Spacecraft smart radiation device with near-zero solar absorption based on cascaded photonic crystals

Smart radiation device (SRD) for spacecraft based on thermochromic material vanadium dioxide (VO2) attracts increasing interest due to its ability of self-adaptive emission regulation. However, the spacecraft SRD is constrained by the high solar absorption at a high temperature and low emission tunability in practical applications. In this paper, a SRD is proposed for spacecraft thermal control, which consists of a solar reflector based on cascaded photonic crystals and a thermal emitter (VO2/BaF2/Ag). By cascading four photonic crystals with photonic band gaps for different central wavelengths, the total reflection range of the SRD in the solar radiation band is broadened. It is found that the SRD can realize near-zero solar absorption and high emission modulation depth, simultaneously. Though optimizing the thicknesses of the VO2 and BaF2, the emission modulation depth can reach 0.69, and the solar absorption can reduce to 0.08. In addition, the physical mechanism is studied by the distribution of the electric field. It is proved that the near-zero solar absorption originates from the broadband total reflection of the cascaded photonic crystals. The phase transition properties of VO2 and the difference in inherent losses at high and low temperatures result in high emission modulation depth. Besides, the low solar absorption and high emission modulation depth performances of the SRD can remain excellent when the angle of incidence is small than 46° regardless of the transverse electric wave or transverse magnetic wave. This work not only provides a new idea for designing SRDs, but also is expected to accelerate the development of intelligent thermal control of spacecraft.