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Suppose we build a parabola made of stationary Solar sails on one side of a star to focus the stars light like a searchlight? We would just have to position the solar sails so the star is the focus of the parabola, it would reflect off the solar sails and turn diverging starlight into parallel star light. the only problem mathematically I the star is a ball, not a point of light, so the rays reflected wouldn't be quite parallel, but would continue for quite some distance. So basically what it is half a Dyson Sphere except not half a sphere but a parabolic mirror made out od solar sails. If we were to do this our own Sun, we would perhaps want to place the closest part of the mirror at 2 AU, so it doesn't interfere with the inner planets. What could it b used for. For accelerating Solar sails a much further distance, and perhaps illuminating distant planets in that direction, another parabolic mirror would intercept the sunlight and focus in on a distant planet to warm it up. or what else? You can focus half the Sun's energy to do something, like maybe produce antimatter in bulk quantities and a safe distance from inhabited planets, maybe create a mini black hole for a black hole drive.
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Tom Kalbfus,
A lampshade for the sun?
1. Most of the light will fall back on the Sun increasing its surface temperature. Effects? I guess it will puff, as well as the "eye" will turn bluer.
2. The system Sun-Lampshade will experience vector thrust. Either the sunshade will be lifted upper or entirely cast away, OR given "hydraulic" stability point, it will turn into massive photon rocket engine with power of
384.6 YW – astro: luminosity of the Sun
.
Given Sun's mass, power, SI of photon rocketry ... what acceleration it'll have? The whole Solar system almost undisturbed gravitationally, shall be dragged along together.
3. The lampshade could be supra-solar habitats.
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The solar sails have to be weighted so that photon pressure = gravitational attraction. I suspect the acceleration of the entire system will be slight, but if aimed at Alpha Centauri, you could use solar sails much further out.
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For a SETI type exercise it could be used as a giant signalling beacon... you would want a set of sails on the other side set up as a Fresnel. You could blink like a lighthouse in a number of interesting directions.
Come on to the Future
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The acceleration of the system would be 6.4e-13 m/s^2, which assuming you wanted to decelerate when you got there, would get you to Alpha Centauri in "just" 31 million years. On the other hand, if you hook Saturn into it, you can get there in only about 10,000 years, though admittedly how you would slow down for the second half of the trip I'm not quite sure.
-Josh
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The acceleration of the system would be 6.4e-13 m/s^2, which assuming you wanted to decelerate when you got there, would get you to Alpha Centauri in "just" 31 million years. On the other hand, if you hook Saturn into it, you can get there in only about 10,000 years, though admittedly how you would slow down for the second half of the trip I'm not quite sure.
Moving a system around could be useful What if you moved Sol towards Alpha Centauri and 31 million years later you get the Sun to make a close flyby of Alpha Centauri B, exchanging momentum with it casting out Alpha Centauri B and replacing it with our Sun, that way you have a binary System with two G2 V class stars as neither star will have aged substantially in only 35 million years. You would want to do the flyby in such a way that the mutual orbit ends up being roughly circular, which would be more useful in having both starts with habitable planets. Another useful thing, put a Solar Sail on one side of a red giant like Betelgeuse, and since that star shines more greatly when compared to its mass, you could try moving it a safe distance before it goes supernova Large stars radiate more relative to their mass than small stars, you can achieve greater acceleration with them. I wonder what happens if you collide Betelgeuse with another star, say for instance a red or orange dwarf, make sure the smaller star hits a bullseye that is it collides with Betelgeuse's core as it punches through the bigger star's outer layers. A stellar collision like that can rejuvenate Betelgeuse and delay its supernova explosion, by forcing some hydrogen into its core where otherwise there isn't any convection, the hydrogen gets used up and the core will implode into a neutron star otherwise, unless of course another star hits it! the force of the impact will basically turn Betelgeuse inside out and rejuvenate it, making it last longer!
Last edited by Tom Kalbfus (2014-06-17 22:31:37)
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I myself tend to wonder if there is a way to "stir" stars, so to speak, so that they can use the Hydrogen in their outer layers in their core. I also wonder how useful these kinds of mirrors might be in turning objects into stars that might not be otherwise, by heating them up; If the heat loss from a brown dwarf, for example, were to be reduced to 1/10 of its natural value at the right time in the stellar evolution cycle, it might become hot enough for fusion to begin and in that way it might develop into a real star. Perhaps by focusing large amounts of the Sun's light onto a small area of the Sun's surface, it would be possible to create a spot of intense heat, causing local fusion, or deuterium production, or who-knows-what!
-Josh
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I've seen the suggestion that Sol could be replaced when it reaches it's red giant stage, though it would require quite a long lead time (but for a civilisation that's already billions of years old, a few hundred million might not be such a big deal) to get a suitable star to steal away the planets. But if we make sure Sol is well mixed, we have ~100 billion years before that's a worry...
