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Dyson Sphere and 100D Jump Limit

True.


One of the GT authors asked Marc Miller about it. MM stated that intervening jump limits along the route did indeed interrupt jumps and that that's the way he'd intended it all along.

Cool. Where did you read that?
 
For the suggestion of an object in the Oort Cloud being causing a ship to drop out of jumpspace: I like it, for two reasons.
One is, it supports the existence of the Scout Service; a high proportion of all Scout missions would be monitoring as many of the more massive objects as possible, and issuing warnings for spacefarers.
The second reason is, it justifies the massive computing power involved in ship computers:
A one parsec jump across empty space is something you could work out with a pocket calculator; add the requirement to plot (as much as possible) a route through the known emptier regions and all that extra computer becomes necessary.
 
If Marc confirms that he said that, then fine... that's what Marc said.

Until then, the claim falls into the "Unh-huh... yeah... Ooh-Kay, right" category.


As for Jump masking in general... I'll just continue to play the way I always have anyway... "it's my TU, and I'll play how I want to...".
 
The central secret of interstellar travel is the concept of jump space. Without this method of travelling around intervening space, interstellar travellers would be restricted by the universal speed limit of 300,000 kilometers per second; the stars would be beyond the reach of most intelligent species, and even the limited travel that did take place would be slow, and relatively unprofitable.
[snip]
The basic concept of jump space is that of an alternate space. Theoretically, jump spaces are alternate universes, each only dimly understood from the standpoint of our own universe.
[snip]
Entering jump is possible anywhere, but the perturbing effects of gravity make it impractical to begin a jump within a gravity field of more than certain specific limits based on size, density, and distance. The general rule of thumb is a distance of at least 100 diameters out from a world or star (including a safety margin), and ships generally move away from worlds and stars before beginning a jump. The perturbing effects of gravity preclude a ship from exiting jump space within the same distance. When ships are directed to exit jump space within a gravity field, they are precipitated out of jump space at the edge of the field instead.
- Marc Miller, JTAS #24, 1981

Marc’s 1981 treatise on Jumpspace doesn’t sound like it includes jump masking except for overlapping ‘gravity fields’ at the exit point. Reading the above and the CT rules, I would conclude that Jupiter would shield its moon if that was your start or end point, but the oort cloud or Neptune would have no effect since your “alternate universe” is travelling “around intervening space” rather than through it. YMMV.

With respect to 'blocking' the jump paths with an asteroid, there are an almost infinite number of straight lines from the 100 diameter of a world to the center of a another world 1 parsec away, but those lines will converge as they approach the destination. At those distances, the diameter of all of the possible paths as they pass say 100 AU from the target world will be very small and could fall within the 100 diameter limit of a pirate asteroid.

Leaving from Earth's 100D limit, travelling 1 parsec and attempting to create a 'jump shadow' 10 au from the destination world - the required jump shadow is only about 61 km in radius which requires an asteroid about 0.61 km in diameter (610 m diameter = 8.5 million dTons). An asteroid 61 meters in diameter (8500 dTons) would shield 117 million square km of the 12 billion square km jump cone and intercept about 1 percent of incoming traffic (far from planetary defenses). Moving the attack further from the world will expand the cone (and required asteroid) and longer jumps will narrow the cone. Sounds like intermediate jump shadows could allow piracy and make J2 routes are vulnerable.
 
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A Dyson sphere doesn't have a significant gravity well. That's the point.

Apparently I didn't get my intention/question across correctly. Sorry 'bout that...

No matter how high the tech of those inside a Dyson sphere, the gravity of the enclosed star will/should still affect orbits of other nearby stars, correct? Even if the star isn't visible, it's gravity effects will still be detectable by its effects on other systems. Thus the star should still be detectable by civilizations in systems nearby, correct? (Assuming their technologies are advanced enough, of course.)
Then there are always neutrinos...

No matter the 100-diameter limit of the sphere itself, the star should still be detectable eventually...
[This is the point I was originally trying to make; I'm not arguing the 100-diameter/mass limit at all...
I believe - if my lack-of-sleep addled brain remembers correctly :confused: - that someone was making the point about the enclosed star being 'hidden' and this was my thought on it.]
 
Apparently I didn't get my intention/question across correctly. Sorry 'bout that...

No matter how high the tech of those inside a Dyson sphere, the gravity of the enclosed star will/should still affect orbits of other nearby stars, correct? Even if the star isn't visible, it's gravity effects will still be detectable by its effects on other systems. Thus the star should still be detectable by civilizations in systems nearby, correct? (Assuming their technologies are advanced enough, of course.)
Then there are always neutrinos...

Even easier than that. A planet with our current tech level would detect it with telescopes that pick up the IR band. http://en.wikipedia.org/wiki/Thermal_radiation

It would be as obvious as the nose on your face. :)
 
It would show up as an IR source with the same total output as the star. Unless it somehow sinks heat into J-space.
 
