The Dyson Sphere (The Dyson Shell)

[Werner]

This is one around a G2 V class star about 1 au in radius, and it is not on any chart as it cloaks its own sun by completely surrounding it.

This is the science fiction kind of Dyson Sphere it is a solid shell that rotates once every 9 days producing 1g of centrifugal force at its equator.

A Dyson sphere may be more useful in a campaign in that they may be placed anywhere in any sector, since its shell would render it invisible in the visible light spectra, particularly in sparsely populated sectors where people have better things to do that to search the skies for unseen objects in the infrared.

Would a Dyson sphere cause a misjump if it drifted between two stars, or would a midjump land the PCs outside the shell of a previously undiscovered Dyson sphere? What do you think?

How would events unfold if player characters were to discover such an object by accident?

 

[whulorigan]

A Dyson sphere may be more useful in a campaign in that they may be placed anywhere in any sector, since its shell would render it invisible in the visible light spectra, particularly in sparsely populated sectors where people have better things to do that to search the skies for unseen objects in the infrared.

But it would also manifest as an unseen gravitational anomaly / source with an associated mass equal to both the star and the entire shell combined, centered on the location of the star.

EDIT: Also bear in mind that a rigid dyson shell would be emitting its infra-red signature accross its entire surface area, which would make it an infra-red source with a luminosity comparable to a Giant (Class III) Star in the infra-red. No known objects that I can think of emit entirely in the infra-red with that level of luminosity (Sub-stellar objects, rogue planets, and Y-Type brown dwarfs have luminosities much smaller than this) as a clear giant "disk" to an observer. So while average merchants/colonists/adventurers might not be particularly trained/interested in making or paying much attention to such scans, the IISS and/or astrophysicists most certainly would be, and would be able to view it from a fair distance in the infra-red (and it of course falls under their job-description).

So if the purpose is to hide it so that it will be a surprise in the course of a campaign, I would explore other "ultratech" options for why it might not be emitting in the EM-spectrum in an easily identifiable way. According to T5.10, Rigid Dyson Shells are TL-29 Standard (TL-27 Prototype) (T5.10 Book 2: p. 235-237). This should be more than enough "handwavium" leeway to come up with something not entirely understandable to TL-15 physics. Perhaps in utilizing the full radiated stellar output of the central star by the shell, some system on the shell is being powered that interacts with a J-space (or other hyperdimensional domain) that bleeds most of the heat-emission into the other domain (Note that prototype Pocket Universe technology is also available at TL-29). Perhaps there is an exchange whereby some systems on the shell acquire energy from said domain in return for bleeding energy back out to the domain as an equal/opposite reactionary response of some sort.
​

Would a Dyson sphere cause a misjump if it drifted between two stars, or would a misjump land the PCs outside the shell of a previously undiscovered Dyson sphere? What do you think?

If the ship's jump-line directly intersected the 100 diameter limit of the shell, it would cause the ship to precipitate out of jump at the 100 diameter limit of the shell after 1 week in jump. This would be at a distance of ~200 AU (or about 5 times the distance of pluto from the sun, or about 28 light-hours).

 

[Werner]

But it would also manifest as an unseen gravitational anomaly / source with an associated mass equal to both the star and the entire shell combined, centered on the location of the star.

EDIT: Also bear in mind that a rigid dyson shell would be emitting its infra-red signature accross its entire surface area, which would make it an infra-red source with a luminosity comparable to a Giant (Class III) Star in the infra-red. No known objects that I can think of emit entirely in the infra-red with that level of luminosity (Sub-stellar objects, rogue planets, and Y-Type brown dwarfs have luminosities much smaller than this) as a clear giant "disk" to an observer. So while average merchants/colonists/adventurers might not be particularly trained/interested in making or paying much attention to such scans, the IISS and/or astrophysicists most certainly would be, and would be able to view it from a fair distance in the infra-red (and it of course falls under their job-description).

