Activities on NOAA-14 and NOAA-15

Following is information received this week relating to activities or
anomalies that may affect NOAA-14 and 15 products.
Emily

NOAA-15 AVHRR: The National Oceanic and Atmospheric Administration
spacecraft, NOAA-15, Advanced Very High Resolution Radiometer instrument
continues to function erratically. As of September 12, examination of the
last 24 hours of trending data indicated that approximately half of the
orbits processed were nominal. Also, over the pass 2 to 3 weeks channel 4
and 5 have demonstrated erratic behavior where most of the data is
affected. This problem is apparently not attributed to the "normal" sync
delta or scan motor problems. Investigations continue.

Information reported by SOCC
NOAA-14 AVHRR Testing: A 24 hour test to reduce the amount of overlap in
the NOAA-14 orbital data will be conducted on all GAC data recorded starting
at 00 Z on Wednesday, September 19. The objective of the test is to try to
reduce the age of the oldest data on the recorders without affecting any
products.

On September 10 at 0513Z , the NOAA-14 spacecraft attitude control mode was
switched from nominal mode to Yaw Gyro Compassing attitude control mode.
An analysis of the data leading up to the switch indicates the sun sensor's
field of view was obstructed (probably by the solar array) as it was
attempting to take a reading. NOAA-14 has entered a period of time where,
over the next several months, it's experiencing spacecraft sun angles lower
than any previously encountered by NOAA-14 on-orbit. This is not unusual
for older spacecraft whose orbits have precessed.

Since the environmental conditions believed to have caused this problem are
expected to continue for several months, SOCC engineers decided to leave
NOAA-14's attitude control mode in the YGC mode. The YGC attitude control
mode typically has no impact on data products.

Then, at 0125Z on J253, redundancy software on NOAA-14 switched buses from
the B-bus to the A-bus and then inhibited further bus switching. The cause
of this bus switch is still under investigation. Aside from the loss of bus
redundancy (because further bus switching is inhibited), there was no
impact to the mission capability of the spacecraft. No NOAA-14 data was
lost as a result of these events.

Reported on September 11: NOAA-14 YGC and bus switch investigations
continue. The most likely reason for the switching of the control mode and
buses is due to apparent shading of the sun sensor by the solar array.
Among other actions, engineers are considering an array movement that would
give the sun sensor a clear view of the sun.

On September 13, NOAA-14 rev 34563 / F at 1731z : Commanding performed to
increase the telemetry time resolution of the sun sensor read output from 8
seconds to 1 second. Executed commands to change the telemetry table 1,
word 13, in the control OBP. The result of the commanding was to increase
the telemetry time resolution of the sun sensor read output from 8 seconds
to 1 second. Other spacecraft systems remain unchanged. Now that the
telemetry sampling rate of the Sun Sensor Assembly (SSA) has occurred,
engineers plan to change the solar array bias from -55 degrees to -20
degrees while continuing to monitor the SSA's output during the update
window. If test results are positive, engineers will (after a suitable time
period) return the spacecraft to the B-bus and re-enable bus switching in
redundancy management software. For the time being, the spacecraft will
remain in the YGC attitude control mode. Aside from the loss of bus
redundancy (because further bus switching is inhibited), there is no impact
to the mission capability of the spacecraft.

Important note to all involved in N14 product generation: As described
above, the N14 array will be moved on Monday, September 17 at approximately
1400z. Short term temperature variations should be expected as the
spacecraft achieves a new thermal balance due to the resultant change in bus
and instrument shading.

--
*******************************************
*
* Emily D. Harrod
* NOAA/NESDIS/OSDPD/IPD
* Product Systems Branch
* Pre-Product Processing Group
* E/SP13, Federal Building #4, room 0318
* 5200 Auth Road
* Suitland, Maryland 20746-4304
* USA
* voice 301-457-5247
* fax 301-457-5199
* email Emily.Harrod@noaa.gov
*
*******************************************

Emily D. Harrod
Mathematician
NOAA/NESDIS/OSDPD/IPD
Product Systems Branch

Emily D. Harrod
Mathematician
NOAA/NESDIS/OSDPD/IPD
Product Systems Branch
E/SP13 FB#4 room 0318 5200 Auth Road Fax: 301-457-5199
Suitland Work: 301-457-5247
MD
20746-4304
US
Additional Information:
Last Name Harrod
First Name Emily