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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

SU-E-T-181: Clinical Implementation of Task Group 176

Purpose: The implementation of TG-176 with regards to immobilization devices and couch tops as they effect dosimetric treatment planning. Methods: The external devices used clinically were scanned to measure their HU values. Plans were created in the Eclipse treatment planning system (TPS) using these devices, one that accounted for the correct HU value of the each device and another that did not include the device as a structure. A dose subtraction was performed between the two plans to evaluate the dosimetric differences. The metrics used for evaluation included attenuation and surface dose. Plan parameters were varied to evaluate the impact of the devices in different clinical scenarios. Results: While the exact HU values of our results are clinic-dependent, the protocol being implemented is widely applicable. We recommend a four step process for implementing this task group. First, physics should scan each treatment device to determine accurate HU values. Second, CT therapists should include in the setup note which table top was used during patient CT simulation and are asked to make immobilization devices as uniform in thickness as possible. Therapists should also index the devices whenever possible so beam will traverse the same area of the device. Third, the dosimetrist should manually correct the HU value for any external device, including the couch. For H&N cases, the rails must be removed from the couch structure. When rails are used during treatments, it is important to make note of their exact position in the setup notes. Finally, physicians should be made aware that there could be changes in surface doses depending on whether or not immobilization devices or couch tops are in the beam path. Conclusion: The protocol outlined above was implemented to reduce the errors that arise from ignoring effects of external devices, thus ensuring safer, more accurate patient treatments.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

Recommended Practices for Managing Induced Seismicity Risk Associated with Geologic Carbon Storage

The geologic storage of carbon dioxide (CO 2 ) is one method to help reduce or eliminate atmospheric CO 2 emissions. The sequestered CO 2 is originally captured from the atmosphere or from a stationary industrial source and subsequently injected into a deep subsurface porous rock formation. To facilitate the successful deployment of field scale carbon storage projects, the U.S. Department of Energy (DOE) is developing tools and protocols for defensible, science-based frameworks to quantify and mitigate risks associated with the long-term storage of CO 2 . This protocol specifically addresses the risk of induced seismicity due to injection in a geologic carbon storage (GCS) site. This integrated and risk-based protocol is a product of the U.S. DOE Fossil Energy’s National Risk Assessment Partnership (NRAP), a multi-year collaborative research effort of Los Alamos National Laboratory (LANL), Lawrence Berkeley National Laboratory (LBNL), Lawrence Livermore National Laboratory (LLNL), National Energy Technology Laboratory (NETL), and Pacific Northwest National Laboratory (PNNL). These recommended practices describe a set of 7 steps to evaluate, manage, communicate, and mitigate the risk of induced seismicity at GCS sites. The base methodology of the recommended practices follows a framework similar to the $\textit{Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems}$ (Majer et al., 2012), developed for the Geothermal Technology Office of the U.S. DOE. These recommended practices present a framework to systematically assess the induced seismicity risk and quantify the associated uncertainties. These recommendations are based on current research and are sufficiently general to allow for modification and application to a variety of different types of sites. The substance of the recommended practices contained herein includes both technical and non-technical issues, and covers all operational stages of the GCS project lifecycle. They start at the preliminary risk assessment phase, continue through site assessment and characterization, include best practice communication and seismic monitoring plan methodologies, discuss the evaluation and mitigation of seismic hazard and risk, and closes with an exploration of operational management plans, which conclude when the induced seismicity risk abates back to background level. The focus of these recommendations is on actively managing the risks associated with induced seismicity by developing an actionable risk management plan that starts at the project proposal stage and continues through site closure through an iterative assessment and improvement process. The audience of this document is expected to include all interested stakeholders (e.g., operators, project developers, regulators, and the general public) and is expressly written to be accessible to this broad range of partners. This document is intended to disseminate knowledge gained through recent advances in the science of induced seismicity hazard and risk assessments, to provide updates based on recent experience gained by similar corollary injection-induced seismicity cases, and most importantly to establish a uniform framework to carry out a successful induced seismicity risk management plan for carbon storage projects in the future. These recommendations do not directly address any domestic or international regulations or standards. A complementary NRAP report makes recommendations for the assessment and management of environmental subsurface risks associated with unwanted fluid migration at GCS sites (Thomas et al., 2021) and should be referred to in order to address those additional GCS site risks

