by Jim Gross, Reaction Research Society
The USC RPL group had a large number of experienced seniors graduating this year. The pandemic had minimized activity over the past two years, so the group had many new students with little experience in conducting firings. Many of the experienced students were graduating so the purpose of this project was to teach the lower classmates how to conduct the firing preparations.
I was the Pyrotechnic Operator (Pyro Op) in charge and arrived at the MTA at 0822-hours and shown the work done so far. The vehicle was on the launcher but the igniter was not yet installed. USC RPL had two 3-bag igniters prepared in fueling area. One was attached to their traditional dowel road but the spare was not.
The Pyro Op gave the safety briefing covering both rocket and environmental hazards at 0900-hours to the 79 participants. The predicted time to impact if the recovery system failed was 89-seconds. Everyone then got under cover in the bunker and final instrumentation checks were conducted. The igniter was inserted at 0913-hours and the vehicle launched at approximately 0922-hours. The ignition was prompt and the flight looked normal. Telemetry was lost during the flight.
Some interesting facts about Jawbone: The predicted altitude was about 34,000-feet. It used their older propellant. It was reported the motor had about 40-lbs of propellant. This contrasted with the 100+ pounds that was reported on the Standard Record Form (SRF). The igniter had a total of 33-grams of igniter composition of which 24-grams was powder and the rest was strips of propellant. The igniter composition was the same AP/HTPB propellant as the motor. The free volume of the motor was reported to be 114-cubic inches. The outer diameter was 6-inches.
Jawbone was recovered late in the afternoon. The data recording system was working and to be downloaded and analyzed when the team returned to USC.
Further details on the event were provided by Jeremy Struhl of USC RPL:
USCRPL successfully launched and recovered Jawbone on Saturday, April 23rd, 2022. The vehicle reached an apogee of 41,300 feet above ground level (AGL), a maximum speed of Mach 1.717, and a peak acceleration of 7.266 G’s.
Jawbone saw multiple new systems in avionics and recovery. First, the avionics unit on Jawbone received a number of upgrades. First flown on CTRL+V, USC RPL’s custom pancake-style PCB stack conforms around the nosecone deployment CO2 canister, allowing more space in the nosecone. The system featured a new custom battery charging and management PCB to prolong pad standby time. Additionally, this was our first flight of the Lightspeed Rangefinder, an in-house designed and built tracking unit that used four ground stations positioned around the launch site to triangulate the position of Jawbone following its flight. This positional data proved valuable during the post-flight recovery of the vehicle.
The Jawbone recovery system featured a next-generation design with improvements from the prior rocket ”CTRL+V “ dual deployment recovery system used in that flight. Using a connector and extension wire running along the forward shock cord segment, USC RPL’s custom avionics unit attempted to control the active deployment of the main parachute when the vehicle reached a decent altitude of approximately 5,000 feet. Unfortunately, the recovery system experienced a partial failure resulting in the main parachute failing to open. The drogue parachute was still successfully deployed, so the vehicle was recovered intact. The main parachute, which was constrained using a Tender Descender, was never deployed due to unexpected loads during nosecone deployment disconnecting the cable attached to the Tender Descender.
