Big Enough to Kill, Too Small to Track

Ground-based radar and optical systems routinely catalog orbital debris objects larger than 10 cm in LEO. Spacecraft shielding can generally survive impacts from objects smaller than 1 cm. But objects in the 1-10 cm range — estimated at over 1 million in LEO — are lethal to any spacecraft on impact yet cannot be individually tracked or cataloged. No measurement standard exists for characterizing this population, estimating its growth rate, or providing conjunction assessment (collision warnings) for these objects.

Megaconstellations are placing tens of thousands of satellites into orbits where over a million lethal-but-untracked debris objects exist. Collision avoidance maneuvers can only be performed against cataloged objects. The probability that a large constellation satellite is struck by an uncataloged 1-10 cm object is non-trivial and rising. Any such collision generates hundreds more fragments, accelerating the Kessler cascade — a self-sustaining chain reaction of collisions that could render entire orbital bands unusable.

Specialized sensors like the MIT Haystack radar can detect 1-10 cm objects during single passes but cannot maintain them in catalogs because their orbits cannot be determined precisely enough from a single pass for re-acquisition. Optical detection at this size requires reflected sunlight geometry available only briefly. The population is characterized statistically (from returned surface samples like the Long Duration Exposure Facility, and limited radar surveys) rather than individually. Space-based detection concepts (e.g., laser ranging from the ISS) have been demonstrated for individual detections but cannot achieve the persistent surveillance needed for cataloging. The Space Surveillance Network was designed for the Cold War threat (tracking large objects) and its architecture is fundamentally mismatched to the small-debris problem.

Either a breakthrough in ground-based radar sensitivity (possibly using distributed coherent apertures or AI-enhanced signal processing to extract tracks from noise) or a space-based sensor network specifically designed for small debris cataloging. The key measurement gap is determining orbits accurately enough from limited observations to enable re-acquisition — this requires advances in initial orbit determination algorithms that work with fragmentary data.

A team could analyze publicly available conjunction data (from CelesTrak or Space-Track.org) to estimate the rate of close approaches by uncataloged objects. Alternatively, a team could model the sensitivity requirements for a space-based debris detection sensor and evaluate whether commercial off-the-shelf components could meet them. Relevant skills: orbital mechanics, radar systems, signal processing, space systems engineering.