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All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

Using an Automated Air Traffic Simulation Capability for a Parametric Study in Traffic Flow Management

Flight delays occur when demand for capacity-constrained airspace or airports exceeds predicted capacity. Demand for capacity-constrained airspace or airports can be controlled by a series of Traffic Management Initiatives (TMIs), which use departure and airborne delays, as well as pre-departure and airborne reroutes, to manage access to the constrained resources. Two systems exist in current and planned future operations to address imbalances between demand and capacity. The Collaborative Trajectory Options Program (CTOP) reduces demand to constrained resources by assigning strategic departure delay and pre-departure reroutes. Reroutes are selected from Trajectory Options Sets (TOSs) submitted by airlines. As flights approach the constrained resource, the Time-Based Flow Management System (TBFM) is used to assign tactical delay to satisfy constraints. This paper describes experiments performed to study the impact of varying levels of airline participation in CTOP via submission of TOSs on ground delay and flight time, and the impact of departure uncertainty on TBFM delays. Results suggest that as CTOP participation increases, average ground delays decrease for all airlines, but to the greatest extent for airlines participating in CTOP. A threshold in CTOP participation, which varies with the constraint capacity, is identified beyond which there is relatively little further reduction in average ground delays. Similarly, given the likely level of CTOP participation, the capacity reduction for which CTOP would be an appropriate TMI is also identified. Results also suggest that high average departure errors and high variability in departure error can make the prioritization of TBFM internal departures in TBFM metering and scheduling infeasible. Departure errors at current levels are, however, acceptable.

CTOP↗
NASA NTRS2018

Using an Automated Air Traffic Simulation Capability for a Parametric Study in Traffic Flow Management

Flight delays occur when demand for capacity-constrained airspace or airports exceeds predicted capacity. Demand for capacity-constrained airspace or airports can be controlled by a series of Traffic Management Initiatives (TMIs), which use departure and airborne delays, as well as pre-departure and airborne reroutes, to manage access to the constrained resources. Two systems exist in current and planned future operations to address imbalances between demand and capacity. The Collaborative Trajectory Options Program (CTOP) reduces demand to constrained resources by assigning strategic departure delay and pre-departure reroutes. Reroutes are selected from Trajectory Options Sets (TOSs) submitted by airlines. As flights approach the constrained resource, the Time-Based Flow Management System (TBFM) is used to assign tactical delay to satisfy constraints. This paper describes experiments performed to study the impact of varying levels of airline participation in CTOP via submission of TOSs on ground delay and flight time, and the impact of departure uncertainty on TBFM delays. Results suggest that as CTOP participation increases, average ground delays decrease for all airlines, but to the greatest extent for airlines participating in CTOP. A threshold in CTOP participation, which varies with the constraint capacity, is identified beyond which there is relatively little further reduction in average ground delays. Similarly, given the likely level of CTOP participation, the capacity reduction for which CTOP would be an appropriate TMI is also identified. Results also suggest that high average departure errors and high variability in departure error can make the prioritization of TBFM internal departures in TBFM metering and scheduling infeasible. Departure errors at current levels are, however, acceptable.