It would show up as an IR source with the same total output as the star. Unless it somehow sinks heat into J-space.

Makes perfect sense. Thank you!

And an IR source with no other 'obvious' signs of a star present. Sounds like a mystery... or is that 'adventure'? :D
 
It would show up as an IR source with the same total output as the star. Unless it somehow sinks heat into J-space.

IANAP (I am not a physicist) but surely the whole point of a Dyson sphere is to encapsulate and trap the energy coming from the star? For obvious processing into some sort o mega-weapon. I mean, with a classic Ancients dyson sphere, the star is covered by a shell at least an AU from the star core.

The other variants (present on the wikipedia page) would be easier(1) to create and wouldn't blot out the star.

I love the concept of dyson spheres and very glad this is space opera.

(1) for various values of "easy"
 
IANAP (I am not a physicist) but surely the whole point of a Dyson sphere is to encapsulate and trap the energy coming from the star?

All energy winds up eventually as IR radiation. THAT IS the simplest way to explain the entropic principle of work.

All that energy you trap, in being used to do work, eventually either converts to heat through inefficiency, converts to heat by causing impact or friction, or directly causes heating in capture. So, you have to let that heat out.

If you don't, then your shell heats until it melts, and then it lets the energy out, anyway, as the shell falls apart.

In order to not heat up to melt, the amount of radiated blackbody heat must equal or exceed the amount the shell is gaining from the star. Note that the higher the temp of the object, the more IR it radiates due to its own heat, and the more is thus required for continued heating.

In order not to drop to the 3°K (~ -270°C) "Background Temp", it must radiate less than the background radiation imparts (enough for 3°K, apparently); again, the warmer the material, the more IR it lets out, so cooling slows as temps drop, and less energy in is needed to return to heating.

When the temperature results in radiating as much energy away as is being received, thermal equilibrium has been reached; it will stay that temp as long as the energy level doesn't change.

So, that dyson sphere, given that the energy is that of a star, must radiate off as much as it recieves; much of it is used for work, but all work eventually results in heat, and that heat still has to go away or contribute to meltdown.
 
So, that dyson sphere, given that the energy is that of a star, must radiate off as much as it recieves; much of it is used for work, but all work eventually results in heat, and that heat still has to go away or contribute to meltdown.

OK, I ken that (though you're living hazardously in 21st Century thinking :)

So - anyone fancy describing how they would present a Dyson sphere?

I'm inclined to present it as a large "cool" body where "cool" is nowhere near the temperature of a "cool star". A body that blots out the stars.
 
OK, I ken that (though you're living hazardously in 21st Century thinking :)

So - anyone fancy describing how they would present a Dyson sphere?

I'm inclined to present it as a large "cool" body where "cool" is nowhere near the temperature of a "cool star". A body that blots out the stars.

It will radiate the same total energy. It has to. It' basic physics... as in conservation of energy.

It will not have the same energy density... it will turn it all into low energy IR. But it WILL radiate it all, given enough time.

IR, however, is readily detectable...
 
It will radiate the same total energy. It has to. It' basic physics... as in conservation of energy.
It will not have the same energy density... it will turn it all into low energy IR. But it WILL radiate it all, given enough time.
IR, however, is readily detectable...

The difference then would be with the same total energy but radiated over the surface of a much larger sphere than the gravity well would indicate?
 
It might also concentrate all that IR waste heat into a single (or multiple) vent/radiator. So instead of a large surface equalized IR source you'd see a single (or multiple) smaller, hotter point(s) IR source. And I think with a little clever design and practice that IR source (if single) could be masked and directed such that it would be undetectable except from a certain part of the sky. Perhaps one that no one has visited... until the PC's misjump into a specific hex :)
 
It might also concentrate all that IR waste heat into a single (or multiple) vent/radiator. So instead of a large surface equalized IR source you'd see a single (or multiple) smaller, hotter point(s) IR source. And I think with a little clever design and practice that IR source (if single) could be masked and directed such that it would be undetectable except from a certain part of the sky. Perhaps one that no one has visited... until the PC's misjump into a specific hex :)

Heat pumping only works to a certain degree... and the visibility is going to be a cone. We're directly imaging things in the 400°K-600°K range at several parsecs; that radiator will be (at smallest) visible, albeit those bodies are single pixel on our best images.

Add then there is that need to keep the temp down to something that the radiator itself doesn't melt...

Radiation into jumpspace breaks physics less...
 
...then there is that need to keep the temp down to something that the radiator itself doesn't melt...

Dang it! I'm always forgetting the melting bit :)

Yeah, probably make it tough (I hate saying impossible). Probably falls outside the "simply an engineering problem" parameters. I'm too lazy to run numbers for various sizes and stars (I suspect someone must have, will google later) but I'm thinking (gut guess) a small star might be enough to run a very large sphere, which might (long shot) permit some form of directional radiation.
 
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