RE-ENTRY OF A SOLAR KITE INTO EARTH'S ATMOSPHERE

摘要

Solar kites are small solar sails which can be deployed and controlled with a minimum of moving parts. A kite is an ideal piggyback payload, as it has low mass and poses negligible hazard to other payloads due to its inert nature and absence of on-board energy sources or volatiles. Due to the reflection of solar photons on the sail surface and thereby transforming the momentum of the photons into a propulsive force, a kite is continuously accelerated and thus suitable for high-velocity missions. A variety of high-value missions are characterised which could be performed by kites. These include in particular lunar-related tasks such as high resolution imaging of the lunar surface from very low altitude with the aid of light reflected from kite itself. A kite could also return flyby images and physical samples of Earth-transiting asteroids to Earth acting as its own low-temperature re-entry parachute. Such missions would have both major scientific utility and significant outreach potential.rnThis paper investigates the re-entry of a solar kite with both trajectory code TRAJ3D from Fluid Gravity Engineering and CFD code CEVCATS-N from DLR. Referring to this combination several Earth trajectories varying mainly kite's mass per unit area are calculated. Afterwards the trajectory point in which the peak of maximum heat flux occurs defines the free stream conditions for the CFD code. A number of computations on 2d grids are performed assuming the flow around the kite as reacting gas including thermochemical nonequilibrium and vibrational excitation. During the study three kite shapes with different half angles are investigated considering 2d-planar as well as 2d-axisymmetric characterisation of the kite. Referring to the mission scenario a ballistic re-entry with zero angle of attack is taken into account and for the initial entry velocity both escape and circular orbital speed are investigated. Altogether a data base for entry bodies with high half angles and Mach numbers from Ma=11 to Ma=30 for altitudes from 90 to 120km has been created.rnFurther research should be undertaken validating the CFD results for the very high altitudes against Direct Simulation Monte Carlo (DSMC) codes.