DLR Institute of Robotics and Mechatronics Planetary Exploration Laboratory

DLR (CC BY-NC-ND 3.0) [2].

A rover wheel-soil model needs two things no orbiter or lander telemetry can supply: a controlled patch of ground whose mechanical state is actually known, and a way to compare a simulated trajectory against a measured one on that same ground. Earth gravity, ambient air and a soil that has never seen the Moon or Mars all stand between a lab bin and the body a rover will drive on, which is why the founding critique of the field’s own governing equations argues that a pressure-sinkage or shear-displacement curve measured on one plate, in one soil, at one scale, is a property of that test setup and not a transferable soil constant [15]. Every facility in this family answers that problem differently: by measuring the ground it actually has rather than assuming a textbook value, by holding gravity, vacuum or temperature fixed and accepting the loss, or by moving outdoors to substitute terrain variety for environmental fidelity. The Planetary Exploration Lab at DLR Oberpfaffenhofen, run by the Institute of Robotics and Mechatronics, chose the first path.

The lab is an indoor soil bin of 55 m2 including a 3 m by 5.5 m variable slope partition, a purpose-built portable bevameter that characterizes the soil actually in the bin, and, since 2024, a 1500 m2 outdoor Moon-Mars test site next to it [1][2]. The indoor bin was specified from what a multibody wheel-soil simulation needs as input and output rather than from a wish list of capabilities: large enough to avoid side wall and bottom effects for an ExoMars breadboard-sized rover, a surface elevation measurement to build the digital elevation model the contact model consumes, a pose tracking system to compare simulated against measured rover position at matched samples, and a soil measurement device to produce a Bekker parameter map of the bin rather than a single averaged value [1]. That last choice is the lab’s answer to Wiendieck’s objection: instead of asserting that a handbook Bekker constant describes the soil, the bevameter measures the bin’s own pressure-sinkage and shear response plate by plate, at the scale the wheel will actually see [15].

Two other DLR terramechanics facilities are often confused with this one and are separate pages. TROLL, the single wheel rig, is a few hundred meters away on the same campus but belongs to the Institute of System Dynamics and Control. Where the Planetary Exploration Lab validates a whole-vehicle multibody model against a tracked rover, TROLL isolates one wheel on a force-controlled industrial robot and automates the soil preparation that used to dominate a terramechanics campaign’s cost: mechanical loosening, pneumatic fluidization, leveling and compaction folded into the same unattended sequence as the traction run itself [3][4]. TROLL grew out of a 2015 feasibility study that first asked whether an industrial robot arm, rather than a purpose-built gantry, could carry the force control a single-wheel rig needs [5], and a companion study on the same rig found that soil preparation, not measurement, is what limits how fast a testbed can turn over soil states, and that semi-automated compaction beats a human board walk on repeatability even though a skilled operator can still reach a higher peak density by hand [7]. The Landing and Mobility Test Facility belongs to the Institute of Space Systems and is 700 km north in Bremen [1].

Laboratory data

Parameter	Value
Operator	DLR Institute of Robotics and Mechatronics [2]
Location	Muenchner Strasse 20, Wessling, Oberpfaffenhofen, Germany [1]
Commissioned	Indoor bin described 2009; outdoor test site opened 2024 [2]
Type	Indoor rover soil bin with pose tracking, plus an outdoor analog terrain
Floor area	Indoor 55 m2; outdoor 1500 m2 [2]
Capabilities	Soil bin, Moon-Mars site, bevameter
Simulant or terrain	Dry quartz sand indoors; basalt, lava and granite outdoors [2]
Instrumentation	Eight-camera infrared optical tracking, better than 3 mm, 60 fps [1]
Ground truth	Tracked pose against simulation; bevameter map of the bin
Fidelity limits	1 g, Earth ambient, no vacuum, no thermal, no solar simulator [2]
Access	Not published. Institute-run
Cited by	rosalind-franklin [1]

