Overview

VOID used a BigRedBee (BRB) 70cm APRS transmitter for GPS tracking on both the rocket and the payload (void *). The BRB has two antennae, one 70cm transmit antenna (1/4-wave whip on the rocket, rubber ducky on the payload) and an L-Band GNSS receive antenna used for GPS (passive ceramic patch antenna on both rocket and payload). The BRB comes default with the patch antenna heat shrunk onto the PCB. In the payload, this heat shrink was removed in order to better orient the antenna with a clear view of the sky, the default orientation of the antenna is horizontally mounted to the PCB. In the rocket, this heat shrink was removed in order to replace the battery as it is secured with the same heat shrink.

During button-up and at the pad, GPS lock was verified on the rocket and payload and consistent APRS packets were being received at 1/2 Hz.

During flight, APRS packets continued to be successfully received and decoded by both Launch ground systems and the ESRA MCC provided receivers. All APRS packets contained stale GPS data showing coordinates of the pad. All packets received continued to transmit this GPS location as the BRB transmits the last known location in the event of losing GPS lock.

During recovery (lasting approximately 5 hours) APRS packets were received and decoded, all showing the same coordinates as before ignition. APRS packets were also received in the tent area showing the same data.

After speaking with an ESRA official, it was suggested that the the ceramic path antennae broke under acceleration at ignition due to the removal of the heat shrink wrap. More info on this failure can be found here (TODO, rocketry forum link).

This issue was not known in 3 design reviews for the rocket and 4 design reviews for the payload, as well as in the technical report submitted. The BRB manual also contains no information on damage to the antenna under acceleration when the heat shrink is removed.

VOID was launched in the morning of the last day and a thunder storm delayed deploying the recovery teams, giving us approximately 5-6 hours of recovery time total. The lack of GPS information due to losing lock led to us not finding the rocket in the amount of time we had to search.

Since we did not recover the rocket or payload, we cannot verify this was the failure we experienced with 100% certainty, but no other proposed theories explain why both BRB's lost lock at the same time and continued to send good APRS packets.

Potential Root Causes

• Lack of knowledge
  • Unknown failure mode prior to flight
  • Hard to mitigate short of a test flight
• Launched too late
  • More recovery time would have given us a better chance to find the rocket without GPS
• Lacked directional antenna
  • A directional antenna could have been used to get a heading using signal strength from the APRS packets that were being transmitted
  • Our recovery teams had dipole antennas making it impossible to get a heading from a single point

Other information

The ESRA official did mention that we can request a BRB with the battery not in the heat shrink so we can swap it without removing the antenna, but that does not mitigate that the primary reason the antenna was moved was for better orientation.