UPDATED | NOVEMBER 3, 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 current prediction window for reentry of the CZ-5B rocket body (ID 54217) is 04 Nov 2022 11:20 UTC ± 3 hours.
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 31 October. This graphic has generated a lot of questions such as, “what exactly am I looking at?” and “am I in the path of debris?”
To clarify, the example below is of the previous CZ-5B rocket body descent that reentered on July 30, 2022. 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 “circles” icon indicating the midpoint of our latest reentry prediction window, with the red icon being near the final reentry.
In the image:
- The yellow icon is the location of the object at the midpoint of the reentry window
- The blue line shows the ground track uncertainty prior to the middle of the reentry window; each tick mark is a five-minute interval
- The yellow line is the ground track uncertainty after the middle of the reentry window; each tick mark is a five-minute interval
- The pink icon indicates the vicinity of an eyewitness sighting or recovered debris, if applicable
- The red icon shows Space Track’s predicted location of reentry, if applicable
Possible reentry locations lie anywhere along the blue and yellow ground track. Areas not under the continuous line are not exposed to debris.
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 a near-circular orbit around Earth where it is being dragged toward an uncontrolled reentry.
For objects that have not yet reentered, the yellow circle 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.
The predicted reentry path shown (before and after the yellow circle 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. As the time to reentry nears, we will add a graphic of the refined predictions.
The plot below shows the narrowing of the prediction window over time for the Long March 5B uncontrolled reentry from 30 Jul 2022, where the red bars indicate the narrowing of the prediction window.
Have additional questions about how this happened? Check out our Q&A with a Space Debris expert.