Star Hero vs. Physics

[PaycheckHero]

I picked up Star Hero this morning for some idle reading and found another elementary physics error (besides the incorrect centrifugal correction to effective surface gravity already discussed): p128 says that a Dyson sphere is stable. In fact, it is unstable in precisely the same way and for precisely the same reason a ringworld is. Possibly worth noting if you're running a hard-SF game.

 

SH needed better science editing. :-(

[dmjalund]

Also Dyson Spheres need artificial gravity to work, whereas Ringworlds could theoretically work without it

[Xavier Onassiss]

The thing is, there are different types of Dyson spheres, and Dyson's original concept didn't have the instability problem, or need anti-gravity to work. It's been bastardized into something ridiculous in many a science fiction tale.

 

A Dyson sphere is a hypothetical megastructure originally described by Freeman Dyson. Such a "sphere" would be a system of orbiting solar-power satellites meant to completely encompass a star and capture most or all of its energy output. Dyson speculated that such structures would be the logical consequence of the long-term survival and escalating energy needs of a technological civilization, and proposed that searching for evidence of the existence of such structures might lead to the detection of advanced intelligent extraterrestrial life. Since then, other variant designs involving building an artificial structure or series of structures to encompass a star have been proposed in exploratory engineering or described in science fiction under the name "Dyson sphere". These later proposals have not been limited to solar-power stations. Many involve habitation or industrial elements. Most fictional depictions describe a solid shell of matter enclosing a star, which is considered the least plausible variant of the idea (see below). In May 2013, at the Starship Century Symposium in San Diego, Freeman Dyson repeated his comments that he wished the concept had not been named after him.^[1]

 

[Tasha]

I think we can thanks Niven for the Solid Shell Dyson Sphere. He mentioned it in the Ringworld novel in passing. Heck, even a ringworld would have real problem with stability in the long run.

[Captain Obvious]

That's why Niven had to build his Ringworld out of unobtanium. Normal materials wouldn't cut it.

[Old Man]

That's why Niven had to build his Ringworld out of unobtanium. Normal materials wouldn't cut it.

You mean cardboard won't work? Dammit! Now I have to start all over!

[NuSoardGraphite]

Not to mention the absolute pummeling such a structure would receive from stellar debris. However I would think that if you want to run a game that has such a structure, the society that built it has solved any of the supposed difficulties that would be inherent in the structures design. I would never call a SF game or fiction that includes a ringworld or Dyson Sphere "Hard" scifi. (I'm not much for hard scifi anyway. I'm a Space Opera guy. I want to let my imagination run wild. Currently known physics is far too limiting a factor to adhere very closely to for me to be satisfied with the end result)

[Vanguard]

Not to mention the absolute pummeling such a structure would receive from stellar debris. However I would think that if you want to run a game that has such a structure, the society that built it has solved any of the supposed difficulties that would be inherent in the structures design. I would never call a SF game or fiction that includes a ringworld or Dyson Sphere "Hard" scifi. (I'm not much for hard scifi anyway. I'm a Space Opera guy. I want to let my imagination run wild. Currently known physics is far too limiting a factor to adhere very closely to for me to be satisfied with the end result)

I only wish I could "like" this post more than once because you've pretty much hit it in one.

[Xavier Onassiss]

I think we can thanks Niven for the Solid Shell Dyson Sphere. He mentioned it in the Ringworld novel in passing. Heck' date=' even a ringworld would have real problem with stability in the long run.[/quote']

 

 

 

IIRC, after the first Ringworld novel, his fans pointed out the instability problem, and he addressed it in the sequel; the Ringworld had attitude jets to keep it in place. They had stopped working because some of the Ringworld's inhabitants cannibalized parts from them to make bussard ramjet type starships.

 

 

[Xavier Onassiss]

Not to mention the absolute pummeling such a structure would receive from stellar debris. However I would think that if you want to run a game that has such a structure, the society that built it has solved any of the supposed difficulties that would be inherent in the structures design. I would never call a SF game or fiction that includes a ringworld or Dyson Sphere "Hard" scifi. (I'm not much for hard scifi anyway. I'm a Space Opera guy. I want to let my imagination run wild. Currently known physics is far too limiting a factor to adhere very closely to for me to be satisfied with the end result)

This was another issue Niven addressed. IIRC, in the first novel, the biggest landmarks the characters saw were two huge meteor punctures. ("Fist of God" mountain and the "Eye Storm.") Also, the Ringworld had an automatic defense mechanism (which obviously wasn't perfect) against debris impacts, and it shot down their ship as soon as their course intersected the surface of the Ringworld.

[Old Man]

Not to mention the absolute pummeling such a structure would receive from stellar debris. However I would think that if you want to run a game that has such a structure, the society that built it has solved any of the supposed difficulties that would be inherent in the structures design. I would never call a SF game or fiction that includes a ringworld or Dyson Sphere "Hard" scifi. (I'm not much for hard scifi anyway. I'm a Space Opera guy. I want to let my imagination run wild. Currently known physics is far too limiting a factor to adhere very closely to for me to be satisfied with the end result)

Shot it down so that it... crashed onto the Ringworld, I take it?

[Christopher]

Some fundamental correction regarding "Dyson Sphere": Never at any point has Freeman Dyson proposed a Spherical Body around a Star.

The Dyson Sphere was a development of the Star Trek TNG Authors.

 

What Dyson described was a Dyson Swarm:

http://en.wikipedia.org/wiki/Dyson_sphere#Dyson_swarm

 

And afaik he thought it up after Niven decribed his Ringworld.

