NOAA KLM User's Guide
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:
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.
|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|
|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
|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:
The S-Band omni antennas (SOA's) (SOA-3, -4) and STX-4 provide launch real-time telemetry to the NASA tracking station at VAFB/WR and to the Advanced Range Instrumented Aircraft (ARIA) aircraft.
The Command Antennas, RF Filters, and Dual Command Receiver recover the signal. Both command receivers operate simultaneously and continuously. The outputs of both receivers are cross-strapped externally to the two Command Demodulators. The Command Receiver-Demodulator provides two isolated sets of outputs. Each set of separate output lines are provided to the Control Interface Unit (CIU) and Decryption/Authentication Unit (DAU) for uplink processing.
The receivers are permanently connected to a set of S-band omni-directional antennas via a hybrid network.
The directional VHF real-time antenna (VRA), RF filter, and VHF real-time transmitter (VTX-1 or -2) provide the APT data in Table 1.2.7-1.
The UDA, DPD and RF filter provide the corresponding service for the SARP.
The directional SRA, the directional Search and Rescue L-Band Antenna (SLA) and RF filters provide the corresponding services for the SARR.
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