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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 NTRS1989

Correction And Use Of Jitter In Television Images

Proposed system stabilizes jittering television image and/or measures jitter to extract information on motions of objects in image. Alternative version, system controls lateral motion on camera to generate stereoscopic views to measure distances to objects. In another version, motion of camera controlled to keep object in view. Heart of system is digital image-data processor called "jitter-miser", which includes frame buffer and logic circuits to correct for jitter in image. Signals from motion sensors on camera sent to logic circuits and processed into corrections for motion along and across line of sight.

Diner, Daniel B.↗

NASA NTRS1991

Jitter model and signal processing techniques for pulse width modulation optical recording

A jitter model and signal processing techniques are discussed for data recovery in Pulse Width Modulation (PWM) optical recording. In PWM, information is stored through modulating sizes of sequential marks alternating in magnetic polarization or in material structure. Jitter, defined as the deviation from the original mark size in the time domain, will result in error detection if it is excessively large. A new approach is taken in data recovery by first using a high speed counter clock to convert time marks to amplitude marks, and signal processing techniques are used to minimize jitter according to the jitter model. The signal processing techniques include motor speed and intersymbol interference equalization, differential and additive detection, and differential and additive modulation.

Liu, Max M.-K.↗

NASA NTRS1993

A pattern jitter free AFC scheme for mobile satellite systems

This paper describes a scheme for pattern jitter free automatic frequency control (AFC) with a wide frequency acquisition range. In this scheme, equalizing signals fed to the frequency discriminator allow pattern jitter free performance to be achieved for all roll-off factors. In order to define the acquisition range, frequency discrimination characateristics are analyzed on a newly derived frequency domain model. As a result, it is shown that a sufficiently wide acquisition range over a given system symbol rate can be achieved independent of symbol timing errors. Additionally, computer simulation demonstrates that frequency jitter performance improves in proportion to E(sub b)/N(sub 0) because pattern-dependent jitter is suppressed in the discriminator output. These results show significant promise for applciation to mobile satellite systems, which feature relatively low symbol rate transmission with an approximately 0.4-0.7 roll-off factor.

Yoshida, Shousei↗

NASA NTRS1994

An examination of anticipated g-jitter on Space Station and its effects on materials processes

This study is concerned with the effects of g-jitter, the residual acceleration aboard spacecraft, on selected classes of materials processes. In particular, the anticipated acceleration environment aboard Space Station Freedom (SSF) and its potential effects are analyzed, but the topic is covered with a sufficient level of generality as to apply to other processes and to other vehicles as well. Some of the key findings of this study include: The present acceleration specifications for SSF are inadequate to assure a quality level low-g environment. The local g vector orientation is an extremely sensitive parameter for certain key processes, but can not be controlled to within the desired tolerance. Therefore, less emphasis should be placed upon achieving a tight control of SSF attitude, but more emphasis should be focused on reducing the overall level of the g-jitter magnitude. Melt-based crystal growth may not be successfully processed in the relatively noisy environment of a large inhabited space structure. Growth from vapor or from solution appears more favorable. A smaller space structure and/or a free flyer can provide better alternatives in terms of g-jitter considerations. A high priority (including budgetary) should be given to coordinated efforts among researchers, SSF designers, and equipment contractors, to develop practical experiment-specific sensitivity requirements. Combined focused numerical simulations and experiments with well-resolved acceleration measurements should be vigorously pursued for developing reliable experiment-specific sensitivity data. Appendices provide an extensive cross-referenced bibliography, a discussion of the merits offered by g-jitter analysis techniques, as well as definitions of relevant nondimensional quantities and a brief description of available accelerometry hardware.

Nelson, Emily S.↗

NASA NTRS1995

Determination of attitude jitter in small satellites

For various reasons, including cost, small satellites are becoming more appealing. Because of their smaller inertias, these spacecrafts are more sensitive to disturbances and likely to have more attitude jitter than the bigger units. These jitter levels may be unacceptable for some scientific instruments and need to be compensated. In the case of line-of-sight type instruments, the attitude jitter could be mitigated by incorporating a fast steering mirror into the system. To take full advantage of these devices, the spacecraft attitude needs to be measured at sufficiently high bandwidth, well beyond what is commonly provided by inertial reference units. This research examines various ways to obtain higher bandwidth attitude measurements for the purpose of jitter control.

Algrain, Marcelo C.↗

NASA NTRS1995

Spacecraft Jitter Attenuation Using Embedded Piezoelectric Actuators

Remote sensing from spacecraft requires precise pointing of measurement devices in order to achieve adequate spatial resolution. Unfortunately, various spacecraft disturbances induce vibrational jitter in the remote sensing instruments. The NASA Langley Research Center has performed analysis, simulations, and ground tests to identify the more promising technologies for minimizing spacecraft pointing jitter. These studies have shown that the use of smart materials to reduce spacecraft jitter is an excellent match between a maturing technology and an operational need. This paper describes the use of embedding piezoelectric actuators for vibration control and payload isolation. In addition, recent advances in modeling, simulation, and testing of spacecraft pointing jitter are discussed.

Belvin, W. Keith↗

NASA NTRS2002

Effect of Magnetic Fields on g-jitter Induced Convection and Solute Striation During Space Processing of Single Crystals

A 2-D finite element model is presented for the melt growth of single crystals in a microgravity environment with a superimposed DC magnetic field. The model is developed based on the deforming finite element methodology and is capable of predicting the phenomena of the steady and transient convective flows, heat transfer, solute distribution, and solid-liquid interface morphology associated with the melt growth of single crystals in microgravity with and without an applied magnetic field. Numerical simulations were carried out for a wide range of parameters including idealized microgravity conditions, the synthesized g-jitter and the real g-jitter data taken by on-board accelerometers during space flights. The results reveal that the time varying g-jitter disturbances, although small in magnitude, cause an appreciable convective flow in the liquid pool, which in turn produces detrimental effects during the space processing of single crystal growth. An applied magnetic field of appropriate strength, superimposed on microgravity, can be very effective in suppressing the deleterious effects resulting from the g-jitter disturbances.

deGroh, H. C.↗

NASA NTRS2019

TSIS Experiences with ISS Jitter from Inception to On-Orbit Operation

The TSIS instrument has been measuring solar irradiance on a continual basis since January 2018 as an external payload on the ISS. In 2014 when TSIS was directed to fly on the ISS, the jitter environment was highly uncertain, so TSIS designed a robust gimbaled pointing system that showed excellent disturbance attenuation throughout the design, test, and on-orbit phases of the program. This paper discusses how TSIS accounted for this uncertain jitter environment through-out the life of the program.TSIS was able to measure the ISS jitter during commissioning and determined that it was a relatively benign environment less than 4 arcseconds 1σ at low frequencies (<0.5 Hz). More importantly, the measured pointing performance of TSIS was consistently found to be 4 arcseconds 1σ, which easily satisfied the jitter requirement of 60 arcseconds 1σ.

solar irradiance instrument↗

NASA NTRSDate not supplied

Spacecraft Line-Of-Sight Jitter Mitigation and Management Lessons Learned and Engineering Best Practices

Predicting, managing, controlling, and testing spacecraft line-of-sight (LoS) jitter caused by micro-vibrations due to onboard internal disturbance sources is a formidable multidisciplinary engineering task. It is especially challenging for those missions hosting high-performance, vibration-sensitive optical sensor payloads with stringent pointing stability requirements. Both NASA and ESA are planning technically aggressive spaceflight missions that include ultra-high-performance optical payloads with delicate, highly vibration-sensitive scientific and observational instruments. The GN&C community of practice will need to leverage and build upon their collective experiences and lessons learned to better address future micro-vibration challenges. To identify lessons learned and best engineering practices the NASA Engineering & Safety Center (NESC) sponsored a two-day Spacecraft LoS Jitter Workshop in late 2019. The workshop’s goal was to provide a multidisciplinary forum to elicit deeper understanding of the issues related to solving the spacecraft LoS jitter/micro-vibration problem. A primary objective was to identify and share best practices, rules of thumb, and options for jitter-related activities. Representatives from NASA, JPL, ESA, along with NASA’s industrial partners, independent consultant subject matter experts, and members of academia participated in the workshop. This paper will describe the motivation for the NASA Spacecraft LoS Jitter Workshop and summarize the identified findings, observations, and recommendations.

Lessons Learned;↗

DOE OSTI2023

Time-walk and jitter correction in SNSPDs at high count rates

Superconducting nanowire single-photon detectors (SNSPDs) are a leading detector type for time correlated single photon counting, especially in the near-infrared. When operated at high count rates, SNSPDs exhibit increased timing jitter caused by internal device properties and features of the RF amplification chain. Variations in RF pulse height and shape lead to variations in the latency of timing measurements. To compensate for this, we demonstrate a calibration method that correlates delays in detection events with the time elapsed between pulses. The increase in jitter at high rates can be largely canceled in software by applying corrections derived from the calibration process. We demonstrate our method with a single-pixel tungsten silicide SNSPD and show it decreases high count rate jitter. The technique is especially effective at removing a long tail that appears in the instrument response function at high count rates. At a count rate of 11.4 MCounts/s, we reduce the full width at 1% maximum level (FW1%M) by 45%. The method, therefore, enables certain quantum communication protocols that are rate-limited by the FW1%M metric to operate almost twice as fast.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2024

A Suppression-based STDP Rule Resilient to Jitter Noise in Spike Patterns for Neuromorphic Computing

Multi-spike models of synaptic plasticity, such as the triplet and suppression spike-timing-dependent plasticity (STDP) rules, exhibit better alignment with neurophysiological data in the brain compared to the pair-based STDP rule. Previous studies have empirically shown that the pair-based STDP rule can detect spatiotemporal spike patterns hidden in equally dense distractor spike trains in an unsupervised manner. However, it fails to detect spike patterns influenced by jitter noise. Given that spiking neural networks (SNNs) exhibit variability in generated spike trains in response to the same inputs, it becomes imperative to have learning rules capable of detecting spike patterns even in the presence of jitter noise. In this study, we introduce a simplified suppression-based STDP rule that demonstrates significantly enhanced tolerance to jitter in spike patterns compared to the pair-based STDP rule. Unlike the ideal suppression STDP rule, characterized by an exponential learning window and requiring high-resolution synapses, the simplified rule limits the synaptic efficacy update to a single bit at any given instant. Moreover, it employs 4-bit fixed-point synapses, facilitating straightforward implementation in neuromorphic hardware.

Gautam, Ashish [ORNL]↗

DOE OSTI2021

The Epoch of Giant Planet Migration Planet Search Program. I. Near-infrared Radial Velocity Jitter of Young Sun-like Stars

We present early results from the Epoch of Giant Planet Migration program, a precise radial velocity (RV) survey of more than 100 intermediate-age (∼20–200 Myr) G and K dwarfs with the Habitable Zone Planet Finder spectrograph (HPF) at McDonald Observatory’s Hobby–Eberly Telescope. The goals of this program are to determine the timescale and dominant physical mechanism of giant planet migration interior to the water ice line of Sun-like stars. Here, we summarize results from the first 14 months of this program, with a focus on our custom RV pipeline for HPF, a measurement of the intrinsic near-infrared RV activity of young Solar analogs, and modeling the underlying population-level distribution of stellar jitter. We demonstrate on-sky stability at the sub-2 m s{sup −1} level for the K2 standard HD 3765 using a least-squares matching method to extract precise RVs. Based on a subsample of 29 stars with at least three RV measurements from our program, we find a median rms level of 34 m s{sup −1}. This is nearly a factor of 2 lower than the median rms level in the optical of 60 m s{sup −1} for a comparison sample with similar ages and spectral types as our targets. The observed near-infrared jitter measurements for this subsample are well reproduced with a log-normal parent distribution with μ = 4.15 and σ = 1.02. Finally, by compiling rms values from previous planet search programs, we show that near-infrared jitter for G and K dwarfs generally decays with age in a similar fashion to optical wavelengths, albeit with a shallower slope and lower overall values for ages ≲1 Gyr.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1975

