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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Acquisition, Tracking, and Pointing Using Earth Thermal Images for Deep Space Optical Communications

The feasibility of using long wavelength Earth thermal (infrared) images for telescope tracking/pointing application. for both Deep Space Free- pace Optical Communications has been investigated and is reported her. The advantage of this technology rests on using full Earth images in this band, which yield more accurate estimates of geometric centroids than that of Earth images in the visible band. Another major advantage is that these images are nearly independent of Earth phase angle. The results of the study show that at a Mars range, with currently available sensors, a noise equivalent angle of 10 to 150 nanoradians and a bias error of better than 80 nanoradians can be obtained. This enables precise pointing of the optical communications beam for high data rate links.

free-space optical communication↗
NASA NTRS1989

Estimation and tracking for deep-space optical communications

The importance of pointing and tracking is demonstrated with current deep-space optical communications system concepts. Maximum-likelihood (ML), minimum square counting-error (MSCE), and maximum product (MP) estimation algorithms (or decision rules) are derived to estimate the location of the receiving station to subpixel resolution. Comparisons of the above algorithms are made, via Monte Carlo computer simulation, in terms of estimator's bias and variance. Optical communication link analyses are made for a typical earth-Mars scenario, to gain engineering insights. It is observed that both the ML rule and the MSCE rule perform better than the MP rule.

Win, Moe Zaw↗
NASA NTRS1988

Optical communications for future deep-space missions

The development of key technologies for an optical communications system for deep-space probes is discussed. Aspects of the technology include the pulse-position modulation technique for data transmission, a solid-state laser with a Nd:YAG crystal end, nondiffraction-limited receivers, and the application of avalanche photodiodes to improve photon detection. Mission benefits and flight opportunities and applications are discussed. Experiments to test optical communication systems are being planned for the Space Shuttle and the Mars Rover Sample Return misson. Future missions which will probably use the system include Cassini and the Mariner Mark II.

Rayman, Marc D.↗
NASA NTRS1990

A Plan for the Development and Demonstration of Optical Communications for Deep Space

In this article, an overall plan for the development and demonstration of optical communications for deep-space applications is presented. The current state of the technology for optical communications is presented. Then, the development and demonstration plan is presented in two parts: the overall major systems activities, followed by the generic technology developments that will enable them. The plan covers the path from laboratory subsystems demonstrations out to a full-scale flight experiment system for the proposed Mars Communications Relay Orbiter mission.

Lesh, J. R.↗
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 NTRS2018

Performance and Characterization of a Modular Superconducting Nanowire Single Photon Detector System for Space-to-Earth Optical Communications Links

Space-to-ground photon-counting optical communication links supporting high data rates over large distances require enhanced ground receiver sensitivity in order to reduce the mass and power burden on the spacecraft transmitter. Superconducting nanowire single-photon detectors (SNSPDs) have been demonstrated to offer superior performance in detection efficiency, timing resolution, and count rates over semiconductor photodetectors, and are a suitable technology for high photon efficiency links. Recently photon detectors based on superconducting nanowires have become commercially available, and we have assessed the characteristics and performance of one such commercial system as a candidate for potential utilization in ground receiver designs. The SNSPD system features independent channels which can be added modularly, and we analyze the scalability of the system to support different data rates, as well as consider coupling concepts and issues as the number of channels increases.

Superconductors↗
NASA NTRS1985

Direct-detection optical communication with color coded pulse position modulation signaling

The performance characteristics of a direct-detection optical communication system which is based on a laser transmitter which produces single light pulses at selected nonoverlapping optical center frequencies are discussed. The signal format, called color coded pulse position modulation (CCPPM), uses more of the total available response bandwidth characteristics of the photodetector than does ordinary PPM signaling. The advantages of CCPPM signaling are obtained at the expense of an increased optical bandwidth of the transmitted signal and a more complicated transmitter and receiver structure. When the signal format is used in conjunction with block length Reed-Solomon codes, high data rates and reliable high-speed optical communications under conditions of optimal energy efficiency are obtained.

Davidson, F.↗
NASA NTRS2014

Networked Operations of Hybrid Radio Optical Communications Satellites

In order to address the increasing communications needs of modern equipment in space, and to address the increasing number of objects in space, NASA is demonstrating the potential capability of optical communications for both deep space and near-Earth applications. The Integrated Radio Optical Communications (iROC) is a hybrid communications system that capitalizes on the best of both the optical and RF domains while using each technology to compensate for the other's shortcomings. Specifically, the data rates of the optical links can be higher than their RF counterparts, whereas the RF links have greater link availability. The focus of this paper is twofold: to consider the operations of one or more iROC nodes from a networking point of view, and to suggest specific areas of research to further the field. We consider the utility of Disruption Tolerant Networking (DTN) and the Virtual Mission Operation Center (VMOC) model.

