World waits to see where a Chinese booster will come down

In late April, China successfully launched a major component of its planned space station. Since then, the booster that put the component into orbit has been circulating in an unstable orbit, and various tracking organizations are indicating that it's likely to come back in a completely uncontrolled manner. It's a big-enough piece of hardware that some parts are likely to survive until they reach the ground. While odds are that will happen over the ocean, there's no guarantee re-entry won't happen over a populated area.

As Ars' Eric Berger described last year, the Long March 5B has an unusual design. Meant for heavy lifts to orbit, the rocket doesn't have an upper stage; instead, its main stage travels all the way to orbit with its payload. Once there, one option is to leave it in a stable orbit, where it would add to the increasing clutter in low Earth orbit. The alternative is to de-orbit the stage.

Most countries have settled on a controlled de-orbit, in which control is maintained over the booster and enough fuel is retained to allow decisions to be made about when the hardware re-enters the atmosphere. That allows any material that survives re-entry to land harmlessly in the ocean.

China has apparently not chosen this path. Following the launch of a Long March 5B last year, the rocket re-entered the atmosphere while on an orbit that took it directly over New York City. Material from that booster ended up causing damage on the far side of the Atlantic in the Ivory Coast, although fortunately nobody was injured. According to experts, the Long March booster was the largest object to make an uncontrolled re-entry in nearly 30 years. And that size makes a difference, since it means larger parts that are more likely to survive the violent trip to the Earth's surface.

China, however, was not chastened by the threat posed by its hardware. In late April, it launched a key piece of its planned space station, Tianhe, a 22-ton module that will include the crew quarters, atop a Long March 5B. Since then, the main booster has been tumbling uncontrolled in an unstable orbit, and the EU's space-tracking program indicates simulations suggest it will re-enter on May 8 or 9. The booster's orbit only takes roughly 90 minutes, so predicting where its debris might land is impossible given that uncertainty.

Predictions regarding its re-entry will undoubtedly improve given additional time to monitor its orbit. But, because of the tumbling, its interactions with the thin atmosphere are going to make any certainty difficult.