The Impulse Propulsion System (IPS) represents the primary means of moving the vessel at sublight velocities. This systems also provides much of the power used to operate the vessel and the equipment aboard it. These engines are active at virtually all times the vessel is not docked at a fully-equipped facility. These engines provide the propulsion used to move around planetary systems and other times that faster-than-light velocities are not used. Velocities above .25c (1/4 speed of light) requires additional power from auxiliary power generation equipment.
Early on in the development of the standard Excelsior class starship program, it was foreseen that the vessel would end up having a mass of several hundred thousand metric tonnes. Existing IPS equipment was quickly seen as being inadequate to allow the vessel to maneuver at the extreme performance levels desired acceptably, and no systems under development at the time held promise of being able to accomplish the task. Engineers devised the idea of installing a space/time actuation convoluter similar in nature to that utilized in the warp drive system. It creates a distortion in the space/time continuum around the vessel too weak to accelerate the vessel to warp speeds, yet enough to "exaggerate" the actual velocity generated by the IPS. This system was already in production for other purposes and was quickly adapted and incorporated into the design.
The fuel supply for the IPS is contained in the Main Deuterium Storage Tank (MDST) on Deck 23 with many smaller auxiliary storage tanks on Deck 16. Redundant feeds in the fuel management system run by the ship's computer system operate the fuel distribution system during times of engine operation as well as refueling operations. The deuterium supply of the IDST, which also supplies the Warp Propulsion System, is normally maintained in a slush state at 13.8 degrees Kelvin, the secondary fuel supply is maintained in a fully liquid condition. If fuel from the main supply must be moved, it is passed through a heater system to make it easier to move.
The MDST and secondary tanks are made of forced matrix cortanium 2378 and stainless steel in alternating parallel/biased layers and gamma-welded. Phased energy cutters create openings for fuel lines and sensor systems. The tanks can be removed and installed via transporter operation. Each secondary tank can store 4.65 metric tonnes of deuterium fuel.
If the need should arise for velocities above that possible by the IPS under normal operational conditions and procedures, the Commanding Officer can order the injection of minute amounts of antimatter into the IPS system. The antimatter for the IPS (main and secondary engines) would come from the supply maintained on the Engineering Deck . 36 of the 40 antimatter tanks are allocated to the Warp Propulsion System and the remaining four are dedicated to the IPS system. Antimatter can be transferred from one group to the other by means of dedicated fuel lines installed for such a situation.
Impulse Engine Configuration:
The Primary (also called Main) Impulse Engines (PIE) are located near the aft section of a Starfleet vessel and are oriented to generate thrust along a parallel equidistant axis down the centerline of the plane. During flight operations, engine thrust is vectored slightly in the -Y direction (downward) to accommodate center of mass movement.
A PIE consists of four impulse engine units clustered together, while SIEs are made of two engine units. Each engine unit is comprised of the following systems:
The ICH is a sphere three cams in diameter intended to contain the reaction of the fusion generator. It is made from eight layers of dispersion-strengthened hafnium excelinide having a total thickness of 337cm. An inner liner of crystalline gulium fluoride 20cm thick protects the sphere from the effects of the reaction and radiation. It is replaceable. Openings are made in the sphere to allow for fuel lines, reaction initiators and sensor devices.
Slush deuterium from the main cryogenic tank is heated and passed to interim tanks on Deck 20. Here the deuterium is chilled until it is frozen solid into pellets of variable size (.25 to 2.5cm depending on needed energy output). A pulsed fusion shock front from initiators around the inner surface of the sphere is generated. Energy output can be adjusted from 109.5 to 1012MW.
High-energy plasma created during engine operations is vented through an opening in the sphere to the accelerator/generator. This is usually an octagon shape 1.55 meters long and 2.9 meters in diameter. It is made of an integral twin crystal polyduranide frame and a pyrovunide exhaust accelerator. In propulsion operations the accelerator is operative, increasing the plasma's velocity and passing it to the space/time actuator conductors. In power-generation mode, with no propulsion being performed, the accelerator is offline. The Electroplasma Assembly diverts the energy into the power distribution grid and exhaust products are vented. In a combined propulsion/power generation mode, part of the exhaust plasma is accessed by the magnetohydrodynamic system (MHDS) to supply the power distribution grid.
