In the 1960s, American physicist Robert W. Bussard proposed a radical idea for interstellar travel: a spacecraft that relied on powerful magnetic fields to harvest hydrogen directly from the interstellar medium. The high speed of this “ramjet” forces the hydrogen into a progressively constricted magnetic field until fusion occurs. The magnetic field then directs the resulting energy towards the rear of the spacecraft to generate propulsion.
As it’s come to be known, the Bussard Ramjet has since been popularized by hard science fiction writers like Poul Anderson, Larry Niven, Vernor Vinge, and science communicators like Carl Sagan. Unfortunately, a team of physicists recently analyzed the concept in more detail and concluded that Bussard’s idea is not practical. At a time when interstellar travel looks destined to become a real possibility, this analysis might seem like a wet blanket but is more of a reality check.
If you’re a fan of the Search for Extraterrestrial Intelligence (SETI) and the Fermi Paradox, then it’s likely you’ve heard of a concept known as the Great Filter. In brief, it states that life in the Universe may be doomed to extinction, either as a result of cataclysmic events or due to circumstances of its own making (i.e., nuclear war, climate change, etc.) In recent years, it has been the subject of a lot of talk and speculation, and not just in academic circles.
Stephen Hawking and Elon Musk have also weighed in on the issue, claiming that humanity’s only chance at long-term survival is to become “interplanetary.” Addressing this very possibility, a research team led by NASA’s Jet Propulsion Laboratory (JPL) recently created a timeline for potential human expansion beyond Earth. According to their findings, we have the potential of going interplanetary by the end of the century and intragalactic by the end of the 24th!
In 2016, Russian-American billionaire Yuri Milner founded Breakthrough Initiatives, a non-profit organization dedicated to investigating some of the most enduring mysteries of the Universe. Chief among their scientific efforts is Breakthrough Starshot, a proof-of-concept prototype that combines a lightsail, a nanocraft, and directed energy (aka. laser) propulsion to create a spacecraft capable of reaching the nearest star (Alpha Centauri) in our lifetimes.
Naturally, this presents all sorts of technical and engineering challenges, not the least of which is the amount of power needed to accelerate the spacecraft to relativistic speeds (a fraction of the speed of light). Luckily, scientists from the Australian National University (ANU) recently came up with a design for a directed-energy array made up of millions of individual lasers positioned across the Earth’s surface.
As Carl Sagan once said, “The sky calls to us. If we do not destroy ourselves, we will one day venture to the stars.” And our first emissaries to the stars will be robotic probes. These interstellar probes will be largely autonomous, but we will want to communicate with them. At the very least we will want them to phone home and tell us what they’ve discovered. The stars are distant, so the probes will need to make a very long-distance call.
Welcome back to our Fermi Paradox series, where we take a look at possible resolutions to Enrico Fermi’s famous question, “Where Is Everybody?” Today, we examine the possibility that the reason for the Great Silence is that colonizing other star systems is hazardous to our health!
In 1950, Italian-American physicist Enrico Fermi sat down to lunch with some of his colleagues at the Los Alamos National Laboratory, where he had worked five years prior as part of the Manhattan Project. According to various accounts, the conversation turned to aliens and the recent spate of UFOs. Into this, Fermi issued a statement that would go down in the annals of history: “Where is everybody?“
This became the basis of the Fermi Paradox, which refers to the disparity between high probability estimates for the existence of extraterrestrial intelligence (ETI) and the apparent lack of evidence. Since Fermi’s time, there have been several proposed resolutions to his question, which includes the Aurora Hypothesis that states that just because planets are habitable doesn’t mean that intelligent life can colonize there.
In the coming decades, multiple space agencies plan to return astronauts to the Moon (or to send them there for the first time) and mount the first crewed missions to Mars. Between that and the explosive growth we are seeing in Low Earth Orbit (LEO), there is no doubt that we live in an era of renewed space exploration. It’s therefore understandable that old and new concepts for interstellar travel are also being considered these days.
Right now, a considerable focus is on light sails that generate their own propulsion by radiation pressure or are accelerated by lasers. These concepts present all kinds of technical and engineering challenges. Luckily, Coryn Bailer-Jones of the Max Planck Institute for Astronomy (MPIA) recently conducted a study where he argues for a “Sun Diver” light sail that will pick up all the speed it needs by diving close to the Sun.
It’s no secret that humanity is poised to embark on a renewed era of space exploration. In addition to new frontiers in astronomical and cosmological research, crewed missions are also planned for the coming decades that will send astronauts back to the Moon and to Mars for the first time. Looking even further, there are also ideas for interstellar missions like Breakthrough Starshot and Project Dragonfly and NASA’s Starlight.
These mission concepts entail pairing a nanocraft with a lightsail, which would then accelerated by a directed-energy array (lasers) to achieve a fraction of the speed of light (aka. relativistic velocity). Naturally, this raises a number of technical and engineering challenges, not the least of which is communications. In a recent study, a team of scientists sought to address that very issue and considered various methods that might be used.
It’s a captivating idea: build an interstellar ark, fill it with people, flora, and fauna of every kind, and set your course for a distant star! The concept is not only science fiction gold, its been the subject of many scientific studies and proposals. By building a ship that can accommodate multiple generations of human beings (aka. a Generation Ship), humans could colonize the known Universe.
But of course, there are downsides to this imaginative proposal. During such a long voyage, multiple generations of people will be born and raised inside a closed environment. This could lead to all kinds of biological issues or mutations that we simply can’t foresee. But according to a new study by a team of linguistics professors, there’s something else that will be subject to mutation during such a voyage – language itself!
In a few decades, the Breakthrough Starshot initiative hopes to send a sailcraft to the neighboring system of Alpha Centauri. Using a lightsail and a directed energy (aka. laser) array, a tiny spacecraft could be accelerated to 20% the speed of light (0.2 c). This would allow Starshot to make the journey to Alpha Centauri and study any exoplanets there in just 20 years, thus fulfilling the dream of interstellar exploration within our lifetimes.
Naturally, this plan presents a number of engineering and logistical challenges, one of which involves the transmission of data back to Earth. In a recent study, Starshot Systems Director Dr. Kevin L.G. Parkin analyzes the possibility of using a laser to transmit data back to Earth. This method, argued Parkin, is the most effective way for humanity to get a glimpse of what lies beyond our Solar System.
The dream of traveling to another star and planting the seed of humanity on a distant planet… It is no exaggeration to say that it has captivated the imaginations of human beings for centuries. With the birth of modern astronomy and the Space Age, scientific proposals have even been made as to how it could be done. But of course, living in a relativistic Universe presents many challenges for which there are no simple solutions.
Of these challenges, one of the greatest has to do with the sheer amount of energy necessary to get humans to another star within their own lifetimes. Hence why some proponents of interstellar travel recommend sending spacecraft that are essentially miniaturized worlds that can accommodate travelers for centuries or longer. These “Generation Ships” (aka. worldships or Interstellar Arks) are spacecraft that are built for the truly long haul.