Warhead

Warhead is a 1989 3D space combat simulator taking place during a war between Earth and alien beings from Sirius starting in 2045. Humanity has been united in the form of the Fist-of-Earth space force and developed an unmanned probe based in SolBase. The player remotely guides the probe through a series of sequential missions, first in the Solar system and later in other star systems, as the craft is equiped with a quad-space drive. Typical mission objectives include intelligence gathering, search and rescue missions, destroying enemy craft and protecting friendly forces.

Warhead spawned a spiritual sequel, XF5700 Mantis.

According to its Wikipedia article, the game is freely downloadable in the form of disk images, by permission of the game creator.