JAXA has a plan to send a spacecraft to the Martian moons in the 2020s. The spacecraft needs to transfer to the orbit of one of the Martian moons. In this study, we investigate the maneuver design method and the characteristics of orbit injection that minimizes the velocity increment Δv for the JAXA's Martian exploration mission. In the previous study, a transfer trajectory with three impulsive maneuvers has been demonstrated and it has been shown that setting the initial argument of periapsis to be zero is effective to reduce the Δv for the transfer. In this paper, we proposed the optimal transfer trajectory with four impulsive maneuvers based on the grid searching of maneuver position. First, it is shown that when the declination of v-

is large relative to the Mars equatorial plane, there exists a region where adopting four impulsive maneuvers reduces the total Δv compared to the three impulsive maneuver transfer. Also, we show that optimal value of the initial argument of periapsis slightly deviates from zero when the declination is large. Finally, we investigate which transfer type has the smaller Δv for each of the possible launch windows of JAXA's Martian exploration mission.

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On July 11th, 2019, the Hayabusa2 spacecraft achieved its second touchdown on the asteroid Ryugu with a 0.6 m accuracy. The landing was accomplished based on the newly implemented Pin-Point Touchdown (PPTD) method. It was extended from the former Touchdown (TD) method established by the Hayabusa spacecraft. When changing the point of view, two TDs of Hayabusa2 are regarded as successful autonomous rendezvous-dockings (RVDs) against the artificial landmark in deep space more than 15 minutes of light time from the Earth. This paper proposes the Deep Space Orbital Transfer Vehicle (DS-OTV) concept inspired and driven by Hayabusa2 technology to economically support various future deep space missions. The DS-OTV usually stays in a parking orbit at the boundary of the Earth system and possesses autonomous RVD functionality against the visiting deep space probes. The OTV provides the following services: (1) refueling of chemical bipropellant to the probe enabling it to transfer into the interplanetary trajectory by itself, (2) insertion of the visiting probe into the high-C3 Earth free-return orbit. This paper introduces the background and the concept of the OTV, and the simulation-based feasibility analysis results applying the Hayabusa2's PPTD method to the DS-OTV mission.

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This paper outlines the operation result of the reentry terminal guidance phase of the asteroid explorer Hayabusa2. Hayabusa2 successfully returned to Earth after 12 months of the return interplanetary cruise using the ion engine. The last 2 months of the return cruise required accurate trajectory control. In this phase, called the reentry terminal guidance phase, a series of precise trajectory correction maneuvers were performed to accurately guide the spacecraft to fly along a reentry corridor so that the sample return capsule could land within a designated zone in the Woomera desert, Australia. In this paper, the design methodology and operation result of the reentry terminal guidance, focusing on the trajectory guidance aspect, were discussed. The entire reentry terminal guidance operation was successful, and the sample return capsule was precisely guided and landed on the Woomera desert on December 6, 2020, contributing to the perfect success of the Hayabusa2’s asteroid sample-return challenge.

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The Martian Moons eXploration (MMX) mission is now under study by the Japan Aerospace Exploration Agency (JAXA). Its scope includes the world's first landing on one of the Martian moons, collecting samples from the surface, and returning to Earth. This paper describes the orbit design for MMX. Nominal and backup trajectories for launch in 2024 and 2026 are discussed. The Mars orbit insertion (MOI) sequence using 3-impulse maneuvers is introduced. A new scheme, the robust MOI, is also proposed as a contingency to enhance the robustness of the mission sequence. A method to design a robust MOI trajectory and examples are presented.

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On February 15th, 2013, a meteor with size of about 20 m in diameter entered the Earth's atmosphere over Chelyabinsk, Russia, and exploded at an altitude of about 20 km, damaging about 4,500 buildings and injuring about 1,500 residents. This incident widely invoked an interest in hazard mitigation caused by a NEO. Motivated by such interests, this study focuses on a new concept of NEO detection and impact warning system. In this concept, a space telescope is placed at the L1 point of the Sun-Earth system to intensively observe the NEOs in-coming from the noon-side, which ground-based observatories hardly detect because of the sunlight. Throughout some cases of simulations, this paper reveals the distributions of NEO directions at detection, V-infinity vectors at the Earth impact, and the NEO orbit determination precision are evaluated.

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