Coryn Bailer-Jones’ The Physics of Interstellar Travel fills a need which has become apparent only in the last twenty years. Indeed, going back to the turn of the century, one would find the idea of traveling to another star discussed only in relatively isolated pockets, often presented at the tail end of conferences devoted to other astronautical topics. Papers, though, were being written at an increased rate, building on early work begun in the 1950s through the efforts of luminaries such as Les Shepherd and Eugen Sänger and continuing into the era of Robert Forward. By the year 2000, a number of mission designs had been created, still very much on the back burner but of high interest to specialists.
In today’s landscape, interstellar travel has become a vibrant topic. The wave of interest that energized the field incorporated high-visibility projects like NASA’s 100 Year Starship and in 2016, the emergence of the Breakthrough Starshot Initiative, which focused directly on the design of a probe that could reach a nearby star, presumably Proxima Centauri, within a human lifetime. Public interest in starflight has likewise been galvanized by the fast pace of exoplanet discovery, and growing attention to the question of studying such worlds through actual missions. Cementing the enthusiasm has been a stream of Hollywood depictions that offered viewers enticing imagery of such journeys.
The surge in papers discussing interstellar flight has exposed the lack of a college- and graduate-level treatment, a textbook wholly devoted to this topic. The Physics of Interstellar Travel meets that need with the precision of a key clicking home in a lock. It is a thoroughly researched analysis that presents travel to a star within the context of known physics, validating the perception that such journeys are within the realm of future engineering. Early chapters on orbital mechanics and the mathematics of rocketry illustrate the fact that each section can stand on its own in specialized classes at higher levels, while the quantitative analysis offered here will be of use to any student who has mastered college physics and is ready for the next educational step.
Although Bailer-Jones accepts the idea that star travel violates no physical laws, he is careful to acknowledge the challenges that emerge and the direction of future work that will eventually meet them. The principles of rocketry lead him to present fusion and beamed lightsail concepts as the likeliest paths forward, with the clarity provided by mathematical analysis applied to options including ion engines and antimatter. The nature of the interstellar medium is considered in terms of dust mitigation as well as the possibility of ramjet solutions. Communications and navigation receive thorough treatment but so do the essentials of orbital mechanics and relativistic motion.
The Physics of Interstellar Travel is, in short, a comprehensive extension of current textbooks in astronautics into the realm of missions once thought to be impossible. This book’s mathematical rigor should clarify for rising students the realization that steps we take today can result in practical outcomes, with the goal of reaching another star conceivable by the end of this century. Bailer-Jones advocates a step-by-step approach in which precursor work always tests new ideas to avoid the problem of future missions making earlier ones obsolete before they have reached their target. Where science and engineering have not yet taken us, this textbook illustrates the direction of steps forward, aiding the community in the construction of the needed roadmap.
Coryn Bailer-Jones’sThe Physics of Interstellar Travel. This is only the 2nd ‘Textbook’ on Relativistic space flight I know of. The other being Relativistic Flight Mechanics and Space Travel by Richard F. Tinder, 2000. (Tho Tinder’s book is mostly Relativistic Mechanics of Star Flight , with some exposition propulsion.)
Bailer-Jones book is more comprehensive. (I know of a lot monographs on Interstellar Flight , not any other textbooks, than those two,I guess?).
Bailer-Jones has lot of material on Classical rockets and astrodynamics , not sure how useful that is , but its ok.
Lots of technical derivations and there are exercises.
There is mention of Star Shot , liked to have seen more about projected energy star flight.
In the antimatter propulsion section, no mention of Eugen Sänger. In the references there is no mention of Sänger. Sänger, in the 1950s wrote more about relativistic space flight than ever had been done before. Sänger’s electron-positron propulsion is too awkward, but it is the first step in thinking about antimatter flight.
(One does note R. Esnault-Pelterie, wrote the first technical monograph that interstellar flight in 1928, L’Astronautique, with several chapters on relativistic flight. In fact Esnault-Pelterie, is the first to derive the Relativistic Rocket Equation.)
Sänger’s treatment of relativistic acceleration motion in Starflight is the most extensive I know of , where Poul Anderson got the idea for Tau Zero. (Acceleration in Special Relativity had been treated earlier in SR literature.)
I don’t see Generation Ships treated, did I miss it?
Hi Paul & Al
No, Generation Ships didn’t get a mention. Nor did Frozen Embryos or Self-Replicating Factories. Perhaps they’re all less “physics” topics? The Magnetic Sails section didn’t cover Claudius Gros’s discussion of non-magnetospheric drag-sails. So a few puzzling lacuna.
