Study of the Formation of Duricrusts on the Martian Surface and Their Effect on Sampling Equipment

Icarus 281 (2017) 220–227

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Icarus

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Study of the formation of duricrusts on the martian surface and their effect on sampling equipment

∗ Norbert Kömle a, Craig Pitcher b, , Yang Gao b, Lutz Richter c a Space Research Institute, Austrian Academy of Sciences, Schmiedlstraße 6, A-8042 Graz, Austria b STAR Lab, Surrey Space Centre, University of Surrey, Guildford, GU2 7XH, UK c OHB System AG, Manfred-Fuchs-Straße 1, 82234 Weßling - Oberpfaffenhofen, Germany

a r t i c l e i n f o a b s t r a c t

Article history: The Powdered Sample Dosing and Distribution System (PSDDS) of the ExoMars rover will be required Available online 20 August 2016 to handle and contain samples of Mars regolith for long periods of time. Cementation of the regolith, caused by water and salts in the soil, results in clumpy material and a duricrust layer forming on the Keywords:

Mars surface. It is therefore possible that material residing in the sampling system may cement, and could po-

Surface tentially hinder its operation. There has yet to be an investigation into the formation of duricrusts under Instrumentation simulated Martian conditions, or how this may affect the performance of sample handling mechanisms. Regoliths Therefore experiments have been performed to create a duricrust and to explore the cementation of Mars analogues, before performing a series of tests on a qualiﬁcation model of the PSDDS under simulated Martian conditions. It was possible to create a consolidated crust of cemented material several millimetres deep, with the material below remaining powder-like. It was seen that due to the very low permeability of the Mont- morillonite component material, diffusion of water through the material was quickly blocked, resulting in a sample with an inhomogeneous water content. Additionally, samples with a water mass content of 10% or higher would cement into a single solid piece. Finally, tests with the PSDDS revealed that samples with a water mass content of just 5% created small clumps with signiﬁcant internal cohesion, blocking the sample funnels and preventing transportation of the material. These experiments have highlighted that the cementation of regolith in Martian conditions must be taken into consideration in the design of sample handling instruments. ©2016 Elsevier Inc. All rights reserved.

1. Introduction saw crusts formed at the surface of cloddy deposits, mechanically resembling those found at the VL2 site, though with smaller cohe- Evidence of soil induration and crusts on the Martian surface sions ( Bickler et al., 1999 ). Both MER rovers also found evidence for has consistently been seen in lander missions. The Viking landers the existence of such crusts. In particular, Spirit saw that soil de- were the first to observe this, with a layer of lightly cemented fine- posits typically displayed surface crusts a few millimetres thick be- grained sediments about 1 - 2 cm thick occurring at both landing neath thin dust covers, and observed surface crusts in wheel track sites. This cemented soil was designated as duricrust. Further indi- disturbances ( Arvidson et al., 2004 ). Opportunity’s Microscopic Im- cations of the presence of duricrusts included a large area of frac- ager observation of disturbed soils also suggested a crust at least tured crust mapped at the Viking Lander 2 (VL2) site and through 1 mm thick caused by cementation of surface particles ( Herkenhoff trench operations, in which the upper layer of shovelled soil indi- et al., 2004 ). Finally, the Phoenix landing site excavated a dozen cated a cohesive strength greater than that of the deeper, uncon- trenches, and saw that the upper few centimetres of soil were solidated soil ( Mutch et al., 1977 ). Crusty to cloddy material was crusted, and clods were seen around the trenches, with mechani- also seen to occupy ∼ 86% of the VL2 sample field, with the co- cal properties again similar to those of the VL2 landing site ( Smith hesion seen at least partly due to cementation of the fine grains et al., 2009 ). From this evidence, it is likely that crusting is a near- ( Moore and Jakosky, 1989 ). The Pathfinder rover, Sojourner, also ubiquitous phenomenon on fine materials of the Martian surface. Currently there have been no conclusive observations concern- ing the chemistry of the duricrusts available, although there are a ∗ Corresponding author. number of hypotheses as to its formation, with the cementation E-mail address: [email protected] (C. Pitcher). process likely caused by mobile salts ( Hudson et al., 2007 ) and/or http://dx.doi.org/10.1016/j.icarus.2016.08.019 0019-1035/© 2016 Elsevier Inc. All rights reserved. N. Kömle et al. / Icarus 281 (2017) 220–227 221 clay components. Evidence of clays in the Martian soil was first noted in the observations by Viking ( Banin and Rishpon, 1979 ), and has been inferred in numerous other studies ( Chevrier and Mathé, 2007 ). Analysis of the surface geology of the VL2 site also revealed the presence of relatively high sulphur and chlorine contents, suggesting that compounds of these elements are a significant factor in crust formation ( Sharp and Malin, 1984 ). The soil in the Viking, Pathfinder and MER landing sites all have sulphur and chlorine contents of 4% and 1% respectively. Two models for the formation of duricrusts at the MER sites were proposed, in which transient liquid water plays a vital role in dissolving and deposit- ing salts. Repetition of these processes over a long time period can explain the widespread distribution of the cemented soils, with the crust’s thickness dependent on the length of time the transient water phase is present ( Landis et al., 2004 ). Only a limited amount of water appears to be required, with soil crusts on the Gusev Plains likely being formed under low water activity and very Fig. 1. PSDDS breadboard model as configured for the sample cementation tests. limited evaporated mineral deposition ( Cabrol et al., 2006 ).

