A tumbling rocket stage resists precise modeling
A piece of human engineering, long adrift in the gravitational embrace between Earth and Moon, is about to complete its unplanned journey. A SpaceX Falcon 9 upper stage — stranded in deep space since the 2015 DSCOVR mission — will strike the lunar far side on March 4, 2022, ending seven years of silent wandering. What began as a consequence of depletion has become, in the patient way of science, an opportunity: the four-ton stage's known mass and velocity offer a rare window into how impacts carve the surfaces of worlds.
- A four-ton rocket stage, adrift since 2015, is on an unavoidable collision course with the Moon — and no one can stop it.
- The impact will vanish behind the lunar far side, invisible from Earth, creating a quiet drama that only orbiting spacecraft will witness.
- Astronomers like Bill Gray and Jonathan McDowell have tracked and confirmed the trajectory, though the tumbling, solar-buffeted stage still resists perfect prediction.
- NASA's Lunar Reconnaissance Orbiter and India's Chandrayaan 2 are positioned to capture the crater and potentially the collision itself.
- Scientists see the known mass and speed as a calibration gift — a chance to sharpen models of crater formation and read deeper into lunar geology.
Seven years ago, a SpaceX Falcon 9 carried the Deep Space Climate Observatory toward Lagrange Point 1, nearly a million miles from Earth. The mission succeeded — but the rocket's upper stage, too high and too fuel-depleted to return home, was left to wander in a long, looping path through the Earth-moon system. That wandering is almost over.
Satellite tracker Bill Gray of Project Pluto has calculated that the stage will strike the Moon's far side on March 4, 2022, at 7:25 a.m. Eastern time. Gray acknowledges the limits of modeling a tumbling object shaped by years of solar radiation pressure, but expects further observations to sharpen the prediction. Jonathan McDowell of the Harvard-Smithsonian Center for Astrophysics confirmed the finding plainly: an old second stage left in high orbit is going to hit the Moon.
The collision will be hidden from Earth, but not from science. NASA's Lunar Reconnaissance Orbiter and India's Chandrayaan 2 are both positioned to study the resulting crater. The stage's four-ton mass and impact speed of roughly 5,700 miles per hour create a rare, well-characterized data point for understanding how craters form and what they reveal about the Moon's geology.
SpaceX engineer John Insprucker offered a wry send-off, dubbing it the first 'Regolith Unplanned Disassembly.' It is SpaceX's first lunar impact, though NASA has walked this road before — most notably in 2009, when a deliberate crash at the lunar south pole revealed significant deposits of water ice. The Falcon 9 stage heads for quieter terrain, but its arrival will still leave its mark on how we understand worlds shaped by collision.
Seven years ago, a SpaceX Falcon 9 rocket lifted off from Cape Canaveral carrying the Deep Space Climate Observatory toward a gravitational sweet spot nearly a million miles away. The mission succeeded. The satellite reached its destination at Lagrange Point 1, where it has been studying Earth and the space weather environment ever since. But the rocket's upper stage never made it home.
After releasing DSCOVR into its distant orbit, the Falcon 9 second stage found itself too high and too depleted of fuel to return to Earth. Instead, it entered a long, looping trajectory through the Earth-moon system—a cosmic holding pattern that has lasted nearly seven years. That chapter is about to end. Satellite trackers led by Bill Gray, who runs Project Pluto, a software company serving astronomers, have calculated that the stage will collide with the lunar surface on March 4, 2022, at 7:25 a.m. Eastern time. The impact will occur on the moon's far side, at coordinates 4.93 degrees north latitude and 233.20 degrees east longitude.
Gray acknowledged the inherent uncertainty in such predictions. A tumbling rocket stage, buffeted by solar radiation pressure over years in space, resists precise modeling. "At a guess, the above prediction may be wrong by a degree or two minutes," he wrote. But he expressed confidence that additional observations in early February would refine the calculation significantly. Other astronomers have already confirmed his work. Jonathan McDowell, a satellite tracker at the Harvard-Smithsonian Center for Astrophysics, called it straightforward: an old second stage left in high orbit is going to hit the moon. "It's interesting, but not a big deal," he wrote on Twitter.
The impact will be invisible from Earth—the far side of the moon faces away from us—but that doesn't diminish its scientific value. NASA's Lunar Reconnaissance Orbiter and India's Chandrayaan 2 spacecraft, both in lunar orbit, will have the opportunity to study the crater and possibly image the collision itself. The Falcon 9 stage, weighing about four tons, will strike at 2.58 kilometers per second, or roughly 5,700 miles per hour. That combination of known mass and velocity provides a rare calibration point for understanding how impacts create craters and what they reveal about lunar geology.
SpaceX engineer John Insprucker marked the occasion with characteristic company humor, calling it the first "Regolith Unplanned Disassembly"—a play on the RUD acronym Elon Musk uses to describe rocket failures on Earth. It will be SpaceX's first lunar impact, though not the first in history. NASA deliberately steered Saturn V upper stages into the moon during the Apollo program. In 2009, the agency intentionally crashed an Atlas V upper stage into a lunar crater at the south pole, an impact that blasted out significant quantities of water ice and confirmed that the resource is abundant in the moon's polar regions. The Falcon 9 stage is headed for less dramatic terrain, but its arrival will still add to humanity's understanding of how worlds are shaped by collision.
Notable Quotes
It's interesting, but not a big deal— Jonathan McDowell, Harvard-Smithsonian Center for Astrophysics
The known momentum and energy of the object making the crater ought to help in calibrating the crater size vs. energy function— Bill Gray, Project Pluto
The Hearth Conversation Another angle on the story
Why does it matter that we know exactly when and where this thing hits?
Because spacecraft in lunar orbit can be positioned to observe it. If you know the time and place, you can point your instruments there and potentially capture images of the impact itself, or study the crater afterward.
So this is basically a free experiment?
Exactly. We know the mass of the stage, we know its velocity, and we'll be able to measure the crater it makes. That gives us real data about how impacts work on the moon—how energy translates into crater size. It's calibration data you can't easily get any other way.
Why couldn't they just bring the stage back to Earth like they do now?
In 2015, SpaceX hadn't yet figured out how to land the first stage. The upper stage went so high delivering DSCOVR that it didn't have enough fuel left to come home. So it's been drifting through space for seven years waiting for gravity to pull it down.
Is there any risk to Earth or the moon?
Not really. One four-ton piece of metal hitting an airless world isn't a concern. The moon has been absorbing impacts for billions of years. It's more about what we can learn from watching it happen.
Will we actually see it?
Not from Earth. It's hitting the far side of the moon, the side that always faces away from us. But the spacecraft orbiting the moon will have a front-row seat.