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A Framework for Interstellar Flight

Those of us who are fascinated with interstellar travel would love to see a probe to another star launched within our lifetime. But maybe we’re in the position of would be flyers in the 17th Century. They could see birds wheeling above them and speculate on how humans might create artificial wings, but powered flight was still centuries ahead. Let’s hope that’s not the case with interstellar flight, but in the absence of any way of knowing, let’s continue to attack the foundational problems one by one in hopes of building up the needed technologies.

Marc Millis, who ran NASA’s Breakthrough Propulsion Physics project at the end of the 20th Century, always points out in his talks that picking this or that propulsion technology as the ‘only’ way to get to the stars is grossly premature. In a recent interview with the Australian Broadcasting Corporation’s Antony Funnell, Millis joined physicist and science fiction writer Gregory Benford, Icarus Interstellar president Richard Obousy and astronomer and astrobiologist Ian Crawford in a discussion of the matter. Asked where we stood with nuclear fusion, Millis said this:

At this point it is really too soon to pick any favourites because…well, let me put it to you this way; in three different studies, one done by looking at the amount of energy available, one done by financing and one done by technology, all of them came in that there is still going to be about two centuries before we could do a serious interstellar flight. So even if you pulled off the technology for a fusion rocket, to develop the infrastructure to mine enough helium-3 to fuel it, it’s still going to take a very long time. In other words, you could make the technology but to have the amount of energy to put into it takes even longer than developing the technology.

We had much the same discussion at the 100 Year Starship symposium last year in Houston, where a backer of the project from the business world asked why an interstellar mission would be so expensive. The answer simply comes down to the amount of money it takes to create the energy needed to push a payload to the kind of speeds we’re talking about. Given all that, we continue to study everything from beam-driven sails to antimatter-induced fusion and the whole boatload of possibilities in between, hoping to find more efficient ways to drive the starship.

VARES-16-Lasers-RT (1)

Image: High-intensity lasers produce particle/antiparticle pairs from the vacuum, in a concept introduced by Richard Obousy. Credit: Adrian Mann.

Timeframes Short and Long

People differ widely on time-frames — some people get positively passionate about them — but my own view is that working toward the interstellar goal is just as valuable for me if it happens three centuries from now than if it happens by 2100. I’m no seer and the few times I’ve tried to predict the future, I’ve been humbled by how surprisingly an ‘obvious’ outcome can change. I’m also reminded of what Richard Obousy often tells his own audiences, that humans tend to overestimate what they can do in the short run and underestimate what they can do over longer periods. So maybe interstellar flight is going to happen sooner than I think. Either way, I’ll keep on writing about the topic in hopes of encouraging research and public involvement.

Whenever interstellar flight comes, assuming it does, we’ll all do better by looking out for our planet in timeframes of centuries rather than years or even decades. Gregory Benford told Funnell that the reason we fall into short-term thinking traps is that we live in a tightly defined environment, one in which the great age of physical exploration on our planet is long past. Moving out into the Solar System and ultimately beyond it in search of resources may once again instill a longer-term view as we seek out elements like helium-3 that fusion reactors will demand.

New human societies should emerge from all that as we move toward the construction of an economy throughout the system. Let me quote Benford on this from the interview, in a section where he’s asked about the 100 Year Starship project and the choice of the time frame. A century may be a symbolic goal, but the act of choosing goals is itself part of the process.:

The expansion of the United States into the West began roughly around 1850 and within a century was accomplished, largely through railroads and use of coal for power. But it went on to new heights, we invented the aeroplane, and a century later we already had intercontinental air flight commonly available. It’s this kind of building upon a model that makes star flight a proper goal for the development of the inter-planetary economy that we believe is coming, and therefore sets a goal; 100 years from now let’s see if we can build a starship, and what does it look like, and is it manned or unmanned or robotic or does it have artificial intelligence aboard? Those are secondary issues. The main thing is let’s have a goal and let’s build toward it.