Numerous experiments have been performed to determine the Table 1 properties of duricrusts. Salt crusts created with magnesium sul- Composition of the S7 regolith simulant ( Durrant and Baglioni, phate, though with significantly more liquid water than would 2013 ). be present on Mars, were used to examine diffusion barriers and Simulant Component Quantity vapour transport ( Hudson and Aharonson, 2008 ). Other experiments have involved examining the spectroscopic identity of sul- Montmorillonite 67% phates on Mars and the effects of soil cementation on the soil’s Magnesium sulphate heptahydrate (Epsom salt) 30% Magnesium perchlorate hexahydrate 3% spectral properties ( Cooper and Mustard, 2001 ). The effect of soil cementation on the thermal inertia of the Martian surface has also been examined ( Piqueux and Christensen, 2009 ), and the thermal properties of the inferred Martian duricrust surfaces have been its sample funnels were filled with Mars analogue material and ex- compared to the indurated surfaces on Earth ( Murphy et al., 2009 ). posed to simulated Mars conditions. Another study developed a model explaining the formation of ce- The outline of this paper is at follows. In Section 2 , an initial mented and crusted soils, investigating how the composition of series of experiments is described in which water vapour is intro- these crusts affects their spectral and physical properties. It was duced to a sample of the analogue material at Mars atmospheric found that material with a high smectite content resulted in a conditions, before undergoing a cooling and heating cycle. The for- harder, thicker crust, while the palagonitic soil produced a thinner, mation of the duricrust over time is then presented. Section 3 ex- more friable crust ( Bishop et al., 2002 ). amines the degree of permeability and subsequent cementation of Although duricrust simulants have been created and their prop- the materials that make up the analogue. Section 4 describes the erties studied, there appears to have been no investigation into the experiments performed with the PSDDS, with the aim of determin- formation of duricrusts under simulated Martian conditions, and in ing if cementation of the sample affects the dosing mechanism. Fi- particular how their properties would influence the performance nally, Section 5 contains our conclusions and recommendations. of sampling and drilling mechanisms. For instance, a sample taken either from the surface or subsurface could spend several days 2. Creation of duricrust in a simulated martian environment in a sampling subsystem before being delivered to an instrument. Within this time, water present in the soil and/or the atmosphere The first aim of the experiments performed was to verify if could cause cementation of the sample, potentially to the extent at the surface of Mars can be chemically cemented under conditions which it hinders the operation and efficiency of the mechanisms it that are similar to the Martian environment. The material used for will interact with. This could particularly happen when the mate- these experiments is the S7 analogue, an unconsolidated clay/salt rial contains larger amounts of loamy analogue materials such as regolith simulant verified for use in the validation and testing of Montmorrillonite, which forms the main component of the ESA- the Drill and SPDS mechanisms of the ExoMars rover, with its com- defined Mars analogue materials ( Durrant and Baglioni, 2013 ). position given in Table 1 . The Powdered Sample Dosing and Distribution System (PSDDS) is a part of the Sample Preparation and Distribution System (SPDS) of 2.1. Experimental Set-up the ExoMars rover currently being developed by OHB System AG. Its dedicated task is to feed crushed Mars surface and subsurface These tests involved a sample of the S7 simulant, held in a material into other instruments for further investigation. There is a cylindrical container of 7 cm diameter and 3 cm height. In order possibility that the crushed material collected by the ExoMars drill to simulate the Martian environment, a number of conditions could become clumpy while lying in the instrument, which could must be met. To account for the presence of water in the soil, the potentially hinder the proper dosing operation of the PSDDS. In sample is wetted by directing the flow generated by a water dis- order to investigate this question experimentally, a series of tests perser producing very fine water droplets (micrometre-size range) have recently been conducted under Mars-like conditions at the in a tube towards the initially dry sample surface. The sample is Space Research Institute/Austrian Academy of Sciences. For these ex- placed in a vacuum chamber of 40 cm diameter and 40 cm height. periments a qualification model of the PSDDS, shown in Fig. 1 , was To simulate the Martian atmosphere, a high precision pressure used. These tests involved the creation of duricrusts using a Mars regulation valve and vacuum pump are used to establish a stable analogue material as suggested by ESA in simulated Martian con- Mars surface pressure of 6 –8mbar, and CO2 can be fed into the ditions, and an examination of cementation of the analogue and its chamber via an inlet. The final part of the test is to simulate the components. This culminated in the testing of the PSDDS, in which cycles of heating and cooling that would be experienced on Mars. 222 N. Kömle et al. / Icarus 281 (2017) 220–227

