For "ELSA-d: On-Orbit Demonstration of Space Debris Proximity and Capture"
Data Sources
OrbitSmith integrates data from multiple authoritative public sources. All displayed values that come from these sources are transcribed as-is or presented with minimal formatting.
Orbital catalog & conjunctions (Tracker · Passes · GS Planner · Statistics)
- Space-Track.org — GP catalog (18th Space Defense Squadron), CDM Public (via CSpOC), TIP predictions, Decay records. Requires account; OrbitSmith fetches hourly via authenticated Worker.
- CelesTrak — GP and Supplemental GP elements by Dr. T.S. Kelso. SupGP provides operator-supplied ephemerides for major constellations (Starlink, OneWeb, GNSS, etc.), typically more accurate than Space-Track GP.
- GCAT — General Catalog of Artificial Space Objects by Dr. Jonathan McDowell (CC-BY). Used for operator / country / launch date metadata.
- ESA DISCOS — Space Debris Office statistics. Static reference for annual object counts in historical charts.
- McCants visual magnitude database — satellite brightness references for Passes page.
The Tracker catalog (~30,000 objects) is fused from Space-Track GP, CelesTrak GP, and CelesTrak SupGP with SupGP prioritized where available (most recent epoch wins). This fusion is an OrbitSmith aggregation; individual object elements are upstream as-is.
Earth imagery (Imagery page)
- NASA GIBS — MODIS Terra/Aqua, VIIRS SNPP/NOAA-20/NOAA-21 true color and scientific layers (NDVI, Nighttime Lights, Snow Cover, Aerosol Optical Depth, Sea Surface Temperature, Chlorophyll, Land Surface Temperature, Precipitation Rate) for the Imagery page.
- NASA FIRMS — Fire Information for Resource Management System. Near-real-time active fire detection from VIIRS and MODIS thermal anomaly data.
- Sentinel-2 Cloudless by EOX — Annual cloud-free mosaics (2022/2023/2024) derived from ESA Copernicus Sentinel-2 data, served by EOX IT Services.
- Esri World Imagery — High-resolution satellite and aerial imagery from Esri, Maxar, Earthstar Geographics, and the GIS Community.
Precision ephemerides (Artemis II)
- JPL Horizons — Precise ephemerides for Artemis II and Moon. OEM-format state vectors.
How We Calculate
Several displays on OrbitSmith are not raw upstream values but computed locally. Each calculation below lists the method, inputs, and assumptions.
Orbit Visualization (3D Globe)
Positions of ~30,000 objects on the 3D globe are propagated client-side using Kepler two-body mechanics. Initial state is computed from TLE mean motion and mean anomaly at epoch; subsequent animation applies a simple Y-axis rotation for visual effect.
Perigee / Apogee / Period
Computed from TLE mean orbital elements: perigee = a(1 − e) − R⊕, apogee = a(1 + e) − R⊕, period = 1440 / n (minutes), where a is semi-major axis from mean motion, e is eccentricity, and n is revolutions per day.
Relative Velocity (Shell Risk Indicator)
When two objects are selected in the Shell Risk Indicator, OrbitSmith estimates a representative relative velocity using spherical trigonometry of orbital planes. The crossing angle θ is derived from inclinations and right ascensions: cos(θ) = cos(i₁)cos(i₂) + sin(i₁)sin(i₂)cos(ΔΩ). Then v_rel = √(v₁² + v₂² − 2·v₁·v₂·cos θ), with v₁, v₂ being circular orbital speeds at each object's altitude.
Shell Risk Indicator (Calculator)
A simplified Kessler-style spatial density model is used as a relative shell indicator: P = 1 − exp(−ρ · σ · v_rel · Δt), where ρ is an implied shell density, σ is combined cross-section, v_rel is representative relative velocity, and Δt is the selected time window. This treats each orbital shell as a uniform population.
Orbital Congestion Index
A spatial flux indicator F = ρ · v_rel · σ is computed per regime, where ρ is object density (count / shell volume), v_rel is a regime-typical relative velocity (10 km/s for LEO, 5 for MEO, 0.5 for GEO, 7 for HEO), and σ = 10 m² is a typical combined cross-section. LEO bucket covers 800–1,000 km only (the highest-density band). CRITICAL / HIGH / MODERATE / LOW labels are derived from F relative to LEO's value.
Reentry Current Altitude
For objects on reentry watch, current altitude is computed in-browser via SGP4 propagation (satellite.js) from the cached TLE. Recomputed every 10 seconds; the underlying TLE itself is from the daily Space-Track refresh.
Visible Pass Prediction
The Passes page uses SGP4 propagation from Space-Track GP TLE lines when available. For catalog objects missing valid GP lines, OrbitSmith generates a synthetic TLE from the current orbital elements as a fallback so the object can still be screened for visibility.
CDM Risk Level
OrbitSmith groups Pc values into four display bands. The thresholds are anchored to public NASA CARA and ESA collision-avoidance references, but the band names are OrbitSmith-defined and are not official NASA/ESA categories. Specifically: HIGH (Pc ≥ 10⁻⁴) corresponds to the NASA CARA mitigation threshold (NASA Step 2) and ESA's ~1-in-10,000 maneuver threshold. MODERATE (10⁻⁵ ≤ Pc < 10⁻⁴) corresponds to the ESA SCARF dashboard highlight threshold documented in Merz et al. 2017 (SDC7 paper 1017). LOW (10⁻⁷ ≤ Pc < 10⁻⁵) is above NASA's operational-attention floor (NASA Step 2) but below ESA's escalation-candidate threshold. NEGLIGIBLE (Pc < 10⁻⁷) is below NASA's operational-attention threshold. The Pc value itself is upstream from Space-Track; only the band assignment is made by OrbitSmith. OrbitSmith is not an operational tool.
Limitations & Known Errors
- OrbitSmith is not an operational SSA tool. It is intended for education, research, and awareness only. All displayed values carry uncertainty.
- CDM Public data from Space-Track contains no state vectors or covariance matrices — the true TCA relative velocity cannot be retrieved, only approximated locally.
- TLE-based propagation ignores high-fidelity forces (drag variability, solar radiation pressure, third-body, J₃+ terms). Position errors can accumulate to tens of km within days.
- Catalog objects without recent epoch updates (>30 days) are excluded from the Tracker display; the "Tracked Objects" count reflects this filtered active set.
- Orbital Congestion labels are OrbitSmith-internal; they do not correspond to any official SSA classification.
- For operational decisions — maneuver planning, licensing, insurance — use official CDM from Space-Track or licensed SSA services (LeoLabs, Kayhan Space, ExoAnalytic, etc.).
References
- Kessler, D.J., & Cour-Palais, B.G. (1978). "Collision frequency of artificial satellites: The creation of a debris belt." Journal of Geophysical Research, 83(A6), 2637–2646.
- Vallado, D.A. "Fundamentals of Astrodynamics and Applications" (4th ed.) — propagation and coordinate references.
- Hoots, F.R., & Roehrich, R.L. (1980). "Models for propagation of NORAD element sets." Spacetrack Report No. 3 — SGP4 specification.
- NASA CARA Analysis Tools — conjunction assessment methodology.
- ESA Space Safety & Space Debris — official debris environment reports.
- Space-Track.org documentation — CDM, GP, TIP, Decay data specifications.
- CelesTrak documentation — SupGP and GP element set usage notes.