This paper presents a space network emulation system based on a user-space network stack named Nos to solve space networks' unique architecture and routing issues and kernel stacks' inefficiency and development complexity. Our low Earth orbit satellite scenario emulation verifies the dynamic routing function of the protocol stack. The proposed system uses technologies like Open vSwitch (OVS) and traffic control (TC) to emulate the space network's highly dynamic topology and time-varying link characteristics. The emulation results demonstrate the system's high reliability, and the user-space network stack reduces development complexity and debugging difficulty, providing convenience for the development of space network protocols and network functions.