Why is it challenging to get to Proxima Centauri? - Perché è
difficile raggiungere Proxima Centauri?
Proxima Centauri is the closest star to the solar system; however, with modern technology,
it would take thousands of years to reach that star. Will we ever have the technology to reach
the closest star to the solar system? Ready? Let's get started! "Introduction"
Proxima Centauri it is located approximately 4.2 light years away and is part of the
Centauri star system, the minor star of the three that make up the entire system.
For years this star has been observed with the most powerful telescopes in the world, and thanks
to this, we have discovered that the star Proxima Centauri has at least one exoplanet that could
have the conditions to host living beings. This makes reaching this star a matter of
great importance for humanity since this distant world could have living beings
or be a human settlement in the future. But how difficult would it be with modern
technology to get to this star? In short, a LOT.
It would be tricky; it would be the most challenging feat that the human race could
perform in the distant future and one of the most important if it were to be achieved;
suffice it to say that, in the modern era, even with the technology we have we have
not managed to send a spacecraft out of our solar system, nor have we taken humans beyond the moon.
Not a human being has set foot on another planet other than Earth, so you can be entirely sure that
there is still a long time before we manage to send the first spacecraft to Proxima Centauri,
but ... How much left precisely? Do we have any estimated dates for when we might reach this star?
Let's see what the science says about it. So close and so far
The fastest human-created object we've ever launched in the Solar System is Voyager 1.
This venerable probe moves away from the Sun at a speed of 17.4 km / s,
equivalent to about 540 million kilometers per year.
But Proxima Centauri is 4.24 light-years away. At this speed, it would take about 76,000 years for
Voyager 1 to reach Proxima Centauri, assuming it traveled toward it (which it doesn't).
To reach Alpha Centauri within an acceptable time, the speeds we have to reach must exceed ten
thousand kilometers per second. At that speed, we would arrive in 130 years,
which can be somewhat annoying considering that most humans die before the age of one hundred.
If we travel at 25,000 km/s, the flight time is reduced to 50 years. Half a century is not
wrong for an interstellar trip, so this should be the speed we aim to achieve,
a challenge if we remember that Voyager 1 moves at less than 18 km / s.
Clearly, we have no choice but to use propulsion systems other than the usual ones, so we better
forget about the conventional chemical propulsion used by ordinary rockets. Why? Because if we want
to reach 1% of the speed of light (3000 km / s) using conventional chemical rockets,
we would need 1026 kg of fuel for each kg of mass of the ship. That is, the ship going to
Proxima Centauri would have a hundred times the mass of Earth! Something completely impossible.
On the other hand, if we want to travel to Proxima Centauri in this century,
we must make certain sacrifices. For example, forget about human-crewed spaceships.
Conventional space probes are infinitely cheaper and more powerful. In addition,
we can conceive of a mission limited to flying over the Alpha Centauri system without breaking
and entering orbit around one of the two main stars, which would mean enormous energy savings.
What propulsion systems can we use? Ion and nuclear thermal propulsion
Electric propulsion – ionic or plasma – is currently used in several spacecraft
and allows a specific impulse to be achieved for hundreds of hours.
Nuclear thermal propulsion follows a bit further back. These propulsion systems are not bad for
traveling through the Solar System, but it would take 40,000 years to reach Proxima Centauri.
It would probably be better to rule out these options now.
VASIMR (Variable Specific Impulse Magnetoplasma Rocket)
This engine was created by Ad Astra Rocket Company,
led by former Costa Rican astronaut Franklin Chang-Díaz.
The project intends to create a plasma ion engine that will serve
as a cheap and efficient alternative as a propulsion power source for spacecraft. He
mainly focuses on exploring other parts of the solar system, such as a possible trip to Mars.
With this technology, the journey would be ten times faster than the current one and enable
manned trips to the red planet, reducing the time from 18 months to approximately 39 days.
Let's assume that, despite complaints from many critics, VASIMR is an economically viable project.
In that case, a spacecraft with the VASIMR engine would only take
2200 years to reach Proxima Centauri. It's certainly much less time than using
ion propulsion, but it's still overcoming the thousand-year barrier, and unfortunately, humans
don't live that long. So this option is ruled out. Pulsed nuclear propulsion
Popularized by the Orion Project of the 60s, this system seems like something from science fiction,
but the truth is that the associated technologies have already been tested.
A pulsed nuclear spacecraft moves by detonating nuclear devices a short distance from the vehicle.
A special plate absorbs the shock wave with shock absorbers, which transfers part of the energy to
the spacecraft so that it accelerates constantly. Orion was a perfect vehicle for traveling through
the Solar System, but this system is not so attractive for interstellar journeys.
To begin with, nearly 300 000 detonations of nuclear fusion bombs (and not nuclear
fission bombs as in the original Orion project) proposal would have to be used,
which is quite possibly beyond our technological possibilities.
An interstellar Orion project with a human-crewed spacecraft should have a mass of 400,000
tons (!) and a plate one hundred meters in diameter. And even with these monstrous
dimensions, it would take about 150 years to reach Proxima Centauri. Not bad for a
generational spaceship, but it doesn't seem best suited for an automatic reconnaissance
mission. Even so, it is a system to consider if we join it to other forms of propulsion.