Thus the method: Create a concrete goal and discover a way to reach it. Benford told Funnell that prosperity grows out of these efforts because the structure is being built every step of the way. I’m also reminded here of the ‘horizon mission methodology’ that NASA has found useful in stimulating thinking in its conferences — John Anderson described this in a 1996 JBIS paper. The idea here is to present a problem that is at present impossible to solve. The team then sets about defining what breakthroughs will be needed if this problem is ever to be conquered.

The Dangers of Presumption

Defining the goal and setting the target is the beginning of the process. This is one reason for the original Project Daedalus, which set out to examine the question of whether an interstellar vessel was even possible. The reasoning was that if a culture at our own level of technological development could identify a conceivable way to reach another star, then future breakthroughs should make the job that much more realistic. No one seriously planned to send a 50,000 ton vehicle to Barnard’s Star, but the project proved, way back in the 1970s, that designs that did not violate known physics could be contemplated. Project Icarus now refines the Daedalus model.

Former astronaut Mae Jemison, who heads up the 100 Year Starship initiative, put the matter this way in her conversation with Funnell:

One of the biggest challenges is, again, to keep people from trying to design every step of the way right now, because we don’t know. And as soon as you start saying ‘I know the answer right now’, then you’re probably going to cut off other avenues. There is something that I would say when you talk about how daunting this is and whether or not people say that it’s not possible. It’s a term that I first heard associated with movies, and that term is ‘suspending disbelief’. At some point in time we have to do move forward by suspending disbelief.

Jemison is not talking about suspending disbelief in known physics, of course. What she’s saying is that setting the goal and collecting the wide range of options is how the process begins, and if we succumb to assumptions — from ‘interstellar flight is impossible’ to ‘there’s only one way to do it, my way’ — then we’re not honoring the need for lengthy and challenging research that’s ahead. Personally, I find this notion invigorating. We are beginning to realize through our exoplanet research that Earth-like planets may be out there in the billions. We now engage scientists and engineers in the great work of studying the options that may one day put a human-made payload into another solar system. Humans themselves may eventually make the journey if we are wise enough to make the foundations of this enterprise deep, strong and true.


Comments on this entry are closed.

  • Rob Flores March 5, 2013, 12:25

    Well things are not as hopeless for our living to see at least a probe sent
    to say Tau Ceti. Our priorities need to be also focused on two other
    technologies to enable our living to see the near future.

    We should put more effort into prompting politicians to support,
    De Gray’s Strategies Engineered Negible Senescence idea. Well maybe
    you wont see the probe get there, but if SENS results in todays younger
    population living 200 years, your chidren just might. It seems to me that
    medicine and the promise of genetic engineering to create repair mechanisms
    for the human body is a technology that will far out pace Space propulsion
    Alternatively or co-existing with a long life, could be hibernation to extend our reach into the future, If you could safely sleep 2 days for every
    1 active day, and that hiberation was deep enough to slow aging along with it would extend our reach forward even more. You could stagger portions
    of humanity so that only 1/3 of the total human population was awake, that
    would save resources also. (yes, I know it’s from a SF story)

    Obcourse there could be sociological bump on the road, the most likely
    is the problem of the dominant paradigm. If future technologies for space
    travel require a reworking of much of advanced physics. Those at the
    top of the heap in their field will not give up their posts, their views, their
    objections to new theories. Just look at the Theory of Continental Drift.
    Even when presented with evidence, many stodgy old geologists refused to
    accept it. It took time and death of the old guard in geology for that theory
    to become the dominant force of geology.

    I don’t think it was just geologist are particularly dense or curmudgeonly,
    it’s just a reaction to the potential of one’s work being rendered obsolete.

    There would need to be Mandatory retirement from all fields of study. So
    no you can’t be department head of Physics for 100 years.

  • Erik March 5, 2013, 14:09

    Interstellar travel may be centuries out, though I doubt it. We have a leg up on our 17th century analogues: people commonly know that human-engineered interstellar travel is at least theoretically possible, whereas most people in the 17th century commonly believed that human-engineered flight would never be achieved.

