A NASA spacecraft is set to make an uncontrolled plunge back to Earth. Here are the risks

The Van Allen Probes, which NASA launched in 2012, studied two cosmic bands of high-energy particles that are trapped in Earth’s magnetic field. (Credit: NASA via CNN Newsource)

A massive space probe could plummet into Earth’s atmosphere as soon as Tuesday evening — years earlier than expected. And while most of the spacecraft will likely disintegrate in a flaming blaze during reentry, a few components could survive, according to NASA.

Early analyses predict the 1,323-pound (600-kilogram) vehicle will strike the atmosphere around 7:45 p.m. ET Tuesday, “with an uncertainty of +/- 24 hours,” according to NASA and the U.S. Space Force.

The odds that a piece of debris will cause harm to a person is about 1 in 4,200, the space agency said in a news release.

That’s a low chance, according to NASA, and more favourable odds than those of space debris incidents of years past.

“We’ve had things that have reentered have a one in 1,000 chance, and nothing happened; if we have a few that are one in 4,000 or 5000, it’s not a horrible day for mankind,” said Dr. Darren McKnight, a senior technical fellow at space-tracking company LeoLabs.

But this risk is decidedly higher than some other notable events — including the 2018 reentry of China’s space station that put parts of the world on edge. The chance of debris hitting a human in that scenario was estimated to be less than one in a trillion, and no one was ultimately harmed.

The spacecraft currently in question is the now-defunct Van Allen Probe A, which NASA launched alongside a twin vehicle in 2012 to study the two cosmic bands of high-energy particles that are trapped in Earth’s magnetic field at altitudes ranging from about 400 to 93,300 miles (640 to 58,000 kilometres).

“The belts shield Earth from cosmic radiation, solar storms, and the constantly streaming solar wind that are harmful to humans and can damage technology, so understanding them is important,” NASA said in a Tuesday statement. The Van Allen probes mission “made several major discoveries about how the radiation belts operate during its lifetime, including the first data showing the existence of a transient third radiation belt, which can form during times of intense solar activity.”

The Van Allen Probe A — along with its twin, the Van Allen Probe B — studied the radiation belts for years longer than expected before concluding their mission in 2019 when the vehicles ran out of fuel.

End-of-life planning

From the outset, NASA intended to dispose of the radiation-studying spacecraft by allowing them to burn up in the atmosphere as they plummeted to Earth. It was understood that a fiery cauldron of physics would likely reduce the probes to trace fragments by the time they reach the ground.

Mission planners mapped out the probes’ return home when the spacecraft concluded its mission — conducting a few maneuvers designed to expel any remnants of fuel and confirm that the vehicles were in a position for atmospheric drag to slowly pull them out of orbit. That ensures the defunct spacecraft aren’t left to spend eternity flying uncontrolled through Earth orbit, where they could run the risk of colliding with active satellites or habitats such as the International Space Station.

Initially, NASA predicted the spacecraft would return home in 2034.

“However, those calculations were made before the current solar cycle, which has proven far more active than expected. In 2024, scientists confirmed the Sun had reached its solar maximum, triggering intense space weather events,” NASA said in a Tuesday statement. “These conditions increased atmospheric drag on the spacecraft beyond initial estimates, resulting in an earlier-than-expected re-entry.”

The Van Allen Probe B is also now on track to be dragged out of orbit before 2030.

The space agency’s policies require that vehicles launched by the U.S. reenter or be safely disposed of within 25 years of the mission’s end. Safe disposal can include deorbiting the spacecraft or positioning it in a graveyard orbit, or an area of space designated for abandoned spacecraft to linger in orbit.

Graveyard orbits have their own issues, noted McKnight. Leaving a spacecraft in one doesn’t completely alleviate the risks of in-orbit collisions, and any run-ins present the possibility of junk spewing into other areas where active satellites are operating.

In the case of the Van Allen Probes, reaching a grave yard orbit also would have expended precious fuel that was used to gather additional science.

In recent years, there have been calls from inside and outside NASA warning about the growing risks of spaceborne debris.

“There’s been a lot more awareness of the importance of this issue,” said Marlon Sorge, a space debris expert with the federally funded research group The Aerospace Corporation. Since the Van Allen probes were launched in 2012, “in that time there’s been increasingly more awareness of the need to try to mitigate what survives to the ground.”

It’s possible, Sorge said, that NASA may have designed the mission differently if it launched today — perhaps aiming to ensure no piece of the vehicle would survive reentry as many modern satellite operators do.

As the cost of spaceflight has been steeply reduced in the last couple of decades, the space debris issue has grown in scope and scale.

Recent headline-grabbing incidents have included a piece of garbage jettisoned from the International Space Station that unexpectedly survived reentry and pierced the roof of a home in Florida in 2024. Pieces of hardware from private rocket companies, including SpaceX and Blue Origin, have also turned up on beaches and private property across the world.

Such instances are actually fairly common, noted McKnight.

“We get about one object a week — a dead rocket body, another payload that isn’t maybe as high a profile as this. So that happens about once a week that some mass will survive to the ground,” McKnight said.