Warp-Drive - 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 Warpspace 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 Warp-capable voidship may move by means of its main reaction drives, following powerful eddies and currents in the Warp, eventually reaching a point in the Empyrean 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 ship 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 Warpspace, 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 ship is in realspace, these algorithms monitor the ever-shifting movements of that part of the Warp corresponding to the voidship's current position. It is essentially 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 in realspace. 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", but is often referred to as a "blind jump" by Imperial Navy personnel. 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: a pilot who can gaze into the Warp and guide the ship around the hazards to be found there, and a stable reference point to triangulate one's position against. The Imperium uses the mutants known as Navigators as Warp pilots and the psychic beacon of the Astronomican as a reference point.The Astronomican is centred on Terra and is not only controlled by, but is directed by, the potent psychic power of the Emperor of Mankind. The Astronomican is a psychic beacon that penetrates into Warpspace all the way out to a diameter of approximately 90,000 light years from its source point in the Imperial Palace on Terra.A Navigator onboard a voidship in the Warp is able to pick up these psychic 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 Warp jumps are no more than 5,000 light years at a time, but longer jumps have been made.Renegade and Chaos voidships often lack Navigators (as most Navigators opt for suicide rather than betray the Imperium), but they compensate by using a Possessed Chaos Space Marine or another Daemonhost as a pilot, as such blasphemous mingling of human and daemon are just as capable as any mortal Navigator of safely guiding a voidship through the currents of the Empyrean.After several solar weeks of travel, the warpship arrives at its first destination. This is the Mandeville Point or "jump-point" lying around the star system like the circumference of a circle. This delineates the point at which interplanetary debris falls below maximum Warp density.Once this invisible line has been crossed, it is safe to activate the vessel's Warp engines. A crew careless or foolhardy enough to prematurely activate its Warp-Drive would be lucky to only find their ship hurled thousands of light years off-course.More likely, the starship 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 ethereal dimension of Warpspace. Its true interstellar journey has begun.