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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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NASA NTRS1976

Multiplexor and sensor system tradeoff study

The influence of certain sensor parameters on the accuracy of information extracted from satellite image data is studied, using a digital processing flow to simulate the effects of the sensor parameters. The method employed was to select representative images; scan and digitize them; process the digital data to simulate the effects of presampling filters, instantaneous field of view (IFOV) size and shape, sampling rates, noise, and word length; record the processed data on film; evaluate the film images; and draw conclusions from the evaluations. The study showed that presampling filters are not required to suppress aliasing, that the choice of square and circular IFOV shapes is not important, and that increased horizontal and vertical sampling rates produce an increase in apparent resolution. Work with low-contrast targets revealed a definite maximum in the tradeoff between IFOV size and SNR.

Ferneyhough, D. G., Jr.↗
NASA NTRS1991

The effects of pressure sensor acoustics on airdata derived from a High-angle-of-attack Flush Airdata Sensing (HI-FADS) system

The accuracy of a nonintrusive high angle-of-attack flush airdata sensing (HI-FADS) system was verified for quasi-steady flight conditions up to 55 deg angle of attack during the F-18 High Alpha Research Vehicle (HARV) Program. The system is a matrix of nine pressure ports arranged in annular rings on the aircraft nose. The complete airdata set is estimated using nonlinear regression. Satisfactory frequency response was verified to the system Nyquist frequency (12.5 Hz). The effects of acoustical distortions within the individual pressure sensors of the nonintrusive pressure matrix on overall system performance are addressed. To quantify these effects, a frequency-response model describing the dynamics of acoustical distortion is developed and simple design criteria are derived. The model adjusts measured HI-FADS pressure data for the acoustical distortion and quantifies the effects of internal sensor geometries on system performance. Analysis results indicate that sensor frequency response characteristics very greatly with altitude, thus it is difficult to select satisfactory sensor geometry for all altitudes. The solution used presample filtering to eliminate resonance effects, and short pneumatic tubing sections to reduce lag effects. Without presample signal conditioning the system designer must use the pneumatic transmission line to attenuate the resonances and accept the resulting altitude variability.

Whitmore, Stephen A.↗
NASA NTRS2016

Analog Testing of Operations Concepts for Mitigation of Communication Latency During Human Space Exploration

OBJECTIVES: NASA Extreme Environment Mission Operations (NEEMO) is an underwater spaceflight analog that allows a true mission‐like operational environment and uses buoyancy effects and added weight to simulate different gravity levels. Three missions were undertaken from 2014‐2015, NEEMO's 18‐20. All missions were performed at the Aquarius undersea research habitat. During each mission, the effects of varying operations concepts and tasks type and complexity on representative communication latencies associated with Mars missions were studied. METHODS: 12 subjects (4 per mission) were weighed out to simulate near‐zero or partial gravity extravehicular activity (EVA) and evaluated different operations concepts for integration and management of a simulated Earth‐based science backroom team (SBT) to provide input and direction during exploration activities. Exploration traverses were planned in advance based on precursor data collected. Subjects completed science‐related tasks including presampling surveys, geologic‐based sampling, and marine‐based sampling as a portion of their tasks on saturation dives up to 4 hours in duration that were to simulate extravehicular activity (EVA) on Mars or the moons of Mars. One‐way communication latencies, 5 and 10 minutes between space and mission control, were simulated throughout the missions. Objective data included task completion times, total EVA times, crew idle time, translation time, SBT assimilation time (defined as time available for SBT to discuss data/imagery after it has been collected, in addition to the time taken to watch imagery streaming over latency). Subjective data included acceptability, simulation quality, capability assessment ratings, and comments. RESULTS: Precursor data can be used effectively to plan and execute exploration traverse EVAs (plans included detailed location of science sites, high‐fidelity imagery of the sites, and directions to landmarks of interest within a site). Operations concepts that allow for presampling surveys enable efficient traverse execution and meaningful Mission Control Center (MCC) interaction across long communication latencies and can be done with minimal crew idle time. Imagery and information from the EVA crew that is transmitted real‐time to the intravehicular (IV) crewmember(s) can be used to verify that exploration traverse plans are being executed correctly. That same data can be effectively used by MCC (across comm latency) to provide further instructions to the crew from a SBT on sampling priorities, additional tasks, and changes to the plan. Text / data capabilities are preferred over voice capabilities between MCC and IV when executing exploration traverse plans over communication latency. Autonomous crew planning tools can be effective at modifying existing plans if the objectives and constraints are clearly defined.