"I'm gonna die surrounded by the biggest idiots in the galaxy." - If this forum was a Mars Colony
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I myself tend to wonder if there is a way to "stir" stars, so to speak, so that they can use the Hydrogen in their outer layers in their core. I also wonder how useful these kinds of mirrors might be in turning objects into stars that might not be otherwise, by heating them up; If the heat loss from a brown dwarf, for example, were to be reduced to 1/10 of its natural value at the right time in the stellar evolution cycle, it might become hot enough for fusion to begin and in that way it might develop into a real star. Perhaps by focusing large amounts of the Sun's light onto a small area of the Sun's surface, it would be possible to create a spot of intense heat, causing local fusion, or deuterium production, or who-knows-what!
Well, beaming Sun's radiation back to it... Increasing the upper layers temperature will decrease the pressure of the core and the Sun will start burning SLOWLIER, won't it?
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I've seen the suggestion that Sol could be replaced when it reaches it's red giant stage, though it would require quite a long lead time (but for a civilisation that's already billions of years old, a few hundred million might not be such a big deal) to get a suitable star to steal away the planets. But if we make sure Sol is well mixed, we have ~100 billion years before that's a worry...
What if we steered the Sun onto a head on Collision with Proxima Centauri or some other star just like it? Proxima would add its mass to the Sun, probably some of the Sun would splash outward in the process, probably enough to make new planets out of, displacing the core of the Sun and forming a new one, the Sun would end up with more mass, but would have its clock set back, we can probably get more than 5 billion years more out of this deal. the question is what would happen to the planets of the Solar System and the Proxima planets in this deal? Probably the orbits of the planets will have to be adjusted as well, the Sun might get dimmer if its clock is reset, or perhaps the extra mass will compensates for its youth.
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Actually, it would burn faster, and you'd end up reducing it's lifespan...
"I'm gonna die surrounded by the biggest idiots in the galaxy." - If this forum was a Mars Colony
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But its life span would start at zero since it would have a new core, so it would have a shortend lifespan from beginning to end on top of the life span of the original star. This for example if we has the Sun with its 10 billion lifespan half over and we collided it with Proxima Centauri and the added mass gave it a 9 billion year lifespan, we'd have 5 billion years + 9 billion years equal to 14 billion years of total lifespan, that is an improvement over the original 10 billion years it originally was going to last. and as that 14 billion year lifespan come to an end, we could hit it with another star giving it perhaps 8 billion more years to last, that is what I was thinking.
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But its life span would start at zero since it would have a new core, so it would have a shortend lifespan from beginning to end on top of the life span of the original star. This for example if we has the Sun with its 10 billion lifespan half over and we collided it with Proxima Centauri and the added mass gave it a 9 billion year lifespan, we'd have 5 billion years + 9 billion years equal to 14 billion years of total lifespan, that is an improvement over the original 10 billion years it originally was going to last. and as that 14 billion year lifespan come to an end, we could hit it with another star giving it perhaps 8 billion more years to last, that is what I was thinking.
No! Stellar lifespan is function of mass only.
http://astronomy.swin.edu.au/cosmos/M/M … e+Lifetime
Proxima is small. It would ass only 12% mass into the Sun, but this will shorten the life of the resulting out of the merger ( do it gentle to not splash out too much ) star with 25% down to remaining 4b yrs?
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http://nextbigfuture.com/2014/07/gregor … gfuture%29
==============
JULY 07, 2014
Gregory Benford and Larry Niven solved the problems with Shkavdov thrusters for a propulsion system for moving stars
Gregory Benford and Larry Niven have created as a ‘modified’ Shkadov Thruster for a propulsion scheme capable of moving stars.
Information from Centauri Dreams
Gregory Benford describes his modified Shkadov thruster.
Shipstars engines are Smart Objects–statically unstable but dynamically stable, as we are when we walk. We fall forward on one leg, then catch ourselves with the other. That takes a lot of fast signal processing and coordination. (We’re the only large animal without a tail that’s mastered this. Two legs are dangerous without a big brain or a stabilizing tail.) There’ve been several Big Dumb Objects in sf, but as far as I know, no smart ones. Our Big Smart Object is larger than Ringworld and is going somewhere, using an entire star as its engine.
Our Bowl is a shell more than a hundred million miles across, held to a star by gravity and some electrodynamic forces. The star produces a long jet of hot gas, which is magnetically confined so well it spears through a hole at the crown of the cup-shaped shell. This jet propels the entire system forward – literally, a star turned into the engine of a “ship” that is the shell, the Bowl. On the shell’s inner face, a sprawling civilization dwells. The novel’s structure doesn’t resemble Larry’s Ringworld much because the big problem is dealing with the natives.
The virtue of any Big Object, whether Dumb or Smart, is energy and space. The collected solar energy is immense, and the living space lies beyond comprehension except in numerical terms. While we were planning this, my friend Freeman Dyson remarked, “I like to use a figure of demerit for habitats, namely the ratio R of total mass to the supply of available energy. The bigger R is, the poorer the habitat. If we calculate R for the Earth, using total incident sunlight as the available energy, the result is about 12 000 tons per Watt. If we calculate R for a cometary object with optical concentrators, travelling anywhere in the galaxy where a 0 magnitude star is visible, the result is 100 tons per Watt. A cometary object, almost anywhere in the galaxy, is 120 times better than planet Earth as a home for life. The basic problem with planets is that they have too little area and too much mass. Life needs area, not only to collect incident energy but also to dispose of waste heat. In the long run, life will spread to the places where mass can be used most efficiently, far away from planets, to comet clouds or to dust clouds not too far from a friendly star. If the friendly star happens to be our Sun, we have a chance to detect any wandering life-form that may have settled here.”