The third portion of the engine is the Actuator Conductor Assembly (ACA). It is 3.25 meters long and 2.9 meters in diameter. It consists of eight split toroids, each cast of verterium cortenide 934. Energy driven through the toroids, creates the effect of:
1. Reducing the apparent mass of the cruiser's inner surface.
2. Aids the vessel in passing the space/time continuum past the cruiser on its outer surface.
The final stage of the system is the Directional Exhaust Thrust Housing (DETH). This is a series of moveable vanes and conduits meant to expel exhaust material in a controlled way. This can perform maneuvering functions or venting operations.
The impulse engines are operated through control software incorporated into the vessel's main computer system. As with the warp propulsion system, the initial algorithms programmed into the vessel at the time of construction are adaptable and are constantly making adjustments to maximize efficiency in operation. Optimum conditions can be "learned" by the artificial intelligence systems and utilized in engine operations. Commands received by the crew are passed through the main computer into the dedicated IPS command coordinator. The IPS command coordinator is linked with its warp propulsion counterpart when passing in and out of warp velocities. The IPS coordinator is also tied into the thruster systems at all times and all velocities.
Engineering Operational Safety:
PIE and SIE systems are maintained according to standard practices based on average time-to-failure studies and work schedules. Those parts that experience the most wear are naturally replaced more often than other devices. The inner liner of the ICH sphere is replaced after 8000 hours of service, or if prescribed amounts of deterioration or structural fracturing is detected. The sphere itself and subassemblies are replaced after 6800 cruise hours. Deuterium/anti-deuterium Infusers, initiators and sensors can be replaced in the field without the need for docking at a Starfortress or other facility.
The accelerator/generator units are changed out after 5200 hours unless wear or failure is detected beforehand by maintenance crews. The main need for replacement here occurs from the radiation present in the system.
ACA units are replaced after 5000 hours. The actuator conductors are replaced due to the effects of electromagnetic and thermal energies. These systems must be replaced at a repair facility; it cannot be done in the field.
The DETH system undergoes the least amount of wear in operation. They are replaced during layovers at a dock facility. Non-replacement maintenance can be performed in the field.
The IPS system requires 1.28x as much maintenance work as the WFPS system due to the nature of the fusion reaction occurring in the IPS system. Thermal and acoustic stresses per unit of area are greater in this system. While the WFPS produces much more power than the IPS, the energy created puts less shock and stress onto the vessel structure.
IPS Shutdown Procedures:
Equipment failure and other conditions can create situations where the IPS must be partially or completely shutdown. This can be initiated by crewmembers or sensors within the IPS detecting problems and activating shutdown procedures within the engine control system. These causes can include:
Shutdown procedures begin with the shutoff of deuterium fuel flow into the IPS system and all injectors. The accelerators are shutdown and remaining energy bled off into space or into the vessel's power distribution grid. The ACA conductor interrupts the conductor phase order, putting them into a neutral power condition, allowing the field to collapse. Power distribution is reconfigured if the problem is limited to one engine unit.
A number of variations of shutdown procedures are programmed into the computer system to handle many possible problem conditions. In addition to these, the engineering personnel are also trained in many methods of engine shutdown procedures. The Commanding Officer must consent to any engine shutdown operation unless the vessel is in jeopardy of immediate loss.
In situations where the damage to the system is of an extreme nature, engineering personnel will wear protective suits and conduct detailed visual/sensor examinations of the IPS equipment. Any damaged equipment will be powered down and repaired if possible. Any equipment found to be putting the vessel at risk of further damage or complete destruction will be removed at the earliest opportunity. All areas around the affected system(s) will be sealed off by blast doors and force fields.