PARALLEL UNSTEADY TURBOPUMP SIMULATIONS FOR LIQUID ROCKET ENGINES

The National Aeronautics and Space Administration’s (NASA’s) Marshall Space Flight Center (MSFC) has established a “cold” airflow turbine test program to experimentally determine the performance of liquid rocket engine turbopump drive turbines. Testing of the space shuttle main engine (SSME) alternate turbopump development (ATD) fuel turbine was conducted for “back-to-back” comparisons with the baseline SSME fuel turbine results obtained in the first quarter of 1991. Turbine performance, Reynolds number effects, and turbine diagnostics, such as stage reactions and exit swirl angles, were investigated at the turbine design point and at off-design conditions. The test data showed that the ATD fuel turbine test article was approximately 1.4 percent higher in efficiency and flowed 5.3 percent more than the baseline fuel turbine test article. This paper describes the method and results used to validate the ATD fuel turbine aerodynamic design. The results are being used to determine the ATD high pressure fuel turbopump (HPFTP) turbine performance over its operating range, anchor the SSME ATD steady-state performance model, and validate various prediction and design analyses.

Overset grid technology development at NASA Ames Research Center

Expendable launch vehicles will be phased out during the first years of shuttle operation and the payloads currently carried to orbit by these vehicles will be placed in low earth orbit by the reusable shuttle. In connection with limitations regarding the weight of the payload which can be launched by the Space Shuttle in its present form, approaches have been considered for increasing the payload capability of the Shuttle. Propulsion systems for Shuttle derived vehicles with larger payload capabilities have been studied. Such systems can potentially be obtained from modifications of the Space Shuttle Main Engine (SSME). Concepts based on modifications to the basic engine include an SSME-35 for low altitude operation with liquid rocket boosters and an SSME-150 for operation over the complete altitude range as might be required in a single-stage-to-orbit vehicle application. Another modification would provide operation with a hydrocarbon fuel instead of hydrogen.

A 3-D Navier-Stokes analysis for turbomachinery flows on C- or O-type grids is presented. The analysis is based on the Beam and Warming implicit algorithm for solution of the unsteady Navier-Stokes equations and is derived from an early version of the ARC3D flow code developed at NASA Ames Research Center. The Navier-Stokes equations are written in a Cartesian coordinate system rotating about the z-axis, and then mapped to a general body-fitted coordinate system. All viscous terms are calculated and the turbulence effects are modelled using the Baldwin-Lomax turbulence model. The equations are discretized using finite differences on stacked body-conforming grids. Modifications made to convert ARC3D from external flow to internal turbomachinery flows and to improve solution accuracy are given in detail. The body-conforming grid construction procedure is also presented. Calculations for several rotor flows have been made, and results of code experimental verification studies are presented. Comparisons of the solutions obtained on the C- and O-type grids are also presented, with particular attention to shock resolution.

There is an increased emphasis on utilizing newer manufacturing technologies such as Additive Manufacturing (AM) for the production of affordable propulsion systems. For instance: The RS-25, formerly the Space Shuttle Main Engine (SSME), a highly reliable and versatile liquid rocket engine from the Space Shuttle Era, is being reused for the Space Launch System (SLS) missions. The long-term success of SLS, however, lies in the ability to deliver affordable engines for future launch manifests. The emergence of digital engineering tools help visualize and assess the benefits of utilizing AM even before actual production begins, saving development costs. While the utilization of Model-Based Systems Engineering (MBSE) for the production restart of the RS-25 engine is an on-going research effort, the objective of this study is to demonstrate one aspect of the model-based framework to visualize and quantify an AM design challenge (surface roughness effects) within the context of the thrust chamber assembly production. While the analysis is exemplified on the RS-25 engine, the model-based methodology expressed and subsequent results are expected to benefit liquid rocket engine architectures in general. Consequently, the selection of the engine for this study is intended to benefit the recertification efforts enabled through a comprehensive model-based framework in development to assess and view affordability options.

