Satellite Megaconstellations Are Becoming a Serious Threat to Space Telescopes, Study Finds

A Growing Problem for Astronomy: Bright Satellite Trails in Space-Based Images

A new peer-reviewed study published in Nature warns that rapidly expanding satellite megaconstellations pose a major and escalating threat—not just to ground-based observatories, but to space telescopes in Low Earth Orbit (LEO).

Reflections from satellites already show up as bright streaks across astronomical exposures, and the contamination is increasing far faster than previously predicted.

Today’s ~15,000 satellites represent less than 3% of what companies have proposed to launch by the mid-2030s. If current plans are realized, the authors forecast that:

One-third of all Hubble images will contain at least one satellite trail
More than 96% of exposures from next-generation observatories—SPHEREx, Xuntian, and ARRAKIHS—will be affected
Many images will contain multiple trails, some bright enough to overpower faint celestial targets

The study concludes that space telescopes are not immune and will face substantial operational challenges as LEO becomes increasingly crowded.

How Satellite Trails Pollute Space Telescope Images

Satellite trails form when sunlight reflects off a passing spacecraft during a telescope exposure. Even in space—far from city lights—these reflections can be:

Bright enough to saturate pixels
Long enough to cross the entire field of view
Frequent enough to degrade major survey programs

The authors simulated millions of exposures for four space telescopes:

Hubble Space Telescope (HST)
SPHEREx (NASA’s near-infrared all-sky survey)
Xuntian (China’s wide-field space telescope)
ARRAKIHS (ESA’s dark-matter mapping mission)

As satellite numbers rise into the hundreds of thousands, each telescope’s exposure becomes increasingly likely to be crossed by bright, Sun-illuminated trails.

Brightness Levels

Simulated satellite trails typically reach:

18–19 mag/arcsec² when Sun-lit
22–23 mag/arcsec² under Moonlight or Earthshine

These values are well within the detection limits of modern imaging sensors.

For reference, a confirmed Starlink trail observed by Hubble in 2020 measured 18.0 mag/arcsec²—matching the new predictions almost exactly.

Why More Satellites Mean More Contaminated Science

The explosion of megaconstellation proposals—driven by cheaper launches and large platforms like Starship—means LEO could hold over half a million satellites by the 2030s.

Many satellites operate at altitudes between 500–800 km, overlapping with the orbits of major space telescopes. As a result:

Trails remain visible over long periods of the night
Telescopes cannot always avoid pointing near satellite-dense regions
Wide-field missions (SPHEREx, ARRAKIHS) suffer the highest contamination
Lower-altitude telescopes (e.g., Xuntian) experience the fastest-moving, brightest trails

The authors note that mitigation techniques used on newer satellites—dark coatings, visor shields, attitude changes—reduce visibility to the naked eye, but do not reduce brightness to levels tolerable for professional observatories.

Some newer “Direct-to-Cell” satellites are much brighter, approaching magnitudes 0–1, rivaling the brightest stars.

Key Forecasts: What Happens if Megaconstellations Reach Full Scale

If planned constellations reach ~560,000 active satellites:

Hubble: ~40% of images affected
SPHEREx: ~96% of exposures affected
ARRAKIHS: ~96% affected
Xuntian: ~96% affected

At one million satellites, contamination becomes extreme:

Some telescopes see trails in nearly every exposure
Trails may occupy large fractions of the detector
Data loss could exceed typical cosmic-ray rejection levels by 4×

Space telescopes designed for faint-galaxy surveys, reionization studies, and mapping the cosmic infrared background will see major quality degradation.

Why Space Telescopes Are Especially Vulnerable

Unlike ground-based observatories, space telescopes:

Cannot rely on Earth’s shadow to block satellites
Observe near Earth’s limb, where satellites are densest
Detect reflected sunlight more intensely due to direct line-of-sight
Are affected by satellite orientation changes, solar panel geometry, and attitude drift

Some newly launched satellites have 125 m² solar panels, dramatically increasing their reflective cross-section.

Even non-operational satellites that tumble unpredictably can become extremely bright and difficult to model.

Mitigation: What the Study Recommends

The authors highlight several actions needed to keep space telescopes viable:

1. Prevention

Establish upper altitude limits for satellite constellations
Reduce the brightness of satellite surfaces

2. Avoidance

Create publicly accessible, high-precision orbital databases
Maintain historical archives of satellite positions, inclinations, and orientations

3. Correction

Improve orbit prediction accuracy to centimeter-level precision
Model satellite brightness across wavelengths and illumination phases
Enable telescopes to plan exposure windows that minimize contamination

The paper warns that current orbit formats (e.g., TLEs) are accurate only to ~1 km, far too imprecise for scientific avoidance.

A Critical Moment for the Future of Astronomy

The study concludes that without coordinated global action, satellite megaconstellations will significantly degrade the scientific return of both current and future space telescopes.

Upcoming missions such as SPHEREx, Xuntian, and ARRAKIHS will face the highest risk, while even longstanding observatories like Hubble will see rapidly rising contamination levels.

The authors compare today’s situation to early warnings about ozone depletion in the 1970s—signals that were recognized only after damage had begun.

As the number of satellites grows by one to two orders of magnitude, protecting the dark and quiet sky—even in orbit—has become a scientific, engineering, and policy challenge for the decade ahead.

Original Study: Borlaff, A. S., Marcum, P. M., & Howell, S. B. Satellite megaconstellations will threaten space-based astronomy. Nature 648, 51–57 (2025).