Can we build something that we can expect to survive the several hundred year journey and still work? Can we build a transmitter powerful enough to send back results? Could we manage more than a flyby?
It’s that first one that’s gonna be a doozy. With current technology, it’s more like several thousand years. But, even if ion propulsion lives up to it’s potential and can get a spacecraft to say, a few percent of light speed eventually, we’re still talking about keeping something highly complex operating in the harsh environment of deep space for a couple hundred years. I don’t see that happening; not with current tech.
On a related note, given the current technology, what’s the fastest speed we could make a space probe fly at?
I’ll settle for 1% of c, so the Centauri are 4-500 years away. But there’s one misconception: we don’t need the probe to work all along the way, just at the start and when it gets there. s there some radioactive substance that will decay sufficiently in that time to engage a switch to switch on the probe?
I don’t think we have any semiconductor processes, even old ones, reliable enough to make things last that amount of time. There are ways of building redundancy into designs, but there are always going to be some single points of failure. Triple redundancy is certainly not going to do it, and I doubt we have the propulsion systems to accelerate anything heavy enough to last.
We don’t even have experience with things lasting that long - ICs are only 50 years old - and even if we could look at the electronics of old telephone switches we probably couldn’t build anything smart enough with the constraints of that old a technology. Add to that the hostile environment accelerating reliability problems, and we’re nowhere near a solution.
People in reliability talk about the bathtub curve. New devices fail more frequently due to infant mortality issues and defects that escape tests. Then there is a long period of low failure rates, and finally, on the other side, a period where we’re hitting the life expectancy of a part. There are equations predicting where this is (nowhere near a century) but for the products I work on we never see it, since by this point the IC is so obsolete that no one cares, and the less reliable parts of the system, like the fans and power supplies, have failed anyway.
So the answer is no, and it would take a lot of work to get anywhere near it from the electronics perspective.
[ul][li]We don’t currently have the technology to accelerate even an unmanned probe up to speeds of crossing the 4.3 light year distance to the Centuri system. The Voyager 1 probe, moving at 17.4 km/s, is moving at .0058c, and would take over 17 millenia to get there (if it were heading in that direction). Using nuclear pulse propulsion (such as the ORION) or a fission fragment or nuclear liquid salt type propulsion could deliver sufficient specific impulse (a measure of rocket performance) to support a reasonable transit interval, delivering the probe to a nearby star in a couple of centuries or perhaps less, but these are all still conceptual designs that have not been proven in practice (although a limited proof of concept was performed for ORION using conventional explosives and scale models).[/li][li]Building a sufficiently powerful transmitter would be tricky, but not beyond conception. Powering it by an internal source would be difficult; it would probably be much more effective to have a central transmitter with an unfolding solar array and a very powerful x-ray or gamma ray laser (to distinguish from the normal bands radiating from the star), and then interplanetary probes that would relay to the transmitter. [/li][li]Given the level of effort required to get the probe to another system it seems intuitive that you’d want it to be able to slow down and explore the system rather than just fly by at very high speed with little opportunity to make detailed scientific observations. Unfortunately, the propellant requirements to carry sufficient propellant for deceleration become prohibitive except at very high specific impulses, even higher than can be achieved with ORION or other fission-based propulsion systems. This means that you need to have an even higher efficiency system–some kind of confinement fusion, or energy conversion, or something else that is, at this point, science fiction–or you need to be able to decelerate without using carried propellant. The trick of planetary capture, done with some interplanetary probes, won’t work here; the interstellar probe would be moving way too fast with respect to the target star to deliver any useful amount of momentum before escaping. You could, however, accelerate the probe up to speed, and then use the drag of the interstellar medium, as thin as it is, to provide a lot of deceleating force. Create a large electromagnetic field which transfers momentum to H[sup]+[/sup] and OH[sup]-[/sup] ions in space, calculated to slow the ship down to captures speeds by the time it reaches the target. You increase overall transit time, but because you don’t have to carry propellant for deceleration you essentially place no upper limit on how large of a payload you can send, provided you can accelerate it to sufficient initial velocity.[/li][li]As for building a probe to last for such a journey with any reasonable degree of reliability: in a word, no. The Voyager and other interplanetary probes have been amazing in how much punishment they’ve been able to take far in excess of design criteria and continue to function, and where they’ve failed or been damaged, engineers and flight controllers have been very clever about figuring out fixes and workarounds, which is pretty amazing considering that all information about the state of the vessel comes via a communication channel that makes a 300 baud modem look like a T-1 connection. But we’re still talking about operation for only a few decades in well-known conditions. An interstellar probe would have to survive for a couple of centuries or more at high speeds where a single grain of dust is as destructive as a tactical nuclear weapon, and delivered to unknown radiation and contamination conditions, and well beyond the capability for mission planners to execute any fix in a useful time period. Such a system, in order to have any reasonable degree of reliability and mission success, would have to be essentially autonomous in evaluation of system status, mission actions to achieve programmed objectives, and self-repair. This is way beyond the current state of the art in machine intelligence and autonomy. [/ul][/li]
This is not to say that it can’t be done in the future–perhaps, given a few revolutionary breakthroughs in applicable technologies, the not fantastically distant future–but we can’t do it with what we have, or what we know that we’ll have in the next ten or twenty years.
