Applying CCSDS Standards to the Air Force Satellite Control ...

Global Science & Technology
Applying CCSDS Standards
to the
Air Force Satellite Control Network
(AFSCN)
James Noles and John Pietras,
Global Science and Technology, Inc.
GSAW 2002
The Aerospace Corporation
El Segundo, CA
March 13-15, 2002

13-15 March 2002
AFSCN Interest in CCSDS
Standards
• AFSCN interest in CCSDS standards
Global Science & Technology
– The AFSCN is investigating the feasibility of evolving from a
circuit-switched network architecture to an IP packet-switched
architecture
– The AFSCN has a longer-range interest in assessing the
suitability of CCSDS link protocols, SLE services, and SCPS
» Greater use of commercial products and services
» Interoperability with NASA and other TT&C networks
– Issues affecting application of SLE in AFSCN
» Current AFSCN client spacecraft don’t use CCSDS link
protocols and data units
• SLE services are formally based on the CCSDS link protocols
• Slow turnover of spacecraft means legacy space link
protocols must be supported for many years
» Tight latency and timing-preservation requirements
– Can SLE infrastructure be “stretched” to cover AFSCN legacy
clients?
» Ease transition to use of CCSDS link protocol and
interoperability with other TT&C networks
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Current AFSCN TT&C Block
Diagram
Global Science & Technology
SV
HPA
Command
Signals
Tracking
Angles
Remote Tracking Station (RTS)
Receiver Demodulator Bit Sync.
Antenna
Control
Unit
Modulator
Error Signals
UL Sig.
Gen.
Commands
Control &
Status
Processor
Time Code
Generator
PCM Code
Converter
Commands
Timing
Signals
Telemetry
Bit Streams
Communications Link
MUX
DEMUX
DSCS or
DOMSAT
Contact
Support &
Planning
Processors
Time-tagging
Decommutation
Timing Signals
Frame Sync.
Decryption
DEMUX
Human-
Computer
Interface
Operation
Confirmation
Commands
Interface
Units
Commands
MUX
Satellite Operations Control Center (SOC)
Diagram taken from “AFSCN Comm Requirements”, Krikorian, Y.Y., et al, 12 April 2001,
The Aerospace Corporation
13-15 March 2002
3

AFSCN SLE-Based TT&C Block
Diagram
Global Science & Technology
SV
HPA
Command
Signals
Tracking
Angles
Remote Tracking Station (RTS)
Receiver Demodulator Bit Sync.
Antenna
Control
Unit
Modulator
Error Signals
UL Sig.
Gen.
Commands
Control &
Status
Processor
Time Code
Generator
PCM Code
Converter
Commands
Timing
Signals
Telemetry
Bit Streams
Communications Link
Unframed
Service
Provider
Block
Command
Service Provider
Unframed
SLE-PDUs
Block
Command
SLE-PDUs
Internet
Contact
Support &
Planning
Processors
Human-
Computer
Interface
Time-tagging
Operation
Confirmation
Decommutation
Commands
Timing Signals
Frame Sync.
Interface
Units
Decryption
Commands
Unframed
Service
User
Block
Command
Service
User
Unframed
SLE-PDUs
Block
Command
SLE-PDUs
Satellite Operations Control Center (SOC)
NOTE: New services needed to transfer tracking, antenna pointing, and RTS status and control data flows
are not being addressed during Phase 1
13-15 March 2002
4

SLE-Based Services to Support
AFSCN Legacy Missions
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• Prototype production extensions to compensate for legacy
environment
– Unframed Telemetry service to deliver bitstreams across a
packet-switched wide area network
» Provide accurate “telemetry received” time over separate
channel (IRIG-B)
– Block Command service to transfer block commands from the
SOC to the RTS
» Processing involves receiving continuous data stream of
command blocks and idle fill, extracting and transmitting
command blocks and inferred timing requirements, and
reconstructing the command data stream with proper
release timing
– Command Stream service to transfer all bits (including idle bits)
from SOC to RTS with consistent delay
13-15 March 2002
5