Fig. 2. Picture of the S7 sample placed on the cold plate within the vacuum chamber, and a schematic of the vacuum chamber, showing the connections and inlets for the water vapour, pressure and cooling systems.

Fig. 3. Set-up for the wetting of the S7 sample, with the water vapour tube connected to the steel container. The numbers indicate temperature sensor placements.

It must be noted that simulating the temperature variations in a Afterwards, the water disperser and any condensation that had ap- real day/night cycle would result in extremely long experiments. peared was removed. The lids were then reattached and the vac- The cycles have thus been scaled down to meet experimental uum pump was activated, slowly reducing the pressure to around constraints. The critical aspect of this is to allow the water present 2mbar. The CO2 supply and regulation valves were then opened, in the sample to undergo cycles of freezing and melting. Sim- increasing the pressure to 6 – 8mbar. Adjustments were made to ilarly, in true Mars conditions multiple layers of thin adhesive allow for the changes in pressure caused by removal of excess wa- films created by the condensation of atmospheric gases result in ter droplets and drying of the sample. After a stable Mars pres- duricrust formation. However the time taken for this to naturally sure was achieved, the cooling machine was activated. The cooling occur is much too long to feasibly be recreated in the laboratory. liquid temperature was lowered to -40 °C for one hour, before be- Therefore a water vapour disperser is used to create a much faster ing raised to 30 °C for another hour, after which this cycle was re- and efficient method of water addition, which will likely produce peated. At the end of the second cycle the cooling machine was similar cementation results. A Huber CC902 cooling machine was switched off, and the sample was kept at atmospheric pressure connected via a feed through for liquids to a cold plate held inside overnight, after which the vacuum was switched off and the sam- the vacuum chamber, on top of which the sample was placed. ple was inspected. During the experiment, the temperatures mea- Other inlets in the vacuum chamber allow the insertion of pres- sured by the sensors were recorded, and the profiles produced are sure and temperature sensors. The initial set-up of the experiment, shown in Fig. 4 . These show that the sample successfully went and a schematic of the vacuum chamber, is shown in Fig. 2 . above and below the freezing point of water during the cycles. The experimental procedure was started by placing the sample cylinder within a small steel container, which itself was posi- 2.2. Duricrust formation tioned on the cold plate. Temperature sensors were placed at several positions of interest, in particular inside the sample near the Fig. 5 (a) and (b) show the S7 sample before and after the surface, around the steel container and on the cold plate, as seen experiment. There is a cracked and uneven, but nevertheless con- in Fig. 3 . The container was closed by a black metal lid with a cen- solidated, crust with a thickness of approximately 5 mm, which is tral hole, into which the vapour flow tube was inserted. The vac- clearly cemented material. The thickness of the crust corresponds uum chamber was sealed, and the sample was then wetted for two to the thickness of the sample. Below this cemented layer the hours under normal room pressure and atmospheric conditions. material is largely unchanged and still has its initial powder-like N. Kömle et al. / Icarus 281 (2017) 220–227 223

Fig. 4. Temperature proﬁle during a cementation experiment.

Fig. 5. The S7 regolith simulant before (a) and after (b) the experiment. Part of the sample was removed (c) to show the difference between the cemented and dry regions. texture. This can be best seen in Fig. 5 (c), which has a section of the cemented crust (lower side of the sample surface in the ﬁgure) removed. The crust could be separated from the rest of the sample without being destroyed mechanically, illustrating the internal cohesiveness of the material caused by the wetting and subsequent drying under low pressure. The evolution of the surface crust during the drying phase of one of these experiments is shown in Fig. 6 . The surface of the sample immediately after wetting (a) is quite even, with only one small crack. During the course of the drying process (combined with heating and cooling cycles) more cracks occur, through which gas trapped below the surface can escape into open space.