So if the purpose is to hide it so that it will be a surprise in the course of a campaign, I would explore other "ultratech" options for why it might not be emitting in the EM-spectrum in an easily identifiable way. According to T5.10, Rigid Dyson Shells are TL-29 Standard (TL-27 Prototype) (T5.10 Book 2: p. 235-237). This should be more than enough "handwavium" leeway to come up with something not entirely understandable to TL-15 physics. Perhaps in utilizing the full radiated stellar output of the central star by the shell, some system on the shell is being powered that interacts with a J-space (or other hyperdimensional domain) that bleeds most of the heat-emission into the other domain (Note that prototype Pocket Universe technology is also available at TL-29). Perhaps there is an exchange whereby some systems on the shell acquire energy from said domain in return for bleeding energy back out to the domain as an equal/opposite reactionary response of some sort.
​

If the ship's jump-line directly intersected the 100 diameter limit of the shell, it would cause the ship to precipitate out of jump at the 100 diameter limit of the shell after 1 week in jump. This would be at a distance of ~100 AU (or about 2.5 times the distance of pluto from the sun, or about 14 light-hours).

Stars also move, so the blockage would only be temporary. The inhabited section would be.around the equator. Shadow squares like for ringworld would work since the uninhabited sections would be black to absorb the maximum amount of light possible. At night the sky will be black and starlets.

Also for access to the interior of the sphere, cut a hole around each pole, since the radius is 150,000,000 km where the gravity is 1g, at 1/100th of that radius, it be 1,500,000 km in radius, the gravity at the edge of the hole will be 0.01 as it will be rotating once per 9 days. Spin gravity is inversely proportional to to the distance from the spin axis. It will also be moving at 1/100th of the velocity of the equator.

From the inside the sphere will look like a ringworld except there would be no stars in the background except through the 3,000,000 km wide holes at the north and south poles of the sphere. As viewed from the habitable section these holes would be elevated by 45 degrees from the north and south tangential horizon. The width of the habitable zone would be a function of 150,000,000 km - (150,000,000 km × Cosine(L)) = 8 km. 8 km is the height if Mount Everest assuming we have a Standard atmosphere at the equator. You solve for L to find the degrees latitude north and south of the equator. The width of the habitable section is therefore W = 150,000,000 km × Sine (L) x 2. W is the width of the habitable section in kilometers.

 

[whulorigan]

Stars also move, so the blockage would only be temporary.

Yes, but that "temporary" might last 100's-1000's of years on the astronomical timescale, depending on the relative velocity. Remember, a 200 AU Jump-shadow is twice the the size of the entire solar system (out to twice the distance of the Kuiper Belt (it is in fact twice the distance of Sol's termination-shock/heliopause)).

The inhabited section would be around the equator. Shadow squares like for ringworld would work since the uninhabited sections would be black to absorb the maximum amount of light possible. At night the sky will be black and starless.

CORRECT. But you would also need to construct equatorial walls on the inside along either side of the equator out to some distance to keep the atmosphere contained (if it has one), similar to a ringworld. Otherwise the gas pressure will cause it to seep into the black uninhabited areas and eventually bleed off into the shell interior as it encounters ever lower centrifuge gravity as it spreads out into lower/higher latitudes.

 

[whulorigan]

Calculation Error

Oops, made an error up thread; I used radii instead of diameters.

The 100 diameter limit of the shell is at a distance of ~200 AU (or about 5 times the distance of pluto from the sun, or about 28 light-hours). This is twice the size of the Solar System.

 

[Werner]

Oops, made an error up thread; I used radii instead of diameters.

The 100 diameter limit of the shell is at a distance of ~200 AU (or about 5 times the distance of pluto from the sun, or about 28 light-hours). This is twice the size of the Solar System.