Interesting question here,…How many books on the topic of Warp Drive are there. I mean based on current research on the subject and not Science fiction.
Best I know of is The Science of Interstellar by Kip Throne.
https://en.wikipedia.org/wiki/The_Science_of_Interstellar
Exactly. He pioneered aviation and then astronautics, and was far ahead of his time. At that time when everything was to be invented, he filed nearly 150 patents !
I knew his name but today it is forgotten :/
https://www.astronauticsnow.com/history/esnault-pelterie/index.html
One of the early books written on Interstellar Travel worth reading is Prospects for Interstellar Travel, by John H. Mauldin:
https://www.amazon.com/Prospects-Interstellar-Travel-Science-Technology/dp/0877033447/
Wrote a detailed review here if anyone is interested:
https://www.linkedin.com/pulse/book-review-prospects-interstellar-travel-parts-1-2-paul-titze/
There’s also a reference list here which I would consider mandatory reading for anyone interested in interstellar travel:
https://github.com/paultitze101/ISVEnterprise
It doesn’t appear that recycling is discussed. Material recycling is presumably a physics question if the aim is to transport active passengers (biological or non-biological entities) rather than inactive cargo.
In Mankind Beyond Earth (2012), Claude Piantadosi suggests that it almost doesn’t matter how efficient recycling is, it will require harvesting the ISM to make up for losses on long interstellar journeys, something that may condemn interstellar flight for active passengers. This is similar to the conclusions of the JBIS Avalon project concerning building space habitats, which state that any such contained biosphere will require trade with Earth for needed supplies, as recycling is not 100% efficient.
Whether this is relevant in such a textbook depends on viewpoints about coverage.
If anything is going to help us its the moon, the sunlit part would produce around 1000 Terawatts, thats 10000 times what sharshot needs. Plenty of resources and co-aligned goals of the private and government sectors. Starship with its heavy lift capacity and the important ability to get fuel into orbit is a game changer that people will in time appreciate.
The physics and engineering questions for interstellar travel that carries human payloads are ultimately going to be joined to economic and political decisions made by these future societies
Funnily enough, I just had a letter published in New Scientist, in which I calculated how long it would take to get to the Trappist-1 system, as measured on a spaceship capable of 1g acceleration for years. (About 7.5 years, to go 40ly. Roughly!) Of course, this reveals the problem: an enormous amount of energy needed, and huge amounts of stuff to chuck out the back. It just can’t be done!
Re books: Try “Can Star Systems Be Explored” by Lawrence Crowell, and “Interstellat Travel: An Astronomer’s Guide” by Sten Odenwald.
Also, any good book on Special Relativity, of course.
Paul B, it is if you have to take your fuel with.
A realistic and practical interstellar (crewed) mission will need to undertake partial refuelling at the destination star system via ISRU (In Situ Resource Utilisation), this is mandatory not optional, and one needs the equipment and spacecraft to do so. That’s why all previous interstellar crewed missions proposed so far are unrealistic (among other reasons as well) because they don’t factor in the return voyage back to Earth and the fuel needed for the required deltaV. World ships, generation ships and warp drive FTL travel also fall into the unrealistic category in my books.
Also anything outside 20 ly radius from our Sun is beyond our current physical sphere of influence for the foreseeable future as far as realistic and practical starship designs are concerned (assuming we don’t go extinct in the next 200 years) so any interstellar studies looking at destinations outside this is purely academic.
Why teh assumption that a return flight is desired, rather than a one-way trip? Human migrations throughout history have often been in one direction only. In more recent history, was the Mayflower expected to manage the trip back to Europe? Or the westward expansion in the Americas from the Atlantic to the Pacific by wagon? There was even a suggestion that Mars astronauts might want to be on a non-return mission.
Isn’t the purpose of a generation ship to deliver the descendants to the new world, not to return another set of descendants to Earth?
As for long flights at close to c, the travellers could not return to the Earth they knew due to the elapsed time. Unless the world has become static, even a 50-year round trip might be very disorienting. (Would my 1960s self be able to handle contemporary life if instantly taken across that expanse of time?
I doubt a generation ship would leave Earth for a new world unless that world was thoroughly explored and characterized by probes first to ensure that it was suitable for humans, and therefore, there would be no need to return to Earth.
“Would my 1960s self be able to handle contemporary life if instantly taken across that expanse of time?”
