SpaceX will be getting to the moon a bit more than a month from now, far
earlier than expected.
But it is all by accident, and it will cause a bit
of a mess.
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SpaceX, the rocket company started by
Elon Musk, has
been selected by NASA to provide the spaceship that will take its astronauts
back to the surface of the moon. That is still years away.
Instead, it is the 3.6-tonne upper stage of a SpaceX
rocket launched seven years ago that is to crash into the moon March 4, based
on recent observations and calculations by amateur astronomers.
Impact is predicted for 7:25am Eastern time, and
while there is still some uncertainty in the exact time and place, the rocket
piece is not going to miss the moon, said Bill Gray, developer of Project
Pluto, a suite of astronomical software used to calculate the orbits of
asteroids and comets.
An artist’s concept of DSCOVR. (Photo: National Oceanic and Atmospheric Administration)
“It is quite certain it’s going to hit, and it will
hit within a few minutes of when it was predicted and probably within a few
kilometers,” Gray said.
Since the beginning of the Space Age, various
human-made artifacts have headed off into the solar system, not necessarily
expected to be seen again. That includes Musk’s Tesla Roadster, which was sent
on the first launch of SpaceX’s Falcon Heavy rocket in 2018 to an orbit passing
Mars. But sometimes they come back around, like in 2020 when a newly discovered
mystery object turned out to be part of a rocket launched in 1966 during NASA’s
Surveyor missions to the moon.
Gray has for years followed this particular piece of
SpaceX detritus, which helped launch the Deep Space Climate Observatory for the
National Oceanic and Atmospheric Administration on February 11, 2015.
That observatory, also known by the shortened name
DSCOVR, was headed to a spot about 1.5 million kilometers from Earth where it
can provide early warning of potentially destructive eruptions of energetic
particles from the sun.
DSCOVR was originally called Triana, an Earth
observation mission championed by Al Gore when he was vice president. The
spacecraft, derisively called GoreSat, was put into storage for years until it
was adapted for use as a solar storm warning system. Today it regularly
captures images of the whole of planet Earth from space, the original purpose
of Triana, including instances when the moon crosses in front of the planet.
Most of the time, the upper stage of a Falcon 9
rocket is pushed back into Earth’s atmosphere after it has delivered its
payload to orbit, a tidy way to avoid cluttering space.
But this upper stage needed all of its propellant to
send DSCOVR on its way to its distant destination, and it ended up in a very
high, elongated orbit around Earth, passing the orbit of the moon.
That opened the possibility of a collision someday.
The motion of the Falcon 9 stage, dead and uncontrolled, is determined
primarily by the gravitational pull of the Earth, the moon and the sun and a
nudge of pressure from sunlight.
Debris in low-Earth orbit is closely tracked because
of the danger to satellites and the International Space Station, but more
distant objects like the DSCOVR rocket are mostly forgotten.
“As far as I know, I am the only person tracking
these things,” Gray said.
While numerous spacecraft sent to the moon have
crashed there, this appears to be the first time that something from
Earth not
aimed at the moon will end up there.
On January 5, the rocket stage passed less than
10,000km from the moon. The moon’s gravity swung it on a course that looked
like it might later cross paths with the moon.
Gray put out a request to amateur astronomers to
take a look when the object zipped past Earth in January.
One of the people who answered the call was
Peter Birtwhistle, a retired information technology professional who lives about 80km
west of London. The domed 40cm telescope in his garden, grandly named the Great
Shefford Observatory, pointed at the part of the sky where the rocket stage
zipped past in a few minutes.
“This thing’s moving pretty fast,” Birtwhistle said.
The observations pinned down the trajectory enough
to predict an impact. Astronomers will have a chance to take one more look
before the rocket stage swings out beyond the moon one last time. It should
then come in to hit the far side of the moon, out of sight of anyone from
Earth.
NASA’s Lunar Reconnaissance Orbiter will not be in a
position to see the impact live. But it will later pass over the expected impact
site and take photographs of the freshly excavated crater.
Mark Robinson, a professor of earth and space
exploration at Arizona State University who serves as the principal
investigator for the Lunar Reconnaissance Orbiter’s camera, said he expected
3.6 tonnes of metal, hitting at a speed of some 2,500 meters of second, would
carve out a divot 10 to 20 meters wide, or up to 65 feet in diameter.
That will give scientists a look at what lies below
the surface, and unlike meteor strikes, they will know exactly the size and
time of the impact.
India’s Chandrayaan-2 spacecraft, also in orbit
around the moon, might also be able to photograph the impact site.
Other spacecraft headed toward the moon this year
might get a chance to spot the impact site — if they do not also end up making
unintended craters.
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