Project Icarus Symposium: Part Two

by Paul Gilster on November 10, 2009

by Pat Galea

Project Icarus will update the Project Daedalus starship designed by the British Interplanetary Society in the 1970s. As we saw yesterday, developments in technology allow new options in a number of areas, but also raise questions about the mission’s scope and choice of targets. Pat Galea now concludes his discussion of the recent Project Icarus symposium in London, after which the terms of reference for the project, now frozen, are listed.

Propulsion Options

Richard Obousy tackled the part of the system that is the most obvious, the most important and probably the most difficult: the engine. As I’ve noted above, the Daedalus propulsion system uses pulsed nuclear fusion to accelerate the craft to about 12% of the speed of light. Even at such an immense speed, the mission time to Barnard’s Star (5.9 light years from Sol) is about fifty years.

Obousy took us through different methods of propulsion that have been proposed, such as chemical rockets, electric ion engines and nuclear thermal rockets. He gave an overview of how nuclear fusion works, and various enhancements that could be made to the fusion process.


One such trick is to use an antimatter seed to initiate the nuclear fusion reaction. This is a compromise design, a hybrid of the extremely powerful pure matter-antimatter engine and the simpler nuclear fusion engine. Small amounts of antimatter are used in this system to initiate the nuclear fusion reaction. The advantage of this idea is that we get some of the power boost of the antimatter reaction, without either the expense of producing large amounts of the stuff, or the problem of storing huge quantities during the mission (as the antimatter cannot be kept in a container made of matter).

Image: The original Daedalus concept, shown here as the second stage separates. Credit: Adrian Mann.

Current Earth-based production of antimatter is terribly meager at the moment. However, Obousy pointed out that much of the criticism we hear of the economics of current antimatter production is unfair, because the facilities were never built to produce antimatter efficiently. We can reasonably expect that truly dedicated industrial techniques to come will give us a much better return on our energy investment because they will be optimized for the purpose.

Onboard Power and Computing

Andreas Tziolas examined the power and computer systems that would be needed for Daedalus-like missions. Despite having a massive fusion pulse engine sitting at the back of the craft, there is still a need for separate systems that can provide the electrical power required for running the ship’s equipment. The engine won’t be running for the whole mission, and there needs to be some redundancy to cope with the inevitable failures which will occur over the lifetime of the voyage.

Tziolas examined several different power systems, such as batteries, fuel cells, flywheels and radio thermal generators (RTGs). Each system has its own advantages and disadvantages, so choosing the right systems depends upon a clear understanding of the mission parameters. For example, some systems work better over certain temperature ranges; other systems might have greater reliability over longer periods. By building a clear idea of the craft and the situations it will be operating in, it becomes possible to choose the most appropriate power systems.

Tziolas also explored the computer systems required on the craft. He emphasized that for such a long duration unmanned mission, there was a clear need for computer systems that have an advanced decision tree to cope with the huge variety of scenarios that the craft will encounter. These systems need to be fault tolerant, having no single point of failure, and be able to recover from any faults that do arise.

Parameters of the Project

Kelvin Long introduced Project Icarus, the aim of which is to produce an updated mission along similar lines to Daedalus, taking advantage of the progress that has been made in science and technology over the last thirty years. The terms of reference for the study have not been finalized yet, though Long presented a rough skeleton as a starting point. In open-floor discussions, the symposium attendees explored the range of mission parameters. It is clear that there is still a lot of work to do here before these parameters can be nailed down.

A couple of the most important parameters are closely related to each other:

  • Mission time
  • Fly-by or rendezvous

The Daedalus team decided that it was important to set an upper limit for the mission time such that a young person at the start of a professional career could join the project at launch time, and still be working when the probe returns data from the destination system. This requires a mission time of no more than 40-50 years. The motive for this restriction stems from the desire to maintain interest in the mission throughout the entire duration, and hence to make the project appear worth doing in the first place.

There was much discussion on this point, as several attendees pointed out that there have been many projects in human history that have taken significantly longer than a single lifetime to complete, such as cathedrals and pyramids. Whether this kind of commitment could be made to support a super-lifetime mission is an interesting question.

Deceleration at the Target System?

The second mission parameter concerns whether we decelerate the probe at the target system, perhaps to place it in orbit around the star. The benefits of doing so are discussed briefly above, in the summary of Crawford’s talk. It would clearly be desirable to do so, but the penalty is that the mission time would be extended significantly, as the ship would have to hold on to a lot of its fuel in order to burn it in deceleration.


So we have a trade-off between the two parameters. It is possible that there may be hybrid solutions available, where the main probe carries on at full speed, while sub-probes are decelerated. There are many options here, but nature is harsh, so the choices are tough. If it’s decided that a super-lifetime mission is acceptable, then a rendezvous becomes more feasible.

Image: Daedalus was designed for a mission to Barnard’s Star. The Icarus team hopes to allow for a variety of target stars. Credit: Adrian Mann.

However, a long mission entails consideration of another potential problem: the “overtake” scenario. If we launch a probe that will take, say, 150 years to reach the target star, we may worry that in fifty years time we’ll be able to launch a probe with greater speed that can reach the target in only fifty years. That would mean we’d get results back from the later probe fifty years before the data from the earlier probe. So we might decide that there’s no point in launching the slow probe at all; we just wait until we can launch the fast one. Some argue that it’s still worth launching the slower probe, because data are data. We may get results from the newer fast probe first, but we’ll still be glad to get data from the older slow probe when it arrives.

