A SpaceX rocket hitting the moon reminds us to clean up our deep space junk


For the past seven years, a leftover piece of an old SpaceX Falcon 9 rocket has been orbiting Earth in a very wide orbit, with a fairly unremarkable time. But that’s all going to change on March 4, when this piece of rocket is predicted to accidentally crash into the far side of the moon. And according to the astronomer who first discovered this, it reminds us that we need to take better care of our clutter in deep space.

The doomed part is part of a rocket launched from Florida in February 2015. The vehicle brought up a particularly valuable satellite for the National Oceanic and Atmospheric Administration called DSCOVR, which tracks the sun’s solar winds to better predict space weather. To do its job properly, DSCOVR was designed to go to a very distant orbit, about 1 million miles from Earth. And to get the satellite there, part of SpaceX’s Falcon 9 — the top stage or second stage on top of the rocket — took the vehicle to an incredibly high altitude above Earth. Once the satellite was deployed, the upper stage was abandoned and left in its extremely high and elliptical orbit around the planet.

Now, after seven years of orbiting the Earth, the orbit of the upper stage will coincide with the moon in a coincidental fashion. It’s certainly not the first time a man-made object has collided with the moon’s surface: NASA has purposely sent rocket parts and spacecraft into the lunar dirt before. But this Falcon 9 could be the first piece of space junk to make an unplanned dive bomb on the moon, when it wasn’t there to begin with. While this won’t pose any problems for our planetary satellite, the incident does serve as a reminder to the space community that we may want to think of better ways to clean up our space junk — even the pieces that travel far into space.

“Ideally, this kind of junk would be removed a little more intelligently,” said Bill Gray, an astronomer and asteroid tracker who runs Project Pluto. The edge.

Gray was the first to find out earlier this month that the Falcon 9 would hit the moon, which was then reported by Ars Technica. He is one of the few people who has tracked the missile fragment since it was launched. After the DSCOVR mission, he and other amateur space trackers equipped with telescopes and cameras periodically observed the object every few weeks or months. After each sighting, Gray would update the stage’s projected orbit around Earth using a software program he developed over the past two decades for his company known as Project Pluto. Originally, the software was created to predict orbits for asteroids and small moons around distant gas giants. But recently, he’s been using the software to track the things humans have made around the Earth. “I reused it when this kind of junk started to become a problem,” Gray says.

Determining the Falcon 9’s path has been a bit complicated over the years. Space junk like this second stage can absorb sunlight and re-radiate it into space. That creates a gentle force that can push the object off its path, making it hard to predict where it’s going in the long run, Gray says. In addition, the stage made a brief flight past the moon on Jan. 5, and the gravity of such an encounter may slightly disrupt the orbit. “It’s kind of like a billiard ball bouncing off another billiard ball,” Gray says. “You know exactly where the billiard ball is going, but once it bounces back, it can go off at a slightly unexpected angle.”

The path of the Space Falcon 9 to hit the moon.
Image: Bill Gray/Project Pluto

Given all this, there were initially some minor uncertainties about the Falcon 9’s collision course. But Gray and others now have a pretty good idea of ​​what’s going to happen. After the second phase reaches its furthest point in its orbit in late February — known as apogee — it will fall back to Earth and cross paths with the moon instead. It will then hit the moon’s far side around 7:25 a.m. ET on March 4, traveling at about 2.58 kilometers per second — or about 5,771 miles per hour. Weighing in at about 4 tons, the impact should create a crater up to 20 meters or more than 65 feet wide. Gray says astronomers will know the exact angle and location of the impact more accurately in early February when they observe the object again.

The fear that this will harm our moon in some way is quite unfounded, as it is a dead rock that we have already hurled many objects at. During the Apollo missions, we crashed several rocket stages onto the lunar surface, and both the US and Russia sent many spacecraft to the moon to win the space race. NASA has also deliberately crashed objects into the moon to excavate the ground and see what materials lurk beneath, as the agency did during the LCROSS mission in 2009.

In fact, the Falcon 9’s impact could provide a similar opportunity for NASA to see what materials are beneath its surface. Gray says he would like NASA’s Lunar Reconnaissance Orbiter and India’s Chandrayaan-2 spacecraft — both orbiting the moon — to observe the aftermath. “They’re interested in looking into this,” Gray says, noting that some contacts have been in touch with the LRO team.

While there’s nothing to fear from the collision, Gray thinks it’s a good reminder that we need better protocols for clearing space debris — even the pieces left in super-high orbits. Most of the concern for space debris revolves around pieces left in lower orbits because they could threaten satellites or the International Space Station. Typically, companies like SpaceX will intentionally remove the second stages of their rockets when they go to lower orbits. On those occasions, SpaceX will deliberately point the object toward Earth at a very low angle so that it burns up somewhere above the ocean in our atmosphere. That way, large chunks are unlikely to survive the breakup, and those that do will fall over uninhabited areas.

But for missions that go to the moon or to extremely high orbits like DSCOVR, sometimes rocket stages are left in the wilderness after the launch is over. Even recently, when NASA launched its new space observatory, the James Webb Space Telescope, the Ariane 5 second stage that launched the spacecraft into orbit remained in space and is now orbiting the sun, Gray says. (There’s also a billionaire’s Tesla Roadster that currently orbits the sun and reaches as far as Mars, though it was purposely sent there.) And most space agencies and official tracking entities like the Space Force keep it. it’s not really full of tabs on these objects.

Gray says these high-altitude pieces of junk can still be a problem if left behind. Such objects are usually left in extremely elongated orbits around the Earth, and if they were to come back and hit our planet, they would enter much faster and at much more vertical angles to the atmosphere. That makes it more likely that certain pieces can survive the return. “If it comes in and hits Earth, there’s an admittedly very slim chance that a little bit will survive and collapse into the ground,” Gray says.

Such events are, of course, extremely rare and pose no realistic threat to humans at this time. However, Gray says he and others tracked a similar piece of space junk that entered the atmosphere over Sri Lanka in 2015, as well as two Chinese lunar rocket stages that re-entered over the Pacific Ocean. Ironically, he states that we might want to try on purpose discarding these stages on the moon instead of accidentally letting them hit the earth. That way we know where they’re going, and we could extract some scientific value from the crashes.

“It’s definitely better to bump it into the moon than bump it into the Earth,” Gray says, “both for safety reasons and because if it hits Earth, we don’t really get to know anything interesting.”

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