The Interstellar Conundrum Reconsidered

by Paul Gilster on August 20, 2008

Just how hard would it be to build a true interstellar craft? I’m not talking about a spacecraft that might, in tens of thousands of years, drift past a star by happenstance, but about a true, dedicated interstellar mission. Those of you who’ve been following my bet with Tibor Pacher on Long Bets (now active, with terms available for scrutiny on the site) know that I think such a mission will happen, but not any time soon. And the proceedings of the Joint Propulsion Conference, held last month in Hartford, go a long way toward explaining why the problem is so difficult.

Wired looked at the conference results in a just published article, the most interesting part of which contained Robert Frisbee’s speculations about antimatter rocketry. Two things have been clear about antimatter for a long time. The first is that producing sufficient antimatter is a problem in and of itself, one that may keep us working with tiny amounts of the stuff for some time to come. Even so, interesting mission concepts, like Steve Howe’s antimatter-energized sail, have grown out of the studies that have been performed on possible hybrid systems.

As to antimatter itself, while the annihilation of matter and antimatter releases vast amounts of energy, controlling the result is even more difficult than producing antimatter in quantity in the first place. Proton/anti-proton annihilation is preferable to electron/positron because the gamma rays produced by the latter can’t be directed to produce thrust, a problem Eugen Sänger wrestled with fifty years ago. But the former is a possibility because the reaction products (pions) can be directed and confined electromagnetically. The idea here is to transfer some of that vast energy of annihilation to a propellant working liquid.

Even so, our rocket still has problems. Check our friend Adam Crowl’s recent piece on antimatter for several good links and some musing on the relatively poorer performance with antimatter than one might have expected (an exhaust velocity of 0.33 c may itself be a surprise, but take a look at this Frisbee presentation). Frisbee (NASA, Jet Propulsion Laboratory) has been studying the interstellar conundrum for a long time, with particular attention to antimatter. The design he presented at the conference, a stack of linked components designed to keep radiation away from crew or payload, is summed up by Wired this way:

At the rocket end, a large superconducting magnet would direct the stream of particles created by annihilating hydrogen and antihydrogen. A regular nozzle could not be used, even if made of exotic materials, because it could not withstand exposure to the high-energy particles… A heavy shield would protect the rest of the ship from the radiation produced by the reaction.

A large radiator would be placed next in line to dissipate all the heat produced by the engine, followed by the storage compartments for the hydrogen and antihydrogen. Because antihydrogen would be annihilated if it touched the walls of any vessel, Frisbee’s design stores the two components as ice at one degree above absolute zero.

So far, so good. We then include basic spacecraft systems in front of the tanks of propellant and then our payload. But theory meets a grim reality in the numbers: Frisbee is talking about an 80 million metric ton starship (the Space Shuttle weighs in at 2,000 metric tons), with another 40 million metric tons each of hydrogen and antihydrogen. The payoff is a forty year mission to Alpha Centauri.

At least it’s designed as a rendezvous mission. A forty year flyby to the Centauri stars would be moving at something better than a tenth of lightspeed once it gets up to cruise. Even if exquisitely targeted, such a probe would operate within 1 AU of the target system (let’s say Centauri B) for something less than three hours. Ponder the challenge presented by collecting imagery and data from Centauri planets in such a scenario.

What to do? These results reinforce much that we already knew about the difficulty of coming up with an interstellar mission design that is remotely affordable, and everything comes down to energy. As noted by Wired, interstellar theorist Brice Cassenti (Rensselaer Polytechnic Institute) comes up with a minimum value of the current energy output of the entire world to send a probe to the Centauri system, a figure Cassenti is quick to note could easily swell to 100 times that value.

It’s useful to ponder the size of the challenge as we continue to scout for concepts that can overcome these problems. The dual track that interstellar studies takes continues to work this way: 1) Push concepts constructed under the parameters of known physics to their utmost, to see where they might lead. Antimatter rockets, laser sails, pulsed fusion and their ilk all fall under this category. 2) Investigate potential concepts that might extend our knowledge of known physics. Here we turn to studies like those sponsored by, among others, NASA’s now defunct Breakthrough Propulsion Physics project. The Tau Zero Foundation hopes to bring philanthropic support to both approaches.

