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Space Science

Road Trip On The Interplanetary Superhighway 146

Posted by timothy from the no-bathroom-breaks dept.
eegad writes: "CNN has an article about a new idea from NASA springing from chaos theory called the interplanetary superhighway. It will purportedly allow easier space travel by steering through regions where the net gravitational force exerted by nearby bodies is smallest. The actual NASA news release is here. Sounds like an interesting concept but it is unclear how the scientists will account for every source of gravity, including the elusive dark matter."
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Road Trip On The Interplanetary Superhighway More

Road Trip On The Interplanetary Superhighway

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  • This actually sounds a lot like the theories exhibited in the star trek series about warp travel and how different vessels in warp flight have to adjust their courses to travel between the stars to minimize gravitational distortions affecting their flight path. Personally I think it's a great theory and very logical. Especially since gravity creates friction and drag and those are both bad for travel in space or not.

    • Re:Warp Theory (Score:3, Informative)

      by Alien54 ( 180860 )
      between the stars to minimize gravitational distortions affecting their flight path

      Which makes sense for interstellar travel.

      in interplanetary travel, these areas are probably constantly shifting, and so I wonder if the speed of shift is faster or slower than current space craft.

      • Each planet and moon has five locations in space called Lagrange points, where one body's gravity balances another's. Spacecraft can orbit there while burning very little fuel. To find the Interplanetary Superhighway, Lo mapped all the possible flight paths among the Lagrange points, varying the distance the spacecraft would go and how fast or slow it would travel. Like threads twisted together to form a rope, the possible flight paths formed tubes in space. Lo plans to map out these tubes for the whole solar system.
      They apparently delivered the software tool to NASA back in 2000 [caltech.edu].

    • Re:Friction likely greater in Super Highway (Score:1, Informative)

      by Anonymous Coward
      Gravity does not cause friction. Friction converts kinetic enery into heat which cannot be feasibly recovered. Total energy (potential + kinetic) in a gravity field is strictly conserved. Friction will most likely be greater in the "Super Highway" as interplanitary dust will collect in these gravity wells.
    • Especially since gravity creates friction and drag and those are both bad for travel in space or not.
      Um, no they don't. On Earth, they may cause it indirectly (gravity mashes your car into the ground, causing friction), but in space, no they don't.

  • come on.... (Score:3, Insightful)

    by LMCBoy ( 185365 ) on Saturday July 20, 2002 @12:12PM (#3922937) Homepage Journal
    Dark Matter?! Absolutely negligible on interplanetary scales.

    • Dark Matter (Score:2, Informative)

      by looseBits ( 556537 )

      I recently read and interesting article in SCIAM proposing an alternative to the mysterious dark mater. He calls his theory MOND (Modification of Newtonian Dynamics) where he states that for extremely weak gravitational fields (a < 10E-5 m/s^2), F approaches ma^2. Apparently, his equation is able to explain the stability of may galaxies well without having to use dark matter. It remains to be seen whether his theroy will hold up to serious scrutiny but already, astronomers are using it to model galaxies (using it as a calculation technique instead of an actual law of nature). He has yet to incorporate it in relativity.

      More information is available at http://www.astro.umd.edu/~ssm/mond/litsub.html [umd.edu]

      • Re:Dark Matter (Score:1, Informative)

        by Anonymous Coward
        Some fairly serious criticisms of MOND have been raised, which to my knowledge have not been adequately addressed. See this paper [arxiv.org] and also this one [arxiv.org].
  • Who cares? The key here is *interplanetary*.
  • Dark matter is only important on galactic scales. We know where all the (important) mass in the solar system is.
    • There's an alternate theorey that seems to be gaining presidence in the scientific community that modifies Newton's Second Law (F=ma) on a galactic scale. The modification of the Second Law eliminates the need for "dark matter." Interesting stuff. An article on the theory is in this month's Scientific American.

  • Confirmation at last (Score:5, Funny)

    by Darth_brooks ( 180756 ) <clipper377@g[ ]l.com ['mai' in gap]> on Saturday July 20, 2002 @12:13PM (#3922946) Homepage
    let's look at the facts: Big government bureaucracy. Foul smelling, funny looking employees. Interplanetary highway construction. It's all there in black and white.

    NASA is run by the Vorgons.

  • 3-body problem? (Score:3, Funny)

    by jedwards ( 135260 ) on Saturday July 20, 2002 @12:13PM (#3922947) Homepage Journal
    the sun is pulling, the Earth and moon and other objects are constantly pulling," said Martin Lo of NASA's Jet Propulsion Laboratory in Pasadena, California.

    "Our theory has refined to the point where we can actually compute these trajectories
    Really? I thought the 3-body problem [uoregon.edu] was not solvable.
    • It says right in there that Lagrangian cases are one of the special cases in which it can be solved.
      • The lagrangian case has nothing to do with interplanetary travel, however; it deals only with semi-stable points where gravity sort-of balances between two massive bodies.
        • And near these lagrange points, a very small maneuver has a great big effect on a spacecraft trajectory. If you know what these small perturbations do you can design a trajectory that gets all the way to Jupiter using very small amounts of fuel.
    • You can't find exact mathematical solutions, but you can certainly run an accurate computer simulation for many, many years.

      In any case, since the mass of the spacecraft is negligible, this isn't the full 3-body problem.
      • In any case, since the mass of the spacecraft is negligible, this isn't the full 3-body problem.

