One way for the deceleration is a black hole close flyby where it’s gravitation and powerful magnetic field could be used by the probe’s magnetic sail. But from practical point of view, it unlikely to work, as the probe will be damaged by intense radiation.
However, my favorit method is to send multiple probes with slightly different speeds by a nanoprobe’s accelerator. The first probe have v-nx speed, the next probe has v-(n-1)x speed and the last probe has the speed v. The difference x is so small that all the probes will reach each other near the target and clump in one large object. All this mass gain is used to built an accelerator-gun which send a nanoprobe with the speed -v, that is back, and this probe will have the near zero speed at the rest frame.
The size and price of the accelerator. For example, aliens have an accelerator which could send 1mg probe every second, and the accelerator’s weight is 1000 tons. Thus, it will send its own mass in 20 000 years. All these probes clump (using some internal navigation and small difference in initial speed) with each other after a few million years, and using some nanotech, they build another accelerator, which send just one probe in the back direction, which is the deceleration, as its speed will be zero.
To send all the probes simultaneously, one need to build a trillion of such accelerators. However, this seems to be achievable even with one Dyson sphere. So clumping make sense only if there are some limits on the size of the accelerators.
Also, any intergalactic probe will experience “natural” deceleration because of expanding universe, similar to red shift, so the back-accelerator may be small than the sending accelerator.
What is a “magnetic sail”? That sounds interesting. Is it just a large electromagnet?
I don’t understand your second method either. What is a nanoprobe? What is an accelerator? You’re saying there’s a small thing in space which can push things? Then you send many probes (which may or may not also be nanoprobes) to the same point. Then something happens involving an “accelerator gun”, and now a (new?) nanoprobe is traveling backwards at the same speed at which the original probes were traveling forward? And it has “near zero speed at the rest frame”—the rest frame of what? Its own rest frame? But everything is at rest in its rest frame! And what’s the motivation? If you can launch things forward at speed v, can’t you just launch things backward at that same speed? How do we benefit from this setup?
Copied form the comment above: aliens have an accelerator which could send 1mg probe every second, and the accelerator’s weight is 1000 tons. Thus, it will send its own mass in 20 000 years. All these probes clump (using some internal navigation and small difference in initial speed) with each other after a few million years, and using some nanotech, they build another accelerator, which send just one probe in the back direction, which is the deceleration, as its speed will be zero.
Nanoprobe is a small starship send by an accelerator, which is similar to electric railgun or hadron collider.
All nanoprobes are send in the same direction.
They are send with the different speeds, in such a way, that later nanoprobes are quicker and will catch up the first ones is some moment in time. They couple each over at that moment. This results in “clumping”.
Resulting large clump of matter which itself is traveling with near с speed reorganise itself in a large starship using nanotech.
This starship builds another accelerator which sends one nanoprobe in the back direction with speed near c.
Rest frame is the frame of the first accelerator here, that is, of the alien civilisation.
The new nanoprobe has 0 speed relative to alien civilisation, but is now located millions light years from it, so the task of deceleration is solved.
This could be also used for deceleration by interaction with interstellar plasma.
But I thought about different thing: to use the magnetic field of the black hole for deceleration. In this case, the space craft generates its small magnetic field which interacts with giant magnetic field of the black hole.
Thanks for explaining. I see what you mean now. But I still don’t get how this is useful. Why not simply send the larger ship in the first place, instead of sending the building materials?
Perhaps it’s easier to accelerate smaller things? You can give the nanoprobe all the necessary momentum in the solar system—it doesn’t have to carry any fuel—whereas you can’t feasibly accelerate an entire ship to near-c within the solar system.
Yes, it is about price: this scheme will be a trillion times cheaper, as I discuss in a comment above. A super-intelligent alien AI may not worry about prices, but if it has some resource limitations, it would use more economical solutions.
One way for the deceleration is a black hole close flyby where it’s gravitation and powerful magnetic field could be used by the probe’s magnetic sail. But from practical point of view, it unlikely to work, as the probe will be damaged by intense radiation.