integrated demand management↗
NASA NTRS2019

Airspace Technology Demonstration 2 (ATD-2): Analysis of APREQ Flights at CLT

5/22/2019 National Aeronautics and Space Administration 1 Airspace Technology Demonstration 2 (ATD-2) Analysis of APREQ Flights at CLT May 22, 2019 5/22/2019 Objective 2 Quantify impact of IADS Phase 1 & 2 capabilities on APREQ flights at CLT with respect to: • Compliance to the Controlled Take Off Time (CTOT) • Benefits for APREQ flights that use IDAC to renegotiate for an earlier CTOT • Benefits of pre-scheduling APREQ flights using the Earliest Off Block Time (EOBT) • Relationship between EOBT compliance and rescheduling CTOT 5/22/2019 CLT APREQ Daily Compliance(Compliance Improvement Since ATD-2 Start) 3 Steady increase of APREQ compliance over the life of the project. Reduced variation in compliance leading to improved predictability. In addition to overall improved compliance into TBM systems, the predictability is increasing 5/22/2019 APREQ Compliance 10K Rolling Window 4 The most substantial APREQ compliance improvements started with Phase 2 capability (AEFS integration, ZTL IDAC, pre-scheduling and scheduler updates). 5/22/2019 IADS Phase 1 & 2 Benefit Mechanisms 5 1. Collaborative surface metering •Reduced engine run time •Reduced fuel consumption and emissions 2. Overhead stream operational integration a.Scheduling controlled flights at the gate •Reduced engine run time •Reduced fuel consumption and emissions b.APREQ renegotiating for an earlier slot •Reduced total delay •Passenger value of time and crew costs •Reduced engine run time •Reduced fuel consumption and emissions Benefits (1) and (2a) achieved through tactical gate holds Benefit (2b) achieved through APREQ renegotiation process described below Step 1: APREQ flight has a release time but is capable of taking off earlier Step 2: FAA TMC uses the IDAC green space / red space to identify and request an earlierslot in the overhead stream Step 3: Aircraft receives earlierrelease time and the difference between the release times is the reduction in delay 5/22/2019 Benefits for APREQ flights using IDAC to renegotiate for earlierCTOT 6 LBS Fuel 270.7 hours of delay saved by electronically renegotiating a better overhead stream time for 2,071 flights. • The benefits described here are associated with better use of existing capacity in the overhead stream, and technology to reduce surface delay. •These benefits are in addition to (distinct from) surface metering savings. 5/22/2019 APREQ Delay For Pre-Scheduled Flights into KATL Have Been Reduced and are More Predictable For the Last Five Months 7 Substantial Improvements in predictability of delay for the last 5 months 5/22/2019 EOBT Compliance / CTOT Reschedulefor Pre-Scheduled Flights into KATL 8 5/22/2019 Wrap-up 9 • Compliance to the CTOT has improved throughout the lifecycle of ATD-2 with biggest improvements following the introduction of Phase 2 capabilities • Rescheduling APREQ flights using IDAC has reduced 270.7 hours of delay at CLT • Predictability of local surface delay for APREQ flights is substantially improved via pre-scheduling with the IADS system • Pre-scheduled flights that reschedule for later times tend to call ready later with respect to EOBT

CLT↗
NASA NTRS1962

An Investigation of the Effects of the Time Lag Due to Long Transmission Distance upon Remote Control. Phase II - Vehicle Experiments. Phase III - Conclusions

An experimental program is undertaken to define the effects upon remote control of long transmission delays. Investigation centers around remote control of a ground vehicle, which is considered to be a representative remote control task. A series of pursuit tracking tests is performed with transport lags ranging from 0 to 6 seconds between the control and the controlled quantity. Various target speeds are tracked with both velocity and acceleration controls. Two types of tracking are performed in an attempt to bracket the actual vehicle situation. In the first the operator attempts to follow the target with his controlled quantity in real time, using the delayed position and rates as feedback. In the second he attempts to follow the target with the delayed controlled quantity. In addition, tests are performed substituting simple electronic models for the human in an attempt to gain an understanding of human response with time delays in the control loop. A series of tests with an actual vehicle are performed with the intent of relating the tracking tests to the actual situation of interest. Time delays of from 0 to 3 seconds are included in the control loop. Performance is scored at various speeds over both continuous and obstacle courses. Both two and four-wheel steering are investigated. In the experiments the effects of all variables except delay magnitude and target complexity are minimized. Curves are obtained showing performance as a function of time delay and target complexity. These curves are discussed. Correlation of the tracking and vehicle experiments is discussed. Comments are made concerning the design of a minimum control system for a remotely controlled lunar roving vehicle.

