*2.3. SpOCK and Its Operation*

Although there are a multitude of functional mission simulation tools available for commercial and research applications, the Spacecraft Orbital Characterization Kit (SpOCK) can better predict the performances of and provide data for mission inputs that operate in a manner similar to CYGNSS. The central capability of SpOCK is a high accuracy numerical propagator of spacecraft orbits and computations of ancillary parameters [18]. The C-based programming of SpOCK allows for data variables, including CYGNSS specular points, to be easily added or subtracted in accordance with user preferences.

When creating constellations for SpOCK simulations, users can select the orbital parameters of individual satellites as well as controlling data processing tools. In text-based input files, users first describe how many satellites will be in the constellation, then provide both the individual sets of orbital parameters of each satellite and the antenna pattern used by all satellites. These inputs are read by SpOCK's C-based simulator, and outputs are provided at a user-specified time delta in the form of multiple data files. Among these outputs is the list of constellation's detected specular points, data that is necessary for CYGNSS's atmospheric measurements and may not be reported by other simulation tools. Using these written output files, various performance metrics can be calculated in other programs.
