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NASA NTRSDate not supplied

An Envisioned Future for Space Optical Communications

Since the beginning of the Space Age, NASA has been a leader in developing space communications and navigation technologies— especially during the Apollo missions to the Moon and NASA’s initial foray into deep space. To support future exploration and science needs, NASA is gradually introducing optical communications technologies to augment its radio frequency (RF) systems. Optical communications will enable new science and exploration missions by providing high data rates and better navigation over long distances. NASA has already flown several optical communications demonstrations, including the Lunar Laser Communications Demonstration (LLCD), the Laser Communications Relay Demonstration (LCRD), and the Terabyte Infrared Delivery (TBIRD) system. Historically, NASA has partnered with the Jet Propulsion Laboratory (JPL) and the Massachusetts Institute of Technology Lincoln Laboratory (MIT/LL) to develop optical communications technology. In addition to pursuing optical communications, NASA’s Space Communications and Navigation (SCaN) Program is undergoing a paradigm shift and moving away from government owned and operated networks to using commercial services whenever possible. In partnership with SCaN, NASA’s Space Technology Mission Directorate (STMD) has identified key technologies that need to be developed to support future space communications and navigation, including enhanced RF, optical, and 3rd Generation Partnership (3GPP) cellular capabilities, as well as high-speed networking. This paper briefly describes some current and upcoming optical demonstrations and provides an overview of STMD’s envisioned future for optical communications and navigation in the 2030+ timeframe.

Bernard L Edwards↗
NASA NTRS2006

Holographic Plossl Retroreflectors

Holographic retroreflectors that function equivalently to Plossl eyepieces have been developed and used in free-space optical communication systems that utilize laser beams. Plossl eyepieces are well known among telescope designers. They have been adopted for use a retroreflectors and as focusing elements (for reception) and collimating elements (for transmission) in optical communication systems. A retro-reflector that incorporates a Plossl eyepiece is termed a cat's-eye retroreflector.

Waluschka, Eugene↗
NASA NTRS1991

Spectral filters for laser communications

Optical communication systems must perform reliabily under strong background light interference. Since the transmitting lasers operate within a narrow spectral band, high signal to noise ratios can be achieved when narrowband spectral optical filters can be used to reject out of band light. Here, a set of general requirements for such filters are developed, and an overview is given of suitable spectral filter technologies for optical communication systems.

Shaik, K.↗
NASA NTRS2016

Photon Counting Detector Array Algorithms for Deep Space Optical Communications

For deep-space optical communications systems utilizing an uplink optical beacon, a single-photon-counting detector array on the flight terminal can be used to simultaneously perform uplink tracking and communications as well as accurate downlink pointing at photon-starved (pW/sq. m) power levels. In this paper, we discuss concepts and algorithms for uplink signal acquisition, tracking, and parameter estimation using a photon-counting camera. Statistical models of detector output data and signal processing algorithms are presented, incorporating realistic effects such as Earth background and detector/readout blocking. Analysis and simulation results are validated against measured laboratory data using state-of-the-art commercial photon-counting detector arrays, demonstrating sub-microradian tracking errors under channel conditions representative of deep space optical links.

beacon tracking↗
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 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 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 NTRS2007

Wide-Band, High-Quantum-Efficiency Photodetector

A design has been proposed for a photodetector that would exhibit a high quantum efficiency (as much as 90 percent) over a wide wavelength band, which would typically be centered at a wavelength of 1.55 m. This and similar photodetectors would afford a capability for detecting single photons - a capability that is needed for research in quantum optics as well as for the practical development of secure optical communication systems for distribution of quantum cryptographic keys. The proposed photodetector would be of the hot-electron, phonon-cooled, thin-film superconductor type. The superconducting film in this device would be a meandering strip of niobium nitride. In the proposed photodetector, the quantum efficiency would be increased through incorporation of optiA design has been proposed for a photodetector that would exhibit a high quantum efficiency (as much as 90 percent) over a wide wavelength band, which would typically be centered at a wavelength of 1.55 m. This and similar photodetectors would afford a capability for detecting single photons - a capability that is needed for research in quantum optics as well as for the practical development of secure optical communication systems for distribution of quantum cryptographic keys. The proposed photodetector would be of the hot-electron, phonon-cooled, thin-film superconductor type. The superconducting film in this device would be a meandering strip of niobium nitride. In the proposed photodetector, the quantum efficiency would be increased through incorporation of opti-

Jackson, Deborah↗
NASA NTRS1974

Dynamic polarization compensating system for optical communications receiver

Electro-optic cell is located in optical path of input light beam. Cell includes crystal for controlling phase between two polarization states. Cell axes are rotated 45 deg to receiver axes defined by vertical and horizontal polarization states. Voltage across cell compensates for bias by introducing different phase retardation along crystal axes.

Fitzmaurice, M. W.↗
NASA NTRS1994

Improved Electro-Optical Switches

Improved single-pole, double-throw electro-optical switches operate in switching times less than microsecond developed for applications as optical communication systems and networks of optical sensors. Contain no moving parts. In comparison with some prior electro-optical switches, these are simpler and operate with smaller optical losses. Beam of light switched from one output path to other by applying, to electro-optical crystal, voltage causing polarization of beam of light to change from vertical to horizontal.

Nelson, Bruce N.↗
NASA NTRS1990

Deep space optical communications - A program update

Technological developments leading toward the use of optical communications on deep-space missions are reviewed. Developments in the characterization of atmospheric visibility and the development of advanced composite materials for use in optical communications systems are discussed. System demonstrations involving the Galileo Optical Experiment and a very lightweight optical communications package intended for the Cassini mission to Saturn are addressed. Proposed flight experiments and a deep-space optical communication long-range plan are discussed.

Lesh, James R.↗
NASA NTRS1992

Confidence range estimate of extended source imagery acquisition algorithms via computer simulations

Spatial acquisition using the sun-lit Earth as a beacon source provides several advantages over active beacon-based systems for deep-space optical communication systems. However, since the angular extend of the Earth image is large compared to the laser beam divergence, the acquisition subsystem must be capable of resolving the image to derive the proper pointing orientation. The algorithms used must be capable of deducing the receiver location given the blurring introduced by the imaging optics and the large Earth albedo fluctuation. Furthermore, because of the complexity of modelling the Earth and the tracking algorithms, an accurate estimate of the algorithm accuracy can only be made via simulation using realistic Earth images. An image simulator was constructed for this purpose, and the results of the simulation runs are reported.

Chen, CHIEN-C.↗
NASA NTRS1983

Guidance and control of MIR TDL radiation via flexible hollow metallic rectangular pipes and fibers for possible LHS and other optical system compaction and integration

Flexible hollow metallic rectangular pipes and infrared fibers are proposed as alternate media for collection, guidance and manipulation of mid-infrared tunable diode laser (TDL) radiation. Certain features of such media are found to be useful for control of TDL far field patterns, polarization and possibly intensity fluctuations. Such improvement in dimension compatibility may eventually lead to laser heterodyne spectroscopy (LHS) and optical communication system compaction and integration. Infrared optical fiber and the compound parabolic coupling of light into a hollow pipe waveguide are discussed as well as the design of the waveguide.

Yu, C.↗