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Space Robotics

DLR Institute of Space Systems Landing and Mobility Test Facility

A KUKA KR500 on its linear rail holds a Philae model over the LAMA soil bed through the weight offloading suspension visible at the flange, with the lander's three-legged gear extended and a photogrammetric scale board along the bin wall.

DLR. Source: [2]. CC BY 3.0.

LAMA is a landing dynamics laboratory, not a drop tower. A six-axis industrial robot on a 12 m linear rail carries the test article through a commanded touchdown trajectory while a suspension device between the robot flange and the article removes most of its weight, so a lander designed for 1.6 m/s2 or for a comet can be dropped onto real soil at Earth gravity [1][2]. The soil is the point: the operators state that the facility exists because footpad and landing gear behavior on granular media cannot be obtained from a pendulum or a tilted plane, which “does not allow tests on granular media”.

It is run by the Institute of Space Systems in Bremen, in the Landing and Exploration Technologies department, which is a different DLR institute some 700 km from the Oberpfaffenhofen terramechanics laboratories, TROLL and the Planetary Exploration Laboratory [1]. The two rigs in the hall correspond to the two halves of the name: a landing rig that flies an article into the soil, and a mobility rig that drags a footpad or a wheel horizontally through it [1][2].

Laboratory data

Section titled “Laboratory data”
ParameterValue
OperatorDLR Institute of Space Systems, Landing and Exploration Technologies
LocationRobert-Hooke-Strasse 7, 28359 Bremen, Germany
CommissionedIn service by 2010; first published campaign 2011
TypeRobotic landing dynamics rig with active weight offloading, over a soil bin
Floor areaSoil bed 10 x 4 m, in a dedicated test cell. Cell area not published
CapabilitiesLanding test rig, mobility rig
Simulant or terrainWF34 quartz sand; MSS-D lunar simulant; concrete
InstrumentationATI Theta force-torque transducer in the robot flange
Ground truthRobot hand pose, 0.15 mm, every 12 ms; video to 600 fps
Fidelity limitsOffload interference remains; soil preparation dominates error
AccessInstitute-run. No external user route published
Cited byphilae [2]; mmx-rover [3]

Source: [1][2].

Capabilities

Section titled “Capabilities”

Landing test rig

Section titled “Landing test rig”
ParameterValue
Working volumeDrops onto a 4 x 3 m part of the 10 x 4 m bed; 12 m rail travel
Test article limitsRobot static load 500 kg; drop object 125 to 300 kg
VacuumNot applicable. No vacuum capability described
TemperatureNot applicable. Not a thermal facility
IlluminationNot applicable. No solar simulator described
Simulant or terrainWF34 quartz sand, concrete, wood, oiled steel
SlopeNot set as terrain. Impact angle from the velocity ratio
Gravity offloadActive, spring suspension on the flange; accuracy not published
InstrumentationATI Theta force-torque; Megatron RC20 stroke transducer, 1 kHz

Source: [1][2].

The robot is the test machine. A KUKA KR500 on a KL1500-2 linear axis gives 12 m of lateral travel over the bed, and flies the article along a commanded trajectory whose horizontal and vertical velocity components set the impact angle; vertical velocity comes from the release height, and a pneumatic parallel gripper on the flange releases the dummy mass at a preprogrammed instant once the robot has reached a horizontal velocity of up to 1 m/s [1]. Bed depth is not published. The facility is described as five elements: the robot, the rail track, the suspension device, the controller and the soil bin, in a dedicated test cell. Of the drop object mass, the operators note that “300 kg is also the maximum payload mass of the test object, caused by the configuration” [2].

The suspension device between the flange and the article is what makes a 1 g facility useful for a low-gravity landing; the chain from the flange down is an upper plate on the robot’s force-torque sensor, linear guide pillars constraining motion to the gravity axis, tension springs sized to the article’s mass, a movable lower plate on slide bearings, a piezoelectric brake, a carbon fiber beam stiff along its length and compliant in bending, and a cardanic joint whose center is trimmed to coincide with the article’s center of gravity [2]. Rotational freedom is about 30 degrees about x and y, reduced to about 17 degrees about y by the hood structure of the Philae model.

Two control modes exist. In the simpler one the robot flies a preprogrammed trajectory. In the sensor-driven mode the force-torque transducer in the hand closes a loop whose objective is to “maintain a constant weight load in the vertical direction and zero lateral forces in the robot hand”, which is how a comet-gravity or lunar-gravity landing is held through a touchdown that involves sliding and rebound [2][4].

Mobility rig

Section titled “Mobility rig”
ParameterValue
Working volumeDrag container 3.2 x 1.2 m, set on top of the large bed
Test article limitsFootpad or leg on the flange; robot static load 500 kg
Simulant or terrainMSS-D fine lunar simulant, used only here; WF34
SlopeFootpad hinge tilts to 30 degrees, locking in 10 degree steps
InstrumentationInstrumented footpad: 3-axis force, accelerometer, potentiometer

Source: [1].

The mobility half of the facility pulls the article horizontally through the soil rather than dropping it onto it. In drag mode the leg is attached to the flange and pulled through the bin either at constant penetration depth with variable force, or at constant force with variable depth held by the robot controller, over a motion composed of a 1 m acceleration phase, a 1.5 m constant speed phase and a 0.5 m deceleration phase [1]. It uses its own smaller container placed on top of the large bed, which is also the only place the fine MSS-D simulant is used. Drag runs are noisier than drops, as the repeatability figures in the soil section below show.

The drag rig measures a footpad or a leg being pulled through soil at a controlled depth and force, which is the small-scale, single-body version of what a rover measures across a whole traverse. The only real-vehicle trafficability record at this scale is the Lunar Roving Vehicle’s: 2 to 3 percent wheel slip at a 6 to 7 km/hr cruise speed, over terrain up to 19 to 23 degrees, at an energy cost of 35 to 56 watt-hours per kilometer of which only about 15 percent went into the soil and the terrain rather than the vehicle itself [7]. LAMA has no rolling-wheel test mode and produces no traverse-scale number to set against that figure; its drag rig is a single instrumented foot or leg, not a wheel, and it runs over a few meters rather than kilometers.

Instrumentation

Section titled “Instrumentation”

Measurement is split between the article, the robot and the room. The article carries accelerometers, potentiometers and force sensors at 1 kHz; the robot contributes hand pose, orientation, forces and torques from the control bus at 12 ms intervals with 0.15 mm position accuracy; and external video runs to 600 frames per second [1][2]. All three streams go to one central data acquisition system so that they share a time base.

The named sensor set is an ATI Theta three-axis force-torque transducer in the robot hand flange, a Megatron RC20 linear transducer on the suspension stroke at 1 kHz, an iMAR iVRU-BB-M inertial measurement unit at 100 Hz, and Kistler 8792A25 and Bruel and Kjaer DeltaTron 4506 accelerometers at 1 kHz, alongside landing gear housekeeping at 1 kHz [1][2]. The Philae specimen carried the flight landing gear housekeeping signals, gear stroke, tilt angle between gear and body, braking currents and touchdown signals, next to a flywheel generating the same angular momentum as the flight unit and ballast trimmed to the flight model mass, center of mass and moments of inertia [2].

The instrumented footpad built for the 2011 campaign is the clearest example of the design constraint the facility imposes: a three-axis accelerometer, a hinge-axis linear potentiometer and a three-axis force sensor, all sealed inside a plastic boot because the sensor is going into the sand [1].

Video is used as an independent check rather than as illustration. In the Philae campaign it established foot contact times to 83 ms and gave a measurement of hood tilt independent of the potentiometer, which is how the tilt limiter’s real performance was found [1].

Soil selection is documented as a compromise rather than a match. WF34 and MSS-D were characterized against lunar regolith: cohesion 0.06 kPa for WF34 and 0.01 kPa for MSS-D against 0.44 to 0.62 kPa; bulk density 1.4 and 1.3 against 1.4 to 1.6 t/m3; Young’s modulus 1900 and 1000 against about 180 kPa; friction angle 32 plus or minus 2 and 31 plus or minus 2 degrees against 42 degrees [1]. The lunar figures are the top-15-cm Table 9.12 values from the Apollo and Lunokhod penetrometer record, recommended as a depth-averaged Mohr-Coulomb fit rather than a direct measurement, and the friction angle falls as the confining stress rises [6][7]. The operators state the position plainly: “the values for the simulants are in the range but not exactly the lunar soil. This is not problematic as long as the numerical simulation uses the same simulant properties”. Preparation uses “special soil preparation methods and a sand glazer” so that “the underground had the same characteristics at each test run”, with no density figure, relative density target or tonnage published [1]. LAMA is therefore a validation rig for a soil contact model, not an environment simulator, and the model is validated against the simulant that was used.

