Incentive Trap 2: Calculating Minimum Time to Arrival

by Paul Gilster on May 9, 2017

When to launch a starship, given that improvements in technology could lead to a much faster ship passing yours enroute? As we saw yesterday, the problem has been attacked anew by René Heller (Max Planck Institute for Solar System Research), who re-examined a 2006 paper from Andrew Kennedy on the matter. Heller defines what he calls ‘the incentive trap’ this way:

The time to reach interstellar targets is potentially larger than a human lifetime, and so the question arises of whether it is currently reasonable to develop the required technology and to launch the probe. Alternatively, one could effectively save time and wait for technological improvements that enable gains in the interstellar travel speed, which could ultimately result in a later launch with an earlier arrival.

All this reminds me of a conversation I had with Greg Matloff, author of the indispensable The Starflight Handbook (Wiley, 1989) about this matter. We were at Marshall Space Flight Center in 2003 and I was compiling notes for my Centauri Dreams book. I had mentioned A. E. van Vogt’s story “Far Centaurus,” originally published in 1944, in which a crew arrives at Alpha Centauri only to find its system inhabited by humans who launched from Earth centuries later. I alluded to this story yesterday.

Calling it a ‘terrific story,’ Matloff discussed it in terms of Robert Forward’s thinking:

“Bob had a couple of concepts of technological advancement. He had a famous plot of the velocity of human beings versus time. And he said if this is true, and you launch a thousand-year ship today, in a century somebody could fly the same mission in a hundred years. Theyre going to be passed and will probably have to go through customs when they get to Alpha Centauri A-2.”

Customs! Clearly, we’d rather not be on the slow starship that is superseded by new technologies. What Heller and Kennedy before him want to do is to figure out a rational way to decide when to launch. If we make assumptions about the exponential growth in speed over time, we can address the question by adding the time we spend waiting for better technology to the time of the actual journey. We can then calculate a minimum value for this figure based on the growth rates we find in our historical data.

This is how Kennedy came up with a minimum figure of 712 years (from 2006) to reach Barnard’s Star, which is about 6 light years away. The figure would include a long period of waiting for technological improvement as well as the time of the journey itself. Kennedy used a 1.4 percent annual growth in speed in arriving at this figure but, examining 211 years of data on historical speed records, Heller finds a higher annual growth, some 4.72 percent.

From the Penydarren steam locomotive of 1804 to Voyager 1, we see a speed growth of about four orders of magnitude. Growth like this maintained for another 112 years leads to 1 percent of lightspeed.


Image: A Bussard ramjet in flight, as imagined for ESA’s Innovative Technologies from Science Fiction project. Credit: ESA/Manchu.

But how consistent should we expect the growth in speed over time to be? Heller points out that the introduction of new technologies invariably leads to jumps in speed. We are now in the early stages of conceptualizing the Breakthrough Starshot project, which could create exactly this kind of disruption in the trend. Starshot aims at reaching 20 percent of lightspeed.

Working with the exponential speed doubling law we began with, we would expect that a speed of 20 percent of c would not be achieved until the year 2191. But if Starshot achieves its goal in the anticipated time frame of several decades, its success would see us reaching interstellar speeds much faster than the trends indicate. Starshot, or a project like it, would if successful exert a transformative effect as a driver for interstellar exploration.

We know that speed doubling laws cannot go on forever as we push toward relativistic speeds (we can’t double values higher than 0.5 c). But as we move toward substantial percentages of the speed of light, we see powerful gains in speed as we increase the kinetic energy beamed to a small lightsail like Starshot’s. Thus Heller also presents a model based on the growth of kinetic energy, noting that today the Three Gorges Dam in China can reach power outputs of 22.5 GW. 100 seconds exposure to a beam this powerful would take a small sail probe to speeds of 7.1 percent of c. Further kinetic energy increases could allow relativistic speeds for at least gram-to-kilogram sized probes within a matter of decades.

Usefully, Heller’s calculations also show when we can stop worrying about wait times altogether. The minimum value for the wait plus travel time disappears for targets that we can reach earlier than a critical travel time which he calls the ‘incentive travel time.’ Considered in both relativistic and non-relativistic models, this figure (assuming a doubling of speed every 15 years) works out to be 21.6 years. In Heller’s words, “…targets that we can reach within about 22 yr of travel are not worth waiting for further speed improvements if speed doubles every 15 yr.”

Thus already short travel times mean there is little point in waiting for future speed improvements. And in terms of current thinking about Alpha Centauri missions, Heller notes that there is a critical interstellar speed above which gains in kinetic energy beamed to the probe would not result in smaller wait plus travel times. His equations result in a value of 19.6 percent of c, an interesting number given that Breakthrough Starshot’s baseline is a probe moving at 20 percent of c, for a 20-year travel time. Thus:

In terms of the optimal interstellar velocity for launch, the most nearby interstellar target α Cen will be worthy of sending a space probe as soon as about 20 % c can be achieved because future technological developments will not reduce the travel time by as much as the waiting time increases. This value is in agreement with the 20 % c proposed by Starshot for a journey to α Cen.

We can push this result into an analysis of stars beyond Alpha Centauri. Heller looks at speeds beyond which further speed improvements would not result in reduced wait times for ten of the nearest bright stars. The assumption here would be that Starshot or alternative technologies would be continuously upgraded according to historical trends. Plugging in that assumption, we wind up with speeds as high as 57 percent of lightspeed for 70 Ophiuchi at 16.6 light years.

