Today we present a very special installment of the Codex Futurius, Science Not Fiction’s look at the big scientific ideas in sci-fi: Kevin Grazier—JPL physicist and friend of SNF—gives an insider’s peek at the workings of and discussion around the Orion antimatter drive used to propel the Phaeton starship in Ron D. Moore’s recent TV movie, Virtuality. Grazier was a science adviser for the movie (which was intended to be the pilot for an ongoing show), so he was right in the middle of these discussions. The screenshot further down in this post shows the actual spreadsheet used in the production to see what stars would be reachable with the Orion drive. Without further ado, here’s some sci in your sci-fi:
DISCOVER: What kind of realistic technology could we use to get to nearby stars? Which stars would be feasibly reachable by such technologies?
Kevin Grazier: It’s a saying plastered on T-shirts and bumper stickers—the kind sold at both science-fiction conventions and physics departments nationwide:
186,000 miles per second:
It’s not just a good idea, it’s the law.
The speed of light, of all electromagnetic energy, in a vacuum is the ultimate speed limit in the universe. Nothing that has mass or carries information can travel faster.
This universal speed limit is a direct fallout from Albert Einstein’s special theory of relativity. Special relativity implies that the speed of light in a vacuum is a universal constant, but values that we tend to think of as constant in our daily experience—mass, length, and the rate of the passage of time—are not. Depending upon the relative velocity of two observers, these values will “adjust” so that both observers see the speed of light as a constant. Two observers travelling at high speeds relative to each other will find themselves in strong disagreement about measurements like the length of each other’s spacecraft and the rate of the passage of time.
Another consequence of special relativity is that, as an object travels increasingly faster, it behaves as if it has increasingly more mass. Therefore the amount of thrust it takes for an incremental change in velocity (known in the space program as a delta-V) is vastly greater at high speeds than at low. This effect is also highly nonlinear: It takes almost an order of magnitude more thrust to accelerate from .9c (nine-tenths of the speed of light) to .99c than it does to accelerate from .5c to .7c. An object travelling at the speed of light would act as if it had an infinite amount of mass and it would, therefore, require an infinite amount of energy (read: an infinite amount of thrust/fuel) to attain it.
This is, of course, a shame for civilizations (like ours) who want to explore planetary systems around other stars first hand. The distances involved are, well, astronomical. Just within the Solar System, it typically takes NASA probes 6 months to a year to reach Mars; it took Cassini 6 years, 9 months to reach Saturn. The (currently) fastest object created by humankind, the Voyager 1 spacecraft, will take 40,000 years, give or take a few thousand years, before it makes its closest encounter with its first star: AC+79 3888—currently located in the constellation Ursa Minor. At that speed few Time Lords, and even fewer humans, would survive the journey to even “nearby” star systems.
As noted over on 
