Since 1978 the TIROS-N satellites have carried instruments that provide data to meet some of the NOAA responsibilities in support of both environmental monitoring and global research programs. The satellite system is a cooperative effort of the United States, the United Kingdom, and France.
The TIROS-N satellite includes an integrated system for guidance and control of orbital injection following separation for the Atlas vehicle. The Reaction Control Equipment (RCE) provides ascent phase, attitude control (3 axis), and orbital velocity trim for final injection. The RCE is operational from Atlas separation to handover to the orbital control system.
The ADACS is required to control spacecraft attitude so that orientation of the three axes is maintained to within plus or minus 0.2 degrees of the local geographic reference. Information to permit computation of yaw, pitch, and roll to within 0.1 degrees by computer processing on the ground, after the fact, is also available. The attitude should generally be maintained to within approximately 0.12 degrees.
S-Band Links: Each of the three 5.25 watt output S-Band transmitters is coupled to one of three quadriphase antennas. Normally, one of the transmitters will be used continuously for transmission of HRPT data while the other two are used to play back tape recorders to one of the centralized data acquisition stations. All three transmitters may be used in parallel when required to retrieve data from the on-board recorders.
Two of the S-Band antennas are right-hand circularly polarized (1698 and 1707 MHz), while the third is left-hand circularly polarized (1702.5 MHz). During the ascent phase only, one of the S-Band transmitters is connected to a S-Band omni-directional antenna to provide spacecraft telemetry.
VHF Links:
The VHF APT transmitter has a 5w output and operates at a preselected frequency of either 137.50 or 137.62 MHz. Choice of transmitting frequency will be made to preclude interference between signals emanating from two satellites in orbit at the same time. Either transmitter is coupled to the VHF realtime quadifilar antenna via an RF switch. Modulation is AM on a 2.4-KHz sub-carrier which in turn frequency-modulates the carrier. The antenna is a four element quadifilar providing a shaped pattern; nominal directivity of the right-hand circularized antenna is +4.5 dBci at nadir and +0 dBci at the horizon.
ADACS Attitude Determination and Control Subsystem AELDS Advanced Earth Location Data System AVHRR Advanced Very High Resolution Radiometer CDA Command and Data Acquisition CEMES Centre d'Etudes de la Meteorologie Spatiale CNES Centre National d'Etudes Spatiales DCS Data Collection System ERBE Earth Radiation Budget Experiment ESA Earth Sensor Assembly ESM Equipment Support Module HRPT High Resolution Picture Transmission HIRS High Resolution Infrared Radiation Sounder IBM International Business Machines IMP Instrument Mounting Platform LST Local Solar Time Met O Meteorological Office MIRP Manipulated Information Rate Processor MSU Microwave Sounder Unit NASA National Aeronautics and Space Administration NESDIS National Environmental Satellite, Data, and Information Service NOAA National Oceanic and Atmospheric Administration RSS Reaction System Support Structure RCE Reaction Control Equipment SA Solar Array SAR Search and Rescue SARSAT Satellite Aided Tracking SBUV Solar Backscatter Ultra Violet Radiometer SEM Space Environment Monitor SSU Stratospheric Sounder Unit TOVS TIROS Operational Vertical Sounder TIP TIROS Information Processor UEF User Ephemeris File