Thus the conclusion: If something like Breakthrough Starshot’s beaming capabilities become available within 45 years — and assuming that the kinetic energy transferred to the probes it pushes could be increased at the historical rates traced here — then we can reach all ten of the nearest star systems with an interstellar probe within 100 years from today.

Just for fun let me conclude with a snippet from “Far Centaurus.” Here a ship is approaching the ‘slowboat’ that has just discovered that Alpha Centauri has been reached by humans long before. The crew has just puzzled out what happened:

I was sitting in the control chair an hour later when I saw the glint in the darkness. There was a flash of bright silver, that exploded into size. The next instant, an enormous spaceship had matched our velocity less than a mile away.

Blake and I looked at each other. “Did they say,” I said shakily, “that that ship left its hangar ten minutes ago?”

Blake nodded. ‘They can make the trip from Earth to Centauri in three hours,” he said.

I hadn’t heard that before. Something happened inside my brain. “What!” I shouted. “Why, it’s taken us five hund… ” I stopped. I sat there.

“Three hours!” I whispered. “How could we have forgotten human progress?”

The René Heller paper discussed in the last two posts is “Relativistic Generalization of the Incentive Trap of Interstellar Travel with Application to Breakthrough Starshot” (preprint).


{ 59 comments… read them below or add one }

Neil S May 9, 2017 at 12:01

” this powerful would take a small sail probe to speeds of 7.1 c” Do you mean 7.1% of c or 0.71c?


Tom Mazanec May 9, 2017 at 12:03

the Three Gorges Dam in China can reach power outputs of 22.5 GW. 100 seconds exposure to a beam this powerful would take a small sail probe to speeds of 7.1 c.

Great to see that we can so easily reach superluminal velocities…NOT!


Paul Gilster May 9, 2017 at 12:15

A typo indeed! Now corrected. Thanks.


ljk May 9, 2017 at 12:07

This reminds me of those who think we only have to wait for some lone genius to come up with warp drive and we’ll be at Alpha Centauri in mere minutes. No need for those “primitive” slowpoke propulsion methods that will only mean we actually have to wait for a starship to get somewhere.

There was a book about the Apollo Lunar Module titled Chariots for Apollo that had one engineer saying they could have waited for the technology to become more sophisticated (the spaceship’s guidance computer had 1600 KILOBYTES of memory – and it was specially made by MIT), but then humans would not have landed on the Moon until decades later (I believe he said 1990 exactly). Now look at how long it has been since an astronaut last explored the lunar surface even though our technology has vastly improved since the 1960s.

Imagine where so much of our current space exploration and science would *not* be if we just sat and waited for that ambiguous “someone” to come along and make us a better way to reach the Final Frontier. No doubt out of the sheer goodness of their hearts and without having to rely on vital past research.


Alexander Tolley May 9, 2017 at 12:58

That is a good point about incentives. In another field, the Human Genome Project started off with quite slow, costly sequencing technology. This steadily improved, but it created the incentive for a more powerful technology, “shotgun sequencing” to emerge that drastically reduced time and costs. The usefulness of genome sequencing became evident and that increased the drive to reduce costs to where today, we have reached/exceeded the $1000/genome cost. Technologies already exist to put sequencing technology in the hands of schoolkids in a decade or so.

10 years ago, gene expression studies were done on tissue samples. Today it can be done on individual cells.

We all recall that period in the 1990’s when computer prices were falling rapidly and we faced the conundrum – buy now or wait 6 months? For most of us, it was “buy now”, because the value of the machine was more important than cost.

Economic issues can create path dependencies. A case in point is electric cars. Their battery charge ranges are limited and recharging options on journeys are very limited. Wait for those problems to be solved and lack of purchases might keep them stillborn. Buy now, and the incentives to solve them will increase.

Nuclear rocket engines were stillborn. Will they reemerge if we use chemical rockets to destinations that would benefit from these engines? My sense is that the requirements of actual travel will more likely result in nuclear rockets being developed again rather than hoping that someone will develop them to make such travel more possible in the future.

Whether Breakthrough Starshot achieves its goals or not, development of beamed power will prove valuable for propulsion and energy delivery within the solar system. It may even incentivize the building of solar power sats to generate the power needed, rather than sending the beam from Earth’s surface.


Robert G May 9, 2017 at 14:28

A phased laser array with serious wattage behind it might also come in handy if we noticed any sizeable asteroids coming our way.


Alexander Tolley May 9, 2017 at 15:49

Indeed, planetary defense from asteroids was Lubin’s pitch for his various DSTAR power levels. I’m sure he was focussed primarily on DoD funding. Pushing sails was a secondary idea that would help publicize his lab’s R&D.


Michael May 10, 2017 at 14:56

If we can accelerate fusion fuels on sails to fusion velocities, 600-1000 km/s it could be a serious means of eroding a comet or asteroid.


ljk May 9, 2017 at 14:00
Betto Davis May 9, 2017 at 14:21

The relationship between science, technology and science fiction + speculation is… complicated.

It is a really novel happening in all of human history, when we can make projections and infer future trends based on past results and metrics.

Of course, imagining the future is an innate human ability, but inferring some wholly new existential scenarios is relatively new.

I’m surprised for example, to learn that the travel speeds we can reach follow a somewhat predictable curve. There is no natural rule making it so, and we will probably verify that lack of connection of events eventually, by reaching a stop in our progression well before we can reach c itself.

