The Bridge to Space: Elevator Sizing Performance Analysis

摘要

The Bridge to Space (BTS), an advanced system concept designed to significantly reduce payload-to-space delivery costs, consists of two major elements as seen in Figure 1: a long Space Elevator cable structure and an aircraft-like Sub-Orbital launch vehicle (SOLV). Preliminary estimates indicate the BTS can meet a launch cost target of $100/lb for 3rd generation launch systems. Previous papers have described the operational concept for launching payloads with the Bridge to Space (Marshall & Mottinger, 2000). These operations include payload transfer from the SOLV to the Space Elevator's Earth Transfer Station (ETS), payload translation along the elevator with a moving carriage platform and processing/transfer/release of the payload at the elevator's Apex Station (AS) as required, or payload release at the uppermost point of the elevator, the Space Transfer Station (STS). This paper will focus on sizing and performance modeling of the Space Elevator segment of the overall Bridge to Space. An elevator model has been developed to accept varying input parameters to determine outputs such as elevator mass and length, and altitude change/reboost requirements during payload transfer operations. Some of the key input variables include payload mass, ETS altitude and handoff velocity with the SOLV, and cable stress/density ratio. Sensitivity analyses have been performed with the model to determine the optimum altitude, velocity and size of the elevator for a given payload mass. Preliminary results of these sensitivity analyses are presented. The paper also includes a discussion of alternate concepts for the Space Elevator that could improve performance (i.e., minimize reboost fuel usage), based upon results of the model described above. Specifically, techniques to reduce the aerodynamic drag of the elevator's lower end and reduction of the overall elevator length and mass are discussed. The paper concludes with a summary of key results and lists technology development areas that would improve elevator performance.