# Xihe Interplanetary Exploration Mothership
## Overview
Xihe Interplanetary Exploration Mothership is the first generation of interplanetary ship. It is designed for crewed exploration to other planets, such as Mars, Venus, or celestial bodies like the moons of Jupiter and Saturn. The mothership serves as a mobile base of operations, providing life support, navigation, and scientific research capabilities for extended missions in deep space. 

Xihe is named after the Chinese Solar Deity, symbolizing its role in exploring the solar system. The ship is equipped with advanced propulsion systems, radiation shielding, and modular habitats to ensure the safety and comfort of its crew during long-duration missions.

## Key Features:
1. **Propulsion System**: Xihe utilizes a mass driver propulsion system, allowing for efficient travel over vast distances in space. The main engines are powered by a large fusion reactor to expel mass at high velocities. It has a delta-v capacity of 1700km/s when carrying a 300-ton payload(including 100 tons for planetary surface exploration vehicles and supplies).
2. **Life Support**: The mothership is equipped with closed-loop life support systems that recycle air, water, and waste, ensuring sustainability for missions lasting several years. The on-board greenhouse can support a crew of up to 15 members. 
3. **Artificial Gravity**: To mitigate the effects of long-term weightlessness, Xihe features a rotating habitat module that generates artificial gravity through centrifugal force. This helps maintain crew health and well-being during extended missions. The habitat module is able to produce up to 0.41g of artificial gravity.
4. **Towing Capability**: Xihe is designed to tow smaller spacecraft, such as landers and shuttles. It has multiple docking ports and a robust structural framework to accommodate the stresses of towing during interplanetary travel.
5. **Scientific Research**: The mothership is equipped with state-of-the-art laboratories and observation decks, allowing for in-depth scientific research and data collection during missions. It also has facilities for remote operation of planetary exploration vehicles.

## Design:
The overall shape of Xihe is an elongated, muti-segmented cylinder or spine, with major modules stacked together along a central axis. This allows for better structural integrity during main engine thrust and towing operations, while minimizing the ship's cross-sectional area to reduce collision risks with micrometeoroids and space debris.

### Front docking hub
At the front of the ship is a large docking hub with 5 docking ports for smaller spacecraft. The front docking port is structurally reinforced to handle the stresses of towing operations, while 4 telescopic side ports are only used when the ship is stationary. The front docking ports is a 2.5m docking port, and the side ports are 2 1.875m ports and 2 1.25m ports.

### Command Center
Directly behind the front docking hub is the command center, which houses the ship's navigation, communication, and control systems. The command center is equipped with advanced sensors and computer systems to ensure safe and efficient operation during interplanetary travel. The command center also packs with two airlocks for crew and cargo EVA operations. With a diameter of 5 meters, the command center is spacious enough to accommodate the ship's crew and essential systems.

### Artificial Gravity Habitat Module
Located behind the command center is the artificial gravity habitat module. This module is a large rotating ring structure that generates artificial gravity through centrifugal force. The habitat module is designed to provide a comfortable living and working environment for the crew, with sleeping quarters, recreational areas, dining facilities, and science labs. The habitat module has a diameter of 25 meters and rotates at a speed of 4 revolutions per minute to generate 0.41g of artificial gravity.

### Stationary Habitat Module
Following the artificial gravity habitat module is the stationary habitat module. This module is non-rotating and provides additional living space for the crew. It includes medical facilities, storage areas, and additional laboratories for scientific research. The stationary habitat module has a diameter of 5 meters and is designed to accommodate up to 15 crew members comfortably.

### Center Docking Hub
After the habitat modules is the center docking hub, which features 4 additional side-mounted docking ports.
2 1.875m telescopic docking ports are directly mounted on the side of the hub, while another 2 1.875m telescopic docking ports are mounted on the side of extension modules. At the top of each extension module is a 2.5 copula module for observation and external monitoring, and the bottom of each extension module houses a communication disk for long-range communication with Earth and other spacecraft. 