Icarus and the Years Ahead

After hammering out and fixing the basic mission parameters, the Icarus project will take several years of hard work to produce a new design for an interstellar craft. How much this design will resemble Daedalus is anyone’s guess at this point, and it’s quite possible that scientific data obtained during the design project (such as exoplanets) will throw a few curve balls along the way. Ultimately, the designs will be completed and submitted for publication in the Journal of the British Interplanetary Society (JBIS), just as Daedalus was all those years ago.

The Daedalus team mentioned that working on the project changed the way they view the universe. I hope Icarus will do the same, not only for those working on it, but for everyone else who takes an interest in humanity’s future.

Terms of Reference

On November 4, the Icarus team froze the terms of reference for the Icarus project. The text below constitutes the Terms of Reference (ToR) for Project Icarus and sets out what is to be achieved by the design study. This is frozen for the duration of the project and essentially represents the initial requirements.

The Terms of Reference are as follows:

  • To design an unmanned probe that is capable of delivering useful scientific data about the target star, associated planetary bodies, solar environment and the interstellar medium.
  • The spacecraft must use current or near future technology and be designed to be launched as soon as is credibly determined.
  • The spacecraft must reach its stellar destination within as fast a time as possible, not exceeding a century and ideally much sooner.
  • The spacecraft must be designed to allow for a variety of target stars.
  • The spacecraft propulsion must be mainly fusion based (i.e. Daedalus).
  • The spacecraft mission must be designed so as to allow some deceleration for increased encounter time at the destination.

There is also the addition of a project scope as follows:

‘The required milestones should be defined in order to get to a potential launch of such a mission. This should include a credible design, mission profile, key technological development steps and other aspects as considered appropriate.’


Carl November 10, 2009 at 11:02

The “overtake” scenario is not a reason to wait for better engine technologies. The interstellar medium will be studied in unprecedented detail by the initial probe into that direction. What is found en route helps or hinders the next voyagers.

Also, faster ships might be sent to systems different from the first attempt. A visual suggestion of our neighborhood is found at

ljk November 10, 2009 at 12:32

Oh, how I wish I could have been at that meeting! At least we can look forward to a published report in the hopefully near future. Did the BIS video or audio tape the conference as well?

I have a number of comments relevant to the Icarus project and interstellar missions in general. Some I have said before so I will only summarize them here. A few are new in light of the information provided in the two articles Paul Gilster has written here.

Right off the bat, I must admit to having issues with fusion being the main means of propulsion for Icarus. Perhaps I am being a bit pessimistic, but I am concerned about hanging hopes on a concept that may or may not be ready even in reactor form several decades from now, let alone a device small enough to be used for a starship.

Obviously fusion or antimatter power would be nice, but they have a lot of hurdles to overcome, which I don’t think will be solved in the lifetimes of anyone currently age forty years or more at least. Though I did like the comment that the places which currently make antimatter were not set up for mass production, certainly not on the scales a star probe would require.

How seriously did they discuss Orion type propulsion? Are they concerned about the use of numerous nuclear bombs, which does have some justification even if it is due to a public that jumps at the mere mention of the word nuclear? Unlike fusion, the Orion concept is a proven one and if they can get over a mission having to happen in one average human lifetime, we could be sending a probe on its way to Alpha Centauri before the end of this century if an Apollo-style effort was put into it.

Now about the computer brain aboard Icarus. While I note they mentioned it would have to be a “smart” system that can take care of itself during the long interstellar voyage, did they discuss at all the possibilities and consequences of having an AI that may need to be aware by its very nature running the mission?

If computer specialists can create an AI that mimics intelligence without consciousness, then we may have solved this problem which I have stated before. However, if the Icarus AI is an aware and conscious entity – thus making it a living being with rights as such – then unless it voluntarily wants to go on this mission after understanding all its aspects, and from which it will likely never return, can we send a conscious being on a one-way mission into the galaxy which will primarily benefit a group of humans that probably won’t even be born when Icarus is launched?

I know, this subject is a whole conference in itself. Maybe the Icarus AI would feel it is better off getting away from the Sol system and having a “virgin” star system to itself, just as a recent article on sending humans on a one-way mission to colonize Mars received many replies from people who would voluntarily hop in a rocket to spend the rest of their lives developing a new society on the Red Planet.

It could be argued that this idea is too esoteric for the Icarus project. Perhaps an aware AI is as distant as my earlier arguments about fusion power for a star probe. What I would like to hear from experts in the AI field is can one make a computer system that is able to handle events and issues both known and unknown in real time and plan ahead for their possible occurrence in the future – and not become conscious by necessity of design in the process?

This is what an interstellar mission with a communication time lag of years and decades is going to require to be a success, so the question remains: Can we have a “smart” AI of the type required for a robotic interstellar mission which at the same time is not smart enough to be aware as a human would be about the parameters of this situation?

