This paper shows the recent results of ISAS Mercury Orbiter mission study from trajectory design point of view, conducted by ISAS Mercury Exploration Working Group. Three options were studied; 1) Multiple Mercury flyby mission via Solar Electric Propulsion (SEP), 2) SEP orbiter, which uses SEP as a primary propulsion system for interplanetary transfer phase as well as Mercury orbit insertion phase and 3) Conventional bi-propellant chemical propulsion option. Detailed mission design description for SEP flyby and ballistic orbiter mission are noted in Ref.1 and Ref.2 respectively, while this paper focuses on the trajectory design strategy for the SEP orbiter (see also Ref.3 and Ref.4).

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A spherical balloon made of metal shell is one of the most capable vehicles to explore the low altitude Venusian atmosphere and to observe its surface directly. It is originated from the idea that the balloon shell functions both as a balloon skin in the dense Venusian atmosphere and as a container of pressurized lifting gas. The most important point for such a super-pressurized Venus balloon system floating at an altitude of 10 to 20 km is how to reduce the weight of balloon shell. We propose a modified Venus balloon probe system with double capsule technique by sharing the function of the shell into balloon skin and gas container. That is, a thin metal shell balloon is transported to the Venusian atmosphere in a pressure vessel of a little larger size so that a load by pressure difference does not develop on the balloon shell. When the capsule reaches the target floating altitude, the outer capsule is split and the balloon inside is jettisoned. Then this type of balloon suffers small stress by only fluctuations of the Venusian environment while floating. Hence, it can be a very thin shell and the payload weight becomes over twice as much as that by a single balloon system.

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NASDA and ISAS have been investigating the lunar explorer vehicle which is based on Japanese technologies. The spacecraft consists of an orbiter, a relay satellite, and experimental landing probe for acquisition of the basic soft-landing technology. The major purpose of this landing probe is demonstration of soft-landing based on Japanese technology for future activity on the Moon. This is the first experience in Japan but the landing probe has a quite challenging technique: the autonomous soft-landing. This paper shows the conceptual design results conducted by NASDA in 1996. At first, we describe the outline of the flight sequence for landing. And we show the investigation results of the guidance algorithms for the powered-descent and vertical-descent phases, and show the results of navigation and guidance simulations for the powered-descent phase. At last, the autonomous obstacle avoidance control during vertical-descent are described which will be required for safe or high-precise landing in the future lunar missions.

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This paper focuses the aerodynamic instability motion of MUSES-C and DASH reentry capsule. Although, both capsules are same design with spherical blunt nose and conical body, reentry conditions, that is, the reentry orbit and the initial attitude, are different. In this paper, the orbital and the attitude parameters of the both missions are compared at first, and then, the attitude motions are analyzed, in which pointing error, spin rate and nutational motion are considered as initial error sources. Experimental results of a balloon drop test are also described to evaluate the dynamic motion of the capsule in the transonic speed.

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