If we’re ever going to explore and eventually colonize the galaxy, we’re going to need
functioning propulsion systems to do it.
This goes for the nearest star, or the other side of the Milky Way.
So here are 10 hypothetical interstellar propulsion systems we might some day use to travel interstellar
space.
Number 10.
Light Sails
Light sails at their simplest are sails that function not on wind, but on light pressure.
Lasers stationed on earth, or in space, can exert pressure on sails.
Sails in general are ancient ideas, and we have lasers so out of all the entries on this
list, we are closest to realizing this one.
In fact, there are multiple programs looking to build and use laser-driven lightsails,
including Breakthrough Starshot, which looks to send a swarm of microprobes attached to
light sails to Alpha Centauri at as much as 20 percent of the speed of light, and get
them there in just two decades.
However, scaling this up to manned capability presents significant challenges.
But as a means of exploring nearby stars, if programs like Breakthrough Starshot are
successful, interstellar exploration may begin within the lifetimes of people alive today,
though one could already argue that we’re doing that using instruments from Voyager
to study the conditions of the fringes of the interstellar medium.
Number 9.
Nuclear Pulse Propulsion
Over the decades there have been several proposals to build spacecraft accelerated by nuclear
detonations to reach high enough speeds for realistic interstellar travel.
The concept is simple, build a spacecraft with a blast shield at the back and then periodically
drop nuclear bombs out of the back of the ship, detonate them, and that in turn pushes
the space craft along.
Increasing public distaste for nuclear projects and nuclear test bans sidelined work in the
field of nuclear pulse propulsion, but it does provide us with a future means of interstellar
travel.
And, nuclear detonations in space aren’t the problem that they are here on earth, space
is already full of sources of radiation, though launching the materials off of earth to fuel
such a spacecraft does pose risk, as is often pointed out when NASA launches radioactive
isotope powered probes such as the curiosity rover.
This type of propulsion is, in principle, something that current technology is close
to being able to do.
Number 8.
Starseed
This option is effectively a nanoprobe gun.
Using a 1000 kilometer long hollow tube lined with electrodes, exploratory nanomachines
could then be electrostatically launched at very high speed, up to one third of the speed
of light.
This puts a one way trip to the alpha centauri system at roughly 13 and a half years.
That’s fast, and the main advantage is that the researchers sending these kinds of probes
would get to see the fruits of their research within their lifetimes.
There are two downsides to this method however, number one would be the tube itself.
Given it’s length, the tube would be difficult to keep straight and would need to be kept
well away from gravitational sources in space to keep the nanomachines from impacting the
tube while being accelerated.
It’s likely that the materials to create this are yet to be fully developed.
The other issue is that nanotechnology is generally still in its infancy, so this method
lays at least decades off.
But one can also imagine many types of hypothetical nanoprobes, such as modular devices that assemble
into a larger probe upon reaching their destination.
Or von neumann probes that can self-replicate on site, or build custom equipment without
having to return to earth.
How far this scales up, or if this could ever be used to do more, such as 3d print custom
humans on site to colonize a planet remains to be seen in the relatively far future.
Number 7.
No Hurry Propulsion and Dyson’s Slingshot
As it stands, at currently attainable speeds, it would take our current rocket-based technology
centuries to get to the nearest star system, voyager II for example will need 42,000 years
before it will come close to another star, and it’s only ten light-years away.
But over vast amounts of time, hundreds of thousands to millions of years, the galaxy
shrinks and can be fully colonized in terms of a few million years at slower speeds.
If you have that kind of time, or you’re in a situation such as a multigenerational
ship built, say, from an asteroid, then slower methods can be used.
Other possibilities include powerful rockets launched not from earth, but from space and
and also gravitational slingshotting.
But if you chose your destination wisely, you can do much more with this than you might
think.
The concept of Dyson’s slingshot comes into play.
If you can get to a certain type of binary system, such as closely orbiting white dwarfs
or even binary neutron stars, these types of systems can be moving very rapidly.
Some of that energy can be imparted to a spacecraft passing closeby and slingshot it out on a
new trajectory at much higher, relativistic speeds.