As they say on NPR, more after the break (of ideas).

djlactin November 10, 2009 at 12:55

I wonder whether this entire concept may be too … er… massive. Time to think out of the box. Why do we assume that the probe must be (a) manned and (b) [consequently] big?
With the ongoing exponential reduction in size, and increase in power, of computing devices, we should perhaps look at much smaller probes (on the order of milligrams or less.)
One concept that I have been dilletanting with for years is that tiny probes could be ejected at a high fraction of c using a laser cannon on the moon. (Don’t ask me for details; I’m a biologist: this is a challenge for the engineers.) This cannon could be solar powered. Given that the solar constant is ~1400 (J/s)/m^2, a collector of 1 km^2, mounted vertically at a pole and kept perpendicular to the sun could easily collect ~10^9 J/s after inevitable inefficiencies; plenty by any measure.
“Simply” fire a series of probes at a range of velocities such that the later ones arrive at the same time as the earlier ones, and have them organize into a dispersed computing system (linked by something like WiFi). [Details, details, details! This is blue-sky stuff…] On arrival they do their stuff and relay the results back.
If a velocity of 0.9c could be attained, a flotilla to Alpha Centauri could pay off in less than 10 years (5 to get there, 4.2 to phone home). This is less time than required for several ongoing in-system missions that I could name…

Eniac November 10, 2009 at 15:46

I like Kare’s concept of microsails. In his scenario, the poor little microsails, which have at least some rudimentary electronic capability, are burnt up by the millions as reaction mass to push a large starship. That made me wonder if the sails themselves could not take the place of the probe. A continuous stream of them could form a massively parallel computer (not unlike the previous poster envisions), sensor array, and communications relay chain back to Earth.

A “probe-beam”, if you will.

ljk November 10, 2009 at 16:15

My comments and observations on the Icarus project, Part 2.

Did any members of the Icarus conference discuss any kind of information package for the star probe ala the Voyager Record? Since Icarus will be heading into relatively unknown regions of the Milky Way galaxy, the probe will serve as a form of ambassador for our species and planetary system. We should have some kind of informational greeting aboard this vessel to explain who built Icarus and why.

While I do not expect that the first system Icarus visits will have intelligent life, as I think we need to send it to the nearest star system, Alpha Centauri, and later versions can investigate our other celestial neighbors farther out, if the probe ends up heading off into the galaxy as Daedalus was planned to, there should be something on board to help explain to whatever ETI (or future humans) might find it why a multiton, nuclear-powered craft is barreling at a decent fraction of light speed through the Milky Way – and one presumably no longer able to receive or send transmissions.

The same rule should apply to Icarus if it is decided to break the probe into the target solar system, as either other galactic explorers or future native intelligences might come upon it one day. I know we would appreciate the same type of cosmic courtesy if a big alien ship suddenly appeared in our neck of the celestial woods.

If the Icarus designers are not interested in working on this information package idea or otherwise feel unable to, then they should farm out that task to a group that is willing and qualified to do this very important aspect of any interstellar mission. I don’t ever want to see such a rare opportunity dropped again as happened with the New Horizons team in 2006, only the fifth probe ever sent out of the Sol system and the first in almost 30 years.

This is why Tibor Pacher has created Faces from Earth, which will put together an information package for future deep space probes in the spirit of the Voyager Record and the CD on the Rosetta comet probe which has samples of over one thousand human languages on it.

The bonus to this greeting to ETI is that it can also be a time capsule preserving information about humanity and our world during the era when the probe was launched (and of course anything else from any other era that may be included) for the descendants of our species. Such a package in deep space could survive far longer than any human artifact on Earth: The side of the Voyager Record exposed to space (under a gold cover) is expected to last about 1 billion years; the side facing the probe even longer.

Tulse November 10, 2009 at 16:50

I wonder about the safety of a fly-by scenario. If you want to pass by a system close enough to get good data, you may be in close enough to encounter the debris around the system (e.g., the Oort Cloud and Kuiper Belt in our case). The problem with going .12c is that you don’t have much time to notice such debris, and something hitting a craft at .12c will pretty much vaporize it. It think that rendezvous may be the only choice that offers reasonable risk.

Enzo November 10, 2009 at 19:03

Can anyone tell me why antimatter induced fission/fusion has not been studied to provide energy here on Earth ?
One would not even need antiproton storage as they could be used as they are produced, no doubt with greater efficiency than with storage losses.
If it would work in space, why not here ?
I even remember reading, to my great surprise, that the left over from antiproton induced fission are not radioactive.
It seems to me thatseeding with antiprotons small pellets of fissionable material and fusion fuel is a lot easier than a giant Tokamak that doesn’t even work yet.

Mark November 10, 2009 at 20:43

Has anyone considered the ethical implications of sending a probe at such incredible speeds off into the unknown? What if there is a galactic expressway or (god forbid) an alien kindergarten or a fleet of generation ships or an inhabited planet or a space station other such targets directly in the path of the probe, a sitting duck for a rocketship heading out at a significant fraction of c forever? Should we put long range scanners on the probe and carry enough fuel for evasive maneuvers? What if we smash the hell out of an alien civilization and what’s left of them decides to get revenge? I’d say we need to reconsider sending probes blindly as if we own the universe. These probes should carry enough fuel to at least swerve out of the way. And to send them off forever at such speeds is reckless. Someone’s going to pay for this someday. They’ll trace it back here, and they’ll say we should have known better, if we were smart enough to send out such a high energy craft, we should have known better than to do it blindly. I’m all for exploring the universe but this is somehow worse than firing a rifle randomly out your window and hoping it doesn’t hit a school bus or your neighbor’s dog.

Kenneth November 10, 2009 at 23:41

Several important excursions need to be run on this whole issue. First using the terms of reference that the Project Icarus team has established why not consider a trip to a nearer star system such as Alpha Centauri. Secondly, why not start the mission from some place like Pluto instead of Earth. If both of these were done the travel times even with deaceleration at the target star would be much less. As for potential destinations, if such a trip is contemplated for starting sometime late in the 21st Century (2075-2100) it is probably safe to say that the only viable targets are in the near Sol Zone extending out to about 12 Light years. Beyond that the ship travel time becomes nearly impossible to deal with even if the ship was to reach .7C instead of the planned .12C. As for the issue of shielding, it is very important, but one has to believe that if Humanity can build a ship that can go .12C then it can probably invent a way to shield the ship without making it excessively big and heavy. The Icarus project is very useful in that it should tell us what can be done with overall technology levels that will likely be available to Humanity over the next ~75 years. It should not be seen as an valid exercise for something that Humanity can do 100-200+ years from now.

