.035”/0.89mm) - 4 fins, 2024 aluminum (0.065”/1.65mm) - 3D printed tangent-ogive PLA nosecone - 3D printed PLA boattail fairing/motor retainer - 42 inch ellipsoidal "Fruity Chutes" parachute
Payload	- Raven3 altimeter (primary role) - BREO-N flight computer for backup apogee separation and backup main deploy - BREO-N flight computer (2^nd backup, apogee only) - BRB900 GPS transmitter - Liftoff-activated and apogee-activated smoke trackers with Legendary formulation. - SJ100 on-board video camera, aft-facing
Liftoff mass	3.190kg.
Stability Margin (minimum)	2.51
Flight objectives	- Flight test of APM-E.12 motor with AXP-AP6.1 propellant. - Trial of new SJ100 on-board videocamera.

Motor details
Motor name	APM-E.12
Propellant	AXP-AP6.1 (Ammonium Perchlorate 76.7% /Epoxy (New Classic) 23% /Lampblack 0.3%)
Grain mass	337 grams
Delivered Impulse	645 N-sec. (est.)
Class	J (38mm)

Additional information

- The APM-E.12 motor had been successfully static fired prior to this flight. This propellant contains no aluminum.

- EggTimer altimeter suffered unrecoverable damage on previous flight. Replaced with a second BREO-N unit for backup apogee pyro and backup chute pyro activation.

- Previous flight (Xi-30), the parachute did not unfurl after being deployed (the preceding 20 flights experienced nominal chute unfurling and blossoming). No reason could be determined for this anomaly. To help unfurl the chute, for this flight, two pieces of polyester sheet (38x24 cm) were rolled into tight balls and placed within the folds of the canopy prior to packing into the rocket compartment. This material has a ‘memory’ and tends to instantly revert to a flat profile when unconstrained. It is hoped that this will provide enough impetus to the canopy to allow it to ‘catch air’ and blossom.

Weather conditions
Temperature	-15 °C (5°F)
Wind	W 10 km/hr (ground level)
Sky	Near twilight
Other	Scattered clouds
Ceiling	unlimited

Launch Event Description

To help prevent the flight computers from getting overly cold, a pair of chemical hand warmers were taped to the outside of the AvBay prior to heading to the launch site. The same was done to the outside of the nosecone, which houses the BRB unit (these hand warmers are removed prior to placing the rocket on the launch rails).

Following our checklist, we proceeded to set up the launch rail system and the rocket. Only one glitch was encountered. Snow (which turned to ice) had gotten inside the socket of some of the bolts of the launch rail connector straps. This made it difficult to insert the Allen key and significantly slowed down the setup process. The cold weather complicated the issue, as our bared hands would become numb after less than a minute and required frequent warming. Once the launcher was set up, the BRB transmitter and receiver were activated and verified that a good GPS signal was obtained. The BREO units and Raven unit were activated and verified to be functioning nominally. The lift-off activated smoke charge was powered-up then armed. Finally, the on-board camera was powered-up and set to record mode.

For filming the flight, I used my Sony HDR-CX240 Handycam fitted with scope tube, as usual. For this flight, which was expected to achieve a fairly high altitude, I decided to once again use my pair of wearable binoculars which worked very well for the previous flight.

After verifying the sky was clear, the countdown proceeded. At the zero mark, the ignition button was pressed, and the igniter fired. The rocket immediately accelerated off the pad, climbing straight vertical. I was able to visually follow the initial ascent, thanks to the Legendary smoke trail. However, we soon lost sight of the climbing rocket, due to the twilight sky and lack of sun to illuminate the rocket and smoke trail (the sun was near the horizon and hidden behind a cloud bank).

After approximately 20 seconds, we heard a faint ‘pop’ sound of the apogee pyro charge firing. We did not spot any smoke clouds or smoke trail from the smoke tracker that would have fired two seconds after apogee. Although the sky was clear overhead, the twilight sky and lack of sun to illuminate the smoke thwarted our efforts to locate the now-descending rocket. After nearly a minute, we heard the distinct ‘pop’ of the chute pyro firing. We did not sight the rocket immediately, but after scanning the sky in the direction of the pop sound, we spotted the rocket descending under parachute, smoke trailing as it descended. The rocket was clearly a significant distance downwind. We estimated ¾ kilometre. The rocket disappeared as it descended below the nearby berm.