It’s just eerie that we can predict some radical outcomes based on apparently unconnected events and past trends.

This state of things has resulted in some kind of triumphalism in some people, making them believe that if something can be imagined (or plotted), it can happen.

Truth is, we don’t really know. It may happen one day, it may never happen.

There’s also the fact that some people are seriously looking into the limits of knowledge, and finding surprisingly feasible ways to break or bend the rules. All this talk about Mach Effect drives being investigated at NASA makes me think there is always room for some really prodigious discoveries in the nor so far future.

Again, interesting times.


ljk May 9, 2017 at 15:05

Let me get this one potential flashpoint and tangent maker clarified and out of the way right now:

I am not saying that warp (or hyper) drives are either impossible or should not be pursued. What I am saying is I am very concerned that folks are focusing on them as the only important means of interstellar travel because they have had too much popular science fiction in their diets and not enough real science.

In addition, the contingencies who support warp drive based largely on the idea that every time some authority says such-and-such is impossible is really a rallying cry that any barrier can be broken by sheer willpower and popular vote only adds to the problem.

Warp drives are not going to be easy to turn into reality, and not just because of the high tech knowhow required. There are also factors involving the limitations of actual physics that cannot be wished away, such as the need for negative matter. Of course someone can always turn up a post where some scientist says the substance could be real after all, but that is a far, far cry from having it exist in reality to say nothing of being turned into a working warp drive.

In the meantime there are methods of interstellar propulsion that are not only far more plausible scientifically, but whose only crime seems to be that they are not used by the starships on Star Trek. Thank goodness for Breakthrough Starshot, even though it has its own collection of issues to be dealt with, because at least it is keeping folks on a path of real science and technology, which is what will really get us to the stars – even if it won’t involve someone ordering “Warp Factor 9.”


J. Jason Wentworth May 9, 2017 at 15:58

Indeed-the “Pioneer 0 – 4 attitude” would be a prudent one for us to adopt in interstellar probe attempts:

Between August 17, 1958 and March 3, 1959, the U.S. Air Force and the U.S. Army launched three and two probes, respectively, toward the Moon; the retrorocket-equipped Air Force spacecraft were hoped to orbit the Moon, while the two tiny Army payloads (Pioneers 3 and 4) were lunar flyby probes. But:

Recognizing the primitive state of the art back then, just months after the first U.S. satellites were orbited (and likely also to avoid raising too-high expectations), each mission’s objective was “to place an instrumented payload in the vicinity of the Moon” and to collect radiation and magnetic field data in cislunar space. Pioneer 1 reached the never-before-reached distance of 70,700 miles from Earth, Pioneer 3 reached 66,654 miles, and Pioneer 4 made a more-distant-than-targeted lunar flyby, passing 37, 300 miles from the Moon (20,000 – 22,000 miles was the planned distance) before entering an independent solar orbit. Now:

While none of these three spacecraft achieved their full mission objectives, they weren’t lamented as failures, either (only Pioneer 0, whose Thor-Able launch vehicle exploded, and Pioneer 2, which rose to only 963 miles when its third stage failed to fire, were), and they returned new data on heretofore-unexplored regions of space (even Pioneer 2 returned data during its brief 45-minute flight). Also:

First-generation solar sail (or laser-pushed lightsail) interstellar medium probes–which might function long enough to reach the Alpha Centauri system (or at least Kuiper belt worlds or Planet X [if it exists])–would be the interstellar age-equivalent of the Pioneer lunar probes. They would return new data on heretofore-un-visited regions of the ultraplanetary and interstellar space around our Sun as well as Kuiper belt objects, while possibly–if they survived long enough–being able to return observations of the Alpha Centauri system. Plus:

Our longevity is “half of the problem” of interstellar exploration. If the human lifespan increases significantly during this century due to advances in medical and biological research (this is a wild card that would be foolish to count on, but it is slowly increasing even now), it would increase what is considered to be a tolerable interstellar probe transit time.


ljk May 9, 2017 at 16:36

Yes some very good points. Even otherwise failed launches always teach us something, even if it is just what not to do next time. They also teach us perseverance, a trait whose importance cannot be underestimated.

In the case of the American lunar exploration effort that you bring up, we went from years of mission failures right from the start in 1958 to placing the first humans on the Moon with Apollo 11 just over a decade later, then repeating the process several more times. A very prime example of learning from your mistakes and never giving up.

Here is another very important reason to launch a slow, “primitive” space vessel mission: Historical record value. The Pioneer and Voyager probes may be taking about 77,000 to 100,000 years to go the distance to Alpha Centauri, and will all become non-responsive long, long before then, but the data they have given us about nearby interstellar space is priceless, not to mention unique as they have recorded regions of space at specific times which will not happen again no matter how fast the next deep space mission can get to where they were/are.

Same thing with those early lunar and planetary probes, recording conditions that will show us how these worlds have changed over decades. Information we cannot ever get again otherwise.


J. Jason Wentworth May 9, 2017 at 21:33

Thank you, and you said it–“data on time-variant phenomena” is the coin of the realm here. One could think of it as “VLBI observations,” but where the Very Long Baseline is in *time* rather than in distance, which reveals long, slow changes (including cyclic ones with long cycle times). Even sounding rockets are still flown for this reason, even though the phenomena they were originally flown to explore decades ago are now well-understood. Plus, even Earth-based lunar astronomy continues, because there are time-variant phenomena there.

