Well done.
Although it is worth mentioning that the Voyagers are still returning usable data. It’s only a trickle, and it won’t last for much longer (as you say, not nearly long enough to reach another star), but there is still a little.
The little space probe that could. I would be privileged to work on such a program.
Stranger
The most feasible proposed design I’ve encountered, is the idea of using nano-technology to develop a tiny probe that doesn’t contain any fuel or traditional engines. You then use a very powerful (and presumably nuclear powered) orbital laser to accelerate the probe to “interstellar” speeds. As the probe is so small, it is quite feasible to obtain speeds of 1/3 of the speed of light quite quickly (e.g. years).
How does such a probe decelerate at its destination or transmit data back to Earth?
Or indeed, maneuver around the system and observe any phenomena of interest?
Stranger
The ‘nano-vehicle’ idea has been around for a while, but as far as I can tell, the level of real thinking behind it amounts to this:
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The only way you can make the math work in terms of being able to send a vehicle to another star system is if the vehicle is very, very small.
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Nanotech is very, very small.
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Nanotech vehicles!
That’s about it. Unfortunately, as more than one engineer in the know has pointed out, “We really don’t know how to make a nano vehicle that can do anything useful.”
There are unfortunate but real requirements for an interstellar probe that nanotech just can’t meet. You can easily do the math to figure out how much power you need to send a signal back to earth given various sizes and directionality of antennas, and nanotech isn’t compatible with any real world values for that. In the real world, you’ll need reaction mass for maneuvering if you want to be able to do anything useful with the vehicle. If you want to image anything, there are real limits on what can be achieved with optics of various sizes, and again, nothing ‘nano’ is really going to work for us there.
I’ve looked at the math behind interstellar flight plenty of times, and it seems clear to me that unless we can come up with a reactionless drive that doesn’t need to throw fuel out the back, we’re pretty much stuck where we are.
Maybe one day we’ll learn how to tap into dark energy or dark matter, or we’ll figure out how to interact with space at a quantum level to drag ourselves along, or some new principle will be discovered which gives us a way to accelerate in space without reaction mass, in which case it’s a whole new ballgame. Until then, I don’t see us meaningfully exploring past our solar system with anything other than telescopes.
I also don’t think FTL is possible. There are two arguments against it: The first is that our current models of physics don’t allow for it. The second is that the evidence has been building for years that the universe is huge (much bigger than the small bit we can see). The Fermi Paradox becomes the key factor then: If we are limited to the speed of light, then our observable universe is finite and there are non-zero probabilities that intelligent life is rare or unique - enough so that it could explain why we’ve seen no evidence of other civilizations and why we haven’t been inundated with Von Neumann probes. But if FTL is possible, then the accessible universe is likely to be so big that the probability of intelligent life that has progressed to the point of creating replicating probes approaches certainty.
In other words, if every point in the universe has access to every other point, then by now we should have seen evidence of other civilizations. For that matter, given the potential vastness of the universe every conceivable outcome should be a near certainty. The fact that we sit here unmolested with no sign of any other intelligent activity is the best argument for believing that faster-than-light travel is not possible in any meaningful way.
If I were writing one for a not-too-distant-future SF novel, I’d probably use some humongous rail-gun-like fixed device to accelerate it to begin with, and then have it start decelerating immediately; I know Bussard ramjets are limited in velocity (in addition to the fact that nobody has the slightest clue what the engineering details would be), but could you use one to decelerate?
This is worth emphasizing. Much of the last few decades progress in electronics that lay people have a view of has been in directions that make for reduced suitability for space use. Mass consumer markets are where the money is, not in making stuff that will last 1000 years in high radiation and deep cold.
Much knowledge has been gained, and progress made, to be sure, but it has happened at levels well below the “Moore’s law” rate that the intels of the world maintain. On the contrary, the cheap consumer stuff makes the custom space rated hardware look even more overpriced and clunky than ever…so it becomes harder to justify to the people that pay the bills.
The money would have to be found for all of these ideas. Sadly, I think that might take a week or two.