 

If you have a dyson sphere, instbailiy is the least of your physics problems:

Such a shell would have no net gravitational interaction with its englobed star (see shell theorem), and could drift in relation to the central star. If such movements went uncorrected, they could eventually result in a collision between the sphere and the star—most likely with disastrous results. Such structures would need either some form of propulsion to counteract any drift, or some way to repel the surface of the sphere away from the star.^[9] For the same reason, such a shell would have no net gravitational interaction with anything else inside it. The contents of any biosphere placed on the inner surface of a Dyson shell would not be attracted to the sphere's surface and would simply fall into the star. It has been proposed that a biosphere could be contained between two concentric spheres, placed on the interior of a rotating sphere (in which case, the force of artificial "gravity" is perpendicular to the axis of rotation, causing all matter placed on the interior of the sphere to pool around the equator, effectively rendering the sphere a Niven ring for purposes of habitation, but still fully effective as a radiant-energy collector) or placed on the outside of the sphere where it would be held in place by the star's gravity.^[17][18] In such cases, some form of illumination would have to be devised, or the sphere made at least partly transparent, as the star's light would otherwise be completely hidden.^[19]

If assuming a radius of one AU, then the compressive strength of the material forming the sphere would have to be immense to prevent implosion due to the star's gravity. Any arbitrarily selected point on the surface of the sphere can be viewed as being under the pressure of the base of a dome 1 AU in height under the Sun's gravity at that distance. Indeed it can be viewed as being at the base of an infinite number of arbitrarily selected domes, but as much of the force from any one arbitrary dome is counteracted by those of another, the net force on that point is immense, but finite. No known or theorized material is strong enough to withstand this pressure, and form a rigid, static sphere around a star.^[20] It has been proposed by Paul Birch (in relation to smaller "Supra-Jupiter" constructions around a large planet rather than a star) that it may be possible to support a Dyson shell by dynamic means similar to those used in a space fountain.^[21] Masses travelling in circular tracks on the inside of the sphere, at velocities significantly greater than orbital velocity, would press outwards on magnetic bearings due to centrifugal force. For a Dyson shell of 1-AU radius around a star with the same mass as the Sun, a mass travelling ten times the orbital velocity (297.9 km/s) would support 99 (a=v²/r) times its own mass in additional shell structure.

Also if assuming a radius of one AU, then there may not be sufficient building material in the Solar System to construct a Dyson shell. Anders Sandberg estimates that there is 1.82×10²⁶ kg of easily usable building material in the Solar System, enough for a 1-AU shell with a mass of 600 kg/m²—about 8–20 cm thick on average, depending on the density of the material. This includes the hard-to-access cores of the gas giants; the inner planets alone provide only 11.79×10²⁴ kg, enough for a 1-AU shell with a mass of just 42 kg/m².^[10]

The shell would be vulnerable to impacts from interstellar bodies, such as comets, meteoroids, and material in interstellar space that is currently being deflected by the Sun's bow shock. The heliosphere, and any protection it theoretically provides, would cease to exist.

I think some scientist once said:

If you can builda dyson sphere to collect all the energy output of a star, you don't need to collect all the energy output of a star. Because you already have powersouces beyond that and what you gain is compenstated by what is need to create artificial gravity (for inside habitation) or artifical lightning (for outside habitation.

 

[Tasha]

Actually Niven mentions a Solid Sphere Dyson Sphere in Ringworld. TNG got their idea from HIM.

Dyson's Dyson Sphere is what people are now calling a Dyson Swarm. It's actually something that shouldn't be hard to start out with. You can also tie Computing resources to the Swarm bits. Which can also move us toward building a High level Computing Mega Structure.

[Gary Miles]

Some fundamental correction regarding "Dyson Sphere": Never at any point has Freeman Dyson proposed a Spherical Body around a Star.

The Dyson Sphere was a development of the Star Trek TNG Authors.

 

Um, no. The Dyson sphere idea (a fully-enclosed sphere) was around YEARS before TNG.

[sinanju]

 

IIRC, after the first Ringworld novel, his fans pointed out the instability problem, and he addressed it in the sequel; the Ringworld had attitude jets to keep it in place. They had stopped working because some of the Ringworld's inhabitants cannibalized parts from them to make bussard ramjet type starships.

 

 

Which, sadly, means that the excuse for the first error is an error. Last I heard, the Bussard ramjet idea is dead. The interstellar medium (hydrogen gas) is too thin to support the "electromagnetic ramscoop fusing hydrogen for fuel" concept. I am disappointed.

[sinanju]

Shot it down so that it... crashed onto the Ringworld, I take it?

 

Well, yeah...but they were in a puppeteer-built indestructible hull WITH a stasis field for backup. Any normal vessel (and certainly any ordinary asteroid) would have been vaporized when it was hit by the mile-wide solar-pumped X-ray laser "meteor defense".

[Michael Hopcroft]

Some "big dumb objects" fall apart mentally when you think too heard about them. Which is why you should think twice before you go around slaughtering catgirls right and left.

 

Of course, in-game when you have something like that the big question is not so much how they work (which the PCs will never really fathom anyway and can be safely handwaved away in play, though you can always discuss it over the after-game pizza if the players are that interested) but why they're there and what their being there means for the PCs. Why do you need the entire energy output of your star? That is a question that, depending on your answer, might well prove very involving for the PCs.

 

And, of course, what happens when the people who built the Big Dumb Object aren't around anymore to maintain and  update their creation? No system can maintain itself forever. Perhaps the PCs arrive at a time when the survival of the trillions who live in the structure are endangered by the systems starting to fail or go haywire.

 

And of course if one can only get it out, ubertech devices are worth a lot of money to the right people. A lot of money....

[Zeropoint]

Some "big dumb objects" fall apart mentally when you think too hard about them. Which is why you should think twice before you go around slaughtering catgirls right and left.

 

I'll be happy to provide a home to any threatened catgirls out there.