Reliability Analysis of Low Earth Orbit Broadband Satellite Communication Constellations
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Large space-based communication networks have been growing in numbers of satellites, with plans to launch more than 10,000 satellites into Low Earth Orbit (LEO). While these constellations offer many advantages over ground-based communication systems, they pose a significant threat when they fail and generate space debris. Given the reliability of current satellites, engineers can use failure modeling to design satellite constellations that are more resilient to satellite failures. Several authors have analyzed the reliability of geostationary satellites, but few have expanded the work to multiple-satellite systems.
To address this gap, we constructed a simulation model to show the performance of satellite constellations with different satellite reliability functions over time. The simulation model is broken down into four key parts: a satellite constellation model, a network model, a failure model, and a performance metric. We use a Walker star constellation, which is the most common constellation for LEO broadband satellite constellations. The network consists of satellite-to-satellite connections and satellite-to-groundstation connections, which routes data using a shortest-path algorithm. The failure model views satellites as either operational or failed (no partial failures) and considers the groundstation operator’s knowledge or lack thereof of the satellites’ operational status and uses satellite reliability to estimate the expected data throughput of the system. We also created a performance metric that measures how well the entire network is operating and helps us compare candidate constellations.
We used the model to estimate performance for a range of satellite reliabilities, and for groundstations with different numbers of communication dishes (effectively, satellite-ground links). Satellite reliability is a significant contributing factor to the long-term constellation performance. Using the reliability of small-LEO satellites, we found that a constellation of 1,200 small-LEO satellites completely fails after less than 30 days, given that we do not consider partial failures. Satellite constellations with higher satellite reliability, such as large geostationary satellites, last less than 50 days. We expect the constellations in our model to perform worse than real satellite systems, since we are only modeling complete failures, however these findings provide a useful worst-case baseline for designing sustainable satellite constellations. We also found that the number of groundstation-to-satellite communication links at each groundstation is not a significant factor for more than five communication links, meaning that adding more communication antennas to existing satellite groundstations would not improve constellation performance significantly.