LEV-1

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

Overview

A rover put down by a pinpoint lander has a mass and power budget set by what the lander can spare after its own landing legs, propulsion and guidance hardware, not by what a free-standing mission would choose. SLIM’s own touchdown was itself a demonstration: a two-step landing in which the vehicle comes down on a primary leg, deliberately tips forward and settles on its side, a sequence whose leg arrangement JAXA had modeled years earlier in 1000-case Monte Carlo sweeps that traded a six-leg configuration’s 92.5 percent success rate against a single-deck-leg design’s 38.7 percent [2]. Landing on a slope with that geometry, verified in flight by SLIM’s own vision-based crater-matching navigation and obstacle detection system [3], rules out a wheeled rover riding straight off a ramp the way earlier surface deployments have used. LEV-1 answers that constraint with a mobility mode that needs no ramp at all: a hop, controlled from a static base by a small pair of wheels used only for attitude and azimuth, repeated until the vehicle has crossed the ground it needs to.

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 [7], [9], [10]. 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, a design JAXA had briefed publicly before launch [11]. Hopping as a low-gravity mobility mode is not a new idea by the time LEV-1 flew it: Stanford’s 1968 analysis of a ballistic hopping transporter for Apollo-era lunar use had already worked out that a leg-mounted thruster accelerating a vehicle up through a parabola, then locking and decelerating on landing, is an efficient way to cross ground where gravity is weak enough that a hop travels far on little energy [1]. LEV-1 is the first vehicle to fly that concept and operate it as exploration mobility on a planetary surface [13].

LEV-1 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 rover LEV-2, also known as SORA-Q, a roughly 8 cm transformable sphere developed jointly by JAXA, the toy maker TOMY, Sony and Doshisha University from an open-innovation proposal that TOMY brought to a JAXA request for proposals in 2016, aiming explicitly to build an inexpensive robot from consumer toy and sensing technology [6]. LEV-2 deployed itself, righted its attitude, drove away from the lander imaging it, and selected and transmitted its own images without ground commands [5]; photogrammetric comparison of two of its returned frames against a shared rock in the scene showed it moved about 0.13 m and rotated about 180 degrees between them, confirming that both the transforming mechanism and the eccentric-wheel drive that keeps its small wheel from sinking in soft regolith worked on the Moon [5].

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 [13].

Specifications

Parameter	Value	Source
Mass	2.1 kg	[7], [9]
Locomotion	hopping
Wheels	a single wheel set, used for attitude control and azimuth pointing	[8]
Power	solar cells, with an internal battery	[8], [9]
Transceiver mass	90 g	[9]
Transmission bands	UHF and S-band	[8]
Antenna	S-band patch antenna on the back of the body
Autonomy	full, with no intervention from Earth	[8], [9]

The mobility cycle is attitude control on the single wheel set, then azimuth pointing, then a hop, repeated [13].

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 [13].

Parameter	Value	Source
Hops executed	7	[8]
Surface activity	the planned duration was completed	[9]
Battery charges through SLIM before deployment	30	[8]

LEV-1’s battery was charged 30 times before deployment through the SLIM multi-band camera electronics [13]. 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 [9]. 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 [8]. 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, the flight result JAXA reported against its pre-launch design [12]. No hop distance has been published for LEV-1 itself; its companion LEV-2 drove and was tracked by photogrammetry instead, moving about 0.13 m between two imaged positions [5], which is the only quantified surface displacement either rover has published.

Power and energy

The vehicle runs on an internal battery charged before deployment and on solar cells [8], [9]. 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 [13]. 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 [8], [9]. 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 [7]; on LEV-2’s side that included autonomously choosing which of several captured frames showed SLIM well enough to send, using a control and image-selection system built on a consumer sensing processor board [4], and reacting to at least one communication dropout with anomaly detection and self-recovery behavior that operated without ground direction [5].

Communications

LEV-1 carries its own transmitter and communicated directly with Earth rather than relaying through SLIM [7], [8]. 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 [9].

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 [13]. Two image data sets from LEV-2 were relayed; the joint announcement of the SLIM image identifies the successful arrival of that image on the ground as itself evidence that the LEV-1 to LEV-2 link worked as designed [4].

UHF transmissions were also made as a public outreach activity for amateur radio operators [9]. ISAS describes the result as the first amateur radio station on the lunar surface [13].

Payload and instruments

LEV-1 carries cameras, and image recording together with environmental observations was attempted during the surface phase [8]. Its most widely published product is the joint photograph of SLIM on the surface, taken and transmitted with LEV-2 [7]. No camera specification has been published for LEV-1 itself.

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 [8], [9]. That sequence begins only once SLIM itself is down: the lander’s own two-step touchdown, verified against the vision-based navigation and obstacle-detection results from its January 2024 landing, is the event LEV-M’s release is timed against [3].

Ground operations

Reception was at the Usuda and Uchinoura ground stations [8]. There was no commanding of the vehicle during surface operations [9]. 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 [8], a 90 g communications unit that closed a direct link to Earth from about 380,000 km [9], and the demonstration that two robots can operate simultaneously and communicate with each other on the surface without ground intervention [7]. It is also the first flight validation of the ballistic hopping principle worked out on paper decades earlier for crewed lunar transporters [1], now flown as an uncrewed exploration mobility system instead.

What is not established

No hop distance, hop height or per-hop energy figure has been published for LEV-1, so its mobility performance can be compared to the concept studies that preceded it only in kind, not in number. No thermal design, processor or data-handling specification is public. A JAXA project review press briefing released after landing would likely hold additional post-landing detail, but its file is corrupted and it could not be read.