Ballustrans were a race from the planet Ballustra. There were eight billion Ballustrans.
A CVE appeared near Ballustra and emitted pressure waves. Estimates suggested that 15% of the population were killed on the first day. A joint scientific and military group was formed to investigate the CVE. While flying near the CVE, they sighted the Doctor's TARDIS; using a ship with "claws," they captured it and deposited it on Letrus, taking Romana II and Adric prisoner. The pair were questioned by Marni Tellis.
They were attacked by the Farrian who came through the CVE. They attacked Ballustra, killing many more Ballustrans. The nations of Ballusta banded together, forming a single effective force. After the Fourth Doctor destroyed the CVE generator in N-Space, the Farrian were forced to recall their officers and retreat. They left behind the ground troops who helped in the reconsruction of the planet. A planetary defence force was developed to fight any furthur invasions. (AUDIO: The Invasion of E-Space)