GNSS-based Hardware-in-the-loop Simulation of Satellite Formation Flight: An Incubator for Future Multi-scale Ionospheric Studies
Abstract
Satellite or spacecraft formation flying (SFF) is an emerging space mission architecture to utilize a group of distributed space systems under cooperative operation. Compared to traditional single satellite missions, SFF offers more robust, flexible, sustainable, low-cost technology and scientific benefits. To achieve SFF, relative navigation and control techniques are required at a high level. For SFF at low Earth orbits (LEO), Global Navigation Satellite Systems (GNSS) are widely used for precise absolute and relative navigation. To develop a reliable onboard navigation and control system for SFF applications, GNSS-based hardware-in-the-loop (HIL) simulation testbeds are often used for software algorithm validations and hardware performance evaluations. Several GNSS-based HIL simulation testbeds have been developed over the past two decades by NASA, the German Aerospace Center (DLR), and a number of research organizations. Some of these testbeds were applied for SFF relevant technology developments and demonstrations, and several others were further used to support space science mission developments. However, none of these testbeds was directly applied to ionospheric applications. Conventional ionospheric observation techniques (e.g. ground-based remote sensing, single satellite probes, and sounding rockets) have collected decades of valuable ionospheric data. However, the existing measurement methods are still limited at certain levels of temporal and spatial resolution. Several recent missions use satellite constellations to increase the measurement quantity. For example, the COSMIC mission and the Spire Global Inc. use a constellation of small satellites to measure atmospheric properties based on the atmospheric radio occultation technique. However, the exact location, size, and full structure of ionospheric irregularities are often not accurate enough to be measured using these approaches. There is a need to design more flexible, agile, and cost-efficient observation techniques to further understand various multi-scale ionospheric problems (e.g. irregularities and turbulence). The Virginia Tech Formation Flying Testbed (VTFFTB), a HIL simulation testbed using multi-constellation, multi-frequency GNSS has recently been developed to simulate closed-loop, real-time LEO SFF. A group of 2 or 3 satellites, each carrying a GNSS receiver, is simulated in scenarios with ionospheric impacts on the GPS and Galileo constellations. Each onboard GNSS receiver can be used to measure the ionosphere while navigating its LEO satellite. The GNSS receivers measure total electron density (TEC) and GNSS scintillation index (e.g. S4). Therefore, TEC can be used to determine localized electron density between each pair of LEO satellite, which is advantageous to sense or monitor the ionospheric irregularities along or nearby the trajectory of the satellite fleet. This talk discusses four scientific applications incubated on the VTFFTB. The first is a measurement technique for electron density in the vicinity of the satellite fleet without in-situ sensing. The second is the observation of the global and microscale morphology (e.g. location, size and structure) of ionospheric irregularities with SFF. The third is the capability to measure different types of ionospheric irregularities by optimizing the LEO formation configuration. Last but not the least, the VTFFTB can also serve as a simulation tool to study the impact of various space weather processes on GNSS-related technologies, by using existing ionospheric models.
- Publication:
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43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E...5P