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Cyclers: Transportation Network Among the Stars?

Last July at the Aosta conference Greg Matloff presented a paper on using near-Earth objects for transportation. It’s an interesting concept (discussed here), one that takes advantage of the fact that there are a few such objects that pass close by the Earth and then go on to cross the orbit of Mars. Greg was able to show that it would be possible to exploit this trajectory to use the NEO as what Buzz Aldrin has called an ‘orbital cycler,’ hitching a ride at least one way and disembarking upon arrival.

Reducing Starship Mass

The idea is useful because space travel requires so much energy. Put all this in the interstellar context, as science fiction writer Karl Schroeder does in this interesting essay, and you realize that whether we’re talking about beamed sails or antimatter or nuclear fusion, most of the mass of the vehicle is involved with accelerating and decelerating it. Schroeder pondered the question of using the cycler idea on an interstellar level. All you decelerate at destination would be your payload, while the cycler vessel simply keeps in motion, available for re-use at a much lower cost.

Schroeder likens a cycler to a generation ship in that it is intended to be self sufficient, and imagines using magnetic or plasma sails and particle beam propulsion for acceleration of rendezvous craft and their deceleration upon arrival in the destination system. A cycler is:

…the way-station for travelers, who embark and disembark at the solar systems it passes. Since it supplies life support, passengers need only carry supplies necessary for them to make the rendezvous, which would probably take a few months’ time. Even more dramatically, a non-living cargo sent to rendezvous with a cycler can be very light. Instead of accelerating an entire starship, you’d only accelerate the cargo, plus a wire to form the magsail and some attitude jets to make the rendezvous and docking. In other words, a cycler rendezvous craft is almost all cargo.

Thrustless Turning Between the Stars

Read Schroeder’s novel Permanence (Tor, 2002), for a look at cyclers in the context of a vividly imagined future universe. Cyclers stay in motion, using a combination of Lorentz-force turning and, if manageable, gravitational slingshot to alter their trajectory to pass by a number of stars before returning to Earth to begin the same journey again. Each cycler, even at fifty percent of lightspeed, takes a long time to make the rounds, but a network of such cyclers could sustain communications and transport needs for colonists on planets around nearby stars.

The cycler becomes a way station for cargo or travelers who rendezvous with it, ride the cycler to destination, and then use a magsail and particle beam propulsion from the destination system to decelerate once they’ve left the cycler upon arrival. This presupposes, of course, the ability to build these resources in the destination system, which Schroeder imagines occurring through a series of cargo drops involving robotic and perhaps nanotech tools to create the needed infrastructure.

How does Lorentz-force turning work? Here’s Schroeder on the subject:

The key to making cyclers work is our ability to use the magnetic fields of the interstellar medium as a way of turning the craft. In Lorentz Force turning, you unreel several extremely long wires (tethers) and give them a high electric charge. Their interaction with the galactic magnetic field results in a slow, constant course correction for the ship. Over time, it can be enough to change the trajectory from one star to another… A Schroeder cycler would use this active interaction with the galactic field to change its course; hence it is using different principles than an Aldrin cycler, which relies on orbital mechanics and is essentially (and preferably) passive.

Is Lorentz-force turning sufficient to manage such a trajectory? It’s possible we might need to use forms of propulsion like ion engines or beamed energy from the systems the cycler passes through to help turn the vehicle, so part of the cargo sent to any cycler might include the necessary fuel. But the advantages of the cycler are still notable. In Permanence, Schroeder writes about the ‘lit’ stars like our Sun, contrasting them with the much harder to find brown dwarfs, noting that there may be more brown dwarfs than any other spectral type in the galaxy. Add brown dwarfs into a cycler network and the power question changes as we exploit their magnetic fields. Schroeder again:

…Jupiter and the sun both display prodigious magnetic fields. A brown dwarf could be expected to do the same. This means brown dwarfs can probably supply the kinds of energy required to launch starships; instead of using solar power, as we might do near Earth, at a brown dwarf we would directly generate electrical power by putting long wires (tethers, like the Lorentz Force cables) in orbit around the dwarf. A wire in a moving magnetic field produces electricity; in the kind of all-encompassing and intense field a dwarf might have, a lot of current would be produced; and if you orbited a million wires… again, things scale up nicely.

Growth of an Interstellar Network

What Schroeder imagines is a ring of connected colonies using a network of cyclers to promote commerce and trade, a network encompassing both ‘lit’ stars and brown dwarfs. A new solar system is ‘seeded’ with robots programmed to build a particle beam system to decelerate incoming traffic. While colonization time frames are still large, the development of regular transport into such a system would allow regular cycler visitation and cargo delivery. A human colony could first be established by settlers leaving a passing cycler on a magsail rendezvous ship, knowing they would be part of the growing interstellar network.

