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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 NTRS2017

Downlink Receiver Algorithms for Deep Space Optical Communications

The goal of the Deep Space Optical Communications project at the Jet Propulsion Laboratory is to demonstrate laser communication links at ranges out to approximately 3 AU. In this paper, we discuss a downlink receiver concept capable of demodulating optical pulse-position modulated (PPM) waveforms with data rates varying from approximately 50 kbps up to 265 Mbps, using a range of PPM orders, slot widths, and code rates. The receiver operates on recorded timestamps corresponding to the times-of-arrival of photons detected by a photon-counting detector array followed by a commercial time-tagger. Algorithms are presented for slot, symbol, and frame synchronization as well as parameter estimation. Estimates of link performance are evaluated through Monte- Carlo simulation for an optical channel that includes optical losses, detector blocking, signal clock dynamics, and pointing-induced downlink fades. Based upon these simulation results, it is expected that link closure may be achieved with at least 3 dB of margin under a variety of relevant conditions.

Tkacenko, Andre↗
NASA NTRS2004

Temporal-Spatial Structure of Magnetic Merging at the Magnetopause Inferred from 557.7-nm All-Sky Images

We demonstrate that high-resolution 557.7-nm all-sky images are useful tools for investigating the spatial and temporal evolution of merging on the dayside magnetopause. Analysis of ground and satellite measurements leads us to conclude that high-latitude merging events can occur at multiple sites simultaneously and vary asynchronously on time scales of 30 s to 3 min. Variations of 557.7 nm emissions were observed at a 10 s cadence at Ny-Alesund on 19 December 2001, while significant changes in the IMF clock angle were reaching the magnetopause. The optical patterns are consistent with a scenario in which merging occurs around the rim of the high-latitude cusp at positions dictated by the IMF clock angle. Electrons energized at merging sites represent plausible sources for 557.7 nm emissions in the cusp. Polar observations at the magnetopause have directly linked enhanced fluxes of > or = 0.5 keV electrons with merging. Spectra of electrons responsible for some of the emissions, measured during a DMSP F15 overflight, exhibit "inverted-V" features, indicating further acceleration above the ionosphere. SuperDARN spectral width boundaries, characteristic of open-closed field line transitions, are located at the equatorward edge of the 557.7nm emissions. Optical data suggest that with IMF B(sub Y) > 0, the Northern Hemisphere cusp divides into three source regions. When the IMF clock angle was approx. 150 deg structured 557.7-nm emissions came from east of the 13:00 MLT meridian. At larger clock angles the emissions appeared between 12:00 and 13:00 MLT. No significant 557.7-nm emissions were detected in the prenoon MLT sector. MHD simulations corroborate our scenario, showing that with the observed large dipole-tilt and IMF clock angles, merging sites develop near the front and eastern portions of the high-altitude cusp rim in the Northern Hemisphere and near the western part of the cusp rim in the Southern Hemisphere.

Maynard, N. C.↗
NASA NTRSDate not supplied

Laser Communications Relay Demonstration Optimetrics Experiment

Within this paper, we report on an Optimetrics experiment conducted on the National Aeronautics and Space Administration (NASA) Laser Communication Relay Demonstration (LCRD). The high precision two-way ranging is conducted on the optical communications link between the LCRD space terminal in a geosynchronous orbit and the Optical Ground Station 1 (OGS1) at Table Mountain, California, and is referred to as optimetrics ranging. The receiver to transmitter clock loopback is implemented in the LCRD space modem. A digital dual mixer time difference phase meter (DDMTD) is implemented in the OGS1 ground modem. The round-trip time is measured with the DDMTD by counting the frame and data clock ticks between transmitter and receiver frame synchronization markers for coarse range, and the relative phase of the transmit and receive clock for high precision range. This approach provides coverage for all potential ranges with no ranging ambiguity. The flight modem FPGA code was modified for frame and data clock loopback and the OGS1 FPGA code was modified for the DDMTD phase meter implementation. The experiment team conducted a 36-hour continuous ranging measurement. Preliminary two-way optimetrics ranging data show a noise floor of 3cm (rms). Based on our theoretical noise analysis and ground tests with spare flight modems, we expected one order of magnitude improvement on ranging precision. We are conducting detailed post data processing to identify the differences to further reduce the noise level and formulating an improved implementation approach for future missions. For reference and comparison, traditional Radio Frequency (RF) ranging between LCRD and OGS1 was conducted at the same time and indicates a ranging noise floor of 30cm(rms). Other telemetry and relevant environmental parameters such as weather and atmosphere temperature were also collected for offline data processing. The high precision ranging and range rate measurements from the laser communications data link clock and clock phase are performed simultaneously with continuous optical communication. No extra hardware added to existing system. This high precision optimetrics measurement implementation provides alternative ranging and range rate measurements for orbit determination (OD) and flight dynamics calculations with higher precision. We see significant improvement on OD for navigation upon implementation in future optical communication systems.