No one can say whether interstellar missions will ever be feasible. What we can insist is that studying physics from the standpoint of propulsion science may tell us a great deal about how the universe works, whether or not we ever find ways of extracting propulsive effects from such futuristic means as dark matter or dark energy. And if it turns out that our breakthroughs fail to materialize, the potential of multi-generational missions supported by human crews still exists. They will be almost inconceivably demanding, but nothing in known physics says that a thousand-year mission to Centauri is beyond the reach of human technology within a future we can still recognize.

How big would an interstellar mission be? Let me close by quoting Robert Frisbee himself, from a presentation he gave at the 2003 iteration of the Joint Propulsion Conference:

In the long term, it will represent a Solar System civilization’s defining accomplishment in much the same way we look to the past accomplishments of humanity, like the Pyramids, Stonehenge, the great medieval Cathedrals of Europe, the Great Wall of China and, not so long ago, a space program called Apollo.

{ 32 comments }

John Hunt August 20, 2008 at 18:36

Sometimes a third choice can resolve an apparent conundrum.

The apparent conundrum is that we have to choose between an approach which would be technically difficult and incredibly expensive or we have to discover new physics. Of course neither of these choices are necessary. There are an array of choices that use known physics and don’t require 80 million metric tons. What this article illustrates is that there are certain mission designs which can be placed in the let’s-be-aware-but-not-seriously-consider category. Personally, for the sake of progress, I’d like to see some concepts formally placed in this category.

But I wonder if another false dichotomy is at work where we feel that the choice is between a short-term scientific mission (i.e. within 100 years) verses multi-generational living crews. Again, both choices pose practical difficulties. Short-term missions usually have significant energy issues and multi-gen living crewed missions involve mass and cost issues.

To minimize the energy requirements one could either:
– keep the mass down or
– extend the mission time.
Again, the best solution might come from the middle ground. i.e. fairly low mass craft (launched in parts?) with a moderately long mission time. As discussed before, the Wait Equation would necessitate that this be a survival-of-the-human-species mission.

By reaching for the middle ground one comes closer to:
– a relatively near-term mission
– using near-term technology
– launched from Earth using as little as a single launch
– within reasonable space budgets
– and hence more likely to get funded

I’m thinking about things such as a fryby, VASIMIR, advanced ion engines, FEEP, MPD, & maybe SailBeam, LightSail & MagSail.

Adam Crowl August 20, 2008 at 19:32

Hi Paul

Makes the case for beamed propulsion even more compelling – except we need those in-space power-sources in the GW range still. But there’s a way there I am sure. Tentatively I would see a natural progression like so…

(a) Earth-launched SPS, robotically assembled and maintained in part
(b) Space-resourced SPS, mined, processed and assembled robotically
(c) Self-replicating SPS from in-space materials
(d) Interstellar mission capable SPS collection in solar orbits

Step (c) is where the economics become feasible for interstellar travel. Mini sail-probes can probably be launched with a few GW, but large probes and manned vehicles will need terawatt range beam-power.

I’ve thought long and hard about the multiple reflection acceleration systems that we’ve discussed here before, but their obligatory short acceleration range is a show-stopper for manned interstellar. However they might produce an energy saving for a system like Jordin Kare’s sail-beam. However reflection off a moving mirror reduces the energy of the reflecting photons by the red-shift. That energy goes into the acceleration of the mirror, but it means that a multiple reflection system will need a mirror able to handle a broad frequency range at high efficiency – something that may not be feasible at high red-shifts, and probably tricky for even low speeds when a thousand reflections are desired. Interplanetary speeds up to ~300 km/s are probably ok, but interstellar speeds are dubious.

Thus we’ll have to bite the bullet and scale up to terawatt beams or settle for 10,000 year missions.

Matt Metcalf August 20, 2008 at 20:30

What I’ve always wondered about beamed power systems is how you stop at the other end. If it takes an external energy source in order to get you up to speed, how do you go about decelerating from that high speed?

Personally, I think that new science/new technology are more likely to be the key, and I’m glad people like Tau Zero are working toward those goals.

