Projections for the first interstellar voyages, based on extrapolations of our current technological state and current investment into space exploration, will almost always place such missions hundreds of years into the future.
To emphasize this point, the Augustine Committee, a review of the United States human space flight program, found that a heavy lift rocket that could return us to the moon - a destination that, in the grand scheme of things, is right on our cosmic front doorstep - would not be available until approximately 2030.
Compound that with the fact that the committee also determined that the lunar lander, necessary for manned landings, would not be ready for many years after. It's therefore easy to grow skeptical about the prospects for an interstellar mission that could be launched this century.
While this is true, I believe it would be a gross misjudgment to write off an interstellar mission so quickly, since it does not take into account disruptive breakthroughs in both technology and the economy that might drastically accelerate such an aspiration.
WIDE ANGLE: Project Icarus: Reaching for Interstellar Space
Broadly speaking, there are three areas of possible 'disruption' that might fast-forward humankind's first exploration of another star system.
1. Ease of Access to Space Access to Earth orbit is expensive, and wildly wasteful. A typical space shuttle mission, capable of transferring about 25 tons into orbit costs close to half a billion dollars, requires months of planning and a small army of support staff. Access to space is neither easy, nor routine.
However, the space shuttle paradigm is only one model of space access. For example, the UK company Reaction Engines has been designing and testing elements of the Skylon launch vehicle, which would utilize an air-breathing rocket to access earth orbit with just a single stage engine.
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Using the 'Sabre' engine, Skylon would require much less propellant than any conventional rocket, and would reduce launch costs by about 23 times, making access to space far cheaper and, possibly, ushering in a new era of exploration as the technology is adopted.
This is just one example of many "disruptive technologies" that would provide us with cheap and easy access to space. Possibly the most exciting examples of 'easy space access' is the Space Elevator concept, popularized by Arthur C. Clarke in his novel 'The Fountains of Paradise.' The central idea behind a Space Elevator involves lowering a cable - perhaps constructed from asteroid material - from geostationary Earth orbit to the surface of the Earth. The cable would connect with some point on Earth located at the equator, and would allow mass to be transferred to orbit using electricity instead of rocket fuel. Prices for space access would be approximately $100 per pound, or about 100 times cheaper than conventional launch systems.
Skylon, the Space Elevator and other pioneering technologies are receiving serious attention within the space community and any breakthroughs over the coming decades would profoundly change our attitudes toward space exploration.
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2. Commercialization of Space
Space exploration is often seen as an expensive adventure, with little return to the economy, or the investor. I would argue that the Apollo program accelerated the development of miniaturization technologies, including the microprocessor - now responsible for multi-billion dollar industries.
However, it's important for investors to see tangible, rapid and direct returns on their investments. Thus, one critical component to accelerating the construction of an interstellar mission will be the commercialization of space.
John Lewis, in his book "Mining the Sky," estimates that one of the closest asteroids to the Earth holds a mineral wealth upward of $15 trillion. To put this in perspective, this is about the same as the entire annual GDP of the United States.
When you keep in mind that there are millions of such asteroids within our solar system alone, one can quickly see how space mining could very quickly become a terrific commercial opportunity. Currently, the Return on Investment for any space mining enterprise would be very low (likely not profitable at all) due to launch costs mentioned earlier. However, if the disruptive technologies currently being explored are shown to be realistic, then the commercialization of space could begin in earnest.
Space policy/law currently imposes extremely high tariffs on any materials returned from outer space, and so this law would have to be revisited to really cultivate an entrepreneurial environment to truly capitalize on the abundant resources within our solar system, but this is certainly within our grasp, and is really nothing more than a bureaucratic hurdle.
3. Breakthroughs in Fusion Technology
The real Holy Grail for an interstellar mission will be breakthroughs in our ability to harness thermonuclear energy - namely fusion. Nuclear fusion is what powers all Main Sequence stars in the universe, and efforts to exploit this energy have been ongoing for decades.
Although the challenges are certainly intricate, to say the least, they are not insurmountable. For example, the National Ignition Facility located in Livermore, California, is predicting a major milestone accomplishment of ignition sometime in 2011/2012. While breakthroughs in fusion may appear slow to the public, leaps in our understanding of how to harness this energy are being made daily around the world, and it's only a matter of time until a working commercial reactor is constructed.
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Interestingly, a number of high profile entrepreneurs are investing a lot of money into non-government fusion research programs. For example, Jeff Bezos, Chairman and CEO of Amazon, with a net worth of about $18 billion, has recently invested almost $20 million in a privately held Canadian energy company. It may be that a maverick research organization beats the government behemoths to the finishing line.
Once fusion is better understood, and is being harnessed routinely, it's a small leap to apply that technology for propulsion purposes. Pound for pound, fusion releases about one million times more energy than conventional chemical rocket fuel, and could conceivably propel a spacecraft to a reasonable fraction of the speed of light, and produce an interstellar rocket that could reach a nearby star on timescales of a human lifetime.
My conclusions are that the 'safe bet' for predicting when the first interstellar mission will occur will always lie hundreds of years into the future. But certain pieces to the interstellar puzzle have the potential to fall into place far sooner, and disrupt our current approaches to thinking about this problem.
If we are to take seriously the notion of interstellar travel, and ultimately construct plans to make this happen, then we are forced to push the limits of what is possible under the most optimistic conditions.
Probes that could accomplish this seemingly extraordinary task may be within our grasp, if the appropriate studies are supported today.
WIDE ANGLE: Read more about Project Icarus, its predecessor "Project Daedalus" and the motivation behind interstellar spaceflight in the exclusive Discovery News Wide Angle: "Reaching for Interstellar Space."