Direct characterization of potentially habitable terrestrial exoplanets around Sun-like stars requires extremely precise instrumentation capable of measuring a planet-star contrast ratio of 10-10. This instrumentation challenge pushes the limits of optical technology, with state-of-the-art coronagraphs requiring extremely precise wavefront control and large, complex, and expensive instrument designs. These bulk optics coronagraph instruments typically have limited measurable optical bandwidths and high sensitivity to the overall telescope pupil design (i.e. on-axis vs off-axis telescope configurations) and high sensitivity to optical aberrations. The AstroPIC project is applying programmable integrated photonics to develop a new kind of coronagraph instrument that is capable of reaching the theoretical limits of optimal coronagraph performance. This will result in a coronagraph instrument that is orders of magnitude smaller, less massive, and more flexible compared to traditional bulk optics designs, with the goal of increasing the Exo-Earth science yield of NASA’s Habitable Worlds Observatory flagship mission. The AstroPIC project is leveraging commercial silicon photonics fabrication to develop a coronagraph instrument that couples light from a telescope pupil plane into a mesh of integrated Mach-Zehnder interferometers on a photonic integrated circuit (PIC). The coupling is achieved by using a lenslet array to sample and focus the telescope pupil into an array of grating coupler waveguide inputs on the PIC, as shown in Figure 1a. Once the light from the telescope pupil is coupled onto the PIC, the interferometer mesh can be controlled by tuning thermal phase shifters in each interferometer to implement a mode-sorting algorithm in order to separate the starlight and planet light modes at high contrast levels. An integrated photonic testbed at NASA Ames Research Center is being developed to demonstrate coupling from a realistic telescope pupil into the PIC and will be used to characterize the contrast, throughput, and optical bandwidth of the coronagraph instrument. Figure 1b shows the design of the testbed, which will be used to experiment with different control algorithms for setting the tunable phase shifters in the photonic mesh and assess the factors limiting contrast on the chip to inform future iterations of the PIC design. Figure 1: (a) Diagram of AstroPIC instrument concept coupling the Habitable Worlds Observatory (HWO) pupil into an array of grating couplers using a microlens array. A mesh of Mach Zehnder Interferometers (MZIs) are tuned to separate starlight spatial modes from planet spatial modes. (b) Design of integrated photonics testbed under development at NASA Ames Research Center. The AstroPIC project has also developed simulations of the PIC coronagraph instrument concept in order to predict the coupling from the telescope pupil into the chip and simulate the photonic mesh behavior. Specifically, we are studying the application of the AstroPIC instrument concept to the NASA Habitable Worlds Observatory (HWO) flagship mission, which is currently in the pre-design phase. These simulations have shown that the AstroPIC concept is very robust to telescope pupil shape and aberrations for both on- and off-axis telescope configurations, and that the potential science yield of the AstroPIC coronagraph is very high even for relatively small numbers of input couplers. We find that the AstroPIC concept is particularly advantageous for accessing planets located at small inner working angles relative to the host star, which is extremely challenging for traditional coronagraph designs. Figure 2 shows these simulation results for an example HWO-like pupil, summarizing the predicted exo-Earth science yield as a function of (a) number of PIC input grating coupler channels, (b) starlight suppression order, and (c) end to end transmission efficiency. Figure 2: Predicted number of exo-Earths characterized over the HWO mission lifetime as a function of (a) number of input grating coupler PIC channels, (b) PIC starlight suppression order (number of output channels that are designated as starlight vs signal light), and (c) end-to-end transmission efficiency of the PIC instrument. These simulations are conducted using the FRIDAY yield calculation package.In this presentation, we will describe the AstroPIC instrument concept and how programmable photonics can be used to implement the optimal coronagraph operator. We will then present the development of an integrated photonics testbed at NASA Ames Research Center, which is being built to demonstrate the AstroPIC concept with a realistic telescope pupil directly coupled into the integrated photonic instrument. We will also review recent simulation results predicting the performance of next-generation AstroPIC instrument designs. Finally, we will discuss the next steps needed to mature this technology for future space telescope missions and ground telescope applications, including incorporating novel photonic component designs into the mesh architecture to improve the throughput and optical bandwidth of the instrument.

