Space Robots Formation Control for Large Solar Sail Deployment

Solar sails use sunlight to propel a vehicle through space by reflecting solar photons off a mirror-like surface made of light reflective material. To be able to work as an interplanetary cargo-ship, the solar sail area should be large enough to receive required acceleration from the sunlight. However, mechanical deploying mechanisms are not reliable to deploy such a large solar sail. This paper presents formation control of space robots for on-orbit assembly of large solar sails. Contrary to previous works, the dynamic equations of space robots in the formation are derived by considering relative motion of the space robots with respect to the sail hub orbiting the Earth. The uncertainties including external disturbances, unmolded dynamics, and parameter uncertainties, are considered as a single time-varying term in the dynamic model. Then, an adaptive sliding mode controller combined with a second-order observer is expanded to control the on-orbit formation of space robots as well as resisting the disturbances. Finally, the efficacy of the proposed approach is demonstrated by a numerical simulation.