Chappell, Steven P.↗
NASA NTRS1985

Analytical and flight investigation of the influence of rotor and other high-order dynamics on helicopter flight-control system bandwidth

The increasing use of highly augmented digital flight-control systems in modern military helicopters prompted an examination of the influence of rotor dynamics and other high-order dynamics on control-system performance. A study was conducted at NASA Ames Research Center to correlate theoretical predictions of feedback gain limits in the roll axis with experimental test data obtained from a variable-stability research helicopter. Feedback gains, the break frequency of the presampling sensor filter, and the computational frame time of the flight computer were systematically varied. The results, which showed excellent theoretical and experimental correlation, indicate that the rotor-dynamics, sensor-filter, and digital-data processing delays can severely limit the usable values of the roll-rate and roll-attitude feedback gains.

Chen, R. T. N.↗
NASA NTRS1985

The Landsat sensor's spatial responses

Based on the geometrical characteristics of the Landsat-4 and Landsat-5 Thematic Mapper (TM) and Multispectral Scanner (MSS), functions defining their spatial responses are derived, i.e., transfer functions (TF's) and line-spread functions (LSF's). These design LSF's and TF's are modified based on prelaunch component and system measurements to provide improved estimates. The two MSS instruments were comparable at their temperatures of best focus; separate calculations were performed for bands 1 and 3, band 2, and band 4. The presample nadir effective instantaneous fields of view, based on the 0.5 modulation transfer function (MTF) criteria, are 70-75 m in the track direction and 79-82 m in the scan direction. For the TM instruments, more extensive prelaunch measurements were available. LSF's derived from component measurements differed from the limited measured LSF data only in the ringing response/overshoot behavior.

Markham, B. L.↗
NASA NTRS1986

Influence of high-order dynamics on helicopter flight-control system bandwidth

The increasing use of highly augmented digital flight-control systems in modern military helicopters prompted an examination of the influence of the influence of rotor dynamics and other high-order dynamics on control-system performance. A study was conducted at NASA Ames Research Center to correlate theoretical predictions of feedback gain limits in the roll axis with experimental test data obtained from a variable-stability research helicopter. Feedback gains, the break frequency of the presampling sensor filter, and the computational frame time of the flight computer were systematically varied. The results, which showed excellent theoretical and experimental correlation, indicate that the rotor-dynamics, sensor-filter, and digital-data processing delays can severely limit the usable values of the roll-rate and roll-attitude feedback gains.

Chen, R. T. N.↗
NASA NTRS1991

Design and status of the RF-digitizer integrated circuit

An integrated circuit currently under development samples a bandpass-limited signal at a radio frequency in quadrature and then performs a simple sum-and-dump operation in order to filter and lower the rate of the samples. Downconversion to baseband is carried out by the sampling step itself through the aliasing effect of an appropriately selected subharmonic sampling frequency. Two complete RF digitizer circuits with these functions will be implemented with analog and digital elements on one GaAs substrate. An input signal, with a carrier frequency as high as 8 GHz, can be sampled at a rate as high as 600 Msamples/sec for each quadrature component. The initial version of the chip will sign-sample (1-bit) the input RF signal. The chip will contain a synthesizer to generate a sample frequency that is a selectable integer multiple of an input reference frequency. In addition to the usual advantages of compactness and reliability associated with integrated circuits, the single chip will replace several steps required by standard analog downconversion. Furthermore, when a very high initial sample rate is selected, the presampling analog filters can be given very large bandwidths, thereby greatly reducing phase and delay instabilities typically introduced by such filters, as well as phase and delay variation due to Doppler changes.