Eniac November 11, 2009 at 0:36

Enzo: I imagine it is because generating anti-matter costs much more energy to make than it could ever produce. I know that this is true for muon catalyzed fusion, and muons 1) are easier to make than antimatter, and b) can produce hundreds of reactions per particle, antimatter just one.

The reason it is considered for space is that while it costs a lot of energy to produce antimatter, this can be done in large facilities before the journey. The antimatter itself is somewhat like distilled energy, packing a large punch in a very tiny package.

Tulse November 11, 2009 at 0:54


“Space is big. Really big. You just won’t believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it’s a long way down the road to the chemist’s, but that’s just peanuts to space.”

Ronald November 11, 2009 at 4:32

djlactin: “One concept that I have been dilletanting with for years is that tiny probes could be ejected at a high fraction of c using a laser cannon on the moon.”

Your idea is not new or original (i have mentioned this myself on this site on a few occasions) but I would say very sensible and probably much more feasible than the moer massive concepts.
With all due respect and admitting my ignorance (I am also a biologist and a system analyst), I find that these huge projects have a rather high ‘Buck Rogers’ content (hopefully not Titanic content!), somewhat like ’50 illustrations of big space ships in comparison with present-day space probes.

The tremendous and obvious advantage of a (solar or fusion powered) laser installation on the moon is that, once you have made the enormous investment for the installation itself, the additional cost per miniature probe are comparatively minute and you can just keep spitting them out. Plus enormous risk-spreading, the opposite of all your eggs in one basket.

Then again, it is well-known by now that, safe an unexpected breakthough in some kind of exotic propulsion, I am rather reserved (not skeptical) with regard to near-future interstellar travel and very (VERY) much geared towards the advancement of telescopic research. All telescopes on all drawing boards plus those in the dreams of any astronomers (incl. world imagers, solar gravitational focus scope, etc.) could be built for just a small fraction of the cost of any interstellar travel attempt.

Adam November 11, 2009 at 4:43


Your concern is understandable, but the odds of collision are miniscule. However deccelerating the probe makes more sense than a high-speed fly-by and is the preferred option.

Paul Titze November 11, 2009 at 9:03

While we are talking about interstellar related studies, do any Centauri Dreams readers know of any current research undertaken my academic/private research that is related to the first two outcomes outlined in the Breakthrough Propulsion Physics Project? (recap):

1. Mass: Discover new propulsion methods that eliminate (or dramatically reduce) the need for propellant.

2. Speed: Discover how to circumvent existing limits (light-speed) to dramatically reduce transit times.

3. Energy: Discover new energy methods to power these propulsion devices.

“These goals are THE breakthroughs needed to conquer the presently impossible ambition of human interstellar exploration.”

I’m not worried about 3. as this will sort itself out in the next 50 years with fusion studies etc. I’m well versed with past research undertaken and been studying in detail Frontiers of Propulsion Science, wanted to put an open question if anyone knows of _current_ research that’s being done in this area of Physics.

Is there any currently funded research being undertaken by anyone regarding 1. and 2. on this planet?

Cheers, Paul.

James M. Essig November 11, 2009 at 10:05

Hi Folks;

Great discussion by the way!

If we humans learn how to medically augment our lifespan to indefinate lengths, commensurate with greatly improved and implemented protocols for avoiding accidents, then even mildly relativistic velocities of nuclear fusion rocket powered craft such as world ships can permit human civilization to spread out to a distance of a few billion lightyears from Earth in about 13.73 billion years which is the estimated age of our universe.


I share your concern. Perhaps the probes should have some nuclear device based self destruct mechanism.

The odd thing about inertial kinetic energy projectiles is that a projectile or a space craft somehow accelerated to a relativistic gamma factor of say 500,000; such as could be accomplished by an almost perfectly efficient matter antimatter rocket that carries both fuel components on board in their entirety from the start of the mission (with an M0/M1 ratio of 1 million as in the relativistic rocket equation Delta V = C{tanh [(Isp/C) ln (M0/M1)]}) and an Isp value assumed to be equal to 1C expressed in units of C, might be much more destructive that a warp drive vehicle traveling at say 1,000 C with respect to planetary impact.

The warp drive vehicle would simply involve the space within which the space craft is located being translated with respect to the surrounding space to the warped space /vehicle combination. The main danger posed by a warp drive craft might simply be that due to the strain energy of the warped space time being released upon any such collision, although perhaps with significant vehicle inertial kinetic energy effects as well

The rest mass specific kinetic energy of a relativistic macroscale projectile can quite literally approach infinity as the gamma factor of a given projectile approaches infinity.

It might even be the case that a projectile traveling at a mere gamma factor of 2 could induce a fusion reaction wave front to propagate through the thick ice covering an atmosphere-less icy world that might have a sub-terranian ETI civilization.

Note that nuclear devices of suitably high mass specific yield might pose a simmilar threat when detonated within Earth’s oceans according to at least one model. A gamma factor = 2, one metric ton rest massed projectile would have an volumetric energy density as much as [(.007) EXP -1](2) times that of a pure nuclear fusion device having the same rest mass and same rest volumetric density. Where such a event to happen in Earth’s oceans, the equivalence of the detonation of a hydrogen bomb with a mass of ~ 10 EXP 18.5 metric tons and a yield of about 10 EXP 27 metric tons of TNT could result. This is equal to the entire mass of the Sun in TNT. The entire Earth would be quickly reduced to a plasma with an average temperature on the order of one million Kelvin.

