User:Marshallsumter/Radiation astronomy2/Sun-synchronous

A Sun-synchronous orbit (sometimes called a heliosynchronous orbit ) is a geocentric orbit which combines altitude and inclination in such a way that an object on that orbit ascends or descends over any given Earth latitude at the same local mean solar time. The surface illumination angle will be nearly the same every time. This consistent lighting is a useful characteristic for satellites that image the Earth's surface in visible or infrared wavelengths (e.g. weather and spy satellites) and for other remote sensing satellites (e.g. those carrying ocean and atmospheric remote sensing instruments that require sunlight). For example, a satellite in sun-synchronous orbit might ascend across the equator twelve times a day each time at approximately 15:00 mean local time. This is achieved by having the osculating orbital plane precess (rotate) approximately one degree each day with respect to the celestial sphere, eastward, to keep pace with the Earth's movement around the Sun.

The uniformity of Sun angle is achieved by tuning the inclination to the altitude of the orbit such that the extra mass near the equator causes the orbital plane of the spacecraft to precess with the desired rate: the plane of the orbit is not fixed in space relative to the distant stars, but rotates slowly about the Earth's axis. Typical sun-synchronous orbits are about 600–800 km in altitude, with periods in the 96–100 minute range, and inclinations of around 98° (i.e. slightly retrograde compared to the direction of Earth's rotation: 0° represents an equatorial orbit and 90° represents a polar orbit).

NOAA-16
NOAA-L is part of the Polar-Orbiting Operational Environmental Satellite (POES) program that provides atmospheric measurements of temperature, humidity, ozone and cloud images, tracking weather patterns that affect the global weather and climate.

Launch date:	21 September 2000, 10:22:00 UTC, still active. Rocket:			Titan 23G Star-37XFP-ISS (Titan 23G S/N G-13).

"NOAA 16 continues the fourth-generation of operational, polar orbiting, meteorological satellite series (NOAA K-N) operated by the National Environmental Satellite Service (NESS) of the National Oceanic and Atmospheric Administration (NOAA). NOAA 16 also continues the series of Advanced TIROS-N (ATN) spacecraft begun with the launch of NOAA-8 (NOAA-E) in 1983 but with additional new and improved instrumentation over the NOAA A-J series and a new launch vehicle (Titan II). NOAA 16 will be in a morning equator-crossing orbit and is intended to replace the NOAA-J as the prime morning spacecraft. The goal of the NOAA/NESS polar orbiting program is to provide output products used in meteorological prediction and warning, oceanographic and hydrologic services, and space environment monitoring. The polar orbiting system complements the NOAA/NESS geostationary meteorological satellite program (GOES). The NOAA 16 Advanced TIROS-N spacecraft is based on the Defense Meteorological Satellite Program (DMSP) Block 5D spacecraft and is a modified version of the ATN spacecraft (NOAA 6-11, I-J) to accomodate the new instrumentation, supporting antennas and electrical subsystems. The spacecraft structure consists of four components: (1) the Reaction System Support (RSS); (2) the Equipment Support Module (ESM); (3) the Instrument Mounting Platform (IMP); and (4) the Solar Array (SA). All of the instruments are located on the ESM and the IMP."

"The in-orbit Attitude Determination and Control Subsystem (ADACS) provides three-axis pointing control by controlling torque in three mutually orthogonal momentum wheels with input from the Earth Sensor Assembly (ESA) for pitch, roll, and yaw updates. The ADACS controls the spacecraft attitude so that orientation of the three axes is maintained to within +/- 0.2 degrees and pitch, roll, and yaw to within 0.1 degree. The ADACS consists of the Earth Sensor Assembly (ESA), the Sun Sensor Assembly (SSA), four Reaction Wheel Assemblies (RWA), two roll/yaw coils (RYC), two pitch torquing coils (PTC), four gyros, and computer software for data processing. The ATN data handling subsystem, consists of the TIROS Information Processor (TIP) for low data rate instruments, the Manipulated Information Rate Processor (MIRP) for high data rate AVHRR, digital tape recorders (DTR), and a cross strap unit (XSU). The NOAA 16 instrument complement consists of: (1) an improved six-channel Advanced Very High Resolution Radiometer/3 (AVHRR/3); (2) an improved High Resolution Infrared Radiation Sounder (HIRS/3); (3) the Search and Rescue Satellite Aided Tracking System (S&R), which consists of the Search and Rescue Repeater (SARR) and the Search and Rescue Processor (SARP-2); (4) the French/CNES-provided improved ARGOS Data Collection System (DCS-2); (5) the Solar Backscatter Ultraviolet Spectral radiometer (SBUV/2); and (6) the Advanced Microwave Sounding Unit (AMSU), which consists of three separate modules, A1, A2, and B to replace the previous MSU and SSU instruments."

