Electromagnetic Railgun Technology for the Deployment of Small Sub- /Orbital Payloads

Railguns are well-known for their capability to reach very high velocities (v0 > 2000 m/s) with overall efficiencies (Ekinetic/Eelectric) over 30 %. The high performance expected concerning velocity, efficiency, cost and repetition rates makes this system attractive not only for military but also for space applications with the aim of accelerating lightweight payloads directly into the low earth orbit (500 km). This last application is very challenging, as far as the energy and power storage, the railgun length and the rail materials are concerned, but seems promising. In a first step towards space launch, we have designed a railgun able to replace a sounding rocket with the aim of accelerating a meteorological probe up to an apogee of about 120 km. In this paper a quantitative assessment of the concept of the railgun – coupled to the object to be accelerated – is proposed. The electric circuit necessary to drive the facility is determined: electric energy sources, switches, pulse forming network as well as a first layout of the railgun itself (length, calibre, materials) and its current injection points. A first assessment of a railgun designed to put nano-satellites into low-earth orbit is also given. Parallel to the railgun study, we have investigated the extreme thermal conditions the projectile's surfaces are exposed to (high temperature and high thermal loads). In a first step the HF3T code of the DLR is applied to estimate time-dependant temperature changes on the projectile's surface and/or within the material's structure as a function of the trajectory parameters. In a second step, the program TRAJECTORY3D of DLR was used to generate a detailed time dependant data set which includes the values for projectile velocity, Mach and Reynolds numbers and atmospheric properties as a function of altitude. A second approach uses the TAU code of DLR to solve the Navier-Stockes equations, enabling pseudo-unsteady flow solutions along the trajectory. The results of these calculations allow checking the feasibility of the proposed design for the railgun launched hypervelocity projectiles.