58 GEOSCIENCES↗
DOE OSTI2019

Assessing time-of-flight signal-to-noise ratio gains within the myocardium and subsequent reductions in administered activity in cardiac PET studies

Background: Time-of-flight (TOF) is known to increase signal-to-noise ratio (SNR) and facilitate reductions in administered activity. Established measures of SNR gain are derived from areas of uniform uptake, which is not applicable to the heterogeneous uptake in cardiac PET images using fluoro-deoxyglucose (FDG). This study aimed to develop a technique to quantify SNR gains within the myocardium due to TOF. Methods: Reference TOF SNR gains were measured in 88 FDG oncology patients. Phantom data were used to translate reference SNR gains and validate a method of quantifying SNR gains within the myocardium from parametric images produced from multiple replicate images. This technique was applied to 13 FDG cardiac viability patients. Results: Reference TOF SNR gains of +23% ± 8.5% were measured in oncology patients. Measurements of SNR gain from the phantom data were in agreement and showed the parametric image technique to be sufficiently robust. SNR gains within the myocardium in the viability patients were +21% ± 2.8%. Conclusion: A method to quantify SNR gains from TOF within the myocardium has been developed and evaluated. SNR gains within the myocardium are comparable to those observed by established methods. This allows guidance for protocol optimization for TOF systems in cardiac PET.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2022

Direct Recycling of Lithium-Ion Battery Cathodes: A Multi-Stage Annealing Process to Recover the Pristine Structure and Performance

Direct recycling is an alternative low-cost process that retains the structure of the lithium-ion battery cathode rather than going through materials dissolution and repurification. While the process shows promise, various steps need to be better understood and studied to identify possible roadblocks, cost intensive steps, and needed variations in protocol that may be necessary based on the feedstock of recycled cathodes available. In this study, we have evaluated the process of thermal relithiation as it applies to end-of-life cathode materials. For recovered end-of-life cathodes, approximately 20% of the useable lithium has been lost due to solid electrolyte interface formation, parasitic reactions, and particle isolation; this lost lithium contributes to higher cell impedance and a gradual shift in electrode potentials. As a first step in the direct recycling process, this lithium needs to be restored not only to recover capacity but also to eliminate surface vacancies and hinder surface reconstruction that may increase impedance and impact performance. Here, we have optimized a coating method followed by a two-stage annealing process that restores a model delithiated NMC333 material to pristine performance. Comparisons to single-stage processes are made, and new characterization tools have been used to better understand the processes.

25 ENERGY STORAGE↗
DOE OSTI2020

Storage Conditions of Human Kidney Tissue Sections Affect Spatial Lipidomics Analysis Reproducibility

Lipids often are labile, unstable, and tend to degrade overtime, so it is of the upmost importance to study these molecules in their most native state. In this study, we sought to understand the optimal storage conditions for spatial lipidomic analysis of human kidney tissue sections. Specifically, we evaluated human kidney tissue sections on several different days throughout the span of a week using our established protocol for elucidating lipids using high mass resolution matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI). We studied kidney tissue sections stored under five different conditions: open stored at –80 °C, vacuumed sealed and stored at –80 °C, with matrix preapplied before storage at –80 °C, under a nitrogen atmosphere and stored at –80 °C, and at room temperature in a desiccator. Results were compared to data obtained from kidney tissue sections that were prepared and analyzed immediately after cryosectioning. Data was processed using METASPACE. After a week of storage, the sections stored at room temperature showed the largest amount of lipid degradation, while sections stored under nitrogen and at –80 °C retained the greatest number of overlapping annotations in relation to freshly cut tissue. Overall, we found that molecular degradation of the tissue sections was unavoidable over time, regardless of storage conditions, but storing tissue sections in an inert gas at low temperatures can curtail molecular degradation within tissue sections.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2026

Challenges, Technological Pathways and Trade-Offs of Perovskite Solar Modules for Long-Term Operation