Design space

Every terramechanics testbed in this family has to trade the same three things against each other: how faithfully it reproduces gravity and vacuum, how large or varied a terrain it can hold, and how directly it can tie a measured run back to a soil-contact model. ESA’s own ExoMars-era answer, developed alongside DLR’s, went a different direction: EADS Astrium’s locomotion subsystem trade study built three full-scale breadboards and tested them across three separate facilities in the UK, Canada and Switzerland rather than converging on one soil bin, and used a flexible-wheel model developed at DLR-Bremen to optimize the wheel design that the DLR Oberpfaffenhofen bin would later help validate at vehicle scale [8]. A parallel Canadian effort built RCAST, coupling a commercial soft-soil tire model to a multibody chassis simulation and checking it against single-wheel tests on Viking-derived lunar soil types, and found the model reproduced sinkage well but overpredicted drawbar pull once slip passed about 0.5, where the measured curve levels off [9]. ESA’s Automation and Robotics Section took a third route with its ExoTeR and MaRTA testbeds, iterating the whole rover platform, mechanical, electrical and software, across five years of campaigns rather than building a fixed soil bin around one model [10].

What the DLR lab shares with all three is the same starting constraint: none of them can buy vacuum, reduced gravity and a mineralogically correct regolith in the same room, so each substitutes something measurable for what it cannot reproduce. NASA Glenn’s answer to the regolith question was to engineer a simulant, GRC-1, by blending four commercial silica sands to match the cone-index gradient Apollo astronauts actually measured on the Moon, then publish a full geotechnical characterization, including bevameter terrain parameters, so any lab running dry sand can at least calibrate against a documented reference [11]. A JPL study went after the modeling side instead of the soil side, showing that a meshfree particle formulation reproduces the classical Bekker pressure-sinkage curve for a rigid wheel where a conventional Lagrangian finite-element mesh visibly fails, penetrating the wheel surface once the soil starts to flow [12]. DLR’s own contact modeling work went a third way, comparing homogeneous and heterogeneous multi-tier Bekker-based Soil Contact Models against a six-wheeled rover multibody model rather than resolving individual soil particles [6]. NASA’s most recent survey of contact models found the same gap at the level of real-time performance: five wheel-soil models run on identical hardware span roughly five orders of magnitude in speed, from a Bekker-based solver at 0.024 times real time to a discrete-element model at 9600, and only the slowest, most physically resolved models reproduce the sharp rise in drawbar pull as slip approaches 1, because Bekker-Wong theory has no term for soil being excavated out from under a wheel at high slip [13]. A NASA study of gravitational offset testing makes the same point from the other direction: a lunar rover’s slip on a slope measured at reduced weight on Earth badly understates its slip at true lunar gravity, so a bevameter reading taken at 1 g, however precise, is not automatically a lunar number [14]. The DLR lab’s response to all of this is narrower than any of them: it does not simulate reduced gravity and does not claim to, and instead concentrates on making the one thing it can measure, the bin’s own soil state, traceable enough that the multibody model built from it is honest about what ground it was validated against.

Capabilities

Indoor soil bin

Parameter	Value
Working volume	55 m2 of floor; original bin 10 x 5.5 x 0.5 m deep [1][2]
Vacuum	Not applicable. Ambient pressure
Temperature	Not applicable. No thermal capability
Illumination	Not published. No solar simulator described
Simulant or terrain	Dry quartz sand; tonnage and density control not published [1]
Slope	3 x 5.5 m variable slope partition; angle range not published [2]
Gravity offload	Not applicable. None in this bin
Instrumentation	Eight-camera infrared tracking, better than 3 mm, 60 fps [2]

The bin was specified from what a multibody simulation needs as input and output: large enough to avoid side wall and bottom effects for an ExoMars breadboard-sized rover, divisible into two parts so that two different soft soils can be held at once, with a surface elevation measurement to build the digital elevation model the contact model consumes, a pose tracking system to compare simulated against measured rover position at matched samples, and a soil measurement device to produce a Bekker parameter map of the bin [1]. The frame is built from standard aluminum tooling profile so the bin can be extended or moved.

The 55 m2 figure and the 3 m by 5.5 m variable slope partition come from DLR’s own 2024 survey of test sites, which is the most recent published description of the lab [2]. The original 2009 specification gives the bin as 10 m long by 5.5 m wide and 0.5 m deep [1]. No open document gives the partition’s slope range, its setting mechanism, or whether it moves under load. No article mass limit is published; the sizing argument is geometric rather than structural.

Bevameter characterization in this bin used dry quartz sand, Martian Soil Simulant D and milled Eifel lava, fitting all three plate sizes to the pressure-sinkage curve at once rather than by Bekker’s original two-plate averaging; the quartz fit was good and the two simulant fits only acceptable [1]. Neither a tonnage, a relative density target nor a preparation procedure between runs is published. The soil state is instead measured rather than controlled, by mapping Bekker parameters over the bin with the bevameter. DLR’s laboratory and infrastructure index carries images of the outdoor test field and of TROLL, but none of this hall [1].

Moon-Mars test site

Parameter	Value
Working volume	1500 m2, 4 m of elevation difference, about two thirds Moon
Test article limits	Crater traversable by wheeled and legged robots to 150 kg
Simulant or terrain	Sand, breccia and gravel of basalt, lava and granite
Slope	Crater slopes 15 to 35 degrees; 15 degrees loose, 35 degrees solid
Instrumentation	Optical tracking, 2 mm in four volumes, cm site-wide

Source: [2].

The outdoor site opened in 2024 and complements the indoor labs and the Scout rover mobility test bed [2]. It packs a crater, a hill, a tunnel, a canyon, bumps, cracks and rough walls into 1500 m2, with boulders of basalt, lava, granite, suevite and conglomerate, 230 V and 400 V three phase power, network access and Wifi, and a dedicated fiber link to the German Space Operations Center for telerobotic experiments from the International Space Station.

The terrain was derived from use cases rather than from a scenic brief. The crater requirements are stated as eleven numbered items: 10 m wide and at least 2 m deep, a bottom at least 2 m wide of loose material, traversable by wheeled and legged robots up to 150 kg, placed next to a hill giving 4 m of height difference top to bottom, with a 15 degree loose slope and a 35 degree solid slope with distributed rocks, mostly of volcanic material, draining rain easily, built to reduce weeding, and visible from a visitors area [2]. The 35 degree slope is drainage concrete, chosen to simulate a rocky descent and to stop the slope sliding off. The tunnel is 4 m long at 1.5 by 1.5 m with 1 m and 0.5 m branches, the smallest exiting directly into the crater [2].

Ground truth is an optical tracking system giving up to 2 mm accuracy in four dedicated tracking volumes and centimeter accuracy across the whole site, used for control as well as measurement [2].

Portable bevameter

Parameter	Value
Working volume	Tripod, used inside the bin; plate radii 0.025, 0.05, 0.075 m
Instrumentation	Electromechanical actuators, 0.05 mm displacement precision
Ground truth	Bekker parameter map of the bin itself, not of a sample

The bevameter was designed without reference to existing bevameter layouts, arriving at a tripod with electromechanical actuators and sensors in a real-time computing environment, delivering 500 N normal force and 20 Nm shear torque at 400 Hz [1]. Portability is the design decision that matters: it characterizes the soil actually in the bin rather than a sample removed from it, which is what makes a Bekker parameter map across the bin possible. Three plate radii, 0.025, 0.05 and 0.075 m, are used, and displacement precision is 0.05 mm [1]. NASA Glenn’s more recent DRAGON M rig automates the same measure-in-place idea a step further, loosening a bin through 96 auger holes and then running a cone penetrometer and bevameter across it, checked for repeatability across nine bin locations with no significant edge effects in the top 100 mm [13]; DLR’s bevameter solves the measurement half of that problem without automating the loosening half.