Read Permanence for a look at cyclers in action. Thrustless turning using the interstellar magnetic field has been discussed in the scientific literature. Both Robert Forward and P. C. Norem considered Lorentz-force turning of an electrostatically charged spacecraft, and Greg Matloff has studied an approach to electrodynamic thrustless turning involving a partially sheathed superconductor. For more on that one, see Matloff’s Deep Space Probes (Springer, 2005). The Forward paper is “Zero Thrust Velocity Vector Control for Interstellar Probes: Lorentz Force Navigation and Circling,” AIAA Journal 2 (1964), pp. 885-889.

The Norem paper, meanwhile, is “Interstellar Travel: A Round Trip Propulsion System with Relativistic Velocity Capabilities,” AAS paper 69-388 (June, 1969). Cyclers are a fascinating scenario for in-system travel, but driving even stripped-down cargo vessels to a rendezvous at half the speed of light, much less getting the cycler accelerated in the first place, remains a mammoth challenge. While there are no easy propulsion solutions, a far future society working with cycler principles could indeed create an interstellar network. All of which leaves those of us in the 21st Century to ponder the continuing conundrum: How do we push that much mass up to such speeds?

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Comments on this entry are closed.

  • Terraformer (a.k.a Tobias Holbrook) January 1, 2010, 11:36

    Beamed power, of course. Or massive fusion starships, exploiting the fuel tanks to create living space when they’re empty. If Lorentz force turning isn’t practicable, though, we’d have to use beamed power to push a giant starship up to speed, to seed the colonies first. Afterwards, we can use their beamed power to turn.

    Thanks for getting the article up, Paul.

  • Administrator January 1, 2010, 12:03

    And thank you, Tobias, for your recent background comments re cyclers. Very helpful!

  • Terraformer (a.k.a Tobias Holbrook) January 1, 2010, 13:28

    The magnetic fields of brown dwarfs might be exploitable in their raw form for Lorentz force turning. Indeed, any magnetic field would be, so we wouldn’t need a different method at lit stars. At lit srars as well, we can use the solar winds for part of the turning.

    I envision cycler networks extending from Sol out to 11-12 light years initially, so that their opposite sides will be at stars like Epsilon Eridani. It would be a mammoth undertaking by the solar system to start with, since they’d be bearing the brunt of the cost in launching the cyclers, but once the stars, dwarfs, and super Jovians are colonized, they can launch there own cyclers.

  • Athena Andreadis January 1, 2010, 14:32

    Hehe! This is the equivalent of public transportation and local trains. I like the concept!

  • Adam January 1, 2010, 16:25

    Cycler crews could develop their own culture – they might see the temporary passengers as ‘tourists’ and living on planets as being tied down to a particular gravity well. I guess Karl probably explores that idea to the hilt in “Permanence” since he’s such a sociologically aware author.

  • Carl January 1, 2010, 16:29

    “A human colony could first be established by settlers leaving a passing cycler on a magsail rendezvous ship, knowing they would be part of the growing interstellar network.”

    As Athena notes, this is akin to public transportation. This would make a large psychological advantage. Interstellar colonists knowing more ships coming by schedule would feel connection to the originating communities, not isolated as colonists by the method of one-way vessels.

  • Terraformer (a.k.a Tobias Holbrook) January 1, 2010, 17:08

    Yeah, and it’s got me refering to stopping at a train station as ‘decelerating in’ to whatever town it’s stopping at.

    I found this paper in my searchings – http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20050215611_2005218372.pdf. Unfortunately, the Norem paper isn’t available online, but the course correction idea is mentioned in there. You’d need a greater charge and tether length than the one they mention there, which may rule out the idea; I don’t know.

  • T_U_T January 1, 2010, 17:50

    I am sorry to rain on your parade, but the turning radius of a 0.5 c turning at 10 G ship is 2300 AU.
    So basically no turning around stars or brown dwarf unless you want to be turned to brown goo by hundreds of thousands of Gees.
    .
    So you are left with interstellar magnetic field at 1nT. Given v = 0.5c, you will need 6.66 C charge for 1 N force, so assuming 1g acceleration and 100 ton spacecraft, you will need 6.66666 MC charge. Breakdown voltage of vacuum is 40 MV/m, so you will need at least 38km sphere to distribute the charge, and voltage of 1.5 GV at its surface ( you will need a 1.5 Gev accelerator to kick ions off the spacecraft to charge it. )
    .
    But that is not the worst part. The worst part is that you wil encounter cca 500 hydrogen atoms for each cubic meter of volume swept by your spacecraft. that atoms get ionized and will discharge your spacecraft with cca 100 A current. So to break even, your accelerator must have 1.5 GV x 100 A 150 GW power. That pretty much kills the concept because a 150GW nuclear engine will give you more delta V per watt.

