Want the Fastest Solar Sail? Drop it Into the Sun First

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.

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What’s the Best Way to Communicate With an Interstellar Probe When it’s Light-Years Away From Earth?

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.

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Languages Will Change Significantly on Interstellar Flights

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!

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How Will we Receive Signals From Interstellar Probes, Like Starshot?

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.

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What is a Generation Ship?

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.

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Riding the Wave of a Supernova to Go Interstellar

When it comes to the challenges posed by interstellar travel, there are no easy answers. The distances are immense, the amount of energy needed to make the journey is tremendous, and the time scales involved are (no pun!) astronomical. But what if there was a way to travel between stars using ships that take advantage of natural phenomena to reach relativistic velocities (a fraction of the speed of light).

Already, scientists have identified situations where objects in our Universe are able to do this – including hypervelocity stars and meteors accelerated by supernovae explosions. Delving into this further, Harvard professors Manasvi Lingam and Abraham Loeb recently explored how interstellar spacecraft could harness the waves produced by a supernova explosion in the same way that sailing ships harness the wind.

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What’s the Best Way to Sail From World to World? Electric Sails or Solar Sails?

In the past decade, thousands of planets have been discovered beyond our Solar System. This has had the effect of renewing interest in space exploration, which includes the possibility of sending spacecraft to explore exoplanets. Given the challenges involved, a number of advanced concepts are currently being explored, like the time-honored concept of a light sail (as exemplified by Breakthrough Starshot and similar proposals).

However, in more recent years, scientists have proposed a potentially more-effective concept known as the electric sail, where a sail composed of wire mesh generates electrical charges to deflect solar wind particles, thus generating momentum. In a recent study, two Harvard scientists compared and contrasted these methods to determine which would be more advantageous for different types of missions.

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How Big Would a Generation Ship Need to be to Keep a Crew of 500 Alive for the Journey to Another Star?

There’s no two-ways about it, the Universe is an extremely big place! And thanks to the limitations placed upon us by Special Relativity, traveling to even the closest star systems could take millennia. As we addressed in a previous article, the estimated travel time to the nearest star system (Alpha Centauri) could take anywhere from 19,000 to 81,000 years using conventional methods.

For this reason, many theorists have recommended that humanity should rely on generation ships to spread the seed of humanity among the stars. Naturally, such a project presents many challenges, not the least of which is how large a spacecraft would need to be to sustain a multi-generational crew. In a new study, a team of international scientists addressed this very question and determined that a lot of interior space would be needed!

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What’s the Minimum Number of People you Should Send in a Generational Ship to Proxima Centauri?

Humanity has long dreamed about sending humans to other planets, even before crewed spaceflight became a reality. And with the discovery of thousands exoplanets in recent decades, particularly those that orbit within neighboring star systems (like Proxima b), that dream seems closer than ever to becoming a reality. But of course, a lot of technical challenges need to be overcome before we can hope to mount such a mission.

In addition, a lot of questions need to be answered. For example, what kind of ship should we send to Proxima b or other nearby exoplanets? And how many people would we need to place aboard that ship? The latter question was the subject of a recent paper written by a team of French researchers who calculated the minimal number of people that would be needed in order to ensure that a healthy multi-generational crew could make the journey to Proxima b.

The study, titled “Computing the minimal crew for a multi-generational space travel towards Proxima Centauri b“, recently appeared online and will soon be published in the Journal of the British Interplanetary Society. It was conducted by Dr. Frederic Marin, an astrophysicist from the Astronomical Observatory of Strasbourg, and Dr. Camille Beluffi, a particle physicist working with the scientific start-up Casc4de.

The Project Orion concept for a nuclear-powered spacecraft. Credit: silodrome.co

Their study was the second in a series of papers that attempt to evaluate the viability of an interstellar voyage to Proxima b. The first study, titled “HERITAGE: a Monte Carlo code to evaluate the viability of interstellar travels using a multi-generational crew“, was also published in the August 2017 issue of the Journal of the British Interplanetary Society.

Dr. Marin and Dr. Beluffi begin their latest study by considering the various concepts that have been proposed for making an interstellar journey – many of which were explored in a previous UT article, “How Long Would it Take to Get to the Nearest Star?“. These include the more traditional approaches, like Nuclear Pulse Propulsion (i.e. the Orion Project) and fusion rockets (i.e. the Daedalus Project), and also the more modern concept of Breakthrough Starshot.

However, such missions are still a long way off and/or do not involve crewed spaceflight (which is the case with Starshot). As such, Dr. Marin and Dr. Beluffi also took into account missions that will be launching in the coming years like NASA’s  Parker Solar Probe. This probe will reach record-breaking orbital velocities of up to 724,205 km/h, which works out to about 200 km/s (or 0.067% the speed of light).

As Dr. Marin told Universe Today via email:

“This purely and entirely rely on the technology available at the time of the mission. If we would create a spacecraft right now, we could only reach about 200 km/s, which translates into 6300 years of travel. Of course technology is getting better with time and by the time a real interstellar project will be created, we can expect to have improved the duration by one order of magnitude, i.e. 630 years. This is speculative as technology as yet to be invented.”

Weighing in at 60,000 tons when fully fuelled, Daedalus would dwarf even the Saturn V rocket. Credit: Adrian Mann

With their baseline for speed and travel time established – 200 km/s-¹ and 6300 years – Dr. Marin and Dr. Beluffi then set out to determine the minimum number of people needed to ensure that a healthy crew arrived at Proxima b. To do this, the pair conducted a series of Monte Carlo simulations using a new code created by Dr. Marin himself. This mathematical technique takes into account chance events in decision making to produce distributions of possible outcomes.