Perovskite solar modules (PSMs) have emerged as a promising photovoltaic technology due to their high efficiency, low fabrication cost and compatibility with lightweight and flexible applications. However, ensuring long-term reliable performance under real-world conditions remains a critical barrier to commercialization. PSMs degrade through mechanisms that differ substantially from those affecting established technologies such as silicon, particularly under environmental stressors like ultraviolet light, oxygen, temperature cycling and reverse bias. Here we provide an analysis of the degradation pathways specific to perovskite modules and discuss why standard accelerated tests often fail to predict outdoor performance. We conceptualize challenges across material, device and module levels and evaluate strategies to mitigate ion migration, interfacial breakdown and encapsulation failure. By highlighting the need for realistic testing protocols and durable materials, we propose a framework highlighting key challenges, technological pathways and the trade-offs required to extend perovskite module lifetimes towards long-term operation, aiming to guide the development of PSMs capable of a 30-year operational lifetime.

14 SOLAR ENERGY↗
DOE OSTI2015

Nanoscale pillar arrays for separations

The work presented herein evaluates silicon nano-pillar arrays for use in planar chromatography. Electron beam lithography and metal thermal dewetting protocols were used to create nano-thin layer chromatography platforms. With these fabrication methods we are able to reduce the size of the characteristic features in a separation medium below that used in ultra-thin layer chromatography; i.e. pillar heights are 1-2μm and pillar diameters are typically in the 200- 400nm range. In addition to the intrinsic nanoscale aspects of the systems, it is shown they can be further functionalized with nanoporous layers and traditional stationary phases for chromatography; hence exhibit broad-ranging lab-on-a-chip and point-of-care potential. Because of an inherent high permeability and very small effective mass transfer distance between pillars, chromatographic efficiency can be very high but is enhanced herein by stacking during development and focusing while drying, yielding plate heights in the nm range separated band volumes. Practical separations of fluorescent dyes, fluorescently derivatized amines, and anti-tumor drugs are illustrated.

47 OTHER INSTRUMENTATION↗
DOE OSTI2014

Statistical model based iterative reconstruction (MBIR) in clinical CT systems: Experimental assessment of noise performance

Purpose: To reduce radiation dose in CT imaging, the statistical model based iterative reconstruction (MBIR) method has been introduced for clinical use. Based on the principle of MBIR and its nonlinear nature, the noise performance of MBIR is expected to be different from that of the well-understood filtered backprojection (FBP) reconstruction method. The purpose of this work is to experimentally assess the unique noise characteristics of MBIR using a state-of-the-art clinical CT system. Methods: Three physical phantoms, including a water cylinder and two pediatric head phantoms, were scanned in axial scanning mode using a 64-slice CT scanner (Discovery CT750 HD, GE Healthcare, Waukesha, WI) at seven different mAs levels (5, 12.5, 25, 50, 100, 200, 300). At each mAs level, each phantom was repeatedly scanned 50 times to generate an image ensemble for noise analysis. Both the FBP method with a standard kernel and the MBIR method (Veo{sup ®}, GE Healthcare, Waukesha, WI) were used for CT image reconstruction. Three-dimensional (3D) noise power spectrum (NPS), two-dimensional (2D) NPS, and zero-dimensional NPS (noise variance) were assessed both globally and locally. Noise magnitude, noise spatial correlation, noise spatial uniformity and their dose dependence were examined for the two reconstruction methods. Results: (1) At each dose level and at each frequency, the magnitude of the NPS of MBIR was smaller than that of FBP. (2) While the shape of the NPS of FBP was dose-independent, the shape of the NPS of MBIR was strongly dose-dependent; lower dose lead to a “redder” NPS with a lower mean frequency value. (3) The noise standard deviation (σ) of MBIR and dose were found to be related through a power law of σ ∝ (dose){sup −β} with the component β ≈ 0.25, which violated the classical σ ∝ (dose){sup −0.5} power law in FBP. (4) With MBIR, noise reduction was most prominent for thin image slices. (5) MBIR lead to better noise spatial uniformity when compared with FBP. (6) A composite image generated from two MBIR images acquired at two different dose levels (D1 and D2) demonstrated lower noise than that of an image acquired at a dose level of D1+D2. Conclusions: The noise characteristics of the MBIR method are significantly different from those of the FBP method. The well known tradeoff relationship between CT image noise and radiation dose has been modified by MBIR to establish a more gradual dependence of noise on dose. Additionally, some other CT noise properties that had been well understood based on the linear system theory have also been altered by MBIR. Clinical CT scan protocols that had been optimized based on the classical CT noise properties need to be carefully re-evaluated for systems equipped with MBIR in order to maximize the method's potential clinical benefits in dose reduction and/or in CT image quality improvement.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

SU-F-J-32: Do We Need KV Imaging During CBCT Based Patient Set-Up for Lung Radiation Therapy?

