LEV-1

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

The problem

A rover carried by a pinpoint lander gets the mass and power left after the lander’s legs, propulsion and guidance. SLIM landed by a deliberate two-step tip-over onto a slope, and its leg arrangement was selected in 1000-case Monte Carlo sweeps in which success rates ran from 92.5 percent for a six-leg design down to 38.7 percent for a design with a single deck leg [2]. Guidance used crater-matching vision-based navigation and 50 m obstacle detection [3]. The landing ended with the lander resting about 90 degrees from its planned posture after one of two main engines lost most of its thrust [9]. A rover that must leave such a vehicle cannot count on a level deck and a ramp.

The surface it then faces is loose regolith, and the equatorial day-night swing runs from 120 to minus 130 degrees C, which restricts most lunar missions to one sunlit day [36]. Wheel behavior in that soil changes with gravity: in parabolic flight a cone index gradient measured in lunar gravity was about 4 times lower than in 1 g at unchanged density [31]. At 2.1 kg the rover also has little mass for a wheel base, a thermal system or a high-gain link, and the pre-launch briefing gave this scaling as the reason for hopping [11].

What has flown

Surveyor 6 (1967). The one propulsive hop flown on the Moon is the reference case for low-cost hopping in a 2019 JPL briefing: a 2.5 s firing lifted the spacecraft 4 m and moved it 2.5 m sideways [19]. Until the Hayabusa2 landers of 2018 it was the only successful hop on another body [19].

MINERVA (Hayabusa, 12 November 2005). The 591 g hexadecagonal rover hopped by spinning a torquer inside its body [15]. It was released, left the asteroid above escape velocity, survived about 18 hours and returned one image, of the Hayabusa solar paddle [15]. Its design maximum hop speed of 9 cm/s was never demonstrated in flight [16].

MASCOT (Hayabusa2, Ryugu, 2018). The lander left Hayabusa2 at 41 m altitude, fell for 5 min 51 s (pre-landing plans called for separation at about 60 m [22]), struck a shadowed boulder at 17.0 cm/s, bounced four more times over 18.64 m, and then worked for 17 h 14 min, including an uprighting maneuver, a 70 cm hop, a 3.6 cm mini-move and an 11.6 cm relocation [21]. One 25 mm brushless motor with a harmonic drive provided both hopping and self-righting [20]. Its hops were commanded from the ground, whereas LEV-1 chose its hop direction onboard [21], [12].

LEV-1 (SLIM, 20 January 2024 JST). LEV-1 was developed by ISAS/JAXA with the Tokyo University of Agriculture and Technology and Chuo University to demonstrate leapfrog locomotion on the lunar surface [9]. It is reported as the first robot to hop on the Moon [12], [7]. The ISAS account describes a deployer, LEV-M, that released both rovers at about 00:19:50 JST at the start of SLIM’s final free fall, and the first S-band signal reached Uchinoura and Usuda at 00:20:20.20 [8]. The vehicle repeated a cycle of attitude control on its single wheel, heading pointing, then a hop [8]. The hop count is six in the JAXA briefing five days after landing and seven in the later ISAS article [12], [13]. Hop direction was chosen onboard from camera imagery, with no command from Earth [11], [9]. Transmission lasted 1 hour 51 minutes from separation and ended at battery depletion [12]. Surface imagery from LEV-1 was not confirmed [7].

LEV-2 / SORA-Q (same mission). The 228 g companion is a transformable sphere of about 80 mm that cannot reach Earth directly and sends data to LEV-1 by Bluetooth [9], [14]. Photogrammetry on two returned images places a 0.13 m move and a rotation of about 180 degrees between them, and telemetry shows operation for at least about 108 minutes [5]. Its image of SLIM reached the ground through LEV-1, which showed the rover-to-rover link worked [4]. It originated in a JAXA Space Exploration Innovation Hub call answered by TOMY in 2016 [6].

What is being tried now

Ballistic hoppers for crewed exploration (proposed in 1968). A Stanford report designed and simulated a one-person hopper and a two-person Lunar Hopping Transporter that accelerate up a thrust leg, fly a parabola and brake on landing, with a simulated average traverse speed of 30 km/h for the larger vehicle [1]. No hardware was built.

Spring and flywheel hopping rovers (ground tested; flown on MINERVA and MINERVA-II). A JPL egg-shaped prototype stored 3.2 J in a spring charged by one motor and weighed 840 g [17]. A Caltech and JPL single-actuator successor reached an 80 cm vertical jump and a 30 to 60 cm leap in Earth gravity at 20 percent spring-to-takeoff efficiency, and a second generation with a six-bar nonlinear spring linkage reached an inferred 70 percent [18]. The internal-torquer mechanism flown on MINERVA was drop-tower tested at 490 m, with measured hop speeds of 28.5 to 69.0 mm/s [16].

