Tuesday, June 1, 2021

uncontrolled reentry of Chinese 'Long March 5B' threatens humanity

In the small town of Oakey Oaks, Chicken Little rings the school bell and warns everyone to run for their lives. This sends the whole town into a frenzy. Eventually, the Head of the Fire Department calms down enough to ask him what is happening. Chicken Little says that a piece of the sky shaped like a stop sign had fallen on his head, but he is unable to find the piece. His father, Buck Cluck, assumes that this "piece of sky" was just an acorn that had fallen from the tree, making Chicken Little the laughingstock of the town.  That was ‘Chicken Little’ movie.

Decades ago in 1979 – rumours ran so high that most people in globe feared a mighty fall from the sky a la Chicken do little – across India, especially Andhrapradesh, fear was high as according to some reports that object from the sky could hurtle in Karimnagar.  Some of them hid their wealth in the wells and some spent all the money they had saved for their enjoyment since they feared that lives would come to an end soon. Reportedly some sold their property and cattle at low prices ! – eventually some pieces were scattered across Australia, but no one on the ground was hit and no property damage was reported

2020 was all about the Corona virus that emanated from China – WHO ensured that it was named Covid 19 with no reflection of its origin but the variants could have the name as British, Indian, South African .. .. et.al. .. now amidst the strong 2nd wave there is another fear – that of a large Chinese rocket stage reentering Earth’s atmosphere in the coming days and the potential impact of the falling debris. !! 


The Long March 5B successfully launched a 22.5-metric-ton core module of China’s first space station last week. During the launch, the first stage of the Long March 5B also reached orbital velocity instead of falling downrange as is common practice. That placed the empty rocket body in an elliptical orbit around Earth where it is being dragged toward an uncontrolled reentry in the coming days. [very clearly a failed launch but no one is talking about that !]

The rocket stage’s orbital inclination of 41.5 degrees means that reentry can be as far north as Chicago, New York City, Rome and Beijing and as far south as New Zealand and Chile. That places any of the locations within the potential reentry path of this giant piece of space junk measuring 98 feet long by 16.5 feet wide and weighing 21 metric tons. The Center for Orbital and Reentry Debris Studies (CORDS) at the Aerospace Corporation is tracking the Long March 5B reentry. Here is something from   Marlon Sorge, CORDS principal engineer about how the situation developed and what happens next.

This stage and its predecessor last May are the sixth and seventh largest objects to ever reenter. The mass of this core stage is 21 metric tons. The list of other comparably-sized objects that have reentered includes early space stations — like Mir, Skylab, Salyut 6 and 7 — and the Saturn V second stage that launched Skylab. These represent a mix of controlled and uncontrolled reentries, however.

Normally the first stage of a rocket and its strap-on boosters are not designed to reach orbit. Their trajectories are planned so that the stage and any strap-on boosters fall into a safe area, usually in the ocean. In this case the first stage core of the rocket reached orbit. That means that it was no longer able to control where it would reenter without a deorbit maneuver. A deorbit maneuver uses a satellite or rocket stage’s engines to drop the low point of its orbit to choose where it hits the earth. This is called a controlled reentry. By doing this a large object can be targeted for an unpopulated region of the ocean where its debris will not injure anyone. The ability to conduct a deorbit maneuver is dependent on the design of the vehicle and the mission.  

The probability that any random reentry will land in the ocean is about 3:4, since the Earth is about 75% covered by oceans. Also, the majority of the land mass is either uninhabited or lightly inhabited: deserts, mountains, forests, and open prairie, farms, or grasslands. The probability that a piece of space debris will land on a city or a densely populated area is usually relatively small. What makes this reentry particularly noteworthy is that it will occur between 41.5 deg N and 41.5 deg S latitudes, where the vast bulk of the world’s population lives !  The 41st parallel north is a circle of latitude that is 41 degrees north of the Earth's equatorial plane. It crosses Europe, the Mediterranean Sea, Asia, the Pacific Ocean, North America, and the Atlantic Ocean.

The chances of it hitting a populated area are small, but not zero. That has raised questions about how the country’s space program designs its missions. That said, the chances are not zero. Part of China’s largest rocket, the Long March 5B, is tumbling out of control in orbit after launching a section of the country’s new space station last week. The rocket is expected to fall to Earth in what is called “an uncontrolled re-entry” sometime on Saturday or Sunday. Whether it splashes harmlessly in the ocean or impacts land where people live, why China’s space program let this happen — again — remains unclear. And given China’s planned schedule of launches, more such uncontrolled rocket re-entries in the years to come are possible.  On Thursday, the Aerospace Corporation, a nonprofit largely financed by the federal government that performs research and analysis, predicts re-entry will occur on Saturday at 11:43 p.m. Eastern time. If that is accurate, debris could shower down over northeastern Africa, over Sudan.

Uncertainty over the time — give or take 16 hours — and location remain large. A day before, Aerospace’s prediction put re-entry more than one hour earlier, over the eastern Indian Ocean.  The United States Space Command and Russia’s space agency are both tracking the rocket core. The Russian statement noted that the re-entry would not “affect the territory of the Russian Federation.” The Space Command promised regular updates ahead of a potential re-entry.

Because the booster is traveling at 18,000 miles per hour, a change of minutes shifts the debris by hundreds or thousands of miles. It is only a few hours before re-entry that the predictions become more precise. China plans many more launches in the coming months as it completes construction of the country’s third space station, called Tiangong, or “heavenly palace.” That will require additional flights of the mammoth rocket and the possibility of more uncontrolled re-entries that people on the ground will watch nervously, even if the risk from any single rocket stage is tiny.

In March 2021, a rocket stage from a SpaceX Falcon 9 lit up the night skies over Seattle and later dropped debris over a farm in Washington State when a planned firing of the engine of the second stage to bring it down safely did not occur as planned. China, by contrast, has a long history of letting pieces of its space equipment come down where they may. Rockets from one of China’s principal launch sites, the Xichang Satellite Launch Center in Sichuan Province, routinely fell on rural areas downrange, occasionally causing damage. China has since moved many of its launches, including last week’s, to a new site in Wenchang, a city on Hainan, an island off the southeastern coast. From there rocket stages can fall harmlessly into the sea.  China’s first space station, called Tiangong-1 and launched in 2011, also fell back to Earth in an uncontrolled descent in 2018 before ultimately crashing harmlessly in the South Pacific.  

Worrisome, but the World is combatting some other worry immersed neck-deep and perhaps has no space for worrying on this.

With regards – S. Sampathkumar                                           
7th May 2021.

Collated from many sources with specific reference to a scholarly article :https://aerospacecorp.medium.com/a-massive-chinese-rocket-is-falling-uncontrollably-to-earth-db7c7b32d773

 

  

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