Sounding rockets have been developed and launched by ISAS for more than 40 years. They have been dedicated to astrophysical observation, upper atmosphere exploration, space plasma physics, etc., for scientific research. Making use of these flight opportunities, ISAS engineering studies have also been conducted to demonstrate new vehicle systems such as attitude control systems, reentry flight technologies, recovery systems, new avionics, etc., some of which will be employed in the coming satellite launch vehicles and spacecraft. The community of micro-gravity utilization for both material research and life science also uses the sounding rockets.
The S-310 is a single-stage sounding rocket, 310 mm in diameter, and can reach an altitude of 150 km. In case of S-310, it is spun positively in the atmosphere to overcome resonance, and thus avoids continued resonance problems. It also corrects for attitude disturbance by aerodynamic damping. The spin is provided by twisted tail fins which cause 2.8 Hz spin to the body.
The thrust programming is designed to peak in the early stage, and to keep the thrust level low in the latter half of burning time, when aerodynamic forces increase dramatically. This contributes to attaining increased summit altitude, and relieving aerodynamic heating by reducing dynamic pressure. The chamber is made of AISI 4340 steel. The CTPB composite propellant grain is single, and has axially two different wagon-wheel port configurations. Since the aftward portion of the grain is consumed earlier, a dual-thrust profile is given. Each tail fin is made of a solid titanium plate, and the ogive nose cone is made of FRP.
In the payload bay is a yo-yo despinner system, which is actuated at 50 sec. after lift-off, to reduce the spin to 1 Hz during the observation period.
The first flight of S-310 in January, 1975, was successful, and it has been launched at Kagoshima Space Center at Uchinoura, and Showa Base in Antarctica.
The S-520 is a powerful single-stage rocket which is optionally equipped with three-axis attitude control and a recovery system. It has a capability for launching a 100 kg payload far above 300 km and provides more than 5 minutes for micro-gravity flight environments.
The S-520 was developed to replace K-9M and K-10 type sounding rockets, and succeeded in doubling the payload capability of K-9M by applying high-performance propellant, optimum thrust program, and lightweight structure.
The experience of S-310 was put to good use in the thrust programming and stabilization strategy of S-310, enabling quite stable flight performance since its first flight early in 1980.
The merits of S-520, such as simplification of flight operation without staging, settlement of impact-related maritime safety, and reduction of launch cost, make the application of this sounding rocket more meaningful.
The HTPB composite propellant grain is cast and molded in the case in the same way as the first stage of Mu launch vehicles. The propellant grain is single, and gives a dual-thrust profile similar to the S-310's. The forward portion of the grain has a seven pointed gear configuration and provides an initial period of high thrust, while the aftward portion with a simple tubular design sustains a lower level thrust period. The nozzle with an initial expansion ratio of 8:1 is designed to improve the effective specific impulse. The chamber is made of high tensile steel HT-140. For weight saving and heat resistance, the leading edge of the tail fins is made of titanium alloy and their body is an aluminum honeycomb sandwich plate with GFRP/CFRP laminated surface plates.
Scientific instruments are stored inside the nose fairing made of GFRP, and common instruments are in the parallel section. As an option, an attitude control module or recovery module can be put into the part between common instruments and the rocket motor.
The fourth flight carried out payload retrieval, and the third flight, launched later than the fourth, performed attitude control of the nose by the hydrazine side jet system. The attitude outside the atmosphere is stabilized by spinning with tail fins. The spin reaches 2.2 Hz at the last stage to be decelerated using a yo-yo despinner system.
The SS-520 is a two-stage rocket, the first stage of which comes from the main booster of the S-520, and has a capability for launching a 140 kg payload to an altitude of about 800 km.
The SS-520 aims at reaching 800 km altitude, and at the same time, carrying out technological experiments concerning the development of a mini-satellite launch vehicle by adding the third stage atop. The first stage is stabilized aerodynamically by use of tail fins like the S-520.
As the second stage is heavier than the head of S-520, the aerodynamic margin is secured more than ever. The whole motor case of the second stage is made of CFRP. The spin generated in the first stage is succeeded by the second stage, and it is utilized in the Rhumb-line control and spin stabilization.
The SS-520 debuted in January, 1998, and ISAS has a plan to launch it from Spitsbergen, Norway, to send a payload into the cusp region of the geomagnetosphere.