Sentinel is a Surface to Air Missile designed by SARA for Solair.
Development
Development of the missile started in 1946.Second Stage
Originally the second stage engine was to be ignited midair however during flight tests it was found that due to unreliable ullage the mid air ignition would often lead to failures, to combat this a truss interstage was added between the stages and a fibreglass-phenolic exhaust diversion cone was mounted to the SRB below the second stage engine in order to protect the SRB.Operation
Upon launch both the first stage solid rocket booster and second stage liquid fuel sustainer engine are ignited. After the first stage has burned through its propellant it is jettisoned allowing the sustainer to propel the missile the rest of the way towards the target.