REMOTE CONTROL↗
NASA NTRS2012

Autonomous Mission Operations

NASA's Advanced Exploration Systems Autonomous Mission Operations (AMO) project conducted an empirical investigation of the impact of time-delay on todays mission operations, and of the effect of processes and mission support tools designed to mitigate time-delay related impacts. Mission operation scenarios were designed for NASA's Deep Space Habitat (DSH), an analog spacecraft habitat, covering a range of activities including nominal objectives, DSH system failures, and crew medical emergencies. The scenarios were simulated at time-delay values representative of Lunar (1.2-5 sec), Near Earth Object (NEO) (50 sec) and Mars (300 sec) missions. Each combination of operational scenario and time-delay was tested in a Baseline configuration, designed to reflect present-day operations of the International Space Station, and a Mitigation configuration in which a variety of software tools, information displays, and crew-ground communications protocols were employed to assist both crews and Flight Control Team (FCT) members with the long-delay conditions. Preliminary findings indicate: 1) Workload of both crew members and FCT members generally increased along with increasing time delay. 2) Advanced procedure execution viewers, caution and warning tools, and communications protocols such as text messaging decreased the workload of both flight controllers and crew, and decreased the difficulty of coordinating activities. 3) Whereas crew workload ratings increased between 50 sec and 300 sec of time-delay in the Baseline configuration, workload ratings decreased (or remained flat) in the Mitigation configuration.

Mission Operations↗
NASA NTRS1982

Flip-flop resolving time test circuit

Integrated circuit (IC) flip-flop resolving time parameters are measured by wafer probing, without need of dicing or bonding, throught the incorporation of test structures on an IC together with the flip-flop to be measured. Several delays that are fabricated as part of the test circuit, including a voltage-controlled delay with a resolution of a few picosecs, are calibrated as part of the test procedure by integrating them into, and out of, the delay path of a ring oscillator. Each of the delay values is calculated by subtracting the period of the ring oscillator with the delay omitted from the period with the delay included. The delay measurement technique is sufficiently general for other applications. The technique is illustrated for the case of the flip-flop parameters of a 5-micron feature size NMOS circuit.

Rosenberger, F.↗
NASA NTRS1992

Present status and future prospects for ionospheric propagation corrections for precise time transfer using GPS

The ionosphere can be the greatest variable source of error in precise time transfer using Global Positioning System (GPS) satellites. For single frequency GPS users, the ionospheric correction algorithm can provide an approximate 50 percent r.m.s. correction to the time delay, but users who desire a more complete correction must make actual measurements of ionospheric time delay along the path to the GPS satellite. Fortunately, at least three commercial GPS receivers, specifically designed to measure and correct for ionospheric time delay, are now, or soon will be, available. Initial operation with two different types of GPS ionospheric receivers demonstrated a high degree of accuracy in measuring the ionospheric group delay. Results of these measurements are presented. For those who use a model to correct for ionospheric time delay, it is tempting to use daily values of solar 10.7 cm radio flux to correct a monthly average ionospheric time delay model for each day's operation. The results of correlation of daily maximum ionospheric time delay against solar radio flux values show a poor correlation will be obtained by this procedure. Prospects for improving ionospheric corrections during the declining phase of the present solar cycle are discussed.

Klobuchar, John A.↗
NASA NTRS1995

A test of water vapor radiometer-based troposphere calibration using VLBI observations on a 21-kilometer baseline

Simultaneous very long baseline interferometry (VLBI) and water vapor radiometer (WVR) measurements on a 21 km baseline showed that calibration by WVRs removed a significant fraction of the effect of tropospheric delay fluctuations for these experiments. From comparison of the residual delay variations within scans and between scans, the total tropospheric contribution t the delay residuals for each of the three 5 to 20 hour sessions was estimated as 1, 17, and 10%, with the first value being uncertain. The observed improvement in rms residual delay from WVR calibration during these three sessions was 4, 16, and 2%, respectively. The improvement is consistent with the estimated 2 to 3 mm path delay precision of current WVRs. The VLBI measurements, of natural radio sources, were conducted in April and May 1993 at Goldstone, California. Dual-frequency (2.3 and 8.4 GHz) observations were employed to remove the effects of charged particles from the data. Measurements with co-pointed WVRs, located within 50 m of the axis of each antenna, were performed to test the ability of the WVRs to calibrate line-of-sight path delays. Factors that made WVR performance assessment difficult included (1) the fact that the level of tropospheric fluctuations was smaller than is typical for Goldstone during these experiments and (2) VLBI delay variations on longer time scales (i.e., over multiple scans) contained uncalibrated instrumental effects (probably a result of slow temperature variations in the VLBI hardware) that were larger than the tropospheric effects.

