NOAA KLM User's Guide

Section 1.2.7

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1.2.7 Communications Subsystems

The functional requirements of the Communications subsystem are separated into three distinct phases: prelaunch, liftoff to handover and the mission phase where the solar array and all antennas are deployed. During the mission phase, the subsystem provides the following function:

Mission Phase

The subsystem comprises 14 antennas, 9 transmitters, and redundant receivers, together with associated filters and other RF feed components. Three 7-watt STX's (STX-1, -2, and -3) and three directional S-band antennas (SBA's) (SBA-1, -2, and -3) mounted on the satellite Earth-facing (+X) surface provide the three principal S-band data links. VHF Omni coverage for real-time TIP telemetry is provided by two 1-watt beacon transmitters (BTX-1 and -2) operating through an omni antenna also mounted on the +X side of the spacecraft. Launch and emergency coverage is provided by a fourth 7-watt (STX-4) and a set of omni antennas mounted on the +X and -X sides of the spacecraft. The two APT 5-watt VTX's (VTX-1 and -2) use a separate dedicated helical antenna; this, like the instrument dedicated antennas, is also directional, Earth-face mounted, and used only in mission mode. The SAR Receiver Antenna (SRA) developed on the ATN program is a unique design incorporating two nested helices: the outer element serving the 121.5 MHz and 243 MHz link, the inner one the 406.05 MHz link.

The fourth SAR uplink (406.025 MHz) is combined with the DCS uplink and is received via the UDA.

The subsystem has two sets of communications links (ascent and operational), which are summarized in Tables 1.2.7-1 and 1.2.7-2.

Table 1.2.7-1. Ascent, Early-Orbit and Contingency RF Communications Link Characteristics Summary.
Link Ground Facility Frequency Modulation Bit Rate
S-Band Command NAGE (pre-launch), CDA, GN 2026 MHz BPSK/NRZ-M 2 kbps
S-Band TIP Real-Time WSMC, ARIA Aircraft, AFSCN, DSN, CDA 2247.5 MHz and 1702.5 MHZ Split-Phase Level Data 8320 bps or 16,640 bps
S-Band TIP Playback WTR, CDA, Lannion 1702.5 MHz 1707.0 MHz as 1698.0 MHz selected Same as above 332.7 kbps
VHF TIP Real-Time CDA, Lannion 137.35 or 137.77 MHz Same as above 8320 bps

Table 1.2.7-2. NOAA KLM Operational Link Summary.
Link Data Contents Ground Facility Frequency
S-Band Command Satellite commands (clear mode or encrypted) CDA 2026 MHz
VHF TIP Real-Time Housekeeping telemetry and payload data from all meteorological instruments except AVHRR and AMSU CDA, TIP Stations 137.35 or 137.77 MHz
HRPT Full-resolution AVHRR data plus concurrent TIP AMSU and TIP data CDA, HRPT Stations 1698 or 1707 MHz
GAC Playback Global reduced-resolution AVHRR data plus TIP data stored on satellite tape recorders CDA 1702.5 MHz and either 1698 or 1707 MHz
LAC Playback Tape-recorded-replica of HRPT data   Same as above.
TIP/AIP Playback Tape-recorded-replica of TIP/AIP real-time data Lannion TIP Playback Station 1698 or 1702.5 or 1707 MHz
APT Reduced resolution, geometrically-corrected analog video from two of the five AVHRR channels, selected by command CDA, APT Stations 137.50 or 137.62 MHz
DCS Uplink Messages Environmental measurements, identification, and a frequency reference for Doppler navigation; from unattended platforms DCS Platforms 401.65 MHz
SAR 121.5 MHz Uplink Signals, 243 MHz Uplink Signals Emergency transmissions from downed aircraft and ships. Aircraft transmitters are ELT's; ship transmitters are EPIRB's 121.5/243-MHz ELT's EPIRB's 121.5 MHz

243 MHz

SAR 406 MHz Uplink Messages Received Separately by SARR 406 MHz Channel and by SARP Same as above, but with improved frequency stability and modulation containing identification of the aircraft or ship 406-MHz ELT's and EPIRB's 406.05 MHz
SARR Downlink Transponded frequency-multiplexed SAR uplink signals and messages from all three uplink frequencies, preserving uplink phase for Doppler tracking by ground stations; also 406-MHZ messages reformatted and tagged with time and Doppler measurements by the SARP; the SARP data transmitted in near-real-time and also cyclically from SARM. SAR LUT's 1544.5 MHz

The following summary describes the relationship of subsystem equipment to the communications links:


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