Purpose: To evaluate the role of 2D kilovoltage (kV) imaging to complement cone beam CT (CBCT) imaging in a shift threshold based image guided radiation therapy (IGRT) strategy for conventional lung radiotherapy. Methods: A retrospective study was conducted by analyzing IGRT couch shift trends for 15 patients that received lung radiation therapy to evaluate the benefit of performing orthogonal kV imaging prior to CBCT imaging. Herein, a shift threshold based IGRT protocol was applied, which would mandate additional CBCT verification if the applied patient shifts exceeded 3 mm to avoid intraobserver variability in CBCT registration and to confirm table shifts. For each patient, two IGRT strategies: kV + CBCT and CBCT alone, were compared and the recorded patient shifts were categorized into whether additional CBCT acquisition would have been mandated or not. The effectiveness of either strategy was gauged by the likelihood of needing additional CBCT imaging for accurate patient set-up. Results: The use of CBCT alone was 6 times more likely to require an additional CBCT than KV+CBCT, for a 3 mm shift threshold (88% vs 14%). The likelihood of additional CBCT verification generally increased with lower shift thresholds, and was significantly lower when kV+CBCT was used (7% with 5 mm shift threshold, 36% with 2 mm threshold), than with CBCT alone (61% with 5 mm shift threshold, 97% with 2 mm threshold). With CBCT alone, treatment time increased by 2.2 min and dose increased by 1.9 cGy per fraction on average due to additional CBCT with a 3mm shift threshold. Conclusion: The benefit of kV imaging to screen for gross misalignments led to more accurate CBCT based patient localization compared with using CBCT alone. The subsequently reduced need for additional CBCT verification will minimize treatment time and result in less overall patient imaging dose.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2020

PC-RPL: Joint Control of Routing Topology and Transmission Power in Real Low-Power and Lossy Networks

We present PC-RPL , a transmission power-controlled IPv6 routing protocol for low-power and lossy wireless networks that significantly improves the end-to-end packet delivery performance under heavy traffic compared to the standard RPL. We show through actual design, implementation, and experiments that a multihop wireless network can achieve better throughput and routing stability when transmission power and routing topology are “jointly and adaptively” controlled. Our experiments show that the predominant “fixed and uniform” transmission power strategy with “link quality and hop distance”–based routing topology construction (i.e., RPL) loses significant bandwidth due to hidden terminal and load imbalance problems. We design an adaptive and distributed control mechanism for transmission power and routing topology, named PC-RPL , on top of the standard RPL routing protocol for hidden terminal mitigation and load balancing. We implement PC-RPL on real embedded devices and evaluate its performance on a 49-node multihop testbed. PC-RPL reduces total end-to-end packet losses by approximately sevenfold without increasing hop distance compared to RPL with the highest transmission power, resulting in 17% improvement in aggregate bandwidth and 64% improvement for the worst-case node by successfully alleviating both hidden terminal and load imbalance problems.

Computer Science↗
DOE OSTI2020

Wide Area 3D Measurement System for Analysis of 3013 Inner Container Closure Weld Region

One of the main focus areas of the 3013 Surveillance Program is a thorough evaluation of the inner container closure weld region (ICCWR) opened for destructive examination (DE). As part of the protocol to investigate the corrosion in the ICCWR, a laser confocal microscope (LCM) is used to perform close visual examination of the surface and to measure corrosion features on the surface. However, in FY20, the introduction of the Wide Area 3D Measurement System (WAMS) was tested as a method for faster inspection of the ICCWR. Optimization of the WAMS parameters for data collection was carried out using a generic tear-drop type sample containing large and fine Stress Corrosion Cracking (SCC) fractures and high resolution images were compared to the image obtained with the LCM. Although the image with the LCM shows higher resolution than the WAMS images, the small features can be still identified in the WAMS images. The advantage of collecting data for the full circumference using the WAMS is that it can take about a week to complete, which represents 1/16 of the time needed with the LCM. Nonetheless, both systems offer capabilities that combined can be utilized to expedite the examination of the ICCWR. The WAMS can be utilized to obtain images for faster screening or identification of corrosion features on the surface while the LCM can be utilized to obtain higher resolution images of those areas identified by the WAMS.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2022

