Lander in Drop test mode on inclined plane
DLR (CC BY-NC-ND 3.0).
Engineers checking the Lander
© DLR, all rights reserved.
Landing technology team
Lander Engineering Model (LEM)
Overview of the laboratory
Philae landing tests
Tests on one leg
The Institute of Space Systems has deployed and operates a facility – the Landing & Mobility Test Facility (LAMA) – to test landing vehicles and exploration rovers. Objectives are to determine and to investigate experimentally on system level the dynamic behaviour of planetary vehicles, being either rovers or landers in their very final landing phase at touchdown when ground contact occurs. Test objects and models used to represent such planetary vehicle shall have a similar dynamical behaviour, identical stress level on load or shock absorbers for landing gears or wheel suspension for roving vehicles.
The key elements of the facility (Figure 1) are a robotic arm for the test object handling and a soil bin to contain a planetary surface set-up. The main reason for using an industrial robot is to provide a fully active, self-supporting and highly flexible device to maintain various load scenarios and different test objects. A large variety of additional off the shelf hardware and support such as software and sensor systems are available from service suppliers from the industrial automation branch. The nominal static load bearing capacity of this robot is 500kg. It sits atop a rail track system allowing a lateral travel distance of 10m. The soil bin contains the planetary soil simulant and, if needed, other terrain features. It has overall dimensions of 10m x 4m. A section of 4m x 4m is tiltable to provide slopes between 0° and 30° in 5° steps. The soil depth is 0.25m in the ramp area and 0.5m in non-tiltable area.
The facility offers two major test modes: These are (a) the weight off-loading mode and (b) the drop test mode. Both modes require a dedicated element which provides the link between robot hand flange and test object. This is a suspension device especially developed and patented for the weight off-loading mode and a commercial off the shelf gripper to release an object in the drop test mode.
Weight off-loading: The test object is hereby permanently suspended and off-loaded during the test. The test object suspension fulfils three functions: (i) transmit a (quasi-)static reduction or weight off-loading force, (ii) provide sufficient degree of freedom to the test object and (iii) decouple the dynamics of the robot and the test object from each other.The build-up consists of the following elements: the upper flange plate connects the suspension to the force-torque sensor in the robot hand and linear guide pillars are limiting the degree of freedom to the vertical or “gravity axis”. A set of tension springs has to be selected dependent to the test object mass. A carbon fibre beam provides the lateral degrees of freedom and is attached to the lower attachment plate. This test mode has been used for example for full-scale landing tests of the Rosetta lander Philae (Figure 2)
Drop Test: The release mechanism for model drop tests uses an off the shelf pneumatic gripper mounted to the robots hand flange. The work pressure to operate the gripper is directed by a manifold valve which receives its lock/release signals from the robots real-time controller. The gripper’s jaws engage into a dedicated form fit interface mounted on the test object. Figure 3 shows a set-up for a system-level drop test campaign with a sub-scale robotic lunar lander engineering model. Figure 4 depicts the similar set-up for a full-scale test campaign with SpaceIL/IAI’s Lunar lander engineering model.
LAMA is complemented by component level test rigs. A single leg drop test stand (Figure 5) is used for development and qualification tests with full-scale (~2.5m height, 250kg lander mass/leg) landing gear assemblies.