My introduction to the Bussard ramjet was Poul Anderson's novel Tau Zero. Being an ignorant and unreflective sprat, it never occurred to me that the device wasn't entirely fictional. I figured it was just another doubletalk drive, like "Ortega's Torch", or "Horst-Conrad Impellers". Oops.

When I found out that there really was a Dr. Robert Bussard, eminent physicist, I was actually rather thrilled. Here was something we might have a chance of building one day!

Well, time has passed, and the critics have whittled away at the notion rather effectively. Still, I cherish the fond hope that some bright boy or girl will find a practical workaround. As Vernor Vinge pointed out, it's too useful a notion to give up on easily. So meet the Leonora Christine, "seventh and youngest of her class." She was my first interstellar ramjet...

A ship accelerating continuously at one gravity would have traveled half a light-year in slightly less than one year of time. And she would be moving very near the ultimate velocity, three hundred thousand kilometers per second.

Practical problems arose. Where was the mass-energy to do this coming from? Even in a Newtonian universe, the thought of a rocket carrying that much fuel along from the start would be ludicrous...

But fuel and reaction mass were there in space! It was pervaded with hydrogen. Granted the concentration was not great by terrestrial standards: about one atom per cubic centimeter in the galactic vicinity of Sol. Nevertheless this made thirty billion atoms per second, striking every square centimeter of the ship's cross section, when she approximated light velocity...

The energies were appalling. Megaroentgens of hard radiation would be released by impact; and less than a thousand r within an hour are fatal. No material shielding would help. Even supposing it impossibly thick to start with, it would soon be eroded away.

However, in the days of Leonora Christine non-material means were available: magnetohydrodynamic fields, whose pulses reached forth across millions of kilometers to seize atoms by their dipoles-no need for ionization-and control their streaming. These fields did not serve passively, as mere armor. They deflected dust, yes, and all gases except the dominent hydrogen. But this latter was forced aft--in long curves that avoided the hull by a safe margin--until it entered a vortex of compressing, kindling electromagnetism centered on the Bussard engine.

The ship was not small. Yet she was the barest glint of metal in that vast web of forces which surrounded her. She herself no longer generated them. She had initiated the process when she attained minimum ramjet speed; but it became too huge, too swift, until it could only be created and sustained by itself. The primary thermonuclear reactors (a separate system would be used to decelerate), the venturi tubes, the entire complex which thrust her was not contained inboard. Most of it was not material at all, but a resultant of cosmic-scale vectors. The ship's control devices, under computer direction, were not remotely analogous to autopilots. They were like catalysts which, judiciously used, could affect the course of these monstrous reactions, could build them up, in time slow them down and snuff them out...but not fast.

Starlike burned the hydrogen fusion, aft of the Bussard module that focused the electromagnetism which contained it. A titanic gas-laser effect aimed photons themselves in a beam whose reaction pushed the ship forward--and which would have vaporized any solid body it struck. The process was not 100 per cent efficient. But most of the stray energy went to ionize the hydrogen which escaped nuclear combustion. These protons and electrons, together with the fusion products, were also hurled backward by the force fields, a gale of plasma adding its own increment of momentum.

The process was not steady. Rather, it shared the instability of living metabolism and danced always on the same edge of disaster. Unpredictable variations occurred in the matter content of soace. The extent, intensity, and configuration of the force fields must be adjusted accordingly--a problem in ? million factors which only a computer could solve fast enough. Incoming data and outgoing signals traveled at light speed: finite speed, requiring a whole three and a third seconds to cross a million kilometers. Response could be fatally slow. This danger would increase as Leonora Christine got so close to ultimate velocity that time rates began measurably changing.

Nonetheless, week by week, month by month, she moved on outward.

Notice how he sneaks in the dual-engine? It's crucial to the plot. When the braking motors are damaged, the crew's only hope of survival is to keep piling on the speed. Eventually, they may hope to reach a region of space empty enough to permit dropping their shields and repairing their braking motors. Of course, they'll need to leave the galaxy altogether to find space that's "clean enough".

Helpfully, Anderson fudged the laws of physics just a little bit by allowing compensator fields for higher boost. Ten gees, twenty, fifty, hey, no problem! If you're heading out to the deepest black, you'll need to put the pedal to the metal, or else die of old age before you've fairly begun. But he posits that such technology only works when you're close to light speed, so that's okay then. Say hi to the edge of the universe.

The resultant novel is rather like Powers of Ten: The Soap Opera.