I believe we’re in a transition state. To what, l’d rather not speculate, but I do not think this is sustainable, and we will reach equilibrium until the next change of state. In between longer term endeavors will be more likely.
“purely academic”
While I agree with all that you said up to that point, I do not agree with this. Yes, it is academic, but so what? Understanding the parameters of interstellar travel, as outlandish as they are, has value by pointing to aspects that are especially challenging. For example, communications from micro-probes envisioned in Breakthrough Starshot.
The problems appear when proponents drift into unphysical speculation and dress it in academic clothes. I don’t take those studies or studiers seriously.
I suspect robot entities will be sent long before biological ones. I mean could we send tesla robots now if we had the craft? I think with upgradeable software sent from earth yes. I personally doubt there will be generation ships carrying humans, more likely embryos which grow into adults on the new world or rotating habs. These growing humans will be tended by robots until they can look after themselves. There will always be a constant flow of information from earth to keep them upto date.
By the time you perceive this, our FTL exploration will have made initial contact with almost all the slower prior craft in most directions that were launched in the past. We are now at year 8796 when FTL was discovered – it was an almost intractable problem!!. In prior years almost all other aspects of science have been explored in depth. The human genome was mapped and understood in depth, as were almost all other species. Human DNA was mapped, and then improved to TNA and QNA -(triple and quadruplicate strings) and the reading/transcribing methods perfected. Each human is now fully mapped into QNA form and almost all elect to be ‘quadded’ as this leads to near infinite life(barring accidents) and the QNA data base allows for a quad replicant to be launched as needed, with the most up to date data back-up installed. Di, Tri and Quad forms are self fertile but not interfertile but people often choose to launch Tri/Quad replicants with updated memories, each of which launches a fork in their life path. There are tens of thousands of these mind clones in all disciplines. As was to be expected, computation grew apace along with cellular science and later human mind cells achieved a 90% reduction in cellular space in all dimensions which allowed for a huge IQ growth, where live IQ’s are in the 30,000 area. AI has also progressed and many fully sentient AI’s are busy with their own tasks. In general they have chosen diverging paths of their own choosing, their being ample material resources that almost no competition for human resources as their are billions of vacant orbital lumps everywjere. The AI’s first foray into intelligence was with other animals, with cats/dogs/chimps and many others being gene/mind edited to human or greated intelligence. Birds progressed faster, with their initial smaller cerebral cellular dimensions and they were the first sentient companions, soon follows by cats/dogs/etc – it is quite a zoo now!!
I digress, an update ship will follow this initial ship and will show your ongoing options. Many will find enormous leaps in their fields as the time lag grew, but almost all of you will have your own sentient AI helper to bridge the gap. There are also mind/data implants that will help and the implants also allow older minds to be fully fluent on the Solar mono language.
Enough for now, see you in the furure!
@William
What does this mean? A DNA helix with 3 or 4 strands rather than 2? How does that work, as they added strand[s], cannot bind to the bases in the double strand?
Why does this extend life span, as each cell would have to use more energy to replicate and transcribe the T/QNA. Which strand becomes the template for proteins? Don’t forget the mitochondria must also be altered to support the increased metabolic needs, likely shortening the life span like smaller animals with faster metabolisms.
Thanks to all the previous contributors for the comments and feedback on my book. To address the lack of coverage on biological aspects, such as frozen embryos or generation ships, I point readers to the book’s preface, where I define the scope of the book: I limit the treatment to sending uncrewed robotic spacecraft. Sending humans involves a lot of biology and psychology that really needs separate treatment (there are books on the market that do that). I didn’t attempt to mention many prominent scientists and engineers in the development of this field, and while more historical treatment would have been interesting, this can be found in books on the history of spaceflight. More discussion of variations on the technologies I do cover – such as magnetic sails – could indeed have been useful, but ultimately space was limited. My aim was to present and explain the underlying physics, which hopefully will be useful when reading the other literature on this fascinating topic.
Hello,
thank you for your book which summarizes well all our updated knowledge on the possibilities of interstellar travel. In France, the astrophysicists Hubert Reeve & Nicolas Prantzos had well discussed the subject but they did not yet talk, for example, about solar sails or biology. H. Reeve has joined the stars and apparently, space travel is no longer a dream for his French colleagues ; only Roland Lehoucq, who popularizes astrophysics, still speaks a little about it. I think we should contact these scientists who are trying to spread astronomy to the public and ask for your works to be translated into European languages because this wonderful discipline is in “free fall”…well… not for everyone ;)
Fred – France
Coryn
It is a good book, none other like it.
