China's Tianhe core module for the Chinese Space Station (CSS) launched successfully on April 29 aboard a Long March 5B rocket from Wenchang. Now, the rocket's massive first stage is hurtling back toward Earth in an uncontrolled descent, with its impact location and timing still unknown.
As reported by SpaceNews, the Long March 5B's first stage is re-entering unpredictably following the Thursday launch. Debris could strike any day now. Odds favor most burning up in the atmosphere, with remnants likely splashing down in the oceans that cover over 70% of Earth. Yet, populated areas remain at risk.
Typically, rocket boosters fall short of orbital speed and land in designated zones. Larger ones perform de-orbit burns to minimize orbital time, reducing collision risks with other spacecraft before controlled re-entry.
Pre-launch data suggested the Long March 5B would execute such a maneuver. It did not, leading to this uncontrolled trajectory.
Predicting its path is challenging due to variables like atmospheric drag— influenced by solar activity that causes the atmosphere to expand or contract—plus the object's size and density.
US military ground radar tracks the 30-meter-long, 5-meter-wide stage orbiting at 170-372 km altitude, speeding at over seven kilometers per second. It circles Earth roughly every 90 minutes.
Drag will gradually slow it until gravity pulls it in. With a 41.5-degree inclination, its path arcs north of New York, Madrid, and Beijing, or south over Chile and Wellington, New Zealand.
SpaceNews notes, "the launcher could therefore re-enter this area at any time." Minutes matter: at these velocities, a brief delay shifts re-entry by thousands of kilometers.
Astronomer Jonathan McDowell calls it 'unacceptable' by modern standards. "Since 1990, nothing over ten tons has been deliberately left in uncontrolled re-entry." The stage's dry mass is estimated at about 21 tons.
Much will likely incinerate upon re-entry, but heat-resistant parts like stainless steel or titanium tanks and engines could survive to ground.
