This repository serves as the top-level hub for the National Severe Storms Laboratory (NSSL)
balloon-borne electric field vector measurement instrument. Documentation for the project
is hosted here via GitHub Pages on the gh-pages branch. In addition, this repository
includes links to several related repositories that contain the hardware designs, firmware,
and mechanical components associated with the instrument.
One of the paddles on the instrument houses a motor driver, which reads motor speed
from an encoder and controls power to the motor to maintain a constant rotation rate
of the instrument. We also monitor the current supplied to the motor and the
temperature of the control board, logging all of this data to a rolling log file.
This log is used for debugging and diagnosing any flight-related failures.
In the paddle opposite the motor driver, an orientation sensor based on a simple IMU
provides rough data on the instrument’s orientation over time. This allows analysis
of pendulum motion and other movements of the full instrument package. The system is
designed for easy sensor replacement, and all orientation data are logged to a
microSD card.
The rotating electronics collect the majority of the scientific data during flight.
This includes the relative orientation of the sensor spheres, electrical charge flow
between the spheres, GPS position, temperature, pressure, and humidity. All data are
logged to an onboard microSD card for post-flight analysis. These measurements are
essential for understanding the electric field structure and environmental conditions
surrounding the instrument throughout its ascent and descent.
The analog charge amplifier performs the actual coulomb counting for the electric field
measurement and filters the signal before passing it to the rotating electronics for
digitization, synchronization, and logging. This board closely follows the design of
the original instrument and includes a small microcontroller that allows temperature-
independent control of the filter's cutoff frequency.
The tracker provides GPS location data to instrument operators via a satellite
connection. It is designed to enable easy location of the instrument package during
and after flight, supporting both flight termination decisions and efficient recovery
of the full payload. The tracker uses a progressive rate strategy to optimize battery
life, providing high-rate position updates during the most dynamic and critical phases
of the flight.
The EFM also includes a range of mechanical components that support and protect the
instrument during flight. These include machined parts, 3D-printed housings, laser-cut
mounts, and structural elements made from foam and composite materials. The design
prioritizes strength, low weight, and ease of assembly in the field. Detailed models,
drawings, and documentation are maintained to ensure consistent fabrication and
support future revisions.