In a universe governed by Special Relativity, the most transformative technology for interstellar civilization may not be propulsion, but longevity.
In seems to me, the leading edge of science is, now, biophysics and biochemistry. What if a civilization can master lifetime. That is what if by mastery of biological science individuals can live hundreds … thousands of years. Interstellar trips of hundreds of years at relativistic speeds becomes a matter of fact. (It is a scenario that has been a part of science fiction, tho not real often. I does wonder what such a mastery does the social philosophy of such civilization?) Still transport of biological beings by relativistic flight demands radiation shielding, probably something such an advanced civilization can also master.
Then why send sophonts at all? Excluding colonization and empires (never bought galactic empires , just never felt viable accounting for astronomical distances). If the instrumentality of FTL is never managed Special Relativity is prime.
Send robots only. Of course that is the baseline right now. Robots can be ‘hardened’ more easily than human beings. Less mass. (Starshot has shown how to make small ships that astound me.) Couple this with long lifespans, making wait times routine. Back at home planet one would have ‘telepresence’ at destination. Light time becomes a part of interstellar exploration.
Perhaps the future of interstellar civilization depends less on discovering ways around Special Relativity and more on learning how to live within it. The decisive technologies may not be warp drives but longevity, robotics, and cultures capable of thinking on timescales far longer than our own.
Then one waits for FTL.
In the interim before significant interstellar spacecraft are launched, we still need to get a good map of places to send them. Exoplanet discoveries since the 1990s have been very encouraging, but also incomplete in nature. The good news has been that they exist, but the other side of the coin has been why yearn to visit any of those identified with what we know about them so far. Much of the real estate iin the solar system would appear just as attractive to explore based on their similar hostility to life as we know or enjoy it.
Unless closer scrutiny of star systems or exoplanets from afar would help the case.
I believe that space based telescopes still have a lot of potential for that. Moreover, they can address the entire celestial sphere. Someone might argue about data that can be returned based on a half dollar sized space probe vs. a James Webb ST successor – and it might have some allure for a target like the Centauri system. But a JWST or a Kepler ST successor can refine data on so many already identified targets…More satisfaction guaranteed.
Of course, argument for a space probe is likely to focus on targets within 10 parsecs. And where most of the exo-earth have been identified with transits come from red dwarfs. They are the low hanging fruit because they are tightly packed with short orbits and transits that generate data quickly. K and G’s do not provide
data as easily or quickly. Tau Ceti as close as it is gives a differing summary every time I read an update, but it is likely to have an Earth like planet, for example. It would be good to know more about it or them, but collecting the data is slow or else requires a next generation of telescopes on orbit with post JWST technology.
Musing this far, one also has to consider what one is looking for: An Earth without complicating clauses? Evidence of extra terrestrial life? A place for habitation with more potential than solar system objects? A civilization to hail for cultural exchange? [ Never got around to reading it, but Jack Vance once had a story of space opera where we actually produced one at location first and then the ETs were supposed to reciprocate…Heaven knows what that would have entailed. Now how their critics would have received ours.] Well, the point is that if there is someone or something out there, we might not want to jump aboard a generations long Beagle-style science expedition. It might be an invitation for the prospective hosts to reciprocate in their interpretation of our style here.
I’m reading through The Physics of Interstellar Travel, and I am enjoying it. There’s certainly a lot of useful information as well as informed opinion in it. It should be used as a textbook and a reliable guide to some features of this very large technical area. A textbook is vitality needed. If the field is going to really developed, it needs a cadre of people who will understand the material in this book and more (see below). That means it’s got to be introduced at university – level courses. Of course, there are some deficiencies in this book. I hope that Coryn Bailer-Jones will consider including more material in what I hope will be a second edition. The emphasis seems a bit unbalanced. As an author of four editions of my textbook, I certainly realize that there are always improvements to be made. I will make some suggestions to him.
I think the largest important matter that’s missing entirely is any treatment of the cost of various interstellar travel approaches. Some technology approaches will probably never be realized because of high cost. For example, fusion rockets, such as Daedalus and Firefly, would be horrendously expensive, on the order of $100 billion dollars. So, they’re unlikely to happen. My experience in building large systems, especially directed energy systems, is that you specify only two things: the goal parameters and that the cost be minimized. Never fall in love and insist on with specific components or technologies.
