OMOTENASHI: A Cornerstone of Japan's Space Exploration, Even After Missing a Lunar Landing

The space probe OMOTENASHI entered the sun's orbit after it missed its chance of achieving Japan's first lunar landing. The problem was due to a loss of control.

In the future OMOTENASHI will gradually separate itself from Earth. But in the process of its "failures," significant lessons were learned.

Moreover, its functionality has not been completely lost. And if the conditions are right, there remains an opportunity to conduct experiments in the summer of 2023.

How has OMOTENASHI made its mark?

Ultra-Small Space Probes Attract Attention

"We apologize for being unable to live up to everyone's expectations."

Dr Eiichi Sato, who leads the investigation team at the Japan Aerospace Exploration Agency (JAXA), gave the apology at a press conference on the current status of OMOTENASHI on December 20. At the press conference, officials also revealed a fuel leak from the gas jet. In turn, the gas jet turns liquid fuel into gas and ejects it to control the spacecraft's position and rotation. This is believed to be the cause of the failure.

Ultra-small space probes are relatively easy to attempt for universities, venture companies, and others that do not have significant financial resources. Because it is possible to try various experimental approaches, it is a field that is attracting a lot of attention as exploration plans for the moon, Mars, and other targets begin in earnest.

High Expectations for OMOTENASHI

OMOTENASHI was among these projects. Launched on November 16, 2022 aboard a large NASA rocket, it was a part of the first phase of the United States' National Aeronautics and Space Administration (NASA) Artemis mission that aims to send humans to the moon.

Its purpose was to collect data, for instance about the force of impact when landing on the lunar surface, that could be used in the development of future landing technology. However, after separation from the rocket, it repeatedly rotated at a high speed with the solar cell facing away from the sun. It was unable to regain its proper position, and landing on the moon was eventually abandoned.

Analysis of the flight data sent by OMOTENASHI determined that the cause of the abnormal high-speed rotation was a fuel leak from the gas jet that controls the aircraft's position and rotation.

Problem Due to a Fuel Leak on OMOTENASHI

OMOTENASHI's gas jet fuel is stored under pressure as a liquid in a fuel tank. The internal pressure is released when the valve attached to the tank is opened, which then turns the fuel into a gas that enters a device called a plenum. Beyond the plenum is the injection port. When the valve of the injection port is opened, the gas spouts out. Its force controls the craft's position and rotation.

Analyses show that liquid fuel leaked from the tank's valve and entered the plenum, which was supposed to hold only gasses. Furthermore, there were issues with the injection port, which was closed and turned off. Liquid fuel leaked in and was ejected, accelerating the rotation of the spacecraft.

JAXA explained that it had previously seen that liquid fuel could leak from the fuel tank to the plenum. However, it had determined that the leakage was at a permissible level. They also confirmed that there were no leaks to the injection port valves. As a result, it is suspected that the parts that sealed the valve of the injection ports had aged. Indeed, due to delays, the launch was three years after the tank was filled with fuel in September 2019.

Effective Hands-On Training for Young Researchers

"It was effective hands-on training for the young researchers on the team," stated Dr Sato during the press conference. Many lessons were learned during the development of the ultra-small spacecraft, which is still in its initial stages.

The gas jet installed in OMOTENASHI is a product of an American company. Although it has been used in overseas ultra-small probes, this was JAXA's first time using it. While JAXA conducted various tests to confirm its performance before use, Dr Sato reflected that better communication was needed. "The manufacturer best understands the characteristics and handling of the equipment. Therefore, when equipment is newly-adopted, it is necessary to make sure there is suffucient communication," he said.

In addition, the space probe is small in size. That allows several spacecraft to be launched together on the same rocket. However, depending on the circumstances of the rocket, the probe may have to wait for an extended period of time before launch. With this in mind, "we needed to further evaluate the impact of this delay on the individual spacecraft," he said.

OMOTENASHI's Contribution to the Future

In addition to these points of reflection, OMOTENASHI has also served as a source of future space development. In other words, this failure has been a valuable experience for young researchers, and will serve as a foundation for Japan's space development.

Dr Sato pointed out, "(Separate from the main investigation team), we formed a parallel team of young researchers and had them do their own analysis. Afterwards, we compared the results (with those of the main team) and had various discussions. For example, about where the analysis was lacking. In this sense, it was effective hands-on training."

Tatsuaki Hashimoto, who leads the OMOTENASHI project team, said that "it was very disappointing that we were unable to succeed in the project as planned." But he also noted that "while it's something we didn't want to have occur, (young researchers) can learn a lot from these types of encounters."

OMOTENASHI's solar cell is expected to receive sunlight in about March. Thereafter, it is expected to directly face the sun in July.

The spacecraft will be in communication range, so if the battery is able to be charged during this time, it may be possible to conduct experiments or collect data. OMOTENASHI's flight is still continuing as a cornerstone of Japan's space development.

(Read the article in Japanese.)

Author: Junichiro Ito