What it does not reproduce

Section titled “What it does not reproduce”

A clean acceleration record. The offload suspension appears in the data. The operators identify a specific run in which “the high negative peak of test run M1234 comes from a hard contact of the sliding part of the weight-offloading suspension to its end block. This is an interference with the effective landing acceleration and has to be separated in the calculation” [2]. More generally, they list weight offloading against the alternatives and concede that model scaling “comes to a practical end… as it leads to unacceptable miniaturization”, that a pendulum or tilted plane “does not allow tests on granular media” and constrains the article’s motion severely, and that weight offloading permits three-dimensional soft soil testing but “however interferences with the offloading device remain” [2]. The 2013 retest quantified the interference against the pendulum it replaced: the LAMA suspension carries a stiffness of 4080 N/m against the earlier pendulum’s 242 N/m, and a damping coefficient of 567 N*s/m is fitted from the combined data so the two rigs’ results can be plotted on the same velocity-against-damper-stroke axes [4].

Free article motion. The rig can suppress real behavior as well as add artifacts. In the 2011 footpad campaign the upward motion of the spherical pads during the slide-out phase was “suppressed here by the robot interface and showed themselves in the higher force levels” [1]. What the pads would have done is inferred from the force record rather than observed, the same kind of inference Surveyor’s own report had to make from imprints and plume craters rather than from a directly observed footpad motion [9].

Repeatable soil. “The main influences of the errors in the test data is caused by the soil properties. Small deviations in the preparation of the soil will lead to large differences in the soil resistance” [1]. The published error figures show where that bites: sinkage 1.1 percent and force 2.6 percent in drop tests, against force 8.7 percent and pitch 32.4 percent in drag tests [1]. The same difficulty runs through the flight-data programs LAMA followed: Surveyor’s own report gives two disjoint cohesion brackets from its vernier engines and its attitude jets that are never reconciled, and Viking’s four surface units carry friction angle and cohesion ranges rather than single values because different reduction methods, footpad penetration, trenching, bearing tests, disagreed on the same ground [9][10]. A controlled ground rig narrows that spread by holding the soil preparation constant, but the LAMA operators’ own error figures show it does not remove it.

Fine regolith at facility scale. MSS-D was restricted to the small drag container “driven by manageability reasons. Too fine grained soils are difficult to handle. They build dust clouds, when they are moved, which affect the measurement equipment and other parts of the test facility” [1]. A drop test therefore lands on quartz sand, not on the fine simulant, and the facility has no answer to the fine-grained dust adhesion behavior that Surveyor measured directly on real lunar material, 250 to 1000 dyne/cm2 on a photometric target and adhesion that grew through the lunar day [9].

Lunar or cometary soil properties. The characterization figures are explicit: the simulants have roughly a tenth to a fiftieth of lunar cohesion, an order of magnitude higher Young’s modulus, and a friction angle 10 degrees lower [1]. For the comet case the operators state outright that “it is acknowledged that surface soil conditions on the comet cannot be reproduced in this type of test facility” [2].

Vacuum, temperature and illumination. None of the three is provided.

Why a robot rig rather than flight-data inference

Section titled “Why a robot rig rather than flight-data inference”

Before LAMA, footpad and landing-gear soil interaction for planetary missions was read back from telemetry after the fact rather than reproduced on the ground. Surveyor’s bearing strength ladder, under 0.1 N/cm2 in the top millimeter rising to 4 to 6 N/cm2 averaged over 6 cm, came from imprints left by crushable blocks, footpads and vernier-engine plumes, reduced through Terzaghi bearing capacity theory rather than measured directly, and its own report gives two disjoint cohesion brackets from two different reduction methods that are never reconciled [9]. Apollo’s soil mechanics report is built the same way, from lunar module descent footage, footpad penetration depth at each landing and astronaut debriefing rather than a repeatable test, closing the loop against the pre-Apollo Surveyor model rather than an independent measurement [8]. Viking’s Mars values likewise came from independently reduced footpad penetration, trench geometry, motor currents, surface bearing tests and backhoe touchdowns on the one flight article each lander carried, with no way to rerun the touchdown; the resulting friction angle and cohesion ranges vary by unit, from 14 to 21 degrees and 0.7 to 3.0 kPa for the drift material up to 27 to 32 degrees and 1.5 to 16 kPa for the blocky material [10]. The lunar cohesion and friction-angle figures LAMA’s own simulant characterization is checked against are themselves an inversion, not a measurement: a cone penetrometer cannot separate the two parameters from a single reading, so the Apollo and Lunokhod record fixes one and solves for the other, and the resulting friction angle falls from about 41 degrees at 5 kPa confining stress to about 21 degrees at 100 kPa in the recommended curved envelope [6][7]. The Apollo lunar module’s own footpad bearing pressure, about 4.6 kPa at touchdown, is roughly a fifth of the pressure a person exerts standing on one foot on Earth, which is the order of load LAMA’s footpad campaign was built to reproduce on a soil bed rather than infer from telemetry [6]. LAMA’s robot-and-offload approach exists to give a granular-media landing a repeatable ground rig instead of a single flight event, or a single penetrometer reading, to read back from.

Where LAMA sits among ground landing tests

Section titled “Where LAMA sits among ground landing tests”

Ground validation of a touchdown splits into five families. Each fixes a different part of the physics and leaves the rest to the model.

Robot-flown article with weight offload on real soil (LAMA). Gravity, soil and article are all physical; only gravity is partly canceled, and the canceling hardware leaves artifacts in the record [2]. It has been used for a flown mission, Philae, and for a mission still pending, MMX [2][3].

Dynamic scaling at full gravity. JPL’s Mars Sample Return lander test avoids offload altogether: with length scaled by 3/8 and acceleration by 8/3, a 155 kg article dropped from under 320 mm reproduces the touchdown of a lander of more than 2300 kg, because full-scale testing would need both a 3000 kg article and a gravity offload [12]. The earlier MSL rover campaign flew a 3/8 mass-scaled rover under a descent stage mock-up on 6 m bridles in more than 80 landings on rigid plate, sand and rock fields at 0.4 to 1.4 m/s, and could not measure initial conditions other than vertical velocity [13]. Scaling needs a single dominant gravity-dependent term to be matched; LAMA instead keeps the article full size and removes weight, which is why it can carry a flight-like Philae model with working landing gear [2].

Multibody simulation with assumed contact. JAXA’s study of the SLIM leg arrangement used 1000-case Monte Carlo sweeps [11] of a 220 kg body [11] on crushable legs and ranked four arrangements from 92.5 [11] to 38.7 percent success [11]. It is simulation only, with contact parameters not measured for the vehicle [11]. A rig such as LAMA is what supplies the measured footpad and soil force data such a model lacks.

Overhead cable and winch offload for people and rovers. The ARGOS facility at Johnson Space Center offloads suited subjects with three active translational axes and passive rotation in a gimbal, avoiding the roughly 30 s limit of parabolic flight at the cost of a small work volume and gimbal-induced motion [20]. Across 14 subjects and 68 configurations the usable gimbal pivot sat 2.5 to 6.4 cm above and 1.3 to 2.5 cm aft of the modeled center of gravity, and a 0.6 cm fore-aft shift was perceptible [19], the same sensitivity that LAMA addresses by trimming its cardanic joint center to the article’s center of gravity [2]. A Michigan Tech overhead trolley tracks an infrared beacon on a rover over a simulant sandbox, and its author describes the control loop as untested [21]. The ATHLETE low-gravity testbed hangs the vehicle from six winches and drives a simulated microgravity trajectory from measured contact forces [22]. None of these lands an article on soil at speed.

Reduced-gravity flight. Parabolic flights put real lunar gravity on soil and wheel together, in 20 to 30 s parabolas that never settle to steady state [23]. They show what an offload rig cannot: reduced-weight testing alone, which is what LAMA’s offload does, overstated mobility, with drawbar pull to weight falling 20 percent or more and sinkage rising up to 40 percent at lunar gravity at equal wheel load, and the equal cone index gradient method overstated it by more [23]. The consequence for LAMA is that its soil stays at 1 g, so soil-body coupling at lunar or cometary gravity is untested in the hall.

