NASA's Lucy spacecraft is on its way to explore
the Trojan asteroids after launching from Cape Canaveral on October 16.
The Trojan asteroids are thought to be an undisturbed population
of fossils leftover from the formation of our Solar System.
And that's why the Lucy spacecraft was named after the famed hominid
Fossil, discovered in Ethiopia in 1974.
Just as Lucy, the Fossil advanced our understanding of human evolution.
Lucy the spacecraft aims to advance our understanding
of the Solar System's evolution.
To that end, Lucy will fly past seven of the Trojan asteroids,
which are trapped in Jupiter's Lagrange points.
Along its way out to the Trojans, Lucy will pass
a small asteroid in the main belt between Mars and Jupiter.
And that makes for a mission total of eight asteroid flybys
- more than any spacecraft has attempted before.
At least that's the plan.
But shortly after it separated from its rocket on October 16,
one of Lucy's two solar arrays failed to deploy and latch into place.
The arrays are designed to unfurl like a pair of Chinese fans.
Controllers got a confirmation signal that the first array
fully deployed and latched, but they never received
a similar confirmation about the second array.
NASA's said in a statement
that it looks like the second array only partially unfurled, but it's otherwise
generating almost as much power as the fully deployed wing.
So the good news is that the spacecraft is safe
and it's getting all the power it needs for the moment.
Because Lucy is drifting further away from Earth each day,
it needs to be able to autonomously point its solar arrays toward the Sun.
So the spacecraft was transitioned from its initial safe
mode into its cruise mode.
But Lucy will need to fire its main engine several more times
over the course of its mission in order to stay on a very complex flight path.
So naturally, the mission team would like to get that array fully
deployed and locked before Lucy begins any of its main maneuvers.
At this point, you might be wondering, Well, why didn't
they just use a radioisotope thermoelectric generator like they did
for the Cassini mission at Saturn and New Horizons at Pluto?
Well, the Lucy mission was originally conceived as being powered by an RTG,
but RTGs are dangerous, and NASA would rather not take a chance on a rocket
exploding in the atmosphere
and scattering toxic plutonium everywhere if they could avoid it.
Fortunately, solar panel technology has come a long way.
Juno demonstrated that a solar powered spacecraft
can operate as far as Jupiter's orbit.
As for Lucy, chances are they'll command it
to redeploy its second wing and see if it latches into place.
Right now, though,
mission controllers are still analyzing the telemetry to verify
that they fully understand
just exactly what the problem is before they take any further action.
So while they're figuring that out, I thought we'd take a closer
look at the Lucy mission, learn more about the Trojan asteroids, and understand how
the solar array problem may or may not impact the mission.
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Our Solar System is home to more than 1 million known asteroids.
Most of them orbit the Sun in the main belt between Mars and Jupiter.
We started to explore some of these asteroids up close in 1991,
when the Galileo spacecraft flew past two of them on its way to Jupiter.
Since then, spacecraft have visited
15 other asteroids and comets in the main belt.
Among them are JAXA's Hayabusa2 mission to Ryugu
and NASA's OSIRIS-REx mission to Bennu.
Both of these missions are bringing samples back to Earth,
but no mission has ever explored the Trojan asteroids.
These are two giant swarms that are clustered
around Jupiter's L4 and L5 Lagrange points.
Lagrangian points are the gravitational balance points
that exist between any two large bodies, like the Sun and a planet.
So if a small body, such as an asteroid, were placed at any of these points,
the gravitational forces
between the two larger bodies will cancel each other in a way that fixes
the body into the same relative position as the system orbits.
These points are labeled L1 through L5.
You might be wondering, If Jupiter has five Lagrange points,
why are the Trojans only found at two of them?
Well, it turns out that the first three Lagrange points are very unstable.
If an asteroid were placed there, it would quickly fall out of place
unless it were perfectly positioned at the Lagrange point.
It's like trying to get a marble
to sit precisely on top of a saddle without rolling off.
By contrast, the L4 and L5 points are more like the gravitational equivalent
of large hilltops on the edge of a giant merry go round.