To be precise, current models of general relativity do not prohibit for certain types of superluminal or apparently superluminal transit, unless you apply expectations of “causal censorship” that are not rigorously established or proven. However, the conditions and amount of energy required to move any useful amount of payload or information by such methods don’t seem practicable, i.e. requiring energy output comparable to several million years of the output of a medium sized start. In regard to the Fermi paradox argument, it may be that a sufficiently advanced alien species simply has no interest in contacting us any more that we would attempt to communicate with an ant colony. Nonetheless, I think we can agree that interstellar transit, even by mechanical proxy, is not really conceivable using anything like conventional technology, and that fictional elements to permit such scenarios have either glossed over the fundamental difficulties (mass of propellant required to accelerate to useful speeds, hazards of the interstellar medium at relativistic speeds, et cetera) or have introduced indistinguishable-from-magic technologies (warp drives, cryogenic suspension, stable wormholes) in order to facilitate the plot.
Bussard ramjets are very likely not feasible to operate due to some technical limitations that are beyond this discussion, but fortunately you don’t need the ramjet part to decelerate; if you can form a large electrostatic grid you can use that to create a drag on the charged parts of the interstellar medium that slows your vessel. The larger problem is this “humongous” “rail-gun-like fixed device”. I did some calculations a few years ago back in [POST=8020473]this thread[/POST] that indicate that such a device would have to be enormous and would take a huge amount of energy in order to accelerate even a small payload to speeds adequate to transit interstellar distances in a reasonable amount of time. It just isn’t feasible for anything like conventional propulsion technology.
Stranger
Ah. 450,000 km (from the linked thread) is a bit longer than I was envisioning (and I’d want to use something closer to 100G than 1,000G of acceleration, too, which probably means an accelerator that’s at least 4.5 million km long). Still seems more plausible than a traditional rocket but maybe a lightsail plus gigantic [del]wave-motion gun[/del] [del]1920s style death ray[/del] laser would be better.
a 4.5 million km structure that can resist reaction loads of a payload being accelerated at 100 g? I’d like to see that. Tidal stresses on such a structure alone would be enormous.
Non-solid state Lasers are hugely inefficient in power throughput (~1% efficiency) and even high frequency (x-ray or gamma ray) lasers have a significant divergence at interplanetary, much less interstellar distances. Ultimately your efficiency of the system would be measured in degrees of fractional magnitudes. Even if practicable, it would be an enormous expenditure of energy for a pretty small scientific gain, and virtually no practical benefit, at least to reach nearby stars, none of which are particularly interesting (don’t have black holes or other exotic phenomena).
Most of the information we could collect from such a probe will probably be available to us by astronomical observation as that technology improves. There is plenty to explore and exploit in our own solar system, and it is reachable in its entirety by evolutionary extensions of existing or nascent technologies. Exploring other star systems will come when and if we have some revolutionary jump in the understanding of physics and propulsion technology.
Stranger
Yeah, I was going to add a bunch of caveats about causation and information transfer and all that. We might be able to make some things go faster than light, but not in any way that would be useful to us.
Here’s my line of thinking: Since the latest measurements of the geometry of space show that it’s flat to any reasonable level of precision we can measure, there are only two possibilities - one is that the amount of mass in the universe is exactly enough to make space perfectly flat, and the other is that the universe is go immense that the part of it we can measure looks flat even if the entire universe has a curved topology. I think the latter is more likely, and that therefore the universe is either infinite or so immensely big that our own ‘light bubble’ is but a tiny dot in it.
A universe that big has a lot of implications. For one, assuming the laws of physics are the same everywhere, then for any non-zero probability of intelligent, spacefaring life existing anywhere else, there would have to be huge numbers of such civilizations. An infinite number if the universe is infinite. If FTL travel was possible, then they would have completely saturated the universe with Von Neumann probes by now. But if FTL travel isn’t possible, then they can never interact with us, and we’ll never know of their existence.
Since we’ve never found any evidence of any other life, that would indicate that FTL transport is not possible.