Small-body landers show the same split between what has been flown and what has not. MASCOT, a 9.8 kg lander with no attitude control in free fall, bounced to rest on Ryugu after release at about 41 m altitude [14][15]. Its separation mechanism was characterized in drop tower campaigns at ambient temperature and pressure, with flight reconstructions at 6.1 and 6.0 cm/s against a ground estimate of 4.94 cm/s [14]. Its mobility figures in the pre-landing description are ground expectations, and its parabolic flight self-righting validation failed on duration [15]; a two-page abstract announcing the mission lists instruments and plan only [16]. Philae’s pre-landing capability and operations papers give design predictions, not touchdown measurements [17][18]. The LAMA campaign for Philae is the only ground work in the corpus aimed at predicting touchdown on soil for such a lander [2].

Soil: what the bed stands in for

Section titled “Soil: what the bed stands in for”

The simulant frameworks were built for composition and handling, not for touchdown loading. The 2005 workshop set out root and derivative simulants [26], a review argues most simulants were built without adequate input from lunar soil scientists [27], and figure-of-merit scoring extended to asteroid simulants excludes cohesion and friction angle because in situ values are unknown [28]. LAMA’s WF34 and MSS-D are characterized by cohesion, density, modulus and friction angle [1], which is the property set that matters for a footpad but is not the one those frameworks score.

Bed preparation is its own source of scatter. A 150 kg BP-1 bin prepared at Marshall showed undried simulant erupting below 2 Torr and vibration compaction raising mean shear strength only from 1.70 to about 2.3 kPa, with shear strength the only property measured [29]. LAMA’s published preparation is a sand glazer with no density target, and its 32.4 percent drag-test pitch error is consistent with that gap [1].

The lunar record the simulants are compared with was itself taken from objects not designed as penetrometers. Apollo 11 reduced soil strength from footpads of about 700 lb each, an astronaut and a core tube, with no soil instrument flown [25]. Apollo 15 added a self-recording penetrometer, larger core tubes and the rover: in situ density 1.36 to 2.15 g/cm3 and an average rover track depth of about 1.25 cm [24]. Contact models fitted to a rig such as LAMA are then compared with those figures. A NASA survey times five tire-soil models on one simulated drawbar test, from a real-time factor of 0.024 for DARTS-Bekker to 9600 for Chrono-DEM, and states that the soil parameters differed between models so the comparison is not an accuracy ranking [30].

Environment the hall does not provide

Section titled “Environment the hall does not provide”

Lunar dust adhesion and abrasion, catalogd in nine problem categories across all six Apollo landings [31], need activated dust under vacuum; the NASA Glenn bell jar documents a protocol of stirring during pumpdown, 200 C bakeout and thermal cycling for that purpose [32]. LAMA has none of this. Large single-article campaigns also need a test-safety and readiness practice, documented for the MSL thermal vacuum test [33]; no LAMA procedure is published.

Campaigns run there

Section titled “Campaigns run there”

Lunar lander footpad shapes, 2011. Four footpads, spherical and flat-with-rounded-edges in 30 and 40 cm chord at 4 cm height, tested at the MoonNEXT landing envelope: 2 plus or minus 1 m/s vertical, 0 to 1 m/s horizontal, 2.5 plus or minus 2.5 degrees attitude, 0.5 degrees per second rate, with 125 to 300 kg of an 800 kg lander on the pad [1]. At 200 kg and 3 m/s the measured sinkage and peak force were 126 mm at 13.2 kN for the 300 mm spherical pad, 115 mm at 13.6 kN for the 300 mm flat pad, 80 mm at 25.0 kN for the 400 mm spherical and 66 mm at 28.3 kN for the 400 mm flat. Drag tests at 30 mm depth and 1 m/s found the spherical pads carrying 25 to 125 percent higher vertical and lateral loads than the flat ones [1]. The conclusion was that spherical pads slide rather than dig in, and that a 78 percent increase in pad size buys about 60 percent less sinkage [1], a size-versus-sinkage trade of the same kind Viking’s blocky and drift units showed at full lander scale, where the denser, coarser unit carried a higher friction angle and a wider cohesion range than the finer drift material [10].

Philae touchdown requalification, 2012 to 2013. Philae’s original qualification used a 3.96 m pendulum rig between 1996 and 2002, which could not touch down on loose material and constrained the lander’s motion [2][4]. When the target changed from comet 46P/Wirtanen to the more massive 67P/Churyumov-Gerasimenko the landing velocity and kinetic energy rose, and the lander was already at the launch site, so the design could not be changed. Four baseline and three special test groups ran at 0.1 to 1.1 m/s vertical and 0 to 0.21 m/s lateral, at 0 and 17 degrees pitch, with the flywheel off, slow and fast, onto wood, oiled steel, WF34, MSS-D, concrete and a slope with mixed surface [2]. Three findings matter. The touchdown indicator’s detection floor is higher on soft ground, 0.5 m/s against 0.2 m/s on hard surfaces [2]. The tilt limiter intended to hold plus or minus 3 degrees was measured allowing “at least plus or minus 9 degrees”. MSS-D behaved closer to hard ground than WF34 did, with the ice screws sinking less but retracting much harder in MSS-D [2].

Philae’s first touchdown at Agilkia gave a way to check the ground work against a real landing. The damper potentiometer trace from that touchdown, read through a lumped two-mass spring-damper model of the lander, backs out a comet surface compressive strength of about 2 kPa for a constant-strength soil model or 3 kPa per meter for a depth-dependent one, converging with an independent multi-body simulation on 1.5 to 2 kPa once ground slope is corrected for [5]. That figure rests on a single event with only a handful of time-resolved damper positions in the first 200 ms of contact, assumes all three feet struck soil at once even though the imagery suggests one foot hit a boulder strut, and extrapolates past the 135 mm depth the model is stated to be valid for to fit penetration depths as deep as 0.73 m [5]. The comet strength the ground campaign was rehearsing against turned out to be lower than either simulant’s characterized cohesion, which is consistent with the operators’ own caveat that comet soil conditions were not expected to be reproduced in the facility [2]. It is also well below the lunar range LAMA’s own simulants were built against, 0.44 to 0.62 kPa in the top 15 cm by the Apollo and Lunokhod record, so the two bodies the facility has been used to prepare for sit on opposite sides of the simulant’s characterized strength rather than bracketing it [6][7].

MMX rover preliminary model, 2020. Drop tests with the preliminary model of the MMX rover were run in LAMA, which is the most recent published evidence that the facility is in use [3]. No campaign report gives the conditions or the results, which leaves the MMX case in the same position Apollo’s own soil mechanics report was in before a dedicated test rig existed: a landing whose ground interaction has to be read back from whatever instrumented record the mission itself returns [8].

What is not established

Section titled “What is not established”

The offload accuracy of the LAMA suspension is not published, and the only quantified interference is the stiffness and damping fit from the Philae retest [4]. Bed depth, density and relative density are not published [1]. No campaign report gives the MMX rover conditions or results [3]. No LAMA data exist at lunar or cometary gravity on the soil itself, and the reduced-gravity flight record shows reduced-weight testing overstates mobility [23]. The Philae comet strength estimate rests on one touchdown with few time-resolved damper positions [5]. Simulation-only landing studies such as SLIM’s have no matching published LAMA test [11]. External access routes are not published.