3. Cementation tests

To further understand the wetting and cementation process with the samples to be used for the PSDDS tests, two dedicated experiments were performed. For both tests brass containers of 24 mm diameter and 21 mm height, with a volume comparable to that of the PSDDS funnels, were used to contain the samples, as shown in Fig. 7 .

3.1. Wetting of the simulant materials

The purpose of this experiment was to determine the extent Fig. 6. Evolution of a surface crust for a wetted sample with S7 composition dur- and speed at which the component parts that make up the S8 re- ing the drying phase. (a) shows the sample after wetting, and the sample is then pictured after being vacuum dried for (b) 39 minutes, (c) 44 minutes and (d) 55 golith simulant are wetted. The S8 is another veriﬁed regolith sim- minutes. ulant given in Durrant and Baglioni (2013 ), and consists of 50% of the S7 mix and 50% of a ﬁne-grained quartz sand, in this case the Schwarzl UK4 ( Seiferlin et al., 2008 ) sand. This mix of sand and the same set-up as shown in Fig. 3 . The water vapour was subse- clay is also likely to be found on Mars and as such testing the per- quently run for two hours, with excess vapour allowed to escape meability of the UK4, absent in the S7, is also required. The four through small openings in the steel container. sample materials tested were: the Magnesium Sulphate, Montmo- The water mass content of the samples was measured before rillonite, UK4 sand and the S8 mixture. The samples were held and after wetting. It should be noted that both the Magnesium within a steel container, as shown in Fig. 7 , and were wetted using Sulphate and the Montmorillonite are extremely hygroscopic 224 N. Kömle et al. / Icarus 281 (2017) 220–227

Table 2 Description and water content values of the sample materials.

Sample Extent of Wetting Water Content (wt. %) Before After

Magnesium Sulphate Fully wetted to the sample base 36 .0 37.2 Montmorillonite Top 4 –5mm 9.1 N/A UK4 sand Wetted to ∼ 4 mm above base 0.4 4 .7 S8 Mix Top ∼ 10 mm wetted 9.9 18 .4

strongly cemented when dried in vacuum. The 5 g and 10 g samples were so strong that they could be removed from their containers as compact pieces, as seen in Fig. 8 (b), and could not be easily split or crumbled by hand without the help of mechanical tools. On the other hand, the 2.5 g sample showed no noticeable cementation, and was quite similar to the dry sample. Though the consistency was still powder-like, there was a tendency for particles to coagulate into several millimetre-sized globules which were cemented to hard material when dried in vacuum. However, it must be noted that it was quite diﬃcult to distribute this small amount of water homogeneously to the sample with the means available. This was due to the water tending to connect immediately to the local environment as the mixture was stirred, and as such small clumps easily form that tend to remain separated from the rest of the sample material. This naturally hinders local cementation. These tests have been designed to provide further information when preparing for the PSDDS dosing tests. It has become clear that if the Martian soil is similar to the S7 or S8 simulants, the uppermost millimetres can form a cemented crust. Fully cemented

