The Chinese Space Station (CSS) Core Module successfully lifted off this Thursday, April 29 aboard a Long March 5B rocket. The launcher's booster is about to re-enter the Earth's atmosphere, but it is not yet known exactly where or when this debris will hit our planet.
The first stage of China's Long March 5B launch vehicle "unpredictably" falls back to Earth after its successful launch on Thursday, April 29 from Wenchang Base, reports SpaceNews . His return to Earth could take place any day. The odds suggest that this debris will burn up in the atmosphere and the "survivors" will fall back into one of the oceans, which cover just over 70% of the planet. However, it is not excluded that the booster threatens an inhabited area.
Most rocket boosters do not reach orbital velocity and re-enter the atmosphere to end up in a predefined area. Some, larger, go a little higher, but operate deorbit maneuvers so as to reduce the time in orbit to avoid the risk of collision with other spacecraft and immediately reenter the atmosphere.
For the launch in question, there was strong evidence that the Long March 5B would perform an active maneuver to de-orbit. Obviously, that was not the case. Hence the uncontrolled fallout.
It is indeed now very difficult, if not impossible, to anticipate the trajectory of this falling rocket stage, as there are so many uncertainties in the calculation of the effect atmospheric drag on the central module (the Earth's atmosphere can expand or contract with solar activity). The size and density of the object are also a factor.
According to ground radar used by the US military, the launcher's main stage, about thirty meters long and five meters wide, is currently evolving at a altitude between 170 and 372 kilometers, traveling through space at more than seven kilometers per second . Given its speed, the booster orbits the Earth approximately every 90 minutes .
The more time passes, the more the object slows down, before being "snatched up" by the gravity of our planet. Its orbital inclination is 41.5 degrees, which means that it sometimes passes a little further north of New York, Madrid and Beijing, sometimes through southern Chile or Wellington, New Zealand.
As Spacenews points out, "the launcher could therefore re-enter this area at any time" . The timing will be essential. At these speeds, a lag of a few minutes in atmospheric re-entry can shift this point of re-entry by several thousand kilometres.
Spaceflight observer Jonathan McDowell found it 'unacceptable' , by today's standards, to allow such a massive object to enter the atmosphere uncontrollably. "Since 1990, nothing over ten tons has been deliberately left in orbit to reenter uncontrollably" , he explains. “However, it is believed that the Long March 5B central stage, without its four side boosters, has a dry mass (vacuum of propellant) of approximately 21 tons of mass” .
For the specialist, it is likely that a large part of this booster will end up burning in the atmosphere a few minutes after its reentry. On the other hand, it is possible that components made of heat-resistant materials, such as tanks and thrusters made of stainless steel or titanium, can reach the ground.
