NASA's RHESSI satellite crashed to the Earth after more than 20 years in space

Before Chris Pratt was guarding the galaxy in the Marvel Cinematic Universe or saving Princess Peach in The Super Mario Bros. Movie (now in theaters), he had a gig as a world-saving meteorologist in the SYFY original movie Path of Destruction. When a swarm of nanobots are accidentally released into Earth’s atmosphere, they start demolishing absolutely everything in their path. That’s probably where the name of the movie came from!

After attempts to murder the swarm with fighter jets fail, authorities do what authorities always do, they plan to kill it with a thermonuclear bomb. That’s where Pratt’s meteorologist character comes in. Working alongside reporter Katherine Stern (Danica McKellar) and Colonel Thomas Miller (Franklin Dennis Jones), he flies an experimental aircraft into the storm to detonate an EMP device and save the world. Nuclear winter having been narrowly avoided, the nanobot swarm falls to the ground, ending their reign of terror in thousands of tiny craters.

In the real world, we’re dealing with a different sort of mechanical swarm in the sky, and sometimes one or two of its members makes a fiery attack on our planet. Despite only having been in space for less than a century, we’ve already littered the area around our planet with a growing cloud of debris. At present, more than 27,000 pieces of space junk are being tracked by the Department of Defense, and that’s only the pieces big enough for them to keep track of. NASA estimates there are more than 100 million bits of orbital debris circling the Earth at 17,500 miles per hour, all the time. And any one of them could do enough damage to punch through a person like a gunshot and even damage or destroy a spacecraft. Last week, one of the biggest pieces of space junk made a run at Earth, and was destroyed in the process.

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NASA’s Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) was a solar flare observatory launched on Feb. 5, 2002. Its goal was to study particle acceleration and energy release during solar flares and associated coronal mass ejections (CME), from low-Earth orbit.

RHESSI was in continuous operation from 2002 until we lost communication with it on April 11, 2018. It was officially decommissioned five days later, ending a 16-year mission during which RHESSI documented more than 100,000 distinct solar events. Images of everything from the smallest microflares to the most powerful bursts are helping scientists refine their understanding of stellar mechanics. After decommissioning, RHESSI remained in a stable orbit, circling the planet under the power of its remaining momentum, until last week when it crashed into the planet and burned up in the atmosphere.

WHERE DID RHESSI COME DOWN?

Figuring out where a spacecraft might come down requires understanding how orbits work and how they degrade. At their foundation, orbits are dependent on speed. Even outside of the atmosphere, the Earth’s gravity is constantly pulling spacecraft toward the ground, and the only way to stop that from happening is to run fast enough to stay ahead of it. Satellites aren’t flying so much as they’re falling toward the planet and just keep missing. That’s why the International Space Station and other satellites have to do regular burns to stay at the right speed (altitude). Keeping a spacecraft in orbit is a matter of getting it up to the right velocity and never letting it slow down. It’s basically Speed rules.

Unfortunately, no one called Keanu for help, the 660-pound RHESSI craft slowed down below the cosmic equivalent of 50 miles per hour, and then it exploded. Sort of. When a spacecraft can no longer be maintained (as is the case when communications are lost), it just continues flying in the same direction it was going. For some satellites, that means circling the Earth for decades or centuries, but no orbit is perfect. Small changes over long periods of time converge to push a craft farther or nearer the planet. If the orbit degrades away from the planet, a satellite will eventually cut itself loose from Earth's gravitational pull and spin off into deep space. That’s probably the ultimate fate of the Moon. By contrast, when a spacecraft is nearby in low-Earth orbit, it’s practically guaranteed to come down.

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Tiny interactions with thin wisps of atmosphere create drag and slow a satellite down. As we’ve already learned, a slower speed means a lower altitude. That means more atmospheric interaction and more drag. Which means a slower speed and a lower altitude and… you get the picture. Once a satellite feels the warm caress of the atmosphere, it’s doomed without intervention. That’s what happened to RHESSI.

The spacecraft re-entered the Earth’s atmosphere at 8:21 p.m. ET on April 19, more than two decades after it launched. It pierced the sky over the Sahara Desert at 21.3 degrees north latitude and 26 degrees east longitude, give or take. If its instruments had still been working, the heat from the atmosphere would have been the last flare of energy it ever detected. NASA expects that most, perhaps even all, of the spacecraft burned up. But it’s possible a few pieces of the craft made their way to the ground. In the end, RHESSI died the way it lived: in uncomfortably close proximity to a fiery explosion.

Catch Path of Destruction, streaming now on SYFY.