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Bernard EdwardsChief, Communications Systems EngineerNASA Goddard Space Flight CenterBernard.L.Edwards@nasa.gov

Overview for Future In-Space Operations

October 2013

The Laser Communications Relay Demonstration (LCRD) will demonstrate optical communications relay services between GEO and Earth over an extended period, and thereby gain the knowledge and experience base that will enable NASA to design, procure, and operate cost-effective future optical communications systems and relay networks.

LCRD is the next step in NASA eventually providing an optical communications service on the Next Generation Tracking and Data Relay Satellites

Mission Statement

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Mission Overview

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LCRD Flight Payload2 Optical Relay Terminals• 10.8 cm aperture• 0.5 W transmitterSpace Switching Unit

Table Mountain, CA White Sands, NM

LCRD Payload and Host

Spacecraft

1244 Mbps DPSK311 Mbps 16-PPM

LCRD Ground Station 215 cm transmit aperture• 20 W transmitter40 cm receive aperture

1244 Mbps DPSK311 Mbps 16-PPM

LCRD Ground Station 11 m transmit and

receive aperture• 20 W transmitter

Mission Concept• Orbit: Geosynchronous

– Longitude TBD between 162ºW to 63ºW

• 2 years mission operations• 2 operational GEO Optical Relay Terminals• 2 operational Optical Earth Terminals• Optical relay services provided

– Ability to support a LEO User

• Hosted Payload• Launch Date: Dec 2017

NASA Optical Communication Technology Strategy

Near EarthFlight Terminal

Deep Space Flight Terminal

SCaN OpticalGround Infrastructure

Near Earth Missions

LLCDLADEE Demo

Optical CommGround Stations

(LLGT, OCTL, Tenerife)

Key DOT Technology Identification

&Development

Technology Transfer

GEO Demo –LCRD

2013

Technology Investment and Development

LCRD

LEO Demo

2017 2020 2025

Commercialization

Optical Module

Controller Electronics

DPSKModem

Mini FOG

Flexured Gimbal Mount

CFLOS Analysis, Optical Comm Cross Support

PPM Laser TransmitterLow-noise laser

Spacecraft disturbance rejection platform, piezo-based point-ahead mechanism

SNSPD arrays, photon counting space receiver, ground receiver detection array, NAF APD/nanowire det., COTS quadrant spatial-acquisition detectors

SCaN Operational Optical Ground StationsAdded as Mission Needs Require

(including International Space Agency Sites)

•Stabilization

• Detectors

• Vibration

• Systems Engineering

• Laser Power/Life

• Pointing

Candidate Deep Space Host Demo Mission

Other Deep Space Missions

Commercialized

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Leveraging the Lunar Laser Communications Demonstration (LLCD)

• …• NASA’s first high rate space laser communications demonstration

• Space terminal integrated on the Lunar Atmosphere and Dust Environment Explorer (LADEE)

• Launched on 6 September 2013 from Wallops Island on Minotaur V– Completed 1 month transfer (possible lasercomm ops)– 1 month lasercomm demo @ 400,000 km

• 250 km lunar orbit– 3 months science

• 50 km orbit• 3 science Payloads

– Neutral Mass Spectrometer– UV Spectrometer– Lunar Dust Experiment

LLCD Flight Hardware

Optical Module• Designed and fabricated by MIT LL• Inertially-stabilized 2-axis gimbal• Fiber-coupled to Modem transmit (Tx) and receive

(Rx)

Controller Electronics• Built by Broad Reach Engineering for

OM, MM control• Telemetry & Command (T&C)

interface to S/C

Modem Module (MM)• Designed and fabricated by MIT LL• Pulse Position Modulation Only• Digital encoding/decoding electronics,1550 nm

fiber Tx and Rx

All Modules Interconnected via electrical cables and optical fibers

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Lunar LasercomSpace Terminal

Lunar LasercomOCTL Terminal (JPL)

Table Mtn, CA

Lunar LasercomGround Terminal

LADEE Spacecraft

1.55 um band

Lunar LasercomOptical GroundSystem (ESA)

White Sands, NM

Tenerife

DL 622 MbpsUL 20 Mbps

DL > 38 MbpsUL > 10 Mbps

DL > 38 Mbps

Modem Module

Controller Electronics

Optical Module

LCRD will leverage designs and hardware from LLCD, with modifications to satisfy mission requirements.

