I disagree, but I’d love it if you could expand on this a little.
We do not currently have the technology to build a starship. If we made it the top priority of humans on this planet, we could develop the technology in relatively short order, so in that sense, the technology is within our grasp… but we don’t have it yet, and absent some incredible incentive, probably won’t any time soon.
The question is only interesting temporally. Technologically, of course we are closer to Starfleet. We were able to conceive of Starfleet.
Ask him what numbers are going to be drawn in the Powerball lottery on 08/30/2014.
Need answer fast (of course).
Pretty much how I see it.
Except that Starfleet assumes concepts that IMHO are fundamentally impossible, like FTL travel. And without that, treating interstellar travel as anything like international or even interplanetary travel makes no sense, and there goes the whole premise of Star Trek and Star Wars.
I think the proper way to regard the speed of light is that it’s a fundamental property of space-time. I’m going to throw this out there and if any physicists want to correct me on this please do:
There is no physical constraint on how fast light can propagate – it propagates as fast as any reality can propagate through space. In terms of “tricks” like wormholes, I think a useful way to conceptualize the problem is to think of a star like Alpha Centauri, 4 light-years away, as actually existing in 2010, just as we see it. It has no meaningful or accessible existence in “our” present; perhaps in some abstract sense it does, but physically the whole notion of true simultaneity is an illusion. The only Alpha Centauri that we can possibly visit is the one that will exist four years in the future, so that’s the fastest that we can ever get there, and it has nothing to do with the method of transit. If we got there any faster, we would arrive in the past and all kinds of impossibilities would occur, like reversal of cause and effect, and by the same token we’d end up coming back to our past, before we left.
So interstellar travel would most likely have to involve large habitats that were complete ecosystems that traveled for hundreds or even thousands of years and the travelers who finally arrived would in most cases not be the original ones but descendants perhaps many generations removed. What the culture of such a society would be like is a fascinating thing speculate on.
Either that, or we’d have to invent some system of long-term suspended animation, or make ourselves into immortal machine-based life forms.
Spoilsport.
If all this is true, then we will never spread to all those planets that we did not evolve upon, and which therefore would be hells not upon Earth were we ever to reach them.
It’s almost as if there must be some other destiny for Mankind but to people every cold rock in the universe with Mankind.
Andrew Kennedy has written a paper for the JBIS which considers the Wait Equation; the first methods that might be expected to be developed to take humans to the stars will be comparatively slow, and might soon be superceded by faster methods that would overtake them. Certainly there would be little point in sending a mission at Voyager speeds, which would take twenty thousand years to arrive. Using a chain of speculations and assumptions that could be endlessly debated Kennedy arrives at a figure of “1,110 years from the year 2007” for the arrival of the first interstellar mission at Barnard’s Star.
Despite the large number of unknowns and imponderables involved in arriving at this figure, it strikes me as quite realistic, assuming that we never attain translight travel. If we compare this figure of just over a thousand years to the period of cave art in France which produced Lascaux, we are taking about 17,000 years compared to 1000 years; a ratio of 17/1.
Of course there was very little actual cavedwelling going on in those days, and conversely there are still people living in caves today - it is likely there are many more cavedwellers nowadays than in the Magdalenian.
Kennedy’s paper is about the Wait Calculation, not Equation; see
I think Stranger is a hard headed and pragmatic rocket scientist, grounded in the harsh realities of the now. I also disagree with him in these threads, but it’s fascinating to get his thoughts, since afaik he’s the only real rocket scientist on the board, so it’s always good when he weighs in with real world experience.
My own thoughts, however, is that he’s a hard headed scientist around 1900 telling all the wide eyed dreamers that travel to the moon is impossible, even though we can conceive it, and that barring some large technological breakthroughs we will never get there…or it will be hundreds of years, at the least, before we can. He is, of course, absolutely right…we couldn’t have gone to the moon in 1900, or even 1930, no matter what the level of effort would have been. But we certainly could and did by the end of the 1960’s, because we decided we wanted too and technology had been developed during those 60 years in various fields to enable us too. To me, ultimately, going to the stars or not will be a political and economic problem, not a technological or engineering one. We might never have gone to the moon (or not when and how we did) but for the cold war.
