The ITOS (Improved Tiros Operational Satellite) series (TIROS-M
was the prototype spacecraft) were the second generation of
operational sun-synchronous meteorological
spacecraft. Operational
... satellites were renamed NOAA.
The primary objective of ITOS was to provide improved
operational infrared and visual observations of earth cloud
cover for use in weather analysis and forecasting. Secondary
objectives included providing both solar proton and global heat
balance data on a regular daily basis. To accomplish these
tasks, the spacecraft carried:
-two television cameras for Automatic Picture Transmission (APT) and
-two Advanced Vidicon Camera System (AVCS) cameras. It also carried
-a low-resolution Flat Plate Radiometer (FPR),
-a Solar Proton Monitor (SPM), and
-two scanning radiometers that not only measured emitted infrared
radiation, but also served as a backup system for the APT and AVCS
cameras.
The nearly cubical spacecraft measured 1 by 1 by 1.2 m. The TV
cameras and infrared sensors were mounted on the satellite
baseplate with their optical axes directed verticially
earthward. The satellite was equipped with three curved solar
panels that were folded during launch and deployed after orbit
was achieved. Each panel measured over 4.2 m in length when
unfolded and was covered with 3420 solar cells, each measuring 2
by 2 cm. The ITOS 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.
Additional information available at
http://www.skyrocket.de/space/doc_sdat/noaa_itos-a.htm 
