(I’m putting this here instead of GQ because it seems like a speculative question that’s open to debate.)
If we wanted to send a probe to another star, what would be the best way to do it?
It seems like there are a number of serious engineering challenges to overcome:
[ul]
[li]Accelerating it so the trip takes a reasonable amount of time.[/li][li]Decelerating it so that it can actually do some science when it gets there.[/li][li]Building a machine that can function reliably after decades or centuries in space.[/li][li]Creating an AI that can make complicated decisions without human intervention.[/li][li]Broadcasting a strong enough signal to get the data back to Earth.[/li][/ul]
Can this even be accomplished with a self-contained probe like we currently use to explore the solar system? Or would it require a “von Neumann probe” … a tiny self-replicating device that would assemble the real probe out of raw materials in the target system?
Well, at least the Voyagers are still communicating and accellerating well after 30 years from being launched, so scaling up from those would be a good place to start. The ion engines will have to be a hell of a lot more efficient. Good luck with the communicator. That probably won’t work until we reach a new star to power up the solar panels, and even then it will take years before the signal reaches earth.
The Voyager probes will take about 75,000 years to travel the 4 or so light-years required to reach the nearest star. A viable interstellar probe would need to be moving 100x to 1000x faster.
Which also raises the issue of shielding against dust impacts … .
As mentioned in another recent thread, for the foreseeable future it will be easier to build better telescopes than send a payload to another star system. If you can build an interstellar probe you can also build a telescope with a mirror kilometers in diameter, linked with another telescope hundreds of millions of kilometers away to form an interferometer. But let’s say that’s been done, and we hit paydirt: an oxygen-atmosphere planet in the Alpha Centauri system has been detected and surveyed as thoroughly as possible from our solar system. So given a high-value target and the closest possible interstellar mission, how do we go about it?
Everything depends on just what propulsion technology is available. A safe bet is that if we are in a position to even consider it we have either fusion, advanced solar beamed-power, or both. A pure fusion rocket with a plausible mass ratio might be able to accellerate to 5% of lightspeed and slow to a stop again at it’s destination. So that’s approximately 90 years to A. Centauri. If some sort of lightsail or magnetic propulsion is available, that might improve either the trip time or the payload ratio. Antimatter is a much longer shot- it depends on just how efficiently it can be synthesized. Perfectly ridiculous amounts of energy would be needed to create large amounts of antimatter, although an extremely energy-rich solar civilization might be able to afford it. Smaller amounts might make it possible to build “catalyzed-fusion” designs with higher performance than a pure-fusion rocket.
Presumably by the time a space-based civilization is cabable of considering an interstellar probe, design will be mature and tested enough to function reliably for the length of the misssion. Communication back to Sol system won’t be a problem: given nuclear power and the ability to unfold a large antenna dish, it could be done with today’s microwave technology.
If the travel time is anything more than a couple of decades (very likely), then some sort of human-level intelligence will be necessary at the end of the trip. Either a very advanced AI, or if hibernation is perfected, a suicide volunteer for a one-way trip(!)
Actually the movie Avatar did a very good job of portraying the most plausible foreseeable technology capable of transporting people to a nearby star system.
We will have nothing to do with the first interstellar probe. It’ll be an entirely AI-conceived and developed thing. And they’ll send their own - when you can set your brain’s clock speed yourself, long voyages become a lot less of a handicap.
Not one dependent on sunlight, but there have been many proposals for launching interstellar payloads using a lightsail and beamed power in either laser or microwave form. Although this approach may or may not be workable, it would avoid the problem of exponentially increasing mass that rockets suffer from.
Given the vast distances and the rate at which technology is changing, I suspect that the first interstellar probes sent out will be passed en route by probes developed later. Until we reach a technological plateau, or bring the travel time down to say 100 years, I don’t see any point in sending one out.
I remember a short story in which the first manned Earth probe to Alpha Centauri was all but forgotten, its crew still in suspended animation, and it caused an accident when, centuries later, a much faster starship on a routine Earth-to-Alpha Centauri cruise almost hit it and had to take evasive action.
To be clear, the Voyagers are not accelerating, other than due to gravity (which is hardly a credit on them). They don’t have ion engines (I’m not sure if you were implying that they do), and most of their rocketeering was right after their launch. They used very small rocket engines for in-flight course corrections, to swing past the various planets just right to get orbital slingshot effects off of them, and it’s those orbital slingshots that gave them most of their speed.
Now, a true interstellar probe almost certainly would also use orbital slingshots, since after all, it’s basically free energy, but there aren’t any planets out in interstellar space, and there’s a limit to how much speed you can get from a slingshot in the Solar System. That’s not nearly enough to get you to another star in any reasonable time span, and the technology to do so bears very little relation to anything used by the Voyagers. They’re not really much of a step forward, in that regard.
The Voyager probes (which are just retasked Mariner buses and propulsion systems with some more advanced science and observation instruments) also don’t have anything like the longevity to survive an interstellar mission. The Voyagers were originally intended to survive about a 10 year mission life, though the RTGs were sized to provide adequate power for far longer, and estimates of power decay have turned out to be conservative. Although both probes have survived substantially longer, despite exposure to the degrading radiation zones and intense magnetic fields around Jupiter, allowing completion of the “Grand Tour” mission originally championed by NASA before accepting the scaled-down Voyager profile, they’ll in no way be functional along any length of time necessary to reach another star. The level of reliability in computing and mechanical hardware just does not exist to support any realistic expectation of functionality for that duration.
The first interstellar probe will most likely look something like Freeman Dyson’s Astrochicken; small, cheap, reconfigurable, and capable of self-repair. We are a long way from producing that kind of technology for a space exploration application.