Stranger
Hmmm…using Project Orion technology (which is not proven, but anything that Freeman Dyson helped design gets big points in my book) we can accelerate pretty much any reasonable mass to some (small) % of lightspeed, yes? If we build a generation ship and stock it with clever people–some from right here on the dope, I’m sure–we should be able to a) get a working ship there and b) do something about it when they arrive.
That’s all using (almost) current technology, and getting rid of most of the left-over-from-the-cold-war A-bombs as well…a bonus! Those pesky we-haven’t-dealt-with-the-timeframe problems will be dealt with by cleverly raised kids who will solve the problems by using their human intellects and advice from Earth humans (if THEY survive that long).
Practical problems? Sure, but no greater than those inherent in any undertaking of this magnitude. The Great Wall took longer than we’re talking about, and certainly there were changes in plan…but it kept going. I’m thinking we could do it.
If they pack a few hundred extra A-bombs, they could stop and colonize. 
Biosphere II was a complete disaster. If we can’t manage to maintain a survivable closed environment right here on Earth for a few years, a few hundred in deep space is entirely out of the question.
One thing that doesn’t seem to have been adressed is the “home base” situation…
IF (Big “IF”) we could somehow manage to design build and launch a starprobe, and it would take many hundreds or years or even longer to reach the star, would there still be a base to listen to it. I can easily see such a project being “Proxmired”… “Y’all want $ to wait 1000 yrs for a beep from space…!!!”
That would be, the biggest hudle, even if we could manage the tech and applications…
FML
Biosphere II was a disaster largely because it was a first attempt, and there were unforeseen problems. A second attempt would be more likely to succeed, given the benefit of learning from experience.
But the OP is, I think, referring to an unmanned probe, so it’s irrelevant anyway. I think a crude probe could succeed. We get round the short lifetime of semiconductors by using good old-fashioned thermionic valve technology. Don’t laugh… all we need is a simple camera attached to a radio transmitter. We don’t need an onboard computer with millions of transistor switches. A large enough probe could do it all using miniature valves (they wouldn’t even need to be in evacuated glass bottles, it’s a vacuum out there anyway).
You realize that the orginal electron tube computers had uptimes measured in hours, right? Vacuum tubes are robust against ionizing radiation, but not so great in shock, vibration, thermal cycling, et cetera. And the size of a machine built with such an architecture capable of performing even the most trivial avionics and guidance control would be prohibitively large; my fifteen year old scientific calculator has more computing capability than ENIAC by a couple orders of magnitude.
As for “…all we need is a simple camera attached to a radio transmitter,” that would be a wholly inadequate system for autonomously exploring a planetary system. If you’re going to go to the considerable bother and astronomical expense of sending a probe across interstellar space, you are going to want to pack every scientific instrument possible onboard (although they’ll all be completely obsolete by the time the probe reaches its destination, but that can’t be helped). And because communication to, say, the Centauri system is 8.6 years round trip, the probe would have to be capable of autonomous decision making using some rough guidelines programmed in.
Transmitting via radio would also not work; because of the divergence of radio frequency emissions most of the energy would be spread out and lost against the emissios of A and B, and the cosmic radio background; even using a finer high frequency laser for communications is going to have the beam spread across the girth of the Solar system, requiring very high transmitting power.
Nothing about going to another star system–even by proxy–is simple by any current standard.
Stranger
Some famous science fiction writer postulated that sending a vehicle to the nearest star was folly. The problem being that by the time it was a few years into its journey, we would be able to build a new probe fast enough to overtake it, and the faster probe would in turn be passed by an even faster probe. I guess the point was we might as well sit tight.
This is a slight hijack, but what exactly limits the maximum speed such a probe could travel? AFAIK, velocity as such is not harmful to physical objects; what causes problems is sudden acceleration or deceleration. I have no idea which is the maximum acceleration such a probe could withstand without suffering damage, but this (admittedly not very scientific) website says the rockets in the Mercury, Gemini and Apollo programs of yore provided acceleration of 6-9g. So I assume that 9g, which is about 88 m/s², should be safe. If countinously accelerated at this rate, our probe could reach 0.01g (which Quartz gives as the limit) in about 34,000 seconds, or approximately 9 hours (unless I goofed something up in my calculation, but I computed it several times over). What would prevent our probe from going on at this rate of acceleration for another while?
The need to burn fuel and oxidiser at several tonnes per second, I believe. Which means that your probe will need to weigh tens of thousands of tons. Which will in turn mean that your rocket will weigh so much more than Apollo/Gemini/etc. that it won’t take off - you’ll need lots more rocket engines. Which will burn up the fuel in a few minutes at most. So you need more fuel, and round and round you go.