LLCD Provides the Foundation for LCRD

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LCRD Design Reference Mission

• Simultaneous multiple real-time user support and multiple store & forward user support multiplexed on single trunkline

• Different user services: frame, DTN, …• Scheduled and Unscheduled Ground Station handovers• Number of Users, Mission Operations Centers (MOCs),

and Payloads scalable• Emulation of different relay and user location and orbits

by the insertion of delays and disconnections in the data paths

User 1 S/C

User n S/CGS-1 GS-m

User 1 MOC User k MOC

LMOC

Active optical link

Future optical link

Terrestrial Internet ProtocolNetwork

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• Hosted on a Space Systems/Loral Commercial Communications Satellite

• Flight Payload– Two MIT LL designed Optical Modules (OM)– Two Integrated Modems that can support both

Differential Phase Shift Keying (DPSK) and Pulse Position Modulation (PPM)

– Two OM Controllers that interface with the Host S/C

– Space Switching Unit to interconnect the two Integrated Modems and perform data processing

• Two Optical Communications Ground Stations– Upgraded JPL OCTL (Table Mountain, CA)– Upgraded LLCD LLGT (White Sands, NM)

• LCRD Mission Operations Center (LMOC)– Connected to the two Optical Communications

Ground Stations– Connected to Host S/C MOC

LCRD Baseline

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LCRD GS and Optical Space Terminal Location

GEO Locations were chosen to ensure at least 20° above horizon for both Ground Stations

161W 112W 63W

OST Possible Location

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LCRD Mission Architecture

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LCRD Flight Payload

Host MissionOps Center (HMOC)

NASA GSFC

Table Mountain, CA White Sands, NM

Host SpacecraftRF Link

LCRD Payload and Host

Spacecraft

1550 nm band

LCRD Ground Station-21 @ 15 cm @ 20 W (PPM/DPSK)1 @ 40 cm (PPM/DPSK)

10 cm @ 0.5 W (PPM/DPSK)DPSK at 1.244 Gbps

PPM at 311 Mbps

NISNLCRD Ground Station-1

1 m @ 20 W (PPM/DPSK)

1550 nm band

Based on Lunar Lasercom

Ground Terminal (LLGT)

LCRD Optical Ground System (LOGS) -

OCTL

LCRD Mission Ops Center (LMOC)

NISN NISN

Chiller for cooling trailer and telescopes

Converted 40-ft ISO container housing controls, modems, and

operator console

18-ft Clamshell

weather cover

4x UL Transceivers4x DL Receivers

Environmental enclosure

surrounding UL and DL telescopes

Relay Optical Link

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Relay Link Features:• Coding/Interleaving at the link edges

o Rate ½ DVB-S2 codec (LDPC)o 1 second of interleaving for atmospheric fading

mitigation• Data can be relayed or looped back• PPM or DPSK can be chosen independently on each

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LCRD Payload

Bus Overview• Existing SS/L commercial satellite bus

Bus and Payload Overview

Star Tracker Star Tracker

Optical Module

Optical Module

CE CE

ModemA

Switch

ModemB

ModemA

ModemB

Radiator (back view)

Equipment Panel& Radiator

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1

2

2

• LCRD package is located on the S/C Earth deck, similar to a typical North panel extension

• The enclosure North-facing surface is the main radiator with Optical Solar Reflectors

• Secondary LCRD radiator panel is on the South side

• Star trackers located on the top of the enclosure for optimal registration with OMs

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Payload Hardware Overview

Integrated Modem (qty 2)– 0.5 W transmitter; optically pre-amplified

receiver– DPSK and PPM modulation– 27 kg, 130 W– Supports Tx and Rx frame processing

