Source library
Where the data comes from
Every number on this site traces back to one of these. Most are free. We note the access rules because respecting them is what keeps the feeds open for everyone.
Catalogs and orbital data
CelesTrak GP (orbital elements) CelesTrak
Current general perturbations orbital elements for public-catalog objects, queryable by catalog number, launch designator, name or named group (e.g. fengyun-1c-debris, starlink, active) in OMM/JSON/CSV/TLE formats.
- Access
- Free, no account
- Updates
- Checked for new data every 2 hours
- Terms
- Usage rules: one download per 2-hour cycle for large groups, under 100 MB/day, stop on HTTP 403/404; TLE format cannot carry catalog numbers above 99999 (https://celestrak.org/NORAD/documentation/gp-data-formats.php)
- How we use it
- Server-side fetch cached for at least 2 hours to plot debris clouds and constellations; never fetched from visitors' browsers.
CelesTrak SATCAT and Boxscore CelesTrak
Satellite catalog records with object type (payload, rocket body, debris) and status, plus counts of on-orbit and decayed objects by country and type.
- Access
- Free, no account
- Updates
- Daily (as-of date shown on page)
- Terms
- CelesTrak usage rules apply (https://celestrak.org/satcat/satcat-format.php)
- How we use it
- Headline on-orbit object counts, with the as-of date shown next to each figure.
Space-Track.org US Space Force (18th and 19th Space Defense Squadrons)
Current and historical orbital elements, satellite catalog, decay and re-entry predictions, TIP messages and public conjunction data messages via a REST API.
- Access
- Free account required
- Updates
- GP data suitable to query hourly; SATCAT daily; CDM up to 3 times daily
- Terms
- User Agreement required; rate limits 30 requests/minute and 300/hour; redistribution of some data restricted (terms not yet fully reviewed)
- How we use it
- Cross-checking catalog and re-entry data; not republished until redistribution terms are confirmed.
ESA DISCOS statistics European Space Agency (Space Debris Office)
Tracked-object totals across networks, launches, satellites in space and working, fragmentation events, total mass in orbit, and the archive of Space Environment Reports.
- Access
- Free, no account
- Updates
- Periodic (latest figures as of 31 Jul 2026)
- Terms
- ESA website terms
- How we use it
- Headline statistics on tracked objects, fragmentation events and mass in orbit.
ESA DISCOSweb object database and API European Space Agency
Object, launch, re-entry and fragmentation records with physical properties such as mass and dimensions.
- Access
- Free account required
- Updates
- Continuously maintained
- Terms
- Space Debris User Portal account and token; API details and rate limits unverified (https://discosweb.esoc.esa.int/apidocs)
- How we use it
- Physical properties of derelict objects for target-list context, pending API verification.
ESA fragmentation database European Space Agency
Records of on-orbit fragmentation events.
- Access
- Free account required
- Updates
- Updated as events are assessed
- Terms
- ESA Space Debris User Portal terms
- How we use it
- Cross-checking breakup events in our timeline.
GCAT: General Catalog of Artificial Space Objects Jonathan McDowell (planet4589.org)
Comprehensive independent catalog of launched objects as TSV downloads, including objects above catalog number 100000.
- Access
- Free, no account
- Updates
- Regular releases (1.8.8, Sep 2026)
- Terms
- CC-BY-4.0; cite 'Data from J. McDowell, planet4589.org'
- How we use it
- Primary redistributable catalog for public tables and derelict context.
McDowell constellation statistics Jonathan McDowell (planet4589.org)
Launched, in-orbit, operational and filed counts for megaconstellations including Starlink, OneWeb, Kuiper, Qianfan and Guowang.
- Access
- Free, no account
- Updates
- Frequently (updated 16 Sep 2026)
- Terms
- Cite J. McDowell, planet4589.org
- How we use it
- Constellation growth figures, linked live rather than hard-coded.
Conjunction screening
CelesTrak SOCRATES Plus CelesTrak
Screening of active payloads against the full catalog for close approaches within 5 km over the next 7 days, with minimum range and maximum collision probability.
- Access
- Free, no account
- Updates
- 3 times per day
- Terms
- Based on public GP data; much less accurate than operator conjunction data messages
- How we use it
- Illustrative close-approach examples, clearly labelled as not operational warnings.
Reentry predictions
CelesTrak recently decayed objects CelesTrak
Objects that decayed in the last 60 days, with their last orbital elements, downloadable as TLE/OMM/JSON/CSV.
- Access
- Free, no account
- Updates
- Rolling 60-day window
- Terms
- CelesTrak usage rules apply
- How we use it
- Recent re-entry feed and illustration of daily re-entry rates.
Aerospace Corporation CORDS re-entry database The Aerospace Corporation
Upcoming re-entry predictions with uncertainty windows and history of re-entries since 2000.
- Access
- Free, no account
- Updates
- Updated as predictions change (frequency unconfirmed)
- Terms
- Site Copyright and Terms of Use (not yet reviewed); CSV for data older than two years
- How we use it
- Linking to upcoming re-entry predictions rather than republishing them.
Population models
ESA MASTER-8 population figures ('By the numbers') European Space Agency
Modelled debris populations by size: objects >10 cm, 1-10 cm and 1 mm-1 cm.