I take the 100 diameter limit as a rule of thumb as the mass of the Dyson Sphere has the mass of Jupiter. If you took the mass of the Sun and the Dyson Sphere and compressed it until it had the density of the Earth, what diameter would that be? The Sun has 1000 times the mass of Jupiter and Jupiter has 318 times the mass of the Earth. I recall that the Sun has 333,000 Earth masses. Take the cube root of that number and multiply it by 12,800 km and multiply that by 100 and that is the Jump Limit I'm going with.

For the Sun I get a Jump limit of 88,720,000 km. If there was nothing around the Sun, that would be its Jump Limit, since there is, for the sake of argument lets place the jump limit at twice the radius of the Dyson Sphere or 2 AU. So whatever is greater, in this case that would be 2 au from the center of the star.

 

[Werner]

Yes, but that "temporary" might last 100's-1000's of years on the astronomical timescale, depending on the relative velocity. Remember, a 200 AU Jump-shadow is twice the the size of the entire solar system (out to twice the distance of the Kuiper Belt (it is in fact twice the distance of Sol's termination-shock/heliopause)).

CORRECT. But you would also need to construct equatorial walls on the inside along either side of the equator out to some distance to keep the atmosphere contained (if it has one), similar to a ringworld. Otherwise the gas pressure will cause it to seep into the black uninhabited areas and eventually bleed off into the shell interior as it encounters ever lower centrifuge gravity as it spreads out into lower/higher latitudes.

actually you don't the Dyson sphere itself will act as the atmospheric wall. As you move away from the equator the atmosphere gets thinner. It starts out as Standard and as you move away from the equator it transitions to Thin. According to Traveller definitions a Thin atmosphere is still breathable, so the edge of the habitable zone is where the atmosphere transitions from Thin to Very Thin. A Very Thin atmosphere is not breathable by humans, on Earth that is about the height of Mount Everest or about 8 km. What walls would do is hold back atmosphere from falling back to the equator. The ground further away from the equator would have a slope and would need walls about 100 km high to create additional habitable zones beyond the equatorial one. As you move further away from the equator the slope gets steeper and the habitable zones get narrower until it doesn't make sense to build these walls any more.

I get a central band 94,250 km wide, the atmosphere is Standard in the center and Thin towards the edges. At the edge a wall is built to hold back as atmosphere from the central region. We can probably build an area as wide as Niven's ringworld with either a lot of walls or flattening the bottom so it is a ringworld built into the Dyson Sphere.

 

[Werner]

The way I'm going with this right now, my Dyson sphere will have an equatorial band the size of Larry Niven's ringworld, but instead of two walls to hold in the atmosphere, the north and south edges of the ringworld will join with the gently sloping surface of the Dyson Sphere, to do this the radius of the Dyson sphere will have to be slightly larger than the radius of the ringworld, and we cutoff the continued curve of the Dyson sphere which would occur under the surface of the ringworld where it to be an actual sphere.

So basically this Dyson Sphere consists of three sections the North Endcap, the Ringworld Equatorial section, and the South Endcap. The landscape continues beyond the edges of the ringworld section starting with a slightly sloped landscape which may not be perceptible to the human eye, as one moves further away from the ringworld section your altitude gets higher and the atmosphere gets thinner. In Traveller terms the entire ringworld section at sea level has a Standard Atmosphere, moving further north and South from they, the atmosphere changes from Standard to Thin (but still breathable by humans) and going further it transitions from Thin to Very Thin, and then from Very Thin to Trace, and then from Trace to Vacuum.