Rafael Garcia↗
NASA NTRS1990

Real-time simulation clock

The invention is a clock for synchronizing operations within a high-speed, distributed data processing network. The clock is actually a distributed system comprising a central clock and multiple site clock interface units (SCIUs) which are connected by means of a fiber optic star network and which operate under control of separate clock software. The presently preferred embodiment is a part of the flight simulation system now in current use at the NASA Langley Research Center.

Bennington, Donald R.↗
NASA NTRS2009

Precise Stabilization of the Optical Frequency of WGMRs

Crystalline whispering gallery mode resonators (CWGMRs) made of crystals with axial symmetry have ordinary and extraordinary families of optical modes. These modes have substantially different thermo-refractive constants. This results in a very sharp dependence of differential detuning of optical frequency on effective temperature. This frequency difference compared with clock gives an error signal for precise compensation of the random fluctuations of optical frequency. Certain crystals, like MgF2, have turnover points where the thermo-refractive effect is completely nullified. An advantage for applications using WGMRs for frequency stabilization is in the possibility of manufacturing resonators out of practically any optically transparent crystal. It is known that there are crystals with negative and zero thermal expansion at some specific temperatures. Doping changes properties of the crystals and it is possible to create an optically transparent crystal with zero thermal expansion at room temperature. With this innovation s stabilization technique, the resultant WGMR will have absolute frequency stability The expansion of the resonator s body can be completely compensated for by nonlinear elements. This results in compensation of linear thermal expansion (see figure). In three-mode, the MgF2 resonator, if tuned at the turnover thermal point, can compensate for all types of random thermal-related frequency drift. Simplified dual-mode method is also available. This creates miniature optical resonators with good short- and long-term stability for passive secondary frequency ethalon and an active resonator for active secondary frequency standard (a narrowband laser with long-term stability).

Savchenkov, Anatoliy↗
NASA NTRS2004

Small Mercury Ion Clock for On-board Spacecraft Navigation

I.Small Ion Clock Approach and Heritage: a) No lasers, uwave cavities, cryogenics, atomic beams, etc. b) Ions are electrically shuttled between separate optical and microwave traps. II. Each trap is optimized for its task: quadrupole for optical state selection; multi-pole for microwave clock. a) Very good stability shown in USNO. Timescale running "open loop." III. "Open loop" operation means no self-measurements of frequency offsets: (Zeeman, ion temperature,... etc.) a) Fewer parts and procedures, produces stable output continuously. IV. Ion clock is not so sensitive to temperature fluctuations a) Measured u:nshielded temperature coefficient of few 10(exp -15) per C. b) No bulky temperature isolation needed.

Prestage, John D.↗
NASA NTRS1995

The IUE Mega Campaign. Modulated Structure in the Wind of HD 64760 (B0.5 Ib)

We highlight systematic variability in the stellar wind of the early B type supergiant, HD 64760, whose UV line profiles were monitored for almost 16 days in 1995 January as part of the IUE 'MEGA Campaign.' The extensive coverage reveals a pattern of rapidly evolving discrete optical depth changes which typically migrate from approx. - 200 km/s to approx. -1500 km/s in less than 12 hr. These features coexist with more slowly evolving structures lasting several days. Time-series analysis of the Si(IV), Si(III), and N(V) profile variations presents a clear 1.2 day periodicity, which is a quarter of the estimated maximum rotation period of HD 64760. The line profile changes are consistent with an interpretation in terms of a set of corotating wind features which occult the stellar disk at least 3 times during the observing run. These data are combined with UV observations collected in 1993 March to argue in favor of rotationally modulated wind variations in HD 64760. The basic result of very regular, large-scale optical depth variations points to a 'clock' whose origin is on the stellar surface, rather than a mechanism that is entirely intrinsic to the stellar wind.

Prinja, Raman K.↗
NASA NTRS1985

Synchronization for Optical PPM Signals

Method based on statistical properties of weak pulse-positionmodulated (PPM) signal enables synchronization of receiver clock with received-signal time base. Method applies to weak optical M-ary PPM signals, for which there is only one pulse of length Tp transmitted during one of timeslots of length T in each successive interval of M timeslots. Method requires small dead time, Td, at beginning and end of each timeslot, during which pulse amplitude is zero.

Vilnrotter, V. A.↗
NASA NTRS2017

Optimetrics for Precise Navigation

Optimetrics for Precise Navigation will be implemented on existing optical communication links. The ranging and Doppler measurements are conducted over communication data frame and clock. The measurement accuracy is two orders of magnitude better than TDRSS. It also has other advantages of: The high optical carrier frequency enables: (1) Immunity from ionosphere and interplanetary Plasma noise floor, which is a performance limitation for RF tracking; and (2) High antenna gain reduces terminal size and volume, enables high precision tracking in Cubesat, and in deep space smallsat. High Optical Pointing Precision provides: (a) spacecraft orientation, (b) Minimal additional hardware to implement Precise Optimetrics over optical comm link; and (c) Continuous optical carrier phase measurement will enable the system presented here to accept future optical frequency standard with much higher clock accuracy.

Precise↗
NASA NTRS2024

Clock Synchronization Characterization of the Washington DC Metropolitan Area Quantum Network (DC-QNet)

Quantum networking protocols relying on interference and precise time-of-flight measurements require high-precision clock synchronization. This study describes the design, implementation, and characterization of two optical time transfer methods in a metropolitan-scale quantum networking research testbed. With active electronic stabilization, sub-picosecond time deviation (TDEV) was achieved at integration times between 1 s and 10 5 s over 53 km of deployed fiber. Over the same integration periods, 10-picosecond level TDEV was observed using the White Rabbit-Precision Time Protocol (WR-PTP) over 128 km. Measurement methods are described to understand the sources of environmental fluctuations on clock synchronization towards the development of in-situ compensation methods. Path delay gradients, chromatic dispersion, polarization drift, and optical power variations all contributed to clock synchronization errors. The results from this study will inform future work in the development of link noise management methods essential for enabling experimental research in developing practical quantum networking protocols.

PIKTime↗
NASA NTRS1983

Laser induced asymmetry and inhomogeneous broadening of the microwave lineshape of a gas cell atomic frequency standard

The possibility of replacing the RF discharge lamp in a rubidium gas cell clock with a single mode laser diode is addressed. Since the short term stability of the rubidium frequency standard is limited by the shot noise of the photodetector, an increased signal-to-noise ratio due to more efficient laser diode optical pumping might improve the short term performance. Because the emission wavelength of the laser diode can be tuned, improved long term performance could be gained through the control of the light shift effect. However, due to the nature of the gas cell frequency standard, various physical phenomena are strongly coupled in their effect on the frequency output, and thus careful consideration must be given to any change in one parameter because of its interrelation with other parameters. Some investigations concerning the coupled effect of the optical and microwave fields in the rubidium atomic clock are reported. It is shown that this type of coupling is an important consideration for any attempt to incorporate a laser diode into a gas cell clock.

Camparo, J. C.↗
NASA NTRS2008

NASA Tech Briefs, July 2008

Topics covered include: Torque Sensor Based on Tunnel-Diode Oscillator; Shaft-Angle Sensor Based on Tunnel-Diode Oscillator; Ground Facility for Vicarious Calibration of Skyborne Sensors; Optical Pressure-Temperature Sensor for a Combustion Chamber; Impact-Locator Sensor Panels; Low-Loss Waveguides for Terahertz Frequencies; MEMS/ECD Method for Making Bi(2-x)Sb(x)Te3 Thermoelectric Devices; Low-Temperature Supercapacitors; Making a Back-Illuminated Imager with Back-Side Contact and Alignment Markers; Compact, Single-Stage MMIC InP HEMT Amplifier; Nb(x)Ti(1-x)N Superconducting-Nanowire Single-Photon Detectors; Improved Sand-Compaction Method for Lost-Foam Metal Casting; Improved Probe for Evaluating Compaction of Mold Sand; Polymer-Based Composite Catholytes for Li Thin-Film Cells; Using ALD To Bond CNTs to Substrates and Matrices; Alternating-Composition Layered Ceramic Barrier Coatings; Variable-Structure Control of a Model Glider Airplane; Axial Halbach Magnetic Bearings; Compact, Non-Pneumatic Rock-Powder Samplers; Biochips Containing Arrays of Carbon-Nanotube Electrodes; Nb(x)Ti(1-x)N Superconducting-Nanowire Single-Photon Detectors; Neon as a Buffer Gas for a Mercury-Ion Clock; Miniature Incandescent Lamps as Fiber-Optic Light Sources; Bidirectional Pressure-Regulator System; and Prism Window for Optical Alignment. Single-Grid-Pair Fourier Telescope for Imaging in Hard-X Rays and gamma Rays Range-Gated Metrology with Compact Optical Head Lossless, Multi-Spectral Data Compressor for Improved Compression for Pushbroom-Typetruments.

Source record↗
NASA NTRS1987

Synchronization tracking in pulse position modulation receiver

A clock pulse generator for decoding pulse position modulation in an optical communication receiver is synchronized by a delay tracking loop which multiplies impulses of a data pulse by the square wave clock pulses from the generator to produce positive impulses when the clock pulse is of one level, and negative impulses when the clock pulse is of another level. A delay tracking loop integrates the impulses and produces an error signal that adjusts the delay so the clock pulses will be synchronized with data pulses. A dead-time tau sub d is provided between data pulses of an interval tau sub p in the data pulse period tau. When synchronized, the average number of positive impulses integrated will equal the average number of negative impulses over the continuous stream of data pulses.

Vilnrotter, Victor A.↗
NASA NTRS2012

Achievable Precision for Optical Ranging Systems

Achievable RMS errors in estimating the phase, frequency, and intensity of a direct-detected intensity-modulated optical pulse train are presented. For each parameter, the Cramer-Rao-Bound (CRB) is derived and the performance of the Maximum Likelihood estimator is illustrated. Approximations to the CRBs are provided, enabling an intuitive understanding of estimator behavior as a function of the signaling parameters. The results are compared to achievable RMS errors in estimating the same parameters from a sinusoidal waveform in additive white Gaussian noise. This establishes a framework for a performance comparison of radio frequency (RF) and optical science. Comparisons are made using parameters for state-of-the-art deep-space RF and optical links. Degradations to the achievable errors due to clock phase noise and detector jitter are illustrated.

estimation theory↗
NASA NTRS2012

Sample-Clock Phase-Control Feedback

To demodulate a communication signal, a receiver must recover and synchronize to the symbol timing of a received waveform. In a system that utilizes digital sampling, the fidelity of synchronization is limited by the time between the symbol boundary and closest sample time location. To reduce this error, one typically uses a sample clock in excess of the symbol rate in order to provide multiple samples per symbol, thereby lowering the error limit to a fraction of a symbol time. For systems with a large modulation bandwidth, the required sample clock rate is prohibitive due to current technological barriers and processing complexity. With precise control of the phase of the sample clock, one can sample the received signal at times arbitrarily close to the symbol boundary, thus obviating the need, from a synchronization perspective, for multiple samples per symbol. Sample-clock phase-control feedback was developed for use in the demodulation of an optical communication signal, where multi-GHz modulation bandwidths would require prohibitively large sample clock frequencies for rates in excess of the symbol rate. A custom mixedsignal (RF/digital) offset phase-locked loop circuit was developed to control the phase of the 6.4-GHz clock that samples the photon-counting detector output. The offset phase-locked loop is driven by a feedback mechanism that continuously corrects for variation in the symbol time due to motion between the transmitter and receiver as well as oscillator instability. This innovation will allow significant improvements in receiver throughput; for example, the throughput of a pulse-position modulation (PPM) with 16 slots can increase from 188 Mb/s to 1.5 Gb/s.