  • T_U_T January 1, 2010, 18:04

    Got the turning radius wrong. It is 1700 AU.

    On a second thought, assuming 0.01G will give you 1/100 charge, 1/10 diameter, 1/10 voltage and 1/100 current, together 1/1000 the power, 150 MWatt, which is still pretty high, but more or less doable. The turning radius will be 2 lightyears though.

  • T_U_T January 1, 2010, 18:06

    and wrong again. At 0.01G the turning radius will be 20 ly

  • James M. Essig January 1, 2010, 21:46

    Hi Folks;

    I rather like the idea of mass beam acceleration of space craft.

    I have taken a liking to the concept of beamed fusion fuel or even beamed antimatter or matter-antimatter fuel.

    With EM beam sail ships capable of relativistic velocities, the issue of relativistic Doppler red-shift losses would present it self with the long-wave redshift mathematical limit of beamed light equal to Z = infinity causing an imaginary or toy model craft to recieve zero forward thrust.

    Mass beam fuel at the very least permits the effective incident energy of the mass beam to be equal to atleast the rest mass of the fuel with respect to the ship frame.

    Once the fuel arrives at the ship location, it can effectively be used as fission fuel, fusion fuel, or matter antimatter fuel in a manner simmilar to fission, fusion, or matter antimatter annihilation rockets, with the result being that the effective M0/M1 ratio for the ship is virutally equal to one.

    For highly relativistic mass beam ships, the need exists to get the beamed fuel up to speed and that takes as much energy as the relativistic kinetic energy of the mass beam stream, however, the space craft will always have at least the fission fuel yield, fusion fuel yield, or the available energy equivalence of the massive species to propell the space craft via fission, fusion, or matter-antimatter reactions.

    For extreme systems, the mass in the form of the as yet unproducible macroscopic rest-massed, quarkonium, higgsinium, or other superdense fuels would largely alleviate kinetic energy limits associated with charged cosmic rays interacting with the CMBR or other energy limiting drag mechanisms.

    Such a mass beam system could provide rocket fuel to power electrical charge generation or electrical charge maintainence apparatus and/or to augment the relativistic Lorentz Turning Force.

  • djlactin January 2, 2010, 2:26

    (This reply turned out to be much longer than I planned, even after deleting a lot of stuff. Please bear with me.)

    Bottom line: the idea doesn’t hold water.

    Terraformer (and others) have used the analogy of a public transit system, but the resemblance is only superficial: (1) the ‘train’ does not stop at the station; (2) ‘passengers’ are vehicles. The correct analogy is something like: A train goes by at velocity v; to get on it you need to accelerate your car to v, match vectors, then drive your car onto a flatbed car and park. You and the train must rendezvous at ‘the platform’ within a very small interval; ANY imprecision would be catastrophic. At your destination you must perform this maneuver in reverse.
    So… every century or so a Cycler rims the Solar system (somewhere out in the Oort cloud) at 0.5 c (T_U_T’s value); to catch it, you need to accelerate your payload to 0.5 c; match vectors; dock. If I’ve done my arithmetic correctly, accelerating an object from 0 to 0.5 c in (say) 1000 AU would require an acceleration of about 15 gee for about 12 days (I neglect the gamma factor).
    If you have the technology to perform such accelerations, the advantage of latching onto a passing ‘bus’ is negligible: why not simply accelerate your craft, cruise, and decelerate at the target? Accelerating at 15 gee for 12 days at each end of the trip, your travel time to Acentauri (cruising at 0.5 c) would be about 8.5 years. Accelerating ‘only’ at 0.5 gee for 1 year at each end (over a distance of ~0.25 lightyear each time), the trip would take about 10 years. (Total energy required is the same in either case: 0.5 mv2 = ~1016 Nm for every kilo, again, neglecting gamma).
    I see little advantage to accelerating a ‘mother ship’ that continues beyond the target as you (the payload) drop off. The only possible advantage is that a mother ship could be big enough to provide living quarters and gardens during the trip, but why throw it away at the destination?
    My conclusion (long-time coming) is that the ‘Cycler’ plan reduces to lugging a huge supply ship along, then abandoning it on approach to the target. The long-term idea to use as a bus seems too far-fetched. It would seem better to leave it in a long-term orbit around the target system, as an emergency backup.

  • Michael Antoniewicz II January 2, 2010, 3:00

    Aaannnndddd we just re-invented the approximate first 300 years of C.J. Cherryh’s Alliance/Union Universe. Ships going out, planting Star Stations, looping back, picking up new Station Modules, planting them at their own stars, stopping off at the older Stations on their loop, picking up and dropping off cargo, adding personnel, getting into Great Circle Trade Routes, etc. etc.