Development of Surface Sampling Techniques for the Canister Deposition Field Demonstration (FY22 Update)

This report describes the proposed surface sampling techniques and plan for the multi-year Canister Deposition Field Demonstration (CDFD). The CDFD is primarily a dust deposition test that will use three commercial 32PTH2 NUHOMS welded stainless steel storage canisters in Advanced Horizontal Storage Modules, with planned exposure testing for up to 10 years at an operating ISFSI site. One canister will be left at ambient condition, unheated; the other two will have heaters to achieve canister surface temperatures that match, to the degree possible, spent nuclear fuel (SNF) loaded canisters with heat loads of 10 kW and 40 kW. Surface sampling campaigns for dust analysis will take place on a yearly or bi-yearly basis. The goal of the planned dust sampling and analysis is to determine important environmental parameters that impact the potential occurrence of stress corrosion cracking on SNF dry storage canisters. Specifically, measured dust deposition rates and deposited particle sizes will improve parameterization of dust deposition models employed to predict the potential occurrence and timing of stress corrosion cracks on the stainless steel SNF canisters. The size, morphology, and composition of the deposited dust and salt particles will be quantified, as well as the soluble salt load per unit area and the rate of deposition, as a function of canister surface temperature, location, time, and orientation. Previously, a preliminary sampling plan was developed, identifying possible sampling locations on the canister surfaces and sampling intervals; possible sampling methods were also described. Further development of the sampling plan has commenced through three different tasks. First, canister surface roughness, a potentially important parameter for air flow and dust deposition, was characterized at several locations on one of the test canisters. Second, corrosion testing to evaluate the potential lifetime and aging of thermocouple wires, spot welds, and attachments was initiated. Third, hand sampling protocols were developed, and initial testing was carried out. The results of those efforts are presented in this report. The information obtained from the CDFD will be critical for ongoing efforts to develop a detailed understanding of the potential for stress corrosion cracking of SNF dry storage canisters.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2024

Expanding Scientific Horizons Through High Field Dynamic Nuclear Polarization with Advanced Organic BiRadicals

This project aimed to advance the capabilities of high-field Dynamic Nuclear Polarization (DNP) Nuclear Magnetic Resonance (NMR) spectroscopy at 800 MHz through the synthesis and evaluation of novel biradicals. While the targeted HyTEK biradical synthesis faced significant challenges, alternative efforts focused on synthesizing intermediate compounds and exploring alternative biradicals. A portion of the BDPA precursor was successfully converted into BDPA-TEMPO, though further DNP testing could not be completed within the project timeline. Benchmarking experiments with existing biradicals, including TEKPol and M-TinyPol, were conducted to evaluate their performance under high-field conditions. These efforts provided valuable insights into DNP enhancements, refined operational protocols for high-field experiments, and established benchmarks for future polarizing agent development.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Refrigerants for a Sustainable Future

Worldwide use of high global warming potential (GWP) hydrofluorocarbon (HFC) refrigerants for space conditioning and food storage results in significant equivalent greenhouse gas (GHG) emissions. This is further exacerbated in developed countries by the current transition from hydrochlorofluorocarbon (HCFC) refrigerants to HFC refrigerants. Under the Kigali amendment to the Montreal Protocol, the proposed phase-out of currently used HFC and HCFC refrigerants has initiated a re-evaluation of some pre-existing refrigerants as well as the development and evaluation of new refrigerants. Making the ideal refrigerant selections for heating, ventilation, air-conditioning, and refrigeration (HVAC&R) applications is thereby difficult in an already overabundant refrigerants market. In this paper, a study of key parameters required of a good refrigerant is conducted, followed by the analysis of refrigerants desired and refrigerants used in two major sectors of the HVAC&R industry, namely commercial refrigeration and residential air-conditioning and heat pumps. Finally, keeping in consideration the global environmental regulations and safety standards, a recommendation of the most suitable refrigerants in both sectors has been made.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1997

