The Authorized Ender Companion (62 page)

The design of the Battle School represents a mixed-approach to the creation of artificial gravity. Normal living quarters and general use areas were designed to provide nominally 1G (Earth-normal) gravity. The Battle Rooms were placed in the stationary central core to provide a reliable zero-gravity environment. The gravitational acceleration on board the Battle School is produced in one of two ways: either through the use of centripetal acceleration from large, revolving habitation rings, or through the use of electro-synthetic planar gravity generators in the central core. For reasons touched upon earlier, all large-scale, long-duration mission space assets (such as interstellar ships, and the Battle School) were intentionally designed to rely on
these two independent systems of artificial-gravity generation. In the event of the failure of one system, the other system remains intact, and can provide the necessary gravitation needed for the occupants of the ship or the space station.

The two rotating habitation rings are each nominally 350 meters in diameter and 33 meters wide. These are exterior dimensions, and account for structural wall thickness, plumbing, piping, power and data, radiation shielding, and the like. The interior, usable dimensions are therefore smaller by approximately 3 meters per exterior wall and 5 meters for the exterior perimeter (the outer hoop). Interior walls and floors are of a more standard construction, and typically take up 0.5 meter and 1.5 meters respectively.

These dimensions place the first level in the habitation ring at nominally 340 meters diameter (170 meters radius). The nominal height of each floor is 2.5 meters (8 feet). Allowing for floor thickness provides for roughly 3.0 meters (9.8 feet) per floor.

The teachers’ quarters are placed along the outermost floor. Most of the support staff are also housed on this deck. The gymnasiums and related exercise rooms are located on the second level. Due to equipment requirements, the floor height for the second deck is increased from 2.5 meters to 3.5 meters (11.5 feet). The next four levels (A through D decks) are reserved for the student soldiers. Mess halls are also located on A Deck. Elevators and escalators provide quick access between decks. Ship’s ladders and descent poles are also provided as a secondary means of moving between floors.

Six independent banks of elevators ascend from the outer habitation rings and feed into the central rotating disk. The central disk provides an additional series of concentric circular deck corridors that serve as station platforms for the shuttle cars that run between the rotating portions of the Battle School and the stationary central core. The outermost such deck is also the location of the “Game Rooms,” a collection of strategy-based video and holographic electronic games that are made available to the students of the Battle School.

Because of the varying radii of all these decks, the centripetal gravitational acceleration is different on each one. The rotational speed of the habitation rings has been selected such that Student Deck D experiences 1G (Earth-normal) gravity. The gymnasiums see 104 percent Earth-normal gravity, and the Teacher’s Deck sees 109 percent Earth-normal gravity. The Game Room Deck, the outermost deck available for accessing the shuttle cars, has a nominal radius of 79 meters, and therefore sees approximately 51 percent (just over half) Earth-normal gravity. The mechanical requirements of the subway cars force the radial spacing between these more central decks to be on the order of 5.5 meters.

The rings rotate at approximately 2.4 rpm (25 seconds per revolution), and have a tangential speed of 44 meters per second (m/s) (98 miles per hour, or 144 ft./sec.) at their circumference.

The rings revolve against a pair of physical bearings set into the central core. The bearings present friction into the system, and therefore require additional energy to keep the rings spinning. However, the alternate—electromagnetic “floating” bearings—would have required more energy to maintain, and presented an unacceptable failure mode (loss of energy results in the rings binding up against the central core, causing a sudden and catastrophic deceleration). Because of the large size (nominally 180 meters diameter) of these physical roller bearings, the radial loads caused by the subtle eccentricities in the dynamic weight distribution of the rings results in minimal stresses in the bearing. Estimated bearing life for each of the four main bearings in the Battle School is greater than a hundred years’ continuous duty, with proper maintenance and lubrication. The bearings are sealed to assist in maintaining a proper pressure differential across them to contain the 80 percent atmospheric pressure within the Battle School. Additional rotating seals are provided adjacent to the bearing interface in order to maintain this pressure differential and provide redundancy.

In order to maintain the proper speed and synchronization of the two rings, large direct-drive torque motors are built into the interface between the rings and the stationary core. High-energy permanent magnets are arrayed in a circle around the rotating rings, adjacent to the support bearings. The wound motor coils are encapsulated in a heat conducting compound, and set into a recessed ring on the central core, adjacent to the ring magnets, with a constant 5-millimeter gap between the two. Because of the large diameter of the torque motor, only a small amount of power (on the order of 200 kW) is required to maintain the speed of each ring. Hall effect magnetic sensors in the stationary core sense the position and speed of the rings, and feed this information back to a servo control system that keeps the rings in synchronization and at proper speed. Because each coil is independently wound and terminated, the failure of a number of coils can be compensated for in the controlling software.

In the unlikely event of a complete motor failure (such as might happen in the case of a large scale power loss), calculations show that it would take three days for a ring to despin, thereby providing sufficient time to relocate personnel to the central core and the adjacent ring. Should a ring lose motorization, the friction of the bearings and seals is sufficient to cause a dynamic counterrotation in the body of the Battle School. Automatic control systems are programmed to respond using the attitude control thrusters and the magnetic torque bars to maintain the School’s orbital orientation if such an event should occur. Enough fuel is stored onboard to react against despin forces in the event that
both
ring motor systems should fail simultaneously.