In this work we present a molecular level study of N2+N collisions, focusing on excitation of internal energy modes and non-equilibrium dissociation. The computation technique used here is the direct molecular simulation (DMS) method and the molecular interactions have been modeled using an ab−initio potential energy surface (PES) developed at NASA's Ames Research Center. We carried out vibrational excitation calculations between 5000K and 30000K and found that the characteristic vibrational excitation time for the N + N2 process was an order of magnitude lower than that predicted by the Millikan and White correlation. It is observed that during vibrational excitation the high energy tail of the vibrational energy distribution gets over populated first and the lower energy levels get populated as the system evolves. It is found that the non-equilibrium dissociation rate coefficients for the N + N2 process are larger than those for the N2 + N2 process. This is attributed to the non-equilibrium vibrational energy distributions for the N + N2 process being less depleted than that for the N2 +N2 process. For an isothermal simulation we find that the probability of dissociation goes as 1/T(sub tr) for molecules with internal energy (epsilon(sub int)) less than approximately 9.9eV, while for molecules with epsilon (sub int) greater than 9.9eV the dissociation probability was weakly dependent on translational temperature of the system. We compared non-equilibrium dissociation rate coefficients and characteristic vibrational excitation times obtained by using the ab-initio PES developed at NASA's Ames Research Center to those obtained by using an ab-initio PES developed at the University of Minnesota. Good agreement was found between the macroscopic properties and molecular level description of the system obtained by using the two PESs.

A linearized one-dimensional lumped-parameter model capable of predicting the occurrence of the low frequency combustion instability (chugging) experienced during preburner shutdown in the Space Shuttle Main Engines is discussed, and predictions are compared with NASA experimental results. Results from a parametric study of parameters including chamber pressure, fuel and oxygen temperatures, and the effective bulk modulus of the liquid oxidizer suggest that chugging is probably affected by conditions at shutdown through the fuel and oxidizer temperatures. It is suggested that chugging is initiated when the fuel, oxidizer, and helium temperature and flow rates pass into an unstable region, and that chugging may be terminated by decaying pressures.

Thetechnicalchallengesassociatedwithmergingdepartureaircraftontotheire ledroutesinacongestedairspace environment is discussed. A cost assessment of merge strategies that are based on four-dimensional e ight manage- ment principles and cone ict detection and resolution is given. Several merge cone icts are studied and a cost for each resolution is computed. In addition, the effects of uncertainties on the cost are assessed. In general, altitude hold for a departure aircraft is a less expensive resolution strategy than vectoring. HEFederalAviation Administration (FAA)has forecasted that thenumberofcommercialaircarrierandcommutere ightswill continue to increase yearly.Unless there are changes made tothe air trafe c control system, the increase in trafe c will resultin substantial delays. As a result, the FAA is undertaking a modernization of the air trafe c control system. This effort includes a hardware upgrade of the existing air trafe c computer system and the development of softwaretoolstocomplementtheairtrafe ccontroller' sexpertskills. Thesoftwaretools areintended toenhance theairtrafe ccontroller' s situational awareness and to provide decision support aids for tac- tical and strategic decisions. The Center terminal radar approach control (TRACON) Automation System (CTAS), which is being developed at NASA Ames Research Center in cooperation with the FAA, is one example of a set of software tools intended to enhance the air trafe c controller' s ability to schedule and control air trafe c through accurate trajectory predictions, scheduling algorithms, and trafe c forecasts. 1,2 Concurrently, Eurocontrol, a multinational con- sortium of western European countries, is developing a modernized air trafe c control system to be used throughout western Europe. These tools are intended to assist controllers with the management of air trafe c in all phases of e ight. Historically, the emphasis of air trafe c control research has been placed on solving problems regarding the handling of arrival trafe c, asthishasbeentheprimarysourceofdelayandcongestion.Morere- cently, the emphasis has moved toward cone ict detection and other concepts related to free e ight. Free e ight is an advanced concept whereby individual aircraft select, and are permitted to e y, optimal trajectories. It is foreseen that the job of the air trafe c controller may become more passive, requiring intervention only when con- e ictsarise.Cone ictresolutionanddetectionstrategieshavebeenthe subject of much research. 3i 5 In the United States the development of cone ict probe tools has occurred independently at the Center for Advanced Aviation Systems Development (CAASD) and NASA Ames Research Center. The foundation on which all decision support tools are built is an ability to accurately predict a given aircraft' s state in the near fu- ture. The necessity oftrajectoryprediction in a time-based airtrafe c controlsystemdue to the presence of aircraftwith and without four- dimensional e ight management systems has been discussed. 6 Ac- curate four-dimensional trajectories enable potential cone icts to be more reliably predicted. As a result the separation between aircraft can be maintained. Four-dimensional guidance and fuel-optimal

