Naoko Ogawa

How to track spermatozoa using high-speed visual feedback

In this paper, we report how to track quickly and vigorously swimming ascidian spermatozoa using high-speed visual feedback at a frame rate of 1 kHz. Ascidian spermatozoa swim as fast as 300 μm/s by rotating their flagella 50 times/s. This vigorous swimming style has prevented stable image observation and made it difficult to track them reliably with our previously developed visual tracking system. Here, we describe how we overcame these problems using image processing techniques to achieve stable tracking of fast, small ascidian spermatozoa for more than 180 s using high-speed visual feedback.

Generalized Attitude Model for Momentum-Biased Solar Sail Spacecraft

This paper describes a method of modeling general attitude dynamics of a nonspinning momentum-biased spacecraft under strong influence of solar radiation pressure. This model, called the “generalized sail dynamics model,” can be applied to realistic solar sail spacecraft with nonflat surfaces and nonuniform optical reflectance. A coarse sun-pointing momentum-biased spacecraft is especially of interest, for which an approximate solution of the equations of motion is analytically derived. Stability and fundamental characteristics of momentum-biased spacecraft dynamics as well as theoretical relations with past dynamics models are discussed in detail. Furthermore, unique attitude motion predicted by the novel model is verified with flight data of the Japanese interplanetary probe, Hayabusa 2.

Laser link experiment with the Hayabusa2 laser altimeter for in-flight alignment measurement

We report results of a laser link experiment between a laser altimeter called light detection and ranging (LIDAR) aboard Hayabusa2 and ground-based satellite laser ranging stations conducted when the spacecraft was near the Earth before and after the gravity assist operation. Uplink laser pulses from a ground station were successfully detected at a distance of 6.6xa0million km, and the field of view direction of the receiving telescope of the LIDAR was determined in the spacecraft frame. The intensities of the received signals were measured, and the link budget from the ground to the LIDAR was confirmed. By detecting two successive pulses, the pulse intervals from the ground-based station were transferred to the LIDAR, and the clock frequency offset was thus successfully calibrated based on the pulse intervals. The laser link experiment, which includes alignment measurement of the telescopes, has proven to be an excellent method to confirm the performance of laser altimeters before they arrive at their target bodies, especially for deep space missions.Graphical abstract.

Simultaneous estimation of shape and motion of an asteroid for automatic navigation

In an asteroid exploration and sample return mission, accurate estimation of the shape and motion of the target asteroid is essential for selecting a touchdown site and navigating a spacecraft during touchdown operation. In this work, we present an automatic estimation method for the shape and motion of an asteroid, which is planned to be tested in future exploration missions including Japanese Hayabusa-2 [1]. Our task is to estimate the shape and rotation axis of the asteroid, as well as positions of the spacecraft from optical images. The proposed method is based on the expectation conditional-maximization (ECM) framework that consists of an auxiliary particle filter and nonlinear optimization techniques. One of our technical contributions is the estimation of the direction of rotation axis of the asteroid from monocular camera images, which are taken by the moving spacecraft. We conducted two experiments with synthetic data and an asteroid mock-up to show the validity of the proposed method and to present the numerical accuracy.

Precise Landing of Space Probe on Asteroid Using Multiple Markers

Abstract We propose a novel strategy for precise landing of a space probe on an asteroid surface. In Hayabusa mission, a Japanese asteroid sample-return spacecraft launched in 2003, a small marker was dropped onto the ground and utilized as a landmark for landing. In this paper, we propose two scenarios to drop multiple markers one by one, with a view to more precise landing. Preliminary Monte Carlo simulation of guidance using multiple markers with assumption of some control errors are presented. It was indicated that more than one markers allow us to increase the landing accuracy compared to the conventional method using a single marker.

How to Establish and Maintain Orthogonal Constellation with Two Orbiters under J2 Perturbation

In this paper, we investigated how to establish and maintain orthogonal constellation of two orbiters around a planet, taking Mars as an example. We assumed a mission where two spacecraft (S/C) will be injected into the Mars orbit simultaneously. One S/C (MOA) has a low altitude orbit, while the other (MOB) has a highly elliptical orbit. It is assumed that MOB should look down upon MOA’s orbital plane at MOB’s apoapsis; i.e., the two orbits should be preferably orthogonal. Such constellation can be actually required in scientific missions featuring both global and in-situ observation of Mars atmosphere, and it can also be extended to application in other celestial bodies. How to keep the orthogonal constellation under perturbations or other restrictions, and how to establish it with small fuel consumption is the main topic of this paper.