Takayuki Yamamoto

DESTINY⁺ is a small-class science program led by ISAS of JAXA and is under development for launch in FY2024−2026 with both engineering and science goals. The engineering goal is to acquire technologies that will enable future high-frequency exploration of the solar system. Ion engine operation technology in planetary orbit and high-speed flyby technology of small bodies will be demonstrated. The scientific goal is to elucidate the characteristics of dust that may have transported organic matter to the primordial earth. In-situ analysis of dust at Earth's orbital position and a flyby observation of the asteroid (3200) Phaethon, the parent body of the Geminid meteor shower, will be conducted. The spacecraft system consists mainly of the proven onboard equipment of the small scientific satellite standard bus and Hayabusa2, and the scope of new development was focused on the minimum necessary to achieve low-cost and short-term development. The science instruments are a dust analyzer for in-situ dust analysis during the entire mission, a telescopic camera and a multiband camera for observing Phaethon's surface. The telescopic camera is equipped with a rotating mirror to track Phaethon during the high-speed flyby with a relative velocity as high as 36 km/s.

DESTINY+ is an upcoming JAXA Epsilon medium-class mission to fly by the Geminids meteor shower parent body (3200) Phaethon. It will be the world's first spacecraft to escape from a near-geostationary transfer orbit into deep space using a low-thrust propulsion system. In doing so, DESTINY+ will demonstrate a number of technologies that include a highly efficient ion engine system, lightweight solar array panels, and advanced asteroid flyby observation instruments. These demonstrations will pave the way for JAXA's envisioned low-cost, high-frequency space exploration plans. Following the Phaethon flyby observation, DESTINY+ will visit additional asteroids as its extended mission. The mission design is divided into three phases: a spiral-shaped apogee-raising phase, a multi-lunar-flyby phase to escape Earth, and an interplanetary and asteroids flyby phase. The main challenges include the optimization of the many-revolution low-thrust spiral phase under operational constraints; the design of a multi-lunar-flyby sequence in a multi-body environment; and the design of multiple asteroid flybys connected via Earth gravity assists. This paper shows a novel, practical approach to tackle these complex problems, and presents feasible solutions found within the mass budget and mission constraints. Among them, the baseline solution is shown and discussed in depth; DESTINY+ will spend two years raising its apogee with ion engines, followed by four lunar gravity assists, and a flyby of asteroids (3200) Phaethon and (155140) 2005 UD. Finally, the flight operations plan for the spiral phase and the asteroid flyby phase are presented in detail.

A nitrous oxide (N₂O) / ethanol propulsion system has been studying in ISAS/JAXA since 2003. The propellant combination can be characterized as a bi-propellant with extremely low toxicity, room temperature storability, low freezing point, and high energy density, which is applicable to spacecraft propulsion systems. So far, seven series of captive firing tests including high altitude tests were performed with a breadboard model (BBM) of 2 kN thrust class propulsion system which was built for evaluating its propulsive performance and system operability. In these tests, the capabilities of prototype of a like-doublet impingement injector and the durability of a combustion chamber made of a heat resistant fiber-reinforced ceramic composite (SiC/SiC) were evaluated. From the viewpoint of the engine system design, a relationship between the wall heat flux determined with the water cooling combustion chamber and the propellant mixture ratio was examined from the test results. Findings and issues to be associated with the injector design and the engine operation were also obtained in the present study. This paper presents an overview of the achievements of the technology demonstrations with the BBM.

<p>In this paper, anomaly detection that is configured as a combination of state observer and Mahalanobis-Taguchi (MT) method is proposed for real time fault detection of rapid and dynamic phenomena such as rocket engine operation. Real time anomaly detecting is recognized as one of the most important elements to realize advanced reusable space transportation system. Conventionally, bottom-up type anomaly detecting logic based on failure mode and effect analysis (FMEA) is usually used for this purpose, however, it requires large amount of time and labor. The proposed method can improve this process. In the present method, error values between calculated ones through rocket engine simulator constructed on autoregressive moving average model and extended Kalman filter (EKF) and measured ones are standardized with existing normal operation data of the rocket engine so as to compute Mahalanobis' distance, which expresses degree of anomaly. We performed engine hot firing tests in simulated anomaly conditions. The obtained data was processed with the present method, and the simulated anomaly in the tests was detected as expected.</p>