Delay Tolerant Networking↗
NASA NTRS2005

Airborne Optical Communications Demonstrator Design And Preflight Test Results

A second generation optical communications demonstrator (OCD-2) intended for airborne applications like air-to-ground and air-to-air optical links is under development at JPL. This development provides the capability for unidirectional high data rate (2.5-Gbps) transmission at 1550-nm, with the ability to receive an 810-nm beacon to aid acquisition pointing and tracking. The transmitted beam width is nominally 200-(micro)rad. A 3x3 degree coarse field-of-view (FOV) acquisition sensor with a much smaller ~3-mrad FOV tracking sensor is incorporated. The OCD-2 optical head will be integrated to a high performance gimbal turret assembly capable of providing pointing stability of 5- microradians from an airborne platform. Other parts of OCD-2 include a cable harness, connecting the optical head in the gimbal turret assembly to a rugged electronics box. The electronics box will house: command and control processors, laser transmitter, data-generation-electronics, power conversion/distribution hardware and state-of-health monitors. The entire assembly will be integrated and laboratory tested prior to a planned flight demonstrations.

optical communications↗
NASA NTRS2009

LDPC-PPM Coding Scheme for Optical Communication

In a proposed coding-and-modulation/demodulation-and-decoding scheme for a free-space optical communication system, an error-correcting code of the low-density parity-check (LDPC) type would be concatenated with a modulation code that consists of a mapping of bits to pulse-position-modulation (PPM) symbols. Hence, the scheme is denoted LDPC-PPM. This scheme could be considered a competitor of a related prior scheme in which an outer convolutional error-correcting code is concatenated with an interleaving operation, a bit-accumulation operation, and a PPM inner code. Both the prior and present schemes can be characterized as serially concatenated pulse-position modulation (SCPPM) coding schemes. Figure 1 represents a free-space optical communication system based on either the present LDPC-PPM scheme or the prior SCPPM scheme. At the transmitting terminal, the original data (u) are processed by an encoder into blocks of bits (a), and the encoded data are mapped to PPM of an optical signal (c). For the purpose of design and analysis, the optical channel in which the PPM signal propagates is modeled as a Poisson point process. At the receiving terminal, the arriving optical signal (y) is demodulated to obtain an estimate (a^) of the coded data, which is then processed by a decoder to obtain an estimate (u^) of the original data.

Barsoum, Maged↗
NASA NTRS1986

An entropy maximization problem related to optical communication

In relation to a problem in optical communication, the paper considers the general problem of maximizing the entropy of a stationary radom process that is subject to an average transition cost constraint. By using a recent result of Justesen and Hoholdt, an exact solution to the problem is presented and a class of finite state encoders that give a good approximation to the exact solution is suggested.

Mceliece, R. J.↗
NASA NTRS1980

Prospects for very deep space optical communication using photon-counting links

An investigation is conducted regarding the feasibility to use an optical communication system in connection with space missions involving a study of stars and, possibly, planetary systems in the vicinity of the solar system. A possible candidate for the considered kind of mission would be Barnard's Star, at six light years distance. Pierce et al. (1981), have shown that the capacity of a photon-counting link in the presence of thermal noise at low temperature is essentially the same as for microwave. The conducted investigation assumes the employment of a pulse position modulation scheme limited by technology to approximately 1,000,000 positions. The use of an optical communication system similar to the considered type is found to be very likely for the contemplated kind of space mission.

Posner, E. C.↗
NASA NTRS1986

Mars to earth optical communication link for the proposed Mars Sample Return mission roving vehicle

The Mars Sample Return (MSR) mission planed for 1989 will deploy a rover from its landing craft to survey the Martian surface. During traversals of the rover from one site to the next in search of samples, three-dimensional images from a pair of video cameras will be transmitted to earth; the terrestrial operators will then send back high level direction commands to the rover. Attention is presently given to the effects of wind and dust on communications, the architecture of the optical communications package, and the identification of technological areas requiring further development for MSR incorporation.

Sipes, Donald L., Jr.↗
NASA NTRS2020

Simultaneous Optical Links with the Inter-Satellite Omnidirectional Optical Communicator

As the onboard data volume for smaller platforms such as CubeSats increases, Radio Frequency (RF) communications systems may be unable to adequately support the required downlink demand. Optical communications (lasercom) systems can relieve the data bottleneck as they can support higher data throughput than RF for comparable Size, Weight, and Power (SWaP). Lasercom crosslinks are of particular interest for spacecraft swarms and constellations because they enable additional mission robustness for distributed science observations and remote sensing applications. The Inter-Satellite Omnidirectional optical Communicator (ISOC) is capable of supporting simultaneous lasercom crosslinks between multiple spacecraft at separations of up to thousands of kilometers in orbit. The ISOC architecture features a truncated dodecahedron chassis containing an array of photodetectors and gimbal-less MEMS mirrors, enabling full-duplex communications. The main objectives of the ISOC terminal include: 1) full sky coverage, 2) Gbps data rates, and 3) the ability to maintain multiple simultaneous links. We show ISOC can support up to 12 simultaneous links with the current architecture at 1-Gbps at 200-km separation with 10-9 BER. Compared to current lasercom transceivers (i.e., point-to-point), ISOC offers increased throughput performance for similar SWaP. A detailed link budget for both scenarios is presented, and the limiting factors for maximum number of simultaneous links are discussed.

Cahoy, Kerri↗