Void Jumping

This description of Void Jump travel is intended as a background for an alternate setting that doesn't have anything to do with Star Frontiers. However, the similarities are close enough that the material could be quickly adapted to the Star Frontiers Setting. It is posted here for your enjoyment.

FTL travel was discovered completely by accident. What is now known as the jump field generator was originally designed as an energy shield to provide defense against both cosmic radiation and kinetic energy weapons. Developed on the human homeworld, it was supposed to be a defensive system to help protect the human military vessels.

By itself the shield worked as desired and first tests in orbit around the planet showed that it behaving properly, effectively creating a kinetic dampening field around the vessel that reduced the velocity of particles traveling through it.

In addition to the new defensive system, the ship testing the shield sported another major innovation, the new Enigma engines. These engines were a major advance over the previous generation, using a special quantum field effect, they could provide the same amount of thrust with only a fraction of the fuel.

It was the combination of these two systems, never tested together before, that ushered in the modern era of interstellar travel. The effect was neither predicted or expected and the original ship, the Dauntless, was lost with all hands.

The ability to enter the Void required the combined effect of both the new Enigma engines as well as the new defensive screen. By themselves, neither of the two systems can produce the strange effect that allows a ship to enter the Void. In fact, both systems were tested independently by the Dauntless, first the engines without the defensive screen on and then the screen while the ship was not under thrust. Neither test caused the Void jump. It wasn't until the ship turned on the defensive screen while accelerating that the strange effect occurred.

The field set up around the ship by the defensive screen created a field effect that was then modified slightly by the special field used in the engines to achieve their high efficiency. It is the combination of these two effects, the whole ship field generated by the defensive screen modulated by the field from the engines that allows the ship to slip into the Void. Removing either of these effects drops the ship back into normal space.

In addition, there is one added ingredient. Gravity. This Void effect only occurs when the gravitation field from a nearby star or planet is relatively small. In the end, you need to be about 4 AU (600 million kilometers) from a one solar mass star in order for the effect to be possible. The Dauntless had run tests with the defensive shield on while accelerating when in was working close in to the homeworld. However, as the planet is only about 0.97 AU from its star the effect couldn't manifest itself. It was only once it was out in the outer solar system that the gravitational field was small enough to allow the effect to occur.

When Void jumping, the velocity vector of the ship is critical. Once the field that causes the jump to occur is activated, the ship enters the Void and continues to travel along the trajectory it had when the jump started. There is no steering while in the Void. Thus it is critical that the ship be properly aligned and traveling toward its destination before the jump field is activated or it will miss the intended destination by a large distance.

There are two, well three really, ways to get out of a Void jump. The first, and typically the usual, way is to just turn off the field generator. Once the field collapses, the ship drops out of the Void. The second way is to turn off the engines so that field modulation that occurs from the effects of the engine stops. This is slightly less reliable because stopping the engines doesn't immediately stop the modulation. Once in effect, there is a bit of a resonance that causes the effect to linger for a few dozen milliseconds after the engines cut off. The exact duration of the lingering effect varies from situation to situation. The effects of this resonance have not really been fully studied and so you never really know exactly how much longer you will stay in the Void.

The final method, and the one that is typically used as a backup failsafe, is to try to enter too deep into a gravity well. Once you get too deep, it immediately causes the Void jump effect to collapse and the ship drops back into normal space. Typically the astrogator will try to arrange the jump such that the ship is aimed directly at the star in the system they are attempting to reach. That way even if the timing is off on the shutting down of the jump field, or something goes wrong and it won't shut down, as the ship approaches the star the gravitational field will cause the jump to end.

Travel time is greatly reduced while in the Void. It takes about one second to travel one light year through the Void. Thus great distances can be covered in very little time. The main difficulty lies in lining up the jump. You can't just point at the star and go. You need to know both the star's apparent current position as well as its actual motion through space so you can "lead" the star based on its proper motion so you come out in the correct location. When jumping lightyears, even a small error in angle can throw you off by millions of miles. That is why most jumps tend to be short. As the jump gets longer and longer, it requires more and more precision in the direction of initial travel to actually arrive at the destination.