This insight helped me [Gregory Benford] think through the Bowl, which has an R of about 10-10!
Image: Artwork by Don Davis, as are all the images in this article.
Stability
Shdakov thrusters aren’t stable. They are not statites, Bob Forward’s invention, because they’re not in orbit. Push them, as the actual photon thrust will do, and they’ll fall outward, doomed. So how to build something that harvests a star’s energy to move it and can be stabilized?
I worried this subject, and thought back to the work my brother Jim and I had done on speeding up sails by desorption of a “paint” we could put onto a sail surface, to be blown off by a beam of microwave power striking it. This worked in experiments we did at JPL under a NASA grant, with high efficiency. Basically, throwing mass overboard is better than reflecting sunlight, because photons have very little momentum. The ratio of a photon’s momentum to that of a particle moving at speed V is
(V/c)(2Ep )/EM
where Ep is the photon energy and EM the kinetic energy of the mass M. So if those two energies are the same, the photon has a small fraction of the mass’s momentum, V/c.
Big human built objects, whether pyramids, cathedrals, or skyscrapers, can always be criticized as criminal wastes of a civilization’s resources, particularly when they seem tacky or tasteless. But not if they extend living spaces and semi-natural habitat. This idea goes back to Olaf Stapledon’s Star Maker: “Not only was every solar system now surrounded by a gauze of light traps, which focused the escaping solar energy for intelligent use, so that the whole galaxy was dimmed, but many stars that were not suited to be suns were disintegrated, and rifled of their prodigious stores of sub-atomic energy.”
Creating and steering a giant standing solar flare
The key idea is that a big fraction of the Bowl is mirrored, directing reflected sunlight onto a small spot on the star, the foot of the jet line. From this spot the enhanced sunlight excites a standing “flare” that makes a jet. This jet drives the star forward, pulling the Bowl with it through gravitation.
The jet passes through a Knothole at the “bottom” of the Bowl, out into space, as exhaust. Magnetic fields, entrained on the star surface, wrap around the outgoing jet plasma and confine it, so it does not flare out and paint the interior face of the Bowl — where a whole living ecology thrives, immensely larger than Earth’s area. So it’s a huge moving object, the largest we could envision, since we wanted to write a novel about something beyond Niven’s Ringworld.
For plausible stellar parameters, the jet can drive the system roughly a light year in a few centuries. Slow but inexorable, with steering a delicate problem, the Bowl glides through the interstellar reaches. The star acts as a shield, stopping random iceteroids that may lie in the Bowl’s path. There is friction from the interstellar plasma and dust density acting against the huge solar magnetosphere of the star, essentially a sphere 100 Astronomical Units in radius.
So the jet can be managed to adjust acceleration, if needed. If the jet becomes unstable, the most plausible destructive mode is the kink – a snarling knot in the flow that moves outward. This could lash sideways and hammer the zones near the Knothole with virulent plasma, a dense solar wind. The first mode of defense, if the jet seems to be developing a kink, would be to turn the mirrors aside, not illuminating the jet foot. But that might not be enough to prevent a destructive kink. This has happened in the past, we decided, and lives in Bowl legend
Mechanical Engineering
We supposed the founders made its understory frame with something like scrith–a Ringworld term, greyish translucent material with strength on the order of the nuclear binding energy, stuff from the same level of physics as held Ringworld from flying apart. This stuff is the only outright physical miracle needed to make Ringworld or the Bowl work mechanically. Rendering Ringworld stable is a simple problem—just counteract small sidewise nudges. Making the Bowl work in dynamic terms is far harder; the big problem is the jet and its magnetic fields. This was Benford’s department, since he published many research papers in Astrophysical Journal in the like on jets from the accretion disks around black holes, some of which are far bigger than galaxies. But who manages the jet? And how, since it’s larger than worlds? This is how you get plot moves from the underlying physics.
One way to think of the strength needed to hold the Bowl together is by envisioning what would hold up a tower a hundred thousand kilometers high on Earth. The tallest building we now have is the 829.8 m (2,722 ft) tall Burj Khalifa in Dubai, United Arab Emirates. So for Ringworld or for the Bowl we’re imagining a scrith-like substance 100,000 times stronger than the best steel and carbon composites can do now. Even under static conditions, though, buildings have a tendency to buckle under varying stresses. Really bad weather can blow over very strong buildings. So this is mega-engineering by master engineers indeed. Neutron stars can cope with such stresses, we know, and smart aliens or even ordinary humans might do well too. So: let engineers at Caltech (where Larry was an undergraduate) or Georgia Tech (where Benford nearly went) or MIT (where Benford did a sabbatical) take a crack at it, then wait a century or two—who knows what they might invent? This is a premise and still better, a promise—the essence of modern science fiction.
