The spent booster phase responsible for placing the first module of China’s next space station into orbit is set to make an uncontrolled encounter with Earth.
The first module of Tiangong-3, “Tianhe”, was launched at the end of April over the Long March 5B rocket and currently safely in orbit.
The same, alas, cannot be said for the Long March 5B (CZ-5B), which features a main stage and four strap-on liquid fuel boosters. The rocket is capable of injecting a payload directly into Earth’s low orbit but, unfortunately, doesn’t appear to have much in the way of self-disposal.
There are many conventional rockets that use a disposable first stage (or reusable, in the case of SpaceX) that it does not do in orbit. Subsequent stages (such as the kick stage used by Rocket Lab) can deorbit themselves in a controlled manner after depositing cargoes.
China appears to do things a bit differently.
The Tianhe launch is the second in the 5B variant of the Long March 5 series. Ang first, in 2020, also resulted in the spent main stage producing an uncontrolled re -entry into the Earth’s atmosphere. Hopes that maybe it will be a lucky second time, and a de-orbiting maneuver may be on the cards, appear to have been dashed and a fierce lottery is being conducted with regard to where the labi.
Chinese Long March 5B (NORAD-ID 48275) is expected to re-enter this week-NORSS ’Monte Carlo results below give a probabilistic re-entry time of approximately 1628UTC on 08/05/2021. The window of uncertainty surrounding the present covers many days. pic.twitter.com/rZIYHC7JbM
– NORSS Orbital Analyst Hive (@HiveNorss) May 4, 2021
The problem is that the spent main stage is enormous, measuring approximately 30 meters long and five meters wide. The peg on the stage is estimated to weigh more than 20 tons. There is therefore a very good chance that some parts will survive the re-entry heating and be scattered over a wide area.
The good news is that that area is probably above the ocean, but since the rocket appears to be out of control, observers will not predict with much accuracy until the time is near. Ang current best guess it will re-enter around 0100 UTC on 10 May, but a heavy 41-hour period of uncertainty exists on both sides of it.
Astronomer Jonathan McDowell tweeted a plot showing the decay of the main stage, but there was consolation for those worried about a Chelyabinsk-style event. Not much less moving force involved in this instance – “worst case,” he said, “is like a little plane crash.”
Sure, but still little comfort for anyone unlucky enough to encounter any surviving ingredients.
Plan Tianhe altitude this morning; the Tianhe space station remains in a 352 x 385 km orbit. The main phase of the CZ-5B was decomposed from the initial 170 x 375 km orbit to 165 x 326 km; the drag and perigee cause the apogee to decrease. pic.twitter.com/X0ZQIiEqUE
– Jonathan McDowell (@ planet4589) May 3, 2021
As well as spent rocket bodies, China has also lost control of the unique spacecraft in recent years: the first space station, the Tiangong-1, unforgettable fall out of control and caused some irritating bottoms before its remnants were not exploded without harm to the Pacific Ocean.
Mockup of Long March Family’s New Generation Launch Vehicles displayed during the 12th China International Aviation and Aerospace Exhibition
To be fair to China, it’s not alone in sending space junk exploding back to Earth in an uncontrolled manner. Russia’s Salyut 7 space station had its own issues in 1991 while NASA’s Skylab pieces were memorable smacked in Australia in 1979. And then there’s Columbia accident. However, according to McDowell, “Before the CZ-5B started flying it was NOT ‘by design’ the uncontrolled reentries above 10 tonnes since 1990”
And, of course, the country has a pretty good reputation when it comes to parts of the rocket hitting the ground following launch. Allowing another heavy chunk of space junk to fall back to Earth would make that reputation unfavorable. ®