ascent vs liftoff

ascent and liftoff both are nouns.

Word	Noun	Adjective	Verb	Adverb
ascent	Yes	No	No	No
liftoff	Yes	No	No	No

As nouns, liftoff is a hyponym of ascent; that is, liftoff is a word with a more specific, narrower meaning than ascent:

ascent (noun)	liftoff (noun)
the act of changing location in an upward direction	the initial ascent of a rocket from its launching pad
a movement upward; rise above the ground
an upward slope or grade (as in a road)