Our own inner solar system contains enough usable material for a classic Dyson sphere. The planets and vast cold swarms of ice and rock, like our Kuiper Belt and Oort Clouds—all that, orbiting around another star, can plausibly give enough mass to build the Bowl. For alien minds, this could be a beckoning temptation. Put it together from freely orbiting sub-structures, stuck it into bigger masses, use molecular glues. Then stabilizes such sheet masses into plates that can get nudged inward. This lets the builders lock them together into a shell–for example, from spherical triangles. The work of generations, even for beings with very long lifespans. We humans have done such, as seen in Chartres cathedral, the Great Wall, and much else.
Alex Tolley proposed An Alternative Structure – The Solar Pulse Jet without the need for scrith
Here is Alex Tolley thought on avoiding the need for scrith.
The bowl structure becomes a Dyson swarm, each orbiting the star. Some of these objects are habitats, most are solar energy collectors and a few are particle beam generators. The job of the collectors is to accumulate the solar energy needed for the beam pulse. One can think of this as being like the LHC or the NIF laser. When the particle accelerators are in the correct position, the collectors send their energy to them to fire a pulse at the star, creating the mass ejection for thrust. Perhaps those particles could be muons.
Each pulse only happens when the beamers are aligned so that the solar jet is generated when the direction of thrust is correct. Because of the time delay, there should be a gap in the swarm behind the accelerators. All the objects in the swarm must track their distance from the star and use some energy to redirect and accelerate the solar wind to adjust their orbits to track the movement of the star.
Another advantage of the swarm is that the timing of the firing can be adjusted, allowing steering in the orbital plane. For a Dyson swarm, with objects orbiting in different planes, the steering can be in 3 dimensions.
Detecting such objects should be relatively easy. Their spectral signatures will be pushed into the IR, and if their direction of travel is away from us, there should be regular transit intensity peaks (swarm gaps) and even stronger peaks as the star flares. The pattern should be regular over a number of years. and would be expected be more frequent than a nova to maximize thrust.
Such an approach might be less efficient than the bowl, but I think it offers a plausible way to move a sun without invoking massive structures. It will require a technical civilization to allow travel between the habs and to ensure that the many objects in the swarm are kept running correctly.
Gregory Benford likes Alex’s swarm idea, and Eniac’s right that there may be better ways of inducing fusion on the star surface. Benford has worked on relativistic beam dynamics and fusion effects, theory & experiment, and there’s continuing research into how to do that. Not easy, no. Without giving away a plot point, the jet is very intricately run, but not by the Folk of the Bowl. Read SHIPSTAR to see how.
Must admit Benford envisioned the Bowl and chose it over the swarm idea, early in the 2000s, because the Bowl is a striking image of vast potential. A swarm is far more likely, yes. That’s on the of tradeoffs hard sf makes! Fiction is not a grant proposal
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Tom Kalbfus wrote:But its life span would start at zero since it would have a new core, so it would have a shortend lifespan from beginning to end on top of the life span of the original star. This for example if we has the Sun with its 10 billion lifespan half over and we collided it with Proxima Centauri and the added mass gave it a 9 billion year lifespan, we'd have 5 billion years + 9 billion years equal to 14 billion years of total lifespan, that is an improvement over the original 10 billion years it originally was going to last. and as that 14 billion year lifespan come to an end, we could hit it with another star giving it perhaps 8 billion more years to last, that is what I was thinking.
No! Stellar lifespan is function of mass only.
http://astronomy.swin.edu.au/cosmos/M/M … e+Lifetime
Proxima is small. It would ass only 12% mass into the Sun, but this will shorten the life of the resulting out of the merger ( do it gentle to not splash out too much ) star with 25% down to remaining 4b yrs?
My point is whether colliding a star with a star would reset its stellar clock back to zero, abet with a larger mass. If a star has a lifetime of 10 billion years and half of it is used up, that means it has 5 billion years left on its main sequence. Now lets suppose the star is directed to collide with another star using a shipstar swarm, the star is a red dwarf, so it hits the larger star precisely creating shock waves down to the star's core displacing that core and moving it aside and forcing the star to create a new core at its new center of mass using fresh material that is mostly hydrogen, the helium built up in the star's core up to this point is pushed to the side and ends up in the new star's outer layers, while the new core of the star has a fresh supply of hydrogen and it is effectively made young again. The star may retain some of the extra mass from the collision so its main sequence life may be shorter, but it would be shorter starting from zero, not from the previous star's mid point in its life. For example if the new star because of its added mass has a 8 billion year main sequence life starting at age zero, that is more years that the original star had left with its 10 billion year main sequence life half over, so originally it had 5 billion years of main sequence life, now it has 8 billion years of main sequence life starting from stellar age zero, this is 3 billion years more.
