The distances between stars are so vast, it's hard to wrap your mind around it.
Even our far flung Voyagers have barely reached interstellar space, and would take tens of
thousands of years to get to even the nearest star.
But scientists and engineers are considering what it would actually take to send a spacecraft
to another star.
It's called Project Dragonfly, and would use existing or near future technologies to
send a 3,000 kg spacecraft to Alpha Centauri within 100 years.
We're in the golden age of exoplanet discovery, with thousands and thousands of new planets
already discovered, and the pace is just picking up.
But the sad reality is that we'll never know much more about these planets than radial
velocity measurements, or the dimming of light from the parent star.
We can know the mass or rotation rates, but for the foreseeable future, we won't get
much more than a couple of blurry pixels.
We want a closer look.
We want to send a probe from here to there, within our lifetimes, if possible, to see
what those other worlds look like, up close.
We want to send interstellar spacecraft.
Several groups considering this kind of mission are investigating laser-sails as a method
or propulsion, using the momentum of photons to accelerate a spacecraft.
The most famous right now is Breakthrough Starshot, which wants to create lots of lots
of tiny spacecraft accelerated by lasers.
But each one won't be able to send much of a payload to another star.
But could we send a larger probe across these vast distances?
Let's talk about Project Dragonfly.
Before I go into this, I'm talking about Project Dragonfly, the interstellar spacecraft,
and not Project Dragonfly, the Google initiative to make a search engine for China.
And I'm definitely not talking about the secret air force project to replace fighter
planes with genetically modified super-dragonflies.
I've already said too much.
In 2014, the Initiative for Interstellar Studies announced a student competition called Project
Dragonfly, where various teams would propose interstellar mission designs using light-sail
laser propulsion systems.
Four finalist teams were chosen, and a winning team from the Technical University of Munich
was chosen.
Their proposal is different from the Breakthrough Starshot program that I'm sure you're
familiar with, which would send a vast armada of tiny probes at relativistic velocities.
Instead, this design would include a much more massive probe capable of being accelerated
up to 5% the speed of light, but also deploy a magnetic sail to slow itself down at its
destination and do a more comprehensive survey of a place like Alpha Centauri.
For acceleration, the spacecraft would use a laser beaming photons at a solar sail.
Traveling at high velocity requires an enormous amount of fuel, but solar sails don't need
to carry any fuel.
Instead, the momentum from photons bouncing off a reflective film imparts the velocity.
The speed you can reach depends on the size of the sail, and the power of the laser you're
using to accelerate it.
They calculated that a 100 gigawatt laser could provide enough of a kick to accelerate
a 2000 kilogram probe attached to a 750 kilogram sail at 5% the speed of light.
Just to give you some comparisons.
NASA's New Horizons spacecraft has a mass of about 500 kilograms, while Cassini has
a dry mass of about 2,500 kilograms.
So imagine a spacecraft somewhere in between.
The researchers proposed building a satellite that would orbit at the Earth-Sun L1 Lagrange
point, which is a relatively balanced spot in between the Earth and the Sun.
The satellite would be equipped with huge solar arrays that would gather up the radiation
from the Sun and use that to fire a 100 gigawatt laser.
The most powerful laser ever built is at the Laser for Fast Ignition Experiments at Osaka
University Japan.
In 2015, it fired for a fraction of a second, blazing with 2 petawatts.
That's 2000 trillion watts.
Which if you do the math is 20,000 times more powerful than the 100 gigawatt laser that
Project Dragonfly calls for.
Super powerful lasers are in the works across the world, such as the National Ignition Facility
in California, the CoReLS laser in South Korea, and the Vulcan laser in the UK.
And a laser with 10 times more power is being built at the Extreme Light Infrastructure,
a European consortium.
Creating a laser that fires at 100 gigawatts is feasible with the technology we have today,
of course, building it in space would be a whole other challenge.
When it was time to set off for Alpha Centauri, the satellite would deploy the interstellar
probe, which would unfurl its solar sail measuring 30 kilometers across made of a graphene monolayer.
