Design work on the prototype space gun began as early as 1985 at the Lawrence Livermore National Laboratory in California and became operational in December 1992.
[2] The firing sequence begins with the ignition of a methane gas mixture in the combustion section behind the piston at the far end of the pump tube.
As the piston accelerates toward the junction point, it rapidly compresses the hydrogen gas in the pump tube to a pressure of 60,000 psi (4,100 atm).
Had the project continued, there were plans to elevate the tube and begin space launch trials potentially reaching speeds of up to 7 km/s (16,000 mph), or about Mach 21.
The largest challenge is maintaining such high velocities, because air resistance and aerothermal heating will significantly slow down any such object.