Solar sails In the language of interstellar flights, a
solar sail is not a simple photonic sail like that of the Japanese space agency's Ikaros space probe.
A solar sail consists of a vast parachute-shaped structure that, like a photonic sail, would use
the radiation pressure of sunlight (and not that of the solar wind as is sometimes mistakenly
believed) to accelerate the spacecraft to escape velocities from the Solar System.
But to take advantage of this system, it is necessary to deploy the sail near the Sun.
Assuming that in the next few decades, we will be able to build giant ultralight sails
capable of withstanding more than 60 Celcius of acceleration and thousands of degrees Celsius,
a solar sail could travel to Alpha Centauri in a thousand or two thousand years.
It is still long, but you can combine this system with others to decrease flight time. For example,
the Medusa [w1] proposal of the 90s linked pulsed nuclear propulsion with a solar sail. In addition,
an interstellar spacecraft could use a solar sail to visit Proxima Centauri and then maneuver to
travel to Alpha Centauri A or Alpha Centauri B. Solar sails are an exciting technology for
interstellar travel, although these are still in a primitive stage of development.
If in the future, we manage to develop them and make the most of their benefits by combining them
with other technologies, they could be the ones we use for the first trip to Proxima Centauri.
Laser candles Laser sails are a specific case
of propulsion systems using energy beams. These consist of a giant photonic sail propelled not
by sunlight but by a set of powerful super-laser beams in Earth orbit or some point of LaGrange.
Suppose we had a set of space lasers of 25 gigawatts of power. In that case, we could send
a 100 kg ship (of which 33 kg would be the payload and the rest the sail) to Alpha Centauri in only
40 years, a fairly reasonable time considering that the Voyager spacecraft have been traveling
non-stop through the solar system for more than 45 years and have not yet managed to leave.
The lasers should constantly work during the four decades that the mission would last,
and the sail would be limited to flying over the system. Still,
we are facing a form of propulsion within the technological possibilities of our civilization.
Of course, 100 kg is tiny, but if we use a slightly more massive ship, the flight time will
shoot up to a hundred years if we do not increase the power of the lasers, so initially, this
technology only serves us for uncrewed missions. Although we cannot send humans to other stars
with this technology, at the moment, this is the most promising method in the short,
medium, and long term. Star Shot Project
As surprising as it may seem, although reaching Proxima Centauri seems an impossible mission to
achieve for modern technology, there is currently a research and engineering project developed by
the Breakthrough Initiatives program that aims to develop a fleet of micro spacecraft (known
as StarChip) powered by solar sails capable of traveling to Alpha Centauri at 15% or 20%
of the speed of light. That is 60 000 km / s (215 million km / h), so it would take between 20 and
30 years to reach its destination and another four years to communicate to Earth its arrival.
The trip would also include a flyby of the planet Proxima Centauri b, which has
characteristics very similar to that of Earth and is also in its star's habitable zone. The
central concept that would allow this project to be launched is explained in the article "Work plan
for interstellar flight," published in April 2015 in the scientific journal British Interplanetary
Society by Philip Lubin, a researcher at the University of California at Santa Barbara.
The concept of Starshot consists of the launch of a "mothership" with a load of thousands of
nano-spacecraft (a few centimeters in size and a few grams in weight), which, when they
reach a high-altitude orbit, will be released into space. Then, high-powered lasers placed in Earth's
orbit would focus a beam of light to propel the spacecraft's sails individually and accelerate
their maximum speed in minutes, achieving an average of 100 km / s2 and an energy of
1 TJ blown into each sail (each one 4×4 m). Suppose the spacecraft finds a planet with
characteristics similar to Earth's in an orbit of the habitable zone of the Proxima Centauri system
(a case that occurred with the ground-based telescopes at the end of August 2016).
In that case, the project will try to bring the nano-spacecraft closer to a distance of 1
astronomical unit (150 million kilometers or 93 million miles) from the planet.
At that distance, the spacecraft's cameras can obtain graphic data of a high enough
quality to know these characteristics. Each spacecraft would have the possibility of
transmitting data to Earth using a compact laser communications system. The swarm of thousands
of units would compensate for the possible loss of spacecraft caused by collisions with
interstellar dust during their long journey. Although this project is currently still in
the development phase, it is estimated that with adequate funding, it would be possible to make
it a reality in just two decades; that is, we would be able to see the execution of a mission
and the arrival of the first spacecraft to Proxima Centauri in this same century.
But even if we don't discover planets — or moons like Pandora from the movie Avatar — in
the habitable zone of Proxima Centauri, a trip to the nearest star is a significant challenge
for humanity. A challenge that would allow us to understand better the processes of planet
formation in the Milky Way and, in the process, understand how our solar system was formed.
As Carl Sagan said, by the time we can visit other stars, we will have changed. Only a mature
and brilliant species can face the vast abyss of interstellar space and overcome it. If we want
to survive in the immensity of the Universe and not fall into oblivion, humanity must travel to
the stars. It is in our hands to make this dream come true. Will we be able to meet the challenge?