Mark August 20, 2008 at 21:18

40 year journey for 3 hours of data collection? Yikes. Has anyone considered sending this huge craft to within striking distance of the system and then pickling off a half dozen much smaller probes (say something with a science payload on the order of the size of a can of coffee) and then decellerating those probes into orbit about the system using ion propulsion or solar sail? The probes could remain in the system taking data for a much longer time.

Administrator August 20, 2008 at 22:17

Mark, the Frisbee concept is itself a rendezvous mission — no flyby intended, but I brought up the flyby concept because that’s one scenario that’s often mentioned. The Daedalus probe, for example, was designed to do exactly what you mention, get to the Barnard’s Star system and then, as it passes through, scatter probes for separate investigations. Moving at these speeds, though, slowing even the much smaller probes down is itself quite a difficult proposition. Magsail technology might prove promising for such a task.

Re the question of stopping when using beamed propulsion — Matt brought this up — Robert Forward figured out an ingenious way of separating the laser sail into segments and actually beaming laser light off one segment back onto the one still attached to the payload to slow it down. I plan to write this up here on Centauri Dreams, with illustrations, in the near future. Like so many Forward concepts, it’s ingenious but quite an engineering stretch!

tacitus August 21, 2008 at 0:04

Wow. 2025. What was Tibor smoking when he made that bet? As one of the commenters said on that site, if we to launch an interstellar mission in 2025 we would be starting the planning phase yesterday. It’s a shame the date for the wasn’t set further out (2050 or 2100). That would have been a much more interesting discussion. (I would still bet against it, even at 2100).

There are very few scenarios under which we launch a mission to another system by the end of this century, none of which is remotely likely.

1) We discover an Earth twin around in the Centauri system that has confirmed life on it and, even better, signs of intelligent life. The impetus to go and discover more about our next-door neighbors would be compelling.

2) Aliens drop in and lend us an interstellar craft or, slightly more likely, they send us an interstellar email a la Contact.

3) We independently discover the secret of practical FTL or near-light travel (i.e. without massive scale engineering or energy requirements).

All in the realm of science fiction, I know, but that’s what it will take to get going before 2100. Longer term, if we continue to prosper as a species, I have no doubt our future is out amongst the stars. It’s just that the journey will take centuries, not decades from this point in our history.

Adam Crowl August 21, 2008 at 7:28

Hi All

One point from the Frisbee papers is that the acceleration is very low – 0.01 gee. Thus the vehicle is accelerating the whole way, hitting a maximum speed of 0.208 c. The mass is so incredibly high because the vehicle is many kilometres long to put the payload a long, long way from the gamma-radiation coming out of the tail, and to provide enough radiator length to keep things cool enough to keep operating.

Is there another option? Charles Pellegrino designed a “Valkyrie” starship with a similar payload (100 tons) but used very long tethers to avoid structural mass. Not sure if he covered all the issues, but who knows?

ljk August 21, 2008 at 9:05

If you asked someone in 1950 if there would be men on
the Moon by 1970, they would say you were smoking
something, too. But it happened because that is how
quickly things can change.

Sending a robot probe somewhere is much different than
a manned expedition, say to Mars. It actually would not
surprise me if some enterprising group built a star probe
using the advancements in technology that could happen
by 2025 and launched it while the major space powers
are still promising space colonies and doing little else.

Jerome Cole August 21, 2008 at 10:43

I think the dealbreaker or dealmaker is going to be our future ability to produce large amounts of anti-matter. Given continuing advances in computing and materials science I am very optimistic about the possibility of manufacturing anti-matter on a large scale sometime within the next few decades.

andy August 21, 2008 at 11:40

What John Hunt misses in his enthusiasm for manned interstellar missions as a total replacement for robotic ones is that it is going to be very difficult to determine whether the target system is capable of supporting human life at a range of several light years: at best we are looking at a list of gross physical properties and very crude maps of the planets and possibly some of the larger satellites as well. If we find evidence of a habitable planet, we get no indication of whether any biology existing there is going to cause problems. No-one wants to end up on Nebel 2 because the data we collect at long range isn’t good enough.

It is also interesting to compare the energy requirements for realistic proposals and compare them to the Fermi crowd’s blasé statements that it would be easy to get von Neumann probes in some kind of working condition across the galaxy.