        Yes, but you have to consider the masses of the planets and moons that the spacecraft interacts with, all interacting with each other. That makes it a many-body problem that must be "solved" numerically.
        • But typically there will only be two massive bodies in the neighborhood at any one time, and those are the ones you consider. As previously mentioned, the probe, being sufficiently small, doesn't constitute a third body.
          • Perhaps, but the positions of those two nearby bodies will depend on the other bodies in the system. You won't be able to predict an accurate trajectory if you don't know where the two nearby bodies are going to be. That was the point I was trying to make.

    • Re:3-body problem? (Score:3, Insightful)

      by gilroy ( 155262 )
      Blockquoth the poster:
      Really? I thought the 3-body problem [uoregon.edu] was not solvable.
      It's not solvable analytically. But it's a breeze to model the diff eq's. Doing it accuractely for long can be tricky, though...
      • I remember vaguely hearing that it is possible to solve the 3 body problem, using elliptic coordinates. But that it's nearly always easier to just throw it at a computer. No references though.

    • Computing versus solving (Score:4, Interesting)

      by sjbe ( 173966 ) on Saturday July 20, 2002 @12:22PM (#3923001)
      You're right in that we (so far) cannot solve (in the sense of a mathematical proof) a 3 body problem using nice neat equations like we can for 2 body problems. However it is possible to calculate a trajectory and has been for some time. Takes a reasonably large amount of computing horsepower and a good idea of the initial conditions but a useful approximation can be calculated. Not an elegant or exact method but does work.
      • I'd hate to take the written exams to pilot one my own space wagon, though.

        You are at an intersection of 17 interstellar space lanes. You will now listen to the astrogation control channel for 30 seconds. Choose an entry vector to the roundabout, calculate a trajectory towards the Hyades Cluster, and engage warp drive. Remember to follow the astrogation control channel protocol. Refer to the attached astrogation table for nearby mass concentrations. You have two minutes to complete the procedure.

        The driving test should be much better: you just grab the joystick, stamp on the warp pedal, and hope for the best.

        • I'd hate to take the written exams to pilot one my own space wagon, though.
          You'd probably wind up with something akin to the old transcontinental railroad where the government builds a series of space stations throughout the solar system with your wagon flying from station to station, mostly following a predetermined route that is downloaded at each port. The only real driving, if any, that you would do would be when you are docking with the station. Otherwise, you would just sit around playing cards, hoping that the course that was laid out for you at Space Central doesn't cross the path of a rogue asteroid.
      • Takes a reasonably large amount of computing horsepower and a good idea of the initial conditions but a useful approximation can be calculated.

        Actually, it really doesn't take all that much computing power. I did a bunch of work on 3-body trajectories during graduate school, and my workhorse computer for that research was my home-PC at the time - a K6-2 (400MHz) running debian. As well, I was computing much more than just the trajectory. I was simultaneously computing a 6x6 matrix differential equation that provided a linearization around the trajectory. Even then, it was only when I got into doing large runs involving hundreds of trajectories that I found I needed to shift things to a server-level machine.

        You are correct that a good idea of the initial conditions is essential. Without it, you are basically flailing blindly in the 6-dimensional phase space - it's unlikely that you'll find the trajectory you want. That's why Lagrange (libration) points are so popular. They are analytical "particular" solutions that provide a starting point for finding initial conditions. In addition, there are approximations for various periodic trajectories near the libration points that also give a nice place to start. From the periodic solutions it is relatively easy to use numerical methods to map out stable and unstable manifolds to/from the periodic solutions. Next thing you know, you're on the interplanetary superhighway...

        • I guess I wasn't clear. All I meant was that you need more than a pocket calculator. (though that's getting less true all the time) Hence I said a "reasonable" amount of computing power. Of course when I was working on problems like this, a 386 was still a fairly fast computer.

          Ugh. I feel old now. I'm gonna go eat some bran or something...

    • Re:3-body problem? (Score:3, Informative)

      by LMCBoy ( 185365 )
      You can't solve the three-body problem for a general case (meaning analytically, with the solution written as an equation). You can numerically model the behavior of a gravitational system with many bodies, given some initial conditions.

      However, over time your numerical model will deviate more and more from the real evolution of the system. As long as the timescale of this error growth is much longer than a typical spacecraft's travel time, these numerical models are good enough to predict orbital trajectories accurately. Given that current models are estimated to be accurate for many thousands of years, it's no problem.
    • Actually, a solution to the 3 body problem exists. It just converges way too slowly to be any use.

      Check out Karl Sundham's 1913 series solution.

      • There's a faster converging series given by Steffensen (in german):
        Steffensen, J.F.: 1957, 'On the Problem of Three Bodies in the Plane', Mat. Fys. Medd. Dansk. vid. Selskap. 31, No. 3.

        Roger Brouke also gives a solution to the n-body problem using Steffensen's method (in english):
        Brouke, R.,: 1971, 'Solution of the N-Body Problem With Recurrent Power Series', Celestial Mechanics, No. 4, pp. 110-115.

        Painleve proved that there were no more integrals of the motion in the 3+ body problem when the mass of bodies were free to change (e.g., with collisions). This means, in this case, that the method used to solve the two-body problem won't work for 3 or more bodies. These series methods don't require integrals of the motion and work just fine for the 3+ body problem.

        Numerical integration usually uses methods similar to these series solutions, but numerical integration only provides a single solution for a specific initial condition. These series solutions are general and provide the solution for any initial condition.
    • Luckily there's a life-size model of the entire solar system available, and it works out and displays the solution in realtime.