To get an idea of how much of the Dyson Sphere the Ringworld section will take up, I am going with the Larry Niven assumption that the ringworld will be one million miles wide, since Traveller strives to use the metric system, we'll call this 1,600,000 kilometers, we'll also define 1 AU as 150,000,000 kilometers and set the ringworld radius to that number. If you draw a line from the center of the Sun to the center of the ringworld, and if you draw another line from the center of the Sun to the northern edge of the ringworld, that will make an angle, the surface of the ringworld forms the back end of a triangle, the hypotenuse of this right triangle formed is the radius of the Dyson Sphere built around this ringworld. The back end of this triangle is the Sine of the angle, the radius of the ringworld is the Cosine of the angle. So let's get the radius of the Dyson Sphere by using Pythagorean's Theorem a^2 + b^2 = c^2.

a = 150,000,000 km.
b = 800,000 km. (Half the width of the ringworld.)

a^2 = 2.25 × 10^16
b^2 = 6.4 × 10^11

Add these two numbers together and take the square root and we have
c = 150,002,133.318 km.
By taking the inverse cosine of the radio of the ringworld radius to the Dyson sphere radius, we get the latitude on the Dyson Sphere where the ringworld meets it, and that is 0.306° north and south, this is also the slope at which the Dyson sphere surface meets the ringworld surface. Rivers and streams will flow downhill from the dyson sphere surface to the ringworld surface.

For every kilometer one travels away from the ringworld proper one will travel 5.34 meters up in altitude since the breathable atmosphere has a height of 8000 meter, 8000/5.34 = 1498 km, which is how much further you can travel before you run out of breathable air. The atmosphere itself tops out at 100,000/5.34 = 18,727 km beyond the ringworld surface, beyond which you might as well call a vacuum, it is at 18,727 km beyond the ringworld surface that the black solar panels begin. An astronaut can walk in a vacc suit from the ringworld edge to the Solar panels and at a rate of 9 meters per combat round (6 seconds) it will take him 18,727,000m/90m = 208,078 minutes to do so or 144.5 days on foot.

 

[whulorigan]

Good write up.

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... a slightly sloped landscape which may not be perceptible to the human eye,...

I would say there would definitely be NO perception of curvature on the human scale standing on the inside surface (much Ringworld artwork notwithstanding). It would look like an effectively "infinite plane" that fades into haziness (atmospheric absorption of light) at a distance much farther than the perceived distance of the Earth's horizon to an observer standing on Earth.
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[FONT=arial,helvetica]In fact, a starship maintaining position exterior to and above the sphere at what would normally be considered an "orbital altitude" for a planetary body would effectively perceive an immense plane as well (with a horizon VERY far away), even in vacuum.
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[whartung]

If the ship's jump-line directly intersected the 100 diameter limit of the shell, it would cause the ship to precipitate out of jump at the 100 diameter limit of the shell after 1 week in jump. This would be at a distance of ~200 AU (or about 5 times the distance of pluto from the sun, or about 28 light-hours).

I was envisioning a collection of derelict space craft caught out of jump with no place to go until they simply ran out of resources and died in space.

 

[whulorigan]

I was envisioning a collection of derelict space craft caught out of jump with no place to go until they simply ran out of resources and died in space.

A very real possibility, as the construction of a sphereworld likely was accomplised by the "dismantling" of the other planetary bodies in the system for raw materials/resources. It would almost demand that the unfortunates abord the "misjumped" ships find a way into the interior of the sphere if for no other reason than to find an adaptable fuel source and possibly provisions in order to survive.

 

[Werner]

You can detect it gravitationally as it's gravity will affect the path of your starship and it will block part of the Stanfield. At 200 au, if it was 2 au in diameter it will have about the same angular size as the Sun does from Earth.
I would go with a 1 diameter jump limit, as mass wise the Dyson has only about one thousandth the mass of our Sun, so the jump limit has something to do with gravitational mass and the 100 diameter limit is only an approximation for planet like bodies, not hollow spheres, black holes, white dwarfs, or neutron stars.

 

[whulorigan]

... the jump limit has something to do with gravitational mass and the 100 diameter limit is only an approximation for planet like bodies, not hollow spheres, black holes, white dwarfs, or neutron stars.

In principle I agree with you, and I would personally house-rule a different formulation than the 100-diameter limit rule-of-thumb for bodies such as you describe^*, but RAW (especially T5) bases everything off of displacement, including other starships 100 "diameter" sphere blocking a smaller jumping ship's jumpline (or suffering a mishap if it tries to jump from within the 100 diameter sphere of the larger vessel), and/or a jumping ship damaging smaller objects/vessels withn the 100 "diameter" sphere of the jumping ship.

