Shinji Mitani

Continuous-Thrust Transfer with Control Magnitude and Direction Constraints Using Smoothing Techniques

This paper treats the satellite formation and reconfiguration problem under constraints on control magnitude and direction. An optimal controller with these constraints is derived using a continuous smoothing method, in which a sequence of unconstrained optimal control problems is solved according to Pontryagin’s minimum principle by introducing barrier functions to the original performance index. The solutions converge to the solution of the original problem and strictly satisfy the treated constraints as the coefficients of the functions approach zero. Optimal controllers are successfully formulated in L1- and L2-norm problems. The magnitude and direction constrained solution is naturally extended from the solution with only magnitude constraints. Numerical simulations demonstrate that a successive optimal controller with such a multiconstraint can be obtained by solving a two-point boundary value problem using the shooting method in a noncoplanar circular orbit and a coplanar eccentric orbit.

Novel Nonlinear Rendezvous Guidance Scheme Under Constraints on Thrust Direction

DOI: 10.2514/1.52491 This paper proposes a new nonlinear guidance scheme to treat rendezvous trajectory planning under constraints on thrust direction. Considering the constraints on the parameters in the general quadratic performance index, a control design process is proposedusing modal analysis to make the thrust angle small at the initial and final phases. Then, using a candidate control Lyapunov function by solving the Riccati equation for the considered performance index, a new control applying “satisficing” concepts is devised to meet the constraints strictly from start to finish. Numerical simulations show that thrust angle can be practically constrained within a small magnitude and the proposed control law leads to convergence at the origin in both a circular orbit and an eccentric one. Nomenclature A0 = semimajor axis of the target c = � cos � e = eccentricity of the target h = angular momentum of the target

Satisficing Nonlinear Rendezvous Approach Under Control Magnitude and Direction Constraints

A rendezvous problem under thrust magnitude and direction constraints is considered. A constraint-satisficing scheme has been newly proposed by introducing two barrier functions. The constraint-satisficing set smoothly establishes an intersection between the unconstrained satisficing set and the input constraint set as the perturbation parameters of two barrier functions tend toward zero. For a simple nonlinear controller, a controller generated by projecting a constraint-free linearized optimal controller onto the input constraint is proposed and its stability is investigated. Some numerical simulations treating nonlinear relative orbit systems show that various control sets, which guide the orbit to the origin, can be generated, whereas the convergence property of the closed-loop system is analyzed by the proposed parameter design with the assistance of a graphical plot.

Thermal Strain in Lightweight Composite Fiber-Optic Gyroscope for Space Application

Thermal strain significantly affects stability of fiber optic gyroscope (FOG) performance. This study investigates thermal strain development in a lightweight carbon fiber-reinforced plastic (CFRP) FOG under thermal vacuum condition simulating space environment. First, we measure thermal strain distribution along an optical fiber in a CFRP FOG using a Brillouin-based high-spatial resolution system. The key strain profile is clarified and the strain development is simulated using finite element analysis (FEA) to understand the mechanism of the strain development. Several materials for FOG bobbins are then quantitatively compared using experimentally validated FEA from the aspect of the thermal strain and the weight to illustrate the clear advantage of CFRP. Finally, a hybrid concept combining low thermal conductivity polyacrylonitrile-based (PAN-based) CFRP and high stiffness pitch-based CFRP is proposed to minimize the thermal strain with minimal weight.

Performance Estimation of the Mid-Infrared Camera and Spectrometer Aboard SPICA

The Space Infrared Telescope for Cosmology and Astrophysics (SPICA) is an astronomical mission optimized for mid- and far-infrared astronomy, envisioned for launch in the 2020s. The Mid-infrared Camera and Spectrometer (MCS) is a model instrument that covers the 5–38μm wavelength range and enables imaging and spectroscopic observations via four modules named WFC-S, WFC-L, HRS, and MRS. Both of the wide field camera (WFC) modules have a 5-arcmin square field of view (FOV) but cover different wavelength ranges; WFC for the short wavelength region (WFC-S) covers 5 to 24μm, whereas WFC for the long wavelength region (WFC-L) covers 18 to 38μm. The High Resolution Spectrometer (HRS) covers the 12–18μm range with a resolving power of 22,000–30,000, and the Mid Resolution Spectrometer (MRS) performs integral filed units spectroscopy with a 12′′ by 8′′ FOV. MRS simultaneously covers the 12–38μm range with a moderate resolving power of 720–2000. Here, we report sensitivity estimates from a detailed modeling process...

Cooled Scientific Instrument Assembly onboard SPICA

The Space Infrared Telescope for Cosmology and Astrophysics (SPICA) is a 3.2m cooled (below 6K) telescope mission which covers mid- and far-IR waveband with unprecedented sensitivity. An overview of recent design updates of the Scientific Instrument Assembly (SIA), composed of the telescope assembly and the instrument optical bench equipped with Focal Plane Instruments (FPIs) are presented. The FPI international science and engineering review is on-going to determine the FPI suite onboard SPICA: at present the mandatory instruments and functions to perform the unique science objectives of the SPICA mission are now consolidated. The final decision on the composition of the FPI suite is expected in early 2013. Through the activities in the current pre-project phase, several key technical issues which impact directly on the instruments’ performances and the science requirements and the observing efficiency have been identified, and extensive works are underway both at instrument and spacecraft level to resolve these issues and to enable the confirmation of the SPICA FPI suite.

Formation Flight Astronomical Survey Telescope (FFAST) mission in hard x-ray

A formation flight astronomical survey telescope (FFAST) is a new project that will cover a large sky area in hard X-ray. In particular, it will focus on the energy range up to 80keV. It consists of two small satellites that will go in a formation flight. One is an X-ray telescope satellite carrying a super mirror, and the other is a detector satellite carrying an SDCCD. Two satellites are put into a low earth orbit in keeping the separation of 12m. This will survey a large sky area at hard X-ray region to study the evolution of the universe.

Thermal strain along optical fiber in lightweight composite FOG : Brillouin-based distributed measurement and finite element analysis

Thermal strain significantly affects stability of fiber optic gyroscope (FOG) performance. This study investigates thermal strain development in a lightweight carbon fiber reinforced plastic (CFRP) FOG under thermal vacuum condition simulating space environment. First, we measure thermal strain distribution along an optical fiber in a CFRP FOG using a Brillouin-based high-spatial resolution system. The key strain profile is clarified and the strain development is simulated using finite element analysis. Finally, several constituent materials for FOG are quantitatively compared from the aspect of the maximum thermal strain and the density, confirming the clear advantage of CFRP.

Current status of fiber optic gyro efforts for space applications in Japan

In response to the maturation of Fiber Optic Gyro technologies, FOGs are being used in various applications. Also in Japan, the demand for FOG is high, and is used in some space applications. In this paper, we introduce examples of Japanese products that apply to space-use. It also describes some efforts for high-grade navigation use in Japan.

Precision pointing control for SPICA: risk mitigation phase study

SPICA (Space Infrared Telescope for Cosmology and Astrophysics) is an astronomical mission optimized for mid- and far-infrared astronomy with a 3-m class telescope which is cryogenically cooled to be less than 6 K. The SPICA mechanical cooling system is indispensable for the mission but, generates micro-vibrations which could affect to the pointing stability performances. Activities to be undertaken during a risk mitigation phase (RMP) include consolidation of micro-vibration control design for the satellite, as well as a number of breadboarding activities centered on technologies that are critical to the success of the mission. This paper presents the RMP activity results on the microvibration control design.