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Jump Points refer to any point at which a JumpShip may initiate or resolve a "jump" through interstellar space. Traditionally, there are two jump points in a system - the zenith and the nadir of a star's gravity well (normally above and below the star's planetary system elliptic). There exist other points, called "pirate points", that a JumpShip can use. However, they are difficult to locate and can be dangerous to use, but in desperate situations or covert missions, the advantages of a speedy insertion can outweigh the inherent risk of a Misjump.
Standard Jump Points
A JumpShip must operate in a zone where gravity levels are below a certain minimum. These zones are generally referred to as "jump points". The typical jump point is found at a minimum distance from the local star known as the "proximity limit", which is where gravity drops below the critical level for the hyperspace field of the Kearny-Fuchida drive to form properly. This zone is determined almost exclusively by the star of a system, which is far and away the largest gravity well in a star system (often by a factor of hundreds or thousands).
The proximity limit is a sphere (but for small planetary distortions) typically several astronomical units (AU) in radius around the star, though stars larger than Sol may have proximity limits many hundreds of AU in radius. Sol's proximity limit is about 10.2 AU. (For comparison, the proximity limits of planets outside their star's proximity limit is typically a few million kilometers, or a few percent of an AU.) That distance is determined by the type of star and can range anywhere from 75 million kilometers (for a low-energy M9 star) to over 347 billion kilometers (for a high-energy B0 star).
Beyond a proximity limit, all of space is a valid jump "point". It is quite possible for a JumpShip to jump into deep space light-years from any star system. Indeed, when imagining jump points, it might be best to consider most of space one giant, valid jump point but for tiny bubbles near stars and even more microscopic bubbles near planets.
The closest proximity point to a planet would be on a direct line drawn between the star, the destination planet, and reaching to the proximity limit. However, such points are deep in the planetary plane of the system, the "plane of the ecliptic", where most planets, asteroids, and debris are found. Besides the damage risk, the multitude of small gravitational effects make navigation to such points difficult to calculate. As a result, they are little used but for military ships looking to shave a few hours off the transit to the planets (which typically requires days of travel at 1G, about 9 days in the case of Terra.)
There are, however, proximity points that avoid all the mess of the ecliptic by being directly above and below the north and south poles of the star. These points are only slightly further from the inhabitable planet and are the furthest possible points on the proximity limit from the interference of the ecliptic. These two locations simplify navigation so much that they were used in the early 2100s by the Deimos Project for test jumps before mankind made interstellar jumps, and have remained the standard jump points for travel by Kearny-Fuchida drive ever since - hence, they are called the "Standard Jump Points". They are also often referred to as "zenith" and "nadir" jump points because of their locations above (zenith) and below (nadir) the star, with respect to the layout of the star system.
These jump points minimize the influence of planetary gravity on jump calculations. Indeed, jump calculations made from a zenith or nadir point are usually satisfactory for up to six months before planetary movement necessitates their recalculation.
While JumpShips have fairly capable fusion rockets that would allow 0.1G of steady acceleration (vastly better than any real world rocket), they are generally left at the jump point. Instead, DropShips, giant shuttles that ride on the exterior of JumpShips and "drop" free at the destination, handle the multi-day flights to and from the destination planet. The fusion rockets of DropShips are so efficient that they can sustain 1G of flight for days and weeks on end. DropShips normally utilize this capability to accelerate at 1G toward the destination for half the flight, followed by a 180-degree rotation and braking at 1G for the remainder of the flight. Such a half-and-half allows DropShips to provide passengers with near-continuous Terra-normal gravity while covering vast distances in days. The 10.2 AU flight from Terra to its jump points would take 2-3 years by the fastest chemical-fueled probes of the 20th Century, but only 9 days for 1G DropShip (or about 28 days for 0.1G JumpShip).
The energy output from the star (also based upon its type) determines how long a JumpShip can recharge its drive and can range anywhere from 151 hours (for a B0 star type) to 210 hours (for an M9 star type). The actual time required between jumps must also include the Jump Sail deployment and recovery times, typically about 100 minutes for deployment and 150-200 minutes for recovery. If the Jump Sail is damaged or cannot be deployed, the JumpShip's power plant can be used to recharge the fusion drive.
With any power supply, the JumpShip's crew must take care to not charge the drive too rapidly. In most cases, charging the drive faster than 175 hours risks damaging the drive, with the risk increasing exponentially as time is decreased. A JumpShip's fusion engine or a recharge station can recharge the KF Drive in 24 hours, but that almost guarantees the KF drive will be damaged beyond operability. Because of the frequent use of fusion engines to "quick charge" the KF drive, it is sometimes not understood that fusion engines can recharge the KF drive safely. However, fusion engines can offer a safe charge if they take more than 176 hours to do so.
Pirate Jump Points
There are some non-standard jump points that will allow a JumpShip to enter a system inside the proximity limit. As these "non-standard" points are much closer to the habitable planets of a star system, they are prime choices for raiders and pirates, leading to their designation as "pirate points".
These jump points exist where the gravitational attraction of all planetary objects cancels each other out and overall gravitation is reduced below the critical limit for hyperspace field formation.
While "pirate point" locations can be estimated by secondary school physics (generally, pirate points inside the proximity limit will be close to a L1 Lagrange Point, which exists due to the cancellation of gravity between two bodies), such jump points are difficult for JumpShips to utilize because they are much smaller than the standard jump points and have much more complicated motions. Rather than only following the star like the Zenith and Nadir points, the pirate points at least also follow a planet, possibly a planet and moon, and are subject to gravity of other moving objects in the star system.
This makes a navigator's job nightmarish when attempting to use a pirate point. Plotting the jump is impossible without computer aid. Missing the jump point is entirely possible, resulting in the JumpShip attempting to arrive in a region of space that is not a valid jump point (a fate discussed under Misjump.)
While the majority of pirate points are stable in the sense they exist continuously despite their mobility, a particular sub-class of pirate points known as "transient points" will periodically appear and disappear due to the influence of other bodies in the star system. Transient points are even more difficult to utilize.
Some systems (particularly Successor State or regional capitals) provide recharge stations at one or possibly both jump points. These stations are capable of beaming stored energy by microwaves directly at a JumpShip's Jump Sail, allowing a firm and predictable 176-hour recharge. (For merchants visiting a red dwarf with a 200-hour recharge and facing 3 wasted shifts, this may be quite attractive.) If the JumpShip takes the extra time to dock with the station and uses a hard line connection rather than its Jump Sail, several vulnerable power systems can be bypassed and safe recharging can take place in as little as 120 hours.
Unlike many examples of high technology, recharge stations survived the Succession Wars fairly well because they were useful to both invaders and defenders. Recharge stations were most often taken by special operations or threat rather than being destroyed.
- Strategic Operations, pp. 134-135, "Jump Points"