      Oh, you want the answers ahead of time. That's different...

  • Great! This finally explains why the Vogons had to destroy earth for a hyperspace bypass.

  • According to MOND [umd.edu] there is no dark matter. So you wouldn't have to worry about its gravitational effect. You also wouldn't have to worry about bumping into it.

  • WOOT! (Score:2)

    by Maeryk ( 87865 )
    As much as I love to hear theorys like this out of NASA, and as much as I love NASA, I think they have a few other bugs to iron out first.

    While this is a great idea.. and something that has been proposed since the earliest days of Sci-Fi, (using heavy masses as centerpoints for gravitational slingshots, among other things), we
    need to get a lot of other things settled first.
    People back on the moon looking for raw materials, some actual exploration of Mars, the ISS up and running properly and actually doing something that John Q Public cares about, would be a good start.

    This is really coool, and Hubble will probably help a lot, as well as that Muckin Huge Telescope they are building, and SETI may even factor in, as it picks up signals from objects that we cant see, but we can hear.

    Its good to see that even in times of "national trouble" NASA is forging ahead and is out on the edge with theorys and predictions, but unfortunately, thats all they are, or are likey to be, unless the Gubmint gets serious about funding space travel. Or NASA becomes self sufficient.. which they could be, if only they collected royalties on the mundane uses of some of the hundreds of things that have been invented/developed by them for the space program.

    *sigh*

    in a perfect world...

    Maeryk

    • Re:WOOT! (Score:2, Informative)

      by zer0vector ( 94679 )
      I don't mean to be picky, but radio astronomy and SETI have nothing to do with hearing. Despite what you may have seen in the movies, there are no headphones hooked up to radio telescopes, and if there were you would hear static no matter where the dishes were pointed. Also if you think SETI is some how going to help out by scanning the sky in radio and finding small objects you are mistaken. SETI only has time on Arecibo, (I believe, unless something has changed) and their reciever setup is not at all optimized for tracking objects. First off because Arecibo can't really move, and second because their entire goal is just to gather up all the static and look for patterns.
      • Right. But astronomical objects put out radio static as well as visible light, in some cases. They have found quasars and double stars just because they have a very rhythmic and repeating radio pattern that they have been able to locate.
        Granted, it might not point RIGHT to it, but it does seem to indicate in what general area it is, which gives us a bit more to work with when looking there with optical and/or IR scopes.

        There is a huge difference between KNOWING something is there and trying to find it, and just scanning in the hopes of locating something.

        (INsert obligatory jedi kids in training comment here, Obiwan.)

        Maeryk
        • Perhaps I was confused about your statement then, I thought the article was referring to local solar system sized objects, very few of which contain high power radio transmitters.
          • Perhaps I was confused about your statement then, I thought the article was referring to local solar system sized objects, very few of which contain high power radio transmitters

            Nono.. my bad. THe article was referring to local, but I was thinking longterm extra-solar-sytem uses. SOrry! I failed to make myself clear. Seti is clearly useless within the solar system, unless the BEMS happen to have the radio cranked in their skimmer while they are cruising our atmosphere to laugh at the locals.

            maeryk
    • While this is a great idea.. and something that has been proposed since the earliest days of Sci-Fi, (using heavy masses as centerpoints for gravitational slingshots, among other things), we
      need to get a lot of other things settled first.

      Gravitational assists are hardly a new idea. NASA has been using them since the earliest days of the space programme. Pioneers 10 and 11 both use a gravity assist from Jupiter to leave the Solar System. Voyager 1 swung around Jupiter, picking up enough speed to get to Saturn. Voyager 2 used *four* gravity assists to get to the gas giants and then a solar escape orbit.

      Even the vaunted Apollo missions used something of a gravity assist around the moon. If the astronauts didn't fire their rockets to brake at the moon, they'd get a "free return" to Earth automatically. The moon's gravity would slingshot them back.

      So this *is* important to those goals.

  • it's local, folks (Score:3, Informative)

    by gung-ho iguana ( 594583 ) on Saturday July 20, 2002 @12:18PM (#3922981)
    The research is about finding low-cost paths through the solar system, not interstellar space. The dynamics of the solar system are very well understood, and all of the important gravitating bodies are known (there isn't any significant dark matter inside the solar system, by the way). You just have to do some heavy-duty computations to take advantage of all that.
  • Interesting concept but doesnt the slingshot effect [raytheon.com] use the gravity of planets (hence zero fuel ?) for travel ? Hence a path with nett gravity pulling the body to its destination would be of more use I think. Already the cassini mission [nasa.gov] used this principle to propel the craft to saturn (since the spacecraft lacked the fuel and the engines to propel itself to saturn).

    -Dracken
    • any "effect" where you use grvity to move with zero fuel is called falling.

      no need to give it fancy names.
    • It is essentially the slingshot effect taken to extremes: calculate all possible "slingshot" effects and all their interactions and plot a trajectory that takes optimum advantage of all of them (that is not literally how it is done, of course).
    • With the slingshoting spacecraft around planets, the goal and effect is to increase the speed of a spacecraft by passing it by a planet in a special trajectory so that the spacecraft takes some of the planet's momentum. There is an upper limit to how fast a craft can get, because the higher the difference in velocity between the planet and the craft, the closer the craft must come to the planet's centre of gravity. If you're too fast, a collision would occur.