Same thing is happening today. Different countries and companies are developing various aspects that could enable us to go to the stars. In addition, there are pure research people who are researching stuff that might seem unrelated or peripheral to space travel, but that could lead to new discoveries in the future. Will we eventually go? Gods know. Maybe yes, maybe no. I think we COULD go either manned or unmanned in the next 50-100 years if we really, really wanted too. But it could be like Mars…something just barely within our abilities to go to and explore but forever pushed into the future as it’s not a priority and no one wants to spend the money or take the risk to do it.
At any rate, I think we are closer to space travelers than ‘cavemen’, since we actually have been to space as a species and taken the first steps in going out to explore planets and other objects in the wider solar system. As a poster said up thread, we are closer because we can conceive of space travel and star fleet, while even as little as a few hundred years ago we couldn’t.
There are a number of reasons why sending an uncrewed interstellar probe, much less any kind of “space ark” will not be feasible within the foreseeable future or using extrapolations of existing propulsion, power, and other technologies. I’ll briefly addresses some of these issues below but these comments are hardly exhaustive.
Propulsion, or “The Tyranny Of The Rocket Equation”
A propulsion system sufficient to deliver a spacecraft to another star significantly faster than the current capability (which has involved sending spacecraft on trajectories using gravitational swing-by maneuvers to achieve a solar escape vector) will have to be far more capable in terms of best propellant mass efficiency (effective specific impulse, the measure of thrust generated per unit mass of propellant carried) than current chemical rocket engines (~450 s), nuclear thermal rocket (~2000 s), nuclear electric ion/plasma (5000 s), nuclear pulse propulsion (~10000 s), or fusion plasma (~20000 s). The rocket equation, properly rearranged, will give a ratio of initial mass to final mass of m[SUB]i[/SUB]/m[SUB]f[/SUB] = e[SUP]dv/(I[SUB]sp[/SUB]*g[SUB]0[/SUB])[/SUP].
To give a feel for this, if you wanted to achieve a delta velocity with respect to the sun of 1% of the speed of light (2.9987x10[SUP]6[/SUP] m/s, with an I[SUB]sp[/SUB] of 20000 s, you’d have to carry almost 4.4 million kilograms of propellant for every pound of “payload” (e.g. all the inert mass of your spacecraft). Mind you, this is just getting up to that speed, at which you would fly through a system the size of our solar system in about seven hours. In order to slow down, you’d have to carry the same ratio of propellant mass to final inert weight; that is, the total mass of propellant carried would be that needed to get up to speed raised to itself. If we contrive to raise specific impulse to 50000 s, the spacecraft now only needs about 450 kg of propellant for every kilogram of inert mass to get up to speed, or over 200000 kg for kilogram mass. At I[SUB]sp[/SUB]~75000 s you finally start to a range within reason (60 kg/kg and 2100 kg/kg, respectively), but practically speaking, that means getting energy density only possible with antimatter, which is its own bag of impracticalities. And even at this, this would be decades of travel to the nearest star system. If you really wanted to get to another system in a practical timespan (e.g. traveling at 10% of c) the require specific impulse is literally astronomical.
This isn’t to say that there may not someday be a method of propulsion or transit that does not rely on acquiring velocity via mass transfer, but our current methods of moving from one geodesic trajectory in space-time to another all governed by the need to conserve momentum and the limitations that come with it.
Avionics, a.k.a. “Somebody Has To Be The Brains Around Here”
Avionics is just aerospace jargon for electronic components and systems which are necessary to operate the spacecraft and its instruments as well as communicate back with a ground station. Avionics components are almost exclusively solid state, which means they have no moving parts and are therefore quite reliable (once they have been qualified and screened, of course). However, reliability is a relative measure. All functioning devices will fail eventually, and avionics are no exception, especially when exposed to regular bombardment by radiation, thermal stresses, power cycle fluctuations, et cetera.