Linfield, R. P.↗
NASA NTRS1998

Apparatus and method for measuring relative phase of signals in a multiple-echo system

An apparatus and method for measuring the relative phase of echo signals in a multiple-echo system. A signal generator generates an exciting tone burst and subsequent tone bursts delayed in phase from the exciting tone burst. The exciting tone burst is gated into a transducer coupled to the multiple-echo system. Each subsequent tone burst is converted into a series of pulses. Each pulse triggers a sample/hold circuit to sample each echo signal. The samples of the echo signal are averaged and then compared to a reference value. The signal generator is controlled to vary the subsequent tone burst phase delay to determine for each echo signal a subsequent tone burst phase delay that causes the average of the samples of the echo signal to be substantially equal to the reference value wherein the determined subsequent tone burst phase delay is the phase delay of the echo signal with respect to the exciting tone burst. The control circuit then determines the difference in phase delay between echo signals to determine the relative phase delay of the echo signals.

Froggatt, Mark E.↗
NASA NTRS2010

Cruise-Efficient Short Takeoff and Landing (CESTOL): Potential Impact on Air Traffic Operations

The National Aeronautics and Space Administration (NASA) is investigating technological and operational concepts for introducing Cruise-Efficient Short Takeoff and Landing (CESTOL) aircraft into a future US National Airspace System (NAS) civil aviation environment. CESTOL is an aircraft design concept for future use to increase capacity and reduce emissions. CESTOL provides very flexible takeoff, climb, descent and landing performance capabilities and a high-speed cruise capability. In support of NASA, this study is a preliminary examination of the potential operational impact of CESTOL on airport and airspace capacity and delay. The study examines operational impacts at a subject site, Newark Liberty Intemational Airport (KEWR), New Jersey. The study extends these KEWR results to estimate potential impacts on NAS-wide network traffic operations due to the introduction of CESTOL at selected major airports. These are the 34 domestic airports identified in the Federal Aviation Administration's Operational Evolution Plan (OEP). The analysis process uses two fast-time simulation tools to separately model local and NAS-wide air traffic operations using predicted flight schedules for a 24-hour study period in 2016. These tools are the Sen sis AvTerminal model and NASA's Airspace Concept Evaluation System (ACES). We use both to simulate conventional-aircraft-only and CESTOL-mixed-with-conventional-aircraft operations. Both tools apply 4-dimension trajectory modeling to simulate individual flight movement. The study applies AvTerminal to model traffic operations and procedures for en route and terminal arrival and departures to and from KEWR. These AvTerminal applications model existing arrival and departure routes and profiles and runway use configurations, with the assumption jet-powered, large-sized civil CESTOL aircraft use a short runway and standard turboprop arrival and departure procedures. With these rules, the conventional jet and CESTOL aircraft are procedurally separated from each other geographically and in altitude during tenninal airspace approach and departure operations, and each use a different arrival runway. AvTeminal implements its unique Focal-point Scheduling Process to sequence, space and delay aircraft to resolve spacing and overtake conflicts among flights in the airspace and airport system serving KEWR. This Process effectively models integrated arrival and departure operations. AvTerminal assesses acceptance rates and delay magnitude and causality at selected locations, including en route outer boundary fixes, tenninal airspace arrival and departure boundary fixes, terminal airspace arrival merge and departure diverge fixes, and runway landing and takeoff runways. The analysis compares the resulting capacity impacts, flight delays and delay sources between CESTOL and conventional KEWR operations. AvTerminal quantitative results showed that CESTOL has significant capability to increase airport arrival acceptance rates (35-40% at KEWR) by taking advantage of otherwise underused airspace and runways where available. The study extrapolates the AvTerminal-derived KEWR peak arrival and departure acceptance rates to estimate capacity parameter values for each of the OEP airports in the ACES modeling of traffic through the entire NAS network. The extrapolations of acceptance rates allow full, partial or no achievement of CESTOL capacity gains at an OEP airport as determined by assessments of the degree to which local procedures allow leveraging of CESTOL capabilities. These assessments consider each OEP airport's runway geometries, runway system configurations, airport and airspace operations, and potential CESTOL traffic loadings. The ACES modeling, simulates airport and airspace spacing constraints imposed by airport runway system, terminal and en route air traffic control and traffic flow management operations using airport acceptance rates representing conventional-aircraft-only and CESTOL-mixed operations. CEOL aircraft are assumed to have Mach 0.8, and alternatively Mach 0.7, cruise speeds to examine compatibility with conventional aircraft operations in common airspace. The ACES results provides estimates of CESTOL delay impact NAS-wide and at OEP airports due to changes in OEP airport acceptance rates and changes in en route airspace potential conflict rates. Preliminary results show meaningful nationwide delay reductions (20%) due to CESTOL operations at 34 major domestic airports.

