Immaterium - Warp Navigation: Before a starship can enter the Warp, it must first travel at sublight speed to a star system's so-called "Mandeville Point." This is the closest distance that a voidship can safely enter or exit the Immaterium from its origin or destination system, respectively.Once a spacecraft activates its Warp-Drive, it is plunged into a dimension very different from the material universe. It is convenient to imagine Warpspace as consisting of a relatively dense, almost liquid, energy, devoid of stars, light and life as it is commonly known. Once within Warpspace a voidship may move by means of its main Newtonian reaction drive (such as a standard Imperial Plasma Drive), following powerful eddies and currents in the Warp, eventually reaching a point in the Warp corresponding to a destination in realspace.The most difficult aspect of Warp travel is that it is impossible to detect the spatial movement of Warpspace once a voidship is in the Warp. The ship can only blindly carry on, its crew trusting that it is going in the right direction. The longer a ship remains in the Immaterium, the greater the chances of encountering some unexpected current that can turn it unknowingly off-course.Navigation of Warpspace can be achieved in two ways: the calculated jump and the piloted jump.All Warp-Drives incorporate navigational mechanisms. When the voidship is in realspace, these monitor the ever-shifting movements of that part of the Warp corresponding to the voidship's current position. It is a "window" into Warpspace. By means of observing these movements in the Warp it is possible to calculate a course, corrective manoeuvres, and approximate journey time to a proposed destination.Calculation relies on the assumption that the Warp-currents observed from realspace do not change significantly during flight. This method is known as a "calculated jump." It is not safe to make a calculated jump of more than four light years at one go. The longer the jump, the greater the chances of a significant change in Warp current movement.The second, and more efficient, form of Warp-navigation is the piloted jump. This method relies upon two factors: the Navigators and the psychic beacon of the Astronomican. The Astronomican is centred on Terra and is not only controlled by, but is directed by, the psychic power of the Emperor.The Astronomican is a psychic beacon that penetrates into Warpspace. A Navigator on board a voidship in the Warp is able to pick up these signals and can steer a spacecraft through Warpspace, compensating for current changes as he does so. A piloted jump can cover a far longer distance than a calculated jump. Most piloted jumps are no more than 5,000 light years at a time, but longer jumps have been made.A typical interstellar voyage might begin with a cargo ship lying in orbit around an Imperial world. Tiny shuttlecraft busily transfer precious minerals, foodstuffs, crew, and manufactured items from the world below. The loading procedure may take solar days or weeks, as the shuttles return time and time again to the huge voidship.Once loading is complete, the colossal spacecraft slowly accelerates out of orbit under the power of its main reaction drive. The voidship heads outwards towards the rim of the solar system, carefully increasing speed by tiny increments as it does so.Although the vessel's engines are capable of terrific acceleration, the risk of collision with inter-planetary debris is high if the voidship accelerates too quickly or too much. As the sun shrinks in the ship's wake, the density of debris lessens and the ship's speed reaches approximately one percent of light speed in a vacuum.After several solar weeks of travel, the voidship arrives at its point of departure into the Warp. This is the Mandeville "jump-point" lying around the star system like the circumference of a circle. This delineates the point at which inter-planetary debris falls below maximum Warp density and gravitic stresses cannot affect the transition from realspace.Once this invisible line has been crossed, it is safe to activate the Warp engines to enter or exit the Immaterium. A crew careless or foolhardy enough to prematurely activate Warp-Drive would be lucky to find their ship hurled thousands of light years off course. More likely, the voidship would be torn apart and destroyed, never to be heard of again.With the safe activation of its Warp-Drive, the ship is plucked out of the real universe and enters the dimension of the Immaterium. Its true interstellar journey has begun. Ships travelling in the Immaterium with the aid of a Navigator do so by means of jumps varying in length up to 5,000 light years. Only a long journey would involve more than a single jump. Even so, almost two solar weeks may pass onboard ship before the craft is ready to end its jump. Meanwhile, because of time shifts in the Warp, it is possible that over a standard year has passed in the real universe.The ship re-enters realspace just beyond the Mandeville Point of its destination solar system. If it is lucky, the ship will come out close to the jump-point, otherwise it may take many extra solar weeks to reach the inner planets. It is always wise to allow a safe margin when jumping towards a star. The results of reentering space within the radius of the Mandeville Point would be the same as prematurely activating the Warp-Drive on the outward journey, and would almost certainly end in disaster.The ship is now ready for its final haul, beginning by broadcasting to its destination and establishing a new time coordinate. Time in Warpspace is so different from time in normal space that the crew has no idea whether their journey has taken a few solar months or standard years. Initially, the voidship travels at approximately one percent of light speed, decelerating gradually through the denser inner regions. Eventually, the ship reaches its destination, where swarms of tiny shuttles once more make themselves busy loading and unloading cargo and passengers in preparation for the voidship's next journey.