Steven Constantine

Design of a high-speed space modem for the lunar laser communications demonstration

The space terminal modem for the Lunar Laser Communications Demonstration (LLCD) provides duplex lasercom capabilities between the Earth and a satellite in lunar orbit with a 0.5-W optical transmitter delivering downlink data rates of 39-620 Mbps and an optically-preamplified direct detection receiver supporting uplink data rates of 10-19 Mbps. The modem consists of four subsystem modules: digital electronics, analog electronics, power conditioning, and electro-optics. This modular approach permits subsystems to be built and tested in parallel and provides design flexibility to address evolving requirements. Other important design considerations for the modem include the utilization of commercial-off- the-shelf (COTS) components to reduce delivery time, cost, minimization of size, weight, and power, and the ability to survive launch conditions and operate over a broad temperature range in lunar orbit.

Ultra-long Distance Free Space Laser Communications

We present a survey of state-of-the-art free space laser communication transmitter and receiver designs and technologies for ultra-long-distance high-speed links. High-performance power-efficient implementations for photon-counting, coherent, and optically-preamplified receivers are discussed.

A New Optical Communication Architecture for Delivering Extremely Large Volumes of Data from Space to Ground

Space-based laser communication has been demonstrated at rates ranging from 10’s of Mbps to a few Gbps for near-Earth crosslinks and for direct-to-Earth downlinks from ranges as far as the Moon. We describe a novel space-to-Earth communication architecture that can deliver many terabytes of data regularly, if the user is willing to accept certain amounts of delay. With careful design of space and ground terminals, and by tapping the recent advances in integrated extremely high rate modems developed by the fiber telecommunications industry, we believe that space terminal cost, ground terminal cost, and operations costs can be kept much lower than present day radio-frequency or proposed optical systems while increasing the amount of data delivery by orders of magnitude.

Overview and On-orbit Performance of the Lunar Laser Communication Demonstration Uplink

We present an implementation overview and demonstrated error-free coded performance over the 400,000-km link between an Earth-based laser communication terminal and the LADEE satellite orbiting the moon at 9.72-Mbps and 19.44-Mbps uplink rates.

Nonlinearity mitigation of a 40-Watt 1.55-micron uplink transmitter for lunar laser communications

Improvements to a ground-based 40W 1.55 micron uplink transmitter for the Lunar Laser Communications Demonstration (LLCD) are described. The transmitter utilizes four 10 W spatial-diversity channels to broadcast 19.4 - 38.9 Mbit/s rates using a variable-duty cycle 4-ary pulse position modulation. At the lowest rate, with a 32-to-1 duty cycle, this leads to 320 W peak power per transmitter channel. This paper discusses a simplification of the transmitter that uses super-large-area single mode fiber and polarization control to mitigate high peak power nonlinear impairments.

Laser communications for human space exploration in cislunar space: ILLUMA-T and O2O

In recent years, NASA has been developing a scalable, modular space terminal architecture to provide low-cost laser communications for a wide range of near-Earth applications. This development forms the basis for two upcoming demonstration missions. The Integrated Low-Earth Orbit Laser Communications Relay Demonstration User Modem and Amplifier Optical Communications Terminal (ILLUMA-T) will develop a user terminal for platforms in low-Earth orbit which will be installed on the International Space Station and demonstrate relay laser communications via NASA’s Laser Communication Relay Demonstration (LCRD) in geo-synchronous orbit. The Orion EM-2 Optical Communication Demonstration (O2O) will develop a terminal which will be installed on the first manned launch of the Orion Crew Exploration Vehicle and provide direct-to-Earth laser communications from lunar ranges. We describe the objectives and link architectures of these two missions which aim to demonstrate the operational utility of laser communications for manned exploration in cislunar space.

TeraByte InfraRed Delivery (TBIRD): a demonstration of large-volume direct-to-Earth data transfer from low-Earth orbit

Delivery of large volumes of data from low-Earth orbit to ground is challenging due to the short link durations associated with direct-to-Earth links. The short ranges that are typical for such links enable high data rates with small terminals. While the data rate for radio-frequency links is typically limited by available spectrum, optical links do not have such limitations. However, to date, demonstrations of optical links from low-Earth orbit to ground have been limited to ~10 to ~1000 Mbps. We describe plans for NASA’s TeraByte InfraRed Delivery (TBIRD) system, which will demonstrate a direct-to-Earth optical communication link from a CubeSat in low-Earth orbit at burst rates up to 200 Gbps. Such a link is capable of delivering >50 Terabytes per day from a small spacecraft to a single small ground terminal.