A Working Group Meeting on Heavy Vehicle Aerodynamic Drag was held at NASA Ames Research Center on September 23, 2002. The purpose of the meeting was to present and discuss technical details on the experimental and computational work in progress and future project plans. Representatives from the Department of Energy (DOE)/Office of Energy Efficiency and Renewable Energy/Office of FreedomCAR & Vehicle Technologies, Lawrence Livermore National Laboratory (LLNL), Sandia National Laboratories (SNL), NASA Ames Research Center (NASA), University of Southern California (USC), California Institute of Technology (Caltech), Georgia Tech Research Institute (GTRI), Argonne National Laboratory (ANL), Freightliner, and Portland State University participated in the meeting. This report contains the technical presentations (viewgraphs) delivered at the Meeting, briefly summarizes the comments and conclusions, and outlines the future action items. The meeting began with an introduction by the Project Lead Rose McCallen of LLNL, where she emphasized that the world energy consumption is predicted to relatively soon exceed the available resources (i.e., fossil, hydro, non-breeder fission). This short fall is predicted to begin around the year 2050. Minimizing vehicle aerodynamic drag will significantly reduce our Nation's dependence on foreign oil resources and help with our world-wide fuel shortage. Rose also mentioned that educating the populace and researchers as to our world energy issues is important and that our upcoming United Engineering Foundation (UEF) Conference on ''The Aerodynamics of Heavy Vehicles: Trucks, Busses, and Trains'' was one way our DOE Consortium was doing this. Mentioned were the efforts of Fred Browand from USC in organizing and attracting internationally recognized speakers to the Conference. Rose followed with an overview of the DOE project goals, deliverables, and FY03 activities. The viewgraphs are attached at the end of this report. Sid Diamond of DOE discussed the reorganization of the Office of Energy Efficiency and Renewable Energy and that the Office of Heavy Vehicle Technology is now part of the Office of FreedomCAR & Vehicle Technologies. Sid reviewed the FY03 budget and provided information on some plans for FY04. The soon to be posted DOE request for proposals from industry for projects related to parasitic energy losses was discussed. A minimum of 50% cost share by industry will be required and the proposal must be submitted by industry. Collaborative efforts in aerodynamic drag with members of the DOE consortium are encouraged. Sid also mentioned interest in aerodynamic drag contribution due to wheel wells and underbody flow. Sid also mentioned his continued interest in the application of our computational and experimental expertise to the area of locomotive and railcar aerodynamics for the reduction of drag effects and thus, the reduction of fuel consumption by trains. In summary, the technical presentations at the meeting included a review of experimental results and plans by GTRI, USC, and NASA Ames, the computational results from LLNL and SNL for the integrated tractor-trailer benchmark geometry called the Ground Transportation System (GTS) model, and by LLNL for the tractor-trailer gap and trailer wake flow, and turbulence model development and benchmark simulations being investigated by Caltech. USC is also investigating an acoustic drag reduction device that has been named ''Mozart'', GTRI continues their investigation of a blowing device, and LLNL presented their ideas for 2 new base drag reduction devices. ANL presented their plans for a DOE supported Cooperative Research and Development Agreement (CRADA) with Paccar Truck Company utilizing commercial software tools to simulate the flow and drag for an actual tractor and showed the results of some preliminary griding attempts. The attendees also had the opportunity to tour the 12-ft pressure wind tunnel the machine shop were the Generic Conventional Model (GCM, a.k.a. SLRT) was being readied for the scheduled November experiments. Much of the discussion involved wind tunnel testing plans, analysis of existing experimental data, investigations of drag reduction devices, simulation results, and needed modeling improvements. Further details are provided in the attached viewgraphs.