References

  1. Schröder, S., Witte, L. and van Zoest, T. (2011). Footpad-Terrain Interaction Tests with the Robotic Landing and Mobility Test Facility (LAMA) . International Astronautical Congress. Source
    BibTeX
    @inproceedings{schroder2011footpad,
  title = {Footpad-Terrain Interaction Tests with the Robotic Landing and Mobility Test Facility (LAMA)},
  author = {Schröder, Silvio and Witte, Lars and van Zoest, Tim},
  booktitle = {International Astronautical Congress},
  address = {Cape Town},
  year = {2011},
  url = {https://elib.dlr.de/102762/}
}
  2. Schröder, S., Biele, J., Block, J., Roll, R., Ulamec, S. and Witte, L. (2013). Philae Landing Test at the Landing and Mobility Test Facility (LAMA) . International Astronautical Congress, IAC-13, A3, 4, 3. Source
    BibTeX
    @inproceedings{schroder2013philae,
  title = {Philae Landing Test at the Landing and Mobility Test Facility (LAMA)},
  author = {Schröder, Silvio and Biele, Jens and Block, Joachim and Roll, Reinhard and Ulamec, Stephan and Witte, Lars},
  booktitle = {International Astronautical Congress, IAC-13, A3, 4, 3},
  address = {Beijing},
  year = {2013},
  url = {https://elib.dlr.de/103154/}
}
  3. (2020). Drop tests in the DLR Landing and Mobility Test Facility. dlr.de/en/images/2020/3/preliminary-model-drop-test
    BibTeX
    @misc{dlrlamammx,
  title = {Drop tests in the {DLR} Landing and Mobility Test Facility},
  organization = {DLR},
  year = {2020},
  url = {https://www.dlr.de/en/images/2020/3/preliminary-model-drop-test}
}
  4. Witte, L., Schroeder, S., Kempe, H., van Zoest, T., Roll, R., Ulamec, S., Biele, J. and Block, J. (2014). Experimental Investigations of the Comet Lander Philae Touchdown Dynamics . Journal of Spacecraft and Rockets. Source
    BibTeX
    @article{witte2014experimental,
  title = {Experimental Investigations of the Comet Lander Philae Touchdown Dynamics},
  author = {Witte, Lars and Schroeder, Silvio and Kempe, Henning and van Zoest, Tim and Roll, Reinhard and Ulamec, Stephan and Biele, Jens and Block, Joachim},
  journal = {Journal of Spacecraft and Rockets},
  volume = {51},
  pages = {1885-1894},
  year = {2014},
  doi = {10.2514/1.a32906},
  abstract = {The comet lander Philae (as part of Europe’s Rosetta mission) is en route to its target, 67/P Churyumov-Gerasimenko. With landing operations coming up at the end of 2014, a partial retesting of the Philae lander’s touchdown system was carried out in spring of 2013. Intensive testing was performed as part of Philae’s design and verification program approximately 10 years ago. However, the new test series specifically addresses touchdown conditions that have been out of capability of the pendulum test facility used at those times. Thus, the follow-up tests focus on touchdown conditions such as asymmetric loads, effects from terrain undulation, and the effect of granular soil mechanics, which could not be studied sufficiently in the original tests. This paper provides insight into the touchdown system of the Philae lander, the characteristics of the used test facility, its weight offloading operating mode, and the specific application to a small-body landing test. The results of the study are presented and discussed in terms of their importance to the ongoing landing preparations.}
}
  5. Roll, R., Witte, L. and Arnold, W. (2016). ROSETTA lander Philae – soil strength analysis . Icarus. Source
    BibTeX
    @article{roll2016rosetta,
  title = {ROSETTA lander Philae – soil strength analysis},
  author = {Roll, Reinhard and Witte, Lars and Arnold, Walter},
  journal = {Icarus},
  volume = {280},
  pages = {359-365},
  year = {2016},
  doi = {10.1016/j.icarus.2016.07.004}
}
  6. Carrier, W. D. I., Olhoeft, G. R. and Mendell, W. (1991). Physical Properties of the Lunar Surface . Lunar Sourcebook: A User's Guide to the Moon. Source
    BibTeX
    @incollection{carrier1991physical,
  title = {Physical Properties of the Lunar Surface},
  author = {Carrier, W. David, III and Olhoeft, Gary R. and Mendell, Wendell},
  editor = {Heiken, Grant H. and Vaniman, David T. and French, Bevan M.},
  booktitle = {Lunar Sourcebook: A User's Guide to the Moon},
  pages = {475--594},
  publisher = {Cambridge University Press},
  chapter = {9},
  year = {1991},
  url = {https://www.lpi.usra.edu/publications/books/lunar_sourcebook/pdf/Chapter09.pdf}
}
  7. Heiken, G. H., Vaniman, D. T. and French, B. M. (1991). Lunar Sourcebook: A User's Guide to the Moon . Endeavour. Source
    BibTeX
    @book{heiken1991lunar,
  title = {Lunar Sourcebook: A User's Guide to the Moon},
  author = {Heiken, Grant H. and Vaniman, David T. and French, Bevan M.},
  journal = {Endeavour},
  volume = {16},
  pages = {96},
  publisher = {Cambridge University Press},
  year = {1991},
  doi = {10.1016/0160-9327(92)90014-g}
}
  8. Scott, R. F. (1975). Apollo Program Soil Mechanics Experiment: Final Report . California Institute of Technology, NASA Contract NAS 9-11454. Source
    BibTeX
    @techreport{scott1975apollo,
  title = {Apollo Program Soil Mechanics Experiment: Final Report},
  author = {Scott, Ronald F.},
  number = {NASA Contract NAS 9-11454},
  institution = {California Institute of Technology},
  year = {1975},
  url = {https://ntrs.nasa.gov/citations/19750023910},
  abstract = {The soil mechanics investigation was conducted to obtain information relating to the landing interaction of the lunar module (LM) with the lunar surface, and lunar soil erosion caused by the spacecraft engine exhaust. Results obtained by study of LM landing performance on each Apollo mission are summarized.}
}
  9. Surveyor Scientific Evaluation Advisory Team. (1968). Surveyor Project Final Report, Part 2: Science Results . Jet Propulsion Laboratory, NASA-CR-101584. Source
    BibTeX
    @techreport{surveyor1968surveyorb,
  title = {Surveyor Project Final Report, Part 2: Science Results},
  author = {{Surveyor Scientific Evaluation Advisory Team}},
  number = {NASA-CR-101584},
  institution = {Jet Propulsion Laboratory},
  year = {1968},
  url = {https://ntrs.nasa.gov/citations/19690019967}
}
  10. Moore, H. J., Hutton, R. E., Clow, G. D. and Spitzer, C. R. (1987). Physical Properties of the Surface Materials at the Viking Landing Sites on Mars . U.S. Geological Survey, Professional Paper 1389. Source
    BibTeX
    @techreport{moore1987physical,
  title = {Physical Properties of the Surface Materials at the Viking Landing Sites on Mars},
  author = {Moore, Henry J. and Hutton, Robert E. and Clow, Gary D. and Spitzer, Cary R.},
  number = {Professional Paper 1389},
  institution = {U.S. Geological Survey},
  year = {1987},
  doi = {10.3133/pp1389},
  abstract = {Estimates of water and carbon dioxide in samples analyzed in_ the gas chromatograph-mass spectrometer for the Molecular Analysis Experiment-----------------------}
}
  11. KAWANO, T., MARU, Y., OKUIZUMI, N., SAWAI, S. and NOHMI, M. (2020). Study of Leg Arrangement for Stable Touchdown during Two-Step Landing for SLIM . Journal of Geophysical Research: Planets, 5. Source
    BibTeX
    @article{kawano2020study,
  title = {Study of Leg Arrangement for Stable Touchdown during Two-Step Landing for SLIM},
  author = {KAWANO, Taro and MARU, Yusuke and OKUIZUMI, Nobukatsu and SAWAI, Shujiro and NOHMI, Masahiro},
  journal = {Journal of Geophysical Research: Planets},
  volume = {18},
  number = {5},
  pages = {222-230},
  publisher = {Japan Society for Aeronautical and Space Sciences},
  year = {2020},
  doi = {10.2322/tastj.18.222}
}
  12. Dizon, A., Karafillis, P., Montalvo, M. and Navalta, E. (2023). 3/8th Scale Testing for the MSR Sample Retrieval Lander Touchdown Event . NASA Undergraduate Student Research Program. Source
    BibTeX
    @inproceedings{dizon2023scale,
  title = {3/8th Scale Testing for the MSR Sample Retrieval Lander Touchdown Event},
  author = {Dizon, Abel and Karafillis, Pavlina and Montalvo, Morgan and Navalta, Edmund},
  booktitle = {NASA Undergraduate Student Research Program},
  publisher = {JPL Open Repository},
  year = {2023},
  doi = {10.48577/jpl.ibrov6}
}
  13. White, C. V., van der Walde, K. and Tippmann, J. (2008). An experimental investigation of the dynamics of the MSL Rover landing event . AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference <br> AIAA/ASME/AHS Adaptive Structures Conference<br> 10t. Source
    BibTeX
    @inproceedings{white2008experimental,
  title = {An experimental investigation of the dynamics of the MSL Rover landing event},
  author = {White, Christopher V. and van der Walde, Keith and Tippmann, Jeffery},
  booktitle = {AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference <br> AIAA/ASME/AHS Adaptive Structures Conference<br> 10t},
  publisher = {American Institute of Aeronautics and Astronautics},
  year = {2008},
  doi = {10.2514/6.2008-1950},