Instrumentation

The three measurement systems in the indoor lab were each specified against a simulation need. Pose comes from eight-camera infrared optical tracking at better than 3 mm position and 1 degree orientation accuracy at 60 frames per second, which is what allows a tracked rover trajectory to be compared against a simulated one at matched time samples [1]. Terrain geometry comes from a five-camera digital elevation mapping beam on a linear rail, giving about 1.5 mm in-plane resolution and 2 to 4 mm altitude error, which produces the digital elevation model the contact model consumes. Soil state comes from the bevameter.

Outdoors the equivalent function is the optical tracking system, at up to 2 mm in four dedicated volumes and centimeter accuracy over the whole 1500 m2, which serves both as ground truth and as the control input for multiple robots at once [2].

What it does not reproduce

Gravity. Neither the indoor bin nor the outdoor site reduces gravity, and neither carries an offload rig. Weight offloading at DLR is the separate LAMA facility in Bremen. That absence is not a minor fidelity gap: a rover’s slip response measured at Earth weight, even on the right soil, does not extrapolate cleanly to its slip at true lunar or Martian gravity, because the coupling between normal load and shear resistance is itself gravity dependent [14].

Vacuum, temperature and illumination. None of the three is provided indoors, and the outdoor site is under natural weather and lighting [1][2].

A mineralogical simulant. The bevameter work used dry quartz sand [1], and the outdoor substrates are terrestrial basalt, lava and granite gravels and sands selected for mechanical and visual relevance rather than for lunar or martian mineralogy [2]. Neither is characterized the way NASA Glenn characterized GRC-1 against Apollo cone-index data [11]; a reader who needs a documented simulant has to look elsewhere.

A controlled soil state. No preparation procedure, relative density target or tonnage is published for the indoor bin. The lab’s answer to soil variability is to measure the state with the bevameter rather than to reset it [1], which sidesteps rather than resolves the older objection that a single soil constant, however carefully measured, does not necessarily transfer between test setups at a different scale [15].

Campaigns run there

ExoMars locomotion model validation, 2009. The testbed and bevameter were built to close the loop between hardware and the three-dimensional multibody wheel-soil model DLR contributed to ExoMars: bevameter-derived Bekker parameters from the bin itself become simulation inputs, and tracked rover pose from the same runs becomes the comparison data [1]. See rosalind-franklin. The vehicle-scale wheel design that testbed validated built on the flexible-wheel model EADS Astrium and DLR-Bremen had already optimized for the ExoMars locomotion subsystem trade study [8].

Moon-Mars test site inauguration, 2024. Three experiments with the Lightweight Rover Units LRU1 and LRU2 and the Scout rover demonstrated the new outdoor site: autonomous navigation and mapping, autonomous manipulation and sampling, and advanced mobility tests [2].

What is not established

No open document gives the indoor bin’s slope range, its setting mechanism, or its behavior under load, and no published tonnage, relative density target or preparation procedure fixes the soil state between runs; the lab measures the state it has rather than resetting to a declared one [1][2]. Access terms are not published. Neither test site reduces gravity or provides vacuum, thermal control or solar simulation, and the outdoor substrates are chosen for mechanical and visual match to basalt, lava and granite rather than characterized against a lunar or martian reference simulant the way GRC-1 was [1][2][11]. How the bin’s measured Bekker parameters compare against the newer wheel-soil contact models surveyed elsewhere, which show order-of-magnitude differences in speed and in high-slip behavior between Bekker-based and particle-based solvers, is not addressed in either primary source [13]. Nor is there a published comparison against the automated single-wheel preparation and test cycle running a few hundred meters away at TROLL [3][4], or against the multi-year campaign histories ESA has published for ExoTeR and MaRTA [10], so how the DLR lab’s throughput and repeatability compare to either peer is a gap in the open literature rather than a settled question.