No on-board coding and interleaving

Optical Module (qty 2)– Gimbaled telescope (elevation over azimuth)

12° half-angle Field of Regard– 10.8 cm aperture, 14 kg– Local inertial sensor stabilization

Controller Electronics (CE) (qty 2)– OM control/monitoring– Interface to Host Spacecraft– 7 kg, 151 W

Space Switching Unit (qty 1)– Flexible interconnect between modems to

support independent communication links High speed frame switching/routing

– Command and telemetry processor

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Flight Payload Functional Diagram

Space Switching Unit

Controller Electronics 1

Optical Module 1 Optical Module 2

Host S/C1553

To & From Ground or LEO Terminals

To & From Ground or LEO Terminals

fiber

Integrated Modem 2Host S/C

1553Host S/C1 PPS Host S/C

1 PPS

Transmitter Receiver

Optical Data & Frame Processing

Integrated Modem 1

TransmitterReceiver

Optical Data & Frame Processing

fiber

Frame SwitchingCommand &

Telemetry Processing

Host S/CInterface

Load Drivers

Sensor Processing

PAT Processing

Controller Electronics 1

Host S/CInterface

Load Drivers

Sensor Processing

PAT Processing

Pointing & Jitter

Control

Optical Telescope

Pointing & Jitter

Control

Optical Telescope

Analog

SpaceWire Downlink communication signal

Uplink communication signal

Uplink acquisition beacon signal

High Speed Serial

Two Ground Stations

JPL will upgrade the JPL Optical Communications Telescope Laboratory (OCTL) to form the LCRD Optical Ground Stations (LOGS)• This is a single large telescope design• Adaptive Optics and support for DPSK

will be added

LCRD will upgrade the Lunar Laser Communications Demonstration (LLCD) Ground Terminal developed by MIT Lincoln Laboratory• This is an array of small telescopes with

a photon counter for PPM• Adaptive Optics and support for DPSK

will be added

Both stations will have atmospheric monitoring capability to validate optical link performance models over a variety of atmospheric and background conditions 16

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Ground Station Components

Ground Station 1 Ground Station 2Upgrade of JPL’s OCTL Upgrade of LLGT20 W transmit power 20 W transmit power1 meter transmit/receive aperture 40 cm receive aperture; 15 cm transmit

apertureIdentical equipment for atmospheric monitoringReceive adaptive optics Receive adaptive optics and uplink tip/tilt

correctionIdentical Ground Modem, Codec, and Amplifier systems for DPSK and PPM Wide angle beacon for initial acquisition Scanning beacon for initial acquisitionLaser safety system for aircraft avoidance Operation in restricted flight airspace

Legacy array of superconducting nanowire single photon detectors

DPSK Modulation/Demodulation

DPSK Receiver

DPSK Transmitter

In the DPSK system, each slot contains an optical pulse with phase = 0 or π. Data carried as a relative phase difference between adjacent pulses.

At the DPSK receiver, the original sequence is demodulated using a fiber delay-line interferometer to compare the phase of adjacent pulses.

The average power-limited transmitter allows peak power gain for rate fall-back via “burst mode” operation.

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PPM SignalingFor PPM, the binary message is encoded in which of M=16 slots contains a signal pulse.o Optical modulation accomplished with the same hardware that implements burst-

mode DPSK, with the applied phase irrelevant for PPM

PPM Signaling

PPM Receiver

PPM demodulation is accomplished by comparing the received power in each slot with a (controllable) threshold valueo Uses the same pre-amplifier and optical filter as the DPSK receiver, but by-passes

the delay-line interferometer

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Line of Sight and CFLOS

• The first consideration in link establishment is whether a line of sight between the source and destination exists.

• Free space laser communications through Earth’s atmosphere is nearly impossible in the presence of most types of clouds.

– Typical clouds have deep optical fades and therefore it is not feasible to include enough margin in the link budget to prevent a link outage.

– Key parameter when analyzing free space laser communications through the atmosphere is the probability of a cloud-free line of sight (CFLOS) channel.