- Access
- Free, no account
- Updates
- With model releases (MASTER-8, Feb 2026)
- Terms
- ESA website terms
- How we use it
- Our standard source for size-class population estimates, always named as a model estimate.
Reports
ESA Space Environment Report 2026 (Issue 10 Rev 1) European Space Agency
Annual assessment of the debris environment: launches, re-entries, fragmentations, disposal compliance and the environmental health index.
- Access
- Free, no account
- Updates
- Annual
- Terms
- ESA publication
- How we use it
- Authoritative source for compliance rates, re-entry counts and the 50x health index figure.
NASA Orbital Debris Quarterly News NASA Orbital Debris Program Office
Quarterly newsletter with catalog counts by country and type, breakup reports, radar measurements and research news.
- Access
- Free, no account
- Updates
- Roughly quarterly
- Terms
- US government publication
- How we use it
- Event details for historic breakups and NASA catalog counts.
NASA History of On-orbit Satellite Fragmentations (16th ed.) NASA Orbital Debris Program Office
Reference compendium of on-orbit fragmentation events.
- Access
- Free, no account
- Updates
- Occasional new editions
- Terms
- US government publication
- How we use it
- Background reference for breakup history.
NASA OTPS Cost and Benefit Analysis of Orbital Debris Remediation NASA Office of Technology, Policy and Strategy
Dollar-valued comparison of remediation methods; finds small-debris removal and just-in-time nudging pay off fastest. Phase 2 (2024) extends to mitigation and tracking.
- Access
- Free, no account
- Updates
- Phase 1 (2023), Phase 2 (2024)
- Terms
- US government publication
- How we use it
- Economics analysis and our 'nudge before capture' principle.
Rules and policy
UN OOSA Online Index of Objects Launched into Outer Space United Nations Office for Outer Space Affairs
Registry of objects launched into space as registered by states with the UN Secretary-General (about 85% registered).
- Access
- Free, no account
- Updates
- Currently unavailable due to website infrastructure changes (Sep 2026)
- Terms
- UN website terms
- How we use it
- Context on registration and state responsibility; linked when the index returns.
IADC Space Debris Mitigation Guidelines, Revision 4 Inter-Agency Space Debris Coordination Committee
International mitigation guidelines: 25-year maximum LEO post-mission lifetime, 90% disposal success, protected regions, passivation and a new section on large constellations.
- Access
- Free, no account
- Updates
- Occasional revisions (Rev 4, Jan 2025)
- Terms
- Voluntary guidelines; UN document
- How we use it
- Baseline for our rules-of-the-road coverage.
FCC orbital debris rules (5-year rule and Part 100) US Federal Communications Commission
Binding 5-year post-mission disposal rule for FCC-licensed and market-access LEO satellites (2022), and the 2026 Part 100 Space Modernization order (fact sheet: https://docs.fcc.gov/public/attachments/DOC-422740A1.pdf).
- Access
- Free, no account
- Updates
- As rules are adopted
- Terms
- US government publication; binding regulation
- How we use it
- Tracking binding disposal requirements.
ESA Zero Debris approach and Charter European Space Agency
Non-binding charter aiming to significantly limit debris creation by 2030 (228 signatories from 34 countries as of May 2026), alongside ESA's binding requirements for its own missions.
- Access
- Free, no account
- Updates
- Signatory count updated periodically
- Terms
- Voluntary charter; ESA website terms
- How we use it
- Tracking voluntary commitments and policy working groups.
Research papers
NASA ODPO FAQ and re-entry pages NASA Orbital Debris Program Office
Explainers on orbital speeds, impact velocities, orbital lifetimes and re-entry survivability.
- Access
- Free, no account
- Updates
- Irregular (population figures dated)
- Terms
- US government publication
- How we use it
- Physics background for explainers; older population figures shown only with context.
Kessler & Cour-Palais (1978), Collision Frequency of Artificial Satellites Journal of Geophysical Research (AGU)
The foundational paper describing a self-sustaining collisional debris cascade.
- Access
- Free full-text scan available (https://archive.org/details/kesslercollisionfrequency1978)
- Updates
- Static (published 1978)
- Terms
- Journal copyright; archive scan freely readable
- How we use it
- Source for our Kessler syndrome explainer.
McKnight et al. (2021), 50 statistically-most-concerning derelict objects in LEO Acta Astronautica
Composite ranking of the 50 most concerning LEO derelicts from 11 international teams, based on mass, encounter rate, orbital lifetime and proximity to operational satellites.
- Access
- Free, no account (open PDF)
- Updates
- Static (published 2021; orbits from 2020)
- Terms
- Journal copyright; open repository copy
- How we use it
- Basis for our derelicts table and target-priority analysis.
Liou, NASA ODPO active debris removal study NASA Orbital Debris Program Office
Modelling finding that about five removals per year, ranked by mass times collision probability, could stabilise the LEO population under high-compliance assumptions.
- Access
- Free, no account
- Updates
- Static
- Terms
- US government publication
- How we use it
- Context for removal-rate targets, presented as a floor under older assumptions.
Companies and missions
LeoLabs LeoLabs
Commercial LEO radar tracking; free public orbital-activity visualisation; often the first public fragment counts after breakups.
- Access
- Commercial
- Updates
- Continuous (commercial service)
- Terms
- Catalog, alerts and API sold commercially; no public pricing
- How we use it
- Cited for early breakup fragment counts, marked as initial estimates.