A new supercomputer simulation study indicates that if 1 million satellites were positioned at different points between Earth and the moon in cislunar space, fewer than 10% would remain stable long enough to be worthwhile. This highlights significant challenges for expanding humanity's orbital capabilities beyond Earth.
Background on Orbital Expansion
Over recent years, the number of active spacecraft orbiting Earth has increased rapidly due to private satellite megaconstellations like SpaceX's Starlink and China's Thousand Sails project.
Experts suggest low Earth orbit (LEO) could safely accommodate up to 100,000 satellites before risking a domino-effect collision scenario known as the "Kessler syndrome," which could prevent future space launches.
Once LEO reaches saturation, the next logical step is to place satellites in cislunar space, the region between Earth and the moon. This expansion aims to benefit Earth's infrastructure and provide services to future lunar colonies.
Challenges in Cislunar Space
Predicting spacecraft orbits in cislunar space is complex due to the gravitational interactions between Earth, the moon, and the sun.
Additionally, the absence of Earth's protective magnetic shield means solar radiation can destabilize orbital trajectories in this region.
The Simulation Study
Researchers at Lawrence Livermore National Laboratory (LLNL) used their Quartz and Ruby supercomputers to simulate the trajectories of approximately 1 million cislunar objects.
The simulations required about 1.6 million CPU hours, a task completed in three days by the supercomputers, which would have taken a single computer around 182 years.
Simulation Results
- Approximately 54% of the simulated orbits remained stable for at least one year.
- Only 9.7% remained stable throughout the simulations' six-year period.
The orbital data was published in August 2025 in Research Notes of the AAS, with the team's analysis uploaded to the preprint server arXiv in December.
Methodology and Discoveries
The team designed the simulated trajectories to be broad, avoiding assumptions about desired orbit types to account for various potential issues.
Unlike LEO trajectories, which are more stable, cislunar orbits exhibit greater uncertainty, requiring computationally intensive calculations that step forward in discrete chunks of time.
One unexpected factor influencing these orbits was Earth's subtle and varying gravitational influence, referred to as its "blobby" nature, with gravity differing across regions such as Canada compared to the Atlantic Ocean.
Implications
Despite the low percentage of stable orbits, the simulations identified around 97,000 potentially stable cislunar orbits.
The researchers noted that understanding which orbits did not work is as valuable as knowing which ones did, providing a rich dataset for further analysis and future exploration of the region.