Space processing convection evaluation - G-jitter convection of confined fluids in low gravity

G-jitter convection, caused by time-varying accelerations imparted on a heated container of fluid in low gravity, is investigated analytically. The mathematical model used is constructed from the Navier-Stokes equations which are solved with a finite-difference method on a digital computer. Results are presented for typical space processing configurations and anticipated g-jitter levels, with emphasis on sounding rocket applications. The calculations indicate that g-jitter can cause significant temperature oscillations, increase or decrease local heat transfer and produce oscillatory convective flow patterns. These factors can have significant effects on important processes such as crystal growth (banding, for example) and separation techniques.

Spradley, L. W.↗

NASA NTRS1982

Jitter in SS 433-A clue to the collimation mechanism

The blue and red shift jitter observed in SS 433 is examined with a view to determining its sources. The jitter is characterized by a Delta-z rms amplitude of 0.01, corresponding to a 3000 km/sec Doppler velocity, which is larger than either the width or the error of measurement of the shifted lines. In addition, the amplitude of the jumps is not strongly dependent on the phase in the 164-day cycle, and the amplitudes of the jitter in the redshifted and blueshifted branches are comparable. It is shown that these features set strong constraints on models proposed for SS 433 by Sarazin et al. (1980), Katz (1980), and Van den Heuvel et al. (1980).

Katz, J. I.↗

NASA NTRS1989

Effect of G-jitters on the stability of rotating bubble under microgravity environment

The instability of liquid and gas interface can be induced by the pressure of longitudinal and lateral accelerations, vehicle vibration, and rotational fields of spacecraft in a microgravity environment. Characteristics of slosh waves excited by the restoring force field of gravity jitters have been investigated. Results show that lower frequency gravity jitters excite slosh waves with higher ratio of maximum amplitude to wave length than that of the slosh waves generated by the higher frequency gravity jitters.

Hung, R. J.↗

NASA NTRS1990

Gravity-jitters and excitation of slosh waves

Hung, R. J.↗

NASA NTRS1990

Zero-crossing detector with sub-microsecond jitter and crosstalk

A zero-crossing detector (ZCD) was built and tested with a new circuit design which gives reduced time jitter compared to previous designs. With the new design, time jitter is reduced for the first time to a value which approaches that due to noise in the input amplifying stage. Additionally, with fiber-optic transmission of the output signal, crosstalk between units has been eliminated. The measured values are in good agreement with circuit noise calculations and approximately ten times lower than that for ZCD's presently installed in the JPL test facility. Crosstalk between adjacent units was reduced even more than the jitter.

Dick, G. John↗

NASA NTRS1990

Stability and slosh wave for rotating bubble due to gravity-jitters under microgravity

Time-dependent fluid behaviors in microgravity environments are examined with particular attention given to the dynamics of bubble configurations. The initial bubble profiles, computed from the steady-state formulation, are used as the initial input for the time dependent computation. The parameters considered are liquid density and its kinematic viscosity, gas density and its kinematic viscosity, surface tension coefficient, angular velocity, and gravity environment. This computer algorithm can be used to simulate the fluid behavior in a microgravity environment, in particular the excitation of slosh waves due to different frequencies of gravity jitters. Results show that lower-frequency gravity jitters excite slosh waves with a higher ratio of maximum amplitude to wave length than that of the slosh waves generated by the higher frequency gravity jitters.

Hung, R. J.↗