The "Armstrong" was an Orbital Space Station in low orbit around the Earth. During the Strogg invasion of Earth, it was used by the GDF to study and store creatures and weapons developed on Mars.
It was located in Earth's lower orbit, just above Africa.
When the Strogg invaded Earth, the station had been turned into an Orbital Defense Platform, but it was ultimately taken down by the Strogg. During this incident, Kane found an old GDF weapon which he used to survive. He turned out to be the only survivor of this attack, but The United Nations kept him quiet about this incident, leading to rumors that the weapon wasn't all he had found.