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McDowell said he hoped China would have enhanced the core stage to perform a controlled deorbit after separating from Tianhe. “I think by current standards it’s unacceptable to let it reenter uncontrolled,” McDowell said.
“Since 1990 nothing over 10 tons has been deliberately left in orbit to reenter uncontrolled.” The Long March 5B core stage, without its four side boosters, is thought to have a “dry mass”, or when it is empty of propellent, of about 21 metric tons in mass.
Holger Krag, head of the Space Safety Programme Office for the European Space Agency, says from their experience, there is an average amount of mass of about 100 tons re-entering in an uncontrolled way per year. “This relates to about 50-60 individual events per year.”
“It is always difficult to assess the amount of surviving mass and number of fragments without knowing the design of the object, but a reasonable “rule-of-thumb” is about 20-40% of the original dry mass.”
Components made of heat resistant materials, such as tanks and thrusters made stainless steel or titanium, can reach the ground. Surviving objects will fall vertically after deceleration and travel at terminal velocity.