Preliminary design considerations for a commercial launch vehicle upper stage.

Abstract

The African small satellite industry (micro and nano satellites in particular) continues to grow with developments in the miniaturization of satellite technology. However, the costs and delays involved with the traditional “piggy backing” satellite launch method is unsustainable for small sat developers and has thus created a niche market for dedicated small satellite launch services. Notably, there is no satellite launch capability whatsoever in Africa, meaning all of the continent’s launch requirements are serviced by foreign providers, incurring additional cost. As its primary objective, the University of KwaZulu-Natal’s (UKZN’s) Aerospace Systems Research Group (ASReG) seeks to enable the establishment of an indigenous small satellite launch capability in alignment with the South African Government’s goals. To this end, ASReG is currently developing the LOX/Kerosene SAFFIRE (South African First Integrated Rocket Engine) to propel a hypothetical two-stage orbital launch vehicle, termed Commercial Launch Vehicle 1 (CLV). The upper stage of the launch vehicle will use a vacuum-expanded variant of SAFFIRE called SAFFIRE-V. The upper stage for both cases must meet the design constraints of a 0.85 mass fraction and a 1.2 m outer diameter. CLV has been envisaged to deliver a 75kg payload to 400 km sun synchronous orbit. This thesis presents a high level analysis focusing on the upper stage of CLV, which intends to guide design decisions by comparing design options based on mass, and develop a methodology for upper stage vehicle design. One of the major design decisions is the type of propellant feed system the vehicle should use; in this regard, the analysis compares an electric pump feed system to a pressure fed system. Another is the selection of propellant tank material, given that the propellant tanks constitute most of the mass of a rocket. Stainless steel (301 and Duplex), aluminium alloy (7075), aluminium-lithium (2195), carbon fibre reinforced plastic (T700/Epoxy), as well as combinations of materials were compared. To perform the preliminary mass analysis, each of the major components/systems of the CLV upper stage were independently designed and the various design options available for each of the components/systems were compared based on mass. These systems and components include: fuel and oxidiser propellant tanks, the propellant pressurization system and the reaction control system. After the individual analyses of the variations of each component, the best suited architectures were modelled in SolidWorks CAD software. The components were then assembled, in CAD. The analysis found that, on a preliminary basis, the Lithium ion (Li-Ion) based electric pump fed upper stages did not meet the mass requirements while Lithium polymer (Li-Po) based upper stages achieved the mass requirements. An upper stage employing stainless steel propellant tanks was found to meet the mass requirements, but only for a pressure fed upper stage. Overall, pressure fed upper stages had lower masses compared to electric pump vehicles. The mass reduction of thin walled, low pressurized, propellant tanks (resulting from using electric pumps) was offset by the mass of the battery packs required to power the pumps.