I am all in favor of sending out relativistic space probes and relativistic manned space craft, but unmanned robotic probes as such should have some sort of sensing and collision aviodance system, and/or self destruct system on board.

Mark November 11, 2009 at 14:12

I’m aware that space is really huge and mostly empty. Still, I think it’s irresponsible to take that chance especially with something moving so fast and essentially travelling that speed forever. Space is huge but the timescale is so long that eventually the probe is going to hit something. Let’s be responsible and not fire relativistic probes blindly. Let’s ensure a controlled end of life.

What would happen to a star the size of the sun if an Icarus probe hit it at 12% of c? What would happen to a neutron star? Maybe we could plan the trajectory of the probe to fly by the target system but then go on to impact the next nearest star after it. Ensure that you come in at a safe angle to any planetary disc to avoid planetary collisions. Probably no planetary discs to worry about with a neutron star.

In the event our long range sensors detected an imminent impact with a civilized planet, I’m not sure an onboard nuclear destruct would even be sufficient. Now instead of one probe impacting at 12% of c, you have millions of probe fragments doing the same. A nuclear explosion doesn’t destroy the mass of the probe. Now if you carried a probe-mass worth of antimatter onboard (hugely expensive and impractical I know), you could totally annihilate the probe and send out back to back gamma rays. That would be the ultimate safety braking system. Of course any civilization near enough to the explosion would fry from the radiation instead.

I can envision a future earth civilization having attained relativistic space travel capability something like a warp drive. One of the first missions will be going out to pick up all our relativistic probes before they do any damage. Or this may be our first contact, when an advanced alien spacefaring civilization returns these probes to us, with a stern warning not to be so irresponsible again.

Ron S November 11, 2009 at 15:43

Mark: “Space is huge but the timescale is so long that eventually the probe is going to hit something.”

Actually, no. This follows directly from Olber’s paradox.

“Now instead of one probe impacting at 12% of c, you have millions of probe fragments doing the same. A nuclear explosion doesn’t destroy the mass of the probe. Now if you carried a probe-mass worth of antimatter onboard (hugely expensive and impractical I know), you could totally annihilate the probe and send out back to back gamma rays. That would be the ultimate safety braking system. Of course any civilization near enough to the explosion would fry from the radiation instead.”

Yes, and in fact shrapnel is far more destructive than one cannonball. However, anti-matter of equal mass is not only a questionable alternative (expensive to carry) you will *not* achieve anywhere near total conversion to photons. What you’ll get is some conversion, and the rest of the material, matter and anti-matter alike, becomes shrapnel. Except now you have nearly twice as much of it as in the first case. On the last point: the gamma rays won’t fry anything since it’ll happen from much too far away from anything.

kelvin November 11, 2009 at 18:07

In reply to Kenneth. Project Icarus will question many of the original assumptions of Project Daedalus, within the constraints of our terms of reference. We could use D/He3, D/D, D/T…..we could go to Barnard’s star, Tau Ceti, Alpha Centauri, Epsilon Eridani…we could use laser driver, electron driver, ion driver….we could launch from earth orbit, earth, moon, moon orbit, mars….Jupiter… get the picture. A lot of variables to work through and we are currently considering a preliminary mission architecture.

djlactin November 11, 2009 at 19:45

Ronald: I never claimed it was my idea! I’m sure you and I are only two of many who mull over such thoughts on a sunday afteroon…

As for all of the worries about a probe-ship colliding with a planet, the possibility is minute (but neither negligible nor trivial), but I think a more serious problem is the possibility (probability, given a length of the path) of smacking a milligram-sized mote of interstellar dust while traveling at (say) 0.3c. I don’t have the physics knowledge to calculate the impact energy (perhaps Mr. Essig would care to do so), but the consequences to the ship would certainly be catastrophic.
Returning to the nanoprobe concept, such tiny probes would present much smaller targets, and being part of a flotilla, would be expendable.

Tulse November 11, 2009 at 23:26

A milligram of dust at .3c has energy equivalent to a tonne of TNT (at least, presuming that the calculations are correct). That will do some serious damage to any craft. It’s hard for me to imagine that even some sort of bulk physical shield (like a big block of water ice or deuterium) could take very many of such hits. Again, I would think one would have to slow down as one approached a system, or risk a catastrophic encounter with bits of rock or ice.

James M. Essig November 11, 2009 at 23:41

Hi djlactin:

Thanks for asking.

The relativistic kinetic energy of a 1 milligram dust particle would be equal to {[M[C EXP 2]](gamma)} – [M[C EXP 2]] = {[M[C EXP 2]]/{[1 – [(v/C) EXP 2]] EXP (1/2)}} – [M[C EXP 2]] = {[0.000001kg[((3 x 10 EXP 8)m/s) EXP 2]]/{[1 – [(0.3C/C) EXP 2]] EXP (1/2)}} – [0.000001kg[((3 x 10 EXP 8)m/s) EXP 2]] = [(9 x 10 EXP 10)(1.04828)] – (9 x 10 EXP 10) = 4.345 x 10 EXP 9 Joules = 4.345 GJ.

Now one metric ton of TNT has an explosive kinetic energy of 1,000 calories/gram = 1 kCal/gram ~ 4.2 kJ/gram. Therefore, the one mg dust mote would have a kinetic energy equal to about 1 metric ton of TNT.