All 4 docking ports are structurally reinforced to handle towing operations when the ship is under acceleration.
Typically, these docking ports are used to dock with Exploration Vehicles with VTOL and side towing capabilities, like Echo Shuttles or Amalthea MPVs. These vehicles can be used to ferry crew and cargo between the mothership and planetary surfaces. Echo Shuttles are preferred for Atmospheric landings, while Amalthea MPVs are used for airless body landings, though both vehicles are capable of landing on any type of celestial body.

### Greenhouse Module
Next in line is the greenhouse module, which is essential for long-duration missions. The greenhouse module is designed to grow food and recycle air and water for the crew. It features hydroponic systems, LED grow lights, and climate control to ensure optimal growing conditions for a variety of crops. The greenhouse module has a diameter of 5 meters and is capable of supporting the dietary needs of up to 15 crew members for 5 years. Greenhouse operations are fully automated, requiring minimal crew intervention, allowing the crew to focus on other mission tasks. 

Greenhouse produce fresh fruits and vegetables, supplementing the crew's diet and improving their overall health and well-being during extended missions. The greenhouse module also plays a crucial role in maintaining the ship's life support systems by recycling carbon dioxide into oxygen through photosynthesis.

The 5-year limit is largely due to fertilizer quantity, as the hydroponic systems require a steady supply of nutrients to sustain plant growth. While water and air can be recycled indefinitely, the finite amount of fertilizer onboard limits the duration of effective greenhouse operations. Resupply missions or the ability to produce fertilizer in-situ would be necessary to extend the operational lifespan of the greenhouse module beyond 5 years.

### Main Storage Module
Behind the greenhouse module is the main storage module. This module is used to store supplies, equipment, and scientific instruments needed for the mission. It is designed to be easily accessible from both the habitat modules and the command center. The main storage module has a diameter of 5 meters and provides ample space for all necessary cargo. Since the life support systems are designed to be closed-loop, there isn't a need for large amounts of consumables storage in normal circumstances. But to prepare for emergencies, the storage module is designed to hold up to 10.5 months worth of extra supplies for the entire crew, allowing a direct abort to Earth or the nearest space station if needed.

### Truss Structure
Following the main storage module is the truss structure, which provides structural support for the ship's propulsion system and other external components. The truss structure is designed to withstand the stresses of interplanetary travel and towing operations. There are also 2 docking ports at the top and bottom of the truss structure for additional docking options, both supporting towing operations. The truss structure is vital for keeping the crew away from the radiation emitted by the main engines during operation.

An additional small Arc-reactor and as well as a secondary storage module are located at the bottom of the truss structure. The small Arc-reactor provides power to the ship in the event of a main reactor failure. It is nowhere near as powerful as the main reactor, but it is sufficient to power essential systems and maintain life support for the crew. The secondary storage module is used to store EVA equipment, spare parts, and other essential supplies needed for maintenance and repairs during the mission.

### Propulsion Module
At the rear of the ship is the propulsion module, which houses the main engines, fuel storage tanks, fusion reactor, additional comms, radiators, attitude control thrusters, and other essential systems needed for interplanetary travel. The propulsion module is designed to provide the necessary thrust and maneuverability for the mothership during its missions. 

The main engine is a mass driver propulsion system, which expels reaction mass at high velocities to generate thrust. The fusion reactor provides the necessary power to operate the engines and other systems on the ship. The engine is capable of operating at 2 different mode: Standard Mode and High-Thrust Mode. In Standard Mode, the engine provides can produce 2400KN of thrust at an ISP of 500,000s, allowing for efficient travel over long distances. In High-Thrust Mode, the engine can provide a higher thrust output at the cost of reduced specific impulse, allowing for quicker maneuvers and acceleration when needed. In High-Thrust Mode, the engine can produce up to 3800KN of thrust at an ISP of 250,000s. Due to the nature of mass driver propulsion, the engine can be throttled smoothly in both of 2 modes, allowing for precise control over thrust and fuel consumption.

The main engine requires a significant amount of power to operate, which is provided by the fusion reactor. The main reactor is a large cold fusion Arc-reactor capable of producing up to 8TW of power, most of which is used to power the engines and other critical systems. In the event of a main reactor failure, the small Arc-reactor located at the bottom of the truss structure can provide backup power to essential systems. But it is too weak to power the main engines, but it can power the ship's attitude control thrusters and life support systems, allowing the crew to maintain control of the ship and ensure their safety until repairs can be made or rescue arrives.

