Acceleration of a suborbital payload using an electromagnetic railgun

Railguns are well-known for their capability to reach very high velocities (v(0) > 2000 m/s) with overall efficiencies (E-kinetic/E-electric) 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, ISL and EADS have investigated, within the scope of two ESA financed studies, the possibility of using a railgun to replace a sounding rocket with the aim of accelerating a meteorological probe up to an apogee of 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 given: electric energy sources, switches, pulse forming network as well as a first layout of the railgun itself (length, caliber, materials), and of its current injection points. A series of preliminary test shots of dummy projectiles with masses ranging from 1 to 4 kg using the existing PEGASUS railgun facility at ISL is reported. The projectiles were launched reliably and in a reproducible way with accelerations not exceeding 13000 g, except for one shot with the 2-kg projectile fired with an acceleration of 15700 g, thus, reproducing the suborbital launch conditions. A first estimation of how to delay the plasma occurrence of the sliding armatures used for the suborbital applications at low accelerations is also given in this paper.