In other words, it may take a while to get to a binary neutron star system, but once
you’re there, you’re on your way much faster to wherever you wish to go.
Number 6.
Nuclear Fusion Drives
Fusion always seems right around the corner, and has been for decades.
But recent developments may be changing that status quo.
While large fusion reactors like what might be developed from megaprojects like ITER wouldn’t
seem useful in space until decades, at least, from now, there is a lesser known, somewhat
more secretive project that may yield results much sooner.
It’s the Compact or High Beta fusion reactor being developed by Lockheed Martin’s skunkworks.
If that project works out, fusion could not just finally be right around the corner, but
the reactor would be small enough to launch into space.
If that ends up the case, and if the idea works, that would allow energy generation
in space on unheard of scales.
The International Space Station for example, has about 75-90 kilowatts available to it
generated by an acre of solar panels.
High beta fusion reactors could produce a hundred or more megawatts, enough to run a
large city, yet be about the size of a city bus.
With that kind of power available, goodbye ISS, hello Battlestar Galactica.
There are several ways to use fusion as a propulsion system.
One is direct thrust using the fusion reaction, and the other would be to generate electricity
for the various electric methods of producing thrust, such as ion drives, plasma drives,
photonic drives and so on.
Number 5.
The Antimatter Valkyrie
Imagine being able to travel at 92% of the speed of light, and then when you need it,
have the means to slow back down.
And unlike some hypothetical faster than light methods of propulsion using exotic forms of
matter, this one can be done with a material we’ve already created here on earth, though
it’s perhaps the most costly material on earth to produce.
Anti-Matter.
Assuming that anti-Matter in the future can be created in sufficient quantities efficiently
enough to make it worth it, you could build the Valkyrie.
How this works is that you create a small matter-anti-matter reaction, and the exhaust
from their total annihilation pushes you along.
Then you add more anti-matter, on the order of a 100 tons or so for the length of your
trip, and in the process, you’ve reached some seriously relativistic speeds.
As designed, the Valkyrie works more like a train of sorts, with the the crew compartments
and payloads suspended between two engines on a long tether, which has the effect of
reducing the overall mass needed to build the ship by eliminating some of the radiation
shielding needed as the engines would produce gamma radiation.
At these speeds, dust and debris in the interstellar medium would be a problem.
Shielding from space debris is accomplished in this design by a dual use radiatior in
front of the ship, droplets of liquid heated by waste heat are sprayed in front of the
ship, they then fall back down cooled back into the radiator for recycling, and the cloud
of liquid in front of the ship has the effect of shielding.
Unfortunately, the biggest problem with this design is the uncertainty over whether we
could ever find a way to manufacture anti-matter on a large scale.
Tons would be needed and it’s currently only available in seriously minute quantities.
Then you have to contain the anti-matter, which is quite hard.
New technologies would be needed and until that changes, if ever, this method cannot
be pursued.
Number 4.
The Alcubierre Star Drive
This option has been thought about for a while, and if it’s possible, it would allow not
only interstellar propulsion, but intergalactic propulsion, faster than light travel and shielding
from the relativistic effects of traveling at high speed through the normal universe.
The idea is that you circumvent the speed of light limit by effectively splitting off
a piece of space time around your spacecraft and accelerating it, and by proxy your ship,
to faster than light speeds.
This ship itself is not actually moving through space time, it’s sitting stationary on a
piece of space time that is moving.
This is possible because spacetime itself is not subject to the faster than light ban,
and can, in principle be made to propagate through the universe far faster than light.
However, this option suffers from a bunch of problems people have thought of over the
years.
One of them is that you’d need some serious energy to get it going, perhaps prohibitively
so for most civilizations.
But, more recent thinking is shrinking this amount of energy further and further.
Another issue is that you’d need negative matter, which is something that the universe
does not prohibit from existing, but that’s it.
So it’s not banned, but we have no clue how to make it, and there’s no evidence
that any of it exists naturally in our universe.
Other problems include surviving the trip, which again, as discussion of the concept
has progressed problems have seemingly cropped up.
But, if it turns out possible, then the warp engines from star trek will seem like bicycles
in comparison.