At first, one metric ton of TNT might seem trivial, but remember, shaped charge chemical explosive rounds can defeat many of main battle tanks using only on the order of a few kilograms of TNT. The armour piercing darts fired from the M1-A2 main battle tank have an impact kinetic energy equivalent to at most a few kilograms of TNT or less.

Given that the size of a dense milligram dust mote traveling at 0.3 C has a kinetic energy at least 2 and 1/2 orders of magnitude greater than an antitank round, and a much smaller effective impact footprint area-wise, the consideration of relativistic dust motes is not trivial. If huge numbers of such dust motes were sent out all over the place, there is a chance that an alien space craft could be damaged were the craft not properly shielded upon any impact.

Note however that such a dust mote entering the atmosphere of a planet would not likely cause any harm to surface dwellers as the particle would be immeadiately reduced to a plasma stream, along with gamma rays and x-rays, and some neutral particles such as relativistic neutrons and the like. The particle stream would be quickly diffused within the atmosphere.

A metric ton rest massed projectile traveling at a high gamma factor would pose a serious problem even for a planet with a thick atmosphere due to the huge release of ionizing radiation upon plunging into atmosphere. A one metric ton rest mass projectile having a extreme gamma factor of a hard to envision 1 million would have an impact yield in an atmosphere in the form of a highly directed jet of mattergy of about (10 EXP 6)(22.5 x 10 EXP 9) tons of TNT or about (2.25 x 10 EXP 16) tons of TNT. This is the equivalent of one million tons of mass converted into a kinetic and photonic energy jet.

Note that the Earth recieves only the equivalent of about 31,000 metric tons of matter converted into energy per year, and on average, the thermal energy stock and wind stream energy stock within the entire atmosphere of Earth is about 1 1/2 orders to two orders of magnitude less yet. Using the ideal gas law as an approximation PV = nRT, and the fact that heat is a measure of the thermal energy contained in a material, since the average temperature of the atmosphere is about 273 Kelvin, even in the case where the gamma factor = 1 miilion one metric ton rest mass object could some how be instantly distributed uniformly throughout the Earth atmosphere, the average atmospheric temperature would would climb to as high as 27,300 Kelvin which is hot enough to vaporize essentially all man made structures almost instantantly. The pressure would instantly climb to about 1,500 PSI on the surface of the Earth due to atmospheric heating.

However, the jet would be concentrated and if a wall of compressed air would build up in front of the mass, even air originally at STP might be induced to undergo a propagating fusion chain reaction provided that fusion temperatures and pressures (and air shock wave front densities) could be maintained in a fusion reaction based self propagating manner.

Clearly, space is huge and so there is not much of a risk of our future relativistic probes or manned space craft colliding with a planet any time soon, however, for planets so impacted, the consequences would be disasterous.

Even though impact as such would be rare, I feel that some caution is need in sending probes a relativistic velocities to other star systems. I think any ETI civilization on the recieving end of a 0.12 C one metric ton probe would have a bad day. Such a colision would have a pure kinetic energy yield of about 157 megatons which is about 15 times the yield of the meteor or comet explosion over Tunguska Russia.

I am a strong believer of future high gamma factor manned space craft and probes, but lets be carefull with our projectiles. I would not want to piss off any interstellar space faring race.

Kenneth November 12, 2009 at 2:42


Thank You for the information. This is great news. As you can tell by my original post I believe the Icarus Project is very important because it has the potential to develop a notional but viable mission concept for unmanned or even manned Interstellar Travel that may be executable within the next 75 years instead of the next 200 years. It is estimated that roughly every 56 years a Maslow window for exploration opens up, and this 56 year cycle seems to be tied to Energy development and exploitation. Since the dawn of the Space Age in the late 1950’s it is believed that the first Maslow Window for Space exploration began circa 1958/1959 and lasted through 1972. The next Maslow Window is now projected to begin circa 2015, and should last until 2025 or 2030 unless cut short by catastrophe since these exploration windows tend to last about 10-15 years. For the purposes of Solar System Colonization and perhaps the first Interstellar Trip the Maslow Window that would start circa 2070 (~56 years from 2015) and could last through 2085 looks extremely promising. This is especially the case since this Maslow exploration window coincides with what I like to call the roughly every 75 year technology boom/ prosperity cycle (late 1840’s California Gold Rush+75 years=Roaring 20’s+75 years equals the late 1990’s+75 years equals early to mid 2070’s) where there is enough new Science and discretionary income to fund and support great exploration projects.

Also, if we are very lucky it is estimated by Michio Kaku and others that Humanity may reach a Kardashiev Type I civilization level by around 2075 CE so we might just barely have enough power generation capability by then to support an Interstellar Trip that is very close to the Sol/Terra system, especially if we used a stepping stone approach through the Ort Cloud and beyond and into a hypothetical Ort Cloud of Alpha Centauri. Of course the assumption here is that we will find something interesting to go to in the near Sol/Terra zone extending out to about 12 Light years, and if we are lucky, Alpha Centauri may be the most promising in terms of other Star systems that we might be able to reach in the next 75-100 years.

