Jonathan McDowell insisted people should not worry about the tiny probability of being hit by the remains of the 21-ton Long March 5B rocket.
“I think it is more likely than not that it will fall in the Pacific Ocean and everyone will go ‘why was everyone excited?’” said Mr McDowell, who works at the Harvard-Smithsonian Center for Astrophysics.
“Just because of the area, it is really just a question of what fraction of the Earth’s surface is covered by people and stuff.
Mr McDowell spoke to The Independent by phone as the world awaits the rocket’s reentry.
“So, it is pretty much equally likely to fall on any spot. I would say this, maybe there is a significant chance it will land somewhere but there is a one in several billion chance that it will hit you,” he said.
“You don’t need to get your Skylab helmet out. You should not lose an iota of sleep on this, do not worry on a personal level, it is not going hit you.
“There are many more things that are likely to take you out than this.”
The rocket was launched last week to deliver the first module of China’s space station into orbit, but then itself made its way into orbit.
Last year the Chinese launched the same rocket, and it also fell to Earth in an uncontrolled reentry, reportedly raining metal on parts of the Ivory Coast.
And Mr McDowell says the Chinese have made a calculated stance on their space junk crashing back to Earth.
“The Chinese have a very different attitude to western space powers in letting rockets fall back to earth, said Mr McDowell.
“I think that the Chinese are some ways behind the sensibilities of the other space-faring countries on this.
“They are just taking the view that ‘yeah, we were fine last time, no-one was killed, we hit a few houses, what is the worry?’
“In fact they were touting this launch as being really more environmentally sensitive because they are no longer dropping lower stages on their own villages, which they used to do from their old launch site.
“They now launch from Hainan Island over the ocean instead of from central China where you would regularly get these videos of people in a village downrange from the launch site with a rocket stage sticking out of their barn leaking toxic propellant.
“This is their improvement.
“But they just didn’t really worry about the upper stage and I think part of this is that we do have plenty of rockets that leave their upper stages in orbit to reenter uncontrolled, but they are smaller rockets with much, much smaller upper stages, and this one is 30 metres long.”
Experts say that it is impossible to predict where those pets of the rocket not burned up on reentry could land.
It is currently circling the Earth every 90 minutes and Mr McDowell said that statistically it will most likely land in the ocean.
Its entry date is most likely to be 8 May, but it could be the day before, or day after, and it could land anywhere on the planet.
“There is an uncertainty in the timing, which is due to fluctuations in the density of the upper atmosphere which are effected by things like solar activity and so right now the uncertainty on that is about a day either side,” he added.
“And that will improve, so by tomorrow it might be plus or minus 12 hours or something and by the day of we will know within three hours.
“But even if you know within three hours, it will go around the world twice in that time.
“So we get into this game late in the process where we think it will come down in the next few hours, we know that continents X, Y and Z are not under its path but continents A, B and C are.
“So you get a warning of like yes, it might come down in the Pacific, or Australia or North America, and it won’t be any more specific than that.”