A total of nearly 200 tons of reaction mass is stored in the propulsion module, allowing for a total delta-v of 1700km/s when carrying a 300-ton payload.

The propulsion module also includes large radiators to dissipate heat generated by the reactor and engines, ensuring the ship remains within safe operating temperatures.

## Construction
Xihe was originally constructed in LEO using via multiple launches of Vulture Shuttles to deliver components and modules. 

The first Vulture Shuttle would deploy the Center Docking Hub from its payload bay and dock with it as an operation base. Several other Vulture Shuttles would then deliver additional modules and supplies as needed. The Artificial Gravity Habitat Module was delivered by another super heavy launch vehicle, as even in stored configuration it is too large for the Vulture Shuttle. Once the mothership was fully assembled, it would perform a series of test maneuvers in LEO before embarking on its maiden interplanetary mission. The first batch of Xihe mothership were constructed in this manner, demonstrating the feasibility of Interplanetary Exploration mothership assembly in low Earth orbit.

Subsequent Xihe motherships were constructed in the Star Port Station. Located at LEO, the Star Port Station is a large orbital shipyard capable of assembling and outfitting large spacecraft. The station provides a controlled environment for construction, allowing for more efficient assembly and testing of the motherships before they embark on their missions. Instead of Vulture Shuttles, components and modules for the motherships are delivered to the Star Port Station using larger cargo spacecraft such as Qingtian, streamlining the construction process.

## History
The first batch of 3 Xihe motherships were constructed between 2050 and 2055, with XH-01(Xihe) being the first to be completed in early 2052. During the construction of XH-01, several design improvements were identified that would enhance the performance and capabilities of subsequent motherships, and a possible new configuration for the propulsion system was proposed. These improvements lead to the development of Stellaria class motherships, which incorporated the new Lightspeed Engine, a more advanced propulsion system that offered improved performance and efficiency over the original mass driver propulsion system used in XH-01. As a result, XH-02 and XH-03--the second and third Xihe motherships--were redesigned to incorporate the new engine and other enhancements, leading to the creation of the Stellaria class. They were later redesignated as ST-01(Stellaria) and ST-02(Kristen) respectively.

Due to growing need of Mars One base expansion and Europa Research Outpost construction, Stellaria and Kristen were built as transitional designs between Xihe class and Stellaria class motherships, essentially Xihe class motherships with the new Lightspeed Engine. This allowed them to enter into service much earlier than originally planned. Both of which are already enter into service to support Mars One and Europa Research Outpost. Upgrades are planned to bring them closer to the full Stellaria class specifications.

Near the completion of Kristen, construction of the second batch of Xihe motherships began in 2054 at Star Port station, with XH-02(Taibai) being completed in 2056. XH-02 incorporated several design improvements identified during the construction of the first batch, including enhanced radiation shielding, upgraded life support systems, and improved scientific research capabilities. XH-03(Changxi) was under construction between February 2058 and November 2059, and is currently undergo testing in LEO. XH-04, whose name is unannounced yet, is currently under construction at Star Port station, with completion expected in mid 2061.

## Naming confusion
The second and third Xihe motherships were originally intended to be XH-02 and XH-03 respectively. However, during the construction of XH-02, the decision was made to redesignate it as ST-01(Stellaria) after significant design changes were made to incorporate the new Lightspeed Engine and other enhancements.  Similarly, XH-03 was also redesignated as ST-02(Kristen) for the same reasons.

Stellaria and Kristen serve as transitional designs between the Xihe class and the more advanced Stellaria class motherships. They are essentially Xihe class motherships with the new Lightspeed Engine. Both of which are already enter into service to support Mars One and Europa Research Outpost. Upgrades are planned to bring them closer to the full Stellaria class specifications. 