I Am Not A Rocket Scientist, but I believe that is what Stranger was alluding to in his first bullet point.
Significant Acceleration = Easy.
Sustained Significant Acceleration = Double-Plus Not-Easy
Do they explain how we get the experience to build better probes without building and testing the early one’s first? It’s sort of like saying that the Spanish shouldn’t have dicked around with all those sailing ships and instead waited for steam powered iron hulled vessels before bothering going to the new world.
To the OP I’d say that propulsion is the only real show stopper. I think we do have the technology to make something robust enough to have some functionality by the time it gets there…if you could actually GET it there in a reasonable time period (say a couple of centuries).
Out of curiosity though, is there even anything interesting to look at wrt to closer star systems? Would it be worth the effort to send a probe there?
-XT
Thats not quite an equivalent analogy. In 1492, it only took two months to transit the Atlantic and newer faster technology was nowhere in sight. Verily, the age of steam was still over 100 years in the future. In the case of trying to reach another star, we are talking about a 500 year transit. Given the pace of current technological advance we can reasonably assume that we will discover some new method of transportation within the next 250 years that is more than twice as fast as currently possible.
Why “harsh environment”? It’s (nearly) a vacuum, and if the probe is unmanned it presumably wouldn’t have to be pressurized, so other than its own propulsion system and radiation there should be no forces acting on it at all, right?
Accelerating even a small grain of dust (by impact) at speeds at a measure fraction of c would do a considerable amount of damage to any reasonable structure. A large ablative shield–water ice matrix with a high tensile fiber reinforcement would be good for this–would have to be accelerated in front of the probe for protection.
We can accelerate a rocket using chemical propellant at several gees for only a few score of seconds before exhausting propellant. Even at equivalent constant propellant velocities on the order of 100,000 m/s (vastly more than can be done with chemical propellants, and at the credible upper limit of nuclear fission propulsion with conventional materials technology) you can only carry enough propellant to accelerate at this level for a few minutes without the mass of the propellant dominating the mass fraction of the vessel. I[sup]sp[/sup] on the order of 100,000 seconds or greater would be necessary to accelerate a payload to a measurable fraction of c and still have enough capacity to carry fuel for deceleration in addition to payload mass.
If you can place your propulsion power source outside of the vessel–say, by using external laser propulsion and a reflective sail–then there is no upper limit to acceleration, though the significance of propulsive effort will decrease with vessel speed in ratio with vessel velocity to propellant velocity. However, the energy required to do this is enormous (especially considering the throughput inefficiencies of high power lasers) and the power density at distance will decrease with respect to the divergence angle; even for a high frequency laser you would have to have an enormously powerful source and a vast reflective lightsail to get any propulsive force per kilogram of payload at interstellar distances.
Stranger
So, if we can’t supply our probe with more than X amount of thrust because it will require too much fuel and therefore be too heavy to achieve orbit/leave our atmosphere… why can’t we just launch it in pieces and assemble it in orbit, like a space station?
It’s not just a matter of getting it to orbit (though for anything much larger than the American Space Shuttle, we would have to launch it piecewise and perform an Earth orbit rendezvous and assembly), but in order to maintain a constant thrust you have to continually expel propellant, which means you have to carry the mass of that propellant along with you until it is ready to use, which means you have to carry more propellant, ad nauseam. This recursive requirement (carrying more propellant in order to carry more propellant) plus the dead mass of the vessel creates a limiting criterion on how much actual payload you can carry per unit mass of propellant for a resultant velocity. Using any conventional technology, you end up needing tens of thousands or more kilos of propellant to accelerate one kilo of actual payload to even interplanetary speeds, which is why gravity assist maneuvers are used on nearly all missions to the outer planets, essentially hitching a ride to get a “free” change in velocity. (It’s not actually free, because whatever momentum the probe gains is lost by the planet, but since planets are vastly more massive than probes they’ll never miss it.)
The only way around this prohibition is to place the propulsion source, or at least the propellant outside the vessel. The laser system mentioned above is one proposed way (i.e. Dr. Forward’s “Starwisp” concept, which used microwave propulsion) but the payload capability is absurdly low for any practical purpose. Another concept is the Bussard-type interstellar ramjet, which would scoop up propellant out of the interstellar medium via electromagnetic fields and compress it to fusion PTD. Unfortunately, for the Bussard-type process to work the ship would already need to be accelerated to a fair clip, and drag and limits on exhaust velocity from incomplete fusion would probably place a limit on maximum vessel speed that would limit it to a few percent of c at best; all of this beyond the technical issues of workable confinement fusion, powerful superconducting magnets, and shielding against said magnetic fields for electronic equipment and organisms.
So even given practical controlled nuclear fusion, traveling between stars is pretty far out there in terms of the technology required. Unless someone develops some kind of indistinguishable-from-magic zero point energy source or space-frame-dragging propulsive drive, getting a payload from one star to another (and protecting it on the journey) is in the realm of science fiction, not technical plausibility.
Stranger