Components that are rated for long term operation in space generally fall into a category called “S-rated”, and are generally qualified for operation on a lifetime of around 10 years. Practically speaking, this means that they can operate, albeit with some reduction in reliability or tolerance, for somewhere around 25 to 30 years. No electronic components have anywhere near the demonstrated capability to operate for centuries required to transit between stars; even if unpowered they are still subject to radiation and aging damage which will cause limit failures (i.e. a failure that is due to exceeding a damage or age threshold) which will not be substantially protected by redundancy.
Power, a.k.a. “The Hungry Beast That Never Sleeps”
We don’t really notice it on Earth, but everything that moves requires power constantly. We are fortunate that we are constantly in close proximity to a source of power that is so massive and wasteful that it expels almost a billion billion gigawatts constantly, mostly rejected to empty space. The Earth receives about 0.2 billion gigawatts of that, and is “designed” such that it moderates the energy such as to keep it at a temperature that water evaporates, is purified and transported around, and keeps the surface from either permanently frying or freezing. This constant stream of unmetered energy also provides us with accessible stores of readily fungible energy, e.g. coal, petroleum, natural gas, solar, wing, hydro, and biofuels.
Even the most basic spacecraft needs power for communications and attitude control. Current spacecraft which operate in the inner system typically use solar energy collected by photoelectric panels, and those which operate at the orbit of Jupiter or further use radioisotope thermoelectric generators (RTG) or (provisionally) fission reactors. The former operate off of natural radioactive decay, and their yield declines exponentially. Moderated nuclear fission can operate at relatively constant rate for the time that fuel elements aren’t consumed (and longer in the case of a breeder-type reactor) but there is no existing or proposed design which can operate for more than thirty years, much less the hundreds of years which would be necessary to go between stars. And even if they were, the spacecraft would require some means to reject the excess “waste” heat that is below the threshold at which useful energy could be recovered. Which then leads to…
Thermal Control Systems, a.k.a. “It Burns! The Goggles, They Do Nothing!”
Every powered system produces waste heat; that is, heat at a temperature level that is below the threshold of being able to extract useable energy but will eventually overwhelm the system. Here in Earth, with the atmosphere and liquid water it is relatively easy to carry away undesired heat via convection. In space, radiation is the only means to reject heat to the ambient environment, and the rate at which a certain amount of heat can be rejected is governed by surface area of outward-facing radiative surfaces. Any spacecraft which is going to be under extended duration of propulsion, communications, et cetera will need to an enormous amount of power, and thus, the large amount of mass devote to heat rejection to ensure that it maintains thermal equilibrium, all of which plays into the inert (non-propelllant) mass of the spacecraft.
Habitat, a.k.a. “The Cost Of Living Is Killing Us”
In the case of an inhabited spacecraft, the vast majority of effort and energy–in excess of 95% in even relatively short duration crewed mission–is devoted to just keeping the bags of contaminated water from freezing, boiling, degrading, or otherwise disseminating in to component molecules. Maintaining the complex setoff conditions for a self-sustaining habitat, even under terrestrial ambient conditions, has turned out to be highly challenging even for a few months. A habitat that can survive decades or centuries is vastly beyond current or foreseeable human experience. In fact, to send “people” to other stars likely requires modification of the organism such that sustaining a terrestrial environment is not necessary, which again, is beyond existing capability. Even a space station in low Earth orbit with a crew of three people requires several tones of supplies every few months. For an interstellar journey, the amount of supplies required is vastly more than all of the tonnage which has been sent to even LEO to date.
No doubt someone will dismiss these issues as just “engineering problems”. But in fact, all of these issues will require fundamental advancements in basic abilities which are far beyond ready extrapolation of current technology. Going to other
Although general relativity assumes a universe that is causally connected, and there are certain consistencies which are satisfied by this assumption including our everyday experience on the macroscopic level, this is in no way assured, and in fact we know that this condition is at least nominally not satisfied in most interpretations of quantum mechanics. It may very well be the case that non-causal connections are allowable and that we can zip around the universe with wild abandon to the normal laws of general relativity. But not with any existing technology or development thereof, nor are we likely to do so in the sense envisioned by Star Trek or other convention space opera.
Stranger
Thanks, Stranger. Much appreciated.
Stranger, did you really just post “kilograms of propellant per pound of payload”?
