When will China's rocket fall?

Forecasts on when and where China's largest rocket will are converging, find out how predicting when and where space junk will de-orbit is a lot like predicting the path of a hurricane,

Posted 12:34 a.m. May 9, 2021 — Updated 12:34 a.m. May 9, 2021

Tony Rice

, NASA Ambassador

The Long March 5B rocket which lifted the first segment of China's space station is expected to re-enter the atmosphere late Saturday night into Sunday morning. The rocket, launched last week, has been observed tumbling out of control.

Forecasts of when and where the rocket will ultimately come down have been regularly updated by Aerospace Corporation, a nonprofit federally funded research and development center based in El Segundo, California, and the United States Space Command, published on the SpaceTrack.org website.

As of 7 p.m. Saturday, the latest Tracking and Impact Prediction (TIP) message from US Space Command estimates the rocket will de-orbit off the northern coast of Spain at 2:04 UTC (10:04 pm EDT). Aerospace predicts the rocket will de-orbit nearly a full orbit later over the South Pacific Ocean at 3:02 UTC (11:02 pm EDT)

De-orbit predictions, like hurricane track predictions, are based on differing models

Why the disagreement in predictions? Forecasting when and where space junk reenters the atmosphere is a lot like forecasting when and where a hurricane will make landfall. Forecasts are based on several models. While each is working from the same starting point and with the same data, the models make different assumptions about how the object and atmosphere will behave.

"There are a variety of ways to predict the reentry, and models differ. The predictions are highly sensitive to the modeling assumptions. We are constantly refining our models, but are satisfied with our approach in the face of the unknowns." explains a spokesperson for Aerospace Corporation.

Re-entering rocket FAQ

Are we in danger? Will someone get hit by debris? It is safe to say: no. The risk of injury from falling space debris is estimated to be less than one in one trillion. For comparison: your odds of winning PowerBall are around 3,500 times better.
Is there a health risk? The core stage is fueled by liquid hydrogen and liquid oxygen, not more toxic options like nitrogen tetroxide or hydrazine.
Can I see it reenter? Probably not, estimates continue to center on the other side of the planet
What will it look like? If you are within a ~1000 mile wide circle, it will look like a meteor, actually many meteors, as the rocket breaks up in streaks across the sky.
Will it burn up in the atmosphere? Mostly but 10%-40% can survive the fall depending on the materials and construction of this rocket, which we know little about. Over the past 40 years nearly 6000 tons of reentering debris is estimated to have survived. The last time a Long March 5B rocket de-orbited (May 2020), debris was reported along Africa's Ivory Coast.

Most large space junk re-enter over the vast open expanses of the South Pacific Ocean after a controlled de-orbit. Some debris has survived the fall to land.

Did something go wrong? Why is this an uncontrolled reentry? Generally a de-orbit burn is executed to begin lowering the orbit at a strategic time to put the debris down in a strategic place, but that didn't happen. Either this rocket is capable of a controlled de-orbit and something went wrong, or it isn't capable. Again, we know little about this rocket and China isn't sharing much more.
Who would be liable for damages/injuries should they occur? China according to the UN's 1967 Outer Space Treaty and 1972 Space Liability Convention, which China has signed onto. It would be up to the countries to negotiate the terms, the UN wont even get involved. This happened in 1978 when the Russian Cosmos-954 satellite broke apart scattering debris across a 75k+ square miles stretching across the Northwest Territories, Alberta, Nunavut, and Saskatchewan including thousands of bits of radioactive material the size of a grain of salt. Final cost of the joint US-Canada cleanup (codenamed Operation Morning Light) was around $12 million Canadian. Canada billed Russia for $6 million, they paid $3 million.
When will we know for sure when and where it will de-orbit? Short answer, when it de-orbits. Long answer, the best estimates, in the hours before actual reentry, still have +/- 10% uncertainty of the time of final reentry or a window of nearly 20 minutes. At atmospheric interface, it is traveling about 20 times faster than a bullet which equates to a footprint ~4k miles long when you consider that window of uncertainty.
What is taking so long? When compared to a similar rocket which also uncontrollably de-orbited last year, is taking longer for the orbit to lower, likely due to the differences in the starting orbits and variations in the upper atmosphere.