Sean Taylor August 21, 2008 at 14:06

It seems to me that humans will have left their current biological substrates far behind (or destroyed themselves) by the time interstellar travel becomes feasible. The revolutionary advances in this century will probably be in genetic engineering, artificial intelligence and nanotechnology, which may fundamentally alter our definition of humanity and its potential in the universe. This makes any predictions extremely difficult, since changing humans themselves changes every other endeavor radically (the so-called “singularity”). I would guess that the first earthlings to reach another star will either be artificial intelligences (perhaps self-replicating probes), or some kind of “beamed intelligence”, i.e. “mind patterns” that are transmitted at the speed of light to receiving apparatus sent in advance which can “download” this intelligence into robotic bodies. The point is, unless there are revolutionary breakthroughs in physics, the universe doesn’t appear well structured for interstellar exploration by humans in their current biological form. Therefore I suggest that re-engineering humans and abstracting their intelligence into more flexible forms is the best path to the expansion of human consciousness into the galaxy.

tacitus August 21, 2008 at 14:52

ljk: The difference with the Moon program is that by 1950 we already had propulsion system we needed (albeit with more development) to get there. We have nothing today that will get us to another star in less than 2,000 years.

Even if there was a breakthrough tomorrow, if the projected flight time was more than about 50 years, we still wouldn’t launch a mission, so even getting to the point where we would have the political will to go is orders of magnitude more difficult than the Moon program was even back in 1950.

But let’s say, for the sake of argument, such a breakthrough happened tomorrow — Alpha Centauri in 40 years is now possible, and the InterStellar program is started in a blaze of publicity. Even assuming that the Washington bean counters gives NASA the green light, the which InterStellar mission would be the first to launch towards another star system?

IS-1? Nope — proving run, perhaps to Jupiter or Saturn if we’re lucky.
IS-2? Nope — second proving run. Irons out the kinks found in IS-1 and perhaps targets Neptune or Uranus since we haven’t been there in a long time.
IS-3? Still unlikely — even if all has gone well with IS-1 and IS-2, there will still be more testing to do on technology needed for a successful multi-decade trip, and still plenty of useful science left in the outer reaches of our own solar system. If this is the final shake down cruise, it will last at least 5-10 years.
IS-4? If all is still going well, then perhaps IS-4 would be the first to attempt the trip and the start of this mission would be the date by which the Long Bet would be judged.

I don’t know about you, but cramming three lengthy missions (each would take a minimum of months and probably much longer) into less than 20 years with all the planning, design, construction, testing, and flight testing involved would appear to be well nigh impossible for NASA or any private or national space agency.

tacitus August 21, 2008 at 14:53

ljk: The difference with the Moon program is that by 1950 we already had propulsion system we needed (albeit with more development) to get there. We have nothing today that will get us to another star in less than 2,000 years.

Even if there was a breakthrough tomorrow, if the projected flight time was more than about 50 years, we still wouldn’t launch a mission, so even getting to the point where we would have the political will to go is orders of magnitude more difficult than the Moon program was even back in 1950.

But let’s say, for the sake of argument, such a breakthrough happened tomorrow — Alpha Centauri in 40 years is now possible, and the InterStellar program is started in a blaze of publicity. Even assuming that the Washington bean counters gives NASA the green light, the which InterStellar mission would be the first to launch towards another star system?

IS-1? Nope — proving run, perhaps to Jupiter or Saturn if we’re lucky.
IS-2? Nope — second proving run. Irons out the kinks found in IS-1 and perhaps targets Neptune or Uranus since we haven’t been there in a long time.
IS-3? Still unlikely — even if all has gone well with IS-1 and IS-2, there will still be more testing to do on technology needed for a successful multi-decade trip, and still plenty of useful science left in the outer reaches of our own solar system. If this is the final shake down cruise, it will last at least 5-10 years.
IS-4? If all is still going well, then perhaps IS-4 would be the first to attempt the trip and the start of this mission would be the date by which the Long Bet would be judged.

I don’t know about you, but cramming three lengthy missions (each would take a minimum of months and probably much longer) using unproven technology into less than 20 years with all the planning, design, construction, testing, and flight testing involved would appear to be well nigh impossible for NASA or any private or national space agency.