  abstract = {A developmental test program was conducted for the touchdown event of the Mars Science Laboratory rover. The test hardware consisted of a full-size 3/8th mass scaled test rover, a descent stage mass mock-up, and a Vectran triple-bridle system over 6 meters in length. More than eighty landing tests were performed on terrains of various types, including level rigid surfaces, level and sloped sand surfaces, and level and sloped surfaces with rocks. Landing velocities ranged between 0.4 m/s and 1.4 m/s. A computational model of the landings was developed using the ADAMS analysis program, and validation of this model has been performed through test-analysis comparisons.}
}
  14. Grimm, C. D., Lange, C., Lange, M., Mierheim, O., Sasaki, K., Meyer, M., Kroth, W., Ulamec, S. and Ho, T.-M. (2020). The MASCOT Separation Mechanism: A Reliable, Low-Mass Deployment System for Nano-Spacecraft . CEAS Space Journal, 3. Source
    BibTeX
    @article{grimm2020mascot,
  title = {The {MASCOT} Separation Mechanism: A Reliable, Low-Mass Deployment System for Nano-Spacecraft},
  author = {Grimm, Christian D. and Lange, Caroline and Lange, Michael and Mierheim, Olaf and Sasaki, Kaname and Meyer, Michael and Kroth, Wolfgang and Ulamec, Stephan and Ho, Tra-Mi},
  journal = {CEAS Space Journal},
  volume = {12},
  number = {3},
  pages = {343--365},
  year = {2020},
  doi = {10.1007/s12567-020-00302-y},
  abstract = {Abstract The Mobile Asteroid Surface Scout (MASCOT), an Asteroid Lander carried by the Hayabusa2 spacecraft, successfully landed on the Near-Earth Asteroid (162173) Ryugu on October 03, 2018. Thereby accomplishing the first-ever landing of a European spacecraft on the surface of this type of celestial body. MASCOT was a prototype design of a new class of nano-size surface science packages for the exploration of small solar system bodies. The very low gravity (thus, very low escape velocity) of the target body required the design of a miniaturized deployment mechanism with a relatively small, well-reproducible separation velocity. In addition, the mechanism also had to safely restrain the lander to the mother spacecraft during the launch and its 3.5-year cruise phase. In this paper, we describe in detail the design, numerical analysis and test of this newly developed separation mechanism. Furthermore, we compare the mechanism to other existing deployment systems and verify its performance with two independent analysis methods using actual flight data taken during the ultimate flight activation event, which initiated the successful delivery and surface operation of the MASCOT asteroid lander.}
}
  15. Ho, T.-M., Baturkin, V., Grimm, C., Grundmann, J. T., Hobbie, C., Ksenik, E., Lange, C., Sasaki, K., Schlotterer, M., Talapina, M., Termtanasombat, N., Wejmo, E., Witte, L., Wrasmann, M., Wübbels, G., Rößler, J., Ziach, C., Findlay, R., Biele, J., Krause, C., Ulamec, S., Lange, M., Mierheim, O., Lichtenheldt, R., Maier, M., Reill, J., Sedlmayr, H.-J., Bousquet, P., Bellion, A., Bompis, O., Cenac-Morthe, C., Deleuze, M., Fredon, S., Jurado, E., Canalias, E., Jaumann, R., Bibring, J.-P., Glassmeier, K. H., Hercik, D., Grott, M., Celotti, L., Cordero, F., Hendrikse, J. and Okada, T. (2017). MASCOT: The Mobile Asteroid Surface Scout Onboard the Hayabusa2 Mission . Space Science Reviews, 1-4. Source
    BibTeX
    @article{ho2017mascot,
  title = {{MASCOT}: The Mobile Asteroid Surface Scout Onboard the {Hayabusa2} Mission},
  author = {Ho, Tra-Mi and Baturkin, Volodymyr and Grimm, Christian and Grundmann, Jan Thimo and Hobbie, Catherin and Ksenik, Eugen and Lange, Caroline and Sasaki, Kaname and Schlotterer, Markus and Talapina, Maria and Termtanasombat, Nawarat and Wejmo, Elisabet and Witte, Lars and Wrasmann, Michael and Wübbels, Guido and Rößler, Johannes and Ziach, Christian and Findlay, Ross and Biele, Jens and Krause, Christian and Ulamec, Stephan and Lange, Michael and Mierheim, Olaf and Lichtenheldt, Roy and Maier, Maximilian and Reill, Josef and Sedlmayr, Hans-Jürgen and Bousquet, Pierre and Bellion, Anthony and Bompis, Olivier and Cenac-Morthe, Celine and Deleuze, Muriel and Fredon, Stephane and Jurado, Eric and Canalias, Elisabet and Jaumann, Ralf and Bibring, Jean-Pierre and Glassmeier, Karl Heinz and Hercik, David and Grott, Matthias and Celotti, Luca and Cordero, Federico and Hendrikse, Jeffrey and Okada, Tatsuaki},
  journal = {Space Science Reviews},
  volume = {208},
  number = {1-4},
  pages = {339--374},
  year = {2017},
  doi = {10.1007/s11214-016-0251-6}
}
  16. Krause, C., Auster, U., Bibring, J.-P., Biele, J., Cenac, C., Cozzoni, B., Dudal, C., Embacher, D., Fantinati, C., Fischer, H.-H., Glassmeier, K. H., Granena, D., Grott, M., Grundmann, J. T., Hamm, V., Hercik, D., Ho, T.-M., Jaumann, R., Kayal, K., Knollenberg, J., Küchemann, O., Lange, C., Lorda, L., Maibaum, M., May, D., Moussi, A., Okada, T., Reill, J., Saiki, T., Sasaki, K., Schlotterer, M., Schmitz, N., Termtanasombat, N., Tsuda, Y., Ulamec, S., Yoshimitsu, T. and Ziach, C. (2018). MASCOT -- a Mobile Lander on-board Hayabusa2 Spacecraft -- Status and Operational Concept for the Asteroid Ryugu . SpaceOps Conference. Source
    BibTeX
    @inproceedings{krause2018mascot,
  title = {MASCOT -- a Mobile Lander on-board Hayabusa2 Spacecraft -- Status and Operational Concept for the Asteroid Ryugu},
  author = {Krause, Christian and Auster, Ulrich and Bibring, Jean-Pierre and Biele, Jens and Cenac, C. and Cozzoni, Barbara and Dudal, Clement and Embacher, D. and Fantinati, Cinzia and Fischer, Hans-Herbert and Glassmeier, K. H. and Granena, D. and Grott, Matthias and Grundmann, J. T. and Hamm, Vincent and Hercik, David and Ho, Tra-Mi and Jaumann, Ralf and Kayal, Kağan and Knollenberg, J. and Küchemann, O. and Lange, Caroline and Lorda, Laurence and Maibaum, Michael and May, D. and Moussi, Aurelie and Okada, Tatsuaki and Reill, Josef and Saiki, Takanao and Sasaki, Kaname and Schlotterer, Markus and Schmitz, Nicole and Termtanasombat, Nawarat and Tsuda, Yuichi and Ulamec, Stephan and Yoshimitsu, Tetsuo and Ziach, C.},
  booktitle = {SpaceOps Conference},
  year = {2018},
  doi = {10.2514/6.2018-2418},
  abstract = {MASCOT (‘Mobile Asteroid Surface Scout’) is a 10 kg mobile surface science package on board JAXA’s Hayabusa2 sample return mission, currently on its way to the near-Earth asteroid (162173) Ryugu. The mission was launched in December 2014 from Tanegashima Space Center, Japan. The Hayabusa2 spacecraft will reach the target asteroid in summer 2018. Hayabusa2 will return its samples to Earth in December 2020. After arrival at the target asteroid ‘Ryugu’ a detailed mapping phase will be performed and the landing site of MASCOT will be selected. The deployment of MASCOT to the asteroids surface is planned for the beginning of October 2018. MASCOT has been developed by the German Aerospace Center (DLR) in cooperation with the Centre National d’Etudes Spatiales (CNES). The main objective of MASCOT is to perform in-situ investigations of the asteroid surface and to support the sampling site selection for the mother spacecraft. Mascot is equipped with four scientific instruments a wide angle camera, a hyperspectral infrared microscope, a radiometer and a magnetometer. The camera (MasCam) provides ground truth for the orbital measurements of the Hayabusa2 orbiter instruments and the in-situ MASCOT sensor suite as well as geological context of the samples. The radiometer (MARA) determines the surface brightness temperature, the thermal inertia of the surface material and the spectral slope in infrared. The radiometer field of view is correlated with the wide angle camera field of view. The magnetometer (MasMAG) observes the magnetic field profile during descent and bouncing and determines any global and local magnetization of the asteroid.}
}
  17. Biele, J. and Ulamec, S. (2008). Capabilities of Philae, the Rosetta Lander . Space Science Reviews. Source
    BibTeX
    @article{biele2008capabilities,
  title = {Capabilities of Philae, the Rosetta Lander},
  author = {Biele, Jens and Ulamec, Stephan},
  journal = {Space Science Reviews},
  volume = {138},
  pages = {275-289},
  year = {2008},
  doi = {10.1007/978-0-387-85455-7_18}
}
  18. Geurts, K., Fantinati, C., Ulamec, S. and Willnecker, R. (2014). Rosetta Lander: On-Comet Operations Preparation and Planning . SpaceOps Conference. Source
    BibTeX
    @inproceedings{geurts2014rosetta,
  title = {Rosetta Lander: On-Comet Operations Preparation and Planning},
  author = {Geurts, Koen and Fantinati, Cinzia and Ulamec, Stephan and Willnecker, Rainer},
  booktitle = {SpaceOps Conference},
  publisher = {American Institute of Aeronautics and Astronautics},
  year = {2014},
  doi = {10.2514/6.2014-1752},
  abstract = {The ESA Rosetta mission is a European cornerstone mission that will study the evolution of comet 67P/Churyumov-Gerasimenko on its trajectory around the Sun and will include the delivery of the Philae lander for in-situ investigation of the comet nucleus and sub-surface. Philae is funded and operated by a European consortium, and consists of an independent spacecraft platform including 10 scientific instruments. Philae operations are scheduled and implemented by the Science Navigation and Operations Center (SONC) at CNES/Toulouse and the Lander Control Center (LCC) at DLR/Cologne. Rosetta was launched in March 2004 and conducted a 7 year cruise phase, after which a 3 year long deep space hibernation phase followed, in order to cope with the large Sun distances around the trajectory aphelion. In January 2014 Rosetta was woken up and the comet rendezvous phase commenced. Landing is foreseen for November 2014 to a landing site which will be selected during the preceding three month landing site selection process. The final descent trajectory and postdelivery Rosetta trajectory, with associated Philae – Rosetta communication windows, will be computed 30 days prior lander delivery. The Philae operations team must ensure that the baseline descent and science timelines developed over the timeframe 2011 – 2013 are adaptable in order to cope with the intrinsic uncertainties. Furthermore, Philae will conduct a long term science phase during which various scientific measurements are performed in order to characterize the evaluation of the nucleus and subsurface as a function of the decreasing Sun distance. The operational process and procedure developed by the Philae operations team will allow for the rapid adaptation to landing site specific features such as the comet local landing epoch, day/night variations and communication window uncertainties.}
}
  19. Jarvis, S. L., Vu, L. Q., Gupta, G., Benson, E., Kim, K. H., Rhodes, R. and Rajulu, S. L. (2023). Development of ARGOS (Active Response Gravity Offload System) Offloading Assessments and Methodology for Lunar EVA Simulations . International Conference on Environmental Systems, 20230002430. Source
    BibTeX
    @inproceedings{jarvis2023development,
  title = {Development of ARGOS (Active Response Gravity Offload System) Offloading Assessments and Methodology for Lunar EVA Simulations},
  author = {Jarvis, Sarah L. and Vu, Linh Q. and Gupta, Garima and Benson, Elizabeth and Kim, K. Han and Rhodes, Richard and Rajulu, Sudhakar L.},
  booktitle = {International Conference on Environmental Systems},
  number = {20230002430},
  institution = {NASA},
  address = {Calgary},
  year = {2023},
  url = {https://ntrs.nasa.gov/citations/20230002430},
  abstract = {The Active Response Gravity Offload System (ARGOS) at NASA Johnson Space Center (JSC) is an analog environment that can offload pressurized suited subjects for various reduced gravity simulations. The suit is suspended from a robotic overhead crane by a cable connected to the suit via a gimbal with an adjustable pivot point (i.e. offload attachment). There has been increased interest in providing planetary pressurized suited training at ARGOS in preparation for lunar missions. Determination of the appropriate gimbal pivot point location for a given subject is vital for a high-fidelity functional lunar simulation. Interactions between the pivot point location and human-spacesuit center of gravity (CG) can result in righting moments that may lead to artificially stable or unrealistically challenging
configurations. Changing the pivot point location is time consuming and repeated adjustment can result in loss of valuable pressurized suited time. This paper aims to share knowledge obtained from the offloading characterization efforts during pressurized suited testing at ARGOS and document the ongoing process to define an appropriate pivot point location through iterative quantitative and qualitative assessments. Human-spacesuit CG locations for the ARGOS lunar simulation were estimated using a 3D body scan and density model combined with spacesuit hardware CAD and specifications. Early pilot testing of the gimbal revealed that setting the pivot point coincident with the modeled CG location was not always possible due to the current gimbal design, and small pivot point shifts had noticeable effects on subject stability. Fourteen subjects performed a series of CG-related tasks in the
Exploration Extravehicular Mobility Unit (xEMU) to assess simulation characteristics. Through iterative testing, this task list evolved to streamline the process needed to efficiently identify a suitable pivot point for a given subject. The developed methodology will be critical for pivot point selection during astronaut training in the ARGOS environment.}
}
  20. Bekdash, O. S., Valle, P. S., Kim, K. J., Jarvis, S. L., Dunn, J. T., Norcross, J. R. and Abercromby, A. F. J. (2020). Development and Evaluation of the Active Response Gravity Offload System as a Lunar and Martian EVA Simulation Environment . International Conference on Environmental Systems, 20205003610. Source
    BibTeX
    @inproceedings{bekdash2020development,
  title = {Development and Evaluation of the Active Response Gravity Offload System as a Lunar and Martian EVA Simulation Environment},
  author = {Bekdash, Omar S. and Valle, Paul S. and Kim, Kyoung Jae and Jarvis, Sarah L. and Dunn, Jocelyn T. and Norcross, Jason R. and Abercromby, Andrew F. J.},
  booktitle = {International Conference on Environmental Systems},
  number = {20205003610},
  institution = {NASA},
  year = {2020},
  url = {https://ntrs.nasa.gov/citations/20205003610},
  abstract = {In preparation for future exploration missions, NASA seeks the ability to simulate partial-gravity operations  for  use  in  ground-based  research,  crew  training,  and  engineering  design  evaluations.  The  Active  Response  Gravity  Offload  System  (ARGOS)  at  the  Johnson  Space  Center (JSC) is designed to simulate reduced gravity environments, such as lunar, Martian, or  microgravity,  using  a  robotic  system  similar  to  an  overhead  bridge  crane.  ARGOS  continuously offloads a portion of a suited human’s weight during all dynamic motions within the test facility, which can include basic functional movements such as walking, running, and jumping, as well as a wide range of planetary surface activities. This system will be used as part of a metabolic-rate task characterization study to determine the workload associated with partial-gravity  extravehicular  activity  (EVA).  Pilot  testing  was  conducted  using  the  MKIII  prototype planetary space suit and two gimbal designs to determine the ability of the ARGOS test environment to simulate planetary EVA operations. This paper will describe the lessons learned from the feasibility testing,  simulation-environment  mockup  design,  and  the results from  the  pilot  tests  and  their  influence  into  the  final  study  design.  Being  able  to  effectively  simulate partial-gravity environments and characterize the performance of crewmembers will have an impact on multiple domains including suit design, task design, thermal models, and life-support-system capacity verification plans, among others.}
}
  21. Wavrunek, T. A. (2021). Active Gravity Offloading System with Infrared Tracking for Rover Testing . Michigan Technological University. Source
    BibTeX
    @mastersthesis{wavrunek2021active,
  title = {Active Gravity Offloading System with Infrared Tracking for Rover Testing},
  author = {Wavrunek, Travis A.},
  publisher = {Michigan Technological University},
  school = {Michigan Technological University},
  type = {Master of Science report, Mechanical Engineering},
  year = {2021},
  doi = {10.37099/mtu.dc.etdr/1213},
  abstract = {Gravity offloading is a tool used to test how different gravitational forces will impact the mobility of rovers bound for Lunar or Martian expeditions. Previous approaches have been successful in simulating partial gravity environments, and this report details how the Infrared- Gravity offload (IRGO) system, developed for the Planetary Surface Technology Development Laboratory (PSTDL) and lunar simulant sandbox, has a similar aim. Through a series of iterations, IRGO has been developed to actively track an infrared beacon and follow a rover within the test chamber to eliminate inertial and friction forces along two horizonal axes. A portion of a rover’s weight is offloaded using a passive counterweight system to provide a third translational degree of freedom. Future plans to incorporate a lightweight gimbal as well as an active vertical axis are also discussed as solutions to improving the IRGO system.}
}
  22. Wilcox, B. H. (2011). ATHLETE: A Limbed Vehicle for Solar System Exploration . IEEE Aerospace Conference. Source
    BibTeX
    @inproceedings{wilcox2011limbed,
  title = {ATHLETE: A Limbed Vehicle for Solar System Exploration},
  author = {Wilcox, Brian H.},
  booktitle = {IEEE Aerospace Conference},
  pages = {1-9},
  year = {2011},
  doi = {10.1109/aero.2012.6187269},