  • djlactin January 2, 2010, 4:24

    Superscript fail:
    “0.5 mv2 = ~1016 Nm” = 0.5mv^2 = ~10^16 Nm”

  • Terraformer (a.k.a Tobias Holbrook) January 2, 2010, 10:31

    “My conclusion (long-time coming) is that the ‘Cycler’ plan reduces to lugging a huge supply ship along, then abandoning it on approach to the target.”

    Except you’re not abandoning it. It’s going to be used, but by other people. What’s the best analogy… okay, I’ll run wit a ship. The ship drops off payload and crew in port, who then proceeds to abandon the vehicle. Except it’s not being abandoned, it’s being reused, and it’s the people who are abandoning the ship.

  • gary.rod@att.net January 2, 2010, 11:39

    Fact check.
    Cycler Orbiters have more immediate application within the confines of the solar system.
    Cycler Orbiters are not intended to be abandoned or converted early in their commission. They derive their name from the fact that they “CYCLE” between at least two planetary bodies, Earth-Moon and Earth-Mars being the typical mission scenario.
    Cycler Orbiters grow over time into very large composite spacecraft which host long-term “permanent party” and “transient” populations. They are intended to provision facilities such as hospitals, libraries, seed banks, dry docks and much more. Think aircraft carrier in extended orbits.
    These platforms would also be ideal for intercept and long-term capture programs to translate the threat of stray asteroids and comets into useful spacecraft and organic masses. Think archology.
    To review these concepts check out no less than the published James Longuski from Purdue who has studied primary, intercept and transfer orbits for these spacecraft. Think insular city.

  • Athena Andreadis January 2, 2010, 13:36

    Michael. the Cherryh Alliance/Union saga is high in my list of thought-provoking SF and, in my opinion, one of the best space opera cycles ever written. It brims with interesting, well-developed concepts — from propulsion systems to serially cloned individuals to exotic but believable aliens to quasi-novel social systems. It also has well-developed characters… and Signy Mallory at its center. Gesamtkunstwerk of Wagnerian heights.

  • Administrator January 2, 2010, 14:27

    Someone needs to tell me more about the Cherryh Alliance/Union saga. I assume it’s a series of novels — which one begins it?

  • Danlo January 2, 2010, 15:11

    Maybe a bit of topic, but I found this on Wiki: http://en.wikipedia.org/wiki/Alliance-Union_universe

  • Athena Andreadis January 2, 2010, 15:26

    I’ll be happy to tell you about the Alliance/Union, Paul! Wikipedia has a very informative link, which describes the back story at length: The Alliance/Union Universe of C. J. Cherryh. The books (or trilogies) can be read in any order, like real history. Wikipedia also links to the author’s site, which contains story lists, timelines, star charts, the usual.

    The best in the series is Downbelow Station, followed closely by Cyteen (get the new edition, which doesn’t split the latter in three parts). Both won Hugos, and deserved them. Merchanter’s Luck, Heavy Time and Rimrunners are solid and very enjoyable but less complex. Forty Thousand in Gehenna and the Faded Sun trilogy are intriguing in presenting truly unusual aliens and/or societies — and the latter handle well one of the problems that bedevils Avatar, that of a representative of a “dominant” culture going native.

  • Administrator January 2, 2010, 16:55

    Thanks, Athena. One of the things I’ve enjoyed in the six years (!) of running this site has been getting good science fiction recommendations. I’m well read in earlier science fiction but know little about the last twenty years or so. Lots of good stuff ahead.

  • david lewis January 3, 2010, 10:06

    I like the cycler idea. If you’re making a long trip, say 20ly, rather than spending 40 years at 0.5C in a minimal environment you’re in an environment where you’re in a community with resources to handle emergencies and resources for some luxury and leisure.

    Of course even the smallest interstellar vessel would probably have a virtual reality setup giving its crew/passengers access to a virtual realm that includes all the luxuries that a cycler could carry.

    Depending on beamed power might not be a good idea. Something happen to one colony and the cycler can no longer make the necessary course changes.

  • george scaglione January 3, 2010, 13:46

    athena,my favorite sf trilogy is the 4 books of the space odyssey series by arthur c clarke! he himself joked that he stopped after book 4 since 4 books is enough for any trilogy! ironically i am currently once again in about the last 75 pages of that final book for about the 4th time.sorry i might be just a little off topic with this reply,but yes,the basic idea seems like a very good one. thank you very much, george

  • Terraformer (a.k.a Tobias Holbrook) January 3, 2010, 14:33

    That’s why I advise that they carry an emergency propulsion system, Lorentz cables (which they’d have anyway) and a magnetic brake (which could be combined with the Lorentz cables).

