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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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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2015

The Role of Margin in Link Design and Optimization

Link analysis is a system engineering process in the design, development, and operation of communication systems and networks. Link models that are mathematical abstractions representing the useful signal power and the undesirable noise and attenuation effects (including weather effects if the signal path transverses through the atmosphere) that are integrated into the link budget calculation that provides the estimates of signal power and noise power at the receiver. Then the link margin is applied which attempts to counteract the fluctuations of the signal and noise power to ensure reliable data delivery from transmitter to receiver. (Link margin is dictated by the link margin policy or requirements.) A simple link budgeting approach assumes link parameters to be deterministic values typically adopted a rule-of-thumb policy of 3 dB link margin. This policy works for most S- and X-band links due to their insensitivity to weather effects. But for higher frequency links like Ka-band, Ku-band, and optical communication links, it is unclear if a 3 dB link margin would guarantee link closure. Statistical link analysis that adopted the 2-sigma or 3-sigma link margin incorporates link uncertainties in the sigma calculation. (The Deep Space Network (DSN) link margin policies are 2-sigma for downlink and 3-sigma for uplink.) The link reliability can therefore be quantified statistically even for higher frequency links. However in the current statistical link analysis approach, link reliability is only expressed as the likelihood of exceeding the signal-to-noise ratio (SNR) threshold that corresponds to a given bit-error-rate (BER) or frame-error-rate (FER) requirement. The method does not provide the true BER or FER estimate of the link with margin, or the required signalto-noise ratio (SNR) that would meet the BER or FER requirement in the statistical sense. In this paper, we perform in-depth analysis on the relationship between BER/FER requirement, operating SNR, and coding performance curve, in the case when the channel coherence time of link fluctuation is comparable or larger than the time duration of a codeword. We compute the "true" SNR design point that would meet the BER/FER requirement by taking into account the fluctuation of signal power and noise power at the receiver, and the shape of the coding performance curve. This analysis yields a number of valuable insights on the design choices of coding scheme and link margin for the reliable data delivery of a communication system - space and ground. We illustrate the aforementioned analysis using a number of standard NASA error-correcting codes.

Cheung, K.↗
NASA NTRS2006

High Capacity Communications From Martian Distances: Spacecraft Link Design Analysis - Part 1

High capacity space communications has been a desire for Human Exploration and Science missions. Current Mars missions operate at data rates of 120 kbps for telemetry downlink and it is desirable to study high rate communication links in the range of 100 Mbps to 1 Gbps data rates from Martian distances. This paper will present some assumed scenarios along with link design assumptions and link analysis for high capacity communications from Mars. The paper will focus on RF subsystems namely antenna and power for the downlink communication from a relay orbiter at Mars. The relay orbiter will communicate with the low orbit spacecrafts at Mars or any Martian surface elements such as robots, and relay the data back to the ground networks on Earth. The study will dive into the spacecraft downlink system design and communication link analysis between the relay orbiter and ground network on Earth for data rates ranging from 100 Mbps to 1 Gbps based on the assumed scenarios and link assumptions. With high rate links at larger distances, there will be a significant impact on the antenna and power requirements and the link design will make an attempt to minimize the mass of the RF subsystem on the spacecraft. The results of this study will be presented for three data rates 1 Gbps, 500 Mbps and 100 Mbps at maximum Mars to Earth distance of 2.67AU. The design will use a Ka-band downlink with 90% link availability, along with various ground network G/T assumptions and possible bandwidth efficient modulations. The paper will conclude with what types of high rate communication links are feasible from Martian distances and also identify a range of requirements for antenna and power technologies for these high capacity communications from Mars.

Ka-Band communications↗
NASA NTRS1975

A statistical model for telecommunication link design

An evaluation is conducted of the current telecommunication link design technique and a description is presented of an alternative method, called the probability distribution method (PDM), which is free of the disadvantages of the current technique while retaining its advantages. The PDM preserves the simplicity of the design control table (DCT) format. The use of the DCT as a management design control tool is continued. The telecommunication link margin probability density function used presents the probability of achieving any particular value of link performance. It is, therefore, possible to assess the performance risk and other tradeoffs.