John Hunt August 21, 2008 at 15:16

Andy,

Depends upon what you mean by “capable of supporting human life”. If you mean liquid water oceans, mild temperatures, atmosphere of N=79%, O2=21%, @ 14.7 psi then I would agree that it’s not likely to be close. But if habitable means a Mars-like planet with frozen water ice under which a habitat can be constructed then I think that we’ll likely be able to determine if a planet is habitable based upon gross physical properties and spectral analysis alone.

Regarding the danger of existing life, the atmospheres of Mars and Venus show little or no evidence of bacterial life despite the fact that Earth could theoretically be a great source of such life. How less likely that life exists within 10 ly of us in solar systems without an Earth-like planet. Secondly, even if bacterial life existed on the target planet, their viruses would be designed for their bacteria and not human cells. Finally, a “manned” mission would be for survival-of-the-human-species and hence any theoretical risk of exobacteria would be worth it.

Energy requirements are 13,000 times less for a mission that takes 5,000 years compared to one that takes 43 years. And then factor in 80 million tons versus less than a ton per launch of a more reasonable mission and you get the idea that we’re talking about orders and orders of magnitude difference. Also, I’m talking about sending a space craft to within 10 ly of Earth not 100,000 ly across the galaxy.

John Hunt August 21, 2008 at 15:30

Sean,

Certainly the points you make are valid. Yes, we likely will be able to beam mind patterns to an aparatus sent ahead which could construct robotic or even biologic bodies. All this is possible IF we survive long enough to make that happen.

But I’m expecting that before the century is out, atom-by-atom molecular manufacturing will have been mastered. This means that any and all self-replicating molecules and devices will be able to be produced by curious scientists, devious hackers, competing militaries, genetic programs, extremely intelligent artilects, whatever.

How confident can we be that such molecular manufacturing will not be developed before we attempt an interstellar mission? Or that, when invented, nobody will ever use it for dangerous purposes? I’m not confident, are you???

So if we’re heading to this danger doesn’t it make sense to try and figure out the most cost-effective way to establish humanity in another star system to be launched at the soonest time possible regardless of how long it will take to get there so long as the biologic components are viable?

andy August 21, 2008 at 18:13

John Hunt: extraterrestrial virus equivalents are not the problem – since viruses operate by manipulating genetic material and it is unlikely that alien biospheres will use the same genetic chemistry. The danger comes from the bacteria-equivalents: I see no guarantee that our immune systems would be able to deal with them, particularly if they don’t trigger it in the first place, or trigger it in such a way to cause massive over-response (e.g. anaphylaxis).

In any case, if it is a survival-of-the-species kind of deal, you wouldn’t want to be putting your hopes on a poorly-surveyed target system. You’d want to be very sure of the capability of the target system to support human life, which would seem to suggest some kind of unmanned survey in advance of the main mission (after all, if it does come down to a survival-of-the-species deal, you’re already saying that cost is irrelevant). It really doesn’t help your chances of species survival if you end up as the Martians in H.G.Wells’ War of the Worlds “slain by the putrefactive and disease bacteria against which their systems were unprepared; slain as the red weed was being slain; slain, after all man’s devices had failed, by the humblest things that God, in his wisdom, has put upon this earth.”

ljk August 21, 2008 at 22:11

Tacitus said:

ljk: The difference with the Moon program is that by 1950 we already had propulsion system we needed (albeit with more development) to get there. We have nothing today that will get us to another star in less than 2,000 years.

Even if there was a breakthrough tomorrow, if the projected flight time was more than about 50 years, we still wouldn’t launch a mission, so even getting to the point where we would have the political will to go is orders of magnitude more difficult than the Moon program was even back in 1950.

If we don’t have the will, whether we have the technology
or not tomorrow or in a century won’t matter. If we didn’t
have the will to send men to the Moon in the 1960s, they
would not have gone and we would still be talking about
sending humans to the Moon some day. Same thing with
the whole space program overall.

Perhaps the problem is our overeagerness to see a
star probe in OUR lifetimes. It would be nice, but I get
the feeling that because we can’t have a star probe at
Alpha Centauri next year we’re dismissing ways that
might take a while but could not only accomplish the
job but might even get us technologies that could
shorten the time even more.

