The Taalo Shield is an incredibly valuable, experimental, defensive weapon and the last known artifact of the ancient Taalo race. The Taalo's unusual silicon-based, mineral-like physiology somehow made their minds alone, of all members of the Sentient Milieu, immune to psychic compulsion from the Dnyarri conquerors. The pacifistic Taalo, unwilling to take up arms against their former friends, worked desperately to find an artificial method of imbuing this immunity into the minds of non-Taalo. Unfortunately, they were unable to develop such a device in time to stop the Dnyarri conquest, and when hordes of Dnyarri-controlled Ur-Quan invaded the surface of the Taalo homeworld, only one prototype Shield had been constructed before the Taalo's final disappearance. The Captain's research into the ancient Taalo allows him to recover this device from the Taalo homeworld 20,000 years later, at which time it plays a crucial role in the Second War.
The Taalo used technology similar to their own biology to build the Shield, which appears to the naked eye as a huge, glowing boulder. The subtlety and complexity of their engineering is staggering, outpacing even the genius of the Chenjesu. All human attempts to analyze the Shield show it to be nothing more than an apparently randomly mixed, undifferentiated lump of common minerals. However, its fluorescence by an unknown process, unaccounted for by any naturally fluorescing substances within the rock, as well as its regular shape and structure are clear signs that it is artificial. Its anti-psi abilities were discovered by accident; even in its quiescent state, any esper-capable Humans who approach it are plagued by headaches and mental confusion as the Shield wars against their natural, unconscious psychic probing. Experimentation discovers that running even a small electric current anywhere on the Shield's surface greatly multiplied this effect until all psi interaction in the Shield's vicinity is completely canceled, at least to the limits of measurements available by human methods.
This jury-rigged system was undoubtedly not the original intended use of the Shield, and this method of generating an anti-psi field is probably much weaker and less efficient than a fully completed Shield would have been. The neo-Dnyarri can perceive this, and is still able to compel The Captain to perform minor actions against his will (such as talking about flowers).
Sources of information
How to get it
Make diplomatic relations with Orz (just talk to any Orz patrol). Then go to their homeworld (patrols will give you the location) and ask them to land.