Black Tortoise

The Black Tortoise (Xuánwǔ or 玄武) was the launch vehicle that replaced the Long March 5 as the primary surface-to-low-earth-orbit transport for the Bountiful Sky project.

Naming
According to some taoist legends, Xuánwǔ was a prince who forsook his royal title to study the tao, and studied it so intensely that he became divine. He slew the demons of his past to prevent them from harming others. Some historians speculate that the Beijing government chose this name to distance themselves from past regimes and forge a connection with deeper traditions. No official documentation of this has ever been found, however.

Configuration
When launched from Earth's surface, the Black Tortoise stack consisted (from bottom to top) of a booster, upper stage, payload/passenger section, and crew section. The booster stage separated a few minutes after launch, and continued in a parabolic trajectory to splash down in the ocean downrange, where it was recovered for later re-use. The upper stage, payload, and crew sections continued into low earth orbit.

Upon rendezvous with the LEO station, the upper stage was most often broken up for parts and materials. Some upper stages, however, were refurbished for orbital use in a similar way to the Long March 5 upper stages. A few of these were taken on the Climb and served as transports and scouts for the early settlers well after Arrival.

Design Lineage
In a radical departure from most boosters before it, Black Tortoise was designed for economical surface-to-orbit shipping and passenger travel. The design took advantage of maritime (especially submarine) construction methods and facilities to create a usable vehicle at a lower cost than traditional rocket-specific techniques. The vehicles were even built in construction slips once used to build massive surface ships that carried hundreds of cargo containers.

Black Tortoise pioneered another innovation that had been often considered in rocket design but never executed on this scale, namely launch from the open ocean. This eliminated the need for an expensive and maintenance-hungry launch facility, and also fostered safety by allowing launch from off the Hainan Island coast with thousands of miles of uninhabited open ocean downrange to the east. While an indigenous chinese project, the Black Tortoise design was heavily influenced by the Sea Dragon heavy lift design by Robert Truax. This design shared Black Tortoise's goal to make large-tonnage launches more economical, and was a natural inspiration for the project.

History
It was known in the earliest phases of the project that the Long March 5 would not be adequate for such a massive endeavor as Bountiful Sky, even when bootstrapped by the Bullets. Launching the personnel alone would have required 72 Long March 5 flights.

In the early planning stages of the project, it became clear that the vehicle needed could not be made ready by the time the project had to be underway, and the plan was revised to make use of the Long March 5 for the earliest construction crews that would rendezvous with the Bullet packages, while a massive joint project between the China Shipbuilding Industry Corporation, the China State Shipbuilding Corporation, and the National Astronautics Bureau rushed to bring the vehicle into production.

Vital Statistics

 * Height: 150 m (490 ft)
 * Diameter: 23 m (75 ft)
 * Thrust: 350,000 kN (78,680,000 lbf)
 * Apogee: 200 km (120 mi)
 * Gross mass: 18,000,000 kg (39,000,000 lb)
 * Payload: 450,000 kg (990,000 lb)
 * Max. Passenger Complement: 1,000