NASA's Double Asteroid Redirect Test mission, or DART, is on its way to test whether or
not we can defend ourselves from an incoming asteroid. It was launched in the early morning
hours of November 24th aboard a SpaceX Falcon 9 rocket from Vandenberg Space Force Base
in California.
DARTs destination is the asteroid Didymos and in particular, its satellite Dimorphos.
Since this is NASA's first planetary defense mission, DART won't explore the asteroid so
much as crash into it. The idea is pretty straightforward; if an asteroid were on a
collision course with Earth, the best thing to do would be to change its direction so
that it misses us. There's a number of ways we could do this. One idea would be to set
off a nuclear weapon either right next to the asteroid or just below its surface to
let the blast push the asteroid out of the way.
Another would be to fly a spacecraft just in front of the asteroid and use their mutual
gravity to alter the asteroid's course. This is called the Gravity Tractor. Yet another
idea would be to fly a giant fresnel lens to concentrate sunlight on one part of the
asteroid and let the vaporizing material act as a thruster.
Those are just some of the redirection ideas that have been proposed, but the most technologically
feasible way of deflecting an asteroid would be to simply crash a spacecraft into it. And
this idea is called Kinetic Impact Deflection. Now, this is not the first time we've deliberately
crashed a spacecraft into something.
In 2005, NASA's Deep Impact spacecraft fired an impactor into Comet Tempel 1 in order to
dig up fresh ice and dust from underneath the comet's surface. The mission taught us
a lot about comets in general, but it wasn't designed to test just how much we could deflect
an object from its original orbit.
And that's because Tempel 1 takes 5.6 years to orbit the Sun once, so it would have taken
a lot of precision monitoring over a long period of time to assess just how much the
comet's path was deflected. So DART will instead be impacting Dimorphos, which is a satellite
of the larger asteroid Didymos. Dimorphos orbits Didymos about once every twelve hours.
Since the impact will change the amorphous orbital period, we should be able to measure
that change relatively quickly. Moreover, Dimorphos is gravitationally bound to Didymos,
so it's not going to fly off and hit Earth or anything.
Now, to be clear, there is no threat of an asteroid hitting Earth any time soon, at least
none that we're currently aware of. But as of today, we know of nearly 28,000 Near-Earth
Objects, or NEOs. Most of these are asteroids that either approach or cross Earth's orbit,
so they're definitely worth paying some attention to.
Most of these objects are so small they would burn up in our atmosphere. That might make
for a spectacular meteor, but they're otherwise harmless. [crashing sounds, glass breaking,
car alarms, people shouting in russian] Mostly harmless. Of those 28,000 near-Earth asteroids,
one third of them are about 140 meters or larger.
That's considered large enough to do some real damage, especially if they were to hit
a populated area. These larger NEOs are classified as Potentially Hazardous Asteroids or PHAs.
It's estimated that Earth is struck by one of these asteroids every few thousand years
or so.
So while there's no threat from an impact now or in the foreseeable future, it's not
really a matter of if one of those asteroids would ever hit us, but when. So now's as good
a time as any to test our ability to redirect one of these asteroids.
Now you might think it should be pretty easy for DART to hit Dimorphos and alter its orbit.
Yet when DART reaches Dimorphos, it'll be more than 11 million kilometers from Earth
and will hit the asteroid at over 15,000 miles per hour.
That's too far and too fast to be controlled from Earth, so DART will have to complete
its mission autonomously with a little help from a CubeSat. So today we're going to talk
about the DART mission in some detail and see just how this mission is going to work.
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Didymos is a near Earth asteroid on an eccentric orbit between Earth and Mars, it's inclined
by about three degrees of the ecliptic. In 2003, Didymos closeed to within 7.2 million
kilometers during the encounter. Astronomers used the Arecibo Radio Observatory to get
a rough idea of the asteroid's size and shape.
They also discovered its satellite Dimorphos. The radar data indicated that the larger Didymos
was roughly 780 meters across and likely widened around its equator, much like the asteroids
Bennu and Ryugu. Dimorphos is estimated at 160 meters across and is likely elongated.
It's expected that these two asteroids are tidally locked to each other, with one side
facing the other at all times. But we don't know that for sure. Nor do we know the exact
size or shape of either asteroid.
And just as importantly, we don't know the exact composition of Dimorphos either. It
could be a single solid chunk of rock or more likely, a rubble pile of smaller rocks held
together by gravity. In early October of 2022, Didymos will approach to within 11 million
kilometers of Earth.
That's why DART launched on November 24th in 2021 so that it has time to catch up with
the asteroid at its closest approach that will allow telescopes on Earth to see if there
are any visible brightening due to the impact.