There doesn’t appear to be a hard and fast upper speed limit for the drive, but there’s
also no guarantee you could figure out a way to slow it back down, but it would allow access
to at least large swaths of the universe.
Number 3.
Black Hole Starships
Intuitively we might think that black holes are by their very nature inherently dangerous.
And, they are, in certain situations such as if you’re falling into one.
But they are also incredible objects that could, under the right circumstances, make
for good propulsion systems.
But in that case, you wouldn’t want to use a natural black hole.
Instead, you’d want to make an artificial one and they are possible to make.
One you had a black hole, you would then use it’s hawking radiation to propel the ship
essentially by creating a dish and directing the radiation.
The materials needed to shield gamma radiation and build such a ship -- it would generate
a lot of heat -- do not yet exist, but if they did, a 606,000 metric ton artificial
black hole could produce 160 petawatts of energy.
With that available energy, you could reach relativistic speeds in a matter of days.
It’s still being debated in physics whether using a black hole to power a starship is
actually possible in practice.
But it’s not the only way you could use an astrophysical object to generate thrust,
you can also use stars.
This idea is relatively simple.
Called a Shkadov thruster, it essentially involves building half a dyson sphere, which
then directs the stars output in one direction, thusly moving the star itself along with the
thruster.
At least initially, this is not a fast way to travel, it would take time, but a civilization
that has nothing but time on their hands might employ the shkadov thruster as a long-term
star management system, moving them around to wherever they might wish.
Number 2.
Traversable Wormholes
The concept of a possible connection, or tunnel to another part of the universe is an alluring
one in science fiction because it’s one of the few ways that the speed of light limit
might be circumvented that’s consistent with general relativity.
It’s the traversable wormhole, and while entirely hypothetical, there are objects in
nature that may, or may not, actually be hosting wormholes, such as the singularity at the
center of a black hole, or very tiny ones that may form in the quantum foam.
The problem with wormholes is that they don’t really appear to be very traversable.
But what could make them traversable is, once again, negative matter.
A shell of negative matter might be able to hold a wormhole open.
But, it’s somewhat unclear where you might end up.
Would it take you to some other point in the universe?
If so, what time period, as they also open up the possibility of time travel.
In fact, Kip Thorne and colleagues advanced that a wormhole normally connecting two points
in space, could be turned into a time machine if you accelerate one of the openings, though
you could never go back to a time before the wormhole existed.
But there’s another aspect.
If you could somehow open a wormhole, and hold it open, and step through, you may not
get what you expect.
One last possibility for wormholes is that they might not lead to some other point in
space-time, but rather an entirely different universe.
This is a problem, because if other universes exist, they may have very different properties,
so stepping into a universe where matter can’t exist in the form it does here, you may simply
dissolve.
Number 1.
The Halo Drive
This option is a very recent addition to the list of possible star drives.
In a recent paper by David Kipping, link below, and links to an in depth video he did on the
subject and a recent interview on the subject I did with him on Event Horizon, he proposes
using binary black holes as a method of propulsion.
To make it work, you would fire a laser at the event horizon of one of the black holes
just slightly above the surface.
The gravity of the black hole would then warp the laser around to the other side, sending
the beam back your way, but having increased the energy of the beam, blue shifting the
light.
This more energetic light could then be used for propulsion to relativistic speeds.
This is a very efficient way to do it, since the only energy you need to invest in is actually
getting to the black hole.
Once past that, the Halo drive is effectively a free lunch.
Also possible here is a method for slowing down.
If you travel from one set of binary black holes to another binary black hole system
you could use the halo drive in reverse to slow back down.
This could allow for a network of binary black holes to serve as a sort of natural highway
system throughout the Milky Way.
Thanks for listening!
I am futurist and science fiction author John Michael Godier currently giving a heads up
again.
In about two weeks from now on Event Horizon, my guest will be Dr. Miguel Alcubierre for
a discussion on faster than light propulsion and other such topics, going to be a good
one and be sure to check out my books at your favorite online book retailer and subscribe
to my channels for regular, in-depth explorations into the interesting, weird and unknown aspects
of this amazing universe in which we live.