^* I would use either a modified/extrapolated formulation of the hyperspace limits from the Ringworld Companion, or alternately use the tidal force model detailed by Hemdian that I mentioned in a previous thread.

​

 

[Werner]

One could use the thickness of a Dyson Sphere's shell as its Diameter, so if the shell is 3 meters thick then the Jump limit would be at 300 meters, and by the way have a rule that incoming emerge from jump space so they have sufficient time to slow down so the don't crash or otherwise match the rotational velocity of the sphere at its equator so the don't crash. The shell can take the impact energy, but not the starship. If you want to jump away from the Dyson sphere, you only have to travel 300 meters away from the hull on the outside of the sphere.

Another weird possibility is the put the entire Dyson sphere, star and everything in Jump Space itself, its not going anywhere, it just sits in jump space and disrupts all jump traffic within 6 hexes of itself. Mark a spot on the map and draw a six hex radius from that hex on the map. Now if you have a jump-2 starship for example and you are 8 hexes away from the Dyson Sphere's location in jumps space, you jump two hexes toward that location, you ship emerges within that pocket of normal space within jump space that contains the Dyson sphere, from there you can jump to any spot within the sphere's 6 hex jump radius plus your ship's jump radius. The Dyson sphere is using the solar energy from its star to maintain a jump bubble around itself. Anyone who jumps from within the sphere's jump radius jumps to it, it takes a second jump to go somewhere else besides the Dyson sphere. No calculations are needed to make that first jump, even a misjump will take you there, this makes travel between anywhere within the Dyson's sphere of influence just two jumps away regardless of jump rating, the first jump is to the Dyson sphere and it is only from that Dyson sphere that you can jump to somewhere else.

Oh by the way I forgot to mention, that first jump doesn't take anytime at all, the moment you make that first jump your starship is within the Dyson sphere jump bubble, travel to it is instantaneous, travel from it takes a week like all normal jumps, a Jump-1's worth of fuel is consumed to get to the sphere and another Jump-1's of fuel is required to jump away again.

 

[Adam Dray]

I interpret the 100-diameter limit as a nod to either gravitational frame dragging or static mass increase due to general relativity.

In the case of frame dragging, a starship in the vicinity of a larger, spinning object experiences small torsional gravity forces from the spinning object. These could throw off very sensitive jump-drive components.

In the case of static mass increase, a starship gains inertia while in the vicinity of a larger object. The change is very, very small -- even hard to measure -- so it's hard to believe that it'd throw off a jump drive, but maybe it's that sensitive of an operation.

Both of these effects are tiny. Furthermore, there is no gravitational formula applying to an object in space that cares about the diameter of the star or planet (all roughly spherical masses can be reduced to a point mass).

Rationalizing the 100-diameter rules with real-universe physics in going to require a lot of handwaving. A real jump-distance formula would need to be calculated based on the mass of the nearby object, not its diameter.

Compare the Earth (~13000 km diameter, ~6e24 kg) to Uranus (~51000 km diameter, ~87e24 kg). That is, Uranus' diameter is 4 times that of Earth, but its mass is 14.5 times larger.

 

[Werner]

I interpret the 100-diameter limit as a nod to either gravitational frame dragging or static mass increase due to general relativity.

In the case of frame dragging, a starship in the vicinity of a larger, spinning object experiences small torsional gravity forces from the spinning object. These could throw off very sensitive jump-drive components.

In the case of static mass increase, a starship gains inertia while in the vicinity of a larger object. The change is very, very small -- even hard to measure -- so it's hard to believe that it'd throw off a jump drive, but maybe it's that sensitive of an operation.

Both of these effects are tiny. Furthermore, there is no gravitational formula applying to an object in space that cares about the diameter of the star or planet (all roughly spherical masses can be reduced to a point mass).