  abstract = {As part of the Human-Robot Systems project funded by NASA, the Jet Propulsion Laboratory has developed a vehicle called ATHLETE: the All-Terrain Hex-Limbed Extra-Terrestrial Explorer. Each vehicle is based on six wheels at the ends of six multi-degree-of-freedom limbs. Because each limb has enough degrees of freedom for use as a general-purpose leg, the wheels can be locked and used as feet to walk out of excessively soft or other extreme terrain. Since the vehicle has this alternative mode of traversing through or at least out of extreme terrain, the wheels and wheel actuators can be sized for nominal terrain. There are substantial mass savings in the wheel and wheel actuators associated with designing for nominal instead of extreme terrain. These mass savings are comparable-to or larger-than the extra mass associated with the articulated limbs. As a result, the entire mobility system, including wheels and limbs, can be about 25% lighter than a conventional mobility chassis. A side benefit of this approach is that each limb has sufficient degrees-of-freedom to use as a general-purpose manipulator (hence the name "limb" instead of "leg"). Our prototype ATHLETE vehicles have quick-disconnect tool adapters on the limbs that allow tools to be drawn out of a "tool belt" and maneuvered by the limb. A power-take-off from the wheel actuates the tools, so that they can take advantage of the 1+ horsepower motor in each wheel to enable drilling, gripping or other power-tool functions. This paper describes the applicability of the ATHLETE concept to exploration of the moon, Mars and Near-Earth Asteroids (NEAs). Recently, the focus of human exploration beyond LEO has been on NEAs. One scenario for exploration of a NEA has been likened to a submarine exploring a wrecked ship - humans would sit in a "bubble" and approach the asteroid for up-close examination and robotic manipulation. What is important is to ensure that the bubble doesn't collide with the asteroid surface, nor float away. Multiple limbs, such as available on ATHLETE, allow for precise positioning and anchoring so as to enable the human bubble to maximize its exploration potential. A microgravity testbed has been constructed in the ATHLETE lab, with six computer-controlled winches able to lift ATHLETE and payloads so as to simulate the motion of the system in the vicinity of a NEA. Accurate 6-axis force-torque sensors will measure the applied forces and moments wherever the vehicle touches a simulated asteroid surface. These measured forces can be used to compute the resultant motion of the vehicle in the microgravity environment, and the winches then move the vehicle along the computed trajectory. Preliminary test results from this system are described.}
}
  23. Daca, A. (2023). Predicting Planetary Rover Mobility in Reduced Gravity Using 1-g Experiments . Unpublished. Source
    BibTeX
    @phdthesis{daca2023predicting,
  title = {Predicting Planetary Rover Mobility in Reduced Gravity Using 1-g Experiments},
  author = {Daca, Adriana},
  journal = {Unpublished},
  school = {Concordia University},
  address = {Montreal, Quebec, Canada},
  type = {PhD thesis},
  month = {February},
  year = {2023},
  doi = {10.13140/rg.2.2.12718.28485},
  abstract = {Traversing granular regolith, especially in reduced gravity environments, remains a potential challenge for wheeled rovers. Mitigating hazards for planetary rovers requires testing in representative environments, but direct Earth-based testing fails to account for the effect of reduced gravity on the soil itself. Here, experimental apparatus and techniques for reduced-gravity flight testing are used to systematically evaluate three existing Earth-based testing methods and develop guidelines for their use and interpretation: (i) reduced-weight testing, (ii) matching soil testing instrument response through soil simulant design, and (iii) granular scaling laws (GSL). \nExperimentation campaigns flying reduced-gravity parabolas, with soil and wheel both in lunar-g, have shown reductions in net traction of 20% or more and increases in sinkage of up to 40% compared to Earth-based testing methods (i) and (ii). Scaled-wheel testing, according to GSL (method iii) has shown better agreement with reduced-g tests (less than 10% error) and also tends to err on the side of conservative predictions. \nLimitations of GSL are investigated including a recently proposed cohesion constraint (that the wheel radius ratio must be the inverse of the gravity ratio) and the effects of wheel size and aspect ratio on GSL’s accuracy. It was found that the cohesion constraint can most likely be ignored for mildly cohesive soils such as lunar regolith. Limits on wheel sizes and aspect ratio variation are also proposed. \nThe application of GSL to planetary rover testing is demonstrated through two studies undertaken in collaboration with NASA’s Jet Propulsion Laboratory. One study compares wheel designs for a skid-steer lunar rover in single-wheel tests scaled by GSL, demonstrating that diagonal grousers improve turning performance without requiring larger wheels. The second study involves application of GSL to the design of two reconfigurable test platforms for evaluating steep-terrain mobility performance. \nAnother aspect of rover mobility testing—normal force control in single-wheel testbeds—is also investigated. An improved method for single-wheel testing, using a 4-bar mechanism, essentially eliminates normal force oscillations from frictional vertical sliders. \nFinally, guidelines for conducting and interpreting 1-g mobility tests for lunar rovers are presented, and potential avenues for future research are outlined.}
}
  24. Mitchell, J. K., Bromwell, L. G., Carrier, W. D. I., Costes, N. C., Houston, W. N. and Scott, R. F. (1972). Soil mechanics experiment . NASA, 19720015171. Source
    BibTeX
    @techreport{mitchell1972soil,
  title = {Soil mechanics experiment},
  author = {Mitchell, James K. and Bromwell, L. G. and Carrier, W. D., III and Costes, Nicholas C. and Houston, William N. and Scott, Ronald F.},
  number = {19720015171},
  institution = {NASA},
  year = {1972},
  url = {https://ntrs.nasa.gov/citations/19720015171},
  abstract = {The Apollo 15 soil-mechanics experiment has offered greater opportunity for study of the mechanical properties of the lunar soil than previous missions, not only because of the extended lunar-surface stay time and enhanced mobility provided by the lunar roving vehicle (rover), but also because four new data sources were available for the first time. These sources were: (1) the self-recording penetrometer (SRP), (2) new, larger diameter, thin-walled core tubes, (3) the rover, and (4) the Apollo lunar-surface drill (ALSD). These data sources have provided the best bases for quantitative analyses thus far available in the Apollo Program.}
}
  25. NASA. (1969). Apollo 11 Preliminary Science Report . NASA Manned Spacecraft Center, NASA SP-214. Source
    BibTeX
    @techreport{nasa1969apollo11,
  title = {{Apollo 11} Preliminary Science Report},
  author = {{NASA}},
  number = {NASA SP-214},
  institution = {NASA Manned Spacecraft Center},
  year = {1969},
  url = {https://ntrs.nasa.gov/citations/19700000726},
  abstract = {Preliminary scientific observation of Apollo 11 mission}
}
  26. Sibille, L., Carpenter, P., Schlagheck, R. and French, R. A. (2006). Lunar Regolith Simulant Materials: Recommendations for Standardization, Production, and Usage . NASA Marshall Space Flight Center, NASA/TP-2006-214605. Source
    BibTeX
    @techreport{sibille2006development,
  title = {Lunar Regolith Simulant Materials: Recommendations for Standardization, Production, and Usage},
  author = {Sibille, Laurent and Carpenter, Paul and Schlagheck, R. and French, R. A.},
  number = {NASA/TP-2006-214605},
  institution = {NASA Marshall Space Flight Center},
  type = {NASA Technical Publication},
  year = {2006},
  url = {https://ntrs.nasa.gov/citations/20060051776},
  abstract = {Experience gained during the Apollo program demonstrated the need for extensive testing of surface systems in relevant environments, including regolith materials similar to those encountered on the lunar surface. As NASA embarks on a return to the Moon, it is clear that the current lunar sample inventory is not only insufficient to support lunar surface technology and system development, but its scientific value is too great to be consumed by destructive studies. Every effort must be made to utilize standard simulant materials, which will allow developers to reduce the cost, development, and operational risks to surface systems. The Lunar Regolith Simulant Materials Workshop held in Huntsville, AL, on January 24 26, 2005, identified the need for widely accepted standard reference lunar simulant materials to perform research and development of technologies required for lunar operations. The workshop also established a need for a common, traceable, and repeatable process regarding the standardization, characterization, and distribution of lunar simulants. This document presents recommendations for the standardization, production and usage of lunar regolith simulant materials.}