So here's the plan. Dimorphos orbits Didymos at a distance of 1.2 kilometers, completing
an orbit once every eleven hours and 55 minutes. Ideally, DART's impact will slow down Dimorphos'
orbit by just a few centimeters per second. That might not seem like much, but it should
be just enough for Dimorphos to fall slightly closer to Didymos and shorten its orbital
period by a few minutes. Since Didymos is an eclipsing binary asteroid, telescopes on
the ground will be able to measure this change in orbit by comparing the timing of eclipses
before and after impact.
In principle, all of this seems pretty straightforward. But then you have to remember that all of
this will be happening 11 million kilometers from Earth at speeds of several kilometers
a second. There's no way to navigate this impact from the ground.
That means DART has to find Dimorphos and hit it autonomously. To do that, DART carries
the Didymos Reconnaissance and Asteroid Camera for Optical navigation, or DRACO, as its sole
imaging payload. It sendds its high resolution imagery into the Small Body Maneuvering Autonomous
Real-Time Navigation or SMART-Nav system. SMART-Nav will use the DRACO imagery to identify
and distinguish Dimorphos from Didymos and then automatically maneuver the spacecraft
during its last four hours before impact. But DRACO isn't going to be the only imaging
system used on this mission. About ten days before impact, DART will launch the Light
Italian CubeSat for Imaging Asteroids or LICIACube. LICIACube was built by the Italian Space Agency
and will monitor DART's impact and examine the crater afterward. To do that, Leach a
cube is equipped with two camera systems.
The LICIACube Unit Key Explorer, or LUKE, and the LICIACube Explore Imaging for Asteroid,
or LEIA. Yeah, those backrooms, anyway, LICIACube will use its onboard thrusters to adjust its
trajectory such that it passes by Dimorphos about three minutes after darts impact, and
that will allow it to view the ejecta cloud and possibly glimpse the impact crater. Not
only would that imagery just be insanely awesome, but it would reveal details of how much material
was kicked out, how fast it was ejected and in what direction. And that information can
further help characterize the momentum exchanged between DART and the asteroid and thus tell
us how effective the kinetic impact was at deflecting Dimorphos. And as an added bonus,
LICIACube will obtain imagery of the backside hemispheres of both asteroids, and that's
something that DART will never see. Now, all of this will take place in October of 2022.
DARTs got some time to kill between now and then, so it'll be demonstrating several other
new technologies along the way.
For example, its Rollout Solar Arrays, or ROSA, are a new design that are lighter and
more compact than traditional arrays. The ROSA design was first tested on the International
Space Station in 2017, and DART is the first planetary spacecraft to fly the new arrays.
By the way, as an aside, those arrays did successfully deploy. Lucy, I'm looking at
you. One of the ROSA arrays will also carry a new Transformational Solar Array design
demonstration. TSA uses a combination of high-efficiency solar cells and reflective concentrators to
generate three times more power output than current array technology.
So if this works out, future arrays can be made smaller and lighter for inner solar system
missions. Or they could support missions in the outer solar system without having to rely
on nuclear power. DART is also demonstrating NASA's Evolutionary Tenon Thruster Commercial,
or NEXT-C.
This is an advanced ion propulsion system that accelerates ions formed in xenon gas
through an electrically charged grid. Now, the thrust generated by this engine is very
low, but it can be sustained for a much longer time than a chemical rocket.
And this makes ion engines ideal for long duration, deep space missions. NEXT-C offers
improved efficiency and thrust over the current ion designs. Since it's a technology demonstrator,
DART will primarily use its hydrazine thrusters for propulsion. But NEXT-C could find its
way on to future missions if everything goes well.
Now, the DART mission is operated by NASA's Office of Planetary Defense, which, by the
way, sounds like a really cool place to work. But they're not on their own as far as saving
the world is concerned. They're also being joined by the European Space Agency, who are
collaborating with their Hera mission, which will launch in 2024 and arrive at Didymos
in 2026. By that time, the outgassing and dust from the DART impact will have long settled,
so that will allow Hera to assess the damage and build up a high resolution visual, laser,
and radio map of Dimorphos. That may not sound as sexy as the DART Impact Mission, but Hera
will effectively turn DART's experiment into the first well-understood planetary defense
technique. And that's certainly going to be a much better technique than sending a bunch
of oil drillers to blow up an asteroid with a nuke.
Now, if you haven't seen the movie Armageddon, do yourself a favor and don't. It's the dumbest
movie ever made. Thanks so much to my patrons for their continued support, and I'd like
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