Rationalizing the 100-diameter rules with real-universe physics in going to require a lot of handwaving. A real jump-distance formula would need to be calculated based on the mass of the nearby object, not its diameter.

Compare the Earth (~13000 km diameter, ~6e24 kg) to Uranus (~51000 km diameter, ~87e24 kg). That is, Uranus' diameter is 4 times that of Earth, but its mass is 14.5 times larger.

It should only apply to planets with the density of Earth. For other objects compare their mass to Earth find its mass in Earth masses then take the cube root of that number and multiply by 100 times Earth's diameter and that is you jump distance, and it shouldn't matter whether that object is a black hole or a red supergiant like Betelgeuse I think for Betelgeuse, its jump limit would be inside the star, so we'll go with 1 Betelgeuse diameter from the star's center just to stay clear of that star.

 

[BackworldTraveller]

A lot of this is based on the Jump Drive theory of 100D being wrong...but what if it is right?

If that is the case then:
a) 100D is defined from the optical surface of a star or planet.
b) There is a direct relationship between that optical surface and the topography of jump-space

Additionally
1) At 100D, a jump bubble of an arriving ship pops and the ship arrives
2) From inside 100D, the jump bubble of a departing ship is hard to control.

So, in jump space a ships jump-bubble acts in a way that it has the momentum-equivalent that can reach 100D up the slope of the body and no further - but if starting from inside it is ejected in a potentially unpredicted manner with direct effects on distance travelled.

This has some side effects.
i) The distance of the optical surface of a star varies. Stellar surfaces may vary because of the type of star, but even the most "stable" star has peaks and prominences. And Flares and CMEs can be optically opaque at quite large distances from the normal surface.
ii) Is a Dyson sphere enclosing a jump-space volume (in which case the entire shell is the surface and the limit is a long way out) or is the surface not enclosing the jump-space volume (in which case there is no issue with appearing inside the shell providing you are outside the star's limit and outside 100xshell thickness). Even a relatively small hole may change the topography provided it is greater than 100xthe tangential thickness of the sphere.
iii) Either (a) The event-horizon is an optical surface: Just not for the same reasons as for stars and planets or (b) it isn't: and black holes become real dangers in jump-space.

 

[Werner]

I like to keep it reasonable I use either the gravitational rule or the optical surface rule, which ever is greater. So a ship never appears at 100 times the swartzchilde radius of a black hole. It mass shadow is many times bigger than that, so we pretend it is a an Earth density planet of the same mass as that black hole and that determines the jump limit, and hint it's a good safe distance from the event horizon of that black hole, for things like Betelgeuse we put the jump limit at twice the optical surface radius of that star so a Starship never appears inside that star when coming out of jump space, this double rule can handle all sorts of objects from stars, to planets, to white dwarfs, and hollow spheres.

 

[BackworldTraveller]

... and hint it's a good safe distance from the event horizon of that black hole...

Hmmm - Safe! Is this a definition of Safe I was previously unaware of? 250,000G (assuming a mass of M(sol)) is be a bit steep for most ACS group ships.

 

[Werner]

Hmmm - Safe! Is this a definition of Safe I was previously unaware of? 250,000G (assuming a mass of M(sol)) is be a bit steep for most ACS group ships.

Only for the purpose of calculating the jump radius, we don't actually compress the star. The Jump limit for the Sun for instance is 89 million kilometers, inside the orbit of Venus but it blocks direct jumps to Mercury, you jump in at the jump limit of Sol and you have some distance to travel before getting to Mercury. That means if you are at a white dwarf planet where the white dwarf has the mass of Sol, but who's habitable zone is much closer in than Sol's, there would be no quick getaways should the PCs get in some sort of trouble.

The typical habitable zone of a white dwarf is a few million kilometers out, but you'd have to travel tens of millions of kilometers to the star's jump-line before you can jump your starship to safety.