    What would the turning radius be for, say, a 0.5c ship, 1000 tonnes, equipped with Loretz force cables and a 1.5Gw engine? Does it scale linearly as each factor in the equation grows, or exponentially?

    TuT wrote (allowing for the correction):
    “On a second thought, assuming 0.01G will give you 1/100 charge, 1/10 diameter, 1/10 voltage and 1/100 current, together 1/1000 the power, 150 MWatt, which is still pretty high, but more or less doable. The turning radius will be 20 lightyears though.”
    If the power and mass is increased by the same amount (i.e. the power/mass ratio for the whole ship stays the same), does the turning radius stay the same? If we increase the power to 15Gw, can we get a 1000 tonne starship at 50% of c to have a turning radius of 50ly, which is doable for a race that plans long enough ahead?

  • Terraformer (a.k.a Tobias Holbrook) January 3, 2010, 15:00

    Oh, you said 0.01g, not 0.1c. I got confused. So, 1.5GW could turn a 1000 tonne starship through a radius of 20ly? Presumably, as the acceleration decreases or velocity increases, the turning radius will go up? So dropping the velocity to 0.4c (with gamma included, it will seem like 0.44c to the people on the cycler) will reduce the turning radius to 16ly, all other things being equal?

  • bigdan201 January 3, 2010, 20:50

    One of the main questions of this is, how easy would it be for cargo to hitch a ride on a cycler? If it’s easy enough, it would be a great idea. But if not, then there’s no reason why you cant simply send ships back and forth on a regular schedule, accelerating and decelerating as necessary, with ships in transit at any given time for more frequent exchange. As I understand it, the main advantage of a cycler would be its continued momentum.

    Anyway, acceleration and deceleration are the main challenges of space travel. Solar sails and beamed propulsion could be a very economic way of getting at least some of the change in speed, and maybe nuclear rockets etc could make up the rest. Still, unless we figure out how to fold space, voyages between stars will always be voyages – journeys taking years. There would be trade and contact between different settled solar systems, but it would be limited by c.
    On the other hand, our local solar system is much less of a hurdle, and moving around the planets within the time frame of several weeks seems doable.

  • T_U_T January 3, 2010, 21:51

    Oh, you said 0.01g, not 0.1c. I got confused. So, 1.5GW could turn a 1000 tonne starship through a radius of 20ly?

    No, You got it wrong. 1 g = 0.2 ly turning radius ans 150 GW power 0.01 g = 20 ly turning radius and 150 MW power.

    turning radius = v^2/acc * gamma

    force = m * gamma * acc
    q = m * gamma * acc / ( v * B )
    ship_diam = sqrt( q / ( 4PI e0 Emax ) )
    Uship =sqrt( ( q /4PI e0 ) Emax)
    Idischarge = particle_density * e * PI * ship_diam ^ 2 * v * gamma = q / ( 4 e0 Emax ) * particle_density * e * v * gamma

    power = Uship * Idischarge = sqrt( ( q^3 /64PI e0^3 )/ Emax) * particle_density * e * v * gamma = sqrt( v * ( m * acc / B ) )^3 * gamma^5 /64PI e0^3 )/ Emax) * particle_density * e

    So, assuming gamma constant,
    power = Const * v^(1/2) * acc ^ ( 3/2 )
    turning_radius = v^2 * / acc

    so, reducing acceleration 100 x will increase turning radius 100 x, and decrease power consumption 1000 x
    reducing velocity by 20 % will decrease turning radius by 36 % and power consumption by 10 %.

  • Terraformer (that's my title, my name's Tobias Holbrook) January 4, 2010, 13:18

    Hmmm, I wonder what a research cycler probe would do for our knowledge of the local interstellar neighbourhood. Imagine a small cycler probe, looping through potential paths to see whether there are any brown dwarfs around.

  • Eniac January 4, 2010, 13:47

    This here paragraph from Matloff’s paper makes me think the idea, while nice, has to be relegated to the fantasy side of things:

    “Substitution in Eq. (10) reveals that the radius of the thrustless turn in the local interstellar medium for the tether, starship mass and starship velocity considered here, is approximately 3.7 X 10^l6 km.
    When the starship has traveled for about 2.3 x 10^17 km, its trajectory has been altered by 360 degrees. But at 900 k/sec, the starship under consideration travels approximately 2.8 X 10^-5 km per year. Thus, the trajectory direction is altered by about 4-X degrees per year. During a 1,400-year journey, the trajectory bend angle is approximately 0.06 degrees.
    To obtain a six-degree trajectory modification during a 1,400-year journey with the tether current assumed, the tether length must be increased by a factor of 100X to equal 10^5 km. This would increase tether mass to 2.7 X 10^5 kg.”

