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.
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.
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.
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!
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.
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.”
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.
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.”
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!
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!
The number of confirmed extra-solar planets has increased by leaps and bounds in recent years. With every new discovery, the question of when we might be able to explore these planets directly naturally arises. There have been several suggestions so far, ranging from laser-sail driven nanocraft that would travel to Alpha Centauri in just 20 years (Breakthrough Starshot) to slower-moving microcraft equipped with a gene laboratories (The Genesis Project).
But when it comes to braking these craft so that they can slow down and study distant stars and orbit planets, things become a bit more complicated. According to a recent study by the very man who conceived of The Genesis Project – Professor Claudius Gros of the Institute for Theoretical Physics Goethe University Frankfurt – special sails that rely on superconductors to generate magnetic fields could be used for just this purpose.
Starshot and Genesis are similar in that both concepts seek to leverage recent advancements in miniaturization. Today, engineers are able to create sensors, thrusters and cameras that are capable of carrying out computations and other functions, but are a fraction of the size of older instruments. And when it comes to propulsion, there are many options, ranging from conventional rockets and ion drives to laser-driven light sails.
Slowing an interstellar mission down, however, has remained a more significant challenge because such a craft cannot be fitted with braking thrusters and fuel without increasing its weight. To address this, Professor Gros suggests using magnetic sails, which would present numerous advantages over other available methods. As Prof. Gros explained to Universe Today via email:
“Classically, you would equip the spacecraft with rocket engines. Normal rocket engines, as we are using them for launching satellites, can change the velocity only by 5-15 km/s. And even that only when using several stages. That is not enough to slow down a craft flying at 1000 km/s (0.3% c) or 100000 km/s (c/3). Fusion or antimatter drives would help a bit, but not substantially.”
The sail he envisions would consist of a massive superconducting loop that measures about 50 kilometers in diameter, which would create a magnetic field once a lossless current was induced. Once activated, the ionized hydrogen in the interstellar medium would be reflected off the sail’s magnetic field. This would have the effect of transferring the spacecraft’s momentum to the interstellar gas, gradually slowing it down.
According to Gros’ calculations, this would work for slow-travelling sails despite the extremely low particle density of interstellar space, which works out to 0.005 to 0.1 particles per cubic centimeter. “A magnetic sail trades energy consumption with time,” said Gros.”If you turn off the engine of your car and let it roll idle, it will slow down due to friction (air, tires). The magnetic sail does the same, where the friction comes from the interstellar gas.”
One of the advantages of this method is the fact that can be built using existing technology. The key technology behind the magnetic sail is a Biot Savart loop which, when paired with the same kind of superconducting coils used in high-energy physics, would create a powerful magnetic field. Using such a sail, even heavier spacecraft – those that weight up to 1,500 kilograms (1.5 metric tonnes; 3,307 lbs) – could be decelerated from an interstellar voyage.
The one big drawback is the time such a mission would take. Based on Gros’ own calculations, a high speed transit to Proxima Centauri that relied on magnetic momentum braking would require a ship that weighed about 1 million kg (1000 metric tonnes; 1102 tons). However, an interstellar mission involving a 1.5 metric tonne ship would be able to reach TRAPPIST-1 in about 12,000 years. As Gros concludes:
“It takes a long time (because the very low density of the interstellar media). That is bad if you want to see a return (scientific data, exciting pictures) in your lifetime. Magnetic sails work, but only when you are happy to take the (very) long perspective.”
In other words, such a system would not work for a nanocraft like that envisioned by Breakthrough Starshot. As Starshot’s own Dr. Abraham Loeb explained, the main goal of the project is to achieve the dream of interstellar travel within a generation of the ship’s departure. In addition to being the Frank B. Baird Jr. Professor of Science at Harvard University, Dr. Loeb is also the Chair of the Breakthrough Starshot Advisory Committee.
As he explained to Universe Today via email:
“[Gros] concludes that breaking on the interstellar gas is feasible only at low speeds (less than a fraction of a percent of the speed of light) and even then one needs a sail that is tens of miles wide, weighting tons. The problem is that with such a low speed, the journey to the nearest stars will take over a thousand years.
“The Breakthrough Starshot initiative aims to launch a spacecraft at a fifth of the speed of light so that it will reach the nearest stars within a human lifetime. It is difficult to get people excited about a journey whose completion will not be witnessed by them. But there is a caveat. If the longevity of people could be extended to millennia by genetic engineering, then designs of the type considered by Gros would certainly be more appealing.”
