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Interstellar Spaceflight: Is It Possible?

Disappointing!
 
Yes very interesting. I eventually might be convinced that reactionless drive is possible; we use the concept in Orion's Arm, but it does cause many problems with conservation of energy that may be fatal.

Two observations; the thrust observed in these experiments remains very low, and is barely distinguishable from experimental error (which is probably all it is). It is also comparable to the tiny thrust available from photon thrusters; if reactionless thrusters are no more powerful than photon thrusters, they are not really worth using (except in certain specialised contexts).

And if reactionless drive were to be useful it would require the creation of free energy out of nothing- a perpetual motion machine. I'd only be happy in this energy could be demonstrated to have an origin of some sort; maybe quintessence (the accelerating rate of expansion of the universe). Quintessence seems to be an effectively free and sourceless form of energy, and if reactionless drive could be shown to exploit that somehow, I might be more inclined to accept it.
 
Isn’t deceleration another factor?

If you are travelling at a fair percentage of light speed that’s fine for taking a few photos as you zip past (slightly blue shifted?) but not if you need to stop.

If it took a year and x tons of fuel for the craft to reach a fair percentage of light speed it will take the same to slow it. If using a light sail it will need an onboard method of slowing it unless or until you have someone with a laser at the other end of the journey. It may be possible to use the gravitational pull of an object in the target system but that will be a pretty hairy business given that the amount of debris will increase as you approach the target.

Maybe future fly pasts will achieve more if they travel above or below the orbital plane of the target system.
 
Deceleration is a big problem, yes.
Tunn11 said:
If it took a year and x tons of fuel for the craft to reach a fair percentage of light speed it will take the same to slow it.
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It's worse than that; if you take x tonnes of fuel with you to decelerate, you have to use y extra tonnes of fuel in the acceleration phase in order to accelerate that extra mass. The extra fuel required to accelerate all the fuel required can easily make the total mass of the ship x-squared, or more. So the ship design should utilise alternative methods of propulsion as much as possible.

My current favourite method is using a powerful beam of small, massive particles to accelerate the ship, and magnetic brakes to decelerate it. The small particles can be projected towards the ship from giant accelerators orbiting the Sun, and intercepted by magnetic sails. These magnetic sails can later be converted into brakes near the destination system. Although this method does not entirely remove the requirement for on-board fuel, it does drastically reduce it.
 
Coal said:
Plus there's the rocks in the way. Even little ones will do a lot of damage.
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There's a lot of emptiness between them though, so fingers crossed, you'll probably get through OK (unless you don't!). I don't think either of the Voyagers have had impact problems yet.
 
SimonBurchell said:
There's a lot of emptiness between them though, so fingers crossed, you'll probably get through OK (unless you don't!). I don't think either of the Voyagers have had impact problems yet.
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tbh, the solar system, although 'rockier' is so many factors of ten smaller than anything interstellar, I suspect rocks will be an issue...
 
Coal said:
Plus there's the rocks in the way. Even little ones will do a lot of damage.
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I've read somewhere that when we send spacecraft through the asteroid belt we don't even take measures to avoid impacts because they're so unlikely. I've seen animations of the asteroids as many huge rocks tumbling through space even on documentaries, but I understand that in reality they are so distant from each other you would probably not notice that you were in the belt. We can probably assume the same of interstellar space for the most part.
 
If you travel any faster than 70%c, the problem with dust becomes acute - and even worse is the problem of interstellar hydrogen, which is converted into dangerous radiation by velocity. It's like flying directly into a solar flare.
 
eburacum said:
If you travel any faster than 70%c, the problem with dust becomes acute - and even worse is the problem of interstellar hydrogen, which is converted into dangerous radiation by velocity. It's like flying directly into a solar flare.
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Anyone might think the universe just doesn't want us to leave the Solar System.
 
I'm getting very excited about the recent discoveries in gravity waves and their preponderance in the universe.
d41586-023-02203-6_25559014.jpg

Giant gravitational waves: why scientists are so excited
Astrophysicists describe what galaxy-wide gravitational waves could mean for our understanding of black holes and the history of the cosmos.

The universe is humming with gravitational waves. Here's why scientists are so excited about the discovery
This isn't the first time that humanity has detected gravitational waves. So why is this discovery so important?

This shows that the basic physics of how gravity manipulates spacetime is becoming better understood.
It also means that the theoretical Alcubierre Drive might be closer to reality than it was previously. Although its proposed waveform has not yet been observed in nature, the mere observance of gravity waves from massive, dense sources shows the feasibility of the concept.

I know we are far away from any kind of control, but to me this is akin to when physics worked out the theory of the aerofoil, and demonstrated lift — the first critical step.
 
Sometimes a spacecraft does display an unexplained amount of displacement due to thrust from an unknown source. The two spaceprobes Pioneer 10 and Pioneer 11 were deflected off course by a tiny amount, which some thought might have been a new phenomenon.

This anomaly was eventually attributed to the slow but steady emission of heat from the radioactive power source on board.
https://en.wikipedia.org/wiki/Pioneer_anomaly#Explanation:_thermal_recoil_force

Even if the 'Quantized Inertia' thrusters do demonstrate a small amount of thrust, it will be necessary to rule out all the sources of conventional energy emission that could be responsible.
 
Materials science is going to have issues engineering a probe or ship that can survive and work for long enough for interstellar travel in the conditions of outer space even if it's robotic. That's before adding in the additional engineering complexity needed to support humans, whether conscious, in hibernation, or even as something like frozen fertilized eggs to thaw out on arrival.

Any ship would thus seem to need self-repair capacity, and to pack along the extra resources needed for that. It would need to be able to do things like print replacement computer equipment. It would need to be able to self-replicate to replace any parts that broke on the journey, aka a Von Neumann type ship.
 
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