After years of bad, intermittent and in some cases no network access from the observatory at all, we fixed it.
The original cat5 cable was laid down almost ten years ago and ran around the house down into the ground and over to the observatory. It has been chewed through numerous times by critters at the house/fence interface, where critters probably prefer to enter the fenced yard. This was spliced, respliced and fixed many times.
There was also a splice inside the house to extend the cable to the nearest network switch.
As it turns out, the cable underground came out fine. The cable above ground had brittle outside casing, exposed wires in some cases and was in pretty rough shape.
The cable entering the observatory was also chewed through, outer casing, some inner wires as well.
It is a wonder there was any data flowing at all!

chewed network cable

The new 100′ cat5e ethernet cable is good for gigabit speeds, is encased in a 75′ garden hose split open lengthwise to get the cable in, and buried deeper than the last.
As a bonus, we will be replacing the old switch out in the observatory that has had a couple of ports fried in nearby lightning strikes with a newer gigabit switch.