I think it would be tempting to build a shipstar around a star like Betelgeuse. The star is near the end of its life, it flares a lot and spews out its atmosphere in addition to putting out a lot of light. What happens with we collide this red supergiant with a red dwarf star of approximately Proxima's mass? We might possibly delay Betelgeuse's upcoming supernova, and that would be a good thing if we wanted to colonize other nearby stars, because we don't want a nearby Betelgeuse going supernova. So if we could set Betelgeuse's clock back to zero, what kind of star would it devolve into? Maybe a Class A or B star. Wikipedia lists its mass as from 5 to 11 solar masses which seems to indicate it would become a type A star if rejuvenated, a white but dimmer star with a stellar main sequence lifetime of around 1 billion years. It would be nice if we could put off Betelgeuse's imminent destruction by one billion years, wouldn't it?
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http://nextbigfuture.com/2014/07/gregor … gfuture%29
==============
JULY 07, 2014
Gregory Benford and Larry Niven solved the problems with Shkavdov thrusters for a propulsion system for moving stars
Gregory Benford and Larry Niven have created as a ‘modified’ Shkadov Thruster for a propulsion scheme capable of moving stars.
Information from Centauri Dreams
Gregory Benford describes his modified Shkadov thruster.
Shipstars engines are Smart Objects–statically unstable but dynamically stable, as we are when we walk. We fall forward on one leg, then catch ourselves with the other. That takes a lot of fast signal processing and coordination. (We’re the only large animal without a tail that’s mastered this. Two legs are dangerous without a big brain or a stabilizing tail.) There’ve been several Big Dumb Objects in sf, but as far as I know, no smart ones. Our Big Smart Object is larger than Ringworld and is going somewhere, using an entire star as its engine.
Our Bowl is a shell more than a hundred million miles across, held to a star by gravity and some electrodynamic forces. The star produces a long jet of hot gas, which is magnetically confined so well it spears through a hole at the crown of the cup-shaped shell. This jet propels the entire system forward – literally, a star turned into the engine of a “ship” that is the shell, the Bowl. On the shell’s inner face, a sprawling civilization dwells. The novel’s structure doesn’t resemble Larry’s Ringworld much because the big problem is dealing with the natives.
The virtue of any Big Object, whether Dumb or Smart, is energy and space. The collected solar energy is immense, and the living space lies beyond comprehension except in numerical terms. While we were planning this, my friend Freeman Dyson remarked, “I like to use a figure of demerit for habitats, namely the ratio R of total mass to the supply of available energy. The bigger R is, the poorer the habitat. If we calculate R for the Earth, using total incident sunlight as the available energy, the result is about 12 000 tons per Watt. If we calculate R for a cometary object with optical concentrators, travelling anywhere in the galaxy where a 0 magnitude star is visible, the result is 100 tons per Watt. A cometary object, almost anywhere in the galaxy, is 120 times better than planet Earth as a home for life. The basic problem with planets is that they have too little area and too much mass. Life needs area, not only to collect incident energy but also to dispose of waste heat. In the long run, life will spread to the places where mass can be used most efficiently, far away from planets, to comet clouds or to dust clouds not too far from a friendly star. If the friendly star happens to be our Sun, we have a chance to detect any wandering life-form that may have settled here.”
This insight helped me [Gregory Benford] think through the Bowl, which has an R of about 10-10!
Image: Artwork by Don Davis, as are all the images in this article.
Stability
Shdakov thrusters aren’t stable. They are not statites, Bob Forward’s invention, because they’re not in orbit. Push them, as the actual photon thrust will do, and they’ll fall outward, doomed. So how to build something that harvests a star’s energy to move it and can be stabilized?
I worried this subject, and thought back to the work my brother Jim and I had done on speeding up sails by desorption of a “paint” we could put onto a sail surface, to be blown off by a beam of microwave power striking it. This worked in experiments we did at JPL under a NASA grant, with high efficiency. Basically, throwing mass overboard is better than reflecting sunlight, because photons have very little momentum. The ratio of a photon’s momentum to that of a particle moving at speed V is
(V/c)(2Ep )/EM
where Ep is the photon energy and EM the kinetic energy of the mass M. So if those two energies are the same, the photon has a small fraction of the mass’s momentum, V/c.
Big human built objects, whether pyramids, cathedrals, or skyscrapers, can always be criticized as criminal wastes of a civilization’s resources, particularly when they seem tacky or tasteless. But not if they extend living spaces and semi-natural habitat. This idea goes back to Olaf Stapledon’s Star Maker: “Not only was every solar system now surrounded by a gauze of light traps, which focused the escaping solar energy for intelligent use, so that the whole galaxy was dimmed, but many stars that were not suited to be suns were disintegrated, and rifled of their prodigious stores of sub-atomic energy.”
Creating and steering a giant standing solar flare
The key idea is that a big fraction of the Bowl is mirrored, directing reflected sunlight onto a small spot on the star, the foot of the jet line. From this spot the enhanced sunlight excites a standing “flare” that makes a jet. This jet drives the star forward, pulling the Bowl with it through gravitation.