• A mitigation technique ensuring a high likelihood of a CFLOS between the source and destination is needed to maximize the transfer of data and overall availability of the network.

– Using several laser communications terminals on the relay spacecraft, each with its own dedicated ground station, to simultaneously transmit the same data to multiple locations on Earth

– A single laser communications terminal in space can utilize multiple ground stations that are geographically diverse, such that there is a high probability of CFLOS to a ground station from the spacecraft at any given point in time.

– Storing data until communications with a ground station can be initiated– Having a dual RF / laser communications systems onboard the spacecraft.

• NASA has studied various concepts and architecture for a future laser communications network. The analysis indicates ground segment solutions are possible for all scenarios, but usually require multiple, geographically diverse ground stations in view of the spacecraft.

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Network Availability

• A ground station is considered “available” for communication when it has a CFLOS at an elevation angle to the spacecraft terminal of approximately 20° or more.

• The network is “available” for communication when at least one of its sites is “available.” • Typical meteorological patterns cause the cloud cover at stations within a few hundred

kilometers of each other to be correlated. – Stations within the network should be placed far enough apart to minimize these correlations – May lead to the selection of a station that has a lower CFLOS than sites not selected, but is less

correlated with other network sites.

• Having local weather and atmospheric instrumentation at each site and making a simple cloud forecast can significantly reduce the amount of time the space laser communications terminal requires to re-point and acquire with a new ground station.

• In addition to outages or blockages due to weather, a laser communications link also has to be safe and may have times when transmissions are not allowed.

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Optical Communications Network Operations Center (NOC)

• In order to provide all of this flexibility for users, the relay network operations center must assume the responsibility for the user data flows.

• The NOC must now keep an accounting of the user data in transit within the provider system (onboard the relay or within a ground station).

• Any handovers or outages that require retransmissions or rerouting within the provider network must all be managed by the NOC transparently to the users.

• The NOC must also be able to provide the necessary insight to resolve any lost data issues reported by users.

• The LCRD Mission Operations Center (MOC) acts as a future NOC in the demonstration

Essential Experiments and Demonstrations

• Experiments will begin immediately following launch and Payload checkout

• During the first six months, the highest priority experiments will demonstrate technology readiness for the next generation TDRS infusion target– Laser Communications Link and Atmospheric Characterization– Earth-Based Relay (Next Generation TDRS)

• The remaining mission time will continue the essential experiments to collect additional data and also include:– Development of operations efficiency (handover strategies, more autonomous

ops, etc.)– Planetary/Near-Earth Relay scenarios (additional delays, reduced data rates,

non-continuous trunkline visibility)– Low Earth Orbit (LEO) - real or simulated

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SCaN’s Optical Communications Strategy for Near Earth

• SCaN has made a considerable investment in the 10 cm optical module design being used on both the Lunar Laser Communications Demonstration (LLCD) and the Laser Communications Relay Demonstration (LCRD)– In the optical module there are minor differences between the two– The major difference is in the modem (DPSK at 1.244 Gbps for LCRD and PPM

at 622 Mbps for LLCD)

• SCaN would like to re-use that design as much as possible:– Future Low Earth Orbit (LEO) compatible terminal– Future lunar missions (far side exploration)– Next Generation TDRS (perhaps with an upgraded higher rate modem)

• For missions deeper in the solar system, SCaN has made a limited investment in the Deep Space Optical Terminal (DOT) concept being worked on at JPL

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The LCRD optical communications terminal leverages previous work done for NASA

With a demonstration life of at least two years, LCRD will provide the necessary operational experience to guide NASA in developing an architecture and concept of operations for a worldwide network

• Unlike other architectures, it will demonstrate optical to optical data relay LCRD will provide an on orbit platform to test new international standards

for future interoperability• LCRD includes technology development and demonstrations beyond the optical

physical link NASA is looking forward to flying the LCRD Flight Payload as a hosted

payload on a commercial communications satellite NASA can go from this demonstration to providing an operational optical

communications service on the Next Generation Tracking and Data Relay Satellites

Summary

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