Yes, MISSILE is a Scrabble word!

Letter values in Scrabble US: M 3, I 1, S 1, S 1, I 1, L 1, E 1.

Is it a valid word?

MISSILE is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a rocket carrying a warhead of conventional or nuclear explosives; may be ballistic or directed by remote control
a weapon that is forcibly thrown or projected at a targets but is not self-propelled