  • Kenneth Harmon March 5, 2013, 15:20

    The key underlying assumption in the article above is that Humans won’t change much over the next 100+ years, and so we will be bound by the same constaints as today, and continue to do things pretty much as we do now, albeit with some better Physics , Technology and Engineering. Same for all 3 of the Studies that Marc Millis sites in terms of time-lines spanning at least a couple of Centuries for initiation of Interstellar flight. If one believes even half of what Ray Kurzweil, Hugh DeGaris and others are forecasting about Conscious AI/Artilects (and even if their projections are off by a hundred years or so on “Hard AI) the challenges of Interstellar Flight may be far less daunting than Humans currently believe, and the amount of time it takes may be much less. Sadly, if Hugh DeGaris is correct the current Human species may not be around by then to see it since the Artilect may have wiped us out. Be that as it may, the projections above seem to ignore the fact that it is rather likely that Humans will change in fundamental ways long before Interstellar Flight is attempted. Therefore, there may be a complete redefinition of the problems associated with Interstellar Flight. For example, for entities with Intelligence levels that exceed those of unmodified Humans by at least a couple of orders of magnitude (Cybernetic Humans or Artilects), and who are not bound by our current flesh and blood limitations there may be many more options. Early 21st Century Humans can and should dream about Interstellar Flight, but the real constraint may be Human Intelligence and the Human Factor, which may no longer be a major issue a mere 100 years from now if some sort of Singularity or even quasi Singularity is achieved.

  • NS March 5, 2013, 17:06

    I’m sorry that I don’t share the optimism of Rob Flores and Erik. Although God willing I have two or three decades ahead of me, at this point I almost despair of seeing even a probe get to near-interstellar space in my lifetime (except for the Voyagers and maybe an extended New Horizons mission). The best (small) chance looks like the Icarus Interstellar NanoSat project. I’d happily be proven wrong but it seems to me that without major advances in propulsion interstellar space (much less other stars) will be out of reach for a long time to come.

  • David March 5, 2013, 20:20

    I will just repeat again and again we could launch Project Orion using Orion from an asteroid and I have to believe we have the technology to get it to 1 percent of c which is alpha centauri in 400 years. We sure have the bombs.

    I also think we will pass it by by 2100 with something faster BUT we should do it because we can afford it -it would be something to build on and it would even provide some economic stimulus now! On top of that it would be a test for comminication and sheildling. and could help us in asteriod deflection

  • Mike Lorrey March 5, 2013, 20:38

    Why is Millis stuck on Helium 3 when EMC2 Corp is making great progress with polywell fusion with DD and pB11 fuel schemes?

  • Brett Bellmore March 5, 2013, 20:44

    I continue to think that the key enabling technology for interstellar travel is self-reproducing industry. Without it our resources can never grow enough greater than our needs to leave the excess needed to afford more than trivial, marginal efforts, small probes at ruinous cost.

    Fortunately we do not appear to be so far away from achieving this necessary technology. We could have it within a couple of decades. And once we have that technology, there’s no reason our industrial infrastructure, power production and manufacturing, couldn’t sustain a growth rate of several hundred percent per year until we’re a K-2 civilization with all the energy needed for interstellar travel… and a population not greatly larger than today.

  • coacervate March 5, 2013, 21:10

    No one seems keen to consider “black swan” tech stemming from breakthroughs in what i can only refer to as quantum weirdness. Worm holes, curved space…none of the hard physicists go near speculation on that front. I know that it is early days, but shouldn’t we be suspending disbelief to at least play out some plausible senarios? and some rippin yarns while were at it?

    NS, don’t despair. We will carry you.

  • GaryChurch March 5, 2013, 21:51

    “-maybe interstellar flight is going to happen sooner than I think. Either way, I’ll keep on writing about the topic in hopes of encouraging research and public involvement.”

    And thank you for your efforts Paul. Special thanks for maintaining this amazing forum; the last couple months have been very enjoyable for me. I love discussing this stuff with people.

