ESSA-9

ESSA-9, also known as TOS-G, was a meteorological satellite.^[4] Its name was derived from that of its oversight agency, the Environmental Science Services Administration (ESSA). ESSA-9 replaced the ESSA-7 satellite.

ESSA-9

ESSA-9 being checked out before launch
Mission type	Meteorology
Operator	ESSA (1969-70) NOAA (1970-72)
COSPAR ID	1969-016A
SATCAT no.	3764
Mission duration	1,726 days (achieved) 56 years, 1 month and 28 days (in orbit)
Spacecraft properties
Launch mass	145 kilograms (320 lb)
Start of mission
Launch date	February 26, 1969, 07:47:01 (1969-02-26UTC07:47:01Z) UTC[1]
Rocket	Delta E1
Launch site	Cape Canaveral LC-17B
End of mission
Disposal	Decommissioned
Deactivated	November 1972 (1972-12)
Orbital parameters
Reference system	Geocentric
Regime	Low Earth
Semi-major axis	7,843.18 kilometers (4,873.53 mi)
Eccentricity	0.00508
Perigee altitude	1,432 kilometers (890 mi)
Apogee altitude	1,512 kilometers (940 mi)
Inclination	101.99 degrees
Period	115.21 minutes
Mean motion	12.49
Epoch	December 7, 2013, 20:28:49 UTC[2]
Instruments
Advanced Vidicon Camera System (AVCS), Flat Plate Radiometer (FPR)[3]
TOS ← ESSA-8 TIROS-M ITOS →

Launch and orbit

ESSA-9 was launched on a three-stage Delta rocket from Cape Canaveral, Florida. The launch occurred at 07:47 UTC (02:47 EDT) on February 26, 1969. The spacecraft was 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.^[1] ESSA-9 operated for 1,726 days before it was deactivated in November 1972.

Spacecraft

The ESSA-9 spacecraft was similar to the TIROS series of satellites, having an 18-sided polygonal shape that measured 42 inches (110 cm) in diameter and 22 inches (56 cm) high. It weighed 320 pounds (150 kg). The body of ESSA-9 was made of aluminum alloy and stainless steel. The shell of the craft was covered with 10,020 solar cells.^[5] The solar cells recharged the 63 nickel–cadmium batteries during the time the spacecraft was in sunlight.^[5] ESSA-9 employed the same cartwheel-style stabilization as the TIROS-9 satellite. The satellite used a magnetic attitude spin coil (MASC) to control its attitude while in orbit. The magnetic field induced by the MASC's current interacted with the Earth's magnetic field to provide the torque necessary to maintain a desired spin rate of 9.225 rpm.^[6]

Instruments

ESSA-9 carried two sets of two main instruments, the Advanced Vidicon Camera System (AVCS) and the Flat Plate Radiometer (FPR). The AVCS was used to collect imagery of cloud cover on Earth. The cameras had a resolution of 2 miles (3.2 km) and covered an area of 2,000 square miles (5,200 km²). The cameras took single images of a particular region of the Earth's surface once a day. The FPR's were used to measure the global distribution of solar radiation reflected by the Earth and the Earth's atmosphere. They also measured long-wave emissions from the Earth. The sensors used in the ESSA satellites were from the earlier Nimbus program.

Gallery

• 
  ESSA-9 is launched aboard a Delta E1 rocket from Cape Canaveral, Florida, on February 26, 1969.
• 
  Mosaic of ESSA-9 weather photographs of the United States, Passes 1504–1505, 1901-2057 GYT, June 26, 1969.
• 
  Part of a ESSA-9 image showing Hurricane Agnes on June 19, 1972 as it approaches Florida.