Future In-Space Operations
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Future In-Space Operations
Overview for Future In-Space Operations October 2013 Bernard
Edwards Chief, Communications Systems Engineer NASA Goddard Space
Flight Center Mission Statement 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 opticalcommunications service on the
Next Generation Tracking and Data Relay Satellites LCRD Payload and
Host Spacecraft
Mission Overview LCRD Payloadand Host Spacecraft LCRD Flight
Payload 2 Optical Relay Terminals 10.8 cm aperture 0.5 W
transmitter Space Switching Unit 1244 Mbps DPSK 311 Mbps 16-PPM
1244 Mbps DPSK 311 Mbps 16-PPM Mission Concept Orbit:
Geosynchronous Longitude TBD between 162W to 63W 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 Table
Mountain, CA White Sands, NM LCRD Ground Station 1 1 m transmit and
receive aperture 20 W transmitter LCRD Ground Station 2 15 cm
transmit aperture 20 W transmitter 40 cm receive aperture NASA
Optical Communication Technology Strategy
2013 2017 2020 2025 Near Earth Flight Terminal LLCD Technology
Transfer Commercialized LADEE Demo GEO Demo LCRD LEO Demo Near
Earth Missions Commercialization Optical Module DPSK Modem
Controller Electronics Deep Space Flight Terminal Candidate Deep
Space Host Demo Mission Other Deep Space Missions Key DOT
Technology Identification & Development SCaN Optical Ground
Infrastructure Optical Comm Ground Stations (LLGT, OCTL, Tenerife)
LCRD SCaN Operational Optical Ground Stations Added as Mission
Needs Require (including International Space Agency Sites)
Technology Investment and Development Stabilization Detectors
Vibration Systems Engineering Laser Power/Life Pointing SNSPD
arrays, photon counting space receiver, ground receiver detection
array, NAF APD/nanowire det., COTS quadrant spatial-acquisition
detectors Mini FOG Spacecraft disturbance rejection platform,
piezo-based point-ahead mechanism CFLOS Analysis, Optical Comm
Cross Support Low-noise laser PPM Laser Transmitter Flexured Gimbal
Mount Leveraging the Lunar Laser Communications Demonstration
(LLCD)
NASAs 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 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) Modem Module (MM) Designed and fabricated by
MIT LL Pulse Position Modulation Only Digital encoding/decoding
electronics,1550 nm fiber Tx and Rx Controller Electronics Built by
Broad Reach Engineering for OM, MM control Telemetry & Command
(T&C) interface to S/C All Modules Interconnected via
electrical cables and optical fibers LLCD Provides the Foundation
for LCRD
Lunar Lasercom Space Terminal Modem Module Lunar Lasercom Ground
Terminal DL 622 Mbps UL 20 Mbps White Sands, NM Controller
Electronics 1.55 um band LADEE Spacecraft DL > 38 Mbps Optical
Module DL > 38 Mbps UL > 10 Mbps Tenerife Table Mtn, CA Lunar
Lasercom Optical Ground System (ESA) Lunar Lasercom OCTL Terminal
(JPL) LCRD will leverage designs and hardware from LLCD, with
modifications to satisfy mission requirements. LCRD Design
Reference Mission
User 1 S/C User n S/C GS-1 GS-m User 1 MOC User k MOC LMOC Active
optical link Future optical link Terrestrial Internet Protocol
Network 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 LCRD Baseline Hosted on a Space
Systems/LoralCommercial Communications Satellite Flight Payload Two
MIT LL designed Optical Modules (OM) Two Integrated Modems that can
support bothDifferential Phase Shift Keying (DPSK) andPulse
Position Modulation (PPM) Two OM Controllers that interface with
the HostS/C Space Switching Unit to interconnect the twoIntegrated
Modems and perform dataprocessing 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 CommunicationsGround Stations Connected to Host
S/C MOC LCRD GS and Optical Space Terminal Location
161W 112W 63W OST Possible Location GEO Locations were chosen to
ensure at least 20 above horizon for both Ground Stations LCRD
Mission Architecture
LCRD Payloadand Host Spacecraft LCRD Flight Payload W (PPM/DPSK)
DPSK at Gbps PPM at 311 Mbps 1550 nm band 1550 nm band 4x UL
Transceivers 4x DL Receivers Environmental enclosure surrounding UL
and DL telescopes Host Spacecraft RF Link Chiller for cooling
trailer and telescopes Converted 40-ft ISO container housing
controls, modems, and operator console 18-ft Clamshell weather
cover Table Mountain, CA Host Mission Ops Center (HMOC) White
Sands, NM LCRD Optical Ground System (LOGS) - OCTL Based on Lunar
Lasercom Ground Terminal (LLGT) NISN NISN NISN LCRD Ground
Station-1 1 20 W (PPM/DPSK) LCRD Ground Station-2 W (PPM/DPSK) 40
cm (PPM/DPSK) LCRD Mission Ops Center (LMOC) NASA GSFC Relay
Optical Link Relay Link Features:
Coding/Interleaving at the link edges Rate DVB-S2 codec (LDPC) 1
second of interleaving for atmospheric fading mitigation Data can
be relayed or looped back PPM or DPSK can be chosen independently
on each leg OST-1 OST-2 Codec/ Interleave Modem Optics Atmosphere