    The regulars here are familiar with “my way.”
    I believe in freezing people and if I was signing the checks I would be pouring billions into researching revivable cryopreservation.
    If we could freeze people we could launch an H-bomb propelled Starship within 20 years (maybe).
    It would be a pretty slow boat though and would probably (unless we go extinct) be intercepted by a faster ship and the crew transferred a couple centuries down the road.
    My guess is black hole propulsion at around 30 percent of the speed of light will be the means to expand slowly into nearby systems for the next several centuries.
    But if we build god-like machines of super intelligence as Hugo (not hugh) DeGaris has forecast, then if anything can figure out how to get there quicker it will be an Artilect (Artificial Intellect).

  • Joy March 5, 2013, 22:15

    “Humans will change in fundamental ways long before Interstellar Flight is attempted.” – Kenneth Harmon

    Agree with that. Even when I first saw Captain Kirk on TV at aged 11, I thought that having baseline humans fly around at warp speed and get beamed through a transporter was silly. They had exponentially advanced engineering with only trivial medical progress and no behavioral changes from 1960s Americans. Not credible.

    I would go off in another direction from what Kenneth Harmon had in mind. Perhaps to acquire the knowledge, wisdom, stability, and longevity required for interstellar flight is also to lose interest in doing so. I recall the occasional old species Captain Kirk would discover, who had chosen to live simple lives on their home planets. That seemed credible to me at the time, and is even more credible now. In general, only children are interested in climbing trees. Once we are grown up enough to launch starships, maybe we won’t need to? One possible answer to the Fermi paradox anyway.

  • Mike Mongo March 6, 2013, 0:52

    Hear! Hear! Let’s pay for the research, the science, the math, while at the same time instilling interstellar aspirations into our children. Great post, Paul.

  • JoeP March 6, 2013, 14:33

    @Mike Lorrey

    Mike, what progress? I haven’t seen much official results from EMC2 in the past couple of years. Last I heard was that they validated some of what Bussard predicted and were doing further testing on WB8.

  • FrankH March 6, 2013, 16:09

    @Mike Lorrey – I agree, using He-3 as an excuse to go into space is very weak and irritating because it’s so easy to dismiss – it’s a weakness in the arguments for “The Cause”, not a selling point.

    He-3 can be fabricated cheaply on Earth, either as a byproduct of Tritium decay or from a reactor configured to produce it. It is not a difficult to obtain gas (although there is a shortage in the US now), production can be scaled up or down and it’s certainly cheaper to produce here than any Moon based production (IF it’s even feasible) will ever be.

    Also, there is a distinct lack of He-3 powered fusion reactors. Typically you need to have a demand before you provide a supply.

  • Adam March 6, 2013, 16:25

    Suspended animation has been part of the conceptual mix since Goddard’s “The Ultimate Migration” (c.1918). Robert Goddard imagined interstellar travel might be achieved by humans being “bred” for reversible mummification. While the genetic manipulation technology he knew – selective breeding – isn’t up to the task, one wonders if there’s not something to be learnt from the tiny organisms that do successfully undergo reversible mummification? Brine shrimp lock up their biomolecules in poly-saccharides thus preserving them against decay for the day they’re rehydrated. Perhaps we’re smart enough to develop means of locking our molecular structure in place? Cryonics already has investigated a variety of ways of mitigating ice-crystal formation through additives, so the idea of replacing blood plasma with something able to interpenetrate our cellular structure intimately isn’t beyond present research thought.

    Incidentally, Gary Church’s propulsion/cryonics preferences aren’t too different to Ernst Opik’s views on achieving interstellar flight – his op-eds are available via NASA’s ADS if anyone is curious. He left his native Estonia in the wake of the Bolshevik take-over and settled in Ireland, doing much to enrich astronomy there.

  • Tarmen March 6, 2013, 16:54

    Not sure freezing adults won’t damage their brains. We could practice the embroyos grown in artificial wombs method here on Earth . But with only the Ship AI for a ‘mother’, the grown up colonists will be a different kind of people. Maybe driven to suceed or maybe crazy. But only the AI would have to remain ‘awake’ for the long trip. Even a couple thousand years may be feasable.