    6 degrees in 1400 years? And this is for 0.003c, it will be worse for faster ships. So, at least for the EDT from that paper, no cyclers, unless you can wait a few hundred thousand years at the bus-stop, so to speak.

    I doubt the situation is any better for Lorentz turning, as the charge/mass ratio is small, the magnetic field weak, and the velocity large, all three factors prevent significant turning. Gravity, magnetic fields, or light pressure around stars are out at relativistic speeds, too, for reasons mentioned by others (deadly and unachievable acceleration, chiefly).

    I could not find Forward’s paper, does anyone have a citation better than the above by Matloff with an actual realistic turning ratio?

    On top of that, as as been pointed out, cyclers provide limited benefits, as non-cycling craft still have to accelerate and decelerate just as much, which is the principal difficulty of interstellar travel. Even in the solar system, where turning is not a problem, the immense cost of starting and maintaining a cycler would be hard to justify by the benefits of having a larger living space during the trip.

  • Eniac January 4, 2010, 14:21

    If T_U_T’s calculations are correct (and they look good to me), a turning radius of 20 ly (and presumably cycle time of ~100 years) would work much better, although a spherical ship of 38 km radius or diameter weighing only 100 tons seems like a structural challengee, especially considering the non-negligible acceleration. Perhaps it is only 3.8 km after the downward adjustment for acceleration, but still… Plus, a source of constant power of at least 150 MW, within that weight limit.

    Maybe a magnetic field extending many kilometers around the ship could be used instead of a solid sphere, and the power somehow derived from the impacting interstellar medium. If 1 g could be reached, cycle times could be outright speedy, albeit still slow compared with even the worst public transit systems on Earth.

  • T_U_T January 4, 2010, 19:04

    Perhaps it is only 3.8 km after the downward adjustment for acceleration, but still… Plus, a source of constant power of at least 150 MW, within that weight limit.

    I assumed spherical shape of the spacecraft, which is great for preventing corona discharge allowing higher charge densities, but utterly inferior for a relativistic craft., which you want to make as thin as possible to expose the minimum of the surface to incoming particles. So by making the shape a long thin cylinder instead of a sphere, adding an insulating shield before the main charged cylinder, and adding some extra coils to push the incoming ionized gas out of the spacecrafts path, you can decrease the discharge by at least two, more likely three orders of magnitude. And say 1 MW power is far more reasonable. ( plus, the accelerator used to charge the craft will act as a high performance ion engine thus shortening the turning diameter by an amount unaccounted in the computation )

  • Bounty January 4, 2010, 19:24

    Reminds me of ISS v.s. Space Shuttle, but with a much bigger orbit.

    Even if you decelerate the cycler say 50% at the target systems (sail?) , there is energy saved. Then you only need to bring the people and fuel up to .25 c and not people, fuel AND habitat. Then the people, fuel and habitat need to accelerate again back to .5 c. You still have to accelerate the fuel, which will be substantial…. so basically this technique lets you splurge a little bit on the habitat for return trips.

    It’s interesting to picture racing away from your star system in direction 1, while the cycler is approaching your system, slowing down…. sails open, from direction 2. Then the cycler slinging around your system to rendevous with you, (avoiding your trail of rocket debris though?) Then eventually meeting you at relative speeds, docking, transferring fuel etc and heading on your merry way.

  • James M. Essig January 4, 2010, 22:37

    Hi Folks;

    I hope this is not too off topic, but since we are discussing ways to bring a stellar cycle up to relativistic speed, I had the following musing after reading a brief new item at the Physics Today Website regarding the discovery of Carbon-22, yes that is carbon with 16 neutrons.

    As a physics guy with a love of nuclear physics and QCD, the study of extreme limits of low atomic number elemental isotopes can give us a better understanding of QCD physics.

    I am interested in extreme low atomic number isotopes for the possible role they can play in high energy density materials.

    Perhaps not only can our military benefit from any such high energy density materials for obvious reasons, but such high energy density materials might make excellent compact power sources for deep space manned rockets. We need to get beyond chemical combustion rockets if we are going to do manned missions to the outer reaches of the solar system and beyond, and so I am all for any advances in safe ultra-high density nuclear materials.

    Extreme low atomic number elemental isotopic ultra-high energy systems might enable useful nuclear energy without the concern for the chemically toxic effects of Uranium and Plutonium.

    If nuclear chemists can come up with stable extreme low atomic number isotopes, the controversy over nuclear power systems in space might be effectively eliminated.

    Check out http://blogs.physicstoday.org/update/2010/01/a-carbon-halo.html for the story.