The jet passes through a Knothole at the “bottom” of the Bowl, out into space, as exhaust. Magnetic fields, entrained on the star surface, wrap around the outgoing jet plasma and confine it, so it does not flare out and paint the interior face of the Bowl — where a whole living ecology thrives, immensely larger than Earth’s area. So it’s a huge moving object, the largest we could envision, since we wanted to write a novel about something beyond Niven’s Ringworld.
For plausible stellar parameters, the jet can drive the system roughly a light year in a few centuries. Slow but inexorable, with steering a delicate problem, the Bowl glides through the interstellar reaches. The star acts as a shield, stopping random iceteroids that may lie in the Bowl’s path. There is friction from the interstellar plasma and dust density acting against the huge solar magnetosphere of the star, essentially a sphere 100 Astronomical Units in radius.
So the jet can be managed to adjust acceleration, if needed. If the jet becomes unstable, the most plausible destructive mode is the kink – a snarling knot in the flow that moves outward. This could lash sideways and hammer the zones near the Knothole with virulent plasma, a dense solar wind. The first mode of defense, if the jet seems to be developing a kink, would be to turn the mirrors aside, not illuminating the jet foot. But that might not be enough to prevent a destructive kink. This has happened in the past, we decided, and lives in Bowl legend
Mechanical Engineering
We supposed the founders made its understory frame with something like scrith–a Ringworld term, greyish translucent material with strength on the order of the nuclear binding energy, stuff from the same level of physics as held Ringworld from flying apart. This stuff is the only outright physical miracle needed to make Ringworld or the Bowl work mechanically. Rendering Ringworld stable is a simple problem—just counteract small sidewise nudges. Making the Bowl work in dynamic terms is far harder; the big problem is the jet and its magnetic fields. This was Benford’s department, since he published many research papers in Astrophysical Journal in the like on jets from the accretion disks around black holes, some of which are far bigger than galaxies. But who manages the jet? And how, since it’s larger than worlds? This is how you get plot moves from the underlying physics.
One way to think of the strength needed to hold the Bowl together is by envisioning what would hold up a tower a hundred thousand kilometers high on Earth. The tallest building we now have is the 829.8 m (2,722 ft) tall Burj Khalifa in Dubai, United Arab Emirates. So for Ringworld or for the Bowl we’re imagining a scrith-like substance 100,000 times stronger than the best steel and carbon composites can do now. Even under static conditions, though, buildings have a tendency to buckle under varying stresses. Really bad weather can blow over very strong buildings. So this is mega-engineering by master engineers indeed. Neutron stars can cope with such stresses, we know, and smart aliens or even ordinary humans might do well too. So: let engineers at Caltech (where Larry was an undergraduate) or Georgia Tech (where Benford nearly went) or MIT (where Benford did a sabbatical) take a crack at it, then wait a century or two—who knows what they might invent? This is a premise and still better, a promise—the essence of modern science fiction.
Our own inner solar system contains enough usable material for a classic Dyson sphere. The planets and vast cold swarms of ice and rock, like our Kuiper Belt and Oort Clouds—all that, orbiting around another star, can plausibly give enough mass to build the Bowl. For alien minds, this could be a beckoning temptation. Put it together from freely orbiting sub-structures, stuck it into bigger masses, use molecular glues. Then stabilizes such sheet masses into plates that can get nudged inward. This lets the builders lock them together into a shell–for example, from spherical triangles. The work of generations, even for beings with very long lifespans. We humans have done such, as seen in Chartres cathedral, the Great Wall, and much else.
Alex Tolley proposed An Alternative Structure – The Solar Pulse Jet without the need for scrith
Here is Alex Tolley thought on avoiding the need for scrith.
The bowl structure becomes a Dyson swarm, each orbiting the star. Some of these objects are habitats, most are solar energy collectors and a few are particle beam generators. The job of the collectors is to accumulate the solar energy needed for the beam pulse. One can think of this as being like the LHC or the NIF laser. When the particle accelerators are in the correct position, the collectors send their energy to them to fire a pulse at the star, creating the mass ejection for thrust. Perhaps those particles could be muons.
Each pulse only happens when the beamers are aligned so that the solar jet is generated when the direction of thrust is correct. Because of the time delay, there should be a gap in the swarm behind the accelerators. All the objects in the swarm must track their distance from the star and use some energy to redirect and accelerate the solar wind to adjust their orbits to track the movement of the star.
Another advantage of the swarm is that the timing of the firing can be adjusted, allowing steering in the orbital plane. For a Dyson swarm, with objects orbiting in different planes, the steering can be in 3 dimensions.
Detecting such objects should be relatively easy. Their spectral signatures will be pushed into the IR, and if their direction of travel is away from us, there should be regular transit intensity peaks (swarm gaps) and even stronger peaks as the star flares. The pattern should be regular over a number of years. and would be expected be more frequent than a nova to maximize thrust.
Such an approach might be less efficient than the bowl, but I think it offers a plausible way to move a sun without invoking massive structures. It will require a technical civilization to allow travel between the habs and to ensure that the many objects in the swarm are kept running correctly.