## Specifications
### Performance
- Propulsion: Endurance Mass Driver Propulsion System
- Main Engine Thrust: 2400KN (Standard Mode), 3800KN (High-Thrust Mode)
- Specific Impulse: 500,000s (Standard Mode), 250,000s (High-Thrust Mode)
- Delta-V: 1700 km/s (with 300-ton payload)

### Weight and Dimensions
- Fuel Capacity: 196.3 tons
- Wet Mass: 365.3 tons without payload
- Length: 83.4 meters
- Diameter: 25 meters (at habitat ring)

### Payload Capacity
- Maximum Payload: 300 tons (including planetary surface exploration vehicles)
- Towing Capacity: Up to 200 tons at the front docking port, 100 tons at each side docking port

### Crew
- Crew Capacity: 15 (sustainable for up to 5 years), 30 (short-term missions)
- Life Support supplies: 315days for 15 crew members without greenhouse support

## Missions
Xihe motherships are primarily used for crewed exploration missions to other planets and celestial bodies within the solar system. These missions typically involve a combination of scientific research, celestial body surface exploration, and technology demonstration. The mothership serves as a mobile base of operations, allowing the crew to conduct extended missions in deep space.

The first Xihe mothership, Xihe(XH-01), carried crew to Mars and Moons of Jupiter for exploration and research. It is heavily involved in the construction of the Mars One base and Europa Research Outpost, providing transportation, logistics support, and scientific expertise for these ambitious projects.

Xihe was used for crew rotation and supply runs to Mars One, as well as ferrying construction materials and equipment for the base's expansion. The mothership's towing capabilities allowed it to transport large planetary surface exploration vehicles and modules needed for the base's development.

As the construction of Europa Research Outpost started, another Xihe class mothership, Taibai, was built to support crew rotation and base expansion of Mars One, while Xihe was reassigned to support the Europa mission. Xihe transported crew and supplies to Europa, as well as scientific instruments and equipment needed for the outpost's research activities.

After the completion of Europa Research Outpost and an expedition to Europa, Xihe was brought back to Star Port for refit and maintenance. Several upgrades from Taibai were retrofitted onto Xihe, including improved radiation shielding, upgraded life support systems, enhanced scientific research capabilities, and better docking hubs. These upgrades ensured that Xihe remained at the forefront of interplanetary exploration technology.

### Mission Planning
With a total delta-v budget of 1700km/s when carrying a 300-ton payload, Xihe motherships will usually perform direct transfers to their destinations. There are 2 typical Trajectory profiles: standard and fast-travel. Standard travel profiles are missions with less than 200km/s departure burns, allowing single Earth-Mars trips to be completed between 20 and 140 days depending on planetary alignment. Fast-travel profiles can reduce travel time to as little as 8 days for Earth-Mars trips when the planets are perfectly aliened, but require higher delta-v burns of up to 250km/s each, significantly increasing fuel consumption.

With the high delta-v capacity, Xihe motherships usually plan their mission profiles to stay within a certain travel time, which means altering the burn durations to achieve the desired travel time. Typical Mars missions will aim for a total travel time of around 30 days one-way, while missions to Jupiter's moons will aim for around 70 days one-way. 


## Stellaria
Stellaria is a class of next-generation interplanetary exploration mothership, building upon the design and capabilities of the Xihe class. It features several advancements in propulsion, life support, and scientific research capabilities, making it well-suited for extended missions to distant planets and celestial bodies within the solar system.
It is envisioned that Stellaria will take over the roles of Outer Solar System Explorations once enter into service, allowing Xihe class motherships to focus on inner solar system missions and support roles.

## Fleet
| Name        | Serial Number | Status             | Notes                                      |  
|-------------|----------------|--------------------|--------------------------------------------|
| Xihe        | XH-01          | Active             | First of its class, supporting Mars and Europa missions.  |
| Stellaria   | ST-01          | Active             | Transitional design to Stellaria class, equipped with Lightspeed Engine.  |
| Kristen | ST-02       | Active             | Transitional design to Stellaria class, equipped with Lightspeed Engine.  |
| Taibai      | XH-02          | Active             | Second of its class, supporting Mars One base expansion.  |
| Changxi | XH-03       | Testing in LEO | Third of its class, intended to support Europa Research Outpost rotation and Venus exploration.  |
| Unnamed     | XH-04          | Under Construction | Fourth of its class, expected completion in mid 2061.  |