We programmed the GPS coordinates of the touchdown site into the hand-held Garmin GPS unit. Indicated distance was 0.47 miles (756 m.). We then looked at our map of the launch site area that was overlaid with a latitude/longitude grid. We pinpointed the touchdown site on the map as being near a side-road southwest of the launch site. We packed up and headed to our parked car, and drove toward the touchdown area. We soon spotted the downed rocket, lying in a snow-filled ditch. The rocket appeared to be in excellent condition with all parts accounted for. The Raven unit beeped out a peak apogee of 3954 feet. The on-board camera, which was still recording, was turned off.

Flight Analysis
Event:	Time (sec)	feet	metres
Apogee*	14.6	3536	1078
Separation*	15.6	3523	1074
Chute deployment	57	691	211
Touchdown	90	-	-
Range	-	2618	798
Max. velocity	698 ft/sec.	213 m/sec.	mach 0.62
Descent rates:	ft./sec.	m/sec.
Free-fall	81	24.7
Parachute	17.6	5.4

* Corrected for non-standard base temperature.

Post-flight analysis and comments:

Post-flight examination of the flight data indicated that the operation of the Raven and primary BREO was fully nominal. The reported apogee for the two units was within 0.5%. The secondary BREO fired both its apogee pyro and chute backup pyro. However, it stopped recording flight data after 1.5 seconds. This anomaly is being investigated.

The BRB (GPS) unit did not record an apogee value. There was a data drop-out beginning shortly after lift-off, lasting 14 seconds. Once data tracking resumed during descent, the GPS altitude corelated closely to barometric altitude recorded by the flight computers. I asked Greg Clark (owner of BigRedBee, LLC) for his opinion as to why there was a data drop out:

It's not uncommon to lose lock during ascent. There are many variables including the GPS constellation itself. Other contributing factors include how the GPS is contained in the rocket (mounted to sled? Bubble wrap inside a nose cone?) , airframe material, paint, proximity to other electronics, etc.

Unfortunately, this response was of little help, as the BRB installation in the Xi nosecone was the same as all previous flights. Losing lock is rather uncommon, based on my experience having flown the BRB on 68 flights to date. On rare occasions, a drop-out of a second or two had occurred during ascent. But never such a long duration as 14 seconds. For this flight, the data did indicate that only 4 or 5 satellites were being tracked prior to drop-out, so it simply may have been unfortunate timing that the GPS satellite constellation was poorly positioned overhead during ascent.

Examination of the Raven flight computer acceleration data indicated the APM-E.12 motor had a nominal burn that closely matched the static test curve.

The SJ100 on-board video camera worked very well, providing good quality footage of the entire flight.

Both smoke charges burned. The lift-off activated charge burned for 46 seconds, indicating that ignition occurred at only one end of the smoke grain, despite both igniters having fired. The smoke trails were not of much help for this flight for two reasons: 1) the lack of sun to illuminate the smoke; 2) the twilight sky did not provide needed contrast to the smoke.

For the next flight, we will cover the launch rail connector strap Allen screw sockets with vinyl tape to prevent snow/ice from plugging the screw socket.

Due to the cold, the Sony videocamera malfunctioned. The video of the rocket descending by chute was consequently of poor quality. For the next cold-weather launch, the camera will be kept in an insulated box, with chemical hand-warmers, until just prior to filming liftoff.

Misc photos:

SJ100 videocamera Xi-31\DSCF6934.JPG

Re-worked av-rack showing BREO units Xi-31\DSCF6935.JPG

Opposite side showing Raven3 Xi-31\DSCF6936.JPG

E.12 rocket motor Xi-31\DSCF6933.JPG

AXP-AP6.1 propellant segments Xi-31\DSCF6931.JPG

Raven data:

Barometric and axial acceleration curves Xi-31\Xi-31_Raven-basic.jpg

Axial acceleration curve Xi-31\Xi-31_Raven-accel.jpg

BREO data:

Altitude versus flight time Xi-31\Xi-31_BREO-1.jpg

Launch photos: