The flat spin of a fixed-wing airplane is usually considered to be dangerous, and should be avoided by all means. However, an airplane in a flat spin descends almost vertically and relatively slowly. It can be used as a means of vertical landing, especially for a small fixed-wing unmanned aerial vehicle. Controlling the impact speed to the ground and touchdown position is necessary to realize the application of flat-spin landing. A large pitch-up moment generated by the combination of an all-flying tail and the gyro precession due to the yawing motion generated by the so-called P-factor of the propeller rotation was found to be effective not only for the rapid entry into flat spin, but also to control the pitch attitude and rate of descent during a flat spin. In this paper, the results regarding the relationships among the deflection angle of the all-flying tail, the rotational speed of the propeller, the spin rate, and the rate of descent obtained by flight tests using a small unmanned aerial vehicle are presented as fundamental knowledge towards the realization of practical flat-spin landing.
This paper aims to assess the risk of mission termination for a large constellation of satellites in a low-Earth orbit. Many large constellations will be deployed to provide broadband network services using thousands of satellites. There is concern that such large constellations will have a serious impact on the long-term sustainability of outer space activities due to the rapid increase in population. First, therefore, the authors conducted an assessment under nominal activities (referred to as “business-as-usual”) on the basis of a prediction by ESA’s MASTER-2009 and NASA standard breakup model 2001 revision. The assessment found that nearly one catastrophic collision may happen in a large constellation, generating more than two million fragments as small as 1 mm in size. Second, the authors conducted a further assessment assuming a hypothetical collision of a satellite in a large constellation using the NASA standard breakup model and a spherical finite element model adopted in ESA’s MASTER-2009. In consequence, another catastrophic collision may happen to a large constellation, generating approximately a half-million fragments as small as 1 mm in size. Therefore, such catastrophic collisions and resulting secondary collisions should be prevented for large constellations.
An efficient implicit time integration method for high-order CFD using the flux reconstruction (FR) approach is studied. The formulation is based on the method called matrix-free defect correction on sub-cells (DECS), which considerably reduces the computational cost of the preconditioned block LU-SGS (BLU-SGS). However, the present method uses the exact FR formulation for the simplified viscous terms in the left-hand-side Jacobian, and it does not explicitly use sub-cell divisions as a result of using the finite-difference formula. The performance of the proposed method is compared with BLU-SGS and DECS. Reductions of the computation time for the convergence are not remarkable, but the slightly improved stability and reduced memory storage suggest the present method as a reliable alternative to the existing methods.
As a post-ISS mission, the construction of Gateway in lunar orbit is planned, and a cargo supply mission to Gateway is also being considered by JAXA. NRHO is a candidate orbit for Gateway, and several methods for the transfer trajectory from Earth are being researched. This study proposes a new transfer technique, the Perilune Rendezvous Method (PRM). With this method, a deceleration maneuver during a lunar swing-by inserts a spacecraft into an elliptical lunar orbit. Then, the spacecraft can enter the NRHO with a small velocity increment by waiting for when the orbital plane coincides with the NRHO. Compared with the Lunar Fly-by Method (LFM) adopted by NASA for manned flight missions, the PRM can reduce the required ΔV, but the transition requires a longer period. This method expands the options for cargo supply and manned flight missions. In this paper, the transfer trajectory from Earth to the NRHO is designed using both methods. Furthermore, the results of the ΔV optimization analysis are compared with the velocity increment and the transition period as variables. This leads to a discussion of the Jacobi integrals of the analysis against the theoretical minimum velocity increment.