      This method of space travel is quite different, much lower speeds are involved, and the trade off is that one can travel the 'space lanes' indefinately, and the craft is essentially coasting anywhere it wants to go. The only fuel needed would be for minor corrections, and to actually get on/off the lane at the beginning and end of the trip.

      Put in short, the slingshot effect is at much higher speeds, and is limeted in use, while this method using lagrange points is slower, more reliable, and can be used indefinately.

      Bork!
      • The Slingshot effect (i.e. the Gravity-Assist) is for trajectories at much higher energies. The Interplanetary Superhighway method is useful at lower energies.

        What will be cool is when we can tie the two methods together and use gravity-assists to get someplace quickly and then use lagrange points to move around after we get there... say to design a mission to orbit each of jupiter's moons one by one.
    • As the spaceship gets closer to the planetary body not much energy would be used up (just small orientations). To give the spaceship enough velocity to eject itself back out from the body would still require energy.

  • should be pretty easy (Score:2, Interesting)

    by lingqi ( 577227 )
    Sounds like an interesting concept but it is unclear how the scientists will account for every source of gravity, including the elusive dark matter.

    i am sure this can be empirically figured out. send hundreds of thousands of little probes all over the solar system and track their movement. each probe only need to be a beacon w/ a solar panel so they should be make very, very light. (prefabbly something degradable so no more space trash! -- or crash all of them into jupiter later, so something).

    this way you can figure out to a good degree what the gravimetric forces are within a good error margin.

    p.s. there is no accepted theory on what, or where dark matters exist. frankly so far their interactions we can see is on a galaxy-level. hence their existance, or effect within something as small (ha!) as the solar system is not well understood; and since we pretty much sent all the other probes etc (say, voyager) on their routes fairly predictably, i would say contemplating about dark matter interactions within the solar system is unnecessary.

    but, if you really wanted to, you could ;-)

    • There are already hundreds of probes out in the solar system. Asteroids, comets, moons, and planets are all easily trackable (well, not so easy when you get to tiny little asteroids), and by studying their motion it is just a matter of computation to solve for all the important interactions in interplanetary space.
    • I'd just like to point out that you can't send degradable stuff into space since there's nothing to degrade it, and even if you did degrade it, the matter would still be floating in space in a different form.
      • It's an interesting concept, though. How about something made of wispy aerogels that the constant blast of the solar wind could slowly erode? There are lots and lots of free protons, neutrons, and electrons being blasted free from the sun, zipping around out there.

        How about a plastic that ablates under heavy UV exposure (much like PVC pipe does here on earth)? Just a thought...

  • "CNN has an article about a new idea from NASA springing from chaos theory called the interplanetary superhighway."

    Uh, just back up a minute there. Chaos theory also punches a massive hole in the idea which none of the articles seem to address. To be able to utilise this idea, you need to know in advance exactly where the planets will move to. Chaos theory states that this isn't possible, since you would need a tremendous amount of precision (down to inches) to be able to predict how and when all of these planets will be just right such that you are in a zero-gravity path. If you're wrong, you have to burn fuel to get onto the path, assuming you aren't too far off in the first place. After all, predicting where planets move requires a "complex iterative model", and if your starting data is even slightly out, then it will drift far away from the correct answer over time.

    Each planet and moon has five locations in space called Lagrange points, where one body's gravity balances another's.

    Right. So what you're saying is if I have the Earth and the Moon, there will be five points where the gravitational forces from the both of them cancel out. Uh, wouldn't there be *TWO* such points? Think about it.

    • Actually, there would only be 2 such points in 2 dimensions. In 3 dimensions, there would actually be an infinite number of points, forming a ring in between the two bodies.
      • Actually if either of you had bothered to do a Google search for "Lagrange Points", you'd know (at least) three things:
        • Lagrange Points don't just refer two any two bodies, but to two bodies orbiting each other.
        • They are not points where gravity "exactly balances out", but rather where the combined gravity of the two bodies exactly cancels the centripetal acceleration needed to rotate along with them.
        • There are exactly five. (But two are unstable if the mass ratio is too low, below 25 or so)
    • Chaos theory does not punch a hole of any size in this idea. It's true that one cannot predict the positions of bodies in the solar system long term but on timescales of decades, centuries, even millenia, current models have more than enough accuracy to predict zero-gravity trajectories.

      Regarding Lagrange points, the Earth-moon system is not isolated, it is significantly influenced by the Sun. The three-body interaction results in 5 L points, a modification of the "ring of stability" mentioned by the other reply to your post.
    • Its not just cancelling of the gravitational forces of the two bodies. All the action takes place into a rotational reference frame, so you have to factor in some subtle forces like the Coriolis Force [uoregon.edu].

      If you do all the math it turns out there are 5 stable Lagrange [nasa.gov] points, two of which even allow a stable orbit around it.

      • All the action takes place into a rotational reference frame, so you have to factor in some subtle forces like the Coriolis Force [uoregon.edu].

        Actually not the coriolis force. In the frame rotating about the center of mass you only have to consider gravity and the 'centrifugal force'. If you draw a map of the overall forces you find that there are 5 points in the rotating frame where there are no overall forces acting; these are the lagrange points. It's all amazingly elegant actually.

        The coriolis forces are important when you are moving around in this rotating frame however.

    • Chaos theory mandates this (Score:4, Informative)

      by WolfWithoutAClause ( 162946 ) on Saturday July 20, 2002 @01:34PM (#3923353) Homepage
      The point is that the earlier you know that you are off the correct path, the earlier you can correct it, the less fuel you need to spend.