If an asteroid starts to wander out of this region, the Coriolis force
comes into play and effectively pushes the asteroid back into a stable orbit.
The practical upshot is that the Trojans orbit around these two Lagrange points.
But how did the Trojans get there in the first place?
Well, it turns out their colors offer a clue.
Trojans range in color from gray to red. Gray trojans are similar in color
to the center asteroids that orbit between Jupiter and Neptune.
While the red Trojans resemble those of distant objects in the Kuiper belt,
so it's widely thought that these asteroids initially formed
in different regions of the Outer Solar System.
After the giant planets formed, they migrated
and scattered the asteroids in pretty much every direction.
Some of them got caught in Jupiter's L4 and L5 points,
and they've been stuck there ever since.
Well, that's the prevailing hypothesis.
But in order to know for sure, we need to explore the Trojans up close.
And that's why Lucy will visit several different Trojans
and compare them to each other.
But to reach the Trojans, Lucy must embark
on the craziest trajectory of any spacecraft in history.
Lucy launched on October 16 into an orbit that more or less follows Earth's.
A year from now, it will approach Earth to get a gravity assist,
followed by a second one in December 2020.
These maneuvers will propel Lucy toward Jupiter's orbit.
Along the way, Lucy will pass by the main belt asteroid
DonaldJohanson in April 2025.
This asteroid is fittingly named after the anthropologist
who discovered the Lucy Fossil in 1974.
This initial flyby will serve
as a kind of dress rehearsal for the Trojan encounters.
Lucy will enter the leading group of Trojans
a couple of years later in the summer of 2027.
It'll first fly past Euybates and its satellite
Queta. Eurybates is thought to be the largest surviving
chunk of a massive collision several million years ago.
It's also a C-type or carbonaceous asteroid.
C-type asteroids are the most common type of asteroid in the main belt,
but they're relatively rare among Trojans.
So naturally, that raises the question, How did a C type asteroid
like Eurybates end up getting mixed up with the Trojans?
About a month later, in September 2027, Lucy
flies past its second target, asteroid Polymele.
This is one of the smaller targets, so they'll have to take
as many pictures as quickly as possible.
Then it's on to another small asteroid Leucus for another photo frenzy.
And then, about seven months later, its final L4 flyby of asteroid Orus.
By this time, Lucy's falling back into the inner solar system.
In December 2030, it encounters Earth for its third and final gravity assist.
This sends Lucy back to Jupiter's orbit, but this time into the L5 swarm or its final encounter.
In March 2033, Lucy will pass a large
binary pair of asteroids called Patroclus and Menoetius.
These are two asteroids of similar size orbiting a common barycenter.
Now that's particularly interesting
because binary asteroids in the main belt are rare.
The closest you'll typically find is a relatively large
asteroid with a tiny companion satellite,
but large binary asteroids are quite common in the outer Kuiper Belt.
So it's possible that the Patroclus binary
formed in the Kuiper Belt and got flung into Jupiter's orbit.
To visit these asteroids.
Lucy takes a trajectory that's unlike anything we've ever seen before
to see what I mean. Take a look at this comparison.
We're hovering over the Sun and letting everything orbit.
Lucy's trajectory seems relatively straightforward, doesn't it?
But let's take a look at it from Jupiter's frame of reference.
Here, we're rotating the camera
to keep Jupiter and the Trojans in the same position of the frame.
In this view, the complexity of Lucy's trajectory becomes apparent
as it visits one swarm of asteroids and then the other. In this perspective,
it's as if Lucy is flying an enormous Figure eight pattern as a crisscrosses
the Solar System.
The trajectory is at once complex and elegant.
The thing about the Trojans is that
their orbits are very highly inclined to the ecliptic plane.
So the fact that.
Lucy can intercept so many of them by being at just the right place
at just the right time is amazing.
And you might be wondering, If Lucy is going to be in Jupiter's L4 swarm,
why not use the giant planet itself as a gravity assist instead of Earth?
Well, the fact is that illustrations like these fail to capture
just how vastly, hugely mind-bogglingly big space is.
The reality is that the closest Lucy will ever get to Jupiter
is right after its first gravity assist at Earth during its first flyby.