A three-component particle image velocimetry (3C-PIV) system was designed installed in the 12-foot (3.7 m) pressure tunnel at NASA Ames Research Center. The system was designed for the testing of a 1/8/sup th/ scale tractor-trailer model called the generic conventional model (GCM). The 12-foot PWT can be pressurized to 6 atmospheres to enable the testing of Reynolds number effects. The data requirements forced a complex system design. Furthermore, the system had to reside inside the plenum where components sensitive to high pressure had to be isolated. Data were obtained in the gap between the tractor and the trailer where Reynolds number effects were suspected to occur. Sample data from this experiment are presented in this paper.

Air traffic management decision support tools have shown the capability to incr ease arrival traffic throughput of congested Terminal Radar Approach Control (TRACON) facilities without significantly impacting air traffic controller workload. NASA Ames Research Center, in cooperation with the Federal Aviation Administration (FAA), is playing a leading role in identifying air traffic management problems, developing and prototyping concepts, and performing field trials for such decision support tools. The Center -TRACON Automation System (CTAS) is a suite of decision support tools devel oped by NASA Ames Research Center, and is included in the FAA's Free Flight Program. This paper describes the concept and development plan of the Expedite Departure Path (EDP) component of CTAS. EDP is a decision support tool aimed at providing TRACON Tr affic Management Coordinators (TMCs) with pertinent departure traffic loading and scheduling information, and radar controllers with advisories for tactical control of TRACON departure traffic. EDP employs the CTAS trajectory synthesis routine to provide conflict -free altitude, speed and heading advisories. These advisories will assist the TRACON departure controller in efficiently sequencing, spacing and merging departure aircraft into the en route traffic flow. The anticipated benefits of EDP include a reduction in airborne delay for departure aircraft, reduced fuel burn and reduced noise impact due to expedited climb trajectories. EDP will eventually share information with both surface and arrival decision support tools to form an integrated decision support system capable of planning, coordinating and executing highly efficient terminal airspace operations.

Thetechnicalchallengesassociatedwithmergingdepartureaircraftontotheire ledroutesinacongestedairspace environment is discussed. A cost assessment of merge strategies that are based on four-dimensional e ight manage- ment principles and cone ict detection and resolution is given. Several merge cone icts are studied and a cost for each resolution is computed. In addition, the effects of uncertainties on the cost are assessed. In general, altitude hold for a departure aircraft is a less expensive resolution strategy than vectoring. HEFederalAviation Administration (FAA)has forecasted that thenumberofcommercialaircarrierandcommutere ightswill continue to increase yearly.Unless there are changes made tothe air trafe c control system, the increase in trafe c will resultin substantial delays. As a result, the FAA is undertaking a modernization of the air trafe c control system. This effort includes a hardware upgrade of the existing air trafe c computer system and the development of softwaretoolstocomplementtheairtrafe ccontroller' sexpertskills. Thesoftwaretools areintended toenhance theairtrafe ccontroller' s situational awareness and to provide decision support aids for tac- tical and strategic decisions. The Center terminal radar approach control (TRACON) Automation System (CTAS), which is being developed at NASA Ames Research Center in cooperation with the FAA, is one example of a set of software tools intended to enhance the air trafe c controller' s ability to schedule and control air trafe c through accurate trajectory predictions, scheduling algorithms, and trafe c forecasts. 1,2 Concurrently, Eurocontrol, a multinational con- sortium of western European countries, is developing a modernized air trafe c control system to be used throughout western Europe. These tools are intended to assist controllers with the management of air trafe c in all phases of e ight. Historically, the emphasis of air trafe c control research has been placed on solving problems regarding the handling of arrival trafe c, asthishasbeentheprimarysourceofdelayandcongestion.Morere- cently, the emphasis has moved toward cone ict detection and other concepts related to free e ight. Free e ight is an advanced concept whereby individual aircraft select, and are permitted to e y, optimal trajectories. It is foreseen that the job of the air trafe c controller may become more passive, requiring intervention only when con- e ictsarise.Cone ictresolutionanddetectionstrategieshavebeenthe subject of much research. 3i 5 In the United States the development of cone ict probe tools has occurred independently at the Center for Advanced Aviation Systems Development (CAASD) and NASA Ames Research Center. The foundation on which all decision support tools are built is an ability to accurately predict a given aircraft' s state in the near fu- ture. The necessity oftrajectoryprediction in a time-based airtrafe c controlsystemdue to the presence of aircraftwith and without four- dimensional e ight management systems has been discussed. 6 Ac- curate four-dimensional trajectories enable potential cone icts to be more reliably predicted. As a result the separation between aircraft can be maintained. Four-dimensional guidance and fuel-optimal

