AEROTHERMAL AND TRAJECTORY ANALYSIS OF SMALL PAYLOADS LAUNCHED TO LOW EARTH ORBIT FROM AN AIRBORNE PLATFORM

摘要

In recent years there has been an ever increasing need to launch small payloads (~1-100 kg) into low earth orbit (LEO); examples include the defense, telecommunications and other civilian industries. NASA's stated mission of launching a manned mission to Mars requires many tons of raw materials to be economically launched into LEO and assembled there. Conventional rocket launch from earth is prohibitively expensive for small mass payloads. Estimates range from 7000 dollars - 20,000 dollars to launch 1 kg of mass into low earth orbit. Several concepts have been proposed to economically launch small payloads from earth, including light gas guns, electromagnetic launchers and the so called “slingatron” concept. The goal of these concepts is to reduce the cost per kg (to under 1000 dollars) to achieve LEO. Each of these concepts involves launching small payloads that traverse the atmosphere and then placed into a circular low earth orbit. As the launch vehicle traverses the dense lower portion of the atmosphere it experiences thermal heating loads that must be absorbed by a thermal protection system (TPS) if the payload is to survive the transit. High launch angles are desirable from the standpoint of minimizing TPS mass. However, for ballistic trajectories, high launch angles require a large propellant mass to achieve a stable circular orbit. This effort performs aerothermal and trajectory analyses on a nominal 10 kg payload launched from 16 km altitude airborne platform into a 200 km circular orbit. The study focuses on two efforts: 1) computing ballistic trajectories of sphere cones with ablation assuming laminar and turbulent flow in order to quantify the total ablation and required propellant mass to circularize the orbit for given launch conditions and 2) study lifting trajectories without ablation by flying axisymmetric sphere-cone projectiles at small angles of attack and asymmetric projectiles (ellipsleds) that turn the velocity vector during atmospheric transit in an effort to reduce the ΔV needed to circularize the orbit. The TPS is assumed to be made of graphite. Total parasitic mass is reported for several launch angles. Even though ablation is not considered for the lifting trajectories, the study allows comparison of relative effectiveness of various lifting trajectories in reducing the ΔV required to circularize the orbit.