The concept of deep-space optical communications was formulated shortly after the invention of lasers. The promise of laser communications, high data rate delivery with significantly reduced aperture size for the flight terminal, led to the pursuit of several successful experiments from Earth orbit and provided the incentive for further demonstrations to extend the range to deep space. This paper is aimed at presenting an overview of the current status of optical communications with an emphasis on deep space. Future perspectives and applications of optical communications related to near-Earth and interplanetary communications are also addressed.

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Deep-Space Optical Communications: Future Perspectives and Applications

Current key initiatives in deep-space optical communications are treated in terms of historical context, contemporary trends, and prospects for the future An architectural perspective focusing on high-level drivers, systems, and related operations concepts is provided Detailed subsystem and component topics are not addressed A brief overview of past ideas and architectural concepts sets the stage for current developments Current requirements that might drive a transition from radio frequencies to optical communications are examined These drivers include mission demand for data rates and/or data volumes; spectrum to accommodate such data rates; and desired power, mass, and cost benefits As is typical, benefits come with associated challenges For optical communications, these include atmospheric effects, link availability, pointing, and background light The paper describes how NASA's Space Communication and Navigation Office will respond to the drivers, achieve the benefits, and mitigate the challenges, as documented in its Optical Communications Roadmap Some nontraditional architectures and operations concepts are advanced in an effort to realize benefits and mitigate challenges as quickly as possible Radio frequency communications is considered as both a competitor to and a partner with optical communications The paper concludes with some suggestions for two affordable first steps that can yet evolve into capable architectures that will fulfill the vision inherent in optical communications

Deep-space optical communications

The nanosatellite optical downlink experiment (NODE) implements a free-space optical communications (lasercom) capability on a CubeSat platform that can support low earth orbit (LEO) to ground downlink rates>10  Mbps. A primary goal of NODE is to leverage commercially available technologies to provide a scalable and cost-effective alternative to radio-frequency-based communications. The NODE transmitter uses a 200-mW 1550-nm master-oscillator power-amplifier design using power-efficient M-ary pulse position modulation. To facilitate pointing the 0.12-deg downlink beam, NODE augments spacecraft body pointing with a microelectromechanical fast steering mirror (FSM) and uses an 850-nm uplink beacon to an onboard CCD camera. The 30-cm aperture ground telescope uses an infrared camera and FSM for tracking to an avalanche photodiode detector-based receiver. Here, we describe our approach to transition prototype transmitter and receiver designs to a full end-to-end CubeSat-scale system. This includes link budget refinement, drive electronics miniaturization, packaging reduction, improvements to pointing and attitude estimation, implementation of modulation, coding, and interleaving, and ground station receiver design. We capture trades and technology development needs and outline plans for integrated system ground testing.

https://www.spiedigitallibrary.org/journals/optical-engineering/volume-55/issue-11/111610/Nanosatellite-optical-downlink-experiment-design-simulation-and-prototyping/10.1117/1.OE.55.11.111610.pdf

Nanosatellite optical downlink experiment: design, simulation, and prototyping

NASA's Space Communications and Navigation (SCaN) program at NASA headquarters is pursuing a vibrant and wide-ranging optical communications program for further planetary and near-Earth missions following the spectacular success of NASA's Lunar Laser Communication Demonstration (LLCD) from the Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft orbiting the moon in 2013. This invited paper will discuss NASA's new laser communication missions, key scenarios and details, and the plans to infuse this new technology into NASA's existing communications networks.

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/9354/93540E/NASAs-optical-communications-program-for-2015-and-beyond/10.1117/12.2087132.pdf

NASA's optical communications program for 2015 and beyond

The Optical Communications Telescope Laboratory (OCTL) located on Table Mountain near Wrightwood, CA served as
an alternate ground terminal to the Lunar Laser Communications Demonstration (LLCD), the first free-space laser
communication demonstration from lunar distances. The Lunar Lasercom OCTL Terminal (LLOT) Project utilized the
existing 1m diameter OCTL telescope by retrofitting: (i) a multi-beam 1568 nm laser beacon transmitter; (ii) a tungsten
silicide (WSi) superconducting nanowire single photon detector (SNSPD) receiver for 1550 nm downlink; (iii) a
telescope control system with the functionality required for laser communication operations; and (iv) a secure network
connection to the Lunar Lasercom Operations Center (LLOC) located at the Lincoln Laboratory, Massachusetts Institute
of Technology (LL-MIT). The laser beacon transmitted from Table Mountain was acquired by the Lunar Lasercom
Space Terminal (LLST) on-board the Lunar Atmospheric Dust Environment Explorer (LADEE) spacecraft and a 1550
nm downlink at 39 and 78 Mb/s was returned to LLOT. Link operations were coordinated by LLOC. During October
and November of 2013, twenty successful links were accomplished under diverse conditions. In this paper, a brief
system level description of LLOT along with the concept of operations and selected results are presented.

LLCD Operations Using the Optical Communications Telescope Laboratory (OCTL)

Optical communications is a key technology to meet the bandwidth expansion required in the global information grid High bandwidth bi-directional links between sub-orbital platforms and ground and space terminals can provide a seamless interconnectivity for rapid return of critical data to analysts The JPL Optical Communications Telescope Laboratory (OCTL) is located in Wrightwood California at an altitude of 22km This 200 sq-m facility houses a state-of- the-art 1-m telescope and is used to develop operational strategies for ground-to-space laser beam propagation that include safe beam transmission through navigable air space, adaptive optics correction and multi-beam scintillation mitigation, and line of sight optical attenuation monitoring JPL has received authorization from international satellite owners to transmit laser beams to more than twenty retro-reflecting satellites This paper presents recent progress in the development of these operational strategies tested by narrow laser beam transmissions from the OCTL to retro-reflecting satellites We present experimental results and compare our measurements with predicted performance for a variety of atmospheric conditions

Development of Laser Beam Transmission Strategies for Future Ground-to-Space Optical Communications

A conceptual design study titled Deep-Space Optical Terminals was recently completed for an optical communication technology demonstration from Mars in the 2018 time frame. We report on engineering trades for the entire system, and for individual subsystems including the flight terminal, the ground receiver and the ground transmitter. A point design is described to meet the requirement for greater than 0.25 Gb/s downlink from the nearest distance to Mars of 0.42 AU with a maximum mass and power allocation of 40 kg and 110 W. Furthermore, the concept design addresses link closure at the farthest Mars range of 2.7 AU. Maximum uplink data-rate of 0.3 Mb/s and ranging with 30 cm precision are also addressed.

Deep-space optical terminals (DOT)

DOT Ground Laser Receiver: Overview and Major Trades

Optical Ground Station 1 (OGS1) is the first of a new breed of dedicated ground terminals to support NASA’s developing space-based optical communications infrastructure. It is based at NASA’s Optical Communications Telescope Laboratory (OCTL) at the Table Mountain Observatory near Wrightwood, CA. The system will serve as the primary ground station for NASA’s Laser Communications Relay Demonstration (LCRD) experiment. This paper presents an overview of the OCTL telescope facility, the OGS1 ground-based optical communications systems, and the networking and control infrastructure currently under development. The OGS1 laser safety systems and atmospheric monitoring systems are also briefly described.

William T. Roberts

Papers

LLCD Operations Using the Optical Communications Telescope Laboratory (OCTL)

Development of Laser Beam Transmission Strategies for Future Ground-to-Space Optical Communications

Deep-space optical terminals (DOT)

DOT Ground Laser Receiver: Overview and Major Trades

Overview of Ground Station 1 of the NASA space communications and navigation program