  • Michael Antoniewicz II January 5, 2010, 1:37

    Ha! Found it. I knew I had seen something on an engine/ship design that fit this thread, even the Alliance/Union comment I made. ;)
    Pellegrino’s and Powell’s “Valkyrie” design.
    http://www.projectrho.com/rocket/rocket3aj.html
    http://www.charlespellegrino.com/propulsion.htm

    To get the ships cycling into and out of systems and back to Sol with Seed Modules, personnel, and unique materials Outbound and cargo of worthwhile stuff Inbound (and lets face it, what is going to drive a Great Circle Trade Route economy 20, 50, 100, or even 300 years in the future, we have no real idea) to support the economics of the System, you’re going to need a sub-light drive that makes the between stops voyage time standable.
    Think Age of Sail time-frames from the PoV of the crews. 0.92c gives the crews an approximately 1/3rd relativity advantage. 6 years external flight time is 2 years to the crew. 15 is 5 and etc.
    And to be honest, we’re not talking NASA, ESA, etc astronauts but crews derived from the likes of “Deadliest Catch”, “Ice Road Truckers”, and “Sandhogs”. So getting ships out to ~ 14 Light Years from Sol becomes “possible”. Then you add in established Stations sending Seed Stations out on ships they build or direct outwards after they’ve arrived from Sol.

  • forrest noble January 5, 2010, 2:04

    These “cycler” bodies have been speculated for years as a great way to get around the solar system with a minimum of fuel and a maximum payload delivery. As was stated they could be made as both places of habitat and large fuel and supply depots for transportation to and from Mars, the asteroid belt, or other destinations — in time maybe to other stars. The technology is here now if the funds were available. I don’t think it’s a matter of whether it’s going to happen, I think it’s a matter of when and exactly to what sophistication such bodies will be used to enable evolving technologies.

  • Terraformer (given name = Tobias Holbrook, getting my digital paper trail up) January 5, 2010, 6:48

    There isn’t much point to decelerating the cycler. The fuel you’d have to accelerate (or the longer beam time you’d have to get) would better be used to accelerate the rendezvous craft up to the required velocity.

    Actually, I’d make the craft a cone, with the base in the direction of travel, and rotating for gravity. This means you’d get different levels of gravity on the ship; good for people coming from different planets.

    T_U_T, what is the gamma factor? Do you mean gamma as in the relativistic gamma factor??

  • Terraformer (given name = Tobias Holbrook, getting my digital paper trail up) January 5, 2010, 9:22

    Given that the cycler will be capable of adjusting it’s trajectory, perhaps it would be best to launch payloads that need to dock with the cycler ahead of it, so that the cycler catches up? If we can get the variation down to maybe 10,000km, the craft trying to dock can then use it’s own engines to manoeuvre in.

  • Eniac January 5, 2010, 14:22

    Bounty: At relativistic velocities, there is no such thing as “slinging around your system”. Even the best imaginable turning radius will still be essentially a straight line on the scale of a planetary system, so the cycler will be going through in a straight shot, in a matter of minutes. You have to accelerate your rendezvous ship well ahead of time, in the same direction and to the same velocity as the cycler, way out into interstellar space. Any mistake, you “miss the bus” and become lost, since the whole point of the cycler is to have the rendezvous craft be smaller than necessary for a full interstellar trip. Thus, you will not be able to continue to the target on your own, and even less able to return home.

    James: These exotic nuclei are all extremely short-lived and there is no hope whatsoever that they will be of any use for lasting materials or energy storage. More generally, the chart of nucleotides is very well charted and the possibility for surprises (such as the fabled transuranic “island of stability”) is extremely remote at this point.

    T_U_T: I agree that a linear shape, like a long tether or tube, is best for a Lorentz cycler. It would be great to get your numbers for that case. With the ISM impact taken care of by a forward shield, current would only still be needed for stray particles coming in at an angle, i.e. those that have a near relativistic velocity by themselves, i.e. cosmic rays. I don’t know this, but it is possible that those tend to be positively charged ions, since they needed to be charged when they were accelerated. Perhaps we can improve things by ejecting electrons instead of ions and making the craft positively charged. This does away with extra thrust you mention, but perhaps it will permit charge to be maintained without energy expenditure, since impacting cosmic rays would help rather than hurt.

  • Terraformer (given name = Tobias Holbrook, getting my digital paper trail up) January 5, 2010, 16:16

    “So, assuming gamma constant,
    power = Const * v^(1/2) * acc ^ ( 3/2 )
    turning_radius = v^2 * / acc”
    What is gamma?

    So, the amount of power required is Gamma * sqrt v * acceleration^(3/2)?

    The turning radius has me confused. What do I multiply v^2 by?

