Various scales of upper atmospheric structures and their coupling mechanisms are not fully understood due to a lack of robust observation. Satellite formation flight enables identification of temporal and spatial variation of multi-scale space weather phenomena. GNSS-based small satellite formation flying enables new applications for future low-cost, versatile, geo-space observations. The Virginia Tech Formation Flying Testbed (VTFFTB), a GPS-based hardware-in-the-loop (HIL) simulation testbed for dual-satellite formation flying, was recently developed to design new ionospheric remote sensing techniques. A simple ESF scenario was simulated on the VTFFTB to demonstrate a new ionospheric measurement technique by GPS-based LEO formation flying. The objectives of this current work are to develop a newer version of VTFFTB to (i) incorporate the Galileo (E1, E5a, E5b) constellation in simulations; (ii) implement natural relative orbits for better fuel efficiency and optimal remote sensing capability, and (iii) simulate scenarios of 3-spacecraft formation flying with applications to multi-scale space weather problems. Multi-constellation GNSS improves the relative navigation performance as well as ionospheric observation capability. Total Electron Content (TEC) and ionospheric scintillation measurements from multiple frequency bands can be sampled by a fleet of LEO satellites in proximity with respect to the GPS and Galileo constellations. HIL simulations with the additional Galileo constellation show the electron density retrieval accuracy is enhanced compared to GPS-only scenarios. Two configurations of elliptic orbits are implemented to measure electron density and thus obtain different characteristics between different GNSS constellations. A polar, sun-synchronous, elliptic orbit was chosen to simulate and validate 3-satellite real-time formation flying scenarios. A decentralized formation scheme is selected as the archetypal approach of orbit estimation and control for the multiple satellite group. Three different formation configurations (leader-follower → elliptic-orbit → side-by-side) are considered in order to test the maneuverability of a multi-scale observation campaign in response to real-time geomagnetic conditions. A number of space weather phenomena can be observed by applying this new observation technique of using scalable small satellite formation clusters. The VTFFTB will ultimately become a mission incubator for future multi-scale geo-space environment observing systems using GNSS-based small satellite formation flying.
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