The chapter called “Laser Sails” doesn’t include a possibility of using microwaves or millimeter waves instead of lasers. The former are serious candidates and could be built now for reasonable cost. Experiments using microwaves have been done on sail flights, spin, beam-riding and materials, but aren’t mentioned. Lasers are far too expensive now and will not probably be cheap enough for several decades to come, as you well know. described in my recent accounts of the Starshot project results. So why focus only on the laser driver for beams?
I also noticed little mention of any experimental work on the several technologies. Actually asking nature a question in the laboratory, which is what experiments are, is the only way to find new unpredicted effects as well as to verify, correct or refute theory. Many important new results have been discovered experimentally, although not predicted by theory. Since I have done both experiments and theory, I appreciate both approaches, for they are both essential to scientific work.
I very briefly mention using microwave – instead of visible/near-infrared – wavelengths at the end of section 11.3.2. But as the wavelengths are of order 1000 times larger, diffraction is 1000 times larger, all other things being equal. Even if the transmitting arrays could be larger than the ~1 km being considered for near-infrared transmitters, there will still be much more diffraction with microwave propulsion. This significantly limits the distance over which energy can be transmitted in practice, so the final velocity that can achieved for a given transmitter power and sail mass/size will be much lower. This appears to makes them less useful for fast interstellar travel, although they are certainly very interesting for sending probes in the solar system, out to a few hundred astronomical units or so.
Coryn, If you use a very large mircowave phased array say the size of the moon then it can concentrate energy a lot more. It can focus fairly well out to millions of km’s. It’s certainly easier and cheaper to build than lasers.
Thanks for the comments. I indeed avoid talking about costs, although 100 billion USD is not that large compared to other mega projects (e.g. ISS).
Pleasantly surprised that this book is open access, ie it can be downloaded for free at the Cambridge University Press web site.
https://www.cambridge.org/core/books/physics-of-interstellar-travel/69C23CDCF164E2C71A65497F299EE38F
Book looks awesome at first glance.
Thanks Coryn and thank you Paul for showcasing this.
– Greg L
Retired aerospace avionics systems engineer
Active stargazer, active private pilot
Ad Astra Per Aspera
Coryn Bailer-Jones: I think we can agree that microwaves and millimeter waves could be used for power beaming for most of this century for missions to the outer solar system and beyond. Cost is a driving factor in human affairs. Lasers now cost 10,000 times what microwaves and millimeter waves cost per watt. That substantial cost difference means that, if power beaming should be developed in the next couple of decades, it’s going to be done with those wavelengths. That will allow us to demonstrate in space key power beam accelerated sail issues: beam-riding, sail fabrication, sail deployment and many other key practical operational factors. Lasers, if they ever do come down in cost, could be used for far more distant targets, but that’s for another generation to decide.
The Starshot models referred to in your book, which were developed by Kevin Parkin, assume the laser cost will be reduced by that four orders of magnitude. That requires completely automated production at high yield. That will only happen if lasers find a new application that requires large production at low cost. For example, to help guide robotic electric vehicles. Microwaves achieved that price level with microwave ovens several decades ago.
Another factor mitigating against lasers is that laser arrays are a concept, not a reality. Although models for laser arrays have been developed, funded by the Starshot project, the reality is that only a few lasers have been coupled together in phase. So much is unknown about the practicalities, which would have to be resolved before anyone would try to build arrays up to the hundred million lasers the Starshot model requires. That’s a striking contrast to microwaves, where phased arrays have been operational for 70 years. Although the large number of microwave sources in these arrays is classified, it’s surely measured in the thousands to hundreds of thousands.
Wouldn’t rule out laser based propulsion quite yet, they could offer power densities that microwave can’t provide in practical terms although agree that at the moment the power and laser aiming requirements are formidable for any meaningful thrust. For eg the precision required to get the optical cavity aligned from the laser base station with the spacecraft is at least 2 orders of magnitude from the state of the art of what we can do today with the best telescopes. Photonic Laser Propulsion (PLP) (special case of Beamed Laser Propulsion) could potentially be useful down the track for solar system based propulsion (photonic railways) and initial boost out of the solar system for interstellar missions however a lot of the technology it requires still needs to be demonstrated and I would consider this a semi-far future propulsion system which relies on extensive solar system wide infrastructure to be useful, free preview of Young Bae’s book on PLP here:
https://www.researchgate.net/publication/384863392_Photonic_Laser_Propulsion
Summary here if anyone is interested:
https://www.linkedin.com/pulse/advanced-propulsion-resources-22-paul-titze-su26c/
Asking AI some reasonable questions about large microwave beams yields some interesting results. For a 10GHz microwave phased array the size of the moon, no mean feat, does allow reasonable focusing distance at 1 AU with a diameter of about 1.6km. The sail would be a mostly open low weight mesh design with known materials. The 1AU does allow for lower accelerations with say 1250g giving you about 20% c over 1 AU. However the skin depth causes issues, in essences you cant have nanometre thicknesses but rather it would be 10 or more microns thick…it then becomes heavy requiring a lot more power to move it. Unless you can reflect the microwaves back and forth for a multi bounce to help with power considerations it would be on the whole less practical at least for very high velocity missions.