Yuen, J. H.↗
NASA NTRS1991

Numerical analysis of nonminimum phase zero for nonuniform link design

As the demand for light-weight robots that can operate in a large workspace increases, the structural flexibility of the links becomes more of an issue in control. When the objective is to accurately position the tip while the robot is actuated at the base, the system is nonminimum phase. One important characteristic of nonminimum phase systems is system zeros in the right half of the Laplace plane. The ability to pick the location of these nonminimum phase zeros would give the designer a new freedom similar to pole placement. This research targets a single-link manipulator operating in the horizontal plane and modeled as a Euler-Bernoulli beam with pinned-free end conditions. Using transfer matrix theory, one can consider link designs that have variable cross-sections along the length of the beam. A FORTRAN program was developed to determine the location of poles and zeros given the system model. The program was used to confirm previous research on nonminimum phase systems, and develop a relationship for designing linearly tapered links. The method allows the designer to choose the location of the first pole and zero and then defines the appropriate taper to match the desired locations. With the pole and zero location fixed, the designer can independently change the link's moment of inertia about its axis of rotation by adjusting the height of the beam. These results can be applied to the inverse dynamic algorithms that are currently under development.

Girvin, Douglas L.↗
NASA NTRS1987

Optical communications link design for the tracking and data acquisition system

The communications performances of laser intersatellite links for a future NASA data-relay system are analyzed, and block diagrams of necessary optical terminals are generated based on technology projected to be available by 1992. Direct-detection optical communications subsystems are selected to interconnect two geosynchronous (GEO) satellites separated by 160 deg along the GEO arc and to interconnect a low-earth-orbit (LEO) satellite and either of the GEO satellites. The terminal designs are based on power budget calculations performed for the various links with and without an optical background in either the receiver or transmitter fields of view (FOVs). Optical antennas with 18-cm and 30-cm primary mirror diameters on the LEO and GEO satellites can achieve a 0.000001 average bit error rate during normal operations in each of the forward and return optical links with beginning-of-life (BOL) power margins of approximately 7 dB. With an optical background in the receiver FOV, communications in the GEO-GEO return link are interrupted, the LEO-GEO return link is undegraded, and the GEO-GEO and LEO-GEO forward links remain functional with reduced BOL power margins. With an optical background in the transmitter FOV, the GEO-GEO forward and return links are noticeably degraded, the LEO-GEO return link is only slightly degraded, and the LEO-GEO forward link remains undegraded.

Marshalek, R. G.↗
NASA NTRS2016

Proximity Link Design and Performance Options for a Mars Areostationary Relay Satellite

Current and near-term Mars relay telecommunications services are provided by a set of NASA and ESA Mars science orbiters equipped with UHF relay communication payloads employing operationally simple low gain antennas. These have been extremely successful in supporting a series of landed Mars mission, greatly increasing data return relative to direct-to-Earth lander links. Yet their relay services are fundamentally constrained by the short contact times available from the selected science orbits. Future Mars areostationary orbiters, flying in circular, equatorial, 1- sol orbits, offer the potential for continuous coverage of Mars landers and rovers, radically changing the relay support paradigm. Achieving high rates on the longer slant ranges to areostationary altitude will require steered, high-gain links. Both RF and optical options exist for achieving data rates in excess of 100 Mb/s. Several point designs offer a measure of potential user burden, in terms of mass, volume, power, and pointing requirements for user relay payloads, as a function of desired proximity link performance.

telecommunications↗
NASA NTRS2016

Proximity Link Design and Performance Options for a Mars Areostationary Relay Satellite