Lucy is traveling fast - between six and nine kilometers
a second. Despite taking twelve years to complete its mission,
The total amount of time Lucy will spend collecting flyby
data amounts to less than one day.
So each encounter will have to be carefully planned
to ensure it gets the maximum amount of science every time.
That's why Lucy is packing a suite of proven instruments
that have been adapted from other missions.
L'Ralph is actually two instruments and one it's MVIC color camera and LEISA
spectrometer will pick up the subtle color variations
in the visible and near-infrared parts of the spectrum,
and that will indicate where things like water and carbon
compounds are concentrated on the asteroid surfaces.
L'LORRI is Lucy's main telescope that takes high resolution black and white images.
It'll be used to count up the number of small versus large craters
on the asteroid surfaces, and that reveals the history of impacts.
It'll also be used to carry out
a search for satellites and possibly even ring systems
that are too close to be seen with any ground based telescope.
These two are based on the Ralph and LORRI instruments that New Horizons used
during its flybys of Pluto and Arrokoth.
L'TES is Lucy's third science instrument.
It measures the infrared radiation coming off the asteroids.
In particular, L'TES will compare the heat coming off
both the sunlit and the shadowed parts of the asteroid surface.
The difference in temperature between these regions will indicate
how dense or fluffy the surface material is.
L'TES is a direct copy of the OTES instrument used on OSIRIS-REx,
which used it to map the temperature of asteroid Bennu.
In addition to these three science instruments, Lucy makes use
of two of its own spacecraft subsystems to gather science data as well.
The terminal tracking cameras are normally used for navigation,
but they'll also take images of the asteroids during the flybys.
Lucy's high gain antenna is normally used for communication,
but during the flybys, the asteroid's gravity will exert
very subtle accelerations on the spacecraft.
Those accelerations will change Lucy's velocity
by just a few millimeters per second.
That will introduce a very subtle Doppler shift into the antenna signal.
Those Doppler shifts will be analyzed and allow the science team
to directly measure the density and mass of the asteroids.
Well, that's the plan,
at least. Right now, though, they need to figure out
what the nature of the solar panel
problem really is and what impact, if any, it'll have on the mission.
This design has been used on spacecraft like the Cygnus cargo ships
that visit the International Space Station
and on Mars landers such as Pheonix and InSight.
But because Lucy is going to the Trojan asteroids,
it'll become the most distant solar-powered mission ever flown.
And that's why its panels are each 7.3 meters in diameter. Near Earth.
They generate something like 18 kilowatts of power, but at its farthest
distance, their power output will fall to just 500 watts, believe it or not.
That's actually more power than the spacecraft will need at that point.
The panels were designed to be bigger than required in order to withstand small
micrometeorite impacts and still provide enough power to the spacecraft.
It's likely that even if the second panel cannot be fully opened,
there will still be enough power generated to fly the mission more or less planned.
If not, then NASA will just do what it's always done,
they'll figure out a workaround.
Remember the Galileo mission we talked about earlier?
It was supposed to open a 4.8 meter high gain antenna like a gigantic umbrella.
The antenna would have transmitted at 134,000 bits per second.
That's very high bandwidth coming all the way from Jupiter.
However, some of the ribs of the umbrella jammed.
Despite all attempts of freeing it, the high gain antenna simply wouldn't open.
Rather than give up, the entire mission was redesigned
mid-flight to use Galileo's low gain antenna.
The mission went on to become a huge success,
transmitting the highest resolution images of Jupiter's
moons at a rate of just ten bits per second.
Lucy's solar panel problem isn't great news,
but there's a solution, and NASA will find it.
By the way, Lucy's namesake fossil was named after the song
"Lucy in the Sky with Diamonds" that was written by the Beatles
and then vastly improved upon by William Shatner.
It turns out that Lucy's L'TES instrument uses a beam splitter
made of manufactured diamond. Coincidence?
Yeah, it is, but a really good one so we'll take it. A big thanks to my patrons for supporting
launch Pad Astronomy,
and I'd like to welcome John Rockefeller and Rudy Yadzi as my newest sponsors.
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Stay curious, my friend.