[habibur]

This won't enable perpetual space travel in case anyone thought so.

Rockets need to eject particles to generate force. And to eject 1 kg of fuel, its photo synthesis system has to lose 1 km of mass in one way or another.

The solution is to find a way to generate thrust without rocket fuel ejection.

[Buttons840]

Can we "swim" through space? Collect particles from space, add energy, expell them backwards to generate a net thrust.

[grues-dinner]

That's called a Bussard ramjet: collect hydrogen and fuse it for power to energise the collection mechanism and thrust to overcome the drag. I think the current consensus is that the interstellar medium round these parts is too thin to make it work in deep space.

[LargoLasskhyfv]

And if it would be dense enough it would work as a brake instead.

[o11c]

There's a huge density difference if you aren't close to a planet or star.

Solar sails are probably more practical.

[m4rtink]

Yep: https://en.wikipedia.org/wiki/Bussard_ramjet

Gather interstellar hydrogen, use it to run a fusion engine for propulsion and power. :)

[themafia]

Also: https://memory-alpha.fandom.com/wiki/Bussard_collector

Star Trek assumed that all warp class vehicles would require them for operation and in-situ fuel replenishment.

[aspbee555]

no particles needed, we already have ion drive, just need electricity

[nosignono]

Just out of curiosity, what do you think an ion is?

[Taniwha]

Ions are atoms ..... tiny particles

[grues-dinner]

Quite big tiny particles in this application: Xenon is a fairly hefty atomic number of 54 - exactly double iron.

And you need quite a bit of it: even fairly small spacecraft like probes can have nearly a tonne of the stuff. Which, considering there's only 30-40ish tonnes extracted per year at a cost of about 1.5ish dollars per gram is quite a bit!

[lmm]

Ions are small enough that you can bring enough for a whole trip pretty easily. Yes they're still consumable, but you need a tiny fraction of the reaction mass you need with a conventional rocket.

[Cthulhu_]

Ion drives ionize particles like xenon and expel them; they're much more fuel/weight efficient than burning fuel but they still use fuel, unfortunately.

There's been a number of pure electric propulsion proposals or prototypes, but they've all turned out to be a hoax; the latest one I recall was the EmDrive [0], where any paper claiming it produced positive thrust was debunked with the measurements having been influenced by outside forces.

The TL;DR is that reactionless drives are not possible due to Newton's third law. This page / this website is always a great resource for things like this, it's in the context of writing science fiction but it has tons of research: [1]

[0] https://en.wikipedia.org/wiki/EmDrive

[1] https://www.projectrho.com/public_html/rocket/reactionlessdr...

[swayvil]

Maybe we could travel without bodies. Ala Lovecraftian astral travel or whatever. I mean you couldn't ship matter like that but for everything else it might work just fine.

[Cthulhu_]

Astral projection isn't Lovecraftian per se (fhtagn), but it's an interesting thing to ponder from a hypothetical / fictional perspective.

At best we'll be able to send out probes. Maybe, but this still feels science fiction too, we can harness quantum entanglement for long distance instant communication.

[swayvil]

In his books, one way of travelling was to switch souls with a creature on another planet. Apparently it worked very well. Though managing a new set of limbs and senses could be difficult.