How Satellite Maneuvers Are Detected
Every satellite in Earth orbit is tracked using Two-Line Element sets (TLEs) published by the US Space Force's 18th Space Defense Squadron. These TLEs encode a satellite's orbital parameters — altitude, inclination, eccentricity, mean motion, and more — at a specific epoch. When a satellite fires its thrusters, these parameters change.
Orbital Radar's detection engine compares each new TLE against its predecessor for every tracked object. When parameters shift beyond natural perturbation thresholds — accounting for atmospheric drag, solar radiation pressure, gravitational harmonics (J2), and lunar/solar perturbations — the system flags a probable maneuver. The event is then classified by type, and an estimated delta-V is computed from the change in semi-major axis using the vis-viva equation.
Detection typically occurs within hours of TLE publication. Very small maneuvers may fall below detection thresholds, and there is inherent latency between the actual thruster burn and when Space-Track publishes the updated element set. For well-tracked objects with frequent TLE updates (such as ISS or Starlink satellites), detection is faster. For less-frequently-updated objects, detection may lag by a day or more.
What Is a Satellite Maneuver?
A satellite maneuver is any deliberate change to a spacecraft's orbit using onboard propulsion. Maneuvers consume propellant — one of the most precious and finite resources on any satellite — so they are only performed when necessary. Common reasons include:
Orbit raising and lowering: Adjusting altitude to reach an operational orbit after launch, avoid space debris, or deorbit at end of life. Starlink satellites perform hundreds of orbit raises as they climb from their deployment altitude (~300 km) to their operational shell (~550 km).
Plane changes: Adjusting the orbital inclination or right ascension. These are among the most fuel-expensive maneuvers and indicate significant operational intent. A large plane change on a military satellite may indicate repositioning for a new surveillance target.
Station-keeping: Small corrections to maintain a precise orbital slot, particularly for geostationary satellites that must hold a fixed position above the equator.
Collision avoidance: Emergency burns to avoid a predicted conjunction with another object. The International Space Station performs multiple conjunction avoidance maneuvers per year.
Learn more about orbital mechanics and maneuver types in the Orbital Academy maneuvers track.
Proximity Operations & Inspector Satellites
Rendezvous and Proximity Operations (RPO) involve one satellite deliberately manoeuvring close to another object in orbit. While RPO has legitimate applications — satellite servicing, refuelling, and debris removal — it also has significant military and intelligence implications.
Several nations operate satellites that perform RPO. Russia's COSMOS 2542 released a sub-satellite (COSMOS 2543) in late 2019, which then manoeuvred close to a US reconnaissance satellite. In 2020, COSMOS 2543 released a projectile on-orbit — characterised by US Space Command as an anti-satellite weapons test. More recently, COSMOS 2558 has maintained proximity to USA-326, a National Reconnaissance Office imaging satellite.
China's SJ-21 made headlines in January 2022 when it towed a defunct BeiDou navigation satellite from geostationary orbit to a graveyard orbit — the first publicly observed active debris removal operation by China. SJ-23 has been observed performing proximity approaches to other GEO satellites.
The US X-37B reusable spaceplane, operated by the Space Force, frequently changes orbit during its multi-year missions. The classified nature of its payload makes each maneuver a subject of international scrutiny.
This tracker monitors all known RPO-capable satellites and flags maneuvers that bring them within range of other high-value objects — a core discipline of space situational awareness. See the anti-satellite weapons reference page for historical context, and Kessler syndrome for why close approaches matter.
Understanding Severity Levels
Low — Routine maneuvers: constellation orbit raises, normal station-keeping, minor phasing adjustments. These are operationally expected.
Medium — Notable maneuvers: larger-than-usual altitude changes, unexpected timing, or maneuvers by infrequently-maneuvering objects.
High — Significant maneuvers: large delta-V events, plane changes, military satellite maneuvers, deorbit burns, or approaches to other objects.
Critical — Watchlisted objects: any maneuver by a strategic watchlist satellite, particularly if it changes proximity to another high-value target.
Data Sources & Methodology
Orbital element data is sourced from Space-Track.org (US Space Force 18th SDS) and CelesTrak. Satellite operator and country data is enriched from the Union of Concerned Scientists Satellite Database. For a full list of data sources, see the data sources page.
Maneuver detection, classification, severity assessment, and delta-V estimation are performed server-side in real time. All thresholds are calibrated to minimise false positives from natural orbital perturbations while catching genuine propulsive maneuvers. Detection accuracy improves for objects with frequent TLE updates.