Dispatching fast, very small sail probes that might–with luck–make it to other stars while still in operating condition would cause no great disappointment if they “only” returned data from as far out as Pioneer 10 and Pioneer 11 did (or from as far away as the Voyagers will), especially if–while en route out of the solar system–they “checked in on” the outer planets years after the Pioneers, the Voyagers, Galileo, Cassini, or New Horizons visited them.


hiro May 11, 2017 at 16:59

If a blueprint of thermonuclear warhead were given to some random emperors in 10th or 15th century, the world history would still be the same. It might be the same if one receives the blueprint of wormhole tech, the energy requires it to operate is way too high (let’s say 10^30 TWh), the current level isn’t enough to do anything and nuclear fusion power is still ….. another 50 years away.

One wonders which one comes first: fusion power ( > 10 TW ), quantum AI (> 100 qubits) or wormhole tech.


Alexander Tolley May 9, 2017 at 12:34

speeds of 7.1 c.

Should be 7.1%c [bottom pg 3].


Paul Gilster May 9, 2017 at 14:17

Yes, now fixed. Thanks.


Jens Knudsen May 9, 2017 at 13:33

We should keep pressing on, not so hard that we get exhausted, but so hard that there is tangible progress made, and so that there are visible results to show for the effort along the way.


DJ Kaplan May 9, 2017 at 16:18

And what if we wait and wait and nobody comes up with something faster? Would that have been an investment or a waste of time?


DCM May 9, 2017 at 16:42

A modest or small biosphere in a ship slow enough to be passed up at some point may still yield interesting results as far as evolution goes. Doesn’t have to have humans aboard or even “higher” creatures.
These could even be experiments purely in biology with return trips taking several hundred years and heading to no particular destination except home.


Adam May 9, 2017 at 16:55

The perception that only warp-drive will get to the stars is surprisingly common. As a species we don’t seem very patient.


J. Jason Wentworth May 9, 2017 at 21:59

Your comment just inspired a strange thought:

Much has been written–and not only in science fiction–about getting around the interstellar velocity/transit time problem (although in an admittedly “brute force” way) by sending crews in some form of cryogenic hibernation, aboard slow starships. With slow probes, it could be done “the other way around” (assuming that a reliable and safe hibernation system could be developed), by enabling the mission controllers on Earth to hibernate (and perhaps be awakened briefly every few years, to check on the mission status and solve any problems that required their intervention). Also:

While *I* wouldn’t care to do such a thing, I wouldn’t be surprised if some scientists–especially if they became widows or widowers as their missions progressed–would like to see their missions reach their destinations. This option might be particularly attractive if the probes’ arrival times weren’t long after the people’s expected lifetime “expirations”–say, twenty or thirty years–because the world they would reawaken in wouldn’t be so unfamiliar as to be totally alien to them. Plus, such relatively short “hiber-sleep” periods would be more likely to be successful than centuries-long or millennia-long ones.


Gerry May 12, 2017 at 14:01

Perhaps in the case of a manned mission, some family members of the starship crew, having mission-relevant skills in their own right, would be able to man the science team Earthside, and hibernate during most of the mission duration, as you describe. That would be an interesting way of addressing one of the big problems of manned, round-trip interstellar flight as potrayed in Science Fiction; the return to a future world in which everything, and everyone familiar is lost to the distant past.


J. Jason Wentworth May 13, 2017 at 21:03

That is an idea that I’ve never seen discussed or addressed, either in scientific speculation or science fiction. That would definitely make such a voyage more emotionally acceptable to the crew members, and:

Earthside people who were involved in designing and/or building the starship would also be helpful in supporting the mission as it proceeded, if they also hibernated and were re-awakened at intervals. The ship could–and likely would–send a continuous stream, or at least periodic “reports,” consisting of engineering telemetry as well as data from the scientific instruments that would function during the interstellar transit. Even though the light-time delay would be much greater, such stay-at-home staff could remotely analyze and correct problems aboard the ship, as is now done with probes in our solar system.


Alexander Tolley May 14, 2017 at 13:03

Isn’t this related to Karl Schroeder’s idea for his novel “LockStep”?idea.


J. Jason Wentworth May 14, 2017 at 17:39

Could be–but I’ve never heard of him.


Alexander Tolley May 15, 2017 at 10:40
J. Jason Wentworth May 16, 2017 at 0:51

Thank you for posting the link. That’s an interesting, if troubling to contemplate, future.

Just as there are now “spatial criminals” (specialized thieves who have robbed the homes of single [un-married] astronauts while they were on long tours aboard the ISS), a Lockstep society would have “temporal criminals” who robbed or even murdered the ‘sleepers.’ Also:

Aside from that, I would fear never re-awakening due to a failure of the automated hibernation system (especially aboard a starship), or–which could be worse–re-awakening to find civilization in ruins. We like to think that civilization will always progress, or at least not go backward to oblivion, but there are no guarantees that it can’t disintegrate.


ljk May 15, 2017 at 9:53

Spoilers be ahead, just in case…

Remember the short-lived television series Ascension? The crew of a multigenerational starship, an Orion no less, think they are going to colonize a world in the Alpha Centauri system in about 50 years. Turns out they were on Earth all the time being studied for very different reasons.

Then there is Brian Aldiss’ work Non-Stop, titled Starship in the US. A multigenerational starship devolves into something like Heinlein’s Orphans of the Sky. The surprise is they have been in Earth orbit for generations, being studied by scientists to see what centuries of confined living does to the crew (makes them primitive and superstitious, apparently).