But for missions like The Genesis Project, which Gros originally proposed in 2016, time is not a factor. Such a probe, which would carry single-celled organisms – either encoded in a gene factory or stored as cryogenically-frozen spores – a could take thousands of years to reach a neighboring star system. Once there, it would begin seeding planets that had been identified as “transiently habitable” with single-celled organisms.
For such a mission, travel time is not the all-important factor. What matters is the ability to slow down and establish orbit around a planet. That way, the spacecraft would be able to seed these nearby worlds with terrestrial organisms, which could have the effect of slowly terraforming it in advance of human explorers or settlers.
Given how long it would take for humans to reach even the nearest extra-solar planets, a mission that last a few hundred or a few thousand years is no big deal. In the end, which method we choose to conduct interstellar mission will come down to how much time we’re willing to invest. For the sake of exploration, expedience is the key factor, which means lightweight craft and incredibly high speeds.
But where long-term goals – such as seeding other worlds with life and even terraforming them for human settlement – are concerned, the slow and steady approach is best. One thing is for sure: when these types of missions move from the concept stage to realization, it sure will be exciting to witness!
Think of the ease. With a simple command of “Make it so” humans travelled from one star to the next in less time than for drinking a cup of coffee. At least that’s what happens in the time-restricted domain of television. In reality it’s not so easy. Nor does Rachel Armstrong misrepresent this point in her book of essays within “Star Ark – A Living Self-Sustaining Spaceship“; a book that brings some fundamental reality to star travel.
Yes, many people want to travel to other stars. We’re not ready for that. We’re still just planning on getting outside Earth’s protective atmosphere (again). Yet making preparations and doing judicious planning is the aim of this book. Wisely though, this book isn’t technical. It has no mention of specific impulse calculations or ion shields. Rather, this book takes a very liberal view of space travel and ponders deep questions such as whether the cosmos is an ecosystem.
Does our species have an appropriate culture for space travel? What exactly is a human? These concerns get raised in some very thought provoking sections. And given that the editor is an architect and one who apparently considers the emotional qualities of a structure as much as functional qualities, then this book’s presentation tends to be a little more on the philosophical side of things.
In particular, it looks at the benefits of living entities. For instance it notes that humans live in symbiotic relationships with a host of internal and external organisms. Most have already gone into space either within people who have traveled in space or possibly upon probes sent to other planets. So we aren’t the only species that’s traveled beyond Earth. But which beings are sufficient and necessary to keep humans alive for the generations needed to travel to another star? That question and many answers come up often.
As well, the essays get into bigger questions such as: What is life? Could the vessel be an organic construct? How might today’s humans evolve to tomorrow’s star travelers? Should humans travel in space and promote/continue panspermia? Yes, these questions and many more are raised in the essays collected within this book. And true to form for any book considering star travel, there aren’t any strict answers. There are however lots of ideas and concepts to better prepare humans.
Much of this book seems to center around the authors’ involvement with the Persephone project of Icarus Interstellar. Yet there’s very little description of either. However, the book does have wonderful descriptions of Biitschli experiments, explanations of living walls and critiques of theatrical productions.
There are a few fictional passages and some poetry. The long list of references indicates a broad knowledge of the technical issues, though the focus is on humanity and the living aspect. This focus flows through the essays, but having a collection of many authors makes for a disjointed flow. The writing styles are unique, the viewpoints are particular and the emphasis specialized for each. One common viewpoint does keep arising though. That is, we are already on a living spaceship; the Earth. Earth gives a unique platform for assessing the ability to travel to other stars. The essays state that it is or at least was a veritable, closed self-sustaining life support system. And, as seems to be the norm these days, the essays acknowledge that solutions for space travel would be just as good for people remaining behind upon Earth or travelling to the Moon or to Mars and so on. This care and concern for living organism keeps the book grounded, so to speak.
The all-encompassing-solution-finder may be a strength or a weakness to Rachel Armstrong’s collection within the book “Star Ark – A Living Self-Sustaining Spaceship”. As the book’s essays describe, humans have an incredible ability to think and act in abstract fashion. Just envisioning an attempt to send sentient beings to another star demonstrates this. But will we be able to enact this idea and what form might a star vessel take? Reading of this is easy. Will taking the necessary steps be just as easy?
