Jerry Sellers

Nitrous oxide as a rocket propellant

Abstract Nitrous oxide is introduced as a multi-purpose propellant for spacecraft. Potential space applications of this propellant are given. Based on comparison to conventional systems, a multi-mode nitrous oxide propulsion concept is expected to deliver higher performance. Main features of a self-pressurising, nitrous oxide storage system are described. A nitrous oxide catalytic decomposition technique is suggested for restartable spacecraft propulsion. Up-to-date experimental results are presented. A conclusion describes the long-term feasibility of novel nitrous oxide propulsion option concepts.

Small satellite thermal modeling and design at USAFA: FalconSat-2 applications

The US Air Force Academy FalconSat program is one in which undergraduate cadets design, build, test, and operate satellites to carry Air Force and Department of Defense payloads for scientific missions. Currently, cadets are working on FalconSat-2, designed to carry the Micro Electro-Static Analyzer (MESA) payload that will investigate the morphology of plasma depletions in the ionosphere. The Engineering Model was completed and tested in April 2001, and cadets will construct the Qualification and Flight Models in the fall of 2001. To aid in the development of the satellite, behavioral models of various spacecraft subsystems have been created using MatLab and used to simulate projected operational modes of the satellite and the effects on major satellite subsystems. We require a detailed thermal model to aid in the development and testing of FalconSat-2. This paper will detail the development process undergone in creating the FalconSat-2 thermal model, will demonstrate how the model works, and will validate the results. Additionally, the paper will describe the thermal control solutions implemented for FalconSat-2 and how the model is used in the development process.

Investigation Into Cost-Effective Propulsion System Options for Small Satellites

The paper summarizes research into cost-effective propulsion system options for small satellites. Research into the primary cost drivers for propulsion systems is discussed and a process for resolving them is advanced. From this analysis, a new paradigm for understanding the total cost of propulsion systems is defined that encompasses nine dimensions – mass, volume, time, power, system price, integration, logistics, safety and technical risk. This paradigm is used to characterize all near-term propulsion technology options. From this effort, hybrid rockets emerges as a promising but underdeveloped technology with great potential for cost-effective application. A dedicated research program was completed to characterize this potential. This research demonstrated that hybrid rockets offer a safe, reliable upper stage option that is a versatile, cost-effective alternative to solid rocket motors. Finally, an innovative technique was derived to parametrically combine the diverse cost dimensions into a useful, quantifiable figure of merit for mission and research planning. Overall, it is shown that the most cost-effective solution is found by weighing all options along the nine dimensions of the cost paradigm within the context of a specific mission.

The Impact of Response Selection and Response Excution Difficulty on the Subjective Experience of Worload

The influence of variations in response selection and response execution difficulty on the workload and performance of 11 experimental subjects was investigated. The 20 laboratory tasks they performed involved a binary response selection that required different levels of mental processing (e.g. choice reaction time, prediction, memory search, etc.). A target acquisition task was added following response selection on half of the trials. A weighted combination of bipolar ratings on nine workload-related dimensions was used to evaluate the workload experienced by the subjects. In addition, subjects rank-ordered the tasks with respect to workload before (a prediction) and again after (a retrospective comparison) performing them. Apparently minor variations in stimulus presentation resulted in significantly increased reaction times and workload ratings, as did the more obvious manipulations of response selection load. The addition of the target acquisition task increased workload ratings and reaction tines, however the “cost” of performing the two-stage task (as indicated by measures of speed, accuracy, and subjective opinion) was considerably less than would be expected by combining measures for the component tasks. Movement times for the target acquisition tasks increased significantly as a function of the index of difficulty of the target, but were not affected by the difficulty of the response selection task.