We have been sending humans into space since 1961, yet no one has stayed up there for even two years at a time – and in Earth orbit at that. Not a single colony yet, either. No, living in Antarctica does not really count, as the participants know if things go wrong they have a chance of being rescued in short order because they are on Earth however remote. Even instant communications are no longer an issue at the poles thanks to comsats.

We are no more ready to send humans on a long interstellar trip than we are building an actual starship, with no offense to the Breakthrough folks. That we have to keep looking back on old science fiction stories for guidance in this area should really tell us something. Imagine if we were still reading Jules Verne for ideas when it comes to manned space flight or submarine voyages. No offense, Jules, I love you, man!

We still don’t know in the end if humans are the best choice for making such journeys, or if they will need to be heavily modified at best. Or if in the end we will need to send machines as we have done so often before and now.


DCM May 10, 2017 at 3:22

No need to be patient unless you have to.


ljk May 10, 2017 at 8:40

That is due to being creatures that only recently starting living about 80 years on average, compared to living on a planet that is 4.6 billion years old in a Universe that is 13.7 billion years old.

Ever see Carl Sagan’s Cosmic Calendar from the original Cosmos series? It really put into perspective how miniscule not only our individual lives are but how long we have existed as a species in comparison to the rest of existence since the beginning of time:

Note that much of those 80 Earth orbits of Sol most of us now get to live is spent on trying to understand the world and dealing with various mundane terrestrial social conventions and often just plain survival. Then by the time we do start to get comfortable and manage our lives, age begins its slow but steady physical and mental decay.

So yes, we are an impatient species and not without reason. Which only further supports my view that those who will “conquer” the stars will not be organic, or at the very least not organic without some major modifications.


James Stilwell May 9, 2017 at 22:26

As pilot of a fast star ship I’d be leery heading out without dust lanes charted and which might intersect my course…maybe space travel is clear sailing ahead and this is all in my imagination…but hitting dust at half light speed could fatally damage the ship…


ljk May 16, 2017 at 9:03

We should send Saturn’s ring system ahead of any interstellar voyages, it seems to be really good at clearing out particles. :^)


David H May 10, 2017 at 8:16

Where’s the evidence that humans are speeding up over time? Forty years ago my grandfather could break the sound barrier on his way to Paris, and he could drive from Oakland to San Jose in … not many minutes. Today I fly in planes that were from my grandfather’s age, except they are jammed with more seats. Our communications have sped up, but we have not. Is it any different with space travel? Or is it actually worse?

There is no law of nature guaranteeing that human speed of travel increases over time. We need to stop thinking like there is. There is also no law that we must get richer, longer-lived and more ambitious and outward-directed over time. We may be peaking soon along all these dimensions. I say that as soon as interstellar colonization becomes possible, we must launch. Yes, they may be lapped by later missions, but they may also be be the last escapees before the collapse of this golden age.


spaceman May 11, 2017 at 11:24

I agree with you, David. The speed at which we move has flatlined in recent decades. Project Starshot could change this, but how likely is it that this endeavour will come to fruition? Furthermore, this brings up a larger point that is often neglected in many futurological discussions– that is, outside of computers and gadgets, where are the major breakthroughs in materials science and energy generation technology that will allow us any chance of reaching the stars? Alex Tolley mentioned next generation genome sequencing which is impressive, however, the applications of having all of this data on hand have turned out to be much more limited in scope than the hype would lead us to believe. Yes, we live in an era of “Big Data”, but in some ways where is this getting us except for information overload. We are still primarily driving cars powered by the ineternal combustion engine and we had more capable rockets during the Apollo era!


ole burde May 12, 2017 at 4:17

At any point in time we should concentrate mostly on advancing with the best of we’ve got here and now …in the last few years robotics and vertual reality technology has advanced far enough that it is now imediately possible to tele-operate a big number of small prosbekcting and later mining robots on the moon…we are not going anywhere without an industrial capacity in space , and this is by far the cheapest way to get started ….and it is also why it was a mistake when the ‘space comunity’ as a whole quietly acepted when Obama scapped the former administration’s plan ‘to back to the moon’


spaceman May 11, 2017 at 11:27

70 Ophiuchi was mentioned…has this system been looked at for planets?


ljk May 16, 2017 at 9:07

The Wikipedia entry on this star has some good sources of information regarding exoplanets:

From this I learned that claims of planets circling that star go all the way back to 1855.


J. Jason Wentworth May 12, 2017 at 5:43

In connection with these two recent “Centauri Dreams” articles about when the best time to launch the first interstellar probes is, an idea occurred to me yesterday:

While the ultra-thin sail material and the launching laser array—which the StarShot laser-pushed lightsail probes will require in order to reach the Alpha Centauri system in 20 years—aren’t yet within our technological grasp (and will be very expensive to develop), the actual mini-spacecraft probably *are* within our ability to build, or soon will be. Moreover, they could probably be made in large quantities for a low per-spacecraft price. Even if this isn’t the case, the idea that I have would almost certainly guarantee that it would “become the case,” and it is as follows:

