YAOKI

Dymon Co., Ltd.

Overview

YAOKI is a 498 g two-wheeled lunar rover built by Dymon Co., Ltd. of Japan, 15 x 15 x 10 cm, built around a single axle with one wheel at each end of a central body [3], [4]. It is designed to keep working after impact and after coming to rest either way up, and is rated to withstand 100 G. It flew on the Intuitive Machines IM-2 Nova-C lander, launched 26 February 2025 [1], and was not deployed because the lander came to rest on its side [2].

The vehicle was originally manifested on Astrobotic’s Peregrine lander under an agreement announced on 14 October 2019, for a 2021 flight [5]. Dymon states eight years of development with the base technology completed in 2018 and more than 100 tests passed.

The name is from a Japanese proverb about getting up again however many times one falls, and the self-righting design is the literal expression of it [3].

No peer-reviewed or conference publication on YAOKI was located. Vehicle numbers below come from Dymon and from Mitsubishi Chemical Group, which supplied the exterior materials [3], [4]. The NASA conference paper cited [1] covers the IM-2 flight, not the rover.

Specifications

Parameter	Value	Source
Mass	498 g	manufacturer [3], [4]
Dimensions	15 x 15 x 10 cm	manufacturer [4]
Wheels	2, on one common axle	manufacturer [5]
Impact tolerance	100 G	manufacturer [3], [4]
Body material	CFRP with cyanate ester resin matrix	supplier [4]
Wheel material	polyamide-imide
Camera lens treatment	anti-soiling coating
Self-righting	yes, operates either way up	manufacturer [3], [4]

Drive speed, slope limit, obstacle capability, power source, battery capacity, radio band, data rate, processor and thermal limits are not published.

Mission profile

These describe IM-2, not the rover.

Parameter	Value	Source
Lander	Intuitive Machines Nova-C, IM-2	[1]
Launch	26 February 2025
Planned surface duration	up to two weeks of lunar daylight
Landing	6 March 2025, Mons Mouton, 250 m from target	[2]
Outcome	lander on its side, rover not deployed
Mission end	7 March 2025

Athena landed on its side inside a crater at Mons Mouton, about 250 m from the intended site [2]. Intuitive Machines did not expect the lander to recharge, given the sun direction, the solar panel orientation and the crater temperatures, and declared the mission concluded on 7 March 2025. NASA’s PRIME-1 suite accelerated several payload milestones before the batteries depleted, and the TRIDENT drill did not penetrate the surface. YAOKI was not deployed.

The earlier Peregrine assignment did not fly with YAOKI aboard; the rover moved to IM-2 [5].

Mobility

Two wheels on a single axle [3], described by the manufacturer as the smallest effective rover wheels produced [5]. The architecture has no suspension and no steering actuators; with two ground contacts and a body suspended between them, attitude about the axle is unconstrained, which is why the vehicle is designed to operate inverted. Dymon states it can be thrown into a cave and continue working [4], which is the same requirement as the 100 G impact rating.

Wheels are polyamide-imide, chosen for cold and heat resistance, wear resistance and impact strength, specifically so the wheels survive being dropped onto the lunar surface from a deployer [4]. No drawbar pull, slip or slope data has been published.

Structure and materials

The body is carbon fiber reinforced plastic in a cyanate ester resin matrix, chosen for low permittivity and temperature resistance [4]. It replaced an aluminum design, and the substitution gave about 30 percent lower mass, a five times better safety factor, and about 4 million yen lower lunar transport cost per unit. The deployer that releases the rover from the lander uses the same cyanate ester CFRP. Mass is the cost driver for a vehicle of this class, and the material substitution is quantified against lunar transport cost rather than against structural performance alone.

Power and energy

No solar array, battery capacity or night survival capability is published.

Thermal

Not published as a subsystem [3]. The only thermal information is at material level: the cyanate ester CFRP body is selected for temperature resistance and the polyamide-imide wheels for cold and heat resistance [4].

Autonomy

None claimed in the manufacturer material [3], [5]. The vehicle is operated through the lander.

Communications

Through the lander, which on IM-2 also hosted a 4G/LTE network for other payloads [1]. YAOKI’s own band, data rate and range are not published [3].

Payload and instruments

A camera is the payload. Its lens carries an anti-soiling coating developed against lunar regolith, whose jagged particle shape and electrostatic behavior make it adhere to optics [4]. The photograph above shows the camera aperture flanked by two lamps on the body face. Sensor format, resolution and field of view are not published.

Modes of operation

Deployment is from a dedicated deployer on the lander, from which the rover is dropped to the surface [4].

Technologies developed

The transferable results are material substitutions with quantified outcomes: a cyanate ester CFRP body replacing aluminum at about 30 percent lower mass and five times the safety factor, polyamide-imide wheels qualified against drop impact, and an anti-soiling lens coating developed specifically against regolith adhesion [4]. The single-axle, two-wheel, operates-either-way-up architecture is the second result, and it has not been demonstrated on the lunar surface because the vehicle was never deployed [2].