Quirk, Kevin J.↗
NASA NTRS2012

NASA Tech Briefs, September 2012

Topics covered include: Beat-to-Beat Blood Pressure Monitor; Measurement Techniques for Clock Jitter; Lightweight, Miniature Inertial Measurement System; Optical Density Analysis of X-Rays Utilizing Calibration Tooling to Estimate Thickness of Parts; Fuel Cell/Electrochemical Cell Voltage Monitor; Anomaly Detection Techniques with Real Test Data from a Spinning Turbine Engine-Like Rotor; Measuring Air Leaks into the Vacuum Space of Large Liquid Hydrogen Tanks; Antenna Calibration and Measurement Equipment; Glass Solder Approach for Robust, Low-Loss, Fiber-to-Waveguide Coupling; Lightweight Metal Matrix Composite Segmented for Manufacturing High-Precision Mirrors; Plasma Treatment to Remove Carbon from Indium UV Filters; Telerobotics Workstation (TRWS) for Deep Space Habitats; Single-Pole Double-Throw MMIC Switches for a Microwave Radiometer; On Shaft Data Acquisition System (OSDAS); ASIC Readout Circuit Architecture for Large Geiger Photodiode Arrays; Flexible Architecture for FPGAs in Embedded Systems; Polyurea-Based Aerogel Monoliths and Composites; Resin-Impregnated Carbon Ablator: A New Ablative Material for Hyperbolic Entry Speeds; Self-Cleaning Particulate Prefilter Media; Modular, Rapid Propellant Loading System/Cryogenic Testbed; Compact, Low-Force, Low-Noise Linear Actuator; Loop Heat Pipe with Thermal Control Valve as a Variable Thermal Link; Process for Measuring Over-Center Distances; Hands-Free Transcranial Color Doppler Probe; Improving Balance Function Using Low Levels of Electrical Stimulation of the Balance Organs; Developing Physiologic Models for Emergency Medical Procedures Under Microgravity; PMA-Linked Fluorescence for Rapid Detection of Viable Bacterial Endospores; Portable Intravenous Fluid Production Device for Ground Use; Adaptation of a Filter Assembly to Assess Microbial Bioburden of Pressurant Within a Propulsion System; Multiplexed Force and Deflection Sensing Shell Membranes for Robotic Manipulators; Whispering Gallery Mode Optomechanical Resonator; Vision-Aided Autonomous Landing and Ingress of Micro Aerial Vehicles; Self-Sealing Wet Chemistry Cell for Field Analysis; General MACOS Interface for Modeling and Analysis for Controlled Optical Systems; Mars Technology Rover with Arm-Mounted Percussive Coring Tool, Microimager, and Sample-Handling Encapsulation Containerization Subsystem; Fault-Tolerant, Real-Time, Multi-Core Computer System; Water Detection Based on Object Reflections; SATPLOT for Analysis of SECCHI Heliospheric Imager Data; Plug-in Plan Tool v3.0.3.1; Frequency Correction for MIRO Chirp Transformation Spectroscopy Spectrum; Nonlinear Estimation Approach to Real-Time Georegistration from Aerial Images; Optimal Force Control of Vibro-Impact Systems for Autonomous Drilling Applications; Low-Cost Telemetry System for Small/Micro Satellites; Operator Interface and Control Software for the Reconfigurable Surface System Tri-ATHLETE; and Algorithms for Determining Physical Responses of Structures Under Load.

Source record↗
NASA NTRS2018

Continuous Carrier Optical Phase Optometric Measurement over Coherent Optical Communication Link

An apparatus for measuring a distance between a first and second terminal includes a frame counter for determining a number of data frames traversing a distance between the first terminal 105 and the second terminal, a frame bit counter for determining a number of data clock bits offset between a transmitted data frame and a concurrently received data frame, a data clock phase detector for determining a phase difference between an RF data clock for the transmitted data frame and an RF data clock for the concurrently received data frame, and an optical carrier phase detector for determining a phase difference between an optical carrier used to transmit the transmitted data frame and an optical carrier for the concurrently received data frame. The distance between the first and second terminal is determined from a round trip transit time T between the first and second terminals.

Yang, Guangning↗