Instead of pushing the state of the art to—and beyond—the bleeding-edge limit in order to get, at great expense, a 20-year transit time to Alpha Centauri, we could soon dispatch similar (but slower, and much cheaper per unit) ^solar^ sail probes that could reach Alpha Centauri in 100 – 150 years *and* enter orbit in the system. With a sufficiently low per-probe price (I think they could be cheap enough to crowd-fund, or at least for a wealthy person to cut a check for them), we could send “Bracewell messenger equipment plus instruments” solar sail probes of this type not only to the Alpha Centauri system, but to Barnard’s star and to the rest of the twenty nearest stars (out to the Procyon system), and:

Their slower speeds would significantly reduce their cost, complexity, and “interstellar medium interactions” (that is, it would reduce the intensities of gas and dust impacts). While they would take longer to reach their destinations than the StarShot probes, the data they would return via laser while en route would be new information about unexplored space, every day that they progressed toward their target stars—plus, they would linger around their stars to search for planets *and* possible inhabitants (and the probes could communicate with any they found). And if the StarShot probes did get built and overtook them to reach α Cen first, so much the better, because:

The slower probes’ “mission advisors” on Earth (they wouldn’t need mission controllers to ‘fly them from the ground’) could take advantage of the StarShot probes’ advance “sneak peeks” at the Alpha Centauri system in order to optimize the slower probes’ scientific return (even “just” entering the best initial orbit to observe any Alpha Centauri A and/or B planets would speed up the data return considerably). With a modicum of shielding (and even redundant chips), there is no reason why such probes–or at least most of them–shouldn’t be able to survive their interstellar passages and function in their destination stellar systems for many years or even decades, and also:

Their launch costs should be quite affordable, with the existing and upcoming launch vehicles. (The final stage could serve as an occulter, so that the probe(s)’ deployed sail(s) could emerge from behind it, close to the Sun, in order to receive the largest sunlight pressure “boost” that the spacecraft could withstand.) Already, Spaceflight Industries (see: and ) and other companies (see: ) are offering inexpensive satellite rideshare opportunities aboard SpaceX Falcon 9, ULA Atlas V, and Rocket Lab Electron launch vehicles; so is ISRO, India’s space agency, which recently orbited 104 satellites aboard a PSLV—Polar Satellite Launch Vehicle—(see: ). The Atlas V has already demonstrated that its Centaur upper stage can enter a Sun-circling “disposal orbit” from a low-altitude *polar* Earth orbit (see: ), so it could very likely do the same—especially when launched into an Easterly orbit from Cape Canaveral—with solar sail interstellar mini-probes aboard as “hitch-hiker” payloads.

I hope this information will be helpful.


Alexander Tolley May 12, 2017 at 11:37

Aren’t you talking about “sundiver” solar sail missions here? Their velocities are nowhere near fast enough to get to the nearest star in 100-150 years.

What calculations are you using for your trip times?


J. Jason Wentworth May 13, 2017 at 21:39

James Essig calculated (it’s somewhere on “Centauri Dreams,” in a comment to an article–I don’t know which one) that a “sundiver” solar sail starship (not just a tiny, sail-equipped starprobe) could reach 1/3 or 1/4 of the speed of light. But even if he was off by a factor of ten in the unfavorable direction (2.5% of c instead of 25% of c), it would still be worthwhile to dispatch such micro-probes, even “just” for the data on the interstellar environment that they would return while en route to their target stars.


Alexander Tolley May 14, 2017 at 12:59

With all due respect to James Essig, Vulpetti et all in “Solar Sails: A Novel Approach to Interplanetary Travel” indicate a maximum velocity leaving the solar system of 0.0034 c [ch 17, p.224. Sailcraft Trajectories ]. The huge discrepancy in velocities suggests that Essig was wrong, or that you have recalled his calculations incorrectly. Perhaps you can find a link to his calculations and we can do some BOE calculations to get a good handle on the correct answer?


J. Jason Wentworth May 14, 2017 at 17:47

He assumed the use of materials (some of which we don’t yet have, at least not beyond laboratory-sample quantities, such as diamond sail-rigging cables, refractory metal composite sails, etc.) that would permit much closer solar approaches behind an occulter, so that a starship could start off with much stronger sunlight pressure pushing it.


Neil S May 15, 2017 at 10:50

Two points:
1. Intuitively it seems like if most of the very large velocity of the probe would be imparted in the first few minutes or less, inevitable errors in aiming would create the need for high energy course changes down the line. Where would that energy come from? Laser batteries in the solar system? Maybe, but there would be very little time to calculate and correct! Slowly between stars? Is there enough turning energy available?

2. If several objects pass through your planetary system at a significant fraction of c might that be considered an unfriendly act?


Michael May 15, 2017 at 15:03

Perhaps we could use shallow angle deflection to move the probe much like an aeroplane does.


J. Jason Wentworth May 15, 2017 at 23:56

The sail’s launch aiming accuracy might be quite good, depending on the sail’s shape. The StarShot illustrations I’ve seen all show a small but otherwise “standard” square sail. A sail in the shape of a shallow cone (or a “multi-faceted cone” that approximates it) and with the payload at its apex would, it would seem, tend to “self-center” itself in the laser beam. Such a sail could be either spin-rigidized (with the light pressure causing the “coning” of a spinning disc sail) or be non-spinning (with a framework maintaining its shape). Also:

If one or more relativistic objects zipping through one’s planetary system hit a moon, planet, asteroid, or spacecraft (particularly if locals were living on, in, or near the body or vehicle that was struck), they–or their surviving fellow beings–would at least consider the projectiles’ senders to be very inconsiderate! :-) In addition:

That thought had crossed my mind, though, with regard to the StarShot sail probes and, before them, Robert Freitas’ electromagnetically launched interstellar “needle” probes. While it isn’t likely, it is possible that such probes might kill some of the very star-folk whom we hope to find. But imagine the havoc that a 54,000 tonne Daedalus or REPRO (Freitas’ self-reproducing version of Daedalus) starprobe hurtling at 12% of c would wreak if it struck an inhabited exoplanet (or even a moon of such a world)?!


ljk May 16, 2017 at 9:13

Not only do we need a way of not destroying and killing the objects and life forms of the star systems we are trying to explore, we also need to send information packages along with these missions so that anyone who does encounter one of our probes can be assisted in understanding why the vessel is in their system and who sent it. It is rude not to bring gifts when visiting, after all.