Current and near-term Mars relay telecommunications services are provided by a set of NASA and ESA Mars science orbiters equipped with UHF relay communication payloads employing operationally simple low-gain antennas. These have been extremely successful in supporting a series of landed Mars mission, greatly increasing data return relative to direct-to-Earth lander links. Yet their relay services are fundamentally constrained by the short contact times available from the selected science orbits. Future Mars areostationary orbiters, flying in circular, equatorial, 1- sol orbits, offer the potential for continuous coverage of Mars landers and rovers, radically changing the relay support paradigm. Achieving high rates on the longer slant ranges to areostationary altitude will require steered, high-gain links. Both RF and optical options exist for achieving data rates in excess of 100 Mb/s. Several point designs offer a measure of potential user burden, in terms of mass, volume, power, and pointing requirements for user relay payloads, as a function of desired proximity link performance.

telecommunications↗
NASA NTRS2004

Link Design and Planning for Mars Reconnaissance Orbiter (MRO) Ka-band (32 GHz) Telecom Demonstration

NASA is planning an engineering telemetry demonstration with Mars Reconnaissance Orbiter (MRO). Capabilities of Ka-band (32 GHz) for use with deep space mission are demonstrated using the link optimization algorithms and weather forecasting. Furthermore, based on the performance of previous deep space missions with Ka-band downlink capabilities, experiment plans are developed for telemetry operations during superior solar conjunction. A general overview of the demonstration is given followed by a description of the mission planning during cruise, the primary science mission and superior conjunction. As part of the primary science mission planning the expected data return for various data optimization methods is calculated. These results indicate that, given MRO's data rates, a link optimized to use of at most two data rates, subject to a minimum availability of 90%, performs almost as well as a link with no limits on the number of data rates subject to the same minimum availability.

Ka-band↗
NASA NTRS2015

Mission Control Operations: Employing a New High Performance Design for Communications Links Supporting Exploration Programs

The planetary exploration programs demand a totally new examination of data multiplexing, digital communications protocols and data transmission principles for both ground and spacecraft operations. Highly adaptive communications devices on‐board and on the ground must provide the greatest possible transmitted data density between deployed crew personnel, spacecraft and ground control teams. Regarding these requirements, this proposal borrows from research into quantum mechanical computing by applying the concept of a qubit, a single bit that represents 16 states, to radio frequency (RF) communications link design for exploration programs. This concept of placing multiple character values into a single data bit can easily make the evolutionary steps needed to meet exploration mission demands. To move the qubit from the quantum mechanical research laboratory into long distance RF data transmission, this proposal utilizes polarization modulation of the RF carrier signal to represent numbers from zero to fifteen. It introduces the concept of a binary‐to‐hexadecimal converter that quickly chops any data stream into 16‐bit words and connects variously polarized feedhorns to a single‐frequency radio transmitter. Further, the concept relies on development of a receiver that uses low‐noise amplifiers and an antenna array to quickly assess carrier polarity and perform hexadecimal to binary conversion. Early testbed experiments using the International Space Station (ISS) as an operations laboratory can be implemented to provide the most cost‐effective return for research investment. The improvement in signal‐to‐noise ratio while supporting greater baseband data rates that could be achieved through this concept justifies its consideration for long‐distance exploration programs.

Jackson, Dan E., Jr.↗
NASA NTRS1974

Data link relay design

The data link for the Ames baseline probe as applied to the MJU spacecraft specifically with an entry at Uranus is analyzed. A frequency analysis, a trajectory analysis, and a discussion of the effects on the spacecraft design by the data link are presented. The possibilities of a two-way link are considered.

Parsons, P.↗
NASA NTRS2016

Characterization of Operational Performance of Ka-Band Links in Deep Space Network

This paper presents a characterization of performance of 32-GHz Ka-band link in an operational environment. The data come from tracking of Kepler spacecraft by the NASA Deep Space Network (DSN) in the past few years. Ka-band link offers a significant signal-to-noise advantage compared to the more common X- or S-band; however, it is subject to more signal fluctuation caused by the weather. Kepler is the first mission supported by the DSN that solely rely on the higher deep space Ka-band communications link to return its high-rate science data. A well characterization of the operational performance of Kepler would benefit future Ka-band missions, especially for those operating with smaller link margin. The study examines how weather conditions at the DSN facilities (e.g., winds, clouds, rains) affect the received signal, particularly on telemetry data. It addresses questions such as how often the weather affects the link and how much degradation the link could suffer. Among the 22 Ka-band passes in 2012, heavy clouds affected one pass and two passes were impacted by high winds. The adverse weather caused at time as much as 3-dB instantaneous change in the signal to noise ratio (SNR). Estimates of degradation to the SNR as a function of wind speeds are captured based on observations. This study also quantifies the probability distribution of the variation of received signal power. With such information, future missions can better plan their link design. An optimal link design aims for just having enough margin to realize the data return with a targeted probability, with neither having too much margin that it reduces the downlink data rate nor insufficient reserve that causes frequent data outages. The study tries to provide some answers to the questions such as how much does SNR vary from one tracking pass to the next, and what is the cumulative distribution of signal fluctuation. Regarding the signal variation over many tracking passes, we found that the averaged symbol SNR (SSNR) for each pass changed by as much as 4 dB. Some variations were due to geometry such as the changing distance between spacecraft and Earth and different antenna pointing elevations. Other variations seem to be random in nature, reflecting the randomness of operational environments. Some passes were found to be quite stable, with a standard deviation of symbol SNR around 0.25 dB while others had greater variation, up to 1.4 dB. Overall, the cumulative distribution of the symbol SNR reflects that 50% of the fluctuations was less than 0.6 dB, 90% of fluctuation was within 1.6 dB and 95% within 2.2 dB. Some of the challenges in data processing, validation and modeling were captured in this paper. We observed some inconsistent measurements where operational data significantly deviate from a normal expectation. These inconsistent measurements made it hard to develop an accurate and consistent performance model, such as the degradation of signal SNR as a function of high wind. The difficulty was compounded by the fact that there were only a few Ka-band passes observed in high winds.

Pham, Timothy↗
NASA NTRS1993

Control design variable linking for optimization of structural/control systems

A method is presented to integrate the design space of structural/control system optimization problems in the case of linear state feedback control. Conventional structural sizing variables and elements of the feedback gain matrix are both treated as strictly independent design variables in optimization by extending design variable linking concepts to the control gains. Several approximation concepts including new control design variable linking schemes are used to formulate the integrated structural/control optimization problem as a sequence of explicit nonlinear mathematical programming problems. Examples which involve a variety of behavior constraints, including constraints on dynamic stability, damped frequencies, control effort, peak transient displacement, acceleration, and control force limits, are effectively solved by using the method presented.

Jin, Ik Min↗
NASA NTRS1988

Design of an optical PPM communication link in the presence of component tolerances

A systematic approach is described for estimating the performance of an optical direct detection pulse position modulation (PPM) communication link in the presence of parameter tolerances. This approach was incorporated into the JPL optical link analysis program to provide a useful tool for optical link design. Given a set of system parameters and their tolerance specifications, the program will calculate the nominal performance margin and its standard deviation. Through use of these values, the optical link can be designed to perform adequately even under adverse operating conditions.

Chen, C.-C.↗
NASA NTRS1991

Control design variable linking for optimization of structural/control systems

In this study a method is presented to integrate the design space of structural/control system optimization problems in the case of state feedback control. Conventional structural sizing variables and elements of the feedback gain matrix are both treated as strictly independent design variables in the optimization by extending design variable linking concepts to the control gains. Examples which involve a variety of behavior constraints, including dynamic transient response and control force limits, are effectively solved by using the method presented.

Jin, I. M.↗
NASA NTRS1982

A note on deep space optical communication link parameters

Topical communication in the context of a deep space communication link. Communication link analysis at the optical frequencies differs significantly from that at microwave frequencies such as the traditional S and X-bands used in deep space applications, due to the different technology of transmitter, antenna, modulators, and receivers. In addition, the important role of quantum noise in limiting system performance is quite different than that of thermal noise. The optical link design is put in a design control table format similar to a microwave telecom link design. Key considerations unique to the optical link are discussed.

Dolinar, S. J.↗