An out of control Chinese rocket is expected to enter Earth’s atmosphere this weekend, but no one knows exactly when or where the debris will land. Here’s why we don’t know yet and, more importantly, when we can expect to find out.
During the Apollo era, the atmospheric reentry time of arriving command modules could be predicted to the exact second. As to when the main phase of China’s Long March 5b rocket – currently in freefall into low Earth orbit – will reentry remains an open question. Without knowing the time of re-entry, predicting a possible impact zone is impossible.
As of this publication, the aerospace company estimates that the body of the CZ-5B rocket will finally fall to Earth at 11:53 p.m. EDT on Saturday May 8 (03:53 UTC Sunday May 9), with a plus-minus 11 hours, while SpaceTrack.org has it event about 30 minutes earlier, with a plus-minus nine hours.
The heavy rocket launched on April 29, but its 98-foot-high main stage, instead of falling back to a predetermined location on Earth, entered orbit, setting the stage for a uncontrolled atmospheric reentry.
As to where the debris will end up, it’s even more uncertain. The potential geographic area is huge, including most of North and South America, Africa, Australia, the Middle East, and all of southern Eurasia, in addition to the Atlantic and Pacific Oceans. . A slightly outdated tweet from Aerospace Corporation, pictured below, shows the possible geographic range (the horizontal area containing all of the wavy lines) for falling debris.
So why were we able to predict the arrival of the Apollo capsules with such precision, but not this central step?
“The problem with the Apollo spacecraft is that they arrived vertically from the Moon, so we knew the exact orbit,” Jonathan McDowell, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics, told me over the phone. “But this rocket moves tangent to the atmosphere – its body rides horizontally over the outer atmosphere and constantly brushes against it as the rocket descends towards it.
As a result, it is difficult to predict when the rocket will heat up to the point that the structure will begin to melt and fall to Earth, he said. That will depend on the various materials the rocket is made of, its particular way of tumbling, and the changing density of the upper atmosphere, which varies daily due to space weather and solar activity, according to McDowell.
Ground experts do their best to track the object, noting its altitude, speed, and other factors, while continually updating the models. The closer we get to the actual re-entry date, the more accurate the forecast will become. It’s like “trying to predict the weather in a week rather than tomorrow,” McDowell said, because “there is less extrapolation involved.” He expects the margin of error to continuously decrease over the next few hours, saying by Saturday morning it should be reduced to a window of around six hours. Eventually we will get to the point where we will know exactly when it will fall from the sky. Unfortunately, predicting a potential landing site is next to impossible until then, because “a one hour error in re-entry time is an 18,000 mile error in location,” as McDowell previously explained.
McDowell predicts two possible outcomes as of when we all know where this thing ended up.
“One possibility is that it will land in the middle of the Pacific Ocean, because that’s most of the Earth,” he said. The US Space Force will know immediately when it re-enters the atmosphere thanks to infrared telescopes, which will see the rocket when the rocket breaks down. The Space Force will know the “exact time to minute” and “exact location” of the point it entered the atmosphere, McDowell said, but the military won’t tell the rest of the world right away. between us because this data is “sorted”. of secrecy.
Space Force “will clear it out at different levels of bureaucracy until it shows up on a space tracking website, and we’ll have to pretend that we don’t know this data is coming from early warning satellites,” said McDowell. In his experience, the approvals, approval, and clearance needed to make this information available on the web take about three hours.
A series of similar events could unfold if the rocket shatters over an uninhabited land mass, with the site of the impact revealed about three hours after the incident. But he predicts a very different finale if pieces of the disintegrating central stage crash into a populated area.
“Then we’ll find out in about 10 minutes, because people’s Twitter will light up furiously,” he said.