Rayhrer, B.↗
NASA NTRS2017

Integration of an Earth-Based Science Team During Human Exploration of Mars

NASA Extreme Environment Mission Operations (NEEMO) is an underwater spaceflight analog that allows a true mission-like operational environment and uses buoyancy effects and added weight to simulate different gravity levels. A mission was undertaken in 2016, NEEMO 21, at the Aquarius undersea research habitat. During the mission, the effects of varied oper-ations concepts with representative communication latencies as-sociated with Mars missions were studied. Six subjects were weighed out to simulate partial gravity and evaluated different operations concepts for integration and management of a simulated Earth-based science team (ST) who provided input and direction during exploration activities. Exploration traverses were planned in advance based on precursor data collected. Subjects completed science-related tasks including presampling surveys and marine-science-based sampling during saturation dives up to 4 hours in duration that simulated extravehicular activity (EVA) on Mars. A communication latency of 15 minutes in each direction between space and ground was simulated throughout the EVAs. Objective data included task completion times, total EVA time, crew idle time, translation time, ST assimilation time (defined as time available for the science team to discuss, to review and act upon data/imagery after they have been collected and transmitted to the ground). Subjective data included acceptability, simulation quality, capability assessment ratings, and comments. In addition, comments from both the crew and the ST were captured during the post-mission debrief. Here, we focus on the acceptability of the operations concepts studied and the capabilities most enhancing or enabling in the operations concept. The importance and challenges of designing EVA time-lines to account for the length of the task, level of interaction with the ground that is required/desired, and communication latency, are discussed.

Chappell, Steven P.↗
NASA NTRS2018

Space-to-Ground Interactions While Conducting Scientific Fieldwork Under Mars Mission Constraints

The Biologic Analog Science Associated with Lava Terrains (BASALT) project is a 4-year program dedicated to iteratively designing, implementing, and evaluating concepts of operations (ConOps) and supporting capabilities to enable and enhance scientific exploration for future human Mars missions. BASALT incorporates three field deployments during which real (non-simulated) biological and geochemical field science is conducted at two high-fidelity Mars analog locations under simulated Mars mission conditions, including communication de-lays and data transmission limitations. BASALT’s primary science objective is to investigate how the redox conditions of altered basaltic environments affect the development of microbial communities in these Mars-relevant settings. Field sites include the active East Rift Zone on the Big Island of Hawaii, reminiscent of early Mars when basaltic volcanism and interaction with water were widespread, and the dormant eastern Snake River Plain in Idaho, similar to present-day Mars where basaltic volcanism is rare and most evidence for volcano-driven hydrothermal activity is relict. BASALT’s primary science operations objective is to investigate exploration ConOps and capabilities that facilitate scientific return during human-robotic exploration under Mars mission constraints. Each field deployment consists of ten extravehicular activities (EVAs) on the volcanic flows in which two extravehicular and two intravehicular (IV) crew-members conduct the science while communicating across time delay and under bandwidth constraints with an Earth-based Mission Support Center (MSC) comprised of expert scientists and operators. Communication latencies of 5 and 15-minute one-way light time and low (0.512 Mb/s uplink, 1.54 Mb/s down-link) and high (5.0 Mb/s uplink, 10.0 Mb/s downlink) bandwidth conditions are being evaluated. EVA crewmembers communicate with the MSC via voice and text messaging and provide scientific instrument data, still imagery, video streams, and GPS tracking information. The MSC reviews this data across delay and provides recommendations for presampling and sampling tasks. The scientists used dynamic leaderboards (priority rank-ing lists), to track and rank candidate samples relative to one another and against the science objectives for the current EVA and the overall mission. Updates to the dynamic leaderboards are relayed regularly to the IV crewmembers to provide scientific feedback from Earth and to help minimize crew idle time (time spent waiting for Earth input during which no productive tasks are performed). EVA timelines are strategically designed to enable continuous (delayed) feedback from an Earth-based science team while simultaneously minimizing crew idle time. Such timelines are operationally advantageous, reducing transport costs by eliminating the need for crews to return to the same locations on multiple EVAs while still providing opportunities for recommendations from science experts on Earth, and scientifically advantageous by minimizing the potential for cross-contamination across sites. This paper will highlight the space-to-ground interaction results from the three BASALT field deployments, including planned versus actual EVA time-line data, ground assimilation times (the amount of time available to the MSC to provide input to the crew), and idle time. Furthermore, we describe how these results vary under the different communication latency and bandwidth conditions. Together, these data will provide a basis for guiding and prioritizing capability development for future human exploration missions.

Beaton, Kara H.↗