Stratosonde Technical Specifications
Living document — Last updated: November 2025
This page consolidates validated specifications from component characterization and system testing. Values are updated as new test data becomes available.
System Overview
| Parameter |
Specification |
Source |
| Total Weight |
<15g target (15.6g prototype) |
Hardware Validation |
| Target Altitude |
12-18 km (40,000-60,000 ft) |
Design target |
| Mission Duration |
Multi-day validation → weeks goal |
Design target |
| Operating Temperature |
-65°C to +60°C (validated) |
Ceramic Cap Testing |
| System Voltage |
3.3V regulated |
Design |
Power System
Energy Harvesting (BQ25570)
| Parameter |
Specification |
Source |
| Harvester IC |
Texas Instruments BQ25570 |
Design |
| Measured Efficiency |
70-75% (cold start to MPPT) |
BQ25570 Characterization |
| MPPT Voltage |
80% of Voc (programmable) |
Design |
| Cold Start Voltage |
330mV minimum |
Datasheet |
Battery (2S LTO Configuration)
| Parameter |
Specification |
Source |
| Cell Type |
Huahui HTC1015 LTO |
Design |
| Configuration |
2S (series) |
Design |
| Cell Capacity |
40mAh nominal |
Datasheet |
| Cell Weight |
2.4g each (4.8g total) |
Measured |
| Nominal Voltage |
4.4V (2× 2.2V) |
Design |
| Voltage Range |
3.2V - 5.6V |
Design |
Internal Resistance vs Temperature (per cell):
Supercapacitor
| Parameter |
Specification |
Source |
| Capacitance |
1.5F |
Design |
| Rated Voltage |
5.5V |
Design |
| ESR |
<100 mΩ |
Datasheet |
| Function |
Peak current buffer for RF transmission |
Cascading Power |
Ceramic Capacitor Bank (Emergency Reserve)
| Parameter |
Specification |
Source |
| Configuration |
15× 100μF X5R 0805 |
Design |
| Total Capacitance |
1.5mF nominal |
Design |
| Operating Floor |
-65°C (voltage collapse below) |
Ceramic Validation |
| Capacity at -50°C |
~40% of nominal |
Ceramic Validation |
Radio & Communication
LoRa Radio (STM32WLE5 Integrated)
| Parameter |
Specification |
Source |
| Frequency |
868 MHz (EU) / 915 MHz (US) |
Design |
| Max TX Power |
+22 dBm |
Datasheet |
| TX Current |
~100mA at +22 dBm |
Power Calculator |
| Spreading Factor |
SF7-SF12 (adaptive) |
Design |
| Protocol |
LoRaWAN Class A |
Design |
Region Detection (H3Lite)
| Parameter |
Specification |
Source |
| Resolution |
R3 (~11,000 entries) |
H3Lite Blog |
| Flash Size |
~44KB |
H3Lite Blog |
| Regions Supported |
16 LoRaWAN frequency plans |
Design |
Sensors
| Component |
Function |
Interface |
| ATGM336H |
GPS position |
UART |
| SHT31 |
Temperature, Humidity |
I²C |
| MS5607 |
Pressure, Altitude |
I²C |
Microcontroller
| Parameter |
Specification |
| MCU |
STM32WLE5JC |
| Core |
ARM Cortex-M4 @ 48MHz |
| Flash |
256KB |
| RAM |
64KB |
| Integrated Radio |
Sub-GHz LoRa |
| Operating Voltage |
1.8V - 3.6V |
Balloon & Flight
Mylar Superpressure Balloon
Thermal Limits
| Component |
Min Temp |
Max Temp |
Notes |
| System |
-65°C |
+60°C |
Validated operating range |
| LTO Battery |
-60°C |
+70°C |
Severely degraded below -50°C |
| Ceramic Caps |
-65°C |
+85°C |
Voltage collapse floor at -65°C |
| MCU |
-40°C |
+85°C |
Industrial grade |
Power Budget Summary
Nominal Operating Power (at 25°C):
| Mode |
Current |
Duration |
Energy/Cycle |
| Sleep |
~3 μA |
Continuous |
Baseline |
| GPS Fix |
15 mA |
3 sec |
150 mJ |
| Sensors |
2 mA |
10 sec |
66 mJ |
| LoRa TX |
100 mA |
400 ms |
132 mJ |
| Total per 5-min cycle |
— |
— |
~350 mJ |
Solar Input (Stratospheric, 45° latitude):
- Peak: 100-150 mW
- Average (day): 50 mW
- Average (24hr): 25 mW
Changelog
| Date |
Change |
Reference |
| Nov 2025 |
Operating floor established at -65°C |
Ceramic cap validation |
| Nov 2025 |
LTO R_int characterized to -60°C |
LTO characterization |
| Nov 2025 |
Supercap updated to 1.5F |
Architecture refinement |
| Nov 2025 |
Balloon burst pressure validated |
Calculator update |
| Nov 2025 |
GPS module confirmed as ATGM336H |
Hardware validation |
For component datasheets, see the hardware repository.