If an alien probe, active or derelict, came barreling through our Sol system, would we not appreciate some help in understanding why it is here?


Alexander Tolley May 16, 2017 at 11:26

It is rude not to bring gifts when visiting, after all.

OTOH. Beware Greeks bearing gifts… ;)


ljk May 16, 2017 at 15:43

Beware alien space probes arriving from the depths of space unknown and unannounced. Even derelict ones.


J. Jason Wentworth May 16, 2017 at 20:36

Since the StarShot sail probes will escape from the Milky Way and have ample velocity to (eventually) reach other galaxies, an interstellar *and* intergalactic version of the Pioneer Plaque might be in order, for both “local” galactic and distant, “extra-Milky Way” potential finders of the probes. The sail itself could contain a holographic message (which would add zero additional mass to the sail), and:

As a back-up (or an addition) to a message on the sail itself, a message or messages could also be etched onto the back side of the ChipSat payload’s graphite erosion shield (or the back side of the ChipSat itself), also with no addition of mass to the probe. Plus:

Even a StarShot sail probe that was rendered inoperative by a debris strike on its ChipSat payload, or whose sail was badly damaged after launch by a large debris particle impact (both of which are unlikely, fortunately, as sufficiently large solid particles are pretty rare out there), would still serve as a decipherable artifact if both “labeling” options were exercised. In addition:

Since the baseline StarShot sail is—I think—4 m (about 13 feet) wide (either from tip-to-tip, or edge-to-edge, if it’s the square sail shown in the illustrations), this makes possible a unique StarShot fund-raising option:

There should be plenty of room for both a “standard” (for all of the probes) interstellar/intergalactic message *and* a personal message “to a galaxy far, far, away,” whose space on each sail could be made available to StarShot donors who donated a certain amount to the project. Such a “personal message space” could even be “sub-divided”; in other words, donating X amount would be good for, say, one entire panel of the sail, while donating lesser amounts (as much as the donors could afford) would entitle them to have messages on areas 1/2, 1/4, 1/8, or 1/16 the size of a panel. As well:

The messages could be either text, images, or both (I was whimsically thinking of, “Got milk? Guess which galaxy I’m from!” [I’d send a more dignified message, of course]). But people pay good money to “Star Registry” outfits that name stars for people (see: ), even though the names aren’t officially recognized by the IAU or anyone else (these outfits fraudulently claim or suggest otherwise…), while such StarShot personal messages would be for real!


ljk May 17, 2017 at 10:02

Every deep space probe whether it leaves our Sol system or not should carry an information package. Not only for identifying itself to nonhuman recipients to potentially alleviate fears and help them understand us, but also as a way of preserving humanity’s knowledge and accomplishments for future terrestrial generations.

Space provides one of the best places to ensure that all of our accomplishments are not lost to the ravages of time, human malice and ignorance, and the corrosive environment that is the planet Earth. For example, the sides of the Voyager Interstellar Records facing outwards from their carrying probes are expected to survive for at least 0ne billion years as they wander between the stars of the Milky Way, and that is a conservative estimate. The record sides facing inwards will last as long as the probes themselves do. In comparison, most human constructions left to the elements on Earth will be gone or buried within a matter of centuries.

My further thoughts on the matter here:

As we learn virtually every day, there is so much we do not yet know about the wide galaxy and beyond. Heck, we just learned that the bow shock of the heliosphere surrounding our Sol system does not exist as scientists once thought – and this is in our celestial neighborhood!

So just how wise is it to loft probes (and their final rocket stages, as is often forgotten) into the galaxy without so much as a how-do-you-do? Again I bring up the idea of some alien probe drifting into our Sol system: Would we not be just slightly grateful (and relieved) if it carried decipherable information about its makers and its purpose, to say nothing of what it may have learned during its mission in the process?

I am still very disappointed that New Horizons, only the fifth probe humanity has ever sent out of the Sol system, carried only the equivalent of trinkets from some small town’s time capsule. Yes, there were some ashes from Pluto discoverer Clyde Tombaugh aboard (labeled with a plaque only in English), but otherwise the rest of the items were random and will probably be very confusing to any recipients.

Yes there is that plan to beam loads of data to NH to be stored in its computers once its KBO missions are done, but that has yet to be approved. More importantly, the data will not last due to cosmic radiation and such, unlike the engraved data on the Pioneer Plaques and Voyager Records. And what if they lose contact with NH before this METI plan can be implemented? The probe’s RTGs will only last until 2030 and there could always be an accident before then.