Couluris, G. J.↗
NASA NTRS2014

Space Link Extension Protocol Emulation for High-Throughput, High-Latency Network Connections

New space missions require higher data rates and new protocols to meet these requirements. These high data rate space communication links push the limitations of not only the space communication links, but of the ground communication networks and protocols which forward user data to remote ground stations (GS) for transmission. The Consultative Committee for Space Data Systems, (CCSDS) Space Link Extension (SLE) standard protocol is one protocol that has been proposed for use by the NASA Space Network (SN) Ground Segment Sustainment (SGSS) program. New protocol implementations must be carefully tested to ensure that they provide the required functionality, especially because of the remote nature of spacecraft. The SLE protocol standard has been tested in the NASA Glenn Research Center's SCENIC Emulation Lab in order to observe its operation under realistic network delay conditions. More specifically, the delay between then NASA Integrated Services Network (NISN) and spacecraft has been emulated. The round trip time (RTT) delay for the continental NISN network has been shown to be up to 120ms; as such the SLE protocol was tested with network delays ranging from 0ms to 200ms. Both a base network condition and an SLE connection were tested with these RTT delays, and the reaction of both network tests to the delay conditions were recorded. Throughput for both of these links was set at 1.2Gbps. The results will show that, in the presence of realistic network delay, the SLE link throughput is significantly reduced while the base network throughput however remained at the 1.2Gbps specification. The decrease in SLE throughput has been attributed to the implementation's use of blocking calls. The decrease in throughput is not acceptable for high data rate links, as the link requires constant data a flow in order for spacecraft and ground radios to stay synchronized, unless significant data is queued a the ground station. In cases where queuing the data is not an option, such as during real time transmissions, the SLE implementation cannot support high data rate communication.

Computer Networking↗
NASA NTRS2010

Kriging as a Means of Improving WAAS Availability

The Wide Area Augmentation System (WAAS), an augmentation of the Global Positioning System (GPS), provides safe and reliable use of GPS signals for airline navigation over much of North America. Currently the largest source of positioning error in the system is signal delay caused by the ionosphere. To allow the user to take account of such error, WAAS computes and broadcasts ionospheric vertical delays at a set of regularly-spaced grid points. In addition, WAAS computes and broadcasts a safety-critical integrity bound at each ionospheric grid point (IGP) called the Grid Ionospheric Vertical Error (GIVE). GIVEs are constructed to be sufficiently large to protect the user against positioning error due to the presence of ionospheric irregularity. In the initial operating capability (IOC) of WAAS, the vertical delay estimate at each IGP is determined from a planar fit of neighboring slant delay measurements, projected to vertical using an obliquity factor specified by the standard thin-shell model of the ionosphere. In WAAS Follow-On (WFO) Release 3, however, the vertical delay will be estimated by an established, geo-statistical technique known as kriging. Compared to the planar fit model, the kriging model is found, in general, to match better the observed random structure of the vertical delay. This paper presents the kriging methodology that will be used to estimate the vertical delay and its uncertainty at each IGP, and it assesses the subsequent improvement in WAAS availability enabled by kriging.

