WordNet records no synonym and no antonym for mercury program. It is the only member of its synset, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a program of rocket-powered flights undertaken by US between 1961 and 1963 with the goal of putting a man in orbit around the earth
“under the Mercury program each flight had one astronaut”
Synonyms, antonyms and the broader and narrower relations for mercury program come from Princeton University’s WordNet. Full sources and licences.