JAXA’s OMOTENASHI: the world’s smallest space probe


Aiming for the ultimate goal of Japan’s first lunar landing, the Air of JapanSpace Exploration Agencyit is (JAXA) ultra-small space probe, OMOTENASHIaboard the United States National Aeronautics and Space Administration (NOTAHER) new rocket, currently plannedyouLEDs to launch just after midnight on the morning of Nov. 16 from Kennedy Space Center in Florida.

This is part of NASA Artemis Project, an international lunar exploration project. If successful, Japan will be the fourth country to reach the moonafter the former Soviet Union, the United States and China.

Science and Engineering at OMOTENASHI

OMOTENASHI has a length of 24 centimeters, a width of 37 centimeters and a height of 12 centimeters. It’s about the size of a small postal parcel, weighing 12.6 kilograms.

It is launched with NASA Orion spacecraft unmanned test flight, taking advantage of the excess capacity of the SLS rocket used for its launch.

Equipped with a solid propellant rocket and communication equipment, OMOTENASHI will separate from the rocket about four hours after launch and head to the moon on its own. The orbit will be remotely controlled from Japan and is expected to reach the lunar surface around 6 daysyes after launch.


The radiation to which OMOTENASHI is exposed during the flight will also be measured. In turn, this information will be useful for future manned missions.

A total of 10 ultra-small satellites from the United States, Japan and Italy will share the SLS. Among them, OMOTENASHI will be the only one to land on the moon.

Equuleus, developed by JAXA and the University of Tokyo, will also be on the SLS. And it will head for the “Lagrange point”, a point on the other side of the moon where the gravity of the Earth and the moon balance each other.

Omotenashi Lunar Lander
Scientists are donkeysassembly of the OMOTENASHI lunar probe. JAXA/NASA)

OMOTENASHI Difficult standards

Can a parcel-sized probe reach the moon? The development of OMOTENASHI was also a challenge to the standard. The world’s smallest spacecraft is full of the dreams and technology of researchers who persisted in aiming for the moon.

“No one has made such a small lander. The project was quite a challenge”, explains the professor Tatsuaki HashimotoPhD (59), Head of OMOTENASHI Development Team at JAXA Institute of Space and Astronautical Sciences.

NASA’s “invitation” came in late August 2015. They asked for proposals by October for ultra-small satellites to be carried by the SLS, and JAXA immediately raised their hands.

Hashimoto is a skilled researcher who has spent more than ten years working on large-scale moon landing projects such as Selene 2. However, due to budget constraints, the Selene 2 project was canceled and he had the bitter experience of seeing a door to lunar exploration close.

The initial period given to the OMOTENASHI development team was approximately one and a half years. This is a very short period of time, unthinkable for the development of a typical spacecraft. However, “with the odds right in front of us, there was no way we could miss presenting a proposal.”


Together with his colleagues, Hashimoto developed and submitted the concept proposal in two weeks. NASA adopted it the following April. A development team was formed with Professor Hashimoto and four new researchers who had just joined JAXA that year.

Omotenashi Lunar Lander
Here is the lander of the OMOTENASHI lunar probe (© JAXA)

A path strewn with pitfalls

The feasibility of their plan, however, was low. Controlled deceleration should be used when landing spacecraft on the moon, which has gravity. Otherwise, it will crash on the surface.

To avoid accidents, lunar landers developed in the past were equipped with large motors and sensors and weighed more than 100 kilograms. On the other hand, NASA has stipulated that the craft must be the size of a small parcel to drive on the SLS.

Problems arose one after another amid the tight constraints, from unsuitable parts to the inability to tighten screws due to space restrictions. The functions of the antenna that sends signals back to Earth have been changed because the hose to inflate the airbag could not fit.

Regarding the deceleration process during landing, a very sensitive control device would be too bulky. So they decided to develop an ultra-small solid-propellant rocket that was harder to control but had powerful propulsion. They also aimed to land minimal parts, such as the antenna, rather than the entire body of the spacecraft.

However, the landing speed can reach 180 km/h, with an impact 10,000 times greater than the acceleration due to gravity on Earth. In order to protect the spacecraft, the shock absorption and resin fixing technology developed for JAXA’s lunar lander”THIN“, which is scheduled to launch this year, and the “LUNAR-A” lunar exploration program, which was canceled, were applied.

The young members visited other project teams on several occasions to learn and implement the technology.

Omotenashi Lunar Lander
The OMOTENASHI spacecraft. (© JAXA)

Origin of the name ‘OMOTENASHI’

The unique name comes from the fact that the launch was originally scheduled to take place before the Tokyo Olympics. Also, it was hoped that OMOTENASHI would welcome humans and spacecraft coming to the moon as the first probe to land on the moon during the lunar exploration era in Japan.

Based on the applications of other teams’ technology, Hashimoto said with a laugh, “I wanted to support the other projects with the knowledge gained during development. But I actually ended up receiving their ‘omotenashi’.”


The name is based on the Japanese word, but it is also the acronym of “Exceptional MOon Exploration Technologies Demonstrated by NAno Semi-Hard Impactor.” In other words, OMOTENASHI.

The development cost of the probe was ¥700 to ¥800 million JPY (5-6 million USD), a significant cost reduction. The technology to transport supplies to the moon, among other developments, is expected to also spread to the private sector, universities and research institutes.

If OMOTENASHI succeeds in transmitting radio waves to Earth after landing on the Moon, the mission will have been a success. He is also equipped with a camera, so if there is energy left, he will attempt to capture photographs of the Earth and the Moon.

According to preliminary calculations, the probability of a successful landing is about 30%. Hashimoto said, “It’s best to have a successful launch, but more than anything, we’d like to pass the technology we’ve gained so far into the future.”

The “world’s smallest spacecraft” challenge, which will pave the way for Japanese lunar exploration, has only just begun.


(Read the related previous report in Japanese to this Iink.)

Author: Yukiko Une


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