  • GaryChurch March 6, 2013, 20:58

    “Not sure freezing adults won’t damage their brains.”

    I am pretty sure it will. That is why they need to do research.

  • Dmitri March 7, 2013, 5:50

    Mentioning of Enrst Öpik struck me how little we actually know about our countrymans’ successes. But then it also stuck that even contemporary astronomers, those who are very active and making actual science in Tõravere also don’t stick out much on news feed or in bigger picture as you would guess from highly respected and renowned scientists. I’m actually quite confident that they are contributing to wider education and knowledge of society and the work but it’s just a small part of the mainstream information. If want to get some, have to search for it.

    Jaan Einasto is only name I can quickly recall but there is many-many more!

    Still, it’s strange we don’t know much about Öpik or of his work, not mentioning his proposals for interstellar travel.

    Last month I’ve been fortunate to have a gig in Gustav Adolf Gümnaasium (GAG) established in 1631 and the oldest active school in Estonia. There is a wall of their graduates who made to Member of Academy of Science. There wasn’t much of them, 6 or 8, but Ernst Öpik was first in the hall of fame. Made a picture of Öpik’s display – http://i.imgur.com/c2Wwgcs.jpg

  • JoeP March 7, 2013, 15:23

    Yes, brain freeze is painful, so I imagine some damage is being done. What kind of sick cryo-experimentalist came up with the Slurpee?

  • johnq March 10, 2013, 11:12

    Here is the statement.

    “One of the biggest challenges is, again, to keep people from trying to design every step of the way right now, because we don’t know. And as soon as you start saying ‘I know the answer right now’, then you’re probably going to cut off other avenues. There is something that I would say when you talk about how daunting this is and whether or not people say that it’s not possible.”

    Here is my objection.

    I can think of nothing more useful and valuable to the NICE (Nascent Interstellar Colonization and Exploration) movement than the exercise of early design, which includes spec writing. We need to be generating questions, lots of them. There was a comment in the early days of Apollo that “10,000 questions would need to be answered,” (whether there is an actual historical basis for that quote I do not know, but it sounds right).

    In any event, for star flight I suspect we need to address a somewhat larger number of questions. So get writing. Contrary to the quote, we should be encouraging people to do this and combining/criticizing/exploring each others efforts. It would be both humbling and inspiring. It would in fact be the quickest most productive way to get past the arrogance of “I know the answer . . .”

    The only rule I would impose is that all these efforts be on-line, accessible to everyone. We shouldn’t worry if most of this is silly or quickly outdated. The exercise will pay for itself many times over.

    There used to be a rule at a large aerospace company that nothing left the ground until the weight of the documentation = the weight of the vehicle. For example, the weight on a hypothetical Enzmann Starship is 12 million tons (24 billion pounds, or ~ 5 billion reams of paper — I know, how quaint). That’s a lot of bits. In the spirit of that aphorism, we need to get to work designing our starship(s) now.

    In other words, in response to the concern “We don’t know”, we’ll never know at this rate.

  • GaryChurch March 10, 2013, 15:10

    “- in response to the concern “We don’t know”, we’ll never know at this rate.”

    If we do know but refuse to accept the cost? There is no cheap.

    We know the main problem with traveling in a spaceship is providing earth-like conditions for the crew. This means a massive radiation shield and artificial gravity probably generated by a tether.

    Chemical propulsion is useless for pushing humans in spaceships with massive spinning shields and nuclear power plants around the solar system. This means some form of nuclear propulsion will have to used.

    So far we have a massive radiation shield, a nuclear power plant, and some form of nuclear propulsion.

    We cannot be playing with nukes in orbit; the Moon is the only place to assemble, test, and launch Atomic Spaceships. Fortunately, in the Space Launch System (SLS), we will soon have a Heavy Lift Vehicle (HLV) with hydrogen upper stages available with which to establish a base. The Moon also has water to fill up the massive radiation shield required for long duration missions.

    What kind of propulsion is the question. Nuclear Thermal Rockets (NTR’s) seem like a good deal since they have already been tested. Actually NTR’s are extremely poor performers. There is only one off the shelf practical form of interplanetary propulsion; bombs.

