Overview for
Future In-Space Operations
October 2013
Bernard Edwards
Chief, Communications Systems Engineer
NASA Goddard Space Flight Center
1
Bernard.L.Edwards@nasa.gov
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 optical
communications service on the Next
Generation Tracking and Data Relay
Satellites
2
Mission Overview
LCRD Payload
and 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 162ºW to 63ºW
Table Mountain, CA
•
2 years mission operations
LCRD Ground Station 1
•
2 operational GEO Optical Relay Terminals
1 m transmit and receive
aperture
• 20 W transmitter
•
2 operational Optical Earth Terminals
•
Optical relay services provided
–
White Sands, NM
LCRD Ground Station 2
15 cm transmit aperture
• 20 W transmitter
40 cm receive aperture
Ability to support a LEO User
•
Hosted Payload
•
Launch Date: Dec 2017
3
NASA Optical Communication
Technology Strategy
2017
2013
Near Earth
Flight Terminal
Technology Transfer
LLCD
2025
Commercialized
GEO Demo –
LCRD
LADEE
Demo
2020
LEO Demo
Near Earth Missions
Commercialization
Optical
Module
Deep Space
Flight Terminal
DPSK
Modem
Controller
Electronics
Candidate Deep Space
Host Demo Mission
Key DOT
Technology
Identification
&
Development
Other Deep
Space Missions
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
Mini FOG
• Detectors
• Vibration
SNSPD arrays, photon counting space
receiver, ground receiver detection
array, NAF APD/nanowire det., COTS
quadrant spatial-acquisition detectors
Spacecraft disturbance rejection platform, piezo-based pointahead mechanism
• Systems Engineering
CFLOS Analysis, Optical Comm Cross Support
• Laser Power/Life
PPM Laser Transmitter
• Pointing
Low-noise laser
Flexured Gimbal Mount
4
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)
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
6
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.
7
LCRD Design Reference Mission
Active optical link
Future optical link
User 1 S/C
GS-1
GS-m
User n S/C
User 1 MOC
•
•
•
•
•
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
Terrestrial Internet
Protocol
Network
User k MOC
LMOC
8
LCRD Baseline
•
•
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
9
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
10
LCRD Mission Architecture
LCRD Payload
and Host
Spacecraft
LCRD Flight
Payload
10 cm @ 0.5 W (PPM/DPSK)
DPSK at 1.244 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
Host Mission
Ops Center (HMOC)
Table Mountain, CA
LCRD Optical Ground
System (LOGS) OCTL
NISN
White Sands, NM
NISN
NISN
LCRD Ground Station-1
1 m @ 20 W (PPM/DPSK)
18-ft
Clamshell
weather cover
Based on Lunar
Lasercom
Ground Terminal
(LLGT)
LCRD Ground Station-2
LCRD Mission
Ops Center (LMOC)
NASA GSFC
1 @ 15 cm @ 20 W (PPM/DPSK)
1 @ 40 cm (PPM/DPSK)
11
Relay Optical Link
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
leg
GS-1
LCRD Payload
GS-2
Codec/
Interleave
Modem
Optics
Atmosphere
Free Space
Optics
Modem
OST-2
Space
Switching
Unit
Modem
Optics
Free Space
Atmosphere
Optics
Modem
Codec/
Interleave
OST-1
12
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
Radiator (back view)
Star Tracker
Star Tracker
Optical
Module
Optical
Module
CE
Modem
1B
Modem
1A
Equipment Panel
& Radiator
Switch
CE
Modem
2A
Modem
2B
13
Payload Hardware Overview
Integrated Modem (qty 2)
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
– 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
Space Switching Unit (qty 1)
Controller Electronics (CE) (qty 2)
– OM control/monitoring
– Interface to Host Spacecraft
– 7 kg, 151 W
– Flexible interconnect between modems to
support independent communication links
 High speed frame switching/routing
– Command and telemetry processor
14
Flight Payload Functional Diagram
Space Switching Unit
Frame Switching
Controller
Electronics 1
Host S/C
1553
Host S/C
1 PPS
Host S/C
Interface
Load
Drivers
Sensor
Processing
PAT
Processing
Command &
Telemetry
Processing
Integrated Modem 1
Integrated Modem 2
Optical Data & Frame
Processing
Optical Data & Frame
Processing
Transmitter
Receiver
Transmitter
fiber
Optical Module 1
Optical
Telescope
Pointing &
Jitter
Control
SpaceWire
To & From Ground or
LEO Terminals
Downlink communication signal
High Speed Serial
Uplink communication signal
Analog
Uplink acquisition beacon signal
Controller
Electronics 1
Load
Drivers
Host S/C
Interface
Sensor
Processing
PAT
Processing
Host S/C
1553
Host S/C
1 PPS
Receiver
fiber
Optical Module 2
Optical
Telescope
Pointing &
Jitter
Control
To & From Ground or
LEO Terminals
15
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
Ground Station Components
Ground Station 1
Ground Station 2
Upgrade of JPL’s OCTL
Upgrade of LLGT
20 W transmit power
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
17
DPSK Modulation/Demodulation
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.
DPSK Transmitter
The average power-limited transmitter allows peak power gain for rate fall-back via
“burst mode” operation.
At the DPSK receiver, the original sequence is demodulated using a fiber delay-line
interferometer to compare the phase of adjacent pulses.
DPSK Receiver
18
Downlink Modulation
PPM Signaling
• 16-ary Pulse Position Modulation (PPM)
For PPM, the binary
message
is encoded in which of M=16 slots contains a signal
• Slot
clock is constant at 4.97GHz
pulse.
– Selectable slot repeat: 1,2,4,8, or 16
o Optical modulation
accomplished
with4.97
theGHz,
same
hardware
that implements burst– Effective
slot clock rates:
2.48GHz,
1.24 GHz,
622.08MHz,
311.04MHz
mode DPSK, with the
applied
phase irrelevant for PPM
PPM Signaling
Source
Data
PPM
Symbols
1
0
1
0
0
0
1
3
10
1
1
1
0
0
12
Slot Repeat
(1)
PPM demodulation is accomplished by comparing the received power in each slot with
Slot Repeat
a (controllable)(2)threshold value
o Uses the same pre-amplifier and optical filter as the DPSK receiver, but by-passes
19-JAG32
the delay-line interferometer
PPM Receiver
threshold
19
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.
20
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.
21
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
22
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
23
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
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
25