518 
is not recoverable. For Landsat-5, the frequency source 
amplifiers in the X-Band and K-Band systems were 
redesigned to include lower drive level into the second 
stage amplifier and modified mounting for the transistor 
Substrate to relieve excessive stress. 
9 The Landsat-4 solar array is in a degrading failure 
condition as flat conductor cables open'due to high 
stresses induced by the cable to connector solithane 
potting. -Conductors have opened in two of the four 
cables which independently connect power from the four 
solar array panels to the spacecraft regulator unit. 
Landsat-4 is being operated in a manner which slows the 
degradation by minimizing thermal stress and power 
demand. For Landsat-5, power cables were redesigned to 
include conventional round stranded wire in a woven flat 
cable configuration, crimp termination at. connector, 
stress relief clamps at connectors and added stress 
relief loops near connector termination. 
e Additional enhancements were made to the Landsat-5 Space 
Segment to improve capability or quality. These include 
the addition of on-board computer software to support 
telemetry monitors for quick assessment of spacecraft 
functions, the addition of floating point capability in 
the attitude update filter to ensure long-term filter 
convergence and additional filtering of MSS detector 
outputs to reduce coherent noise. 
LANDSAT-5 SPACE SEGMENT PERFORMANCE 
The Landsat-5 launch and activation sequence was 
executed without problem. All subsystems are performing 
properly. Performance levels for subsystems of interest can 
be characterized based on Landsat-4 experience as follows: 
e The Precision Attitude Control System has performed well 
within its design specificaton of .03 degrees, 3 sigma. 
The system routinely maintains earth pointing attitude 
control of less than .015 degrees, 3 sigma and attitude 
knowledge of less than 10 arc seconds. Attitude pointing 
transients of .05 degrees have been observed to occur due 
to Solar Array thermal shock which is experienced for a 
period of one minute at sun rise. Since this occurs only 
at the North Pole it does not pose any problem to image 
processing. A second attitude pointing transient of .05 
degrees occurs when the High Gain Antenna drive is 
started up. This low frequency (.3Hz) disturbance 
settles out after 5 minutes. The High Gain Antenna is 
Currently being managed to ensure that spacecraft 
pointing. is within specification during imaging periods. 
In addition, the onboard antenna start up control law is 
being revised to reduce the amplitude and duration of the 
distrubance.