      Contrary to what you say, the position of the planets is known to astonishing accuracy- it's only over millions of years that they move significantly chaotically, over a few months their position is entirely known.

      A small body bouncing around between them is rather different however- that can be very chaotic.

      Plotting a course through the solar system is quite routinely achieved. Remember Voyager?

      Uh, wouldn't there be *TWO* such points? Think about it.

      Do a web search on Lagrange points, you'll find it. There's 5. One between the earth and moon, one the other side of the moon, one opposite from the moon, one 60 degrees ahead of the moon and one 60 degrees behind.

    • Nowhere did Mr. Lo describe in his paper that the gravity cancels out on these paths (only that they were minimum energy and connected the Lagrange points).

      The whole idea of a minimum energy paths through the solar system is that it's a dynamical systems of greater than 2 dimensions. The weird thing about dynamical systems of 3 dimensions is that trajectories in some of these systems exhibit a type of predictability called a "strange" attractor.

      Strange attractors for trajectories are different than the attractors you normally see in 2 dimensions (like local minima or orbits that retrace themselves) in that small pertubations can cause greatly divergent behavior. Even though the behavior appears chaotic, in some systems, the behavior can still be described as nearby a "strange" attractor. This is effect is often called chaos, and the study of strange attractors is called chaos theory.

      Apparently Mr. Lo has worked out a theory where the minimum energy trajectories under this complicated dynamical system (planetary gravitational attraction) exhibits attractors that looks like "tubes" that exhibit the chaos-like behavior of strange attractors.

      At first glance, these tubes appear to have the dynamical structure similar to n-body orbits (this factoid about orbits was first discovered by Michel Henon in the 60's). "orbits" in n-body systems don't actually retrace themselves, but sort of looks like a coiled up extension cord. The envelope or attractor of the orbits look sort of like a mis-shaped torus (squished donut), where the orbits can pretty much be anywhere on the surface of the donut (the attractor), but the path it takes is somewhat unpredictable (chaos) and highly dependent on initial conditions. There are more complicated attractors (some involving little islands of stability inside the donut) depending on the energy level, but this is the basic idea. This discovery seems to extend this known factoid about orbits to the structure of minimum energy trajectories in n-body gravitational fields.

      All this will be moot, however, when in the 2004 election, Al Gore wins the presidency by taking credit for inventing the Interplanetary Super-Highway while giving a campaign speech for an increased budget for Nasa leading all the l337 geek-crackers to rig the newly approved, non-tamperproof election computers... I boldly predict this will be henceforth called the "butterfly-ballot" effect... But I digress... ;^)
      • Oh yeah, one other thing...

        This is an interesting discovery since it's not obvious that the minimum energy trajectories between lagrange points follows a strange attractor (and aren't simply random or divergent). This means that if the trajectories are truly chaotic (i.e., follow tube-like strange attractors), once you get near the attractors (matching position/velocity vectors), maybe you can't predict exactly how you are going to get there, but you can be pretty sure that you will stay near the attractor so you needn't waste all your manuvering fuel trying to make minor course adjustments to try and stay on a specific trajectory. If it all pans out, this would probably turn out to be a pretty important discovery for inter-planetary minimum energy trajectories...
  • would be the correct title of the article.
    The idea of using gravitational forces of other bodies in the solar system is neither new nor wasn't used yet.
    Modern computational power allows to drag in the forces of several bodies, making better result possible, but that's hardly surprising.
    And the "chaos theory" probably means that they just considered the stability of their trajectories. This is hardly very exciting. The problems of unstable trajectories should be known to any maths undergrad.

    So it just boils down to the mad buzzword attack on the holy quest for more govermental funding.

    • And the "chaos theory" probably means that they just considered the stability of their trajectories. This is hardly very exciting. The problems of unstable trajectories should be known to any maths undergrad.

      No, no. You've missed it a little. Gravity is very nonlinear. It really is a chaotic system, particularly with a space vehicle, bouncing around between say the earth and the moon. With this technique they can search for and find a trajectory around bodies, and because the vehicle has small thrusters and the solar system is very predictable, they can make sure they stick to the chosen trajectory, and they end up using miniscule amounts of fuel.

    • And the "chaos theory" probably means that they just considered the stability of their trajectories. This is hardly very exciting. The problems of unstable trajectories should be known to any maths undergrad.

      Yeah, but they found a way to make unstable trajectories go exactly where they want them to without using hardly any fuel. Before we just avoided unstable areas because we thought that being unstable was bad, now we can use instability to our advantage. That's the breakthrough.

      It's kinda like figuring out how to get from LA to New York without using any gas by planning one big chain reaction car wreck.
  • A similar idea was proposed many years ago (and used for one of the satellites studying the moon). Do a google search for "Earth-Moon fuzzy boundary" for references to that particular application.

    The idea is that you can more or less coast through regions where the competing gravitational effects of many bodies cancel out, making part of your path from point a to point b less expensive than the standard transfer orbit.

    The article describes an extension of this idea.
    • This is an extension to ideas that pre-date the "fuzzy boundary" techniques by about 100 years. The "fuzzy boundary" people just made up a new name for work that had been done before in hopes that they could patent it. Compare their stuff to Tisserand for example.

      See this: http://www.space.com/news/space_routes_000726.html
      for more info about what these guys are trying.
  • The Genesis Mission is the technical application of this data.

    Go to the website here:

    http://www.genesismission.org/ [genesismission.org]

    includes pictures, decent diagrams, etc.

