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 was launched in October 1978. TIROS-N has been followed by NOAA-6 through NOAA-14 and further satellites in the series are planned for operation into the 1990's. The primary instruments aboard these satellites are the Advanced Very High Resolution Radiometer (AVHRR) and the TIROS Operational Vertical Sounder (TOVS) complex.
The TIROS-N series of satellites is a cooperative effort of the United States (NOAA and NASA), the United Kingdom, and France. NASA funded the development and launch of the first flight satellite; subsequent satellites were procured and launched by NASA using NOAA funds. The operational ground facilities including the Command and Data Acquisition (CDA) stations, the Satellite Control Center, and the data processing facilities (with the exception of the Data Collection System [DCS] processing facility) were procured, funded and operated by NOAA. The United Kingdom, through its Meteorological Office (Met O), Ministry of Defense, provided a Stratospheric Sounding Unit (SSU), one of three sounding instruments for each satellite. The Centre National d'Etudes Spatiales (CNES) of France will provide the DCS instrument for each satellite and will provide the facilities necessary to process and make available to users the data obtained from this system. The Centre d'Etudes de la Meteorologie Spatiale (CEMES) of France will provide ground facilities for receipt of sounder data during the blind orbit periods.
Platform Mission Objectives:
The main objectives are:
(a) to view the global atmosphere regularly and reliably both day and night. To provide direct readout data to local ground stations within communication range of the satellite.
(b) to provide for sounding the global atmosphere regularly and reliably and to provide quantitative information for use in numerical weather prediction, and
(c) to provide for continuous viewing of weather features and for collecting and relaying meteorological data from remote platforms such as buoys, ships, automatic stations, aircraft and balloons. (Ensor, 1978,p.1-2)
Platform Parameters:
The TIROS-N satellite is an integrated system designed to provide for and control injection into a nominal 833- or 870-Km circular, sun-synchronous orbit after separation from an Atlas-E/F launch vehicle. The spacecraft structure consists of four components: 1) the Reaction System Support Structure (RSS); 2) the Equipment Support Module (ESM); 3) the Instrument Mounting Platform (IMP); and 4) the Solar Array (SA). Instruments are located on both the IMP and the ESM. With the exception of the SEM, all instruments face the Earth when the satellite is in mission orientation.
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.
Coverage Information:
The Polar Orbiting satellites operate in relatively low orbits, ranging from 700 to 1,700 km above the earth, and circle the earth 12 to 14 times per day. The orbits are timed to allow complete global coverage twice per day, per satellite (normally a daytime and a nighttime view of the earth) in swathes of about 2,600 km in width. High resolution (1 kilometer) data are transmitted from the satellite continuously, and can be collected when the satellite is within range of a receiving station. Recorders on board the satellite are used to store data at a 4 kilometer resolution (processed by the on-board computers) continuously, and a limited amount of data at a 1 kilometer resolution on demand. The recorders are dumped when the satellite is within range of a NOAA receiving station.
Attitude Characteristics:
The on-orbit Attitude Determination and Control Subsystem (ADACS) provides three axis pointing control for the satellite. The ADACS maintains system pointing by controlling torque in three mutually orthogonal wheels (a fourth skewed wheel is available in the event of failure of one of these three). The torque is determined by analysis of spacecraft orientation in space. Input to these computations are acquired from the Earth Sensor Assembly (ESA) for pitch and roll, and an inertial reference with sun updates for yaw.
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.
Data Collection System:
The Data Collection and Location System (DCS) for TIROS-N was designed, built, and furnished by the Centre National D'Etudes Spatiales (CNES) of France, who refer to it as the ARGOS Data Collection and Location System. The ARGOS provides a means for obtaining environmental data from, and Earth locating, fixed or moving platforms. Location information, where necessary, may be computed by differential doppler techniques using data obtained from the measurement of platform carrier frequency as received on the satellite. When several measurements are received during a given contact with a platform, location can be determined. The environmental data messages sent by the platform will vary in length depending on the type of platform and its purpose. The ARGOS (DCS) system consists of three major components. The terrestrial platform, the On-board instrument, and the Processing center.
Communication Links:
There are seven primary TIROS-n communications links.
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.
List of Sensors/Instruments:
Advanced Very High Resolution Radiometer (AVHRR/2)
High Resolution Infrared Radiation Sounder (HIRS/2)
Stratospheric Sounder Unit (SSU)
Microwave Sounder Unit (MSU)
Data Collection System - ARGOS (DCS)
Space Environment Monitor (SEM)
Search and Rescue (SAR) Satellite Aided Tracking (SARSAT)
Solar Backscatter Ultra Violet Radiometer (SBUV/2)
Earth Radiation Budget Experiment (ERBE) (NOAA F and G only)
Ground Segment Information:
Tracking and Control:
The on-orbit Attitude Determination and Control Subsystem (ADACS) provides three axis pointing control for the satellite. The ADACS maintains system pointing by controlling torque in three mutually orthogonal wheels. The torque is determined by analysis of spacecraft orientation in space. Input to these computations are acquired from the Earth Sensor Assembly (ESA) for pitch and roll, and an intertial reference with sun sensor updates for yaw.
Data Acquisition and Processing:
The NOAA AVHRR processing flow begins with sensor data receipt by the command and Data Acquisition (CDA) stations where the data is re-broadcast via communications satellites, to NOAA/NESDIS in Suitland, MD. The ephemeris data is funneled through the Advanced Earth Location Data System (AELDS) software on an IBM mainframe which feeds an IBM 921 for Level 1b production. Earth location and calibration data are appended (but not applied) to the data as part of the Level 1b processing. AELDS is a completely on-line data driven system within the preprocessing system. The earth locations are computed for specific pixels using the data time corrected for clock drift, if any. The earth location values are computed by using the exact equations of the physical algorithm. The use of raw data time as corrected for satellite clock drifts, combined with the use of exact equations, eliminates a major source of error in the earth locations. Further, AELDS uses the most up-to-date User Ephemeris File (UEF) available within NOAA in contrast to one day old UEF data used by the previous system.
Latitude Crossing Times:
The TIROS-N satellite series has been designed to operate with a south-bound equator crossing between 0600 and 1000 Local Solar Time (LST), or a northbound equator crossing between 1400 and 1800 LST. Power and thermal constraints preclude normal operation within 2 hours of noon (midnight) LST.
References:
This information is not available at this time.
Glossary of Terms:
Please see the GHRC Glossary for terms related to the GHRC and see EOSDIS Acronyms for a general listing of terms related to the Earth Observing System Project.
List of Acronyms:
Please see the GHRC Glossary for terms related to the GHRC and see EOSDIS Acronyms for a general listing of terms related to the Earth Observing System Project.
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
URL
Uniform Resource Locator
Document Information:
Document Revision Date:
January 13, 1999
Document Review Date:
January 13, 1999
Document ID:
TRMM Source Document
Citation:
GHRC Data Citation
Document Curator:
GHRC User Services
support-ghrc@earthdata.nasa.gov
