An interesting fragment of modern space exploration will soon strike the farside of the Moon. Recent observations, combined with calculations made by Bill Gray of Project Pluto have shown that a spent Falcon 9 rocket upper stage will strike the lunar surface on March 4th around 7:26 a.m. EST (12:26 UT) near the edge of Hertzsprung Crater.

The Impact

Unfortunately, because the unintentional impact will occur on the lunar farside, it won’t be visible for Earthbound observers. Astronomer Gianluca Masi and the Virtual Telescope Project will, however, feature two viewing sessions of the Falcon 9 booster pre-impact, one on February 7th and another on February 8th.

Gray first noticed the upcoming encounter in early 2022: A close flyby that took the booster within 9,600 km of the Moon on January 5th set it up for impact in March. Gray then put out an appeal to the amateur astronomy community via the Minor Planet Mailing List (MPML) to observe the errant booster in an effort to pin down its exact orbit. The stage is in a wide-ranging Earth orbit that currently takes it out beyond the orbit of the Moon.

Keep in mind, relatively lightweight objects like empty rocket boosters are more at the whim of the solar wind’s push than are solid asteroids. Plus, the booster appears to be tumbling. But at this point, an impact on the lunar surface is certain, though the timing may vary by a minute or so as may the exact location (by a few kilometers). Additional observations in February will help further pin down the impact’s time and location.

The Falcon 9 upper stage was part of SpaceX’s launch of NASA’s Deep Space Climate Observatory (DSCOVR) in 2015. DSCOVR was sent to a heliocentric orbit between the Sun and Earth, at the L₁ Lagrange point, which affords a fully lit view of Earth’s Sun-facing side.

Though we won’t see the booster’s impact in real time since it’s occurring on the farside, it’s quite possible that NASA’s Lunar Reconnaissance Orbiter or India’s Chandrayaan 2, both currently orbiting and imaging the Moon, could see the crater that results from the impact.

A Brief History of Things Hitting the Moon

Though lots of Space Age hardware has hit the Moon over the years, this is the first time we know of that a human-launched space artifact on a non-lunar mission has unintentionally hit the Moon.

The very first object to reach the lunar surface was the Soviet Union’s Luna 2 on September 13, 1959. Discarded Apollo-era boosters often also hit the Moon, and NASA’s Lunar Reconnaissance Orbiter (LRO) has documented the resulting scars.

Sometimes, discarded boosters end up as “quasi-moons” instead. A spectrum of J002E3, a quasi-moon spotted in 2002, showed the signature of titanium dioxide paint, which helped astronomers determine it to be the Apollo 12 Saturn V third-stage booster. Observers also recently recovered another quasi-moon, which turned out to be the Surveyor 2 rocket booster.

And sometimes, missions have even sent boosters toward the Moon intentionally, for the sake of science. The Lunar Crater Observation Sensing Satellite (LCROSS) observed its spent Centaur upper stage as it hit Cabeus Crater in 2009, providing data that helped scientists deduce the presence of water ice on the Moon.

The LCROSS mission is a useful point of reference because its impact velocity was about the same as that calculated for the Falcon 9’s upper stage, about 2.5 kilometers per second (5,500 mph). But while LCROSS’s Centaur upper stage weighed in at 2,300 kg (5100 pounds), the Falcon 9 upper stage has almost twice the mass, at 3,900 kg.

However, it’s quite possible that unintentional impacts have occurred in the past, since boosters leaving Earth often remain in space rather than reentering the atmosphere.

“There’re at least 50 objects that were left in deep Earth orbit in the 1960s, ’70s and ’80s that were just abandoned there,” said Jonathan McDowell (Center for Astrophysics, Harvard & Smithsonian) told the AFP News Agency. “Now we’re picking up a couple of them . . . but a lot of them we’re not finding and so they’re not there anymore. Probably at least a few of them hit the Moon accidentally and we just didn’t notice.”

With the launch of a fleet of lunar missions this year, the Moon is about to become a busy place. SpaceX is actually launching the first Commercial Lunar Payload Services flight for Intuitive Machines and their Nova-C lander this summer. It’s ironic that SpaceX will actually already reach the Moon on March 4th, just maybe not the way they originally intended.

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