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Currently, we're able to aim probes at various bodies in the solar system pretty well.

Do we have the technology to send a probe to Alpha Centauri? If we're aiming at a star, approximately how far does it have to be (an order of magnitude answer is OK) before we lose precision in aiming and have an appreciable chance of missing altogether?

Note that the probe is allowed to have mechanisms that correct its path

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We have the much of the technology needed, but not the engineering and patience.

Sending a Voyager-like probe to Alpha-Centauri would take many, many, many years. Around 50,000 years given a 25 km/sec speed (that's a good deal faster than Voyager is going). Because of the time-frame, we'd need to engineer something that could last that long. Several of the Voyager sensors have already malfunctioned, and it's only been 40+ years - 1 one-thousandth of the interstellar time. Another example is power - solar-cells that far out in space don't give us much power, and batteries just ain't going to help.

At the moment, we need a major technological jump before an interstellar probe is really feasible. We can certainly send something now, but it probably wouldn't make it.

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    $\begingroup$ So aiming is not a problem, it's durability and other things? $\endgroup$ – Manishearth Sep 13 '13 at 4:36
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    $\begingroup$ Given that we'd have 50,000 years mid-travel to correct that aim, no, it wouldn't be a problem. The kind of things that actual rocket-scientists pull-off are fairly impressive, (note: I'm just a guy who reads lots of Wikipedia articles at work.) so there shouldn't be much trouble with hitting a star. $\endgroup$ – john3103 Sep 13 '13 at 5:19
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    $\begingroup$ Hitting a star wouldn't be an issue (+: It's not hitting something en route that we should be concerned about and having the fuel to maneuver in transit if necessary, and at the destination. Then of-course there is the little matter of having someone in place a few millenia into the future to process that knowledge with the transmission lag. $\endgroup$ – Everyone Sep 13 '13 at 6:51
  • $\begingroup$ @Everyone Details, details :p $\endgroup$ – Manishearth Sep 13 '13 at 8:46
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    $\begingroup$ It's also worth adding that one of the biggest fears with sending such a long duration mission is that something faster will come along first, making the point of sending the spacecraft quite moot. $\endgroup$ – PearsonArtPhoto Sep 13 '13 at 15:55
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In addition to what John provided, it's also worth noting that given the scale of tens of thousands of years, the stars will actually move. This is clearly shown in a Wikipedia article. As can be show, Alpha Centauri will only be 3 Light Years away in about 30,000 years.

Nearby Star Movement

Okay, so the fastest mission I've heard of using nearly obtainable technology is the method detailed in this question, graphic provided from XKCD. It results in a speed of 20 au/year, or about 95 km / second. Give that speed, how long would it take to go to another star? Well, that speed is equivalent to 1 light year per 3000 years, give or take. Thus, given the fact that Alpha Centauri is getting closer, I'd say around 12,000 years or so would be possible.

xkcd comic

(image license: CC BY-NC 2.5)

What are the challenges associated with this? I'm going to include a very unscientific list, in my thoughts about what order they should be.

  1. Power- Keeping the spacecraft powered in the void.
  2. Longevity- It's hard to make something that still works after 50 years, let alone 12,000... Furthermore, space is a difficult environment by it self, including a high amount of radiation, making it even more difficult.
  3. Future Faster Space Probe- A huge expense could be spent to launch this spacecraft, and have a spacecraft 100 years later that travels 10% faster reach the system well before. Or it could even be much faster, leading to even more discrepancies.
  4. Communications- There is a significant link margin required to make this work.
  5. Light Speed Delay- Being so far away, the spacecraft would need to decide 100% of what it did, there would be no way to take a few pictures and command a new stack
  6. Objects of Interest- Some work would need to be done to find objects of interest to photograph, such as planets
  7. Course correction- This should be easy enough to accomplish, but would require keeping fuel in the void for a long period of time. Fuel usually has requirements about what temperature to store it at, which might be difficult for such a long journey.
  8. Technology not getting out of date- It's hard to make something still compatible with 50 years of technology, let alone 10,000+..
  9. There's always a fear with such long term items that someone a thousand years later will find a better method to send the probe that only takes 8,000 years, thus making the probe you sent out entirely useless, as it will arrive 2,000 years too late.

And there are no doubt quite a few other very serious issues. Bottom line is, I think the following minimum technology is required to make this feasible.

  1. A way to make the journey in less than 100 years.
  2. Careful observation of the star system to ensure that targets of interest are identified.
  3. Perfecting Laser Communications, or similar, to allow for rapid far communications to occur.
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  • $\begingroup$ I was assuming that the guidance technology would be sufficiently advanced to be able to correct path (or be initially aimed) in the correct direction. But this is a great answer :) $\endgroup$ – Manishearth Sep 14 '13 at 10:48
  • $\begingroup$ @Manishearth: Ideally, yes. It probably isn't that difficult, but keeping the fuel in a state where it can be used is actually quite a difficult problem... And some course correction would have to be done, if nothing else to aim for the planets. $\endgroup$ – PearsonArtPhoto Sep 14 '13 at 10:50
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    $\begingroup$ If anything could be added to this comprehensive list, it would be cosmic rays as a reason for problems with longevity. One might need some exotic biology-like technology which reproduces it self. $\endgroup$ – LocalFluff Oct 13 '15 at 12:40
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In the eighties there was this project 'Longshot' to go to Alpha Centauri B.

Project Longshot was a conceptual design for an interstellar spacecraft, an unmanned probe, intended to fly to and enter orbit around Alpha Centauri B powered by nuclear pulse propulsion.

It was expected to reach and start orbiting Alpha Centauri B in ~100 years.

The journey to Alpha Centauri B orbit would take about 100 years, at an average velocity of approximately 13411 km/s, about 4.5% the speed of light, and another 4.39 years would be necessary for the data to reach Earth.

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