Is interstellar travel doomed to remain in the realm of science fiction
with faster than light travel and infinite improbability drives?
Never mind warp speed, is light speed even possible?
Technically no
Light is massless and travels a little over 1 billion km/h
Since spacecraft are not massless you need energy to accelerate
as you keep gaining speed, you’ll need increasingly larger amounts of fuel
Eventually, even tiny gains in acceleration require huge amounts of energy
Getting to exactly one hundred percent light speed would require an infinite amount of energy
which is why it’s an impossible goal
Before we look at how close we can get to the speed of light
et’s consider what we’ve accomplished so far
When it comes to space travel, everything starts with a rocket
still the best way we know of to literally get our feet off the ground
ockets give spacecraft that initial massive boost to escape Earth’s gravity
t’s the first step in getting people to the moon
sending probes to the planets
our sun
and even the edge of our solar system
pollo 10, the dress rehearsal for Apollo 11
never landed on the moon, but at reentry it did set the world record
for the fastest manned spacecraft
at just under 40,000 km/h
in order to get all the way to the moon, it needed the help of Saturn V
still the most powerful rocket ever launched
The New Horizons probe, hitching a ride on the Atlas V
holds the record for fastest launch velocity
at over 58,536 km/h
t was also the first spacecraft to reach Pluto in 2015
sending back the first detailed images ever taken of Pluto
Launched in 1977, Voyager 1’s mission
was the exploration of Jupiter and Saturn
and once complete
to leave the solar system entirely
It couldn't do it with rocket power alone
so it used gravity assists at Jupiter to slingshot to Saturn
and again at Saturn to fling itself out to the edge of the solar system
Voyager 1 reached a top speed
of 62,000 km/h
but it still took over 30 years to reach interstellar space in 2012
In 1976, the Helios-2 probe set off to study the sun and the interplanetary medium
To do so they were put in highly elliptical orbits
with the Sun at one end and all the way out to the Earth's orbit at the other
Each time it approached the Sun
the massive gravitational force sped it up to a record setting speed
of 253,000 km/h
the fastest any spacecraft has ever travelled
Solar Probe Plus will study the corona and outer atmosphere of the sun
ith an expected launch in 2018
Over the course of seven years
multiple gravity assists will be used at Venus
to bring it into an orbit around 7 times closer to the sun than Helios
With that close of an orbit it will crush the Helios record
with a top speed of just under 725,000 km/h
Even still, that’s just a meager .07% the speed of light
and would take over 6,000 years to travel 4 and a quarter light years to get to Proxima Centauri
the closest star to our own
In 2016 a planet, Proxima b, was discovered around the star
It’s probably rocky like the Earth and in the right orbit
to be potentially warm enough for liquid water on the surface if it has any
This makes it an excellent target for the first interstellar spacecraft
Staying in the realm of current or near future technology only
can we improve on that speed?
Ion propulsion is currently employed in some satellites
but most notably, the Dawn spacecraft which studied the asteroid Vesta and the dwarf planet Ceres
Inside the thruster, electrons bombard neutrally charged atoms
ausing them to lose electrons and become positively charged ions
Thrust is produced as they are shot out in an ion beam
The resulting thrust is miniscule
but since it’s fuel supply can last for years, unlike a rocket
that tiny amount of thrust keeps compounding on itself
and in time, it can potentially reach speeds of up to
324,000 km/h, although no spacecraft currently has
While not the fastest
it’s a practical method to study multiple celestial bodies in one mission
an exciting potential for solar system exploration
In the 1970s, the British Interplanetary Society conducted a study
Project Daedalus
for an unmanned fusion propelled interstellar spacecraft
With help from the Tau Zero foundation in 2009
hey initiated Project Icarus to update the concept
with the Ghost team’s design winning the internal competition in 2013
For propulsion, Ghost uses Inertial Confinement Fusion
Small fuel pellets are shot into a fusion chamber
Lasers bombard each pellet from all sides, compressing it
then one final laser pulse shoots into the core, igniting the fusion process
The resulting plasma is expelled from the ship, producing thrust
The older Daedalus design would have reached a remarkable 12% light speed
Ghost can only get to 2.33% light speed
reaching Proxima Centauri in around 186 years
While much slower,  Ghost allows for deceleration at the star for scientific study
using it’s own fusion engine
and a magnetic sail 400 km in diameter
Ghost also uses a more practically sourced fuel
Deuterium and Tritium
while Daedalus used the more efficient combination of
Deuterium and Helium-3
Unfortunately, Helium-3 is too rare and inaccessible on Earth
You would have to mine a gas giant like Jupiter or possibly the moon to get enough fuel
Though it’s the fusion process itself that may be the biggest challenge
We have yet to achieve a sustained fusion reaction in the lab
Until we figure that out, these ships won’t leave the ground
Weighing in at 1.4 million tonnes and over a kilometer long
Ghost couldn’t launch from Earth it would have to be assembled in parts
This is no small task as
The International Space Station, the largest spacecraft ever built
is 450 tonnes and 109 meters long, peanuts compared to Ghost
Since almost all of the mass of a fusion spacecraft is fuel
imagine not having to carry any with you
Enter the solar sail
IKAROS is a small solar sail spacecraft
built by the Japanese space program JAXA
Launched in 2010, it was the first successful demonstration of solar sail propulsion
Similar to ion propulsion
sunlight results in only a small amount of thrust
but it keeps compounding on itself
and only stops when the spacecraft is too far from the sun
The total thrust is determined
by the surface area of the sail
versus the mass of the spacecraft
With a big sail you can catch more light
With less mass, the light can push you faster
There’s also more solar energy imparted on the spacecraft
the closer you can get to the sun
As long as you don’t burn up in the process
Unfortunately this may not be good enough
to get to another star within a lifetime
It would take a 1 kg spacecraft
with a 1km x 1km sail
travelling extremely close to the sun
about 100 years to reach Proxima Centauri
But we may be able to improve on this
Breakthrough Starshot is another proof-of concept project
to design an unmanned laser propelled spacecraft.
A mothership containing thousands of nanocrafts will be launched into orbit
This allows for redundancy in case of failure and a variety of payload options
These tiny, gram-scale nanocraft
have a sail only 4 meters to a side
and just a few hundred atoms thick
The Light Beamer is a ground based array of lasers
that combine together in a single beam
to propel each nanocraft to 20% light speed within minutes
At that speed, they could reach Proxima Centauri in as little as 20 years
While just a flyby mission
they could get close enough to Proxima b
to take pictures with enough detail
to see continents and oceans if it has any
While the team doesn’t see any deal breakers that could stop the project
that’s not to say there won’t be any challenges
especially building the light beamer
At 100 gigawatts, the array would be 100 times more powerful than a nuclear power plant
It will also need to contend with the scattering effects of the atmosphere
as an orbital laser of this scale is too expensive
Speaking of which, the projected cost is nearly 10 billion dollars
about half of NASA’s 2016 budget
But it does start to look like a bargain compared to the $100 billion dollar cost
of the International Space Station
Breakthrough Starshot may represent not only the most practical interstellar spacecraft
but at 20% light speed it would be the fastest
