As has been pointed out upthread, ion engines have limitations that may make it impossible to scale them up. But that’s ion engines proper; I suspect what many posters have been using the term really mean is what’s properly called a plasma engine. Or more broadly, “nuclear-electric”.
Regarding lasers and accelerators: given that anything that could boost a mass to a substantial fraction of the speed of light means generating and concentrating enormous amounts of energy, pretty much any interstellar technology is inherently also a potential weapon of stupendous power.
Not crazy. Just ignorant. The problem is that the distance between stars is enormous. That means an object traveling from Earth to wherever has to be accelerating for a long time to reach some nontrivial fraction of c. But the longer it has to accelerate, the more fuel it has to carry. The more fuel it has to carry, the more massive the ship becomes and the more fuel it needs.
IOW, accelarating an object to some nontrivial fraction of c requires a rail gun with a barrel length some nontrivial percentage of the distance between Earth and your destination.
No. We have a knowledge of basic theory of nuclear fission reactors, but the practical experience and applied knowledge available today of reactors compact and light enough to be flown as vehicle upper/transtages or spacecraft propulsion is virtually nil, owing to the fact that no one has worked on actual hardware since the early 'Nineties.
In a priority crash program where money, regulatory approval, and environmental impact were not considerations we could probably develop, test, and fly such a thermal fission engine within ten years. However, it would be comparable in terms of maturity to the first atomic weapons developed by the Manhattan and ‘Super’ Projects; inefficient, unsafe, and of shockingly low reliability. An offhand estimate would be that it would take a minimum of twenty years of concerted effort, including an extensive test program, to get the technology to a level where it could be considered to be reliable enough to be practical for use.
Although that is a SWAG without any detail analysis behind it, I’m basing that on the overall trend for developing new technologies from a proof-of-concept state to a level of maturity suitable for commercial/production use. If you look at the maturity trends of any complex, multidiscipline technology (automatic/electronic fuel injection, digital computing, inertial navigation, et cetera) there is a definite threshold at or beyond the twenty year mark at which you can now go to manufacturer and say, “Build this special thing for me,” at which you’ll get something that looks and performs more or less as you’d expect it to without constant tinkering and replacement. What is interesting that after that point such technologies (provided there are commercial applications for them) are typically only five to fifteen years from specialty or unique items to being “off the shelf” components with lower cost and vastly improved reliability.
So if we started working on nuclear thermal engines today and provided we didn’t run into any fundamental hiccups requiring breakthrough discoveries or technologies (as controlled nuclear fusion has), we could have a “working” (i.e. reliable enough for medium risk-tolerant usage) by about 2030, and something that could be a standard configuration propulsion system by about 2040-2045. Of course, if we’d never stopped working it back in the early 'Seventies, we could have had a working nuclear thermal engine in the 1980-85 timeframe, and a standard configuration item in about 1990-2000. Studies on the use of NERVA-derived engines (SNTE) for the Apollo-N and STS, as well as new design space vehicles like STCAEM and LANTR, while perhaps optimistic as advocacy studies tend to be, support these timelines.
Hm? 4.5 million km (from Stranger’s link earlier), while it’s not remotely plausible as a construction project by our current understanding of the laws of physics, is something like .0001% of the distance to Alpha Centauri. The difficulty is the absolute difficulty of building a structure that would be much larger than Jupiter.
Are you asking about theoretical technical ability, or including political realities? If the former, a ‘Project Orion’ style nuclear pulse propulsion craft could probably reach alpha Centauri in about a century. However, it would create fallout and EMP tons of satellites, so there’s no political way it could be done.
(One could of course be assembled in a sufficiently high orbit to avoid these problems – but not in a decade.)
For that you just need to boost it a short ways from Earth (ideally a few million km outward from the sun) and let it rip. No need to worry about fallout or planetary devastation if the entire thing goes up and then comes back down.
Perhaps we could create micro-probes small enough to carry a payload of strictly information of how to construct a communication device using a universal, mathematical primer. We send out hundreds of these. Fire them up to a reasonable fraction of C, using whatever method, and with an adequate AI aboard, it can course correct to aero-brake using local planets, or the star(s), and eventually devise a course for a crash landing (or orbit) to the target planet.