}
  27. Taylor, L. A., Pieters, C. M. and Britt, D. (2016). Evaluations of Lunar Regolith Simulants . Planetary and Space Science. Source
    BibTeX
    @article{taylor2016evaluations,
  title = {Evaluations of Lunar Regolith Simulants},
  author = {Taylor, Lawrence A. and Pieters, Carle M. and Britt, Danial},
  journal = {Planetary and Space Science},
  volume = {126},
  pages = {1-7},
  publisher = {Elsevier BV},
  year = {2016},
  doi = {10.1016/j.pss.2016.04.005}
}
  28. Metzger, P. T., Britt, D. T., Covey, S., Schultz, C., Cannon, K. M., Grossman, K. D., Mantovani, J. G. and Mueller, R. P. (2019). Measuring the fidelity of asteroid regolith and cobble simulants . Icarus. Source
    BibTeX
    @article{metzger2019measuring,
  title = {Measuring the fidelity of asteroid regolith and cobble simulants},
  author = {Metzger, Philip T. and Britt, Daniel T. and Covey, Stephen and Schultz, Cody and Cannon, Kevin M. and Grossman, Kevin D. and Mantovani, James G. and Mueller, Robert P.},
  journal = {Icarus},
  volume = {321},
  pages = {632--646},
  year = {2019},
  doi = {10.1016/j.icarus.2018.12.019}
}
  29. Mantovani, J., Langton, A., Kemmerer, B., Atkins, A. and Batcheldor, D. (2022). Regolith Simulant Preparation and Geotechnical Characterization for Plume Surface Interaction Testing . NASA, 20220013110. Source
    BibTeX
    @techreport{mantovani2022regolith,
  title = {Regolith Simulant Preparation and Geotechnical Characterization for Plume Surface Interaction Testing},
  author = {Mantovani, James and Langton, Austin and Kemmerer, Beverly and Atkins, Austin and Batcheldor, Daniel},
  number = {20220013110},
  institution = {NASA},
  year = {2022},
  url = {https://ntrs.nasa.gov/citations/20220013110},
  abstract = {Descent engine plumes interact with the lunar surface and accelerate regolith particles to potentially high velocities. These ejecta create risks to surface assets that have yet to be fully assessed. To better understand these risks, plume surface interactions can be simulated on the ground by firing a test engine plume into a bin of lunar regolith simulant under vacuum conditions. The dynamics of the resultant ejecta can then be recorded. In this technical memorandum we discuss the processes used in preparing a 150 kg bin of lunar regolith simulant for plume surface interaction ground tests under vacuum conditions for the NASA STMD Plume Surface Interaction project. We present our approach to mitigating regolith simulant eruptions during pump-down, the methods used to fill and reset the regolith simulant bin for each test, and the techniques used to characterize the consistency of regolith simulant geotechnical properties before each new firing. The challenges of preparing a regolith simulant test bin below an ambient pressure of one atmosphere, particularly on the large scale, could largely be overcome with a system that could fill the test bin with simulant inside the chamber and under vacuum conditions.}
}
  30. Schepelmann, A., Creager, C. M., Proctor, M. P., Johnson, K. A., Breckenridge, J. R., Elmland, A., Naghipour Ghezeljeh, P. and Oravec, H. A. (2025). An Overview of Tire-Ground Contact Modeling Approaches for Surface Mobility Applications . NASA Glenn Research Center, NASA/TM-20250006958. Source
    BibTeX
    @techreport{schepelmann2025overview,
  title = {An Overview of Tire-Ground Contact Modeling Approaches for Surface Mobility Applications},
  author = {Schepelmann, Alexander and Creager, Colin M. and Proctor, Margaret P. and Johnson, Kyle A. and Breckenridge, John R. and Elmland, Asher and Naghipour Ghezeljeh, Paria and Oravec, Heather A.},
  number = {NASA/TM-20250006958},
  institution = {NASA Glenn Research Center},
  year = {2025},
  url = {https://ntrs.nasa.gov/citations/20250006958},
  abstract = {Wheels and tires serve as the critical interface between vehicles and the ground, enabling traction, force transmission, and ultimately mobility. As planetary exploration systems adopt increasingly complex wheel and tire designs, look to explore increasingly extreme terrains, and adopt increasingly aggressive performance requirements, physics-based modeling has become essential for both designing these mechanisms and predicting performance under conditions that are difficult or impractical to replicate experimentally, such as reduced gravity. This paper provides a high-level overview of commonly used modeling approaches for simulating tireground interaction, including those currently employed or under development at NASA Glenn Research Center, NASA Johnson Space Center, and the Jet Propulsion Laboratory. The paper first categorizes modeling techniques based on their fidelity and underlying assumptions. It then discusses the applications, benefits, and limitations of each approach, highlighting current knowledge gaps and modeling challenges. Finally, the paper outlines ongoing and future work aimed at addressing these limitations, including initial results from automated soil preparation experiments that support the generation of consistent physical test data and the development of terramechanics simulations for evaluating and comparing model fidelity.}
}
  31. Gaier, J. R. (2007). The Effects of Lunar Dust on EVA Systems During the Apollo Missions . NASA, NASA/TM-2005-213610/REV1. Source
    BibTeX
    @techreport{gaier2007effects,
  title = {The Effects of Lunar Dust on EVA Systems During the Apollo Missions},
  author = {Gaier, James R.},
  number = {NASA/TM-2005-213610/REV1},
  institution = {NASA},
  year = {2007},
  url = {https://ntrs.nasa.gov/citations/20070021819},
  abstract = {Mission documents from the six Apollo missions that landed on the lunar surface have been studied in order to catalog the effects of lunar dust on Extra-Vehicular Activity (EVA) systems, primarily the Apollo surface space suit. It was found that the effects could be sorted into nine categories: vision obscuration, false instrument readings, dust coating and contamination, loss of traction, clogging of mechanisms, abrasion, thermal control problems, seal failures, and inhalation and irritation. Although simple dust mitigation measures were sufficient to mitigate some of the problems (i.e., loss of traction) it was found that these measures were ineffective to mitigate many of the more serious problems (i.e., clogging, abrasion, diminished heat rejection). The severity of the dust problems were consistently underestimated by ground tests, indicating a need to develop better simulation facilities and procedures.}
}
  32. Gaier, J. R. and Sechkar, E. A. (2007). Lunar Simulation in the Lunar Dust Adhesion Bell Jar . AIAA Aerospace Sciences Meeting, NASA/TM-2007-214704. Source
    BibTeX
    @inproceedings{gaier2007lunar,
  title = {Lunar Simulation in the Lunar Dust Adhesion Bell Jar},
  author = {Gaier, James R. and Sechkar, Edward A.},
  booktitle = {AIAA Aerospace Sciences Meeting},
  number = {NASA/TM-2007-214704},
  institution = {NASA},
  year = {2007},
  doi = {10.2514/6.2007-963},
  abstract = {The Lunar Dust Adhesion Bell Jar has been assembled at the NASA Glenn Research Center to provide a high fidelity lunar simulation facility to test the interactions of lunar dust and lunar dust simulant with candidate aerospace materials and coatings. It has a sophisticated design which enables it to treat dust in a way that will remove adsorbed gases and create a chemically reactive surface. It can simulate the vacuum, thermal, and radiation environments of the Moon, including proximate areas of illuminated heat and extremely cold shadow. It is expected to be a valuable tool in the development of dust repellant and cleaning technologies for lunar surface systems.}
}
  33. Evans, J. P. (2010). Managing the Mars Science Laboratory thermal vacuum test for safety and success . IEEE Aerospace Conference. Source
    BibTeX
    @inproceedings{evans2010managing,
  title = {Managing the Mars Science Laboratory thermal vacuum test for safety and success},
  author = {Evans, Jordan P.},
  booktitle = {IEEE Aerospace Conference},
  pages = {1-9},
  publisher = {IEEE},
  year = {2010},
  doi = {10.1109/aero.2010.5446861},
  abstract = {The Mars Science Laboratory is a NASA/JPL mission to send the next generation of rover to Mars. Originally slated for launch in 2009, development problems led to a delay in the project until the next launch opportunity in 2011. Amidst the delay process, the Launch/Cruise Solar Thermal Vacuum Test was undertaken as risk reduction for the project. With varying maturity and capabilities of the flight and ground systems, undertaking the test in a safe manner presented many challenges. This paper describes the technical and management challenges and the actions undertaken that led to the ultimate safe and successful execution of the test.}
}