The NH team said they did not want to spend the time putting together an information package, but they could have asked for a volunteer external group to take care of it, and you know many would have jumped at the chance. Plus NASA is extremely particular about what goes on every one of their space probes so I cannot believe that those trinkets and especially the ashes of a human being being placed aboard NH was a trivial matter that took no time or paperwork. Did you know NASA almost rejected the Voyager Records in 1977 because a simple engraving the record team wanted on the golden disc was not listed in the specs?!

In any event, NH should serve as a prime example of what not to do when we send all future vessels into the unknown void. Our alien neighbors or at least our children will thank us.


J. Jason Wentworth May 18, 2017 at 2:30

Sometimes it seems that we live in the blandest possible planetary system–just one star instead of two or more, and now, no bow shock–just a bow wave. But it could be worse; if our Sun was F-class, at its age it would already be beginning to swell into a red giant (or at least be showing ominous signs of it), and in that connection:

If nothing else, a suitably-modified (to show the outline of the spacecraft or final stage that it’s attached to) and appropriately-sized version of the Pioneer Plaque should be affixed to every space probe and upper stage that leaves the solar system. That could be a “default,” basic message, and other messages (also making at least some use of the Pioneer Plaque ‘binary glyph language’) could be added in addition to the basic plaque.

The waste of this opportunity for the New Horizons mission is almost infuriating (as you said, others would happily have created a message for it), because such missions aren’t flown frequently.


ljk May 18, 2017 at 10:32

Funny that you bring up the Pioneer Plaques:

I cannot recommend this video about the Pioneer Plaque highly enough:

Neil S May 16, 2017 at 12:03

“The sail’s launch aiming accuracy might be quite good, depending on the sail’s shape. The StarShot illustrations I’ve seen all show a small but otherwise “standard” square sail. A sail in the shape of a shallow cone (or a “multi-faceted cone” that approximates it) and with the payload at its apex would, it would seem, tend to “self-center” itself in the laser beam. Such a sail could be either spin-rigidized (with the light pressure causing the “coning” of a spinning disc sail) or be non-spinning (with a framework maintaining its shape).”

Think about how far off track at the nearest star an error in aiming of just 0.001º would cause (~4.5AU I calculate). Laser powering can perhaps be more accurate because the direction of the laser can be well controlled and the objects can be set up before the laser is fired, but the direction of a parasailed object released near the sun would be perturbed by any error in the position of release relative to the line from sun center to desired track, by minuscule motion at time of release, by error in instantaneously releasing all sides, by random solar brightness changes, by any tiny error in orientation of the sail and probably etc.


J. Jason Wentworth May 16, 2017 at 20:54

As Einstein said (or was said to have said), “It’s all relative…” :-) But seriously:

While a Sun-pushed sail would be subject to greater “dispersion” at the far end of its trajectory for the reasons you gave, a laser “guide star” (located on the ground or in Earth orbit or solar orbit) could be used for such missions. The solar sail probes would use the laser guide star to correct their aim points as they left the Sun’s vicinity (even out where the solar “accelerating thrust” is very weak, the sails could still–although slowly–maneuver to adjust their trajectories if desired or needed at those distances).


Michael May 12, 2017 at 16:49

Even using a CME (example) ~1200km/s (a good one) it would still take a over a 1000 yrs to get to the nearest star, mini-starshot, as it gets bigger will be needed. I am confident we have the ‘technology’ now to at least get a’dumb’ sail going at 1/10 the speed of ‘starshot’ or 2 % c, the problem is not only finance but getting the tech to dove tail together. This velocity is still huge compared to what we have now by a factor of around 200 of our fastest probes! I feel we can at least get to around a 300 to 500 nm sail meta-material now but will it survive the high g forces, looking at picosecond laser pulses research suggests it could survive and a whole lot more.


Phil May 12, 2017 at 19:04

Is comparing a probe, like starshot, to any number of vehicles that can carry passengers fair? Isn’t that kind of like comparing a horse to a cannon in Napoleon’s time?


Michael C. Fidler May 15, 2017 at 9:59

Relativistic Light Sails.

“One proposed method for spacecraft to reach nearby stars is by accelerating sails using either solar radiation pressure or directed energy. This idea constitutes the thesis behind the Breakthrough Starshot project, which aims to accelerate a gram-mass spacecraft up to one-fifth the speed of light towards Proxima Centauri. For such a case, the combination of the sail’s low mass and relativistic velocity render previous treatments incorrect at the 10% level, including that of Einstein himself in his seminal 1905 paper introducing special relativity. To address this, we present formulae for a sail’s acceleration, first in response to a single photon and then extended to an ensemble. We show how the sail’s motion in response to an ensemble of incident photons is equivalent to that of a single photon of energy equal to that of the ensemble. We use this principle of ensemble equivalence for both perfect and imperfect mirrors, enabling a simple analytic prediction of the sail’s velocity curve. Using our results and adopting putative parameters for Starshot, we estimate that previous relativistic treatments underestimate the spacecraft’s terminal velocity by ~10% for the same incident energy. Additionally, we use a simple model to predict the sail’s temperature and diffraction beam losses during the laser firing period, allowing us to estimate that for firing times of a few minutes and operating temperatures below 300C (573K), Starshot will require a sail of which absorbs less than 1 in 260,000 photons.”


Michael May 15, 2017 at 15:00

Silicon absorbs very little light at certain frequencies, it can be lower than 1 part in 1 billion! It is also a good reflector around 1.5 microns. Silicon has many atributes that make it a material worth considering in the starshot design.


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