In 2015, Russian billionaire Yuri Milner established Breakthrough Initiatives, a non-profit organization dedicated to enhancing the search for extraterrestrial intelligence (SETI). In April of the following year, he and the organization be founded announced the creation of Breakthrough Starshot, a program to create a lightsail-driven “wafercraft” that would make the journey to the nearest star system – Alpha Centauri – within our lifetime.
This past June, the organization took a major step towards achieving this goal. After hitching a ride on some satellites being deployed to Low Earth Orbit (LEO), Breakthrough conducted a successful test flight of its first spacecraft. Known as “Sprites”, these are not only the smallest spacecraft ever launched, but prototypes for the eventual wafercraft Starshot hopes to send to Alpha Centauri.
The concept for a wafercraft is simple. By leveraging recent developments in computing and miniaturization, spacecraft that are the size of a credit card could be created. These would be capable of carrying all the necessary sensors, microprocessors and microthrusters, but would be so small and light that it would take much less energy to accelerate them to relativistic speeds – in the case of Starshot, up to 20% the speed of light.
As Pete Worden – Breakthrough Starshot’s executive director and the former director of NASA’s Ames Research Center – said in an interview with Scientific American:
“This is a very early version of what we would send to interstellar distances. In addition, this is another clear demonstration that it is possible for countries to work together to do great things in space. These are European spacecraft with U.S. nanosatellite payloads launching on an Indian booster—you can’t get much more international than that.”
Professor Abraham Loeb also has some choice words to mark this historic occasion. In addition to being the Frank B. Baird Jr. Professor of Science, the Chair of the Astronomy Department and the Director of the Institute for Theory and Computation at Harvard University, Prof. Loeb is also the chairman of the Breakthrough Starshot Advisory Committee. As he told Universe Today via email:
“The launch of the Sprite satellites marks the first demonstration that miniaturized electronics on small chips can be launched without damage, survive the harsh environment of space and communicate successfully with earth. The Starshot Initiative aims to launch similar chips attached to a lightweight sail that it being pushed by a laser beam to a fifth of the speed of light, so that its camera, communication and navigation devices (whose total weight is of order a gram) will reach the nearest planet outside the solar System within our generation.”
The craft were deployed on June 23rd, piggybacking on two satellites belonging to the multinational technology corporation OHB System AG. Much like the StarChips that Starshot is proposing, the Sprites represent a major step in the evolution of miniature spacecraft that can do the job of larger robotic explorers. They measure just 3.5 by 3.5 cm (1.378 x 1.378 inches) and weight only four grams (0.14 ounces), but still manage to pack solar panels, computers, sensors and radios into their tiny frames.
The Sprite were originally conceived by Zac Manchester, a postdoctorate researcher and aerospace engineer at Cornell University. Back in 2011, he launched a Kickstarter campaign (called “KickSat“) to raise funds to develop the concept, which was his way of bringing down the associated costs of spaceflight. The campaign was a huge success, with Manchester raising a total of $74,586 of his original goal of $30,000.
“The Sprites project is led by Zac Manchester, a Harvard postdoc who started working on this during his PhD at Cornell. Sprites are chip-size satellites powered by sunlight, intended to be released in space to demonstrate a new technology of lightweight (gram-scale) spacecrafts that can communicated with Earth.”
The purpose of this mission was to test how well the Sprites’ electronics systems and radio communications performed in orbit. Upon deployment, the Sprites remained attached to these satellites (known as “Max Valier” and “Venta”) and began transmitting. Communications were then received from ground stations, which demonstrated that the Sprites’ novel radio communication architecture performed exactly as it was designed to.
With this test complete, Starshot now has confirmation that a waferocraft is capable of operating in space and communicating with ground-based controllers. In the coming months and years, the many scientists and engineers that are behind this program will no doubt seek to test other essential systems (such as the craft’s microthrusters and imagers) while also working on the various engineering concerns that an instellar mission would entail.
In the meantime, the Sprites are still transmitting and are in radio contact with ground stations located in California and New York (as well as radio enthusiasts around the world). For those looking to listen in on their communications, Prof. Loeb was kind enough to let us know what frequency they are transmitting on.
“The radio frequency at which the Sprites that were just launched operate is 437.24 MHz, corresponding to a wavelength of roughly 69 cm,” he said. So if you’ve got a ham radio and feel like tuning in, this is where to set your dials!
And be sure to check out Zac Manchester’s Kickstarter video, which showcases the technology and inspiration for the KickSat: