The aim of the 320 billion yen ETS-7 project is to acquire rendezvous-docking (RVD) and space robotics technologies, said ETS-7 program director Koichi Kibe. If ETS-7 works, it will enable future Japanese supply missions to dock reliably with the International Space Station (ISS), the first segments of which are due for launch by U.S. space shuttle in 1998. The tests, which began in February and ended in October at NASDA's Tsukuba Space Center, involved trying out crucial technologies vital to the future development of the Japanese Space Program.

ETS-7 consists of two units, a chaser and a target satellite. Injected into a 550 km orbit, the satellite will separate into two. It is hoped that the chaser unit, controlled via an earth station through NASDA's Communication and Broadcasting Test Satellite (COMETS), will then be steered to a distance of 10 kilometers from the target portion before returning and recombining. This maneuver, which will build Japan's experience in RVD, will be repeated four times during the satellite's eighteen month operational lifetime.

Considering that this is Japan's first time trying RVD, this year's proto-flight tests have proved critical, while simulating it on the ground has proved difficult, with the two units sliding along three-axis guide ways at Tsukuba's custom-built site, said Kibe.

Success in orbit will be reliant on an internal navigation system which contains three sensors. A GPS receiver will be used to compute the relative positions and speeds of the separated satellite units from 10 km out to the 600 meter final approach stage. The rendezvous laser radar (LR) will then take over, computing the target satellite's position and azimuth from 660 to 2 meters, whereupon the proximity sensor will make final attitude and positional adjustments. Of the three sensing systems, the LR and the proximity sensor represent cutting-edge technology, according to Kibe.

Taking six years to develop at NEC's Yokohama works, the LR is Japan's first laser ranging system. "We have learned much knowledge through the ETS-7 subsystems development. Especially, image-compression technology, image processing subsystem, spread-spectrum technology for communication subsystems, and laser ranging technology for rendezvous radar subsystems. We expect this new technology will be used widely in the future programs," said Tadaaki Morimura, a senior engineer at NEC's space division's satellite subsystems department.

NEC is also responsible for the proximity sensor, which is capable of autonomously acquiring the target satellite when it comes into the sensor's field of view. Emitting a modulated laser beam toward a reflector on the target satellite, the OBC calculates distance by measuring the degree of phase shift suffered by the demodulated reflected beam.

"As for these systems, high speed image recognition, stable laser emission, and effective bias/random error rejection method in a harsh orbital environment has been a big technical challenge for NEC. Another challenge has been to overcome the tight schedule for these newly developed subsystems," said Morimura.

The rushed schedule has been a problem for the satellite subsystems integrator Toshiba Corp. too, said Yoshiharu Shimamoto, a manager in Toshiba's space program division's planning group.

"The ETS-7's total systems package presents a very challenging program for us. Not only have we had a short development schedule of four and a half years, but this satellite's multi-mission tasks are very complex. We'll be operating two spacecraft at the same time and doing it with an inter-satellite communication link," he said. Grumbles from the contractors reflect the real pressure on all concerned to make a success of ETS-7, which is scheduled for a dual payload lift-off with the earth observation satellite TRMM next summer via NASDA's main workhorse launcher, the H-2. The ETS program is under intense scrutiny after 1994's ETS-6 fiasco when, despite a perfect lift-off, H-2 number two flung the 40-billion-yen, two-ton experimental communications test satellite into a highly elliptic orbit through the Van Allen radiation belt. It quickly disintegrated.

NASDA is heavily reliant on the ETS program for major technology development and research, and as such puts all it's eggs in one basket with each launch. The ETS-6 disaster helped spurn what will become the Mission Demonstration Satellite program (MDS), in which NASDA will use smaller, much simpler technology demonstration satellites on standard busses, saving money and decreasing the price of failure.

However, if ETS-7 courts catastrophe, the results will seriously hinder Japan's growing reputation in space, wrecking NASDA's ambitions to autonomously re-supply the Japanese Experiment Module on ISS and leaving NASDA embarrassingly reliant on the U.S. shuttle.