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Thread: Dyson Spheres - Thoughts and Questions

  1. #16
    Senior Contributor SteveDaPirate's Avatar
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    Quote Originally Posted by Ironduke View Post
    Because of factors such as the changing relative positions of all of the orbital bodies and their LaGrange Points to one another, I'd also imagine there would be spacecraft that would essentially serve the same functions as routers, routing transmissions in the Solar System in the fastest, most efficient way possible. It would be an internet of sorts for the entire Solar System. The time it took information to arrive would, of course, be measured in light-seconds, minutes, and hours, given the distances involved.
    In theory if you could devise a communication system that could handle the immense distances involved, putting relay satellites in a polar orbit of the Sun should give them an unobstructed view of all the orbital bodies in the system.

  2. #17
    Former Staff Senior Contributor Ironduke's Avatar
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    Quote Originally Posted by SteveDaPirate View Post
    In theory if you could devise a communication system that could handle the immense distances involved, putting relay satellites in a polar orbit of the Sun should give them an unobstructed view of all the orbital bodies in the system.
    You have a good point. Relay satellites in Sol's polar orbit would be of great use for communications, especially when planets, ships, and satellites are in opposition to one another in the Solar System. It would then be the shortest hop, with the least amount of latency.

    The rest of what I've written assumes a relatively tight Sol polar orbit of several million kilometers. If it's possible to have satellites in Sol polar orbit at distances of tens or hundreds of millions km, disregard everything I'm about to write.

    As far as space traffic control, reconnaissance, communications, relay, and monitoring satellites are concerned, there would be obstructions if only satellites in Sol polar orbit were utilized for these purposes. Anything the remained on the dark side of an orbital body relative to satellites' positions in this orbit could go unseen and undetected.

    A spacecraft could, for example, maintain a position on the dark side of Neptune, and remain completely unseen.

    Spacecraft could also possibly hide in the tail of a comet, or keep an asteroid between themselves and the view from such polar orbit satellites, thus being able to travel through the Solar System, potentially undetected.

    Hence there would need to be a network of such satellites in orbit around all of the planets, as well as their LaGrange Points, to avoid orbital bodies, asteroids, and comets from being utilized as a means of obstruction from detection and monitoring, and to avoid loss of communications.
    Last edited by Ironduke; 03 Jun 18, at 20:19.
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  3. #18
    Former Staff Senior Contributor Ironduke's Avatar
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    Quote Originally Posted by SteveDaPirate View Post
    L4 and L5 are very stable and would require almost no reaction mass to stay balanced and have the advantage of existing at the same distance from the sun as earth does, reducing the need for excessive heating or cooling requirements. However they tend to be so stable that they collect asteroids and dust as well since they form big gravitational bowls that things slide into then can't escape.
    This got me thinking about something. In sci-fi fantasy series such as Star Wars, asteroid belts are depicted as being dense, dangerous, with quick reactions and maneuvering being needed to avoid collisions. In reality, in our own Asteroid Belt, NASA estimates there's something like in a 1 in however many billion of a chance that a spacecraft passing through would collide with something. As far as I know, not a single spacecraft has been lost navigating through the Asteroid Belt.

    Is the density of asteroids and dust in L4 and L5 that much more than the Asteroid Belt? If so, by how much? It makes sense though that there would be more risks of collision to a stationary object in a place such as L4 or L5, than there would be one to an object simply passing through, for example, the Asteroid Belt, even if the density of objects were similar to one another.
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  4. #19
    Senior Contributor SteveDaPirate's Avatar
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    Quote Originally Posted by Ironduke View Post
    Is the density of asteroids and dust in L4 and L5 that much more than the Asteroid Belt? If so, by how much? It makes sense though that there would be more risks of collision to a stationary object in a place such as L4 or L5, than there would be one to an object simply passing through, for example, the Asteroid Belt, even if the density of objects were similar to one another.
    I'd be surprised if the density was anything approaching Star Wars levels. L4 and L5 are called points, but in reality they are huge elongated gravity bowls and the objects that slide into them without enough oomph to get out again tend to fall into orbits within that bowl and are known as Trojans.

    You can see below how within the inner solar system the two biggest concentrations of asteroids are either within the asteroid belt itself, or are Trojans captured by Jupiter at the L4 and L5 points. In the second picture you can see a view from the orbital plane that shows how the Hildas (Black) and Trojans (Grey) are distributed vertically as well.

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    Last edited by SteveDaPirate; 04 Jun 18, at 15:17.

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    Quote Originally Posted by Ironduke View Post
    As far as space traffic control, reconnaissance, communications, relay, and monitoring satellites are concerned, there would be obstructions if only satellites in Sol polar orbit were utilized for these purposes. Anything the remained on the dark side of an orbital body relative to satellites' positions in this orbit could go unseen and undetected.
    The only Solar System Positioning System proposal i've seen (from the Advanced Studies Group of DLR) placed the orbits at around the Kuiper Cliff, both for ISRU robotic construction of these satellites and for full, unconditional coverage of the entire Solar System.

