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THE POLAR GROUND SYSTEM
The NOAA Polar Ground System (PGS) receives telemetry and science
data from a large array of Low Earth Orbiting (LEO) satellites. In
addition, the PGS controls the LEO set of satellites using various
commanding schemes. The vast array of LEO satellites consists of
NOAA’s legacy Polar-orbiting Operational Environmental Satellites
(POES) and DoD's Defense Meteorological Satellite Program (DMSP).
Also, the PGS is collecting data from various non-NOAA satellites
such as ADEOS, EOS, Jason, QuickScat, SEAWIFS, TRMM, WinSat Coriolis,
and etcetera.
Instruments that are carried aboard the satellites mentioned above
perform measurements of temperature and humidity in the Earth's atmosphere,
surface temperature, cloud cover, water-ice boundaries, greenhouse gases,
and proton and electron flux near the Earth. The POES satellites also
have a capability, via their on-board ARGOS system, of receiving,
processing, and retransmitting data from weather balloons, buoys, and
remote automatic data collection stations distributed around the world.
In addition, the POES satellites have an onboard Search and Rescue transponder
and processor for receiving transmissions from people in distress.
The PGS is comprised of the Satellite Operations Control Center (SOCC) and
Central Environmental Satellite Computer Center (CEMSCS) located in Suitland,
Maryland, and the NOAA Command and Data Acquisition (CDA) Stations at
Fairbanks, Alaska (FCDAS), and Wallops, Virginia (WCDAS). Command and data
acquisition control of the polar-orbiting and geostationary operational
satellites is conducted from the SOCC, through communications links with the
ground system facilities at the CDAS.
At SOCC, the automated features of polar-orbiting system operation are
supported by the Polar Acquisition and Control Subsystem (PACS) command,
control, and communications (C3) system, a computer based real-time system.
The present PACS was developed in the late 1980's to support the changes
brought on by the NOAA-H/I/J and NOAA-K/L/M series satellites. Prior to this
NOAA used the Data Acquisition and Control Subsystem (DACS) to control
earlier versions of the POES. The collection of instrument data and the
data transmission (downlink) to ground facilities is under the control of a
Stored Command Table (SCT) loaded into memory of the on-board redundant
Central Processing Units (CPU) of the spacecraft. The PACS performs the
processing and display of spacecraft health and safety telemetry for operator
monitoring, and generates commands for control of spacecraft subsystems.
A feature of the PACS is a schedule generation function conducted in non-real-time
to produce time tagged schedules for automated operation of spacecraft
subsystems and ground system equipment.
The PACS C3 uses three DEC VAX 8550 computers in a VAXcluster, sharing 11.2
Gbytes of disk storage. These three computers, designated Telemetry and Command
Subsystems (TCSs), serve as the central computing facility for SOCC polar
operations. They perform the real-time functions of telemetry processing,
including decommutation, limit sensing, data trend generation, and telemetry
history archiving. The TCS computers also perform textual and graphics display
generation for distribution through a dual rail Ethernet network to 17 VAXStation
3100 workstations and associated peripheral devices.
The ground systems at Gilmore Creek near Fairbanks, Alaska, and the Wallops,
Virginia, stations for polar-orbiting operations are identical in function.
They consist of the following subsystems: 1) antenna, 2) RF, 3) Command
Transmission, 4) Data Handling, and 5) PACS.
NOAA polar satellite data are processed centrally at the Suitland, Maryland
site on the CEMSCS. The global images are processed into polar stereographic
and Mercator maps of cloud cover. The sounding data are processed for use by
the National Meteorological Center (NMC) and placed on the GTS for national
and international distribution.
Ground system changes are necessary to support new and/or modified instruments
and to achieve the goal of taking more satellite passes with the same or fewer
people. The new satellites have a larger command memory, which requires changes
to the ground software used to simulate the satellite, generate loads, and verify
the proper operation of the satellite.
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