How to make satellite more autonomous in realizing intended mission functions becomes more and more important as many constellation projects and small satellite deep space missions are appearing. As it is difficult to predict all the anomalies in-orbit and prepare countermeasures for them, it would be better to reconstruct operation plan onboard when some anomaly happens, considering available resources, times and required mission functions. This technology is especially important for small/micro/nano/pico-satellites, for which ground operation work load had better be reduced as much as possible. In this paper, ``state transition model'' based method of autonomous satellite operation is proposed and its application to real satellite project is described. The first in-orbit demonstration was conducted in small scale in 2018, which will also be discussed.
This paper describes a modeling technique of the solar radiation pressure (SRP) exerted on spacecraft which can incorporate general surface with anisotropic reflectance property. The SRP torque is a major disturbance for the attitude of spacecraft especially in deep space missions. It depends not only on the shape and attitude of spacecraft, but also on their surface optical reflectance property. The aim of this paper is to create a precise reflectance distribution model by measurement of a bidirectional reflection distribution functions (BRDF). A BRDF, a technique originally developed in the field of Computer Graphics, describes a reflectance map between arbitrary incident and emitted rays in a general mathematical form. This model successfully describes the inconsistency between the conventional SRP torque and the flight data and relates material's microscopic structure to the optical property.
We propose a Mars aerial exploration mission using a micro Mars airplane released from CubeSat. In this paper, the airplane is designed, and its feasibility is evaluated in terms of maximum flight Mach number and wing structure mass. The airplane is small enough to be stored in 1U (a cube of 10cm) and has a total mass of 950g. A glider type is suitable considering the severe constraints of size and mass. The airplane also requires a relatively large wing to fly through the thin Martian atmosphere. Therefore, we adopt an inflatable wing to develop a compact and large wing. The cross-section of the wing is bumpy airfoil due to the multiple pressurized tubes that extend in the spanwise direction. Aerodynamic measurements are conducted in a wind tunnel to study the aerodynamic characteristics of the wing. Finally, the specifications of the airplane are proposed based on the wind tunnel tests results. The proposed airplane with its wingspan of 0.9m is capable of gliding over 40km in nine minutes.
A small airplane is strongly affected by crosswind in take-off and landing phases, because the flight velocity and gravitational force acting on it are not much larger than the crosswind velocity and aerodynamic force due to crosswind, respectively. A vertical tail volume can be decreased dramatically for a smaller airplane for the stability of lateral/directional motions. The NDD (Neutral Dihedral effect and Directional stability) airplane defined as Clβ = Cnβ = 0 was conceived so that it has a tolerance to crosswind. An airplane without a dihedral effect and directional stability is not accepted in the current regulation for airplane design. Then, an airplane with small values of Clβ and Cnβ has been newly proposed. All of the modes in the lateral/directional motions can converge without oscillating in the proposed airplane, named ``QNDD'' airplane, which is not observed in the NDD airplane.
Super Low Altitude Test Satellite (SLATS) nicknamed “TSUBAME'' was successfully launched on December 23, 2017. The purposes of SLATS are 1) Test of keeping satellite's altitude with its own ion engine against high atmospheric drag at super low altitude, 2) Data acquisition of atmospheric density and atomic oxygen, and 3) Test of optical earth observations. SLATS operation was finished on October 1, 2019. SLATS got following results in terms of the attitude and orbit control. 1) Orbit transfer from initial orbit which is 643 Χ 450km elliptic and descending node local sun time (LST) 10:30 orbit to initial super low altitude orbit which is 271.5km circle and LST 16:00 orbit using a chemical gas jet system (RCS) and an atmospheric drag for about one year, 2) Altitude keeping at 271.5, 216.8km altitude for 38days respectively and at 250, 240, 230, 181.1, 167.4km altitude for 7days respectively, 3) Guidance and longitude keeping at 271.5km/1day, 216.8km/5days and 181.1km/3 days recurrent orbits. This paper shows the on-orbit results in terms of the attitude and orbit control of SLATS.
This paper reports the safety confirmation of flight control system of an Unmanned Aerial Vehicle (UAV) with a pair of high-aspect-ratio wings via nonlinear simulations and hardware-in-the-loop simulation tests with various flight conditions (steady winds, gusts, etc.). The UAV successfully had a safe flight in Taiki town in Hokkaido after the safety confirmation process.