    Quote Originally Posted by Ironduke View Post
    If it's possible to have satellites in Sol polar orbit at distances of tens or hundreds of millions km, disregard everything I'm about to write.
    Solar Orbiter (ESA) has a planned perihelion of around 40 million km, slightly within Mercury's orbit at that point. Parker Solar Probe (NASA) will attempt to close to within 6 million km of the Sun's photosphere.

    With the caveat that both operate elliptic orbits with aphelions of around 0.75 AU. The two are due to launch in the next 3-4 months. Parker Solar Probe will only run a single perihelion at that distance (its 22nd, in 2024); Solar Orbiter will stay in its elliptic orbit with that 40 million km perihelion for 3.5 years while raising its inclination through Venus flybys in order to improve coverage of the Solar Poles (from 25 inclination; 34 if extended past 2025).

    Quote Originally Posted by SteveDaPirate View Post
    I'd be surprised if the density was anything approaching Star Wars levels.
    In the asteroid belt density is on the order of asteroids - of any size - being separated by few million km. The density of Jupiter Trojan and Greek clouds (mostly the latter) is typically considered to be on a similar, possibly less dense level.

    Among the Neptune Trojan and Greek clouds you interestingly mostly have relatively large objects, and these outnumber the Jupiter Trojan and Greek clouds by an order of magnitude - however there are very few small rocks of a few hundred meters intersparsed between them, making average separation a whole lot bigger.
    Last edited by kato; 04 Jun 18, at 17:34.

  6. #21
    Senior Contributor Monash's Avatar
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    Quote Originally Posted by Ironduke View Post
    Is the density of asteroids and dust in L4 and L5 that much more than the Asteroid Belt? If so, by how much? It makes sense though that there would be more risks of collision to a stationary object in a place such as L4 or L5, than there would be one to an object simply passing through, for example, the Asteroid Belt, even if the density of objects were similar to one another.
    Pending the no doubt imminent arrival of my degree in astrophysics in the mail the following are purely a layman's observations;

    Firstly as far as I am aware objects captured by the Sun's gravitational field and spiraling inwards towards it from the edge of the solar system pick up far too much velocity to be 'captured' by a Lagrange Point. As a result they would pass through one without stopping. The same thing applies to objects in very eccentric orbits around the Sun - on their inwards path they would pick up to much speed to be trapped and would usually be deflected by the gravitational influence of the Earth and Moon in any case.

    This would leave a very few rare orbits that would permit random moving objects to be captured long term at any one of the L points. Even then I suspect that over eons there would be forces acting on any such objects that would tend to draw (or push) them towards the edges of the L points whereupon they would resume their travels. Dust grains and other small objects would (I think) be influenced by the impact on solar radiation, magnetic fields and sunlight, all of which would tend to impart subtle velocity changes over time. Larger meteorites etc would over eons also tend to be effected by these and other factors. And of course the further you are away from the the exact centre of an L point the less 'stable' their position would be.

    End result (I think) is that Lagrange points wouldn't retain any trapped matter over the longer term (thing millions of years) which explains why, as far as I am aware astronomers haven't detected significant amounts of debris trapped in these zones. This means that man made objects like satellites or space habitats would also probably need station keeping drives at Lagrange points. They would just need to be used very, very sparingly because the forces I am talking about would tend have a negligible effect over a human life time.
    Last edited by Monash; 06 Jun 18, at 12:58.
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    Here's a paper on that: https://arxiv.org/ftp/arxiv/papers/1003/1003.2137.pdf

    We find the likelihood of a given planetesimal from [a primordial trans-Neptunian disk] being captured onto an orbit within Jupiter’s Trojan cloud lies between several times 10^-6 and 10^-5. For Saturn, the probability is found to be in the range <10^-6 to 10^-5, whilst for Uranus the probabilities range between 10^-5 and 10^-4. Finally, Neptune displays the greatest probability of Trojan capture, with values ranging between 10^-4 and 10^-3.
    I.e. for any random million objects in such a disk one would end up as a Saturn trojan, 1-10 as a Jupiter Trojan, 10-100 as a Uranus Trojan and a 100-1000 as a Neptune Trojan.

    Jupiter's capture mechanism is outlined on page 8.

    The Trojan populations of Saturn, and those that Jupiter didn't keep stable (75% of captures leaving again within 4 billion years) became the centaurs and short-period comets:
    Consequently, taken together, the lost Trojans of Jupiter and Saturn probably contained 3-10 times the current mass of observed Jovian Trojans, which implies the release of ~3x10^-5 - 10^-4 M⊕ of material onto unstable orbits over the time since planetary migration ceased. On the other hand, the loss of Uranian and Neptunian Trojans probably amounted several tens or even hundreds times 10^-5 M⊕, thus providing an important additional source of material on unstable orbits among the giant planets. Such unstable wanderers are known as the Centaurs, and represent the direct parent population of the Jupiter family of comets.
    Quite interestingly they also suggest that the instability of the Uranian Trojan cloud may have contributed to the Late Heavy Bombardment.
    Last edited by kato; 06 Jun 18, at 13:54.

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