Weather Satellites: ESSA IV

ESSA IV - Environmental Science Services Administration Satellite IV

Launch date: January 26, 1967

Launch site: Vandenberg AFB, California

Launch vehicle: Thrust augmented Three-stage Delta

PROGRAM OBJECTIVE:

To replace ESSA II and provide direct readout cloud cover photography to ground stations world-wide using APT.

SATELLITE DESCRIPTION:

The spacecraft was an 18-sided polygon, 42 inches in diameter, 22 inches high and weighed 290 pounds. The craft was made of aluminum alloy and stainless steel then covered with 9100 solar cells. The solar cells served to charge the 63 nickel-cadmium batteries.

The two cameras were mounted 180 degrees opposite each other along the side of the cylindrical craft. The "cartwheel" configuration of the TIROS IX was selected as the orbital configuration of the operational series of ESSA satellites. Therefore, a camera could be pointed at some point on Earth every time the satellite rotated along its axis. The spacecraft operating system was the same as on the TIROS IX. The craft was placed in its planned sun-synchronous 101 degree inclination retrograde orbit. The satellite spin axis was rotated using the magnetic attitude control system into an alignment perpendicular to the orbital plane and tangent to the EarthÕs surface. The APT system was designed to transmit an image every 352 seconds, each photo covering a 2000 mile square area with 2 mile resolution.

ESSA IV was able to transmit two to three images daily to individual ground stations regardless of their location. ESSA IV remained operational for 465 days until deactivated by NASA on May 5, 1968.

PARTICIPANTS:

NASA, ESSA, RCA, US Weather Bureau, NMC.