X0306 4 2018-02-21 0 0000866121 ORBITAL ATK, INC. OA 0001045853 THOMPSON DAVID W C/O ORBITAL ATK 45101 WARP DRIVE DULLES VA 20166 1 1 0 0 President and CEO Common Stock 2018-02-21 4 A 0 11961 0 A 107664 D Common Stock 2018-02-21 4 F 0 4253 131.80 D 103411 D Common Stock 2018-02-21 4 A 0 188 0 A 103599 D Common Stock 2018-02-21 4 F 0 188 131.80 D 103411 D Common Stock 10147 I By Spouse Common Stock 2374 I By 401(k) Plan Deferred Stock Units 2018-02-21 4 A 0 7786 0 A Common Stock 7786 7786 D Shares acquired represent payment of a performance share award (PSA) under the Issuer's 2005 Stock Incentive Plan, and shares disposed represent shares withheld from the PSA to pay withholding taxes. 31,036 of these shares are subject to certain restrictions including possible forfeiture under Orbital ATK, Inc.'s stock incentive plans. Shares simultaneously acquired and disposed represent shares withheld to pay Medicare taxes in connection with the payment of a PSA and the reporting person's deferral of the remaining performance shares under the Issuer's Nonqualified Deferred Compensation Plan (NQDCP) (reported in Table II of this Form). The Deferred Stock Units were credited to the reporting person's account under the Issuer's NQDCP in lieu of a payment by the Issuer of performance shares under the Issuer's 2005 Stock Incentive Plan. The number of units credited to the reporting person's account was determined on a 1-for-1 basis equal to the number of shares of common stock that would have been paid, reduced by the number of shares having a value equal to the Issuer's Medicare tax withholding obligation as a result of the deferral of the payment of the shares. The units will be settled 100% in shares of the Issuer's common stock following the reporting person's termination of employment or such other date specified by the reporting person under the terms of the NQDCP. /s/ Richard N. Osborne, Attorney-in-Fact 2018-02-23