Cornerstone Capital, a middle-market investment firm, has acquired Keystone Engineering from UTC Aerospace Systems, a division of United Technologies. Based in Long Beach, CA, Keystone designs and manufactures satellite propellant tanks, launch vehicle domes and other ancillary space products. The company also services and refurbishes the rotodome bearing assembly for the Airborne Warning and Control System aircraft and is the sole-source supplier of bearing assembly refurbishment for the U.S. Air Force and NATO. The transaction marks the sixth acquisition for Cornerstone and its fourth investment in the aerospace industry. Penn Mezzanine and Fifth Third Bank provided acquisition financing for the deal.