Quantum Computing in Space: Engineering Challenges, Fundamental Limits, and Perspectives

Quantum computer deployment in space remains constrained by demanding hardware, environmental, and communications requirements. This paper reviews the opportunities and challenges of using quantum computing in space systems. It focuses on payload integration, radiation protection, quantum-memory stability, autonomous hybrid classical–quantum control, and quantum-network performance. The work is integrative, not novel in algorithms, architecture, optimization, or experiments. It organizes reviewed literature around system-level deployment barriers and highlights open research gaps. Compared with existing reviews, this paper adds a category taxonomy, a system-level constraint framing, updated coverage, and an integration of rate–loss fundamentals. The analysis highlights the need for standardized interfaces, autonomous classical–quantum control, and evolutionary qualification of subsystems in orbit. Modular, radiation-adaptive payloads and calibration-aware classical processing are identified as important strategies for improving reliability and mission resilience. The industrial outlook indicates a gradual transition from subsystem demonstrations toward standardized, interoperable, and vertically integrated quantum-communication services, including LEO QKD constellations, space-qualified protocol stacks, and CubeSat-scale photonic devices. Readiness claims are classified using a multi-stage ladder: launch, power-on, communication, calibration, quantum operation, and peer-reviewed useful computational performance. Fully fault-tolerant quantum computing in orbit remains a longer-term objective requiring advances in logical-qubit overhead, radiation tolerance, low-power control, memory performance, and repeater architectures.