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As thermal errors are reduced instrumental and troposphere correlated errors will increasingly become more important. Work in progress shows that troposphere covariance error models improve data analysis results. We expect to see stronger effects with higher data rates. Temperature modeling of delay errors may further reduce temporal correlations in the data.
We present a high-precision ranging and range-rate measurement system via an optical-ranging or combined ranging-communication link. A complete bench-top optical communication system was built. It included a ground terminal and a space terminal. Ranging and range rate tests were conducted in two configurations. In the communication configuration with 622 data rate, we achieved a two-way range-rate error of 2 microns/s, or a modified Allan deviation of 9 x 10 (exp -15) with 10 second averaging time. Ranging and range-rate as a function of Bit Error Rate of the communication link is reported. They are not sensitive to the link error rate. In the single-frequency amplitude modulation mode, we report a two-way range rate error of 0.8 microns/s, or a modified Allan deviation of 2.6 x 10 (exp -15) with 10 second averaging time. We identified the major noise sources in the current system as the transmitter modulation injected noise and receiver electronics generated noise. A new improved system will be constructed to further improve the system performance for both operating modes.
The Columbia Scientific Balloon Facility provides Telemetry and Command systems necessary for balloon operations and science support. There are various Line-Of-Sight (LOS) and Over-The-Horizon (OTH) systems and interfaces that provide communications to and from a science payload. This presentation will discuss the current data throughput options available and future capabilities that may be incorporated in the LDB Support Instrumentation Package (SIP) such as doubling the TDRSS data rate. We will also explore some new technologies that could potentially expand the data throughput of OTH communications.
None. This is a series of viewgraphs from a presentation given at the meeting. Covers tests of high data rate transmission by airborne antennas.
In this paper we design high rate protograph based LDPC codes suitable for binary erasure channels. To simplify the encoder and decoder implementation for high data rate transmission, the structure of codes are based on protographs and circulants. These LDPC codes can improve data link and network layer protocols in support of communication networks. Two classes of codes were designed. One class is designed for large block sizes with an iterative decoding threshold that approaches capacity of binary erasure channels. The other class is designed for short block sizes based on maximizing minimum stopping set size. For high code rates and short blocks the second class outperforms the first class.
The Data Distribution Satellite (DDS), operating in conjunction with the planned space network, the National Research and Education Network and its commercial derivatives, would play a key role in networking the emerging supercomputing facilities, national archives, academic, industrial, and government institutions. Centrally located over the United States in geostationary orbit, DDS would carry sophisticated on-board switching and make use of advanced antennas to provide an array of special services. Institutions needing continuous high data rate service would be networked together by use of a microwave switching matrix and electronically steered hopping beams. Simultaneously, DDS would use other beams and on board processing to interconnect other institutions with lesser, low rate, intermittent needs. Dedicated links to White Sands and other facilities would enable direct access to space payloads and sensor data. Intersatellite links to a second generation ATDRS, called Advanced Space Data Acquisition and Communications System (ASDACS), would eliminate one satellite hop and enhance controllability of experimental payloads by reducing path delay. Similarly, direct access would be available to the supercomputing facilities and national data archives. Economies with DDS would be derived from its ability to switch high rate facilities amongst users needed. At the same time, having a CONUS view, DDS would interconnect with any institution regardless of how remote. Whether one needed high rate service or low rate service would be immaterial. With the capability to assign resources on demand, DDS will need only carry a portion of the resources needed if dedicated facilities were used. Efficiently switching resources to users as needed, DDS would become a very feasible spacecraft, even though it would tie together the space network, the terrestrial network, remote sites, 1000's of small users, and those few who need very large data links intermittently.
The wider adoption of hydrogen in multiple sectors of the economy requires that safety and risk issues be rigorously investigated. Quantitative Risk Assessment (QRA) is an important tool for enabling safe deployment of hydrogen fueling stations and is increasingly embedded in the permitting process. QRA requires reliability data, and currently hydrogen QRA is limited by the lack of hydrogen specific reliability data, thereby hindering the development of necessary safety codes and standards [1]. Four tools have been identified that collect hydrogen system safety data: H2Tools Lessons Learned, Hydrogen Incidents and Accidents Database (HIAD), National Renewable Energy Lab's (NREL) Composite Data Products (CDPs), and the Center for Hydrogen Safety (CHS) Equipment and Component Failure Rate Data Submission Form. This work critically reviews and analyzes these tools for their quality and usability in QRA. It is determined that these tools lay a good foundation, however, the data collected by these tools needs improvement for use in QRA. Areas in which these tools can be improved are highlighted, and can be used to develop a path towards adequate reliability data collection for hydrogen systems.