This is mostly correct. c is in fact a fundamental property of spacetime, and is the upper limit for how fast information can propagate. Light travels at c because it’s massless (or so close to it that we’ve never been able to tell the difference), and anything massless must travel at this maximum possible speed. Given a reference frame, it is possible and meaningful to speak of “alpha Centauri, right now”, but just when that is depends on your reference frame, so absolute simultaneity is impossible. And if there is some method to achieve a faster-than-c effect, whether by warp drives, wormholes, hyperjumps, magic carpet rides, or whatever, then according to special relativity, that same method could also be used for time travel with all the paradoxes that entails.
Just a regular mechanical engineer checking in to back up Stranger, who always seems to get a bit of flak in these threads (or is it meteorite bombardment?) when he posts how hard the technical problems are for interstellar spacecraft.
He’s right, they’re HARD in the sense that we can’t solve them at all with known technology.
Fast simple probe - OK, our fastest extant probe is the New Horizons Pluto mission, at 21 km/s. At that rate of speed, it could reach Alpha Centauri in about 57 000 years. Building something that can work for that amount of time is not possible, especially in space. Getting the signal back is a big issue as well.
Slow colony ship - OK, estimating the energy required to keep a modest sized closed ecosystem alive at equal to the sunlight falling on a 10 km sq area for, say, a million years) means that we don’t extract enough energy as a civilization yet to do this, even if we could store it all compactly enough to send it off with our travelers (which we can’t).
We really need almost infinite durability materials (or self-repairing), infinite energy density, magic genetic engineering so people can live to million year lifespans with no food and radiation aplenty, or grow from “seeds,” or “hacks” to the universe to make this stuff work.
Nothing can travel faster than light. Physics says so in no uncertain terms.
It pains me to understand that maybe we will always be closer to cavemen than space travelers.
I’m not really disagreeing with you, since I know that there are extreme difficulties associated with interstellar travel, but some of these impossibilities are somewhat overstated. I’m still not clear on when the human race is supposed to have been ‘cavemen’, but if it was 17,000 years ago we have a long time to tackle these problems
Very durable materials, including bulk-synthesised diamond and carbon nanotube based materials, could be available within the next thousand years or so, probably much less. Self-repairing materials are also very likely to become available for this sort of project, although reversing the entropy of decay will always require an input of energy.
Probably the biggest problem facing interstellar flight is energy density. For a million-year flight vast amounts of energy will need to be stored; and for a much faster flight even more energy will need to be stored to decelerate at the destination.
This problem can be reduced by a sort of cost benefit analysis; a million year flight to Alpha Centauri implies a speed so slow that you couldn’t escape the Solar System (unless you started the mission from Haumea or somewhere right out on the fringes).
A Generation ship would need to go a couple of orders of magnitude faster, say 300km/s or so, limiting the duration between the stars to a few tens of thousands of years; still a long time, but requiring much less stored energy. On arrival you would need to slow down from this speed, requiring much more stored energy in the form of fuel - but the great thing is you don’t have to decelerate the entire massive spaceship which has protected you for ten thousand years, but only a fraction of the vessel, just enough to support you on arrival.
So it is possible to calculate the trade-off between stored energy for life-support and stored energy for deceleration, and pick the point at which the sum of these two values is lowest; to be honest I have no clue where that sweet spot would lie, but in the next thousand years or so we could get a better idea.
Now you are talking. Lots of people only look at the problem of interstellar flight from the mechanical engineering point of view. But developing interstellar flight will take so long that there will almost certainly be remarkable leaps forward in the biological sciences, as well as in information technology. Our first ships to the stars won’t take ordinary, vanilla humans, but humans that have been radically engineered to persist in space, or seedbanks and artificial wombs of various kinds, or digitised DNA, or digitised minds that can be switched off while in transit. No Captain Kirk sitting in a chair, but a clutch of almost unrecognisable technologies that haven’t been developed yet.
But almost certainly not technologies of this sort. ‘hacks’ to the universe would be wonderful, but they don’t seem to be available - if they were, the Fermi Paradox would be even more paradoxical.
Do you mean emotionally closer? Because I have a fondness for neanderthals that I will never have for space fare.