A New Facility for Lander Touchdown and Rover Mobility Testing at DLR Lutz Richter, Antje Brucks, Lars Witte DLR Institute of Space Systems, Bremen, Germany
New DLR Institute of Space Systems Systems Analysis (Concurrent Engineering Facility) Small satellite bus Advanced launcher upper stage R & D in precision attitude control Exploration technologies Landing systems (with local industry) Surface mobility (lateral & vertical) Mission studies
Landing systems at DLR: timely activity to support future lunar landers (and possibly ExoMars) Lunar Orbiter view of later A12 landing site (courtesy: Astrium-ST)
Landing systems lunar soft landers Surveyor III, visited by Apollo 12 Downslope landing leg
Landing systems lunar soft landers Issues: Propulsion GNC (N.B.: vision systems affected by dust in final phase) Impact attenuation & dynamics Challenging (and poorly known) terrains for some missions (courtesy: Astrium-ST)
Landing systems Mars soft landers Phoenix (EDL: May 24, 2008) Implementations: Viking Lander Mars Polar Lander / Phoenix Mars Sample Return
Landing systems ESA Rosetta lander Philae Rapid dissipation of impact energy critical (low g environment)
Motivation for a new test facility at DLR Seize the opportunity of new DLR infrastructure build-up: approval of planetary landing and mobility test facility ( LAMA, Landing & Mobility Test Facility) High speed soil deformation as in landing impacts not amenable to faithful numerical simulation LAMA objectives: Realistically simulate touchdown dynamics and tip-over stability of lander spacecraft in presence of terrain slopes and lateral velocity component Realistically study mobility of rovers at their operational weight while moving on soils Feature configurable realistic terrain: granular material + rock coverage -> Requires offloading device to adapt weight of test object during dynamics phase to lunar/planetary one under study
LAMA side view y x z cardanic joint force torque sensor force torque sensor (tilteable) test surface 2-axis inclinometer and yaw angle sensor IMU industrial robot with translation system translation axis
Salient features (1) Industrial robot system moving alongside and above soil bin to provide real-time controlled offloading force to test object during dynamical phase (from contact onwards) Test objects need not be scaled but may (and should be) full mass and full size: afford realistic simulations of dynamics -> landing impact & rover mobility Allowable upper limit of test object mass ~500 kg (add: specification/requirements from quant. requirements doc ; results of deceleration computations)
Salient features (2) Provide lander impact conditions (+z along g vector): 0.1 m/s < v x < 1.0 m/s (TBC) 0.1 m/s < v y < 1.0 m/s (TBC) 0.5 m/s < v z < 2.0 m/s (TBC) During contact phase: Provide test object commandeable weight reduction Weight reduction force to follow test object motion Predicted durations of dynamical phase: 20 ms < T < 2000 ms Predicted movement of test object CoM during dynamical phase: 10 mm < s < 2000 mm
Salient features (3) Intended mass, weight, speed and soil properties are simultaneously met in a given test* Concepts with passive weight offloading considered for LAMA but discarded: passive offloading schemes with countermasses or buoyancy systems (balloons) introducing additional inertia -> may be counteracted by active elements, however leading to active system themselves Passive Russian weight reductor from Lunokhod era *effects of reduced g on soil properties: studied separately experimentally & numerically
LAMA geometry in ZARM high bay (December 07 late 09) (dimensions in m) (dimensions in cm)
Terrain simulation Moon: Descartes (Apollo 16) Mars: Gusev Crater ( Spirit, McMurdo pan)
Terrain simulation Relevant experience available at DLR from rover work physical planetary soil simulants (grain size distribution, bulk density) Only feasible in horizontal testbeds as in LAMA DLR single wheel testbed Previous rover testbed at DLR
LAMA build-up & initial usage schedule
Summary LAMA: unique facility Hereby extending invitation to users: Development tests on lander impact dynamics (for upcoming lunar landers: NEXT, SELENE-II, Chang e-2, Chandrayaan-2, ) Rover mobility tests Planning campaign supporting ExoMars rover Breadboard tests in 2008 Currently preparing for NEXT-related lander development tests
Backup material
Airbag landers: Beagle 2
Airbag landers: MPF & MER
Airbag landers: ExoMars
Ausgewählte Projekte: Radentwicklung Rover ESA- Mission ExoMars (Drittmittelprojekt: ESA-Auftrag) Flexibles Metallrad; aufbauend auf Vorarbeiten bei DLR-RS Demonstrator Bridget
Influence of rover weight on drawbar pull
Test soil properties 22mm 30mm R^2 0.9996 0.9989 n [-] 0.854 0.849 Vertical loading parameters k* [Nm -(n+2) ] 410865.807 379664.508 = > k c [Nm -(n+1) ] k φ [Nm -(n+2) ] 1287.05 293861 Shear strength parameters c=40 Pa φ=25.6 Shear Stress Tau [N/m^2] 450 400 350 300 250 200 150 100 50 0 Sigma vs. Tau 0 200 400 600 800 1000 Pressure Sigma [N/m^2] y = 0,4791x + 40,71 R 2 = 0,9349 Reihe1 Linear (Reihe1)
Predicted lander deceleration paths Assumption: level ground (worst case) E=R*s (R assumed to be constant along set s due to shallow penetration in most cases) Bernstein model for flat plate footprint radius [m]: 0.1 number of (equal) footprints [-]: 4 footprint area [m^2]: 0.1256636 mass [kg]: 200 vertical impact speed [m/s]: 2 p = k * z n * k k = c + b k φ soil z [m] deceleration duration [s] mean force from soil per footing [N] DLR MSS-A 0.211 0.2 474 DLR MSS-C 0.119 0.11 843 DLR MSS-D 0.021 0.02 4788 MER 'loose' 0.069 0.06 1456 MER 'dense' 0.012 0.011 8389 Dry sand 0.059 0.06 1688 Sandy loam 0.030 0.027 3375 Clayey soil 0.026 0.027 3810 Deceleration distance to be = indentation depth from Bernstein model
Effect of g-level on soil strength e.g., Nakashima et al.: angle of repose of dense (left) and loose sand at 1/6 g
LAMA in context with proximity simulators Lander- Anflugphase Lander- Aufprallphase Satelliten AOCS? RDV & Docking EPOS+ LAMA angewiesen auf realistische Oberflächensimulation Rovertraktion, Fahrdynamik