October 1981:Japanese rockets

On 11 February 1981, Japan’s National Space Development Agency (NASDA) successfully placed a 640 kg satellite, Kiku 3, into a geostationary transfer orbit using the first of its N-2 launchers. The N-2 and its predecessor (the N-1) are closely based upon the US Delta launcher.

The initial orbital parameters of Kiku 3 (formerly the Engineering Test Satellite 4) were given by NASDA as: 258kmx258km; inclination 28.6°. Kiku 3’s mission was defined as testing the functions of the on-board systems of the satellite with regard to obtaining the necessary technological experience for the operation of large-scale heavy satellites. Additional programme objectives included monitoring the performance of the N-2-1 launcher. Launch was accomplished from the Tanegashima Space Centre. The N-2 is capable of launching up to 330 kg (satellite plus apogee kick motor) into geostationary orbit, compared with the N-1’s 130 kg capability to the same orbit.

Although closely based upon the US Delta launcher, the N series launchers exhibit several Japanese innovations. The N-1 used a Japanese-developed (with US technical assistance) second stage motor, the LE-3. The first stage motor for the N-1 and N-2 is the US designed MB-3, manufactured in Japan under licence from the US. The Japanese also construct the launch vehicles under the same terms.

The N-1 has three solid rocket boosters (SRBs) clustered around the base of the first stage. These US developed engines are also built under licence. These Castor 2 motors were developed by the Thiokol Corporation, who also provide the third stage of the launchers. Following the failure of the solid fuel third stage, provided by Thiokol. on the N-1-6 launch in February 1980, which resulted in the loss of the ECS-b satellite, NASDA has accelerated efforts to develop its own solid fuel kick motor. Completion target for the stage is the mid-1980s.

The N-2 features several major improvements in its design which enable it to launch heavier geostationary satellites. These include the increased number of SRBs (9 on the N-2 instead of 3 on the N-1), lengthening of the first stage and the introduction of a US motor for the second stage propulsion system (SSPS). The first stage is manufactured from an aluminium alloy with a monocoque structure with a machined isogrid lattice. It has been lengthened to accommodate a 23% increase in fuel over the N-1. N-2 first stage propellant weight is 82 tonnes. The MB-3 main motor comprises a main chamber and two vernier engines. The verniers provide roll control to the time of main engine cut-off and control pitch, roll and yaw thereafter until separation of the first and second stages. The MB-3 provides thrust for 269 seconds. At launch, six of the SRBs are ignited simultaneously and the remaining three are ignited after thrust tail-off of the MB-3. All of the SRBs burn for about 38 s and are jettisoned simultaneously 85 s after lift-off. Trajectory and attitude control of the first stage is provided by the second stage Delta Inertial Guidance System (DIGS) via commands to an electronic control package in the first stage which gimbals the MB-3.

The SSPS uses an Aerojet AJ10-118F engine which has a restart capability and a firing duration of a total of 420s. The SSPS is an integral type stainless steel construction with a maximum propellant weight of 6 tonnes. During SSPS operation pitch and yaw commands are provided by the gimbal actuation system through thrust vector control of the main engine. Roll commands are controlled by the cold nitrogen gas Attitude Control System (ACS). During periods of coasting flight all three control functions are provided by the ACS which is also used to settle the propellants prior to SSPS restart. All manoeuvring commands originate from the DIGS located i the guidance section atop the SSPS. DIGS is a strapped-down inertial guidance system with an inertial measurement unit and a computer, providing commands to separate control packages in the first and second stages.

The third stage of the N-2 consists of a solid fuel Thiokol TE-M-364-4 motor, supplied by the US company, a spin-table and a spacecraft attach fitting. The motor is constructed from polybutylene with a total propellant weight of 1.1 tonnes providing thrust for 44 s.

The N-2 will be used as the launch vehicle for several important Japanese satellites scheduled for launch up to 1986. The first operational launch of the N-2 is due in August 1981,when it should place a US-built Geostationary Meterological Satellite (GMS-2) into an orbital slot located at 140°E longitude. Other geostationary satellites to be launched by the N-2 include two more medium communications satellites (CS-2a and b), two direct broadcast satellites (BS-2a and b) and AMES, the Aeronautical Maritime Engineering Satellite which will be used for communications experiments to small receiving terminals on ships and planes. In addition, the Maritime Observation Satellite, for Earth/ocean resources observations, will be placed into a Sun-synchronous orbit inclined 99° at an altitude of 900 km circular. Preliminary launch dates are: GMS-2 September 1981; CS-2a January/February 1983; CS-2b August/September 1983; MOS-1 (2-stage N-2) early 1985; BS-2a early 1984; BS-2b late 1985; AMES early 1986.

Japan will continue to develop improved launchers which,although still based upon the Delta, will continue to have Japanese equipment phased into them. The next launcher will be called the H-1A and will, by 1987 at the earliest, be capable of putting 550 kg into geostationary orbit. Before the first H-1A is flown, NASDA will launch an Engineering Test Vehicle in 1986 to verify the construction of the improved second stage which will incorporate a Japanese LOX/LH2 stage called the LE-5.