GOES-8 STATUS last update: 15 April 2004

Summary

The GOES-8 spacecraft was operational as GOES-EAST at 75W, working until 9 years after launch (with a 5 year design life).

After launch, there was at least 6 years of station-keeping fuel remaining on GOES-I, and at least 7 years of full electrical power. As of early 2002, the satellite had sufficient power and fuel to operate for at least two more years, although there is no longer enough fuel to maintain the orbital inclination to within 0.5 degree of the equator.

GOES-12 was activated as GOES-EAST in the spring of 2003. There was an elaborate plan to swap-in-place with GOES-8 to provide as much data continuity as possible.

GOES-8 Results are on-line.

In October 2003, the primary attitude control computer (AOCE#2) developed troubles that triggered the SAFE HOLD mode on the spacecraft. Transfer of control to the secondary computer (AOCE#1) is being investigated.

As of January 2004, GOES-8 was on standby in an inclined orbit, still potentially useful.

For a geosynchronous spacecraft, deorbit consists of raising the orbit at least 300 km above the geosynchronous altitude at all points.

On May 4 and 5, GOES-8 will be be boosted to supersynchronous orbit via three planned deorbit maneuvers. The first maneuver is scheduled for May 4 at 1400z for 73.9 seconds, the second one is scheduled for May 5 at 0200z for 150.0 seconds, and the third one is scheduled for May 5 at 1400z for 81.3 seconds.

Launch

GOES-I's night launch on 13 April 1994 was on a picturesque Atlas-Centaur rocket and animated by the mid-night conditions. The first official visible image was taken 9 May 1994.

Imager

The Imager cranks out two to four multispectral pictures per hour of the CONUS region, and one full-disk every three hours.

Sounder

The Sounder is producing products for NOAA.

Operations

The GOES-EAST baseline schedule calls for 4 looks hourly at the continental United States, plus hourly northern hemisphere soundings. NESDIS data products (remapped images, winds, soundings, etc.) are still being phased in and evaluated for NWS forecast offices.

GOES-EAST has a complicated Imager schedule. The routine scanning schedule is being exercised most of the time by NOAA. The rapid (7.5 minute intervals) and super-rapid (1 minute intervals) scan modes are occasionally exercised for severe storms.

GOES-8 delivers WEFAX routinely to the western hemisphere, which is particularly useful in Central and South America.

Known Failures

The electro-mechanical failures on GOES-I have all been in redundant systems. There have been other temporary outages.

At 11:10z on March 31, GOES-8 downlink transmitters (SD and MDL) and power amplifiers A & B turned off. CDA was used to verify that it was a spacecraft problem. SOCC maintained telemetry and command capability. Engineering investigation showed a problem with the spacecraft's auto load shedding function which effected not only the transmitters but effected DIRA, storage and panel heaters. With auto load shedding disabled, Sensor Data transmitter and power amplifiers were turned on at 15:14z. Normal scheduled operations resumed at 15:17z. GOES-8 was in a nominal configuration by 16:31z. During eclipse, systems were turned off through a mini-schedule.
On March 30 around 17:00z, GOES-8 momentum wheel average current began to rise. This increase continued through March 31 at 04:50z when the average current reached 1.0A. The current slowly decreased to an average of 0.6A by 02:37z. No effect was detected in the pitch earth sensor but errors were detected in the roll/yaw earth sensor, up to 0.4 degrees.
On 27 October 1998, the GOES-8 attitude system suffered a large anomaly, and the Imager lost South America during the 0739 UTC scan. The satellite went into safe-hold mode. By 2300 UTC the spacecraft had normal earth-lock using the redundant earth sensor, and the instruments were brought back on-line at 0145 UTC on 28 October. GOES-8 found the Earth again (0.5 MByte QT movie) on the following day.
On 29 August 1998, the Sounder's filter wheel slowed to a stop, slewing the entire spacecraft about one-half degree during a full-disk image, producing a wrinkle midway through South America. The Sounder's filter wheel was restarted a few hours later. A stall also happened in mid-1997.
Imager scanline shear began to appear about once per hour early in 1997. This has been traced to a switch that tells the attitude control system that the Imager is actively scanning. Briefly thinking that the Imager is not scanning, the spacecraft computer stops calculating pointing corrections for the scan mirror.
One of the momentuum wheels lost its tachometer in January 1997, so there is no feedback to the speed control on that wheel. That wheel has been shut down, and the satellite is now balanced using the spare wheel, with some loss of pointing stability. Loss of another wheel would disable 3-axis pointing, as it threatens to on GOES-J.
The redundant winding in the Sounder's scan mirror's motor has failed. There is not loss of performance, only of torque margin.
The Sounder's filter wheel stalled in mid-1997. It was restarted by commanding both sets of motor windings to torque the wheel, and it was run for a few months with both windings driving the wheel. In January 1998, the torque was cut back to a single winding to minimize heating, but the filter wheel stuttered again in February 1998, so they went back to driving it with both windings.
The redundant power supply for WEFAX and GVAR broadcasts has failed.
Electrostatic discharge has zapped a 512-byte chip in the redundant onboard attitude control computer. If the main computer fails, this RAM-damaged computer could still be used, but with fewer programmable pointing corrections.
A redundant relay in the Imager does not properly switch over from a fine- to coarse-pointing correction mode.
There are some performance issues with the quality of the pictures from the Imager: (1) the frame-to-frame jitter due to spacecraft motions, and (2) the faint striping due to small differences in the sensitivity of the upper/lower IR detector pairs.

Lessons Learned from the GOES-I Experience

Post-launch Schedule

SCHEDULE                               DATE
 Launch                                 April 13, 1994
 Circularize Orbit                      April 14-27
 Deployments                            April 27 - May 1
 Start-ups and liveness tests           May 1-9
 Outgassing and engineering tests       May 10-30
   first official visible image          May 9
   first official infrared image         May 31
   first official Sounder data           June 6
 Functional tests                       June 1-20
 Image and Navigation spin-up           June 20 - August 20
  Image every 1/2 hour, Sounder off      July 1 - July 24
  Imager routine, Sounder spin-up        July 25 - Aug 21
  NOAA crew starts                       August 22
 Routine Imaging and Sounding           August 22 - September 3
 Special Science testing                September 4 - September 18
 Performance evaluation                 September 19 - October 12
 NOAA operations spin-up                October 12-26
 Image and Navigation Tuneup            October 26 - November 30
 NOAA pseudo-operations                 December 1994 - May 1995
 GOES-EAST operations begin             June 9, 1995
 3-year forecast End-Of-Life            April, 1997
 5-year design End-Of-Life              April, 1999
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GOES Project