This unique re-entry is possible because of Salsa's unusual oval-shaped orbit. During its swing around the planet, which takes two and half days, the satellite strays as far as 130,000 kilometers (80,000 miles), and comes as close as just a few hundred kilometers.
Bruno Sousa, head of the ESA's inner solar system missions operations unit, said it had been crucial that Salsa came within roughly 110 kilometers during its last two orbits.
"Then immediately on the next orbit, it would come down at 80 kilometers, which is the region in space already within the atmosphere, where we have the highest chance (for it) to be fully captured and burned," he told a press conference.
When a satellite starts entering the atmosphere at around 100 kilometers above sea level, intense friction with atmospheric particles—and the heat this causes—starts making them disintegrate.
But some fragments can still make it back down to Earth.
Fear of 'cascading' space junk
The ESA is hoping to pinpoint where Salsa, roughly the size of a small car, re-enters the atmosphere to within a few hundred meters.
Because the satellite is so old, it does not have fancy new tech—like a recording device—making tracking this part tricky.
A plane will be flying at an altitude of 10 kilometers to watch the satellite burn up—and track its falling debris, which is expected to be just 10 percent of its original mass.
Salsa is just one of four satellites that make up the ESA's Cluster mission, which is coming to an end. The other three are scheduled for a similar fate in 2025 and 2026.
The ESA hopes to learn from these re-entries which type of materials do not burn up in the atmosphere, so that "in the future we can build satellites that can be totally evaporated by this process," Sousa said.
Scientists have been sounding the alarm about space junk, which is the debris left by the enormous number of dead satellites and other missions that continue orbiting our planet.
Last year the ESA signed a "zero debris" charter for its missions from 2030.
There are two main risks from space junk, according to the ESA's space debris system engineer Benjamin Bastida Virgili.
"One is that in orbit, you have the risk that your operational satellite collides with a piece of space debris, and that creates a cascading effect and generates more debris, which would then put in risk other missions," he said.
The second comes when the old debris re-enters the atmosphere, which happens almost daily as dead satellite fragments or rocket parts fall back to Earth.
Designing satellites that completely burn up in the atmosphere will mean there is "no risk for the population," Bastida Virgili emphasized.
But there is little cause for alarm. According to the ESA, the chance of a piece of space debris injuring someone on the ground is less than one in a hundred billion.
This is 65,000 times lower than the odds of being struck by lightning.
© 2024 AFP