Performance comparison between gas generator and electrically pumped rocket engines under ablative and regenerative cooling.

Abstract

In recent years, there has been a dramatic advancement in the global satellite industry, with new technologies allowing for smaller and more powerful satellites to be developed. Despite this, South Africa and other African countries developing satellite technologies still depend on foreign launch services as there is no indigenous capability in Africa, incurring additional costs and delays. Against this backdrop, the University of KwaZulu-Natal’s (UKZN) Aerospace Systems Research Institute (ASRI) is pursuing the development of a two-stage Commercial Launch Vehicle (CLV) to provide South Africa with a sovereign launch capability. ASRI is currently developing the booster engine for CLV - the South AFrican FIrst Rocket Engine (SAFFIRE). The booster stage will utilize a cluster of nine of the SAFFIRE engines, and the second stage will use a vacuum derivative of the SAFFIRE engine called SAFFIRE-V and will give CLV the envisioned payload capacity of 200 kg to a 500 km Sun Synchronous Orbit (SSO). Although the design of the SAFFIRE engine is largely complete in terms of injector design, combustion chamber and nozzle geometry, and thrust output, the feed cycle responsible for delivering the propellants to the combustion chamber is undecided. In this report, the gas generator and electropump cycles are under consideration to supply propellants to the SAFFIRE and SAFFIRE-V chambers. In addition, although the chambers are currently ablatively cooled, ASRI remains interested in the possibility of using regenerative cooling. This study, therefore, considers the gas generator and electropump cycles under both cooling methods to identify which SAFFIRE engine combination can provide the best performance for CLV. To measure the performance of each engine combination, the payload mass capabilities of a hypothetical CLV are calculated using results attained from 1- dimensional simulations run in Flownex®, models coupled with Mass Estimating Relationships (MER) that evaluate the components that make up a two-stage liquid rocket engine. The performance comparison found that each engine configuration exceeded the set payload capacity of 200 kg. For the electropump cycle, the ablative and regenerative engines achieved payload masses of 303 kg and 290 kg, respectively. The gas generator performed even better due to a lower dead mass than the electropump cycle, achieving payload masses of 392 kg and 386 kg, respectively. For both cycles, the ablatively cooled rocket engines had better payload capabilities than the regeneratively cooled engines due to a regeneratively cooled engine having a smaller expansion ratio. When the expansion ratios were made the same, the regeneratively cooled engines achieved a payload capacity of 308 kg and 405 kg for the electropump and gas generator cycles, respectively, due to the increased thrust from the heated fuel, which has an increased energy density, producing more thrust. When the dead mass of the electropump cycle was decreased by ejecting the depleted battery packs for each engine stage during the launch, the electropump payload deficit decreased from 98 kg to 29 kg for the ablative engines and 96 kg to 32 kg for the regenerative engines. Based on this study, the best performing SAFFIRE engine configuration is a gas generator cycle with ablative cooling, giving the conceptual CLV rocket a payload of 392 kg to 500 km Sun Synchronous Orbit.