Project TinTin is exploring the possibility of interstellar cubesats. It's obviously rather early days since we don't yet have interplanetary cubesats. But the interplanetary ones are on the horizon, maybe in the next decade or so. Interstellar ones apparently are worth studying.
Project Tin Tin | Icarus Interstellar
These Cubesats Could Use Plasma Thrusters to Leave Our Solar System
That's not quite as small as you suggest. But it's perhaps not impossible. The biggest difficulty is to find a way for them to communicate back. Also to slow down when they get to the target system, unless you want to just do a flyby.
For slowing down, one option for tiny satellites (not sure if this is what they plan for TinTin) is to use a combination of the Olberth effect and a form of aerobraking - they navigate really close to the target star - where you need less deceleration anyway to get into orbit - and then you use the atmosphere of the star itself to decelerate. Or the atmosphere of the target planet - or both. Combined probably with large ultra thin solar sails to both help slow down, increase the amount of drag, and navigate.
The faster it travels, the harder to stop. If you travel at a twentieth of the speed of light,you could get to Alpha Centauri in less than a century. And a star atmosphere is much more extensive than a planetary atmosphere and you can use solar sails to slow down as you approach the sun as well. But you still have to shed 15,000 kilometers per second compared with just a few kilometers per second for planetary aerobraking. Probably talking about rather huge solar sails for your tiny craft, also used for the fryby for increased drag
For discussion of the issues: Slowing Down The Icarus Probe & Induced Deceleration.
Once you get there and are in orbit, then you have the problem of communication back to Earth. Again things like ultra thin mirrors could help. Smart materials that automatically go into mirror shapes or whatever.
Laser communication would be most efficient if you can find a way to target Earth precisely enough - which is the big issue over interstellar distances. Earth can send a laser to the spaceship which it can use to help with targeting but still, over distances of light years, it would have issues targeting Earth.
I've also seen proposals for really tiny interstellar spacecraft in swarms, like your idea. I think they would work together to signal back. But can't remember where I read it.
So anyway though I can't give a cite right now (maybe someone reading this can?) - that's an idea that seems feasible in principle anyway. Either launch a swarm of them all at once - the advantage then is that it doesn't matter if a few or even most of them get destroyed, so long as a fraction of them get through, while if anything hits a cubesat it doesn't matter if most of it is still functioning, that's still an end of mission scenario if it hits something vital.
Or if they are going to stop in the target system and have lots of smarts so they can navigate to be close together once there, you could launch them one after another and once enough of them arrive at the target you have a cloud of satellites that come together in a cloud to signal back. Which could be through phased array type methods so they don't need to form a giant mirror shape to signal back.
Anyway that's rather hand waving, would be better to find a proper cite about it. Anyone got a cite? I'll update this if I find it.
Project Tin Tin | Icarus Interstellar
These Cubesats Could Use Plasma Thrusters to Leave Our Solar System
That's not quite as small as you suggest. But it's perhaps not impossible. The biggest difficulty is to find a way for them to communicate back. Also to slow down when they get to the target system, unless you want to just do a flyby.
For slowing down, one option for tiny satellites (not sure if this is what they plan for TinTin) is to use a combination of the Olberth effect and a form of aerobraking - they navigate really close to the target star - where you need less deceleration anyway to get into orbit - and then you use the atmosphere of the star itself to decelerate. Or the atmosphere of the target planet - or both. Combined probably with large ultra thin solar sails to both help slow down, increase the amount of drag, and navigate.
The faster it travels, the harder to stop. If you travel at a twentieth of the speed of light,you could get to Alpha Centauri in less than a century. And a star atmosphere is much more extensive than a planetary atmosphere and you can use solar sails to slow down as you approach the sun as well. But you still have to shed 15,000 kilometers per second compared with just a few kilometers per second for planetary aerobraking. Probably talking about rather huge solar sails for your tiny craft, also used for the fryby for increased drag
For discussion of the issues: Slowing Down The Icarus Probe & Induced Deceleration.
Once you get there and are in orbit, then you have the problem of communication back to Earth. Again things like ultra thin mirrors could help. Smart materials that automatically go into mirror shapes or whatever.
Laser communication would be most efficient if you can find a way to target Earth precisely enough - which is the big issue over interstellar distances. Earth can send a laser to the spaceship which it can use to help with targeting but still, over distances of light years, it would have issues targeting Earth.
I've also seen proposals for really tiny interstellar spacecraft in swarms, like your idea. I think they would work together to signal back. But can't remember where I read it.
So anyway though I can't give a cite right now (maybe someone reading this can?) - that's an idea that seems feasible in principle anyway. Either launch a swarm of them all at once - the advantage then is that it doesn't matter if a few or even most of them get destroyed, so long as a fraction of them get through, while if anything hits a cubesat it doesn't matter if most of it is still functioning, that's still an end of mission scenario if it hits something vital.
Or if they are going to stop in the target system and have lots of smarts so they can navigate to be close together once there, you could launch them one after another and once enough of them arrive at the target you have a cloud of satellites that come together in a cloud to signal back. Which could be through phased array type methods so they don't need to form a giant mirror shape to signal back.
Anyway that's rather hand waving, would be better to find a proper cite about it. Anyone got a cite? I'll update this if I find it.
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Robert Walker
Writer of articles on Mars and Space issues - Software Developer of Tune Smithy, Bounce Metronome etc.Studied at Wolfson College, Oxford
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