European remote sensing satellites
European remote sensing satellite (ERS) was the European Space Agency's first Earth-observing satellite, launched on July 17, 1991 into a Sun-synchronous polar orbit at a height of 782–785 km.

ERS-1 carried an array of earth-observation instruments that gathered information about the Earth (land, water, ice and atmosphere) using a variety of measurement principles. These included:
 * RA (Radar Altimeter) is a single frequency nadir-pointing radar altimeter operating in the Ku band.
 * ATSR-1 (Along-Track Scanning Radiometer) is a 4 channel infrared radiometer and microwave sounder for measuring temperatures at the sea-surface and the top of clouds.
 * SAR (synthetic aperture radar) operating in C band can detect changes in surface heights with sub-millimeter precision.
 * Wind Scatterometer used to calculate information on wind speed and direction.
 * MWR is a Microwave Radiometer used in measuring atmospheric water, as well as providing a correction for the atmospheric water for the altimeter.

To accurately determine its orbit, the satellite included a Laser Retroreflector. The Retroreflector was used for calibrating the Radar Altimeter to within 10 cm.

Its successor, ERS-2, was launched on April 21, 1995, on an Ariane 4, from ESA's Guiana Space Centre near Kourou, French Guiana. Largely identical to ERS-1, it added additional instruments and included improvements to existing instruments including:
 * GOME (Global Ozone Monitoring Experiment) is a nadir scanning ultraviolet and visible spectrometer.
 * ATSR-2 included 3 visible spectrum bands specialized for Chlorophyll and Vegetation

NOAA-2
"NOAA 2 was the first in a series of reconfigured ITOS-M satellies launched with new meteorological sensors onboard to expand the operational capability of the ITOS system. NOAA 2 was not equipped with conventional TV cameras. It was the first operational weather satellite to rely solely upon radiometric imaging to obtain cloudcover data. The primary objective of NOAA 2 was to provide global daytime and nighttime direct readout real-time cloudcover data on a daily basis. The sun-synchronous spacecraft was also capable of supplying global atmospheric temperature soundings and very high resolution infrared cloudcover data for selected areas in either a direct readout or a tape-recorder mode. A secondary objective was to obtain global solar-proton flux data on a real-time daily basis. The primary sensors consisted of Very High Resolution Radiometer (VHRR), a Vertical Temperature Profile Radiometer (VTPR), and a Scanning Radiometer (SR). The VHRR, VTPR, and SR were mounted on the satellite baseplate with their optical axes directed vertically earthward."

"The NOAA 2 dynamics and attitude control system maintained desired spacecraft orientation through gyroscopic principles incorporated into the satellite design. Earth orientation of the satellite body was maintained by taking advantage of the precession induced from a momentum flywheel so that the satellite body precession rate of one revolution per orbit provided the desired earth-looking attitude. Minor adjustments in attitude and orientation were made by means of magnetic coils and by varying the speed of the momentum flywheel."

"The spacecraft was deactivated on January 30, 1975."

ESSA 9
ESSA-9, also known as TOS-G, was a meteorological satellite of its oversight agency, the Environmental Science Services Administration (ESSA).

The image on the right is a night launch of ESSA 9 aboard a three-stage Delta E1 rocket from Cape Canaveral, Florida, at 07:47 UTC (02:47 EDT) on February 26, 1969, placed in a sun-synchronous orbit of 101.4° inclination, immediately after launch ESSA-9 had a perigee of 1,427.0 kilometers (886.7 mi) and an apogee of 1,508.0 kilometers (937.0 mi), giving it an orbital period of 115.2 minutes, or a mean motion of 12.5 orbits per day. ESSA-9 operated for 1,726 days before it was deactivated in November 1972.

ESSA 1
"ESSA 1 was a spin-stabilized operational meteorological spacecraft designed to take and record daytime cloudcover pictures on a global basis for subsequent playback to a ground acquisition station. The satellite had essentially the same configuration as that of the TIROS series, i.e., an 18-sided right prism, 107 cm across opposite corners and 56 cm high, with a reinforced baseplate carrying most of the subsystems and a cover assembly (hat)."

"Two redundant wide-angle cameras were mounted on opposite sides of the spacecraft and canted 75 deg from the spacecraft spin axis."

"The satellite was placed in a cartwheel orbital mode, with its spin axis maintained normal to the orbital plane. The satellite spin rate and attitude were determined primarily by a Magnetic Attitude Spin Coil (MASC). The MASC was a current-carrying coil mounted in the cover assembly. The magnetic field induced by the current interacted with the earth's magnetic field to provide the necessary torque to maintain a desired spin rate of 9.225 rpm. Five small solid-fuel thrusters mounted around the baseplate provided a secondard means of controlling the spacecraft spin rate. The satellite performed normally after launch until October 6, 1966, when the camera system failed. The spacecraft was deactivated on May 8, 1967".

Hypotheses

 * 1) Being repelled by the Earth is a lofting technology.