Using a 1 micron laser with the same huge moon sized array gives an incredible 10 cm diameter focus at 1AU ! And a 28 Km focus at Proxima Centauri and if 600 Gigawatts was transmitted to Proxima it would be about the same irradiance from the sun as earth gets per sq meter. Lasers are expensive but very powerful.
If you can work out a material (engineered nanostructured multilayer metamaterial?) that provides at least 99.999% reflectivity for high powered X-ray lasers then that would be even better as far as beamed propulsion goes however that’s likely a far future tech if it ever happens, however the mass savings on the spacecraft side would be very significant.
Paul T, its a good way there already. Getting them to phase array would be something else.
https://www.nature.com/articles/nphoton.2011.197
A tool and a weapon are essentially the same thing; the primary difference lies in how they are used.
I have only had time to skim the book, but one of my 1st impressions is that almost everything will utilize an extremely large amount of energy. These energy levels mean they have an inherent capacity to be considered or used as weapons of mass destruction.
There has been some discussion regarding the feasibility of using high-power microwave beams to propel a sail for a space probe. Such a device, also referred to as a high-power microwave (HPM) beam weapon, constitutes a form of directed energy weapon. At the energy levels required for propulsion, it would disable (destroy) the electronics of any satellite in Earth orbit.
Even if the primary intent were not weaponization and safeguards were implemented, significant unintended consequences would remain. At the required energy levels, even the unavoidable side lobes could destroy any satellite intersecting them. The near field at these energy levels would be destructive to any object in proximity during operation. For instance, aircraft within the vicinity would be at considerable risk.
Some of these challenges might be mitigated by situating the device in a remote location. However, the presence of numerous satellites in orbit today, as well as the projected increase in their number, would still pose massive, insurmountable obstacles. Even if the beam were minimized near Earth, it would remain virtually impossible to avoid intersecting with satellites, particularly if the beam were active for more than brief intervals.
Given these risks and consequences, the most suitable location for deploying such a device would likely be the moon’s far side. This placement would also facilitate the use of mass drivers to launch initial payloads above the transmitting beam. Mass drivers are also referred to as railguns or coil guns.
All technologies entail inherent risks, and their benefits are evident; otherwise, they would not have been developed. It is essential to systematically study both the short-term and long-term risks of technology and their impacts on civilization. Consideration of these risks should be integrated into the design process. For instance, evaluating the risks associated with the operational environment and incorporating inherent safeguards is crucial. To reduce the potential for weaponization, systems utilizing microwave beams or lasers could be equipped with a two-key protection mechanism from the outset. In this configuration, the power source could serve as the first authorization key, while the device itself could function as the second key.
These considerations are, in my view, largely absent from current academic studies. I recommend that future editions of this book address these issues. My focus is not on the morality of these technologies, but rather on the ethical imperative to assess and mitigate their associated risks.
There is an upside: this kind of technology could be a good target for SETI searches. But as the SETI Institute has shown, it probably will not help much given SETI’s current situation.
SETI Institute Looks for Signs of Technology in Interstellar Visitor 3I/ATLAS.
https://www.seti.org/news/seti-institute-looks-for-signs-of-technology-in-interstellar-visitor-3iatlas/
I’m glad the SETI Institute decided to look for technology on 3I/ATLAS. I believe they did their best, but sadly, their efforts were extremely limited. I’m not criticizing the results, but rather the resources they had to work with.
The most important thing is slowing down.
The physical constraints you describe — propulsion, distances, radiation — are precisely what led me to argue that interstellar human travel is not merely difficult but constitutionally impossible, not provisionally but ontologically. I have recently published a philosophical essay developing this thesis through eight converging arguments, including the antibiotic nature of space for biological life and the impossibility of navigation in a space without fixed reference points.
https://www.academia.edu/170680613/SPACE_TRAVEL_myth_or_reality_
Antonio Gentile