A Tether-Assisted Space Launch System for Super-Earths

Super-Earths are one of the most common types of extrasolar planets currently known. Hundreds of these planets have been discovered by the $Kepler$ spacecraft and other surveys, with masses up to 10 $M_\oplus$ and consequently higher surface gravity than Earth. These planets would have greater escape velocities than Earth, reaching as high as 27 km s$^{-1}$ for the largest super-Earths. To launch a spacecraft from the surface of such a world with chemical rockets would be cost-prohibitive or nearly so, while another commonly proposed launch system, the space elevator, would lack the necessary tensile strength to support its weight. However, we find that a hybrid launch system combining chemical rockets and a space-based momentum-exchange tether could reduce the $\Delta v$ to be provided by chemical rockets to reach escape velocity by 40\%, bringing it back into the realm of feasibility. Such a system could also function on Earth with considerably less exotic materials.