Understanding Skill in EVA Mass Handling: Theoretical and Operational Foundations - Volume 1

This report describes the theoretical and operational foundations for our analysis of skill in extravehicular mass handling. A review of our research on postural control, human-environment interactions, and exploratory behavior in skill acquisition is used to motivate our analysis. This scientific material is presented within the context of operationally valid issues concerning extravehicular mass handling. We describe the development of meaningful empirical measures that are relevant to a special class of nested control systems: manual interactions between an individual and the substantial environment. These measures are incorporated into a unique empirical protocol implemented on NASA's principal mass handling simulator, the precision air-bearing floor, in order to evaluate skill in extravehicular mass handling. We discuss the components of such skill with reference to the relationship between postural configuration and controllability of an orbital replacement unit, the relationship between orbital replacement unit control and postural stability, the relationship between antecedent and consequent movements of an orbital replacement unit, and the relationship between antecedent and consequent postural movements. Finally, we describe our expectations regarding the operational relevance of the empirical results as it pertains to extravehicular activity tools, training, monitoring, and planning.

Riccio, Gary↗
NASA NTRS2003

Monitoring of Observation Errors in the Assimilation of Satellite Ozone Data

The stratospheric ozone layer protects life on Earth from the harmful effects of solar ultravioiet radiation. The ozone layer is currently in a fragile state because of depletion caused by man-made chemicals, especially chlorofluorocarbons. The state of the ozone layer is being monitored and evaluated by scientific experts around the world, in order to help policy makers assess the impacts of international protocols that control the production and release of ozone depleting chemicals. Scientists use a variety ozone measurements and models in order to form a comprehensive picture about the current state of the ozone layer, and to predict the future behavior (expected to be a recovery, as the abundance of the depleting chemicals decreases). Among the data sets used, those from satellite-borne instruments have the advantage of providing a wealth of information about the ozone distribution over most of the globe. Several instruments onboard American and international satellites make measurements of the properties of the atmosphere, from which atmospheric ozone amounts are estimated; long-term measurement programs enable monitoring of trends in ozone. However, the characteristics of satellite instruments change in time. For example, the instrument lenses through which measurements are made may deteriorate over time, or the satellite orbit may drift so that measurements over each location are made later and later in the day. These changes may increase the errors in the retrieved ozone amounts, and degrade the quality of estimated ozone amounts and of their variability. Our work focuses on combining the satellite ozone data with global models that capture atmospheric motion and ozone chemistry, using advanced statistical techniques: this is known as data assimilation. Our method provides a three-dimensional global ozone distribution that is consistent with both the satellite measurements and with our understanding of processes (described in the models) that control ozone distribution. Through the monitoring of statistical properties of the agreement between the data and the model, this approach also enables us to detect changes in the quality of ozone data retrieved from satellite-borne instrument measurements. This paper demonstrates that calculations of the changes in satellite data quality, and the impact these changes on the estimates of the global ozone distribution, can assist in maintaining the uniform quality of the satellite ozone data throughout the lifetime of these instruments, thus contributing to our understanding of long-term ozone change.

Stajner, Ivanka↗
NASA NTRS1999

Reconfigurable Data Communications Packet-Switch Emulation Test Bed Demonstrated

The Communications Technology Division at the NASA Lewis Research Center has an ongoing program to develop advanced switching and routing technology concepts for future satellite onboard processing systems. Through a university grant as a part of this research, the Cleveland State University is using a flexible reconfigurable data communications packet switch emulation test bed to investigate packet switching techniques. Because of the switching speed and protocol complexity, implementing a data communications network is a tremendous task. Various alternatives should be carefully studied and evaluated in the development stage so that the optimal system configuration can be obtained and implemented later. Therefore, it is desirable to predict the performance of the network before it is actually constructed. This is especially true in the case of satellite systems. In the past, theoretical analysis, software simulation, and prototyping were used to evaluate performance. However, each method has its drawback. There are basic tradeoffs among accuracy, cost, and required evaluation time. No method is completely satisfactory.

Chu, Pong P.↗