The Battle Rooms, as previously described, are cubes with an interior dimension of 75 meters to a side. They are built in three arrays of three Battle Rooms each. Each array has a series of circular corridors connecting, at one level all the Battle Gates, and at a lower level all the Student’s Gates. Secondary corridors coming from the Student’s Gate corridors feed to the Teacher’s Gates on the south face of the cubes. For orientation purposes, the south faces of the Battle Rooms are all located at the radially outermost points. As an example, if the central core were to rotate with the habitation rings, the Teacher’s Gates would be “down.” However, by placing the Battle Rooms in the stationary central core, they experience no gravitational acceleration, and provide the ideal zero-G training environment.

The spacing and orientation of three Battle Rooms in their “array” allows for large otherwise empty volumes between them. These volumes are taken up by storage spaces for the “Stars” and ancillary support equipment, and by the specialized electro-synthetic gravity generators and focusing apparatus needed to fix the stars in place and permit the Hooks to work in their intended way.

BATTLE SCHOOL: SHUTTLE CARS (SUBWAY CARS)

As mentioned previously, the method of moving between a rotating habitation ring and a stationary central core is of utmost importance for the effective functioning of a large space station such as the Battle School. The immense size of the Battle School both creates the problem and provides a means for its solution.

Given a rotational speed of 2.4 rpm, the outermost point of the habitation rings moves at a tangential speed of 48 m/s (98 mph). Further in, closer to the center, the tangential velocity is proportionally reduced. At the radius of the Game Room Deck (roughly 89 meters from the center axis of the Battle School), the tangential velocity is 22.3 m/s (50 mph). This Deck is also the first access level to what are called the “shuttle cars” that allow movement between the rotating habitation rings and the stationary central core.

The shuttle cars are similar in concept to subway cars. They run in de pen -dently of each other, as single car units, on concentric pairs of linear tracks. There are a series of four such tracks, arranged at each interface between the rotating habitation wheel and the fixed core, for eight tracks per wheel, sixteen
tracks overall. The innermost (“uppermost”) of these tracks is allocated to service cars that allow equipment and supplies to be moved between fixed and moving elements. The remaining three outer tracks per location are dedicated to personnel. The tracks and the track beds are part of the fixed central core. The shuttle cars run on the tracks, and either remain at zero velocity on the tracks (aligned with marks on the central core), or are brought up to speed and synchronized with the central disk area of the rotating habitation rings.

For reference and orientation, the sense of gravity in the Battle School is always directed outward. Moving higher in the station brings one closer to the central axis, and results in a reduction of the effective centripetal gravity.

For the purposes of this illustration, the shuttle car system shall be described as viewed from the Battle Room Access Deck. This deck is located three levels above the Gaming Area, and is therefore aligned with the access corridors to the Battle Gates of the adjacent Battle Rooms. For reference, its radius from center is approximately 72.4 meters.

The Battle Room Access Deck is a part of the rotating habitation rings. It is accessed by taking an elevator from one of the six available elevator banks in each ring. The Access Deck is above the living quarters, closer in to the central axis of the Battle School. These floors have a more severe upward curvature to them, and the centripetal-gravity effect is lower (very roughly half of normal Earth gravity). The Access Deck is approximately 30 meters (100 feet) wide, interrupted by regular support columns and the elevator banks, and runs the full circumference of the central disk. Facing the long axis of the open deck area (along the circumference), with the floor curving up in front of and behind the viewer, one views walls to the left and right. The upper portions of the walls are clear Plexiglas, and the lower portions are opaque. Automatic, electrically operated doors are set into these walls at regular intervals. A call button is provided to the left and right of each door.

Looking through the Plexiglas and down, the viewer sees two polished tracks, raised on short supports above the track bed. These are the tracks for the subway car. There is a third track, a wide, flat black ribbon that runs parallel to the polished tracks. This central ribbon carries signal and power to the subway car (transmitted via induction), and houses the coils for the linear electric motor that drives the car along the track. The tracks are moving relative to the viewer at 18 m/s (41 mph).

On the far side of the tracks, and sharing a common support structure with them, is another wall: Plexiglas on top and opaque below. Automatic doors are set into those far walls at the same intervals as the near wall.

The far wall, however, is not fixed with relation to the Access Deck. The
far wall, as described, is part of the central, stationary core. Because of the constant relative motion between the habitation ring and the stationary core, the far wall also moves with a relative velocity of 18 m/s as compared to the near wall and the Access Deck. Even though the Access Deck is a part of the rotating habitation rings, a viewer standing on the Access Deck will perceive himself (herself) as stationary, with the opposite wall moving past.

Visible beyond this far wall is another hallway. This is the access corridor for the Gates. Since there are three Battle Rooms along this corridor, these three Battle Gate entrances will pass by a viewer on the Access Deck every twenty-five seconds.