TRAnsit Characterization ExploreR Ground Systems and Mission Operations
Jaime Esper / 592
10/31/2007
Technical & Management Review
GSFC Competition Sensitive
Ground Systems
GSFC Competition Sensitive
Ground System Requirements
• Data volume per contact ~2.16 Gb, 5 contacts/day,
total daily volume ~10.8 Gb
• Playback 4.5 Mbps, S-Band QPSK (includes 17%
CCSDS overhead and 30% contingency)
• Transmission T1 line from Ground station to MOC
• Uplink load commands once per week. Autonomous
time-tagged commanding in the intervening
• Capability for real-time commanding in emergencies
and for targets of opportunity
• Support ground autonomy to monitor downlinks,
evaluate health and safety and alert on-call
operations personnel
GSFC Competition Sensitive
TRACER MOC Characteristics
• MOC at CfA
– Colocated with Science Operations Center
– Uses existing operations expertise
– Shares infrastructure with Chandra
– Connected to GSFC through T1/VPN for
spacecraft I&T support
GSFC Competition Sensitive
TRACER MOC Architecture
SSA
TRACER
5 kbps tlm
2 kbps cmd
TDRS
MOC/SOC @CfA
Critical Events
Monitoring /
Contingency
Communications
Mission Ops Center
TLM, Eng/HK
Wallops
Alaska/ Svalbard/
LRO White Sands
CMDs
RT health/safety processing
Commanding
Mission scheduling
Instrument data handling
Trending/Analysis
Orbit determination/control
Mission planning
Network & contact schedule
S/C monitor/control
Mission Ops testing
Level 0/product processing/distribution
Level 0 Data Archive
CMDs@2kbps
TLM, Eng/HK
Level Zero Eng/HK
Data Products
White
Sands
Complex
Coordination
SOC Ops and Processing
Legend:
Eng= Engineering data
HK=Housekeeping data
CMD=Commanding
TLM= Telemetry data
Wallops
Remote S/C
support
Observer Support
Observation planning
Science trending
Data validation
Calibration
Level 1-3 processing
GSFC Competition Sensitive
CMD/TLM
“Virtual”
SOC
Ground System
Options/Characteristics
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Leverage existing ground station network, including use
LRO/White Sands complex
Combine TRACER ops in existing ops facility
SOC may be extended by several “virtual” stations
around the country/world
Level-zero processing done at MOC, and data delivered
to SOC for further processing
Use TDRSS link though White Sands for critical event
coverage and/or contingency operations
GSFC Competition Sensitive
Mission Operations
GSFC Competition Sensitive
Basic Operations Timeline
Week
1
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5
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7
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10
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Launch and Early orbit
Spacecraft/Instrument Checkout and Science Commissioning
Normal Operations
8x7
2 to 4 years
• Launch event coverage through L10-11
• Spacecraft telemetry through TDRSS after fairing separation
• Critical Event coverage through TDRSS
• Spacecraft commissioning and checkout 30-day allocation
• Normal operations begin L+30 days.
• Operations staffing around the clock for early phases of checkout,
then back to 5 days per week, 8 hr shifts.
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Early Operations Timeline
• Early on-orbit operations
– Following separation (8 minutes after launch) ACS is
automatically enabled in Initial Acquisition/Safehold
mode
– Deploy solar array
– Control system points spacecraft such that solar array
normal is pointed to sun (CSS, TAM, wheels,
magnetic torquers)
– ACS maintains the spacecraft in a power positive
thermal safe attitude
– Ground commands switch to normal mode
– Focal Plane Aperture is Opened: First Light
GSFC Competition Sensitive
Normal Mode Operations Timeline
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Turn on and check out instrument
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Assure bus & instrument have sufficient time to outgas (contamination)
Instrument turn on
Calibration maneuvers
Determine offset between instrument boresight, guide telescope and ACS frames
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Nominal science mission starts
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User scripted inertial target attitudes
In science mode
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3 Axis zero momentum
FGS used for both attitude and rate
Reaction wheels used for control
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Magnetic torquers used for unloading accumulated momentum
Failure detection logic with backup safehold mode
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Launch induced shifts
PIID controller ~0.1 Hz bandwidth
Weekly observation runs are event or time-triggered execution driven
Observatory enters safehold when:
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Sunlight detection threshold is violated
Solar array current drops below threshold
On-board computer re-sets
Keep-alive signals are not received by the on-board computer (monitoring RW, MTB, CSS/FSS,
Gyros, Instrument, TAM, FGS Signal)
Spacecraft attempts recovery autonomously once, and then waits for ground commands if
unsuccessful
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Eclipse Duration with Drag Effects
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Drag causes 6 AM orbit to enter constant shadow season after 3rd year
Moving ascending node back to 5:30 AM and adjusting initial inclination
to 97.45° will result in 4 full-Sun periods over a 4-year mission (baseline)
6 AM Nominal
launch – Max Drag
5 AM Nominal
launch – Max Drag
5:30 AM Nominal
launch – Max Drag
6 AM Nominal
launch – No Drag
GSFC Competition Sensitive
Lifetime Analysis
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NASA Policy Directive (NPD) 8710.3 requires limiting orbit lifetime after mission
completion to 25 years or maneuvering to an approved disposal orbit
Analysis indicates that TRACER re-enters within 5 - 25 years from 550 km
No propulsion system is needed for EOL decommissioning
GSFC Competition Sensitive