    I am not going to play the I don’t know game and listen to what I know will not work. I know what I know and it starts with accepting the radiation, gravity, and resulting propulsion problems. We have everything we need;

    1. An HLV to carry payloads, humans, and fissionable material, to the Moon.
    2. Assemble, test, and launch facilities on the Moon to allow nuclear missions to depart from outside the Earth’s magnetosphere resulting in no contamination.
    3. Nuclear weapons grade fissionables. There are hundreds of tons of it stored all over the world. Japan, for example, has 40 tons of it and they do not even have nuclear weapons.

    A Base on the Moon from which to launch nuclear powered, propelled, and armed missions- to intercept impact threats being one necessary use. Once the Moon becomes developed it will hit a tipping point sooner or later and really big projects like solar energy on the order of 3 to 5 times what the Earth produces right now will become practical.

    With this kind of energy we can begin to at least talk about star travel and building starships.

  • GaryChurch March 11, 2013, 12:32

    “-really big projects like lunar solar energy on the order of 3 to 5 times what the Earth produces right now will become practical.

    What I meant was 3 to 5 times the energy the ENTIRE Earth produces; not just solar.
    Building infrastructure- closer to the Sun-solar energy conversion devices hundreds or even thousands of miles long- is the scale of power required to begin manufacturing small singularities for use as Starship engines.

  • Bob O'Donnell March 12, 2013, 22:42

    For sake of argument, lets eliminate part of the equation as stated. Let us say instead that some form of energy became feasible to power a ship(s) to perhaps 1.5C or more. Now what would be the problems in navigation? First we are moving through space in a certain direction. The target is moving through space in another direction. The galaxy is moving too. NOW how would you navigate to your destination and return? This would be somewhat simple if you didn’t get to far from Earth but lets say you went 500LYR or perhaps 200 parsecs, how would you find your way back to Earth? Certainly finding it in the heavens wouldn’t solve the problem at all.

    The problem, as I see it, is that we have no guide posts and everything is moving all the time. Where do you aim for knowing that the star that you are wanting to target is far away from where you are aiming? The math that we have at present just doesn’t handle this as far as I know.

    Just thoughts to ponder.
    Respectfully someone who knows very little about navigation out there.

  • GaryChurch March 13, 2013, 21:55

    “The math that we have at present just doesn’t handle this as far as I know.”

    Actually, supercomputers can do calculations like this. But you must not go 1.5C because you will get a speeding ticket from your physics professor.

  • Dmitri March 14, 2013, 4:08

    Bob O’Donnell March 12, 2013 at 22:42
    [The problem, as I see it, is that we have no guide posts and everything is moving all the time. Where do you aim for knowing that the star that you are wanting to target is far away from where you are aiming? The math that we have at present just doesn’t handle this as far as I know.]

    I’m no expert on interstellar navigation but the question you raised recalled that some other experts has done thinking on this. Proposal is to use pulsars as navigation beacons. Maybe there are other standard candle worthy star combination for insterstellar navigation plotting. There are ways.

    Dead stars could be the future of spacecraft navigation – http://phys.org/news/2012-10-dead-stars-future-spacecraft.html

  • Eniac March 18, 2013, 0:24

    Bob O’Donnell: Stars move on extremely predictable trajectories, on the scale of centuries that you are contemplating. It would not be a problem at all to calculate where exactly that target would be at the time you are aiming to reach it.

    And for verifying your calculation, you can use the Pulsars that were mentioned, but also simple parallax measurements. We can can detect the proper motion of nearby stars due to the Earth’s orbital motion with fairly regular instruments. This means that by simple astrometrics of a few nearby stars we could fix our position to within 1 AU.

  • fes auto ecole May 2, 2013, 7:46

    I am fascinated by interstellar travel and I am like most of you upset that I wasn’t born a century from I still cling to the hope that using our actual resources we can achieve a vehicle or a least a probe capable of making the journey to our nearest galaxy within 40 years travel time which is still within the time frame of most people on this blog