From what I have been able to gather the Icarus Project is looking at a notional Interstellar Craft which is on the order of 54,000 tons-100,000 tons or the size of a modern U.S. Aircraft Carrier which seems viable for an Interstellar Craft that can also be built on a conceivable budget (~$1-2 Trillion if we can get launch costs down to a few hundred dollars per pound), and within the next 75 years. Building and launching an Interstellar Craft the size of a modern U.S. Aircraft Carrier will be an extraordinary feat of Engineering and technology, but it seems to be a manageable project even for Human Civilization circa 2075-2085. I hope that the Icarus Project keeps the 54,000-100,000 ton weight class since I believe that while Humans may be able to do better then fusion propulsion and .12C by 2075 the size of the ship is likely to remain about the same for almost any viable Interstellar craft using 21st Century technology unless it used beamed propulsion. If a new more efficient type of propulsion system is developed by then based on breakthrough physics such a zero point energy manipulation the Interstellar Craft is still going to be about the same size especially if it is manned since all that is likely to happen is that more stuff will be carried at a higher velocity. If the Icarus Project does an elegant job it should be able to define a flexible Interstellar Craft design of 54,000-100,000 tons that could eventually swap out its Fusion or Fusion/antimatter Engines for a more advanced propulsion system as they become available in a spiral evolution of the Interstellar Craft. However the basic design of the Interstellar Craft would remain the same, but just get better and more efficent with any propulsion breakthrough where the Interstellar Craft in question carries its own propulsion system. It is usually better to start with allot of extra design margin in the craft under development and then design it out as technology becomes better and more efficient then to try and add margin later. An Interstellar Craft of 54,000-100,000 tons should have extensive design margin and therefore be a robust design that only gets better with new more advanced propulsion systems.

A few years ago it was postulated by several scientists that objects including Space Ships able to achieve velocities of about 60% the speed of light would also exhibit a strong antigravity effect at least in front of the object traveling through space, and that Human Civilization would be able to achieve velocities of .6-.7C by the end of the 21st Century, although getting to .8 to.9C would be much harder and take many centuries. The Icarus project is based on current or near term technologies (next 20 years?), but hopefully the eventual design will be developed with enough flexibility that it can retain its basic configuaration and inccrporate more advanced technology as it becomes available. This approach will initially sub-optimize the design to some extent, but eventually it should pay off by making it a classic design that could endure for a few centuries such as today’s B-52 Air Craft is now almost 60 years old and still going strong because it a highly robust design with lots of design margin.


Adam November 12, 2009 at 8:03

Talk about worst case scenarios!

Relativistic bombs are a bit of a favourite discussion topic around here. Are we so afraid of ourselves and our creations?

James M. Essig November 12, 2009 at 11:06

Hi Adam;

Good point!

One of my hopes for distant future manned space travel that does not so much rely on inertial travel through space at extreme relativistic gamma factors is some form of Higgs Field suspension technology wherein the inertial mass of a space craft can be reduced to zero by completely or nearly so eliminating the Higgs Field around the space craft by an onboard Higgs Field eliminator. I hope the LHC detects any Higgs Field Bosons, even in the case where the MSSM is validated as the number of Higgs Bosons species would be shown to be equal to four. Four different Higgs Bosons may offer a lot of thermodynamic degrees of freedom in any future Higgs Field elimination technology. With such a technology, we might not only realize Einstein’s youthfull thought experiment dream of riding along side a beam of light, but we might in a real sense, become the beam of light.

Note however, that I remain a champion of extreme relativistic gamma factor inertial travel as well to the extent that such can be accomplished becuase of relativistic time dilation. Funny thing is, a space craft traveling at an impossible seeming gamma factor of 10 billion will travel 10 billion lightyears in one year ship time or 1 trillion light-years in one hundred years ship time. A warp drive craft traveling at 100 million C would take 10,000 years ship time to travel 1 trillion lightyears. I would rather take the high gamma factor sub-C craft myself given that I will probably be lucky if I live 100 years.

I see high gamma factor space craft and light speed and/or superluminal space craft as potentially all being used simultaneously as each craft type can have its own niche. I want however to conduct space travel in a safe manner for all of the citizens of the Milky Way and beyond just as we humans here currently have the FAA and lots of ATCs to help ensure safe airline travel.

ljk November 12, 2009 at 14:02

Mark said on November 10, 2009 at 20:43:

“Has anyone considered the ethical implications of sending a probe at such incredible speeds off into the unknown? What if there is a galactic expressway or (god forbid) an alien kindergarten or a fleet of generation ships or an inhabited planet or a space station other such targets directly in the path of the probe, a sitting duck for a rocketship heading out at a significant fraction of c forever?”

Yes, Mark, please see my post on these very issues near the beginning
of the comments in this thread.

While staying at home and hiding under our beds out of the fear that
there is a big bad Universe out there is not an option for a growing
society such as ours, we also need to be cautious where feasible. And
as many human cultures will attest to, it is always the correct and
polite thing to bring a gift with you when visiting others.

Henry November 12, 2009 at 15:11

I hope this isn’t a really stupid question as I’m not a scientist, but could a large solar sail be unfurled and used as a brake as the ship approaches the target system? Why is fuel necessary for deceleration (or indeed acceleration)?

James M. Essig November 12, 2009 at 20:04

Hi Folks;

I have come to believe after thoughfully reflecting on the many responses that have been posted on this tread, that despite the risk that some interstellar probe scenarios might pose to ETI civilizations, planets, and space craft, the risks are indeed very low at least for the comming following few eons, simply because space is so big compared to the volume occupied by planets and any ETI space stations and craft.

There are some risks, technically, however small the chance of near term impacts, but we never advance science and human civilization without risk. No endeaver is ever absolutely 100 percent risk free, but we must have the courage to press forward and boldly in the name of human progress and also the hope that we will be able to meat any of our ETI brothers and sisters one day.

Note that I will be away from Tau Zero for about a week as I take care of personal matters, but as one who has contributed a lot of text so far to this thread’s commetary as has also the other contributors, I encourage others to continue this discussion. This thread is very active and active discussions are encouraging.

