The TRACER ground system facilities are shown in Figure x. S-band TT&C services are
provided by NASA Ground Network (GN) stations during routine science operations or
by Space Network (TDRSS) SSA service during critical event coverage and
contingencies. Commanding is at 2 kbps, real-time housekeeping is telemetered at 4.68
kbps, and the on-board recorder is played back at 4.5 Mbps. Downlink rates include 17%
CCSDS overhead. Five GN contacts per day of 8-9 minutes duration are required during
science operations to play back data recorded on-board at 104 kbps (100 kbps science + 4
kbps housekeeping), resulting in ~1.8 Gbits/playback or ~9 Gbits/day. Contacts are
scheduled weekly by the GN based on a generic templates and antenna predicts provided
by the Mission Operations Center (MOC). Real-time telemetry is forwarded to the MOC
during a contact for health and safety monitoring, as well as 2-way Doppler, range, and
angle tracking data for updating orbit ephemeris. Playback data are staged to the central
Standard Autonomous File Server (SAFS) at GSFC and transferred to the MOC postpass. Science activities are scheduled into a load of time-tagged commands, uplinked
once or twice per week, that autonomously directs on-board observing. The ground
system can command in real-time to accommodate contingencies and targets of
opportunity.
RealTime
Tele
metr
Com
y
ma n
ds
TRACER
ds
ma n
try
Com
leme
e Te
im
T
c
Reala
b k
Play
rd e r
Reco elemetry
T
Mission Operations
Commands
NASA
Space
Network
Real-Time Telemetry
SAFS
NASA
Ground
Network
SAO /
GSFC
Playback Telemetry
T1 Line
Predicts
Tracking Data
Contact
Scheduling Data
§ Spacecraft Activity Planning
§ Command processing, constraint
checking, load generation
§ Spacecraft and instrument
Health/Safety monitoring
§ Telemetry L0 Processing and
Storage
§ Orbit Determination and Prediction
§ Ground Station Predicts
MOC
ITOS
stk
L0 Data
Tracking, Telemetry and
Command
Science Telemetry,
Ancillary Data,
Trends & Status
Reports
Observing
Plan
PI
Science Prods.
Science Results
·
·
·
·
·
·
Target Plan,
Instrument
Commands
Target planning
Level 1-3 Processing
Data Validation
Science Archive
Instrument Trending
Instrument calibration
SOC
Science Operations
SAO at
Cambridge, MA
Day-to-day spacecraft operations are conducted from the MOC located at the
Smithsonian Astrophysical Observatory (SAO) in Cambridge, MA. The MOC shares
facility infrastructure with the Chandra OCC and leverages off of existing SAO
operations experience, reducing both cost and risk. The MOC is connected to GSFC via
dedicated T1 for GN and SN access, spacecraft I&T support, and on-orbit engineering
support. The principal MOC data systems are ITOS for satellite command and control
functions and Satellite Toolkit (stk) for orbit determination and station predict generation.
The data system provides display and commanding functions for the spacecraft controller
during staffed contacts as well as capabilities to autonomously monitor downlinks,
evaluate health and safety, and alert on-call operations personnel during unstaffed
contacts. The MOC L0-processes and archives telemetry data for the duration of the
mission. The planned 2 TB archive will be more than sufficient to store the expected
~0.4 TB/year of telemetry plus orbit and other ancillary data. The science team at the
Science Operations Center (SOC), colocated with the MOC, performs target sequencing,
instrument planning and calibration, and Level 1-3 data processing. The science team is
responsible for maintaining the science data archive and providing data products to GSFC
and other team members as needed.