During thunderstorm events, high-energy gamma-rays are emitted from electrons colliding with ionized air, called Terrestrial Gamma Ray Flashes (TGF's). Dr. David Smith, a member of not only the Santa Cruz Institute of Particle Physics (SCIPP), but participated on the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) mission at NASA, theorizes that there are lower energy x-rays that are emitted during these thunderstorm events.
Although several satellite missions proved the existence of TGF's during thunderstorms in low-Earth orbit, none have detected and classified radiation created from the events. Identifying these x-rays will improve our understanding of lightning theory, and gamma ray emission from the Earth's atmosphere.
The Science Experiment team will perform the crucial role of completing the design and implementation of a radiation detector, as well as developing a system that will accurately calculate the CubeSat’s relative position to Earth.
SlugSat's technical proposal is to adopt a system similar to that of LAFTR as well as that from IMPRESS. Our design will consist of a Scintillator that is optically coupled to a SiPM held in reverse bias that is AC coupled to a node that also has a DC bias voltage as well as the input to the Charge Sensitive Preamplifier (CSP). The CSP is essentially just an inverting op-amp that will take the resulting negative current pulse and integrate it into a voltage pulse that is proportional to the amount of charge from the detected radiation. The output from the CSP will have a semi-long (50 us) decay but at a small time-step (50 ns) it will appear to be a step-function. This step-function will be input to the Pulse Shaper (PS) which is essentially just 2 Sallen-Key Filters that translate the voltage into an amplified gaussian pulse. normally a baseline restorer is added in series but after 20kHz+ it becomes ineffective. By taking a commercial CSP and commercial PS and modifying them to have shorter tau constants could help prevent pulse pile up and prevent the shifting of the baseline from fast count rates. The output from the PS will then feed to our A2D section where we essentially have 4 comparators that will be able to discriminate if the pulse was < 5keV, >5 keV, >10 keV, >30 keV, or >100 keV. Each of these thresholds will be tied to a flipflop so that once we clock a detection that event will be held high or low for it's respective thresholds while OBC runs through their Interrupt Service Routine to read all the data, timestamp it, and buffer the data while counting the detection. Once we have counts of >8 detections/ms averaged over a 3 ms period that will constitute as a flag for an event of interest while >500 detections/ms averaged over a 10 second period will determine noise.