However, my favorit method is to send multiple probes with slightly different speeds by a nanoprobe’s accelerator. The first probe have v-nx speed, the next probe has v-(n-1)x speed and the last probe has the speed v. The difference x is so small that all the probes will reach each other near the target and clump in one large object. All this mass gain is used to built an accelerator-gun which send a nanoprobe with the speed -v, that is back, and this probe will have the near zero speed at the rest frame.
Hum, what does this gain over sending out all the probes in one clump from the start?
The size and price of the accelerator. For example, aliens have an accelerator which could send 1mg probe every second, and the accelerator’s weight is 1000 tons. Thus, it will send its own mass in 20 000 years. All these probes clump (using some internal navigation and small difference in initial speed) with each other after a few million years, and using some nanotech, they build another accelerator, which send just one probe in the back direction, which is the deceleration, as its speed will be zero.
To send all the probes simultaneously, one need to build a trillion of such accelerators. However, this seems to be achievable even with one Dyson sphere. So clumping make sense only if there are some limits on the size of the accelerators.
Also, any intergalactic probe will experience “natural” deceleration because of expanding universe, similar to red shift, so the back-accelerator may be small than the sending accelerator.
What is a “magnetic sail”? That sounds interesting. Is it just a large electromagnet?
I don’t understand your second method either. What is a nanoprobe? What is an accelerator? You’re saying there’s a small thing in space which can push things? Then you send many probes (which may or may not also be nanoprobes) to the same point. Then something happens involving an “accelerator gun”, and now a (new?) nanoprobe is traveling backwards at the same speed at which the original probes were traveling forward? And it has “near zero speed at the rest frame”—the rest frame of what? Its own rest frame? But everything is at rest in its rest frame! And what’s the motivation? If you can launch things forward at speed v, can’t you just launch things backward at that same speed? How do we benefit from this setup?
Copied form the comment above: aliens have an accelerator which could send 1mg probe every second, and the accelerator’s weight is 1000 tons. Thus, it will send its own mass in 20 000 years. All these probes clump (using some internal navigation and small difference in initial speed) with each other after a few million years, and using some nanotech, they build another accelerator, which send just one probe in the back direction, which is the deceleration, as its speed will be zero.
Nanoprobe is a small starship send by an accelerator, which is similar to electric railgun or hadron collider.
All nanoprobes are send in the same direction.
They are send with the different speeds, in such a way, that later nanoprobes are quicker and will catch up the first ones is some moment in time. They couple each over at that moment. This results in “clumping”.
Resulting large clump of matter which itself is traveling with near с speed reorganise itself in a large starship using nanotech.
This starship builds another accelerator which sends one nanoprobe in the back direction with speed near c.
Rest frame is the frame of the first accelerator here, that is, of the alien civilisation.
The new nanoprobe has 0 speed relative to alien civilisation, but is now located millions light years from it, so the task of deceleration is solved.
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Typical magnetic sail uses magnetiс field generated by the spacecraft to capture stellar wind. https://en.wikipedia.org/wiki/Magnetic_sail
This could be also used for deceleration by interaction with interstellar plasma.
But I thought about different thing: to use the magnetic field of the black hole for deceleration. In this case, the space craft generates its small magnetic field which interacts with giant magnetic field of the black hole.
Thanks for explaining. I see what you mean now. But I still don’t get how this is useful. Why not simply send the larger ship in the first place, instead of sending the building materials?
Perhaps it’s easier to accelerate smaller things? You can give the nanoprobe all the necessary momentum in the solar system—it doesn’t have to carry any fuel—whereas you can’t feasibly accelerate an entire ship to near-c within the solar system.
Yes, it is about price: this scheme will be a trillion times cheaper, as I discuss in a comment above. A super-intelligent alien AI may not worry about prices, but if it has some resource limitations, it would use more economical solutions.