Gregory Benford likes Alex’s swarm idea, and Eniac’s right that there may be better ways of inducing fusion on the star surface. Benford has worked on relativistic beam dynamics and fusion effects, theory & experiment, and there’s continuing research into how to do that. Not easy, no. Without giving away a plot point, the jet is very intricately run, but not by the Folk of the Bowl. Read SHIPSTAR to see how.
Must admit Benford envisioned the Bowl and chose it over the swarm idea, early in the 2000s, because the Bowl is a striking image of vast potential. A swarm is far more likely, yes. That’s on the of tradeoffs hard sf makes! Fiction is not a grant proposal
Also you could drag some Earthlike planets along with the star that is being accelerated, so long as the acceleration due to gravity is greater than the acceleration of the star system, a planet can remain in a stable orbit. I am thinking that the planet will need to be inside the bowl and would have to be shielded from the star's excessive output if used as an engine, that is a small trivial task for any civilization capable of building the bowl in the first place.
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Also you could drag some Earthlike planets along with the star that is being accelerated, so long as the acceleration due to gravity is greater than the acceleration of the star system, a planet can remain in a stable orbit. I am thinking that the planet will need to be inside the bowl and would have to be shielded from the star's excessive output if used as an engine, that is a small trivial task for any civilization capable of building the bowl in the first place.
Tom,
The important info inside this article which I quoted from nextbigthing is Dyson's R value. It amounts dozens of thousands of tonnes per watt for a planet. And dozens of tonnes per watt for interstellar colony, or grams per watt for Big Smart Object...
A Bowl of 100mln miles across ( a semi-spheroidal ), would have 100s of millions of Earths of habitable area ( if only 1 floor ).
We do not need planets if we build Bowls.
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karov wrote:Tom Kalbfus wrote:But its life span would start at zero since it would have a new core, so it would have a shortend lifespan from beginning to end on top of the life span of the original star. This for example if we has the Sun with its 10 billion lifespan half over and we collided it with Proxima Centauri and the added mass gave it a 9 billion year lifespan, we'd have 5 billion years + 9 billion years equal to 14 billion years of total lifespan, that is an improvement over the original 10 billion years it originally was going to last. and as that 14 billion year lifespan come to an end, we could hit it with another star giving it perhaps 8 billion more years to last, that is what I was thinking.
No! Stellar lifespan is function of mass only.
http://astronomy.swin.edu.au/cosmos/M/M … e+Lifetime
Proxima is small. It would ass only 12% mass into the Sun, but this will shorten the life of the resulting out of the merger ( do it gentle to not splash out too much ) star with 25% down to remaining 4b yrs?
My point is whether colliding a star with a star would reset its stellar clock back to zero, abet with a larger mass. If a star has a lifetime of 10 billion years and half of it is used up, that means it has 5 billion years left on its main sequence. Now lets suppose the star is directed to collide with another star using a shipstar swarm, the star is a red dwarf, so it hits the larger star precisely creating shock waves down to the star's core displacing that core and moving it aside and forcing the star to create a new core at its new center of mass using fresh material that is mostly hydrogen, the helium built up in the star's core up to this point is pushed to the side and ends up in the new star's outer layers, while the new core of the star has a fresh supply of hydrogen and it is effectively made young again. The star may retain some of the extra mass from the collision so its main sequence life may be shorter, but it would be shorter starting from zero, not from the previous star's mid point in its life. For example if the new star because of its added mass has a 8 billion year main sequence life starting at age zero, that is more years that the original star had left with its 10 billion year main sequence life half over, so originally it had 5 billion years of main sequence life, now it has 8 billion years of main sequence life starting from stellar age zero, this is 3 billion years more.
I think it would be tempting to build a shipstar around a star like Betelgeuse. The star is near the end of its life, it flares a lot and spews out its atmosphere in addition to putting out a lot of light. What happens with we collide this red supergiant with a red dwarf star of approximately Proxima's mass? We might possibly delay Betelgeuse's upcoming supernova, and that would be a good thing if we wanted to colonize other nearby stars, because we don't want a nearby Betelgeuse going supernova. So if we could set Betelgeuse's clock back to zero, what kind of star would it devolve into? Maybe a Class A or B star. Wikipedia lists its mass as from 5 to 11 solar masses which seems to indicate it would become a type A star if rejuvenated, a white but dimmer star with a stellar main sequence lifetime of around 1 billion years. It would be nice if we could put off Betelgeuse's imminent destruction by one billion years, wouldn't it?
NO!
Tom,
more mass = definitely shorter lifespan.
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Tom Kalbfus wrote:karov wrote:No! Stellar lifespan is function of mass only.
http://astronomy.swin.edu.au/cosmos/M/M … e+Lifetime
Proxima is small. It would ass only 12% mass into the Sun, but this will shorten the life of the resulting out of the merger ( do it gentle to not splash out too much ) star with 25% down to remaining 4b yrs?
