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.

Reentry prediction for the Long March 5B rocket body from the Center for Orbital and Reentry Debris Studies. Credit: The Aerospace Corporation

The Aerospace Corporation’s Center for Orbital Reentry and Debris Studies (CORDS) is tracking the reentry path of the rocket body from the Chinese Long March 5B (CZ-5B) launch of April 29. The CORDS’ graphic has generated a lot of questions such as, “what exactly am I looking at?” and “am I in the path of debris?”

Latest update from Twitter @AerospaceCorp

For context, the previous “normal” rocket body descent, Long March 3B (CZ-3B) that reentered on May 3, is shown below:

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

In the image above:

• The white line and shaded area show day and night around the globe
• The blue line shows the orbital path prior to 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 circle around the reentry point is the vicinity in which the reentry could be seen

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.

Currently, the rocket body could reenter anywhere along the blue or yellow paths, with the satellite icon indicating the latest informed prediction:

The ground traces shown in the above image extend the full uncertainty window. Credit: The Aerospace Corporation

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.

The predictions for time and location will become more specific as reentry time draws closer, as shown below:

This plot shows the history of predictions over time. The dots are predicted reentry date and time, and the vertical bars represent the nominal error of the estimated reentry. The prediction is currently holding steady for Saturday night (US time), and the error bars are shrinking. Credit: The Aerospace Corporation

CORDS experts are continuing to 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 the Q&A with our Space Debris expert.