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OD Quality Ratings

An OD quality rating indicates whether the tracking data behind a state was sufficient and processed adequately. Satcat rates the primary and secondary state of any CDM that reports OD quality metrics, and shows both per CDM in the conjunction event CDM table.

note

A rating describes the orbit determination fit at the epoch of the OD solution, not the accuracy of the prediction at TCA. Use it to judge whether a data source is tracking an object well enough, or whether additional tracking should be requested.

Rating System​

Satcat rates three metrics as Poor, Good, or Excellent: OD span ratio, weighted RMS, and percentage of residuals accepted. Those ratings score 0, 1, and 2, and the sum gives the state's overall rating:

  • 0 to 3: Poor
  • 4 to 5: Good
  • 6: Excellent

A CDM reports all three metrics or none. A state from a CDM without them is rated Unknown and shows no rating.

OD Quality Metrics​

OD Span Ratio​

The OD span, sometimes called the Length of Update Interval (LUPI), is the time span of tracking data used to generate the OD solution. The ratio divides it by the recommended fit span for an object with similar orbit characteristics.

  • Poor: < 0.3
  • Good: ≥ 0.3 and < 0.7
  • Excellent: ≥ 0.7
Recommended fit span

Recommended fit span is itself reported in each CDM by the originator. There is no public standard, but values are typically based on the object's energy dissipation rate (EDR) and eccentricity. A higher EDR means a more rapidly changing orbit from non-conservative perturbations such as atmospheric drag, suiting shorter fit spans of 1 to 7 days. A lower EDR, common in higher orbits where drag is negligible, suits longer spans of 7 to 14 days.

Weighted RMS​

The weighted RMS error measures the residuals processed during OD, normalized by the expected measurement uncertainties. A value of 1 means the residuals match those expectations. Significantly below 1 can indicate overfitting or unrealistic measurement uncertainties; significantly above 1 often indicates dynamical mismodeling, poor measurement quality, or insufficient tracking data.

  • Poor: ≥ 10.0
  • Good: < 0.5, or > 1.5 and < 10.0
  • Excellent: ≥ 0.5 and ≤ 1.5

Percentage of Residuals Accepted​

The ratio of measurements actually processed during OD to the total available. Measurements are rejected as outliers, so a low percentage can indicate noisy tracking data, cross-tagging, or dynamical mismodeling.

  • Poor: < 50%
  • Good: ≥ 50% and < 90%
  • Excellent: ≥ 90%