Fourth Planet, Inc. - Santa Clara, CA 95054Formerly:NASA Ames Research Center - Intelligent Mechanisms GroupMoffet Field, CA 94301flueckiger@dmt.epfl.chABSTRACTThe expansion of robotic systems’ performance, as well as the need for such machines to work in complex environments(hazardous, small, distant, etc.), involves the need for user interfaces which permit efficient teleoperation. Virtual Reality b asedinterfaces provide the user with a new method for robot task planning and control: he or she can define tasks in a very intuitiv eway by interacting with a 3D computer generated representation of the world, which is continuously updated thanks tomultiple sensors fusion and analysis.The Swiss Federal Institute of Technology has successfully tested different kinds of teleoperations. In the early 90’s, atransatlantic teleoperation of a conventional robot manipulator with a vision feedback system to update the virtual world wasachieved. This approach was then extended to perform teleoperation of several mobile robots (Khepera, Koala) as well as tocontrol microrobots used for microsystems’ assembly in theµm range.One of the problems encountered with such an approach is the necessity to program a specific kinematic algorithm for eachkind of manipulator. To provide a more general solution, we started a project aiming at the design of a “kinematic generator”(CINEGEN) for the simulation of generic serial and parallel mechanical chains.With CINEGEN, each manipulator is defined with an ascii file description and its attached graphics files; inserting a newmanipulator simply requires a new description file, and none of the existing tools require modification. To have a real timebehavior, we have chosen a numerical method based on the pseudo-jacobian method to generate the inverse kinematics of therobot. The results obtained with an object-oriented implementation on a graphic workstation are presented in this paper.Keywords: robot manipulators, general kinematic chains, inverse kinematics, user interface, virtual environment.1. INTRODUCTIONHumans design and build robots to assist or substitute them in a large range of tasks. This leads to machines with incrediblepower and features, which can perform more and more sophisticated tasks. But too many times, the difficulty for the user tocommand the robot, increases with the complexity of the system. Virtual Reality (VR) based interfaces provide a powerful toolto overcome this problem.This paper focuses on a “general kinematic generator” which aims at simulating robots in Virtual Environment. Such a toolhas appeared as a real need for several research labs as well as industrial companies involved in robotics. Two research labs,both working in the robotic field and using Virtual Reality tools for efficient teleoperation have joined their efforts to achievesuch a kinematic generator.1.1. BackgroundThe Micro-Engineering Department (Institut de Microtechnique: IMT) of the Swiss Federal Institute of Technology(EPFL) is involved in robotic design and development, with a special focus on industrial applications. The experience gainedwith industrial partners showed that classical methods for robotic systems programming (off-line as well as on-line) usuallylack on user-friendliness and performance. This is why since 1990 the IMT is developing VR interfaces to simplify robot taskdefinition.Rather than writing down complicated code, the user can interact with a 3D model of a robot in a virtual world. The user isable to define high level tasks (like move to this point or grab this object) in just one hand movement or a button press. The v ir-tual world is continuously updated, thanks to different sensors (camera, scanner, etc.), with all detected objects around therobot. After a simulation stage to check all the potential problems, a concrete task can be achieved by sending the automati-

<div class="htmlview paragraph">The development of virtual environment technology at NASA Ames Research Center and other research institutions has created opportunities for enhancing human performance. The application of this technology to training astronaut flight crews planning to go onboard the International Space Station has already begun at the NASA Johnson Space Center. A unique application of virtual environments to crew training is envisioned at NASA Ames Research Center which combines state of the art technology with haptic feedback to create a method for training crewmembers on critical life sciences operations which require fine motor skills. This paper describes such a concept, known as the Virtual Glovebox, as well as surveys other applications of virtual environments to astronaut crew training.</div>