# A Review of Requirements for Gamma Radiation Detection in Space Using CubeSats
## 4 Operating Scenarios  
One critical task operating CubeSat missions consist in carefully defining operating scenarios (or operation modes). Given the power and budget requirements, the communication with ground stations is generally constrained to a few minutes per day, and therefore the payload might not be interactively operated. To put things into perspective, a CubeSat deployed from the ISS (average altitude 400 km at 51.6\({}^{\circ}\) inclination) would complete an orbit in about 93 min (about 15 orbits per day) and in average one passage per day above the mission ground station (maximum transmission time window of about 10 min). The typical CubeSat (with no active propulsion) orbiting at ISS altitude can have a lifetime of up to 1.5 years [23]. Figure 12: (**A**) A set of PMT-simulated waveforms corresponding to a 20 keV release of energy in the detector. (**B**) The corresponding charge integrated signals obtained from the set of PMT simulated waveforms. (**C**) The matched filter output. (**D**) Histogram of S/N distribution. For most of the missions operating in similar orbits, a payload switch off might be required, for example, in proximity of high radiation regions, such as the South Atlantic Anomaly (SAA) [24] and during Polar transits [25], where the Earth's magnetic field does not offer an effective shielding against cosmic rays. The typical operating mode of the payload passing through the SAA, can be outlined as follows. * The OBC continuously checks the GPS coordinates and, if in proximity of the SAA, it issues a command that will ask the payload to run the internal powering off procedure (ramping down the photosensor voltage biasing, storing the current payload operating configuration, and registering the time of the event). * The Payload acknowledges the reception of the command and once ready for the powering off procedure, issues a command to the OBC to cut the biasing lines. From this moment onward, the payload is unresponsive and needs to be rearmed by the OBC to restart its operations. * The OBC periodically checks the GPS Coordinates and once the spacecraft got over the SAA, it powers on the biasing lines. The payload automatically restarts. In order to protect the photosensors, the bias ramping up is subject to a series of functional conditions: the particle rate measured by the VETO is below a given threshold and the payload electronics temperature is within the operating range. * Once the conditions are satisfied, the payload electronics will operate the procedure to ramp up the detector bias according to the last operating scenario uploaded. The position of the CubeSat along the orbit can be also predicted by taking into account the characteristics of the environment (altitude, dragging, solar activity) and the satellite attitude determination. It is also possible to pre-load mission time windows in which the satellite is required to activate specific functionalities (i.e., powering off or on the payload). This technique can be either alternative to the GPS crosscheck, or used in combination in order to increase redundancy. Of course, each operating mode has to be strengthened by layers of redundancy for example by coding multiple commands producing the same effect to the payload, time delay between consecutive operations, and by designing very similar operating scenarios. Once implemented the final release of the software in the flight model, it is a good practice to reproduce a series of consecutive orbits, for example, by operating the CubeSat in a Thermo-Vacuum Chamber (TVAC), simulating the orbital conditions at a given mission epoch and validating the operating scenarios. Further steps regarding risk mitigation can be considered, especially when the payload performance strongly depends on the environmental conditions, such as for a gamma-ray detector immersed in a charged particle background and subject to a rapid variation of temperature.