GPS↗
NASA NTRS2018

Mechanisms of Oxide Formation in the Self-Reacting Friction Stir Weld Process

The initial objective of this study was to evaluate the effect of an extended delay time between preweld cleaning and the completion of a self-reacting friction stir welding (SRFSW) process on the resulting quality of various thickness panels of AA2219-T87. The current NASA standard specifies no more than a 48 hour delay between preweld cleaning and actual welding. The concern is whether increasing the cleaning delay time results in development of the residual oxide defect (ROD) in SRFSW. This concern emanates from the possibility of increased time correlating with increased oxide layer thickness on the faying surfaces. Oxide content on the faying surfaces has been reported to correlate with the occurrence of the ROD which reduces mechanical properties. When the SRFSW process was first adopted by the NASA Marshall Space Flight Center (MSFC), unexpected low tensile values that resulted were attributed to oxides within the weld that appeared to follow the former faying surface contours. Mitigation of the ROD was achieved through a combination of modifications to the processing parameters, tool designs, and incorporation of a weld seam offset. Two operations are involved in preweld cleaning: the first is removal of oil and grease, and the second is removal of surface oxides. In arc welding, improper cleaning of the faying surfaces of aluminum welded joints can increase the sensitivity toward development of defects. As the aluminum is locally melted, these contaminants contribute toward the development of porosity, inclusions, entrapped oxides, and other discontinuities which can degrade the strength of the weld joint. For weldment of large structures, the weld joint is typically cleaned, fit-up, and tack welded prior to the final full penetration welding pass. Because of the stringent joint fit-up requirements for mismatch and peaking for launch vehicle structures, the joint fit-up can sometimes contribute to lengthy delays between cleaning and tack welding, especially for circumferential weld joints on large diameter components. When the conventional friction stir welding (CFSW) process was introduced at the NASA MSFC, there was no procedure for cleaning prior to the solid-state joining process. As the process expanded to include SRFSW, preparation of the faying, crown, and root surfaces were implemented to overcome the ROD. Although the solid-state process is not expected to reach temperatures high enough for dissociation of the native oxide layer, concern remained regarding the redeposition of the native oxide layer within the stir zone. NASA has previously established the allowable time at 48 hours between preweld cleaning and a SRFSW process. The effect of potential 2 contamination resulting from an extended delay to 188 hours was subsequently evaluated for SRFSWs using tensile testing and metallographic imaging. Tensile specimens were tested at room temperature (RT), and at cryogenic conditions of liquid nitrogen (LN2) and liquid hydrogen. No detrimental effect on weld quality, as determined by weld strength, was reported for cleaning delays of 48, 120, 168, 240 or 288 hours. While no trends were established in this study, which extended the delay from 48 to 188 hours, there were a few outliers in terms of ultimate tensile strength (UTS). According to M. Fisher's 2014 Boeing Company Memo no. EYBF-MAF-14-029, all outliers were above the minimum acceptance criteria, but out of family with respect to the average values. As the robustness and reliability of any process ultimately depends on the average values as well as the outliers, an understanding of the cause of these outliers will ultimately improve the process. This report examines those outliers and their possible causes.

Schneider, J. A.↗
NASA NTRS2005

Unequal-Arm Interferometry and Ranging in Space

Space-borne interferometric gravitational wave detectors, sensitive in the low-frequency (millihertz) band, will fly in the next decade. In these detectors the spacecraft-to-spacecraft light-traveltimes will necessarily be unequal, time-varying, and (due to aberration) have different time delays on up- and down-links. By using knowledge of the inter-spacecraft light-travel-times and their time evolution it is possible to cancel in post-processing the otherwise dominant laser phase noise and obtain a variety of interferometric data combinations sensitive to gravitational radiation. This technique, which has been named Time-Delay Interferometry (TDI), can be implemented with constellations of three or more formation-flying spacecraft that coherently track each other. As an example application we consider the Laser Interferometer Space Antenna (LISA) mission and show that TDI combinations can be synthesized by properly time-shifting and linearly combining the phase measurements performed on board the three spacecraft. Since TDI exactly suppresses the laser noises when the delays coincide with the light-travel-times, we then show that TDI can also be used for estimating the time-delays needed for its implementation. This is done by performing a post-processing non-linear minimization procedure, which provides an effective, powerful, and simple way for making measurements of the inter-spacecraft light-travel-times. This processing technique, named Time-Delay Interferometric Ranging (TDIR), is highly accurate in estimating the time-delays and allows TDI to be successfully implemented without the need of a dedicated ranging subsystem.

gravitational waves↗
NASA NTRS1975

An optimized output stage for MOS integrated circuits

An output device for optimizing propagation delay and minimizing chip area is described. An optimum means of tapering the output stages to minimize propagation delay is determined. The minimum delay is a function of the capacitive load to node ratio, the number of output stages, and the interstage propagation delay. The effects on area are also presented. A figure of merit which is a function of area and propagation time is defined which is of use in designing output stages. An optimum exists which can be considered the best compromise between further decreasing propagation delay and increasing chip area. Data are also presented which allow a designer to determine the minimum chip area once the capacitive load and the maximum allowable delay are known.

