Huge Survey vs. Tiny Space Junk

As construction continues on the Vera Rubin Observatory, the skies above its mountaintop home grow more and more crowded following every rocket launch. Astronomers, conscious of the plans for mega-constellations of new satellites in the next few years, are rightfully worried: will these satellites and the tiny bits of debris that come with every deployment and collision affect the new telescope’s long-awaited, gigantic survey?

Threats to Ambitious Plans

After several decades inhabiting only the dreams and blueprints of astronomers, the Vera Rubin Observatory is finally a real, physical place. Now a building and construction site near the summit of Cerro Pachón in Chile, its concrete and steel structure already houses most of what’s needed to begin one of the most ambitious surveys of the sky ever conceived. The Legacy Survey of Space and Time, or LSST, promises to revolutionize every sub-field of astronomy from cosmology to planetary science, and scientists around the world are eagerly awaiting its kickoff.

photograph of Vera Rubin Observatory

The Vera Rubin Observatory. [RubinObs/NSF/AURA/H. Stockebrand; CC BY 4.0]

The plan is to use the largest camera ever built to photograph the entire night sky, repeatedly, for a decade. Unfortunately, though, stars and galaxies aren’t the only objects that will show up in these wide-angle images. Anything placed in orbit around Earth will blunder through the pictures as well, potentially reflecting sunlight towards the telescope as they zip along their looping trajectories. This will cause streaks and flashes in some of the images, which, without careful filtering, could either obscure or mimic the subtle signal of a fleeting astronomical event.

Tiny Pieces, Potentially Large Impact

Astronomers have known this might be a problem for a while now, and the LSST team has spent considerable time figuring out how to handle satellites and large chunks of space debris. While challenges remain and the correction techniques won’t ever be perfect, the community is prepared to handle anything large enough to be tracked by ground-based radar, or about 10 cm. But, what about smaller objects, like the bits of debris created when two satellites collide?

In a February Research Note, one astronomer voiced concerns that these tiniest pieces of space junk could overwhelm LSST’s transient detection algorithms. This prompted a team led by J. Anthony Tyson, University of California, Davis, to model more thoroughly how glints from small, nearby objects would appear in LSST images.

Closer and Faster Than The Stars

An illustration of how a nearby, moving satellite would be blurred out compared to an equally bright but faraway and stationary star. [Adapted from Tyson et al. 2024]

Thankfully, the researchers concluded that there likely isn’t much cause for alarm. While they point out that it should be possible to build filters for these events, they also point out a more important and ironic conclusion: because the objects are so close to the telescope, they’ll actually appear fainter than you might initially expect. Since the observatory is designed to concentrate light from objects that are effectively infinitely far away, objects as close as a few thousand kilometers will appear blurry and out of focus. This means a flash that otherwise would have occupied just a few pixels will be smeared out across many, and in most cases will become lost in the noise.

The authors conclude that “In general… the large population of [low Earth orbit] debris below a few centimeters in size may pose little challenge for LSST transient science.” While there are still hurdles to overcome and challenges to solve before LSST can deliver on its extraordinary promises, thankfully, dealing with tiny bits of space junk likely won’t be one of them.


“Expected Impact of Glints from Space Debris in the LSST,” J. Anthony Tyson et al 2024 ApJL 966 L38. doi:10.3847/2041-8213/ad41e6