Complex space systems have lots of flexible components such as antennas and solar panels. The nonlinear vibration of these flexible components can have negative impact on the performance of the space systems and may even results in the instability of the systems. Therefore, it is crucial to suppress the nonlinear vibration of flexible structures. The state equations for these flexible structures, however, are very high-dimensional when the flexible structures are modeled via finite-element methods. Real-time control for such high-dimensional nonlinear dynamical systems is infeasible due to the bottleneck of simulating the high-dimensional systems. Here we construct low-dimensional reduced-order models (ROMs) via invariant manifolds [1-3] for the flexible structures subject to control inputs, and use the developed ROMs to achieve real-time control. The construction of the ROMs are simulation-free, which is in contrast with the data-driven approach [4]. Moreover, the nonlinear control is reduced to a linear control problem of the ROMs, which significantly facilitates the control analysis and design. We demonstrate the effectiveness of the proposed control scheme via finite element models of beams and plates.