An evaluation is presented of the approach and landing performance of a Kalman filter aided inertial navigation system using flight data obtained from a series of approaches and landings of the CV-340 aircraft at an instrumented test area. A description of the flight test is given, in which data recorded included: (1) accelerometer signals from the platform of an INS; (2) three ranges from the Ames-Cubic Precision Ranging System; and (3) radar and barometric altimeter signals. The method of system evaluation employed was postflight processing of the recorded data using a Kalman filter which was designed for use on the XDS920 computer onboard the CV-340 aircraft. Results shown include comparisons between the trajectories as estimated by the Kalman filter aided system and as determined from cinetheodolite data. Data start initialization of the Kalman filter, operation at a practical data rate, postflight modeling of sensor errors and operation under the adverse condition of bad data are illustrated.
Development of a scientific rationale for an atmospheric probe designed to be capable of entry into either Saturn or Uranus. The effects of the NASA Monograph model atmospheres (SP 8091 and SP 8103) on the entry and descent trajectory specify instrument sampling design. The cool model atmospheres require descents to the vicinity of 20 bars to satisfy the objectives while about 4 bars is sufficient for the warm models. The measurement performance for a descent sampling time of 44 minutes shows that the atmosphere can be reconstructed from measured data. The required total probe entry weight is 103 kg, of which about 15 kg is for the science instruments. The descent data rate varies from 32 to 51 bps, depending upon the mode of transmitting preentry data. The resulting common probe can be redirected in flight between Saturn and Uranus.
The performance of a 5-Mbps coded system developed for Shuttle Ku-band communications is described. The system consists of a rate 1/2, constraint length 7 convolutional encoder-decoder and soft decision symbol synchronizer; the system has been band-limited at the transmitted symbol rate. Five convolutional decoders are operated in parallel to permit operation at the required data rate. It is found that the multiplexed encoder-decoder system does not exhibit any observable coding gain degradation when the channel is limited to the symbol rate at baseband.
Four measures of pilot workload were tested in the NASA C-141 Kuiper Airborne Observatory. The measured included a communications analysis, subjective ratings of workload, subjective ratings of additional factors related to workload, and heart rate. Data were collected for 11 flights, each of which lasted approximately seven hours. Heart rate was found to be significantly higher for the pilot who was flying than for the pilot who was not flying and it varied significantly across flight segments, peaking during landing and take off, particularly for the pilot in the left seat who was resonsible for aircraft control. For both left and right seats, the subjective assessment of stress rather than the subjective assessment of workload was significantly correlated with variation in heart rate. Frequencies of different types of communications varied significantly across segments of flight, however, they were not correlated with subjective ratings of workload. There was a significant difference between the left and right seats in the types of activities that contributed to their workload, however, workload was considered to be equivalent for the two.
Viewgraphs are presented which outline the overall system and component concepts for a 60 GHz intersatellite communications link system (ICLS). The ICLS was designed to augment the capabilities of the current Tracking and Data Relay Satellite System (TDRSS), providing a data rate capacity large enough to accommodate the expected rates for user satellites (USAT's) in the post-1995 timeframe. Two methods of data relay on-board the planned TDAS (Tracking and Data Acquisition) satellites are described. One is an all-baseband system with a bi-directional 2 Gbps data stream; the other is a channelized crosslink system wherein some of the channels are baseband and others are merely frequency translated before re-transmission. The general system and technology design drivers are outlined along with the acquisition architecture design. Descriptions of the TDAS antenna, transmitter, receiver, and mechanical hardware are presented.
A semi-empirical model has been developed to determine the complete crystallographic orientation dependence of the growth rate for vapor phase epitaxy (VPE). Previous researchers have been able to determine this dependence for a limited range of orientations; however, our model yields relative growth rate information for any orientation. This model for diamond and zincblende structure materials is based on experimental growth rate data, gas phase diffusion, and surface reactions. Data for GaAs chloride VPE is used to illustrate the model. The resulting growth rate polar diagrams are used in conjunction with Wulff constructions to simulate epitaxial layer shapes as grown on patterned substrates. In general, this model can be applied to a variety of materials and vapor phase epitaxy systems.
This report covers the period September 1, 1992 through August 1, 1993 for NASA grant NAG 5-1260 through the Astrophysics Data Program (ADP), for the project 'High Time Resolution Studies of Binary X-ray Pulsars'. During the past 11 months, we have concentrated on scientific analysis of the data, and have had to reanalyze several data sets, due to a newly discovered error in the unpacking of the count rate data. This error has now been corrected, but may have caused us to miss some scientific results, so we have gone back and reanalyzed the affected data sets, as well as continuing our analysis of other objects.
For the second German Spacelab Mission D-2 all activities related to operating, monitoring and controlling the experiments on board the Spacelab were conducted from the German Space Operations Control Center (GSOC) operated by the Deutsche Forschungsanstalt fur Luft- und Raumfahrt (DLR) in Oberpfaffenhofen, Germany. The operational requirements imposed new concepts on the transfer of data between Germany and the NASA centers and the processing of data at the GSOC itself. Highlights were the upgrade of the Spacelab Data Processing Facility (SLDPF) to real time data processing, the introduction of packet telemetry and the development of the high-rate data handling front end, data processing and display systems at GSOC. For the first time, a robot on board the Spacelab was to be controlled from the ground in a closed loop environment. A dedicated forward channel was implemented to transfer the robot manipulation commands originating from the robotics experiment ground station to the Spacelab via the Orbiter's text and graphics system interface. The capability to perform telescience from an external user center was implemented. All interfaces proved successful during the course of the D-2 mission and are described in detail in this paper.
An interferometric synthetic aperture radar (SAR) onboard processor concept and algorithm has been developed for the Ka-band radar interferometer (KaRIn) instrument on the Surface and Ocean Topography (SWOT) mission. This is a mission- critical subsystem that will perform interferometric SAR processing and multi-look averaging over the oceans to decrease the data rate by three orders of magnitude, and therefore enable the downlink of the radar data to the ground. The onboard processor performs demodulation, range compression, coregistration, and re-sampling, and forms nine azimuth squinted beams. For each of them, an interferogram is generated, including common-band spectral filtering to improve correlation, followed by averaging to the final 1 1-km ground resolution pixel. The onboard processor has been prototyped on a custom FPGA-based cPCI board, which will be part of the radar s digital subsystem. The level of complexity of this technology, dictated by the implementation of interferometric SAR processing at high resolution, the extremely tight level of accuracy required, and its implementation on FPGAs are unprecedented at the time of this reporting for an onboard processor for flight applications.
This hot-fire test continues NASA investigation of green propellant technologies for future missions. To show the potential for green propellants to replace some hydrazine systems in future spacecraft, NASA Marshall Space Flight Center (MSFC) is continuing to embark on hot-fire test campaigns with various green propellant blends.NASA completed hot-fire testing of 5N and 22N HPGP thrusters at the Marshall Space Flight Center’s Component Development Area altitude test stand in April 2015. Both thrusters are ground test articles and not flight ready units, but are representative of potential flight hardware with a known path towards flight application. The purpose of the 5N testing was to perform facility check-outs and generate a small set of data for comparison to ECAPS and Orbital ATK data sets. The 5N thruster performed as expected with thrust and propellant flow-rate data generated that are similar to previous testing at Orbital ATK. Immediately following the 5N testing, and using the same facility, the 22N testing was conducted on the same test stand with the purpose of demonstrating the 22N performance. The results of 22N testing indicate it performed as expected.The results of the hot-fire testing are presented in this paper and presentation.
As a laboratory for scientific research, the International Space Station has been in Low Earth Orbit for nearly 20 years and is expected to be on-orbit for another 10 years. The ISS has been maintaining a relatively pristine contamination environment for science payloads. Materials outgassing induced contamination is currently the dominant source for sensitive surfaces on ISS and modeling the outgassing rate decay over a 20 to 30 year period is challenging. Materials outgassing is described herein as a diffusion-reaction process using ASTM E 1559 rate data. The observation of -1/2 (diffusion) or non-integers (reaction limited) as rate decay exponents for common ISS materials indicate classical reaction kinetics is unsatisfactory in modeling materials outgassing. Non-randomness of reactant concentrations at the interface is the source of this deviation from classical reaction kinetics. A diffusion limited decay was adopted as the result of the correlation of the contaminant layer thicknesses on returned ISS hardware, the existence of high outgassing silicone exhibiting near diffusion limited decay, and the confirmation of non-depleted material after ten years in the Low Earth Orbit.Keywords: Materials Outgassing, ASTM E 1559, Reaction Kinetics, Diffusion, Space Environments Effects, Contamination