Rocket-propelled hoppers for shadowed terrain (in development). The Intuitive Machines Micro-Nova, called S. P. Hopper on the IM-2 mission, is a 30 kg, 70 cm demonstration vehicle with a 60 kg variant quoted at a one-way range over 30 km [34]. The planned five-flight sequence included hops of 20 m, 90 m and 300 m [35]. IM-2 landed in March 2025 and the hopper was never released, so no hop result exists [34], [35].

Small-body landers and rovers (flown, and in preparation). MASCOT and MINERVA are the flown cases. Its descent was modeled with discrete element simulations of bouncing on regolith, 270 runs at 19 cm/s impact speed [24], and the landing-site rock was later compared with returned samples, with porosity of 0.50 and grain density of 2848 kg/m3 [23]. IDEFIX, the 23.47 kg CNES/DLR rover for Phobos, weighs about 0.1 N in Phobos gravity, caps its driving speed at 1 mm/s, and carries a nominal requirement of 100 m of traverse in 100 days [33]. Its WheelCams resolve about 100 micrometers per pixel to measure wheel-soil interaction [32]. Neither paper reports flight results.

Wheel design for light lunar rovers (ground tested, then flown on LEV-1). LEV-1’s roughly 300 mm wheel used a 90-degree-tilted octagonal grouser chosen with a resistive-force-theory model, validated in single-wheel tests at 54 N in Tohoku silica sand No.5 and in DEM simulation, and then compared with operation on the Moon [29]. Those tests ran in Earth gravity on a terrestrial sand [29]. In slope tests of a 35 kg rover in Toyoura sand, 12-grouser wheels cut slip ratio from 0.9 for grouserless wheels to 0.2 [30]. Granular scaling laws came within 8.5 percent on drawbar pull in parabolic flight, and the equal cone index gradient method overstated mobility [31].

Legged hoppers and walkers (simulation and bench only). A reaction-wheel bipedal hopper of 8.2 kg was simulated over a 7-hop sequence on synthetic cratered terrain, with 0.8 m hops and 15 to 20 degrees of pitch deviation [26]. A tethered 3-DOF hopping leg of 12.45 kg with a custom knee gearbox produced repetitive hopping, a step-up and a front flip on the bench [25]. A reinforcement-learning controller for the 15.65 kg Magnecko cut locomotion power from 19.2 W to 12.2 W in lunar gravity simulated by a constant-force spring offload [27]. A 13.5 kg derivative raised mean joint torque from 0.418 to 0.521 Nm when a granular foot-soil model replaced rigid contact in simulation [28]. None has flown.

The numbers

Parameter	Value	Source
Mass	2.1 kg	[7], [9]
Locomotion	hopping, with a single wheel for attitude control and heading	[8]
Power	solar cells with an internal battery	[8], [12]
Transmitter	90 g; UHF and S-band	[11], [7]
Antenna	S-band patch antenna on the back of the body	[8]
Autonomy	full, with no commanding from Earth	[7], [12]
Direct-to-Earth range	about 380,000 km	[7]
One-way signal delay to Earth	about 1.3 s	[13]
Onboard computer temperature during activity	above 70 degrees C	[12]
Battery recharges from SLIM during cruise	30	[13]
Hops	6 or 7	[12], [13]
Transmission duration	1 h 51 min from separation	[12]

Rover or lander	Mass	Hop or move data	Source
LEV-1	2.1 kg	no distance published	[9], [7]
LEV-2	228 g	0.13 m and 180 degrees between two images	[14], [5]
MINERVA	591 g	design maximum 9 cm/s, never flown at that speed	[15], [16]
MASCOT	about 9.8 kg	70 cm hop, 3.6 cm mini-move, 11.6 cm relocation	[20], [21]
Surveyor 6	spacecraft	4 m high, 2.5 m sideways	[19]

The beacon was charged 30 times through the SLIM multiband camera electronics over four months of cruise, and Earth-orbit operations in September 2023 were battery charging and UHF beacon transmissions for amateur radio operators [13], [11]. UHF downlink was opened to amateur radio operators, and ISAS describes the result as the first amateur radio station on the lunar surface [7], [8]. The lander, with no isotope heater, was recontacted after three lunar nights, while LEV-1 was not, and JAXA kept a reception watch in case a changing sun angle restored power [9], [7]. Reception was at the Usuda and Uchinoura stations [8], [12].

What is not established

No hop distance, height, heading accuracy, landing attitude or per-hop energy has been published for LEV-1, so its mobility cannot be compared numerically with MASCOT’s 70 cm hop [21]. The hop count is six in one source and seven in another [12], [13]. Whether LEV-1’s planned imaging failed to be taken or to be returned is not stated [7]. No thermal control design, processor, camera or data rate specification is public, and the peer reviewed flight record describes the rovers only qualitatively [9]. The JAXA releases carry no telemetry, and every mass figure traces to JAXA [7]. The wheel design is validated on Earth sand in Earth gravity, with lunar operation as the only flight check [29]. Hopper concepts for shadowed terrain and legged hoppers have no published lunar hop data in the held sources [34], [26], [27].