If there’s intelligent life, and we’re extremely lucky, the information will have survived the impact. They construct our interstellar telephone, and then so begins First Contact and transmit shared information and tech.
If there’s no intelligent life, Perhaps it can send back pics and other data.
The problem with this is that the smallest ORION-type craft have a minimum mass of between 5000-10000 metric tons (forced by the mass-damper-impulse propulsion method) the largest rocket ever launched, the Saturn V, has a capacity to Earth escape of 45 metric tons. While improvements in propulsion technology and concepts to size up the payload capacity might give more payload–the Energia Vulkan rocket could theoretically carry up to about 80 tons to escape orbit–you’re not going to see a two order of magnitude or more improvement of capability using chemical propulsion, nor is it going to be feasible to launch hundreds of payloads and assemble them into a working ORION craft with anything like conventional logistics and on-orbit assembly technology. And even if you could, even an ORION isn’t going to be able to deliver a useful payload at interstellar distances over a mission duration in which the reliability of microprocessor-based control systems or fluid-cycle thermodynamic systems are going to be reliable, much less slow it down once it gets there.
Although your concept has some merit, there are some significant problems that would have to be addressed before even discussing particulars of the necessary technology and implementation. First of all, the concept of a “universal, mathematical primer,” is problematic; while there are certain numbers that fall out of basic geometry and number theory, such as 0, e, and π, we cannot take it for granted that any alien race would use a particular number base or indeed, discrete number theory at all. It is entirely plausible that their entire understanding of mathematics is so foreign that any attempt to try to render our own into a universal format, like binary, will be completely incomprehensible to them.
Second, while the propulsive difficulties of achieving speeds anywhere close to c have already been addressed, attempting to use aerobraking to slow the probes down has its own set of difficulties, including knowing the positions of planets and the composition of their atmospheres to a sufficient degree of precision to be able to use aerobraking without risking catastrophic destruction, having propulsive capability adequate to alter course to perform aerobraking, and the fact that at interstellar speeds intercept by even a small amount of matter–even a sparse cloud of individual molecules–will be enough to destroy an unprotected craft.
Third, the assumption that an alien species will construct a transmitter and beam communications back–even assuming they have the capability to do so–is highly questionable. The probability of inviting an alien race to invade seems pretty low, but the logic or motivation for an alien race expending a phenomenal effort to return the message in a bottle is not apparent. We assume that our curiosity beyond profit or direct benefit would be shared by any intelligent species, but that is a very anthropocentric point of view.
Fourth, the probe itself sending back pictures and data is going to require both a very powerful transmitter–somewhere in the tens of gigawatt range or better–and a giant array of receivers. This isn’t like sending messages back from the Moon or Jupiter, which are complex enough; this is many, many orders of magnitude more difficult due to both distance, obscurance, and having to locally “outshine” the star about which the probe is in orbit.
Basically, the “micro-probe” concept only works if the probe is self-repairing and self-replicating, and ultimately capable of building and powering said transmitter out of raw materials extracted from the system in question. This technology is, of course, beyond anything in our current toolbox, though not beyond comprehension; Freeman Dyson’s “Astrochicken” concept, which used a lifeform adapted to the conditions of interstellar space, could perform this mission, albeit still requiring bioengineering technology that is essentially science fantasy at this point.
Basically, it is going to be a very, very long time before we can start to contemplate any kind of realistic probe to explore another star.
Actually there was a proposal for a nuclear-pulse design scaled down enough to be boosted into orbit by a Saturn V, though it’s performance tradeoffs mean it wouldn’t be useful as an interstellar vehicle.
If the O.P.
is seriously interested in this subject it would be very worthwhile them checking out The British Interplanetary Society.
I used to be in this years ago and assume it is still in existance.
It is a serious organisation made up of intelligent, and often highly qualified, enthusiasts and is most certainly not a loony tunes, "The aliens are amongst us "type outfit.
In spite of its title it was also interested in interstellar travel.
I haven’t read my way all through the thread(due to time constraints) so apologies if someone else has already mentioned it.
