Spacecraft in cislunar space can determine their three-dimensional positions by tracking solar array voltage drops during orbital eclipses, offering a zero-cost backup when NASA's Deep Space Network is overwhelmed, Universe Today reported.
Our capacity to monitor every satellite currently operating in deep space is being rapidly overwhelmed, as noted by Eclipse Observables for Navigation in Cislunar Space. NASA’s Deep Space Network has been the workhorse for tracking such missions for decades, but it is rapidly being overwhelmed by the sheer volume of requests it receives.
That surge in traffic makes it harder to monitor newer missions launched into deep space. To bypass active radio tracking bottlenecks, researchers Ian Down, James McElreath, and Manoranjan Majji—representing Advanced Space, Space Exploration Engineering, and Texas A&M respectively—proposed using solar array data gathered during spacecraft eclipses.
Every spacecraft already tracks solar panel output using Maximum Power Point Tracking algorithms designed to maximize incoming solar radiation. When a spacecraft positions itself so that an orbiting body sits between it and the Sun, it experiences an eclipse.
Engineers typically design trajectories to avoid eclipses because they drain batteries and cause temperatures to plummet. However, the precise timing of how those blackouts travel across a spacecraft’s solar panels holds valuable positional data.
Astronomers know the exact positions of the Sun, Earth, and the Moon years in advance through planetary maps. Within every shadow projected into space lie two distinct, nested cones: the penumbra, where sunlight is partially obscured, and the umbra, where it is entirely blocked.
When a spacecraft crosses into one of these cones, solar radiation drops sharply while onboard batteries keep electronics running. By recording the precise timestamp when voltage drops and when it recovers after leaving the shadow, a navigation algorithm calculates its three-dimensional location without cameras, star trackers, or radio signals.
Execution remains challenging because the Moon lacks an atmosphere, causing its shadow to track jagged mountains and craters that alter eclipse timing by seconds. Earth’s shadow introduces further complications due to polar flattening and atmospheric refraction.
To solve this, the researchers utilized a dataset of over 22,000 historical observations of lunar craters covered by Earth’s shadow, collected by astronomers between 1842 and 2011. This data allowed the algorithm to map parts of Earth’s shadow to specific ground features for finer positional granularity.
To validate the system, the research team analyzed actual flight telemetry from CAPSTONE, a CubeSat mission operated by Advanced Space. CAPSTONE completed its mission in July 2026 after testing the orbit for NASA’s now-discontinued Lunar Gateway.
On January 11, 2026, CAPSTONE traveled through the Moon’s shadow, experiencing a solar panel voltage drop from 23V to near zero before recovering to 31V in sunlight. Using that telemetry, the algorithm timed the spacecraft’s entry and exit within 15 seconds of its actual path.
Simulating a scenario where a spacecraft missed a ground station check-in and experienced a position uncertainty drift of several kilometers, the eclipse data processing cut that uncertainty by more than 60 percent.
The system requires no additional hardware, fitting the spacecraft engineering standard of “zero-Size Weight and Power” (zero-SWaP). While it does not replace ground-based radio tracking entirely, it establishes a vital safety net for missions venturing beyond low Earth orbit.
