Failure of Japan’s Epsilon rocket blamed on attitude control system

A Japanese Epsilon rocket lifts off Oct. 12 with eight small satellites. Credit: JAXA

Engineers investigating the Oct. 12 launch failure of a Japanese Epsilon rocket have traced the problem to the attitude control system on the second stage, Japan’s space agency said Tuesday.

The solid-fueled launcher took off from Japan’s Uchinoura Space Center in Kagoshima prefecture, located in the southwestern part of Japan, at 0050:43 GMT on Oct. 12 (8:50:43 p.m. EDT on Oct. 11) to boost payloads into orbit for the Japan Aerospace Exploration Agency, the Japanese commercial remote sensing company iQPS, and Japanese universities.

The Epsilon rocket aimed to place its eight satellite passengers into a polar orbit about 350 miles (560 kilometers) above Earth, using three solid-fueled stages and a liquid-fueled “post boost stage” to reach the missions target orbit. The 85-foot-tall (26-meter) rocket headed southeast from the Uchinoura Space Center, then veered south in a planned steering maneuver to avoid flying over populated islands.

The rocket’s first stage and second stage fired in succession to propel the launch vehicle to a speed of 10,800 mph (17,400 kilometers per hour) in the first five minutes of the flight. The Epsilon rocket also shed its nose cone after climbing above the thick lower layers of the atmosphere.

But the mission ran into trouble after burnout of the second stage motor. The launch profile included a coast phase lasting more than a minute-and-a-half before the planned separation and ignition of the Epsilon’s third stage to continue accelerating to orbital velocity.

Telemetry showed the rocket was misaligned for separation and ignition of the third stage motor. Eight small reaction control system thrusters on the Epsilon’s second stage were supposed to maintain the orientation, or attitude, of the rocket during the coast phase. Then tiny rocket motors around the cylindrical second stage were programmed to fire and spin up the rocket before releasing the third stage, which uses the spin to stabilize its orientation for its burn.

“At the time of deciding on separation of the second and third stages, we observed that the vehicle’s flight attitude was deviating from the target, and determined that it would be unable to enter the Earth’s orbit as planned,” JAXA, the Japanese space agency, said in a statement after the Oct. 12 launch.

A range safety officer uplinked a destruct command to the rocket at T+plus 6 minutes, 28 seconds, terminating the mission. Debris from the rocket was expected to fall into the Philippine Sea.

The failure was the first for Japan’s Epsilon rocket since the first flight in 2013. The Oct. 12 mission was the sixth launch for an Epsilon rocket, which serves the small satellite launch market in Japan alongside the heavier H-2A and future H3 rockets. The Epsilon was developed by IHI Aerospace in partnership with JAXA.

Officials updated the status of the Epsilon failure investigation Tuesday. The launcher performed normally until burnout of the second stage, when the reaction control system thrusters were supposed to point the rocket on the proper orientation for the third stage burn.

The reaction control system, or RCS, on the second stage consists of eight small hydrazine-fueled thrusters divided into two sets of four. Flight data showed one set of thrusters worked as expected, but the other set of four control jets did not function. Engineers determined the pressure in fuel pipes leading from the hydrazine tank to four of the RCS thrusters did not rise as expected when the rocket’s computer issued the command to activate the system, according to an Oct. 18 presentation by Toshiaki Sato and Takayuki Imoto, two JAXA engineers who oversee the Epsilon rocket program.

The problem caused the rocket’s attitude to deviate 21 degrees from the planned orientation. The second stage’s spin-up motors fired normally to impart the expected rotation on the third stage, eliminating that system as the cause for the launch failure.

Artist’s concept of the Epsilon rocket’s second stage motor firing, with the mission’s satellite payloads visible. Credit: JAXA

Investigators are still probing the root cause for the failure in the second stage reaction control system. Telemetry data indicated the computer issued the command to fire pyrotechnic systems to open a “pyro valve” on both sides of the RCS, allowing fuel to flow the thrusters.

Engineers so far cannot rule out a problem transmitting the signal to the pyro valve associated with the non-functioning thrusters, a failure of the pyro valve itself, or a blockage in the fuel supply line leading to the thrusters, engineers said Tuesday.

The investigation team will continue pursuing the root cause of the failure by analyzing flight data and evaluating imagery and records from the manufacturing and pre-launch inspection of the suspect hardware. Then engineers will propose corrective measures before the the next launch of an Epsilon rocket, according to JAXA.

The satellites lost on the Epsilon rocket Oct. 12 included JAXA’s Rapid Innovative Payload Demonstration Satellite 3, or RAISE 3, technology demonstration satellite. The 242-pound (110-kilogram) spacecraft, built by Mitsubishi Heavy Industries., carried seven technology experiments for a planned one-year mission.

The experiments on-board RAISE 3 included the demonstration of a new communications payload for Internet of Things applications, a new software receiver, a commercial computer design, water-based and pulse-plasma propulsion systems, and deployable structures to provide power generation, communications, and deorbit capability for future small satellites.

Two 375-pound (170-kilogram) satellites for the Japanese remote sensing company iQPS were also lost on the Epsilon launch failure. The QPS-SAR 3 and 4 radar surveillance satellites were built to become the first operational spacecraft in the company’s planned fleet of 36 orbiting Earth observation platforms, following the launch of two demonstration satellites in 2019 and 2021.

Five smaller CubeSats from Japanese universities and research institutes were also aboard the Epsilon rocket on the doomed Oct. 12 mission.

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