Void jump calculations are complex but fairly routine. You need ephemeris for all the known objects in both the origin and destination systems as well as true space motions for all of the stars that you will use to line up your jump. You then calculate the vector you need for the ship to have based on the true space position of your ship and the destination system. Remember, once you enter the Void you travel along the direction of motion in a straight line.

This vector changes slowly over time since all the stars are in motion relative to one another and you are always starting from a different location within the system you are leaving each time you make a jump. Calculations also need to take into account the actual motion of the other stars you will use to determine your vector. The calculations are complex and lengthy but modern computers are fast and it takes about 10 hours to do the calculations for a jump regardless of the distance to be traveled.

On top of the calculation time, you need time to line up the ship on the right velocity vector. Properly aligning the ship's velocity vector is harder the further you jump since the target system covers a smaller and smaller angle on the sky the further away it is. For example, the four AU radius of the stellar "no jump" zone covers a 13.3 arcsecond angular size at a distance of one light year but at ten light years it is only a tenth of that or 1.33 arcseconds. As the required accuracy increases, it takes progressively longer to verify your alignment to make sure you won't miss. Because of this, it takes one half hour times the distance in light years squared to line up the ship or 2 hours, whichever is longer. So for a one or two light year jump, it only takes two hours to align the ship. For a ten light year jump, it will take fifty hours.

In general, most of the time for an interstellar journey is taken up just getting far enough away from the star to be able to make the jump. Under one standard gravity of acceleration, starting at a planet one AU from the star, it takes about 86 hours to get out to a distance of 4 AU to be able to make the jump. That's a little over three days.

The time spent lining up the ship for the jump does not have to be extra time once you get out to the jump distance from the star. It can be included in the process of acceleration as you head out to jump distance. Of course, this assumes that you are accelerating almost directly toward your destination from the start or are nearly at rest. If you've been accelerating on a greatly different vector to get out to jump distance, all the motion in the wrong direction needs to be canceled out and it will take much longer to get ready. The details depend on the circumstances.

This also represents the amount of uninterrupted time you need before a jump. If anything happens that causes you to maneuver your ship off of its course (i.e. avoiding obstacles, pirates, engaging in combat, etc) you will have to start over. In addition, if you do have to maneuver, the time required is doubled to allow you to get your ship back on roughly the correct vector before making the final adjustments.

Also, if you had some sort of maneuver in the hours before you started the final adjustment, the adjustment time gets doubled as well to represent the time needed to make the corrections to your direction. The time frame for this to happen is half the time needed to make the final adjustments. So, if you are making a five light year jump, you need at least 12.5 hours to line up the jump. If you get disturbed any time after ~18 hours before the jump, you'll need to start over and it will take 25 hours of time to line up the final vector before jumping.

The jump itself only takes a few seconds, one per light year traveled. Once the ship is lined up, simply engage your engines to set up the modulating field and then turn on the Void field generator. The Void field will develop around the ship, modulated by the engine field and you'll enter the Void. At the appropriate time, you shut off the Void field and you are back in real space at your destination. This is typically all handled by computers as the sensation of entering the Void can be quite distracting and upsetting for many people. Plus the timing for turning off the field is fairly precise, on the order of milliseconds, and the computers can time it better. Of course, if your computer is down but you've made the calculations, you can still do it by hand. Just don't expect as precise an arrival.

So for a concrete example. Say you want to make a seven light year jump. Initially you need to make your jump calculations based on when and where you will be departing the system and where you want to end up at your destination. This is complex but routine and takes the standard ten hours. Your astrogator gets to work and starts the computation while you begin to accelerate out of the system. After a day's hard work he has everything figured out and you are ready to go. You still have a couple of days of travel time to get out beyond the jump line. Along the way, he checks regularly with the pilot to make sure you are generally on course and makes tweaks to the travel direction to keep the errors down. Finally, you are approaching the jump limit. For the next twenty-four and a half hours (half of seven squared), the astrogator puts in a long watch with the pilot, tweaking every so slightly the direction of travel and making sure everything is lined up. Finally, he declares all is good and the Void field generator is engaged. After a few seconds of distorted reality you drop back out of the Void and are in the destination system. Now you flip the ship around and start decelerating toward the planet.