A Nerst generator was a component of the USS Antares's drive systems. The generator was shielded by a series of baffle plates.

When Captain Ramart of the Antares tried to contact Captain James T. Kirk of the USS Enterprise and warn him of Charles Evans, Evans used his psionic powers to remove a warped baffle plate from the generator which subsequently destroyed the Antares. (TOS novelization: Charlie X)

The name appears to be a misspelling of Nernst generator, which appeared in several of James Blish's other works.