UPDATED | July 30, 2022

A Quick Guide to Understanding Orbital Debris Reentry Predictions

Wondering if you’re in a debris path? Here’s what all those blue and yellow lines mean.

The ground tracks shown in the above map display the full uncertainty window for Long March 5B. As time to reentry shrinks, the uncertainty and predictions for time and location will become more specific. Credit: The Aerospace Corporation

The current prediction window for reentry of the CZ-5B rocket body (ID 53240) is 30 Jul 2022 17:08 UTC ± 1 hour.

The Aerospace Corporation’s Center for Orbital Reentry and Debris Studies (CORDS) is tracking the reentry path of the rocket body from China’s Long March 5B (CZ-5B) launch from 24 July. This graphic has generated a lot of questions such as, “what exactly am I looking at?” and “am I in the path of debris?”

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To clarify, the example below is a previous “normal” controlled rocket body descent, Long March 3B (CZ-3B) that reentered 3 May 2021. The map shows the prediction window as one continuous path. The rocket body was predicted to reenter anywhere along the blue or yellow paths, with the yellow satellite icon indicating where the final reentry occurred.

The prediction for the Long March 3B rocket body reentry on 3 May 2021 from the Center for Orbital and Reentry Debris Studies. Credit: The Aerospace Corporation

In this image:

• The white line and shaded area show day and night around the globe
• The blue line shows the orbital path prior to the reentry, and each tick mark is a five-minute interval
• The yellow line is the predicted future path with tick marks at five-minute intervals
• The text label and satellite icon indicate where the rocket body ultimately reentered
• The orange circle around the reentry point is the vicinity in which the reentry could be seen

The Current Situation

The Long March 5B reentry is unusual because during launch, the first stage of the rocket reached orbital velocity instead of falling downrange as is common practice. The empty rocket body is now in an elliptical orbit around Earth where it is being dragged toward an uncontrolled reentry.

For objects that have not yet reentered, the yellow satellite icon indicates the center of the predicted reentry window, the blue track is the first half of that window, and the yellow track is the second half. Reentry is not expected outside of the paths.

Reentry prediction from 30 Jul for the Long March 5B rocket body launched 24 Jul launch from the Aerospace Center for Orbital and Reentry Debris Studies. The current prediction for reentry is 30 Jul 2022 17:08 UTC ± 1 hour. Credit: The Aerospace Corporation

The predicted reentry path shown (before and after the yellow satellite icon) indicates a window of uncertainty around the prediction of ± 20% of the remaining prediction time. As an example, if the predicted time of reentry were in five days, the window of uncertainty would be ± 1 day.

Debris Footprint of Long March 5B

The spread of debris, referred to as the “debris footprint,” is not something experts can speculate on at this time, given the degree of uncertainty remaining for the reentry point. However, any spot away from the lines are very unlikely to be at risk from debris.

As the time to reentry shrinks so will the uncertainty, and the predictions for time and location will become more specific. The plot below shows the narrowing of the prediction window over time for the current Long March 5B uncontrolled reentry, where the red bars indicate the narrowing of the prediction window.

This plot shows the history of predictions over time for the estimated 30 Jul reentry of a Long March 5B rocket body. The dots are predicted reentry date and time, and the vertical bars represent the nominal error of the estimated reentry. The prediction becomes more consistent, and the error bars shrink. Credit: The Aerospace Corporation

CORDS experts update the tracking frequently throughout the day. Follow The Aerospace Corporation on Twitter @AerospaceCorp for the latest developments.

Have additional questions about how this happened? Check out our Q&A with a Space Debris expert.