  • The Layman's Translation (Score:4, Funny)

    by MadFarmAnimalz ( 460972 ) on Saturday July 20, 2002 @12:42PM (#3923106) Homepage
    Scientist1: Well, it appears that there's some parts of space where there's no gravitational pull. So, if we chuck the craft along one of these paths, it will umm...
    Scientist2: It will probably need less energy.
    Scientist1: Right. Since it doesn't have to do any work counteracting any gravity.
    Reporter: Makes sense fellas. Now, you called a press conference. What's that all about?
    Scientist1: Well, that was it.
    Reporter: (short pause) I see. (another longer pause - an uncomfortable silence, actually) Now, seeing as you just worked this out, how did you fly craft before then?
    Scientist2: Well, gas was so cheap and all...
    (Scientist2 slaps Scientist1 and NASA lose what funding they have left)

    IN RELATED NEWS: Liberal Arts graduate? Want to work for the JPL? We're hiring! Call NOW!

  • Another overhyped article (Score:4, Interesting)

    by BlowCat ( 216402 ) on Saturday July 20, 2002 @12:44PM (#3923114)
    My understanding is that the JPL come with a way to calculate gravitational effects with more precision, thus saving fuel required to correct the orbit. Hardly anything exciting, but it became the "planet freeway" in the journalist's imagination. Another uninformed, overhyped article on CNN, not to mention the "Artist's concept of interplanetary superhighway", apparently not reviewed by any knowlegeable person.

    The reference to "dark matter" makes no sence to anybody ever studied general relativity. External gravitational field doesn't vary significantly in the Solar system, therefore it's irrelevant. Even if we all accelerate in the gravitational field of some dark matter, we do it uniformly.

    • "Artist's concept of interplanetary superhighway", apparently not reviewed by any knowlegeable person.

      Actually the picture is a pretty accurate representation of six-dimensional phase space, as far as representations of six-dimensional phase space go.
    • The point of the article isn't that they've calculated with more precision, more that they've worked out a way to plot courses through the solar system, more or less for free.

      Basically what happens is that there are certain points near to the earth and every other body in the solar system called the Lagrange points. The researchers have worked out a way of calculating a route that passes through the regions around the Lagrange points to jump from planet to planet with almost no expenditure of fuel.

      The only downside to this is that the route is probably going to be slow; several years to go from place to place. Still, the implications of being able to move cargo/fuel to say, Mars ahead of human habitation cannot be overestimated. The other downside is you have to be fairly high above the earth initially to be able to reach the 'superhighways', so don't expect the program to give directions from route 66 ;-)

    • This is a concept I ran across in some aero industry publication about three or four years ago. The math is so far beyond my ken, I can't even think about it for very long without getting a great big headache. However, the principle is pretty straightforward. Computationally hideous, but straightforward.

      If you're a lot better at math than me, you might get something out of this paper on the subject of manifold orbits.

      http://www.cds.caltech.edu/~koon/presentations/a as .pdf

      Now, I don't know if NASA or CNN came up with this idea of a "space freeway", but I think it's just a pretty stupid way to try to explain things to people. People aren't that stupid. Take some time to make an explanation and skip the stupid metaphors.

      I'm also faintly annoyed that this is billed as a NASA innovation. It's been the major thrust of orbital mechanics for a decade, and I'm sure the NASA people have contributed, but it's NOT their "discovery".

  • It certainly seems like as the position of the planets change, the highway itself would alter radically, closing routes entirely in certain circumstances. So, 6 month trip to Mars until February, then no (special) route until two years later.

    I wonder what relationship, if any, this highway bears to the routes that Voyager and Pioneer missions took. Maybe a slingshot route is a continual HOV lane ;).
  • CHAOS THEORY...

    It does apply to everything, but the little bit that is applies to really big things like planets and their effect on a space craft is negligile.

    SLING SHOT...

    A lot of people are talking about using gravity to propel a space craft, but don't seem to understand exactly how it works. When a space craft sling shots around a planet, what happens is this. The SC is captured by the gravity of the planet. The SC begins to fall towards the planet. However, it is falling at such an angle that it will never hit the planet or a significant portion of its atmosphere and is therefore release back into space. Now, conservation of energy applies and says that the kenetic energy gained by falling towards the planet is lost when it escapes on the other side. BUT (this is the heart of how the sling shot works) the planet is orbiting the sun. When the SC begins falling towards the planet, it also gains some of the energy from the planet itself. The SC picks up a significant portion of the velocity of the planet in it's orbit around the sun. When you apply the law of gravity for 2 bodies, you will figure out that the planet actually slows down because some of its energy is given to the SC. The end result is a SC that is going much faster and it didn't have to burn any fuel.

    SPACE CRAFT'S FUEL...

    several people are saying that the SC doesn't need to use fuel. If we could calculate exactly where everything is in the universe, then we could do it with almost no fuel. But we can't. Also, as all the calculations are only a pretty good estimate, the SC carries enough fuel to make in flight corrections.

    LAGRANGE POINTS...

    There are 5 points where gravity cancels exactly.

    1. directly between the earth and the moon.

    2. leading both the earth and the moon. It is in orbit around both the earth and moon, but does not move realtive to them because it can't fall around both.

    3. same as 2, but trailing instead of leading

    4. on the opposite side of the earth from the moon

    5. on the opposite of the moon from the earth.