    Oh, and I wasn’t wondering if you could turn round brown dwarfs using their magnetic fields – at least, not all the way. I was thinking more along the lines of a one degree turn.

  • Eniac January 5, 2010, 18:38

    Life on a cycler would be strange. Many, many years of featureless deep space would be punctuated with the occasional sequence of shuttle departure, quick flyby of a planetary system, and shuttle arrival. In that order, with weeks or months in between. During the flyby, news could be obtained, and at shuttle arrival, provisions. The rest of the time, communication with the outside world would be of very limited capacity and extremely time-lagged.

  • T_U_T January 5, 2010, 19:54

    gamma is the relativistic gamma factor. I’ve forgotten to add it in the second equation.

  • Wedge January 5, 2010, 23:56

    The public transit analogy is not quite apt, in my opinion. It still takes an enormous effort to accelerate anything to 0.5c or 0.1c, the advantage is that perhaps you have to accelerate much less payload to get to the destination. The cycler is essentially host to a more or less self-sustaining colony, or civilization. The advantage is that you need only accelerate passengers and high priority cargo rather than the massive support infrastructure needed to survive the trip. This makes an orders of magnitude difference in scale, which is, suffice it to say, significant.

    One can imagine a cycler with several reusable daughter ships. On the first visit to a system a set of daughter ships is dropped off. They deploy mag-sails and decelerate into the system. One autonomously collects Deuterium and other fusion fuels for use in a fusion rocket taxi that accelerates to meet the cycler as it passes through the system.

  • Terraformer (a.k.a Tobias Holbrook) January 6, 2010, 8:13

    Thanks. So, the two equations are:
    power = gamma * v^(1/2) * acc ^ ( 3/2 )
    turning_radius = v^2 * gamma / acc?

    How do I put the gamma factor in? As a percentage, decimal, or what?

    Gamma for 0.4c is about 10%. Say I want an acceleration of 0.01g (0.1m s^-2), would it then be:

    Power = 0.1 * 120,000^0.5 * 0.1^1.5?

  • george scaglione January 6, 2010, 13:58

    forrest,yes i agree these are very good ideas that deserve some serious thought ! we should take a serious look. but as with everything else : perhaps not so easily done or even developed here in the real world! maybe that will change some day. :) george

  • Darrell E January 6, 2010, 14:55

    There was also a brief mention of turning a spacecraft using interstellar magnetic fields in “The Mote In God’s Eye” by Niven / Pournelle. During a discussion about the laser accelerated light sail probe that the Moties sent to a nearby human star system one of the characters (Renner?) asked why the Moties did not use the background interstellar magnetic field to turn their probe around, relight the lasers in the home system and use them to decelerate the probe into the new star system, instead of the method that the probe actually attempted. Which was to dive nearly directly into the local star in order to decelerate from its laser boosted high velocity.

    The interstellar cycler idea is interesting, but it is an enormously complex scenario. We do not have anywhere near the experience, yet, that will be required to determine if this concept is more efficient than other concepts, or even feasible. The first, of many, big problems for this concept is the “thrustless turning between stars. If this can’t be done for dirt cheap then I think the concept will fail right there.

    In some of the above discussions the mass of the cycler being discussed is in the 1000 ton range. If I understand the concept correctly, this cycler is supposed to provide life support without being dependent on each new group to bring its own life support with it. If not then the cycler concept is bust right their. This means it would need to have and maintain a viable ecosystem capable of staying productive and healthy for very long periods of time. With this in mind it seems that the 1000 ton mass estimate is wildly optimistic. Adding in propulsion systems, power systems, shielding systems, decent cargo capacity, etc., I think a mass of 100,000 tons is likely on the light side of what such a craft would have to be.

  • Terraformer (a.k.a Tobias Holbrook) January 6, 2010, 15:12

    “One autonomously collects Deuterium and other fusion fuels for use in a fusion rocket taxi that accelerates to meet the cycler as it passes through the system.”
    Don’t you mean ‘the next cycler’? The first one will have overshot the system by that time.

    T.U.T – is the gamma factor in terms of how much mass it adds, or what the total mass is after it’s factored in?

  • T_U_T January 6, 2010, 17:05

    gamma is simply the lorenz factor. For 0.5c it is 1/sqrt( 1 – 0.5^2 ) = 1.1547.

    I would also add that the magnetic turning could also be used for braking at the destination The smaller craft will brake by solar sail a bit, then fly out of the system, turn by the same mechanism as the cycler 180 degrees and pass through the system again, progressively making smaller and smaller turns and becoming slower. It will surely take an order of magnitude longer, but maybe it could cost orders of magnitude less energy.

  • Wedge January 6, 2010, 22:26

    @Terraformer, yes the next cycler, that should have been stated more clearly.