My point is whether colliding a star with a star would reset its stellar clock back to zero, abet with a larger mass. If a star has a lifetime of 10 billion years and half of it is used up, that means it has 5 billion years left on its main sequence. Now lets suppose the star is directed to collide with another star using a shipstar swarm, the star is a red dwarf, so it hits the larger star precisely creating shock waves down to the star's core displacing that core and moving it aside and forcing the star to create a new core at its new center of mass using fresh material that is mostly hydrogen, the helium built up in the star's core up to this point is pushed to the side and ends up in the new star's outer layers, while the new core of the star has a fresh supply of hydrogen and it is effectively made young again. The star may retain some of the extra mass from the collision so its main sequence life may be shorter, but it would be shorter starting from zero, not from the previous star's mid point in its life. For example if the new star because of its added mass has a 8 billion year main sequence life starting at age zero, that is more years that the original star had left with its 10 billion year main sequence life half over, so originally it had 5 billion years of main sequence life, now it has 8 billion years of main sequence life starting from stellar age zero, this is 3 billion years more.
I think it would be tempting to build a shipstar around a star like Betelgeuse. The star is near the end of its life, it flares a lot and spews out its atmosphere in addition to putting out a lot of light. What happens with we collide this red supergiant with a red dwarf star of approximately Proxima's mass? We might possibly delay Betelgeuse's upcoming supernova, and that would be a good thing if we wanted to colonize other nearby stars, because we don't want a nearby Betelgeuse going supernova. So if we could set Betelgeuse's clock back to zero, what kind of star would it devolve into? Maybe a Class A or B star. Wikipedia lists its mass as from 5 to 11 solar masses which seems to indicate it would become a type A star if rejuvenated, a white but dimmer star with a stellar main sequence lifetime of around 1 billion years. It would be nice if we could put off Betelgeuse's imminent destruction by one billion years, wouldn't it?
NO!
Tom,
more mass = definitely shorter lifespan.
Were in the middle of our Sun's lifespan right now, the previous 5 billion years of our Sun's life span is not available to us, we can't live in the past, we can only live in the present onwards, So what is longer 5 billion years of our Sun's continued existence or 8 billion years of a more massive star? The thing I keep trying to explain to you is that not all of the Sun's fuel is available to it. The Sun uses up the fuel in its core only, the hydrogen in the Sun's outer layers don't get a chance to be fused. So what we want to do is hit a star with another star, and hit it so hard that the shock waves bore a hole all the way through the star's core, knocking the core out of the core of the star, inrushing matter will then fill the empty space with mostly hydrogen, and the star's "clock" is reset, it doesn't matter if the star's lifetime is shorter than the original because we're starting with a new star, not a previously aged star. Betelgeuse is an aged star, it may go supernova at anytime. So what are you saying, that we should just let it go supernova and ruin all those surrounding star systems, or do we delay it by colliding it into another star?
Last edited by Tom Kalbfus (2014-07-09 14:15:21)
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Tom Kalbfus wrote:Also you could drag some Earthlike planets along with the star that is being accelerated, so long as the acceleration due to gravity is greater than the acceleration of the star system, a planet can remain in a stable orbit. I am thinking that the planet will need to be inside the bowl and would have to be shielded from the star's excessive output if used as an engine, that is a small trivial task for any civilization capable of building the bowl in the first place.
Tom,
The important info inside this article which I quoted from nextbigthing is Dyson's R value. It amounts dozens of thousands of tonnes per watt for a planet. And dozens of tonnes per watt for interstellar colony, or grams per watt for Big Smart Object...
A Bowl of 100mln miles across ( a semi-spheroidal ), would have 100s of millions of Earths of habitable area ( if only 1 floor ).
We do not need planets if we build Bowls.
There is a big difference between a statlite reflector to heat the surface of a star until it flares, and a surface you could actually live on. It is relatively easy to build a Dyson Sphere out of Solar Sails. If a Solar Sail can support its weight against solar gravity with photon pressure, it can do so at any distance from the Sun if it maintains the same reflectivity. If a Solar Sail can maintain its position at 1 AU, it can also maintain its position at 100 AU, because as the Sun's solar output diminishes with distance, so does its gravity. One can wrap a large enough solar sail completely around the Sun, this is called a Dyson Bubble, and the thing about the Dyson Bubble is that it doesn't have to be a complete sphere, it could be half a sphere for instance, but we can't live on the surface of a Solar sail. We also can't build a Dyson Sphere with a thick shell, say 3 meters for instance, because it would collapse under its own weight, we could spin the Dyson, but that would only support the area at the equator, and if we spun it fast enough for artificial gravity I would fly apart! Getting a Dyson to support itself and also spin fast enough for gravity would require the mass of another star! We can do this with Alpha Centauri by using the mass of the B Star to build a Dyson Shell around Star A.
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Tom Kalbfus,
Yes it is. And no need to be photonic statite, once the authors are discussing plasma jet.
Anyway photonic lampshade will give us only 20km/s for BILLION years - totally impractical as an engine.
Plasma "dynamic compression members" would hold it upright.
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Indeed better to shell the stars as underbodies the P.Birch's way then to move them around.
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