    HOWEVER, only 2 points are STABLE. Points 1,4 and 5 are unstable, points 2 and 3 are stable. If you solve the problem, you realize that points 1,4, and 5 are sources and points 2 and 3 are sinks.

    Now to qualify myself. I've only had 2 astro engineering courses (taken for fun) a few years ago back in college, so if i've made any mistakes, please forgive me and correct me.

    • All your science sounds good, I just thought I would throw in this link to picture of the Lagrange Points [montana.edu] to make it easier to understand.
    • CHAOS THEORY... It does apply to everything, but the little bit that is applies to really big things like planets and their effect on a space craft is negligile.

      There are places where the gravity from the Earth and the Sun pull on your spacecraft at almost the same amount (near Lagrange points) in these places small maneuvers can put you on vastly different trajectories... small actions have big effects... and this is where you can use chaos theory for trajectory design.
  • Does anyone have a rough estimate about the difference in time-of-flight for an object taking the "interplanetary highway" versus the old-fasioned fuel assisted "off-road" travel? I would imagine that in some cases the fuel and gravity assisted flights, while more expensive, would be able to reach its destination faster than some of the roundabout pathways of the highway.(?) Or is the travel time difference not very substantial for an interplanetary mission because the old-fasioned travel methods involved their own roundabout gravity assists from various intermediary planets along the way to its real destination?
    • I first heard about this in the late 1980's. As I understood it, the time to travel along this "highway" is, in fact, longer... but it is also substantially cheaper because of the savings in fuel. A space craft does not need to carry nearly as much fuel as it would for an "off road" trip. This may not be practical for manned missions, since excessively long travel times can have nasty psychological effects (to say nothing of the physiological effects of extended stays in zero G). However, it's great for unmanned craft because if they don't have to use as much fuel, they should be able to go much further. What I had heard was that it would not be unrealistic to expect a probe would be able to reach the outer areas of our solar system within 20 years using this method with lots of fuel to spare.

      Of course, this was what I had heard over 10 years ago. Maybe things have changed since then.

  • In my day, we didn't have no inter-planetary sup-er high-way. We got to Triton O-45 the old fashioned way, and it was up a gravity well both ways!

    Some scientists theorize that a killer asteroid traveled along the highway when it smacked into Earth and wiped out the dinosaurs 65 million years ago.

    Oh my gosh! Interplanetary superhighways facilitate terrorism! Tear it down! Think of the children!
  • Probably I just know too little about this to make any sense (kinda like how I couldn't understand Enron's bandwidth trading operation) but isn't this sort of like what Benjamin Franklin did with studying the Gulf Stream and other oceanic currents? Only this time, the ship makes its own current and just steers itself away from things which would slow it down. Hm. Maybe it isn't quite like that.

    Maybe it is more like get launched, then just coast and steer. I kinda don't see why this is such a big deal... Wouldn't some kind of gravitational radiation antenna be able to just figure out where the gravitation is lowest?

    Somehow, I don't think I'm qualified yet for the space pilot position. (Also, for some reason, probably the coast and steer part, I was thinking about Japanese pagodas, with the central stability beam and all the layers resting on each other, but not using the beam for structural support, only stability. Maybe just randomness...)
    • (* what Benjamin Franklin did with studying the Gulf Stream and other oceanic currents? *)

      Interesting analogy. They could have called the article "Cosmic Gulfstreams" or "Gravity Gulfstreams".

      (* Maybe it is more like get launched, then just coast and steer. I kinda don't see why this is such a big deal... Wouldn't some kind of gravitational radiation antenna be able to just figure out where the gravitation is lowest? *)

      More likely, I think that one's position would be often checked by trangulation of appearent planet positions, etc. (or dopler radio) and if it is deviating from the modeled path, then correct the course. IOW, your ship's position is the "gravity antenna".

      The idea of "lowest gravity" is probably a misnomer. As the ol' fuzz-head discovered, it is all relative.
  • Being that humans tend to overdue things, I imagine that eventually we will start stealing momentum from some of the planets to such a degree that their orbits will be noticably different, possibly throwing off orbit frequency balances [1] that have been acheived over billions of years, and asteriods in otherwise stable circular orbits will start to go wacko.

    I am sure they laughed at the idea that cars and factories could ruin (alter) the Earth's atmosphere. But, we did it. Maybe it will take longer to bust Jupiter, but I woudn't put it past us. If we can harness the energy of the sun from places beyond earth, then we have the potential for *huge* population growth. The energy falling on Earth is a speck compared to all the energy potentially capturable via solar panels made from asteroid materials, etc. The raw materials are all out there and so is the energy. It is only a matter of time until we learn to combine the two.

    [1] I forgot what they call that. Synchronicity? Orbit Ratio patterns? Orbital Vibration? stumpage.
    • I believe the Voyager flybys slowed Jupiter down by something like three centimeters per trillion years. There's no worries about screwing anything like that up. Did you see all the pictures from that huge comet that hit Jupiter a few years ago? Nature can be more destructive than we will be for a long time.
      • (* I believe the Voyager flybys slowed Jupiter down by something like three centimeters per trillion years. There's no worries about screwing anything like that up. Did you see all the pictures from that huge comet that hit Jupiter a few years ago? Nature can be more destructive than we will be for a long time. *)

        For one, I think that the direction of comets is probably random enough that the total will add up to no difference (There might be a general "drag", but it would affect *all* items roughly equally perhaps.)

