This was the second attempt by the Soviet Union to send an advanced lunar sample return craft to the Moon, equipped with the capability to dig for a deeper core.
The first spacecraft (Luna 23) was damaged during landing on the Moon in October 1974. On this mission, the first three stages of the Proton-K launch vehicle worked without fault, but the Blok D stage, during its first burn for insertion into Earth orbit, failed.
The expensive payload burned up in Earth’s atmosphere without ever reaching Earth orbit.
Siddiqi, Asif A. Beyond Earth: A Chronicle of Deep Space Exploration, 1958-2016. NASA History Program Office, 2018.