“We are using a new numerical software that I have created,” said Dr. Marin. “It is named HERITAGE, see the first paper of the series. It is a stochastic Monte Carlo code that accounts for all possible outcomes of space simulations by testing every randomized scenario for procreation, life and death. By looping the simulation thousands of times, we get statistical values that are representative of a real space travel for a multi-generational crew. The code accounts for as many biological factors as possible and is currently being developed to include more and more physics.”

These biological factors include things like the number of women vs. men, their respective ages, life expectancy, fertility rates, birth rates, and how long the crew would have to reproduce. It also took into account some extreme possibilities, which included accidents, disasters, catastrophic events, and the number of crew members likely to be effected by them.

They then averaged the results of these simulations over 100 interstellar journeys based on these various factors and different values to determine the size of the minimum crew. In the end, Dr. Marin and Dr. Beluffi concluded that under conservative conditions, a minimum of 98 crew members would be needed to sustain a multi-generational voyage to the nearest star system with a potentially-habitable exoplanet.

Illustration of the Parker Solar Probe spacecraft approaching the Sun. Credits: Johns Hopkins University Applied Physics Laboratory

Any less than that, and the likelihood of success would drop off considerably. For instance, with an initial crew of 32, their simulations indicated that the chances for success would reach 0%, largely because such a small community would make inbreeding inevitable. While this crew might eventually arrive at Proxima b, they would not be a genetically healthy crew, and therefore not a very good way to start a colony! As Dr. Marin explained:

“Our simulations allows us to predict with great precision the minimum size of the initial crew that will leave for centuries-long space travels. By allowing the crew to evolve under a list of adaptive social engineering principles (namely, yearly evaluations of the vessel population, offspring restrictions and breeding constraints), we show in this paper that it is possible to create and maintain a healthy population virtually indefinitely.”

While the technology and resources needed to make an interstellar voyage is still generations away, studies of this kind could be of profound significance for those missions – if and when they occur. Knowing in advance the likelihood that such a mission will succeed, and what will increase that likelihood to the point that success is virtually guaranteed, will also increase the likelihood that such missions are mounted.

This study and the one that preceded it are also significant in that they are the first to take into account key biological factors (like procreation) and how they will affect a multi-generational crew. As Dr. Marin concluded:

“Our project aims to provide realistic simulations of multi-generational space ships in order to prepare future space exploration, in a multidisciplinary project that utilizes the expertise of physicists, astronomers, anthropologists, rocket engineers, sociologists and many others. HERITAGE is the first ever dedicated Monte Carlo code to compute the probabilistic evolution of a kin-based crew aboard an interstellar ship, which allows one to explore whether a crew of a proposed size could survive for multiple generations without any artificial stocks of additional genetic material. Determining the minimum size of the crew is an essential step in the preparation of any multi-generational mission, affecting the resources and budget required for such an endeavor but also with implications for sociological, ethical and political factors. Furthermore, these elements are essential in examining the creation of any self-sustaining colony – not only humans establishing planetary settlements, but also with more immediate impacts: for example, managing the genetic health of endangered species or resource allocation in restrictive environments.”

Project Starshot, an initiative sponsored by the Breakthrough Foundation, is intended to be humanity’s first interstellar voyage. Credit: breakthroughinitiatives.org

Dr. Marin was also quoted recently in an article in The Conversation about the goals of his and Dr. Beluffi’s project, which is all about determining what is needed to ensure the health and safety of future interstellar voyagers. As he said in the article:

“Of the 3757 exoplanets that have been detected, the closest Earth-like planet lies at 40 trillion kilometers from us. At 1% of the speed of light, which is far superior to the highest velocities achieved by state-of-the-art spacecraft, it would still take 422 years for ships to reach their destination. One of the immediate consequences of this is that interstellar voyages cannot be achieved within a human lifespan. It requires a long-duration space mission, which necessitates finding a solution whereby the crew survive hundreds of years in deep space. This is the goal of our project: to establish the minimum size of a self-sustaining, long duration space mission, in terms of both hardware and population. By doing so, we intend to obtain scientifically-accurate estimates of the requirements for multi-generational interstellar travel, unlocking the future of human space exploration, migration and habitation.”

In the coming decades, next-generation telescopes are expected to discover thousands more exoplanets. But more importantly, these high-resolution instruments are also expected to reveal things about exoplanets that will allow us to characterize them. These will include spectra from their atmospheres that will let scientists know with greater certainty if they are actually habitable.

With more candidates to choose from, we will be all the more prepared for the day when interstellar voyages can be launched. When that time comes, our scientists will be armed with the necessary information for ensuring that the people that arrive will be hail, hearty, and prepared to tackle the challenges of exploring a new world!

Further Reading: arXiv, arXiv (2), The Conversation

Pros and Cons of Various Methods of Interstellar Travel

It’s a staple of science fiction, and something many people have fantasized about at one time or another: the idea of sending out spaceships with colonists and transplanting the seed of humanity among the stars. Between discovering new worlds, becoming an interstellar species, and maybe even finding extra-terrestrial civilizations, the dream of  spreading beyond the Solar System is one that can’t become reality soon enough!

For decades, scientists have contemplated how humanity might one-day reach achieve this lofty goal. And the range of concepts they have come up with present a whole lot of pros and cons. These pros and cons were raised in a recent study by Martin Braddock, a member of the Mansfield and Sutton Astronomical Society, a Fellow of the Royal Society of Biology, and a Fellow of the Royal Astronomical Society. Continue reading “Pros and Cons of Various Methods of Interstellar Travel”