For the beginning of its journey, the probe would use the light pressure from the Sun
for acceleration.
Then it would make planetary flybys, using the gravity of the planets to put it into
the right flight direction towards Alpha Centauri.
Once it was going in the right direction and more than 2 astronomical units from Earth,
the laser would fire at the probe for 3.9 years, accelerating it on its journey.
Over the course of the acceleration phase, it would reach 5909 astronomical units from
the Sun, or about 0.1 of a light year.
It's a colossal distance from a human engineering point of view, but still a tiny part of the
total trip.
Over this time, the laser would continue to adjust its focus so that the beam continues
to fall on the sail.
Pointing the laser will become a greater and greater challenge, even more challenging that
pointing space telescopes like James Webb or Hubble.
This is made even more complicated by the time it takes light to get to the probe.
The laser will take more than a month to reach the probe, and any targeting adjustments will
need to be communicated back to Earth and take another month.
Imagine waiting a month to hear "a little to the left".
And I'm sure you can imagine how dangerous a laser like this might be if pointed at Earth.
One idea would be to put the laser at the Lagrange point on the far side of the Sun,
where it couldn't be used as a weapon against Earth.
Now traveling at 5% the speed of light, the probe ejects its solar sail.
Then there would be decades and decades of waiting as the spacecraft cruised for 81.5
years.
The engineers who built and launched the probe would die.
Generations would come and go in between, and finally, and new team would be ready to
watch over the next phase, arrival at Alpha Centauri.
And we'll get to that in a second, but first I'd like to thank:
Brodie McLoed Dehavilland Mosquito
Balash Suhajda
Zachary Fluke Jim O'Leary
Gertrude Braden Jeremy Kerwin
And the rest of our 808 patrons for their generous support.
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Bend their minds: As I said earlier, the key distinction between
Project Dragonfly and other mission concepts to Alpha Centauri is the mass - this is a
seriously big spacecraft - and the ability to decelerate once it reaches its destination.
And it'll do this with a magnetic sail.
Stars like the Sun are constantly blasting out charged particles as stellar winds.
In fact, the interstellar medium, the vast gulfs between stars, is made up of all the
particles fired out by all the stars in the galaxy.
A magnetic sail works by creating drag against this interstellar environment.
Think of a parachute, but for space itself.
The spacecraft would deploy a huge loop of superconducting wire 35,368 meters in diameter.
This is one of the most challenging engineering elements right now.
To make a superconducting wire that would only weigh 1000 kilograms would be at the
very limits of our current capability.
Over the next 20 years, this loop would drag against the interstellar medium, slowing down
the spacecraft's velocity.
As it gets slower and slower, the sail provides less drag, but everything will have been timed
so that it arrives within the solar wind bubble of Alpha Centauri at exactly the right time.
As it gets closer and closer to the star, the stellar winds provide the most deceleration.
When it reaches the inner planets, it will have decelerated enough that it can now just
maneuver itself to any place it wants within the system.
Humanity would now have a fully operational interstellar probe ready to explore another
star system, sending back the same kinds of photographs and scientific data that we've
become spoiled with here in the Solar System.
Alpha Centauri is a big place, with twin stars like our Sun and the smaller red dwarf Proxima
Centauri.
So many places to visit.
In fact, so many scientific mysteries that choosing the spacecraft instruments would
be almost impossible.
Instead of sending a single spacecraft, it might be best to send multiple probes with
all the different instruments you would need to fully analyze whatever mysteries are encountered.
Once the laser system had accelerated its first probe, it could be used to send out
a second, third and so on.
Every 3.7 years, another interstellar probe would be on its way to a new destination,
beyond the Solar System.
I really want humanity to explore other stars.
Even if it doesn't happen in my lifetime, it would be an incredible accomplishment.
It would make a vast, endless Universe seem a little smaller.
I hope we do it.
I really enjoyed reading the Project Dragonfly paper, and I think you'll get a lot out
of it.
I'll put a link to it in the show notes.
What do you think?
Let me know your thoughts in the comments.
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