2,000 years is a lot to humans, but it’s a drop in the
ocean on a cosmic scale. The great thing is that not
only can we think about making actual journeys to the
stars, something that was not possible even a century
or so ago, but that we can do a lot to help our descendants
turn this dream into a reality. That is no minor thing.

John Hunt August 22, 2008 at 2:36

Pathogenic bacteria have mechanisms specific to cells of certain species as illustrated in this article. So I think that exobacteria may not be able to attach to our cells, invade our gut, or perform other life-cycle processes in humans. In short, I don’t know that they would be able to replicate very well within us and hence may not be able to set up much of an infection.

It is also fortunate that we have an adaptive immune system which is able to recognize that an antigen is non-self and to produce antibodies to it even if that antigen has never before existed. So I think that our immune system would be able to respond to exobacteria with it’s many antigens.

I personally don’t think that life is all that common out there. Also, there’s so much to be gained by interstellar colonization that I really don’t see the small chance of life as being a reason to not plan a “manned” interstellar mission.

you wouldn’t want to be putting your hopes on a poorly-surveyed target system.

Once one craft is launched it will be a lot less expensive to launch the next. So I would imagine that we’d be able to launch to numerous targets to increase the chances of success. I anticipate that if we launched towards the end of this century we’ll be able to tell the atmosphere and if the planets had continents and oceans. I would think that ice caps would be accuragely predicted based upon planet mass and distance from it’s star.

I don’t think that we can afford to wait for an unmanned probe to survey the planets first. We’re going to have to wait a long time before probes reach 0.1c and even then we will have lost 47 years in which humanity could have gone extinct. Can we really be certain that noone will develop highly destructive self-replicating technology within something like 147 years?

Tom Craver August 22, 2008 at 16:50

Regarding the “only 3 hours in system” issue:

I’d think that could be addressed by using a large number of smaller probes and getting them strung out over a long line, about 9 light hours apart. Each one might spend only 3 hours in system – but the chain could spend days or months passing through. They’d each beam their results back to the next in the chain, and the last unit in the chain would have to be able to transmit it back to Earth. (Redundancy is also easy to build in – if one fails, the next in line could be close enough to still get the signal.

You might create a “chain of double-sided mirrored probes” and direct lasers to bounce simultaneously between all the probes – those closest to the source would gain some momentum from the direct laser, but then lose some reflecting the beam from the 2nd back to it. In essence, the whole chain would “inflate” from the light pressure, with those furthest away gaining the most velocity. As one moves out of range, another can could be inserted into the chain at the “base”, so that the next-furthest can gets the same velocity boost. The main advantage here is that any pair of mirrors would be closer together spatially and in terms of relative velocity – dealing with both beam divergence and red-shift.

Send as many probes as you like, to provide as much multi-probe “passage” time as you want or can afford, for the target system.

baley August 22, 2008 at 17:12

Perhaps the interstellar conundrum is thinking a bit ahead, too far ahead that is.

Firstly you need to consider how you are make space travel cheaper, next you would need to create self sustained and maybe independent space colonies. Hauling through the earth’s gravity well millions of kg of supplies would be mindbogglingly expensive and stupid.

Once you have the capacity to built large structures in space, using solar sails or a combination of more than one technology can make an interstellar trip in the order of 100′s of years.

As for self replicating molecules and molecular assembly, I would like to know how we are supposed to do this when we hardly can predict normal chemical reactions. For most of industrial chemical reactions we are completely oblivious to the actual reaction mechanism much less construct actual molecules.

Lee August 23, 2008 at 17:02

Why not go with a proven design? Back in the 1960s, Freeman Dyson did outlines for Orion designs that could reach several percent lightspeed. That was with 1960′s era technology. With modern technology we could improve upon that. Using advanced alloys, metamaterials, compact shape charged thermonuclear pulse units in the several hundred kt – 1 MT range, and other advances, an Orion vehicle could be built with a cruise velocity of at least .1c. Relativistic effects would be minimal at those speeds and could be dealt with fairly easily. That’s more than fast enough to start reaching for the stars.

