SSI VALBAL:

SSI's World-Record Breaking Low Cost, High Endurance, Altitude-Controlled Latex Balloon for Near-Space Research

Code Architecture:

The avionics flight software operates on a read-eval loop in order to change states and respond to its environment and is written in compliance with NASA JPL's Safety-Critical Code standards.

Files

main.cpp - Start point of flight controller

config.h - Mission specific configuration values

data.h - Structure of current data frame

Classes

Avionics - Implementation of flight logic

Controller - Interface to feedback control algorithm

Sensors - Interface to raw data from hardware

Filters - Interface to corrected data from filters

Actuators - Interface to valve and ballast mechatronics

Charger - Interface to superCap charging circuit

Hardware - Interface to PCB hardware

Logger - Interface to compressed SD card stream

Payload - Interface to external research payloads

Simulator - Client side code for Hardware in the Loop simulations

Libraries

GPS - Wrapper library for GPS with added features

RockBLOCK - Wrapper library for RockBLOCK with added features

AD5246 - Library for i2c Resistor

Utilities

Parser - De-parser of compressed flight telemetry

readsd - De-parser of compressed SD card stream

Implementation Details:

Here is the current status of the code:

Flight Critical Systems

1. Altitude readings from filtered and error checked BMP280s
2. Feedback control algorithm for equilibration at altitude
3. Custom charging circuit feedback control
4. Valve mechanical actuation and de-jamming
5. Ballast mechanical actuation and de-jamming
6. MicroSD logging of current data frame
7. Integration of uBlox M8Q GPS
8. Satellite data downlink over RockBlock
9. 1Hz LED in compliance with FAA
10. Payload interface for communicating with research payloads

Useful Flight Features

1. Ascent rate calculations from Kalman filtered data
2. External temperature readings
3. Subsystem current readings
4. Subsystem shutdown if reboot failure
5. Low power mode for ARM Cortex M4 processor
6. GPS set to flight mode
7. Compression of data frame into bitstream for comms
8. Satellite uplink command parsing over RockBlock
9. Manual control of flight parameters over satellite uplink
10. Stable loop rate regulation
11. Extended debug mode
12. HITL & modular simulations testing suite