Shares of Orbital ATK (NYSE: OA) are soaring today, up 21% as of 11:41 a.m. EDT to around $132.73 per share, following the announcement that fellow defense contractor Northrop Grumman (NYSE: NOC) has agreed to acquire the company for $134.50 per share in cash.Northrop Grumman has offered to acquire all the outstanding shares of Orbital ATK in an all-cash deal valuing the company at $7.8 billion, plus the assumption of $1.4 billion of net debt.