Lin, H. C.↗
NASA NTRS1980

Autoignition characteristics of aircraft-type fuels

The ignition delay characteristics of Jet A, JP 4, no. 2 diesel, cetane and an experimental referee broad specification (ERBS) fuel in air at inlet temperatures up to 1000 K, pressures of 10, 15, 20, 25 and 30 atm, and fuel air equivalence ratios of 0.3, 0.5, 0.7 and 1.0 were mapped. Ignition delay times in the range of 1 to 50 msec at freestream flow velocities ranging from 20 to 100 m/sec were obtained using a continuous flow test apparatus which permitted independent variation and evaluation of the effect of temperature, pressure, flow rate, and fuel/air ratio. The ignition delay times for all fuels tested appeared to correlate with the inverse of pressure and the inverse exponent of temperature. With the exception of pure cetane, which had the shortest ignition delay times, the differences between the fuels tested did not appear to be significant. The apparent global activation energies for the typical gas turbine fuels ranged from 38 to 40 kcal/mole, while the activation energy determined for cetane was 50 kcal/mole. In addition, the data indicate that for lean mixtures, ignition delay times decrease with increasing equivalence ratio. It was also noted that physical (apparatus dependent) phenomena, such as mixing (i.e., length and number of injection sites) and airstream cooling (due to fuel heating, vaporization and convective heat loss) can have an important effect on the ignition delay.

Spadaccini, L. J.↗
NASA NTRS1984

Review of Teleoperator Research

A predictor display to overcome time lag problems with remote control systems is discussed. The video picture is a (necessarily) time-delayed picture from the remote location, generated as a coherent frame (snapshot) so that all picture elements in a single scan are delayed the same. The computer-generated graphics is a line drawing of the present configuration of the manipulator arm, vehicle or other device. The latter is generated by using the same control signals which are sent to the remote manipulator (device) to drive a computer model of it. The computer model is drawn on the video display in exactly the same location as where it will actually be after a one-way time delay and where it will be seen to be on the video after one round-trip time delay. If one waits at least one round-trip delay without moving, both the graphics model and the video picture of the manipulator (device) are seen to coincide. The predictor technque proved to work well and was shown for time delays in the 1-3 second range to reduce completion times for a variety of manipulation tasks by 50-150 percent reliably.

Sheridan, T. B.↗
NASA NTRS1993

Subjective response to simulated sonic booms with ground reflections

The Sonic Boom Simulator at NASA LaRC was used for the following: (1) quantify subjective loudness of simulated composite sonic booms, each of which was comprised of a simulated direct (non-reflected) boom combined with a simulated reflection of the direct boom; and (2) evaluate several metrics as estimators of loudness for these composite booms. The direct booms consisted of selected N-wave and minimized signatures having front-shock rise times of 3, 6, and 9 milliseconds and durations of 300 milliseconds. Delay times of the reflected booms ranged from 0 to 12 milliseconds. Subjective loudness results indicated that composite booms formed using reflections with non-zero delay times were generally rated as being less loud than composite booms containing non-delayed reflections. The largest reductions in loudness occurred when delay times were equal to the front shock rise times of the direct booms and were, in some cases, equivalent to reductions in Perceived Level of 6 to 7 dB. Results also showed Perceived Level to be an effective metric for assessing subjective loudness effects for the composite signatures. This was confirmed by statistical analysis, which showed that, for equal Perceived Level, no significant differences existed between the subjective loudness responses to composite booms containing reflections with zero delay and those containing reflections with non-zero delays.

Sullivan, B. M.↗