Free Space Optics Modem Space Switching Unit Modem Optics Free
Space Atmosphere Optics Modem Codec/ Interleave GS-1 LCRD Payload
GS-2 Bus and Payload Overview
Bus Overview Existing SS/L commercial satellite bus 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 Star Tracker Optical Module CE
Modem A Switch Modem B Radiator (back view) Equipment Panel &
Radiator 1 2 1 2 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 Space Switching Unit (qty 1) Flexible interconnect
between modems to support independent communication links High
speed frame switching/routing Command and telemetry processor
Controller Electronics (CE) (qty 2) OM control/monitoring Interface
to Host Spacecraft 7 kg, 151 W Flight Payload Functional
Diagram
Space Switching Unit Frame Switching Command & Telemetry
Processing Controller Electronics 1 Integrated Modem 1 Integrated
Modem 2 Controller Electronics 1 Host S/C 1553 Host S/C 1553
Optical Data & Frame Processing Optical Data & Frame
Processing Host S/C 1 PPS Host S/C Interface Load Drivers Load
Drivers Host S/C Interface Host S/C 1 PPS Receiver Transmitter
Transmitter Receiver Sensor Processing PAT Processing Sensor
Processing PAT Processing fiber fiber All these elements involved
in optical communication and influence link budget Optical Module 1
Optical Module 2 Optical Telescope Pointing & Jitter Control
Optical Telescope Pointing & Jitter Control To & From
Ground or LEO Terminals To & From Ground or LEO Terminals
SpaceWire Downlink communication signal High Speed Serial Uplink
communication signal Analog Uplink acquisition beacon signal 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 Both stations will have
atmospheric monitoring capability to validate optical link
performance models over a variety of atmospheric and background
conditions Ground Station Components
Upgrade of JPLs OCTL Upgrade of LLGT 20 W transmit power 1 meter
transmit/receive aperture 40 cm receive aperture; 15 cm transmit
aperture Identical equipment for atmospheric monitoring Receive
adaptive optics Receive adaptive optics and uplink tip/tilt
correction Identical Ground Modem, Codec, and Amplifier systems for
DPSK and PPM Wide angle beacon for initial acquisition Scanning
beacon for initial acquisition Laser safety system for aircraft
avoidance Operation in restricted flight airspace Legacy array of
superconducting nanowire single photon detectors DPSK
Modulation/Demodulation
In the DPSK system, each slot contains an optical pulse with phase
= 0 or . Data carried as a relative phase difference between
adjacent pulses. DPSK Transmitter The average power-limited
transmitter allows peak power gain for rate fall-back via burst
mode operation. In DPSK pulse is not self consistent (like in OOK)
it needs reference neighbouring pulse. Because neighbouring pulse
serves as a LO the requirement for transmitter and receiver
coherences is drastically relaxed comparing to the coherent
systems. At the DPSK receiver, the original sequence is demodulated
using a fiber delay-line interferometer to compare the phase of
adjacent pulses. DPSK Receiver PPM Signaling For PPM, the binary
message is encoded in which of M=16 slots contains a signal pulse.
Optical modulation accomplished with the same hardware that
implements burst-mode DPSK, with the applied phase irrelevant for
PPM PPM Signaling PPM demodulation is accomplished by comparing the
received power in each slot with a (controllable) threshold value
Uses the same pre-amplifier and optical filter as the DPSK
receiver, but by-passes the delay-line interferometer PPM
modulation suits to be efficient for energy starved, but BW not
limited links. PPM requires an accurate knowledge of the pulse
position; therefore imposing strict requirements on clock jitter
requirements. threshold PPM Receiver 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 Earths 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.
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. 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
Payloadcheckout During the first six months, the highest priority
experiments willdemonstrate technology readiness for the next
generation TDRS infusiontarget Laser Communications Link and
Atmospheric Characterization Earth-Based Relay (Next Generation
TDRS) The remaining mission time will continue the essential
experiments tocollect additional data and also include: Development
of operations efficiency (handover strategies, more autonomousops,
etc.) Planetary/Near-Earth Relay scenarios (additional delays,
reduced data rates,non-continuous trunkline visibility) Low Earth
Orbit (LEO) - real or simulated 23 SCaNs 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 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 24 Summary 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
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