Since we're already in the realm of far out engineering, you could get the energy from a laser beam from a source orbiting the sun. Your spaceship would have some kind of array to capture the energy beam.

This gives you energy, but I'm not sure how to turn that into velocity. Presumably you'd want some kind of ion beam emitter on board to propel your craft forward. Halfway through the journey, you'd turn the ion beam around to decelerate as you approach your destination.

In the Arthur C Clarke novel Songs of Distant Earth, spacecraft pushed huge blocks of ice ahead of them to absorb stray interstellar dust.

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stouset 3 hours ago | parent | next [-]

As you get going further and faster, this energy redshifts further and further making it less and less useful. Also there’s of course the problem of focusing a laser with that amount of energy tightly enough on an object increasingly far away.

	▲	iso1631 2 hours ago \| parent [-]
		And crucially ensuring that beam continues to run for billions of years. a few decades may pass for you, but not for the laser that's pushing you

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m4rtink 4 hours ago | parent | prev | next [-]

So there is also the idea of a ramjet that uses interstellar hydrogen as fuel for fusion, which provides energy & propulsion: https://en.wikipedia.org/wiki/Bussard_ramjet

Some recent findings do give it lower feasibility though.

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__MatrixMan__ 4 hours ago | parent | prev [-]

Another option is to visit as many massive objects as possible on the way there, doing gravitational slingshots until you're half way, and then gravitational brakes on the approach. Of course now you're taking detours, but since certain amounts of fuel make the trip impossible, any workaround at all is an improvement. What's an extra few thousand years between friends?

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stouset 3 hours ago | parent | next [-]

First, what “many objects along the way”? There are basically none. To do this requires many detours that significantly increase the distance you’re having to travel.

Second, the faster you’re going, the less useful a gravitational slingshot is because you spend less time in the object’s gravity well.

It’s a fun and useful trick within our solar system, but I don’t think the physics plays out well for interstellar travel.

	▲	__MatrixMan__ 2 hours ago \| parent [-]
		Stars is what I meant. Although upon further thought I think you're right. I guess the intervening stars are unlikely to be moving at helpful velocities for such a game of pinball, metric expansion being what it is.

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m4rtink 3 hours ago | parent | prev [-]

Slingshots require very specific conditions and configurations of orbiting bodies that won't really work in deep space - all the Kuiper Belt/Oort Cloud bodiees are far too small and too far away to be usable.

But assume for example that you don't care about how long it is going to take (you are an immortal cyborg, an upload living in the computer or a popsicle in hibernation & the AI is driving. Then you can just "island hop" between Kuiper Belt/Oort Cloud objects, never gaining any high % of the speed of light but always having the next body in your sights, not farther than a few decades or a couple hundred years of flight at most.

You reach the body, refuel, repair, maybe upgrade and then off you go, to the next one. And eventually, you might be at you destination, with a fully fueled and repaired ship. It might just take like 20000 years for start to finish, but hey, you can use it for something productive like learning to play Go or something. :)

	▲	__MatrixMan__ 2 hours ago \| parent [-]
		You're right, I overlooked some important slingshot requirements. As for the longevity, I figure the ship can build a facility for growing settlers when it arrives. With no humans on board it can sustain heavier accelerations.