Two concepts of rocket based combined cycle for single stage rocket are examined. Concept of SSR power plant consisted of liquid rocket engine and liquid air cycle engine is proposed and substantiated. The advantage of LACE with mixed air+oxygen oxidizer over pure LACE is shown. This combination provides increase of payload fraction of SSR up to 2.7% of the vehicle initial mass compared to rocket with pure LRE. Performance and specific mass of the combined engine are determined. Optimal range of oxidizer/hydrogen mixture ratio is shown. Methods of liquefaction ratio increase are discussed.Second concept considers LRE cycle integration with atmospheric air separation system. The main feature of the scheme is that air separation system provides positive thrust at the initial acceleration. With the same assumption for mass estimation, the concept shows close results to LACE/LRE combination in terms of rocket payload fraction.