LEV-1

JAXA / Tokyo University of Agriculture and Technology / Chuo University.

Overview

LEV-1 is a 2.1 kg microrover carried by the SLIM lander and separated from it just before touchdown on the Moon on 20 January 2024 JST [1], [3]. It was developed by ISAS/JAXA in cooperation with the Tokyo University of Agriculture and Technology and Chuo University, and its main purpose was to demonstrate leapfrog locomotion on the lunar surface. It carries its own transmitter and returned data direct to Earth without passing through the lander. The photograph of SLIM on the surface was captured and transmitted autonomously and collaboratively by LEV-1 and its companion LEV-2, also known as SORA-Q.

The LEV system consists of three elements: LEV-M, the deployment device, and the two rovers LEV-1 and LEV-2. LEV-M released both rovers independently to the surface at the start of SLIM’s final free fall [2].

Specifications

Parameter	Value	Source
Mass	2.1 kg	[1], [3]
Locomotion	hopping
Wheels	a single wheel set, used for attitude control and azimuth pointing	[2]
Power	solar cells, with an internal battery	[2], [3]
Transceiver mass	90 g	[3]
Transmission bands	UHF and S-band	[2]
Antenna	S-band patch antenna on the back of the body
Autonomy	full, with no intervention from Earth	[2], [3]

The mobility cycle is attitude control on the single wheel set, then azimuth pointing, then a hop, repeated [2].

Mission profile

Event	Time, 20 January 2024 JST
Deployment from SLIM	about 00:19:50
First S-band signal received at Uchinoura and Usuda	00:20:20.20
Last amateur radio reception	about 02:10

Times from [2].

Parameter	Value	Source
Hops executed	7	[2]
Surface activity	the planned duration was completed	[3]
Battery charges through SLIM before deployment	30	[2]

LEV-1’s battery was charged 30 times before deployment through the SLIM multi-band camera electronics [2]. Ground receipt of the first S-band signal at Uchinoura and Usuda came about 1.3 seconds after it left the patch antenna on LEV-1’s back. After the final coherent data, an overseas amateur operator received a signal from LEV-1, and no intelligible data reached the ground after that.

The vehicle completed its planned surface activity and exhausted its battery as expected [3]. It now stands by on the surface with its power gone; JAXA kept a reception watch in case a changing sun angle restored solar generation and let it resume.

Mobility

LEV-1 moves by hopping, and it is the first hopping exploration rover to have operated on the Moon [2]. The wheels are used to control attitude and to point the vehicle in the chosen azimuth before each hop; the sequence of attitude control, azimuth pointing and hop was executed repeatedly, for seven hops in all. No hop distance has been published.

Power and energy

The vehicle runs on an internal battery charged before deployment and on solar cells [2], [3]. It operated until the battery was exhausted, which is what ended the surface phase. The battery was topped up 30 times during cruise through the lander’s multi-band camera electronics [2]. JAXA held open the possibility that a changing sun angle would restore solar generation and let the vehicle resume.

Thermal

No thermal control design has been published for LEV-1.

Compute and avionics

No processor, memory or data handling specification has been published for LEV-1.

Autonomy

Operation was fully autonomous, with no human intervention from Earth for either LEV-1 or LEV-2 [2], [3]. The vehicle ran the attitude control, azimuth pointing and hop cycle continuously and independently until its battery was exhausted. LEV-1 and LEV-2 cooperated without ground involvement to capture and return the surface photograph of SLIM [1].

Communications

LEV-1 carries its own transmitter and communicated directly with Earth rather than relaying through SLIM [1], [2]. Transmission used S-band and UHF, from a patch antenna mounted on the back of the body. The communications unit accounts for 90 g of the 2.1 kg vehicle, which JAXA assesses as the smallest and lightest system to have transmitted data directly to Earth from about 380,000 km [3].

The vehicle also carries a rover-to-rover link with LEV-2, receiving SORA-Q’s imagery over a short-range connection and forwarding it direct to Earth without passing through SLIM [2]. Two image data sets from LEV-2 were relayed.

UHF transmissions were also made as a public outreach activity for amateur radio operators [3]. ISAS describes the result as the first amateur radio station on the lunar surface [2].

Payload and instruments

LEV-1 carries cameras, and image recording together with environmental observations was attempted during the surface phase [2]. Its most widely published product is the joint photograph of SLIM on the surface, taken and transmitted with LEV-2 [1]. No camera specification has been published.

Modes of operation

The documented sequence is deployment by LEV-M during SLIM’s free fall, landing on the surface, S-band transmission and the start of surface activity, then repeated cycles of attitude control, azimuth pointing and hop with imaging and environmental measurement between hops, until battery depletion [2], [3].

Ground operations

Reception was at the Usuda and Uchinoura ground stations [2]. There was no commanding of the vehicle during surface operations [3]. Before deployment, ground operations consisted of battery charging campaigns through SLIM.

Technologies developed

The results LEV-1 established are a hopping mobility system that worked on the lunar surface with wheel-based attitude and azimuth control [2], a 90 g communications unit that closed a direct link to Earth from about 380,000 km [3], and the demonstration that two robots can operate simultaneously and communicate with each other on the surface without ground intervention [1].