Administrator August 23, 2008 at 18:17

Do be aware that Dyson has long abandoned the Orion concept for interstellar flight, although he did indeed study it. When I interviewed him in 2003 for my book, he pointed to the poor return that fission/fusion concepts get on the one hand and the sheer magnitude of the nuclear stockpile required for Orion as reasons for changing to a non-rocket based alternative. Beamed propulsion fits that category, but of course there are others. The main thing is, leave the propellant at home. Even so, I can see the attraction of Orion — what a bold, breathtaking concept, and Dyson was a key player in developing it. Maybe you’re right, Lee — it would be interesting to see how Orion might be modified with current thinking and materials.

Lee August 23, 2008 at 19:55

But the point is that at the end of the day thermonuclear pulse units can be built in the real world, right now, with known materials and common elements. Producing and storing millions of tons of antimatter and/or aiming multi terrawatt lasers precisely over many lightyears for years on end is nothing more than a substitute for unobtainium.

The way to the stars is simple and clear, but political hurdles will prevent it from happening until self governing colonies are established of world in deep space.

James M. Essig August 24, 2008 at 4:13

Hi Paul;

Excellent article!

One way that huge quantities of antimatter might be generated involves the concept of using inflatable, ultralow pressure, reflective membranous structures in solar orbit for concentrating solar energy onto photovoltaic, thermoelectric, or photo-thermal-turboelectric steam powered electrical generators that in turn would power huge high luminosity particle accelerators to generate the antihydrogen or stable forms of positronium or protonium.

With the solar output of about 4 x 10 EXP 26 watts or the equivalent of converting 125 trillion metric tons of matter into energy per year, collecting just one millionth of this output and converting it to antimatter by some efficient means by inflation deployable or otherwise deployable membranous reflectors onto electrical energy producing apparatus might do the trick.

It might not be required to power a single huge collector with a single huge concentrator. One alternate type of antimatter producing mechanism might involve using multiple smaller collector/generator systems in the form of an array of devices dedicated to producing a bulk electrical power output. A very large number of smaller devices might do the job.

Another option for efficient antimatter production might entail beaming low energy but relativistic particles into fuels, fissionable or fusionable, to produce positrons from the nuclear reactions wherein nuclear reactions that produce such would be utilized. I can imagine that particles incident on such nuclei might only need to be traveling at 0.05C or just enough for perturbative nuclear fission reactions or nuclear fusion reactions to occur. Once again, such reaction mechanisms could be deployed in space in order to produce the antimatter for storage at a safe distance from Earth: 40 million metric tons of antimatter would have the potential energy of (8 x 10 EXP 7)(10 EXP 3)(2.4 X 10 EXP 7) tons of TNT or 1.92 X 10 EXP 18 metric tons of TNT! Thus, the need for safety.

Note that my brother John and I have several patents issued on various configurations of inflatable membranous solar energy concentrators and are patent pending in roughly 40 foreign applications on the same general subject matter. These foreign applications are roughly three sets of degenerate versions of 3 PCT applications filed as various national stage foreign applications. Although we have mainly worked within the field of disaster relief and survival gear/camping accessories, we clearly disclose that the devices can be used within a space based, Earth based, and/or planetary environment.

Thanks;

Jim

James M. Essig August 25, 2008 at 22:17

Hi Folks;

Another possible more efficient approach to antimatter powered manned interstellar vessels would be to use hydrogen ice/antihydrogen ice, positronium, protonium, or whatever as fuels to power heat energy based electrical energy systems which would intern be used to accelerate electrons, ions, or interstellar ionized gas to high gamma factors as a reaction mass thereby effectively outdoing the .33 C exhaust velocity for proton antiproton reactions.

The heat energy could power good old fashioned steam driven electrical turbines which could drive generators to power the electrical rockets. Regenerative heating and multi-cycle steam turbine systems utilizing different working fluids with different vaporization temperatures would be used to much more efficiently convert matter/antimatter reaction generated heat into turboelectric energy.

Utilizing such a system and a matter/antimatter fuel to dry vehicle weight of 100:1 or even 1,000:1 could in theory allow very high gamma factors to be reached. Electro-dynamic breaking mechanisms could be used to slow the craft down to the target systems thus alleviating the need for extra fuel for reverse thrust slow down. Alternatively, only antimatter fuel might be carried onboard the craft and the reactive normal matter could be drawn from the interstellar medium thus permitting significantly increased gamma factors per initial load of onboard fuel.

