The 1st test of the mole penetrator ‘KRET’ in the 5m test-bed system was a big success

On July 13th and 14th 2010 the first test of penetrator KRET (Fig. 1.) in a new test-bed built at the Space Research Centre PAS was conducted (Fig.2.). The test was successful – the penetrator had gone through the whole test-bed filled with sand and reached a record depth of five meters.


The mole penetrator KRET, developed at the Space Research Centre PAS, is a unique device intended for subsurface analyses of solar system bodies during i.a. future outer planet missions (e.g. to Titan). It belongs to a group of self-driven space penetrators. The depth achieved by this type of penetrators is limited to energy efficiency of the device and the penetrative resistance of the soil.

The tests conducted at the Space Research Centre PAS allowed finding out how the progress (descend of the penetrator during subsequent strokes) of KRET depends on the depth. Both a degree compactness of loose material (e.g. sand) at different depths, as well as the frictional force of the feeding cord’s, which KRET pulls behind, material  have the effect on the penetrator’s progress. The greater the depth, the longer the section of the cable KRET must pull behind at each impact. The new test-bed allows for verifying how KRET operates at certain depths (up to five meters). Such tests have never been done before - the previous test-bed allowed only for studies at a depth of two meters.


During the test KRET reached the maximum depth allowed in the test-bed (5 meters) in 16 hours. KRET’s progress decreased progressively with increasing depth, and at some point reached a constant level (about 2.5 mm per stroke) – this level of progress continued until KRET was 5 meters deep. The results suggest that KRET can very likely descend more than that.

The duration of the descend (5 meters within 16 hours) should not pose a problem while using KRET during a space mission since the operation of lander supplying penetrator with power may take several months. An important limitation connected with the capabilities of solar batteries used on landers is the power absorbed by all the research devices. KRET charges electricity from the lander and stores it in the form of mechanical spring energy and then (every 30 seconds) releases the accumulated energy by hitting the internal hammer (Fig.3.). This allows for the average power absorbed by KRET to be very low - only 0.28 W.


The carried out test was the first one in the new test-bed (Fig. 4.). In the coming months it is planned to conduct tests of KRET in the lunar regolith analogue - AGK 2010. This simulant was developed at the Faculty of Drilling, Oil and Gas of the AGH University of Science and Technology in Krakow. Material that simulates the lunar regolith is an essential element for testing any equipment that during future space explorations are to land on the Moon because the mechanical properties of the lunar regolith differ significantly from the properties of typical loose materials encountered on Earth (e.g. sand).

The next step will be the tests of a new version of KRET which was designed to work in lunar gravity conditions. These tests will take place in a tilted test-bed, which will simulate the operation of the penetrator at different values of gravitation.