- Determining GPS coordinates, altitude, speed (horizontal and vertical), and heading
- Transmit GPS data plus other flight data of interest to the ground via satellite
- Receive ground commands, if needed, via satellite (normally the HAPP is autonomous)
- Process all flight data and commands and decide what actions to take, such as firing pyros to cut the umbilical with the balloon or pyros to deploy the parachutes
- Monitor the AP status and abort the mission if the AP stops responding normally (recall that the AP is listening similarly to the FC and can also terminate the mission independently if needed)
- GPS: u-blox MAX-M8Q
- Satellite: RockBLOCK 9603; uses the Iridium satellite constellation
- microSD: Adafruit MicroSD breakout
- Antennae: External Helical w/SMA (Satellite), Active PatchAntenna w/SMA (GPS)
|Unit #2 installed on the HAPP|
as flight hardware
|Autopilot (AP) on the left and|
Flight Controller (FC) on the right,
as installed on the Electronics Deck
GPS chips are constantly sending data to the communication bus. If you don’t devote time to servicing that stream of data, you risk losing characters and your GPS location fixes are in jeopardy. The cadence of the fix message is approximately one per second – more than enough for our positioning needs as GPS data is not involved in any kind of real-time steering of the craft. There is another class of GPS chips that provides higher accuracy and higher fix frequency. Coupled with predictive algorithms, that’s what your Tesla or military drones use for navigational guidance.
- Ask the AP for its state
- Sync onboard clock with GPS satellite time
- Log positional and operational data
- Evaluate states for flight control logic (the secret sauce)
- Repeat ...
- Are we well outside of the bounds of the expected flight plan? Yes? ABORT! (There is a good story here from the first flight test. I’ll let Chris post about that later...)
- Are we descending unexpectedly? Yes? ABORT!
- Did we go supersonic on descent? Yes? Cool! Tell us about it.
- Did we lose contact with the AP? Yes? ABORT!
- More …