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Using black holes and lasers to accelerate spaceships
#1
https://www.space.com/halo-drive-black-h...ravel.html

Future spaceships could use black holes as powerful launch pads to explore the stars.

A new study envisions firing laser beams that would curve around a black hole and come back with added energy to help propel a spacecraft to near the speed of light. Astronomers could look for signs that alien civilizations are using such a "halo drive," as the study dubs it, by seeing if pairs of black holes are merging more often than expected.

Study author David Kipping, an astrophysicist at Columbia University in New York, came up with the idea of the halo drive through what he calls "the gamer's mindset."

"Sometimes, in a computer game you find an 'exploit,' a hack which allows you to do something overpowered that would otherwise be forbidden by the rules of the game," Kipping told Space.com. "In this case, the game is the physical world, and I tried to think about exploits that would allow a civilization to achieve relativistic flight back and forth across the galaxy without the vast energy expense that one might naively assume."



I've tried reading the full article, and I can sort of understand how this would work. It's a bit like how space probes often make close approaches to planets, to use them as gravitational slingshots to increase their speed. The main differences are that: 
  • This technique uses a black hole instead of a planet, and; 
  • Instead of going near the black hole itself, the ship fires a laser beam near the black hole. The laser beam then comes back to the ship with increased energy. 
I don't know whether the physics checks out here, but if it does, then it sounds like a rather powerful technique. I doubt it's any good for alien civilisations who want to hide themselves, though :lol: !
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#2
That sounds interesting.
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#3
I think they may have underestimated the use of lasers here. What wavelength are they going to use? How are they going to generate and amplify the laser light? It takes a lot of power to set this up, and depending on the wavelength you generate, that power will be decreased markedly. I'd go with the fundamental 800nm here, as you can generate a high power beam, rather than making further modifications that reduce the power in my lab from watts to milliwatts. How are they going to align the beam so that it curves back towards the ship? It takes forever to align a simple laser beam inside a laboratory (I would know :P ) - how do they propose to do that in space? Especially in an environment that they can't control the positions and types of particles that may absorb the laser light and reduce the power. In my lab, we use a system of boxes and gas pumps to purge our infrared system, so that water and CO2 aren't present to absorb light. I realise that space is largely a vacuum, but with the kind of distance it'll take to curve around a black hole, I'd expect the beam to make contact with some particles during the round-trip. There's not really any means of testing this, either, except perhaps by simulation. I suppose you'd have to have some way of doing alignment without physical presence, as surely the first test couldn't be done with a human inside the ship.

It's a curious idea, but it really needs to be thought through more. Although having said that, I'm no expert on space technology - there may be some ways around these problems that I don't know of - but my inclination would be that this might be harder than they think.
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  • Kyng
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#4
Good points :) . I guess it depends on how much precision is required for the laser: if they can fire it a couple of light years either way and still get the same effect, then it should still work for them - but if there's a millimetre-wide window which they need to hit, then they're pretty screwed, unless they have access to some advanced precision alignment technology :lol: .
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#5
I would assume that firing such a laser from a starship in the first place would mean its weapons grade and at that stage do you REALLY want to fire an ASL that can take out a starship towards a blackhole to curve it around and hit your ship with even greater power? while it sounds neat to me it sounds more like a way to atomize a ships armor more efficiently. 

Also we need to take into consideration that by this point we would have extremely powerful laser weapon systems of different wavelengths/spectrum's.
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#6
Well, I do hope no other spaceships would get accidentally hit by any of these lasers. However, I think it's vanishingly unlikely that any will be: even if any other space-faring civilisations did exist, interstellar space is simply so vast and so empty that they'd have to be seriously unlucky to get hit by mistake. (Just to put into perspective just how empty it is: when the Milky Way collides with the Andromeda Galaxy in about 3.75 billion years' time, it's unlikely that there will be any collisions between individual stars, simply due to how far apart they are - and, of course, stars are much larger than spaceships and lasers!!!)

Of course, if any spaceships do get their armour atomized like this, then it won't be a pretty sight - and I can't see interstellar civilizations wanting to risk pissing off their neighbours like that -_- .
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#7
your not getting what i mean, if we are using a laser to somehow slingshot boost our ships then why would we try? the laser impact would be devastating when you think of how large it would have to be to have the power to travel around a black holes event horizon.
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#8
(03-21-2019, 09:46 PM)GrieferLord Wrote: your not getting what i mean, if we are using a laser to somehow slingshot boost our ships then why would we try? the laser impact would be devastating when you think of how large it would have to be to have the power to travel around a black holes event horizon.

I guess it would depend on where we are in terms of the focus of the beam. Yes, the impact would be incredible at the beam's focal point, but if the ship is at a significant distance away, it may be possible to for the beam to be at some fluence (energy per unit area) that only propels the ship, without causing damage. When I'm doing pump-probe spectroscopy in my lab, we position the sample at the focal point of the beam, where our fluence is highest and so we get the most possible excitation of our sample. But if we shift the position, the beam becomes wider, our fluence and thus our signal is reduced. In other words, less impact. Although this is still a good point - it's another thing that would need rigorous testing to get right, and I'm not quite sure we will ever have the capability to simulate it.

I wonder, is it more feasible to try something with magnetism? I'm not sure how black holes affect magnetic fields, but perhaps we can send out some field that repels the ship further away?
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