Thanks;

Jim

James M. Essig August 26, 2008 at 18:03

As far as man’s journey out into the cosmos, we have to start somewhere, and the start perhaps involves going back to the Moon and then to Mars.

Issues such as long duration space flight, and insitu Lunar and Martian resource acquisitions and utilization for long duration missions on these planetary bodies will definitely need to be studied.

While we learn to have long dwell times on the Moon and then on Mars, we will develop the technology for missions further abroad. Whether of not physics will ever permit faster than light travel, wormhole travel, macroscopic tunneling, and teleportation; or for that matter even high relativistic gamma factor inertial travel through space, I think the human urge to explore and travel ever further outward and our desire to expand the meaning and significance of our race will lead us to travel ever further out from Earth. Assuming the Human Race might just last for trillions of years, or for that matter, perhaps forever, there seems in principle no limit to the distance we can project our species out into the cosmos. Assuming an average colonization wave propagation for the human race at a paltry 3 kilometers per second, in 10 billion years, we could colonize the entire Milky Way Galaxy.

Perhaps mankind needs to start thinking on so large and grand of scale so that we can unite all of humanity as never before. Some will say that mankind will die out within a dozen millennia or less, but I am not so skeptical to assume such. We can chose that path of life or the path of death. If we choose the path of life, think of all of the grateful descendants we will have just as we are grateful to the intellectual giants, institutions, and movements that have allowed us to progress thus far.

As we propagate outward into our Galaxy, no matter how slowly, if all else fails although I am very optimistic about future physics breakthoughs, we can still develop fusion runway concepts, antimatter or matter/antimatter runway concepts, perhaps with ever continuing improvements in the mass density and linear mass density of such runways to for all practical purposes, allow ever higher craft gamma factors, perhaps in the eternal scheme of things unlimited gamma factors. Binding and uniting the hearts and minds of all of humanity just might require thinking so big.

Thanks;

Jim

philw1776 August 27, 2008 at 12:07

Couple points:
1. I believe that the technology for solar system based deep space imaging and detailed spectroscopy of distant terrestrial planet candidates is far easier than sending robotic probes on decades + missions. Space based interferometry with huge collectors spaced across the solar system is far easier than launching an interstellar robotic probe. Plus, results are much sooner and don’t require 1 probe per star.

2. As to bacterial or viral problems, I agree with those posting that our immune system has evolved a genetic capability to attack anything “foreign”. It’s the stuff that looks too similar that poses the worst problems. That aside, it’s folly to assume that we would not have developed huge advances in biological engineering enabling our interstellar colonists to analyze and counteract alien intruders. Such biology is at the nascent level today and requires NO breakthroughs similar to those required for interstellar crewed vehicles. Alien microbes will be the least of our problems, not to be ignored, but readily addressed by reasonable scientific advance.

ljk September 26, 2008 at 21:43

According to this, we could have fusion energy for space
travel by the 2010 decade!

http://www.paleofuture.com/2007/04/fusion-energy-in-space-1984.html

Gordon P. April 8, 2009 at 22:29

It seems pointless to design a mission or technology until such time as we have in hand a complete theory of physics. Even then, advances in micro-technology, biology and artificial intelligence are needed. I’m guessing maybe in 150 years we can start designing a mission.

In the meantime, Terrestrial Planet Finder is nifty. Likewise we can continue to understand the nature of intelligence through brain study, understand in detail biology so we can construct organisms at destination on-site etc.

William Blight February 5, 2010 at 16:21

So you’re thinking about going to an Earth-like planet (like Mars) in another star system. What’s wrong with Mars; not sexy enough for you?

William Blight February 5, 2010 at 16:31

And Mars is still far enough away to keep away the riffraff – hopefully Republicans as well as Democrats. And employment should be full for many years ahead. Also, there might be alien methane-producing bacteria with which to deal. It’s all there and relatively under our noses waiting to be exploited!

TampaDude March 2, 2010 at 0:04

We should take a century or two exploring and colonizing our own planetary system first, then once we have accomplished that, then we would have the resources and knowledge to mount a campaign of manned interstellar exploration.

However we go about it, one thing is clear: WE MUST DO IT to ensure the long-term survival of humanity. If we remain solely on Earth, our species will eventually perish, but if we establish a permanent presence on other worlds, our species will almost certainly live forever.

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