Japanese first interplanetary mission PLANET-A for Halley’s comet exploration was successfully completed when the two spacecraft launched by M-3SII rockets, passed by the comet on March 8 and 11, 1986, and made scientific measurement. This paper gives a description of the M-3SII rocket, the latest version of the Mu launch vehicle. History of development, vehicle composition and a typical flight profile are presented with a review of the two successful flights.

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The M-3SII, the newest version of Mu launch vehicles, is a three stage, all solid propellant rocket motor enhanced by a strap-on booster system. It can carry 770 kg of payload to the low earth orbit (250 km circular) against the total mass of 62t. The paper will review the design and main characteristics of the M-3SII propulsion units.

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This paper describes newly developed structures and mechanisms of Mu-3SII launch vehicle, the process of development and some design features. Although Mu-3SII is a version of Mu-launch vehicles, most of the structural and mechanical items were newly developed or redesigned from it predecessor. A second stage motor casing made of newly developed maraging steel and two types of spherical motor casings made of Ti-4A16V were developed. An open-petal directly-fastening inter-stage joint, an open-petal marman-clamp joint and a marman clamp joint with light CFRP lattice structure are also described. The joints and jettison mechanism for strap-on boosters were designed so that brace push away the boosters from the core motor utilizing the acceleration of the core motor, resulting in a collision-free jettison. A unique clamp and jettison mechanism was developed for the nose-fairing, which clamps the halves of the fairing with each other at many points along the split line and releases by an action of a small number of initiators. The fairing is capable of collision-free jettison under an acceleration of up to 5 G. The tail cylinder and tail fins were redesigned from those of the preceding version of Mu-vehicles.

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Japanese first interplanetary explorer “SAKIGAKE” and “SUISEI” were successfully launched by M-3SII rocket last year. And they achieved close encounter with comet Halley providing satisfactory scientific data. In this paper, the attitude control system of M-3SII racket is described, focusing our attention on the 1st stage robust controller design and their flight results. The M-3SII series rockets are composed of 3 stage solid motors, in which control capability is given to the 1st/2nd stages and the strap-on boosters. The control electronics is the fully digital type system, and the sophisticated control logic together with the weight and power reduction has been achieved. Thus the inherent control difficulty of solid propellant rockets has been overcome.

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In this article, we summarize a number of scientific results from the Sakigake and Suisei missions to comet Halley, the first explorations of interplanetary space launched by Japan’s Institute of Space and Astronautical Science.

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