GST Testbed Activity
Global Science & Technology
• Beginning in June 2001, USAF funded a testbed activity at
GST to evaluate TCP, UDP and SLE-based approaches to
supporting current-day client space vehicles
• Fundamental approach to compensate for varying delay
through packet-switched networks
– Transfer of data in minimum time
– Annotation of data to allow recovery of timing aspects of data
at the receiving end
– Buffering of data at receiving end until time to release
– Release of data in accordance with timing information
– “Fill data” mechanisms if data fails to arrive in a timely manner
13-15 March 2002
6

GST Testbed Activity (concluded)
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• SLE-based services built on existing NASA Jet Propulsion
Laboratory (JPL) SLE API software
• Minimal-capability TCP and UDP prototypes establish
baseline measurements for use of internet protocols to
transfer bitstream and time-critical blocked data
• Testbed configurations
– Unframed telemetry over TCP or UDP
– Unframed telemetry over SLE RAF
– Block command over TCP
– Block command over SLE CLTU
• Experimentation with COTS IPsec (3DES)
• Performance measurements include:
– Delay and delay variation
– Data loss and sequence errors (when using UDP)
– Overhead
– Time tagging accuracy
13-15 March 2002
7

Unframed Telemetry over RAF:
GST Testbed Configuration
Global Science & Technology
GPS signal
Time
Server
Network Time Protocol
IRIG
Data
Generator
serial
IRIG
time
signal
serial
bitstream
Blocker
Processor
RTS
RAF
Provider
R
T
R
w/
I
RAF
User
Re-serializer
Processor
Data
Receiver
IRIG sys
sys
IRIG IRIG
clock
clock
buffer
IRIG
time
signal
serial
bitstream
IP/ IP/ IP/
P WAN P
IP/ IP/ IP/
serial s
s
eth eth eth
eth eth eth
serial serial
e
c
simulator
R
T
R
w/
I
e
c
SOC
13-15 March 2002
8

Results and Observations
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• Performance
– TCP met a delay goal of 1.25 seconds for lower data rates and
network delay/error values. Higher rates and/or network
propagation delays required additional delay to ensure reliable
delivery.
» Standard TCP slow start, congestion recovery, and
retransmission window size are largely responsible for
observed performance limits
» Preliminary tests with variants of TCP, such as Vegas and
Tranquility (SCPS-TP), improved performance
– SLE RAF performance is marginally less than that of straight
TCP, but not prohibitively so
» Delay needed averages 194 millisec more for RAF than
TCP for comparable network delays and error rates
» Due to added complexity of RAF software and state
machine, but also artifacts of testbed configuration (e.g.,
distributed processing across multiple processors)
13-15 March 2002
9

• Performance (concluded)
13-15 March 2002
Results and Observations
(concluded)
Global Science & Technology
– IPsec protocol (with 3DES) has negligible effect on performance
» No multiplication of packet loss, insignificant added delay
» Performance in real-world situations will depend on
selection of services (e.g., authentication, privacy, etc.) and
security algorithms, which will be mission-dependent
• Applicability of SLE services to AFSCN
– SLE services allow for annotations (e.g. timestamps) to be
added in a standardized and interoperable way, but benefits of
other capabilities of SLE depend on upgrade of SOC and RTS
processing systems
» Legacy command and telemetry processing systems have
no way of handling SLE notifications and reports
» Upgrade of command and telemetry processing systems
could utilize SLE notifications and reports, even while the
format of the spacecraft data itself remains unchanged
– To provide interoperability of legacy support services,
standardization of the blocking and time correlation functions is
just as important as the transfer service interface specifications
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Next Steps
Global Science & Technology
• GST is incorporating into the prototypes some of the
enhancements identified in Phase 1
• GST will install prototype systems at the QRD (Kirtland AFB)
and CERES SOC (Schriever AFB) in March/April
– Tests and demonstrations in late spring/summer
• Longer-term follow-on testbed activities may include further
refinements of enhanced SLE and TCP/UDP services,
experimentation with SLE service management, and
experimentation with the Space Communications Protocol
Standards (SCPS)
13-15 March 2002
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