I encourage any new viewers of the Centauri Dreams threads who have not commented and/or feel shy about commenting to also post your comments. Our initial efforts to the cause of manned interstellar space travel right hear at Tau Zero will likely go down in history and be remembered as early pioneering efforts, and it is quite possible that any future ETI civilizations that we might meet and enter political, scientific, cultural, technological, and economic treaties with will likewise have references to our early pioneering efforts in their recorded media for all time.

Tibor November 14, 2009 at 13:56

Mark, ljk,

Kelvin has mentioned briefly the first spin-off project during his talk at the symposioum – this is the “Icarus Message” project, led by me. It is in its nascent phase right now; first thoughts about it can be read here. The Icarus Message will be a Faces from Earth project, in close coordination with the Icarus Project Team.


djlactin November 15, 2009 at 10:09

After Dr Essig’s reply ({[M[C EXP 2]](gamma)} – [M[C EXP 2]] = {[M[C EXP 2]]/{[1 – [(v/C) EXP 2]] EXP (1/2)}} – [M[C EXP 2]] = {[0.000001kg[((3 x 10 EXP 8)m/s) EXP 2]]/{[1 – [(0.3C/C) EXP 2]] EXP (1/2)}} – [0.000001kg[((3 x 10 EXP 8)m/s) EXP 2]] = [(9 x 10 EXP 10)(1.04828)] – (9 x 10 EXP 10) = 4.345 x 10 EXP 9 Joules = 4.345 GJ.! gaaak, you need to implement some version of Microsoft equation editor), I have come to two conclusions.
1) Relativistic probes will encounter matter. Even though matter is rare in the universe, its effects are not. Consider that the density of the universe is ~10E-30 g/m^3 (wikipedia), neglecting that this density is greater in mass accumulations such as galaxies, and and assuming that “most” matter is hydrogen, a probe with cross-sectional area of 100 m^2 would intersect 6E18 hydrogen atoms per light year.
The relativistic kinetic energy K of these impacts, summed over distance, varies according to v/c = beta: at beta = 0.3, K = 9.45E8 Newtons; at beta = 0.6, K = 1.13E9 N; at beta = 0.9, K = 2.07E9 N. These are huge numbers, despite the low density of matter. Two consequences: 1) Size is a deficit. 2) A relativistic probe would need to be streamlined!
The alternative, as I mentioned in a previous post, is to broadcast a flotilla of milligram-mass probes with limited intelligence that co-compute and broadcast their conclusions. Assuming that each probe masses 1 mg and assuming a density of 5 kg/m^3, and that they are cubes, each would have axes of 5E-7 mm and a frontal area of 25E-7; although the amount of matter that they would intersect is trivial, the consequences would in each case, be catastrophic. However, if a large number of such probes were broadcast, loss of a few would not be serious.
But then…
(2) We have replaced the consequences (of impact on some target planet) of launching one massive probe with the same consequences of launching (essentially) a burst of relativistic buckshot at a stellar system. Despite Dr. Essig’s dismissal of the consequences, such risks to the target culture should not be dismissed.
As a final speculation: perhaps we should closely examine hyperbolic comets: a tiny proportion of them may be interstellar probes.

Paul Titze November 16, 2009 at 6:38

James Essig,

Time to get your equations sorted so they are easier to read. Google has the option to convert LaTeX formatting online, see the following:\LaTeX

or any equation you want, another example:\nabla^2 f(x,y) = {\partial^2 f \over\partial x^2}+ {\partial^2 f \over\partial y^2}.

Wordpress also has the capability to display LaTeX. However not sure if this works in the comments, maybe just paste the link for eg as shown above so people can look at it themselves unless someone else has a better idea?

Cheers, Paul.

Cheers, Paul.

James M. Essig November 16, 2009 at 10:16

Hi djlactin and Paul;

Thanks for the advice.

I will definately look into LaTex before I resume posting at Tau Zero by this Saturday or Sunday.

MS Word also has a rich variety of symbols but I have never uploaded comments to Tau Zero for which I ihave included such symbols.


By the way, just so that folks know what my true credentials are, I must admit that I am not a PhD. I do hold a BS is physics from George Mason University in Fairfax VA, and although I have taken several graduate level physics and math courses, I enrolled again in GMU as a non-degree graduate student, an option that allows me time to consider a possible major for grad school. I am not sure whether I want to continue to obtain a MS in Applied Physics or whether to persue to MS in math. I will probably go back to school this spring. At this point in time, I am only considering course work that would make me a better practicioner of Tau Zero and an improved Space Head.

Regardless, I consider Tau Zero the in place to be and I have made many good friends since I first started posting about 2 or 3 years ago.



Paul Titze November 16, 2009 at 11:28

Re: James Essig

I also had a look at your blog, your posts are very long with (again) many formulae to go through and it’s very difficult to follow some of your calculations. Just so you and others know, there is now where you can submit papers (open to anyone). Download if you’re running Windows to write your paper, I’ve written a post in my blog about all this if that helps as I’m also learning LaTeX etc.

Regarding PhD etc, if you feel you need one that’s your call however everything that you need to be a “better practicioner of Tau Zero” is either online or in books. Speaking for myself I found I learnt much better just reading the materials myself instead of attending lectures at uni… I also have a BSc in Physics (Sydney University) but decided to make my living on the water which was my other calling :-) Remember a good Physicist is only as good as the papers he/she publishes all those brilliant theories are no good if they’re stuck inside ones head ;-)

Cheers, Paul.

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