Luna 21 ( Ye-8 series ) was an unmanned space mission , and its spacecraft , of the Luna program , also called Lunik 21 , in 1973 .
PROPN NUM ( PROPN NOUN ) AUX DET ADJ NOUN NOUN , CCONJ PRON NOUN , ADP DET PROPN NOUN , ADV VERB PROPN NUM , ADP NUM .