        Second, I am talking about a grand scale of human population. If we start hogging all the resources in the solar system, there is anough material to support many many humans. After they start zipping around in their cosmic SUV's by borrowing gravity in mass numbers, things might start to happen. Keep in mind that we mostly use just the surface of the earth now. Using asteroid material etc. we can make huge relatively flat orbiting surface areas (say 30 feet thick) to grow crops and people.

        Imagine a whole free-way of comets, not just one.

  • While the CNN article is truely hyped and mostly fluff there is an informative paper here [caltech.edu].

    In summary: If you find yourself in orbit around a Lagrange point you only need to change your velocity a little to change your orbit radically (thats the chaos part). The orbits you can enter in the Sun-Earth system is forming two horseshoes with the Earth placed in the gap (or perhaps more precisely: Like the figure 8 with the smallest of the loops folded within the larger one and the Earth placed in the cross between the loops). One of the orbits lies within earths orbit. The other lies outside of Earths orbit.

    What makes this particular interesting is that the horseshoes of the Sun-Earth system overlaps the horseshoes of the Earth-Moon system. So, if you're travelling along one of the horseshoes in the Sun-Earth system, you can pull the trick again when you cross the horseshoe of the Earth-Moon system and enter an orbit around earth with virtually no fuel consumption. It works the other way around too: If you place a spaceship in one of the Lagrange points of the Earth-Moon system you can reach far into the solar system for almost free by entering the horseshoe of the Sun-Earth system at the right time. The only catch is that you're travelling pretty slow.

    Now the CNN article talks a lot about interplanetian travel, but the reality is that the mechanics have only been worked out for the earth-moon-sun system and the Jovian system. Interplanetarian travel requires heavy computatios and is still in the works.

    And to dispell some of the confusion in this thread about the nature of the Langrange points this [nasa.gov] page gives a good explanation.
  • Oh sure, you could calculate a series of mathematically elegant trajectories that would allow spacecraft to use minimum energy to traverse the solar system by surfing along various gravipotential boundaries. Or you could build big, throbbing manly Orion rockets.

    http://www.amazon.com/exec/obidos/ASIN/0805059857 [amazon.com]

    http://www.islandone.org/Propulsion/ProjectOrion.h tml [islandone.org]

    I personally favor building big manly throbbing Orion rockets, but that's because chaos theory makes my brain hurt and because things that explode are cool.

  • This is just silly PR; but of course his colleagues say nice things, it probably helps NASA.

    Another guy from JPL had a Berkeley dissertation circa 1965 on this topic; the minimum energy orbits are called Hohman transfer trajectories. They neglect the rest of the planets, but those are minor perturbations -- that's what the "tubes" are about.

    There are five orbits around the Earth-moon neighborhood where the derivative vanishes, the Euler points and the Lagrange points; the forces [including momentum!] all balance out, but they aren't necessarily stable [the 60 degrees ahead/behind in the moon's orbit are, if some mass ratio condition is satisfied, cf "trojan asteroids" in Jupiter's orbit].

    The guy may know something, but NASA is a big organization, and the press release writers in any such were typically English majors. The chaos theory angle is largely bullshit [but heaven forbid I should utterly squelch young spirits, as one of my professors used to say:]

    If this leads someone to learn the math, great, but it's really a crock (tm).

  • I never much liked the theory of dark matter. "Our calculations indicate a bunch of stuff we don't observe...must be invisible stuff." Uh, yeah. It's the ether, guys, and planets spontaneously generate from it.

    Seriously, though, when a calculation doesn't match up with oberservable fact, you're supposed to adjust the calculations (chaos theory, heisenberg, quantum mechanics), not invent something. And there's a theory right now, explained in the latest scientific american (you ARE a subscriber, right? If not, drop the $35 per year, it makes you a better person), that does just that -- adjusts gravitational constants unchanged since Newton's days when matter moves very quickly. I kind of like it...it makes more sense to me than this "hey, 95% of the galaxy is invisible and undetectable and that's why things spin in wierd directions!" crap.

    Dark Matter. Feh. In another 70 years it'll rank with phrenology, dowsing and psychoanalysis.
  • Absolutely fascinating work by Martin Lo. If highway coordinates are publicized this might be the best place for spaceguard and amateur asteroid searchers to look. Currently amateurs are discovering asteroids very frequently.

    I also wonder if this implies a similar superhighway among the stars which could determine where a stream of matter might be coming over the millenia from outside the solar system. (i.e. where are the off-ramps to our solar system?)

    The interview [genesismission.org] with Lo is much more interesting; he believes we are on a cusp of where advanced theoretical mathematics is going to inform a new generation of engineering.

    I would like to understand the math better, specifically to see if it might have applications to software. I'd also like to plot the superhighway, or understand how they are doing it. But only have a year of college math. Where is a good and free place to learn about it online? Been to Mathematica.
    • I would like to understand the math better, specifically to see if it might have applications to software. I'd also like to plot the superhighway, or understand how they are doing it. But only have a year of college math. Where is a good and free place to learn about it online? Been to Mathematica.
      Well, it's pretty dry but very complete: Weisstein's World of Physics [wolfram.com] has a Celestial Mechanics [wolfram.com] section, with topics on the two-body problem [wolfram.com] and the restriceted three-body problem [wolfram.com], Lagrange points [wolfram.com], etc. The heavy duty math can be overwhelming, but it's really fun to navigate the hyperlinked topics, and the articles have references listed which could be useful. See also the World of Mathematics [wolfram.com] for a very extensive reference with loads of cool illustrations/applets.

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