Search Results

During teleoperation in space, there are two major sources of performance degradation: (1) spatiotemporal displacements in visual feedback; confounded by (2) microgravity effects, attributable to kinetic and inertial properties of large masses maneuvered in low gravity. Both sources contributed to the Progress-Mir collision in 1997. This report describes findings from two sets of studies directed at modeling possible effects on teleoperation tracking performance of spatial, temporal, and microgravity perturbations in visual feedback presented to the teleoperator. In the first set of studies, effects of both temporal and angular displacements in visual feedback on control of tracking behavior by individual subjects were evaluated under conditions of both continuous pursuit and discrete movement tracking.

Modern aircraft systems employ numerous processors to achieve system functionality. In particular, engine controls and power distribution subsystems rely heavily on software to provide safety-critical functionality, and are expected to move toward multicore architectures. The computing hardware-layer of avionic systems must be able to execute many concurrent workloads under tight deterministic execution guarantees to meet the safety standards. Single-chip multicores are attractive for safety-critical embedded systems due to their lightweight form factor. However, multicores aggressively share hardware resources, leading to interference that in turn creates non-deterministic execution for multiple concurrent workloads. We propose an approach to remove on-chip interference via a set of methods to spatio-temporally partition shared multicore resources.

This paper addresses the issue of fault diagnosis in the heat exchanger of an aircraft Air Conditioning System (ACS). The heat exchanger cools the air by transferring the heat to the ram-air. Due to a variety of biological, mechanical and chemical reasons, the heat exchanger may experience fouling conditions that reduces the efficiency and could considerably affect the functionality of the ACS. Since, the access to the heat exchanger is limited and time consuming, it is preferable to implement an early fault diagnosis technique that would facilitate Condition Based Maintenance (CBM). The main contribution of the paper is pre-flight fault assessment of the heat exchanger using a combined model-based and data-driven approach of fault diagnosis. A Simulink model of the ACS, that has been designed and validated by an industry partner, has been used for generation of sensor data for various fouling conditions.

A number of amine-based carbon dioxide (CO2) removal systems have been developed for atmosphere revitalization in closed loop life support systems. Most recently, Hamilton Sundstrand has developed an amine-based sorbent, designated SA9T, possessing approximately 2-fold greater capacity compared to previous formulations. This new formulation has demonstrated applicability for controlling CO2 levels within vehicles and habitats as well as during extravehicular activity (EVA). Our current data demonstrates an amine-based system volume which is competitive with existing technologies which use metal oxides (Metox) and lithium hydroxide sorbents. Further enhancements in system performance can be realized by incorporating humidity and trace contaminant control functions within an amine-based atmosphere revitalization system. A 3-year effort to develop prototype hardware capable of removing CO2, H2O, and trace contaminants from a cabin atmosphere has been initiated.

Supported amines have been shown to absorb CO2 cyclically under temperature swing absorption (TSA) conditions, and show a substantial decrease in desorption energy compared to zeolite materials. Supported amines may therefore be a viable alternative for cyclic capture of CO2 on long-term space missions where minimal energy expenditure is a critical consideration. The research described in this paper presents efforts to improve the TSA-supported amine system with a focus on relationships between important parameters affecting cyclic CO2 capacities, as well as reaction effects of CO2 with the modified amine tetraethylenepentamine.

In this study, a parametric examination of the main factors affecting cyclic CO2 absorption into supported amine sorbents has been conducted. A bench-scale test apparatus and Taguchi statistical design of experiments were used to assess the importance of cycle time, inlet CO2 concentration, residence time, humidity, absorption temperature, desorption temperature and desorption pressure on cyclic CO2 capacity. Two amine sorbents were considered: TEPAN and modified E-100. Amine decomposition, amine oxidation, and the effects of amine chemical composition were also examined. For typical ranges of system variables found on-board the space shuttle orbiter, results indicated that desorption pressure over the range of 25–85 torr, desorption temperature over the range of 50–60°C, absorption temperature over the range of 20–30°C, and CO2 concentration over the range of 6–9 mmHg were the most important variables affecting cyclic CO2 removal capacity.

The Environmental Control System (ECS) of an aircraft provides thermal and pressure control of the engine bleed air for comfort of the crew members and passengers onboard. For safe and reliable operation of the ECS under complex operating environments, it is critical to detect and diagnose performance degradations in the system during early phases of fault evolution. One of the critical components of the ECS is the heat exchanger, which ensures proper cooling of the engine bleed air. This paper presents a wavelet-based fouling diagnosis approach for the heat exchanger.

This paper addresses the issues of Fault Detection and Isolation (FDI) in complex networked systems such as the Environmental Control System (ECS) of an aircraft. The ECS controls and supplies pressurized air to the aircraft and consists of multiple subsystems that in turn consist of interconnected components, heterogeneous sensing devices, and feedback controllers. These complex interconnections and feedback control loops make fault detection and isolation a very challenging task in the ECS. For example, a faulty component yields off-nominal outputs which are inputs to the other coupled components. This coupling leads to off-nominal outputs from otherwise healthy components, thus causing unwanted false-alarms. Secondly, due to off-nominal inputs, the healthy components are driven beyond their normal operating conditions, leading to cascading failures.