Talk:Stellar engine

should this article
should this article include explanation/hypothesis of why it would ever be necesary to move a star? user:vroman


 * Maybe in a short paragraph at the end... I can only think of exploration and moving out of dangerous areas of space. --Pablo D. Flores (Talk) 10:37, 3 October 2005 (UTC)


 * Perhaps the stars are being moved for aesthetic reasons? Thomas Purnell 15:27, 12 November 2006 (UTC)


 * Stellar husbandry, perhaps—moving stars into or out of nebulae could be used to control the rate of formation of new stars within them. Or, on a larger scale, to move whole galaxies.  Andromeda may collide with our own galaxy in a few billion years.  That could cause much inconvenience to a developed galactic civilization. &mdash; Xaonon (Talk) 21:08, 19 June 2008 (UTC)


 * Generally this sort of thing is suggested as a means to either shift an inhabited star system out of the path of a potential danger or to move the danger itself, for instance a large star which might go supernova is arguably easier to move, since acceleration is force divided by mass. The force provided by this engine is linear to its brightness, but more massive stars produce much more light relative to their mass. Usually the relation between luminosity and mass is given as M=L^3.5, so double the mass and you need double the force to get the same acceleration, but that same star produces 11 times the light, rather than simply double the light. A star that might go supernova, at 20 times the sun's mass, has more than 20,000x the light to push itself even though it only needs 20x to produce the same acceleration. Plus it is usually assumed anyone in a position to be building these has likely already spread out to some other nearby stars and thus would rather eject the supernova threatening multiple of them rather than move their own stars. Caasi560 — Preceding unsigned comment added by Caasi560 (talk • contribs) 21:18, 14 February 2013 (UTC)

Caasi560's comment reasons well based on the Mass–luminosity relation, but his formula reverses the relation.Elias (talk) 13:53, 21 October 2020 (UTC)

Direction of thrust
It took me a while to understand why the star moves in the direction of the mirror. It seems necessary to utilize the fact that absorbed radiation is emitted omnidirectionally in order to explain this. If so, could someone please add this fact to the explanation. Taken from page on radiation pressure: "If the blackbody absorbs 1,080 watts on its sun-facing surface, it must also emit all 1,080 watts omnidirectionally. The omnidirectional emission is self-cancelling". — Preceding unsigned comment added by 131.107.0.86 (talk) 21:58, 9 May 2012 (UTC)


 * If radiation was emitted from the satellite omnidirectionally, it would feel no net radiation pressure, & fall towards the star. It has to be a mirror for this kind of engine to work Stutheboo22 (talk) 15:46, 13 May 2024 (UTC)

Can somebody explain why the direction of acceleration is towards the mirror? Without the mirror, there is no net force exerted on the star. With the mirror, wouldn't the net force be away from the mirror since the photons are being sent back to the star? — Preceding unsigned comment added by 71.60.119.198 (talk) 21:17, 9 July 2019 (UTC)

I think I understand this. The mirror should not send the photons back to the star, but back past it. Then there will be a net flux of photons (from the combination of star and mirror) in the opposite direction of the mirror. If one instead of a mirror in front of the star has a black sheet "behind" the star, the black sheet will, according to the first comment in this section, absorb some backward radiation and emit it equally forwards and backwards, which should also give a slight net propulsion of the star, I think. Elias (talk) 14:06, 21 October 2020 (UTC)


 * The way this satélite works is it has a gravitational attraction towards the star, but a radiation pressure away from the star. The star feels the same gravitational attraction, but no net radiation. What actually moves the star is the gravitational attraction to the satellite. Given the system as a whole (star & satélite), the net radiation pushes the system. I feel like this could be clarified. The satellite should be a parabolic mirror, which the sun at the focus so radiation from the star is emitted backwards & parallel. Stutheboo22 (talk) 15:44, 13 May 2024 (UTC)

Magnetic Satellites
I've heard a theory that if you could somehow manipulate magnetic fields with a series of large satellites, you could cause, say, a star and a planet to repel each other. Is that feasible? I slighly doubt the veracity of that claim, but I'm no physicist. Does anything know anything about that? Scourgeofsmallishinsects 15:45, 19 May 2006 (UTC)

Speed?
So how fast would a star move under the influence of a stellar engine? Anyone have a guess? --Brasswatchman 05:18, 5 June 2007 (UTC)
 * The article contains an answer to that now. ··gracefool&#9786; 04:46, 6 July 2009 (UTC)
 * in the calculations the speed goes from 20 m/s to 20km/s in 999 milion years so a factor of 1000. should it not be a factor of 31 ($$\sqrt{1000}$$), according to $$e=\frac{mv^2}{2}$$ .130.240.109.53 (talk) 16:47, 1 May 2016 (UTC)

Laser Stars
Lasers Stars can be qualified as class B stellar engines?

ake a look:


 * I'm not sure ... I think a good argument can be made both for and against that. A class B stellar engine extracts energy for a usable purpose, and a laser star does indeed do that. At one end of the spectrum you have something as small and insignificant as a solar panel, and at the other end a Matrioshka Brain. Both harness the output of the star for a purpose. The later is clearly a Stellar engine; I think few people would label the former that way. Laser stars fall somewhere in the middle. Where the "dividing line" is, is a matter of interpretation. - Vedexent (talk) - 05:23, 28 July 2007 (UTC)

"After one billion years, the speed would be 20 km/s and the displacement 34,000 light-years, a little over a third of the estimated width of the Milky Way galaxy."
Perhaps this can be contrasted to the fact that the solar system would orbit around the centre of the Milky Way a little over four times? - The "voluntary displacement" is still only middling compared to the natural gravitational motion, which will automatically bring several interesting systems within just a few LY over that sort of time span. If you have a billion years to spare, you might just as well take nature take its course... 2A01:CB0C:1704:9A00:94A5:1263:7E15:7E81 (talk) 09:04, 28 March 2024 (UTC)

"in principle (assuming perfect efficiency), accelerate the Sun to ~27% the speed of light (after burning enough of the Sun's mass to transition it to a brown dwarf)"
Perhaps add the remark that slowing down is no small feat at relativistic speeds and takes up a hefty portion of the energy budget before the Sun is burned up? This is assuming that the goal is to get to a planet around another star and colonise that planet. (If the goal were to merely live among the stars using the Sun as our energy source - we have always been doing that!) (If we expect to be able to make the planet that we find out there "work" for our biology, we must first dispose of the requisite mega-eco-engineering skills, and a good place to start developing such skills is to put a near-optimal planet in order - you are sitting on one such planet right now.) 2A01:CB0C:1704:9A00:94A5:1263:7E15:7E81 (talk) 09:11, 28 March 2024 (UTC)