Yep. The math just doesn’t work. But telescopes are another matter. The theoretical resolution of an interferometry array can be so high that we’ll be limited simply by the amount of photons that actually make it to the telescope from a distant planet. Given enough processing power, we may be able to build telescopes that can image planets in other star systems down to features a few hundred meters across. We should certainly be able to image the light from major cities, the change in color of continents from vegetation, etc. That kind of capability will keep us busy surveying planets and making new discoveries for a long, long time.
And I don’t think we’d ever bother to send an interstellar probe to another system unless we knew exactly what we were looking for there. We’d need to have a specific question that is of burning importance but which can’t be answered with telescope technology. We’re not just going to fire interstellar probes out to random systems or even systems with earth-like planets, unless we knew there was something there of high value to discover.
I think the only way we’ll ever send useful probes to other star systems will be to start with a large amount of mass like a large asteroid, and very slowly accelerate it by consuming the asteroid mass itself and ejecting it. At first, the acceleration would be trivial, even with something like a fusion reactor heating the mass up to insane temperatures or a NERVA-style nuclear fission propulsion. And this thing would never get up to significant fractions of the speed of light - I’m thinking huge because it would have to be a self-sustaining generation ship if it contained people, or it would have to be packed with redundant equipment if not. We would also put the valuable stuff deep in the center of it to protect it from cosmic collisions. It might take hundreds or thousands of years to get to the nearest star, but by the time it got there is would be much smaller and lighter, and therefore easier to decelerate.
We’d basically be building a wandering rogue planet.
I haven’t done the math on that, but it seems at least remotely feasible. Start with something the size of Ceres maybe. Obviously the engineering required for this means we wouldn’t even have the capability to do this in our lifetimes or even our great-great-grandkid’s lifetimes, but maybe one day.
The problem with this is that if you are producing great gobs of energy, you’re also going to be creating a lot of waste heat. Heat is something we get rid of very easily on the surface of the Earth because there are plenty of cool reservoirs to reject heat into, and the amount of heat produced by artificial industrial processes is dwarfed by the massive influx of solar energy. On a long term space probe, however, where the only means to reject heat is via radiation (which is proportional to T[sup]4[/sup]), getting rid of a lot of moderate temperature heat energy is really hard; you basically have to have giant radiators rejecting heat in a spherical pattern around your craft, or else dump the heat into some kind of coolant reservoir that you regularly exhaust into space, which comprises yet another amount of mass that has to be carried with you. The amount of heat you produce depends upon the efficiency of your energy generation process, but for any conventional process it becomes problematic very quickly at the required energy levels to achieve anything like interstellar flight.
Aside from that, keeping any conventional technologic functioning autonomously for eons is vastly beyond existing capability; basically, you’d have to have some kind of self-replicating, autonomous control and repair, for all intents and purposes an artificial life form, in order to sustain such a mission for the duration required.
Stranger
It’s never going to happen. What would motivate the trip? What would motivate people to sacrifice the time (lifetime) necessary to do so? What would the return be in relation to the expense?
Quoth Stranger:
I can see plenty of practical application. The probe gives you the excuse to build the big friggin’ laser, which is a potent enough weapon to give the faction that controls it overwhelming power, thereby hastening the war that leads to the fall (and eventual re-emergence) of civilization.
Human beings have made greater sacrifices before for something they thought was for the common good; the urge to explore and to be the first to do something - even something very dangerous - is also a strong one. We’re discovering new planets all the time. If our telescopes get good enough to find another earthlike world, there’d be no lack of governments, corporations and people interested in getting there first at virtually any price.
On a related note, what is the fastest we can make a space vehicle fly using current technology? And by “current technology” I mean start design work now with the goal of flight within 10 years.
It isn’t just the amount of energy that would be required to accelerate (and deccelerate at the other end to have any real shot of checking anything out), but the enormous amount of energy and the size of the equipment necessary to output that energy in a form of communications discernable at interstellar distances.
Doesn’t do any good to get a small probe up to 0.1c for a 42+ year voyage to Proxima if, upon arrival, it has no means of communicating what it finds.