Bullets

The Bullets were the first visible, public sign of the Bountiful Sky Project. Planning and activity had been in process for years before the launches, but the Bullets were what effectively announced the project to the world.

Purpose
Although the Long March 5 rockets were advanced launch vehicles in their day, lifting the entire mass needed to establish the project would have required thousands of launches over a period of years. Even the planned Black Tortoise HLLV, which would greatly increase lifting capacity, would require too many launches.

Verne Cannon
The earliest recorded instance of the cannon launch vehicle concept was in the novel De la terre à la lune, published in 1865 by the writer Jules Verne.

Project Orion
A 1955 document from the Los Alamos Laboratory claims explosive nuclear propulsion was conceived by Stanislaw Ulam and F Reines starting in 1946, though the actual project was initiated in 1958 by Ted Taylor at General Atomics and physicist Freeman Dyson.