Fig. 7. The four samples used in the cementation experiments before wetting. samples with a water content close to saturation would never be suitable for correct operation of the PSDDS, as their granular structure has changed to a strongly cemented solid body with consider- substances, and as such already contain a considerable percentage able internal cohesion. of bound water even when they are not explicitly wetted. The samples were then carefully removed from their containers and 4. PSDDS dosing tests their appearance qualitatively described, with the results given in Table 2 . The PSDDS mechanism consists of four key parts, as labelled in From this test it can be concluded that it is difficult to obtain a Fig. 9 . The material collected from the sampling mechanism is de- homogeneous wetting for materials such as the S8 mix simply by posited in the entrance funnel (1). A small portion of this material keeping them in a water-saturated environment. This is largely due falls into a small opening in the dosing device (2). The material to the low permeability of the Montmorillonite, whose tiny parti- captured in this small opening is then transported into the lower cles swell when taking up more water, quickly blocking the diffu- exit funnel (3) by the action of a motor, which drives a hinge that sion into deeper layers. As a result, even small samples of S8 such rotates the dosing device and the sample portion by 180 ° clock- as these are not homogeneously wetted, unless they are stirred wise/anticlockwise around a central pivot. To support the move- and mixed during the process. It is therefore not expected that the ment of the material, a piezo vibrator built in the vicinity of the deeper parts of the samples collected and stored inside the PSDDS motor (4) can be operated. funnels would become wetted and subsequently cemented within For all tests performed, the S8 material was used. 50 g samples the timescales expected for the planned investigations on Mars. were mixed with controlled volumes of distilled water, used here to keep the PSDDS free from impurities, to create mixtures with 3.2. Cementation with various water contents 5, 7.5 and 10% water mass contents. These were then kept in a freezer at -20 °C in tightly closed containers to avoid any loss of This experiment furthers the cementation investigation by de- moisture. Although all three samples maintained a granular con- termining how much water content should be added to the dry S8 sistency after wetting, when frozen the 10% sample showed some samples in order to obtain a cemented material. For this purpose, internal cohesiveness, and as a result was not used for the tests. It 50 g samples of the S8 mixture had water added in increments of should be noted that for these tests the cemented duricrust created 2.5 g, 5 g and 10 g, giving water mass contents of 5%, 10% and 20% in Section 2 was not tested. This is because, given its clumpy na- respectively. A portion of the dry and each of the mixed materials ture and significant strength, even broken-up pieces would not be were then filled into one of the brass containers. In this condi- able to pass through the dosing mechanism and funnels. Instead, tion, the 2.5 g sample had the appearance of a wet powder, while focus was placed on the unconsolidated material below the crust, the 5 g and 10 g samples had a paste-like consistency. The samples and how its properties change when it is allowed to rest in simu- were then stored in a cooler at -20 °C for two hours, after which lated Mars conditions. they were placed inside the vacuum chamber and subjected to a Four tests were performed, each following the same general pressure of 1 mbar for approximately 18 hours, shown in Fig. 8 (a). procedure. As the water had already been added to the samples, The samples were then removed and inspected. the water disperser was not needed. The PSDDS was placed on the The results of this test seem to indicate that the samples will cold plate in the vacuum chamber. One of the funnels was filled have a paste-like consistency if they contain enough water, likely with the selected S8 sample and, to avoid dispersion of the sam- equivalent to a value nearing saturation, and as a result become ple or any water during depressurisation, was covered by a glass N. Kömle et al. / Icarus 281 (2017) 220–227 225

Fig. 8. (a) The four samples of varying water content after 18 hours of vacuum drying, and (b) the 5 g and 10 g samples.

Fig. 9. Side view and schematic of the PSDDS, showing (1) the entrance funnel, (2) the dosing device, (3) the exit funnel and (4) the piezo vibrator.

Table 3 Summary of the conditions for the PSDDS tests performed.

Experiment Duration (hours) Sample Water Content (%) Minimum Temperature ( °C)

1 22 5 -40 2 7 7.5 -40 3 25 5 -50 4 21 5 -60

lid. Temperature sensors were attached to the plate, the base and top of the PSDDS and on the funnel cover. The chamber was then brought down to the Mars atmospheric pressure of 6 –8 mbar, but for these experiments no CO2 was used. The temperature of the cold plate was then lowered to a set value. Although the cold plate was able to reach temperatures of -60 °C, the poor thermal contact between the plate and the funnels containing the samples resulted in the sample temperature being significantly higher, gen- erally reaching a minimum temperature of -10 to -20 °C. A summary of the details of the experiments is given in Table 3 and the typical temperature profiles seen during an experiment are shown in Fig. 10 . Once the cooling began, the piezo vibrator was applied in five consecutive bursts of five seconds at a frequency of 250 Hz every fifteen minutes throughout the day. The sample was then allowed to rest at a constant minimum temperature overnight. The dosing tests were performed next morning, with the piezo actuated five times before and after each dose. Section 4.1 details the success of Fig. 10. Temperature profiles for Experiment 4. these dosing tests.

4.1. Experiment results had been reached, and the second after several hours of cooling. Both were successful, with material seen to be falling out of the The first experiment was largely successful in terms of the exit funnel. The conditions were maintained overnight and further dosing operations. The first was performed after the Mars pressure dosing tests were performed. The first eight were successful, 226 N. Kömle et al. / Icarus 281 (2017) 220–227

Fig. 11. Comparison of the dosed material (left) with the original dry S8 regolith simulant. however afterwards the dosing mechanism did not work on all occasions. This was likely due to the clumpy parts of the sample causing the rotating axis to get stuck. The piezo vibrations tended Fig. 12. Experiment 2 with the overlying material removed, showing the large to raise the larger particles to the top of the sample, hence why pieces blocking the funnel exit. the problems occurred towards the end of the test, since at this point only the clumpy material remained. By frequently using the piezo vibrations and alternating the direction of the dosing rota- placing it on the table, the blockage in the funnels was removed or tion, it was possible to eventually empty the funnel of all sample broken apart, allowing the material to be transported as normal. material. Some material remained in the exit funnel, and this was removed Another observation made here, and subsequently seen in the by applying further slight shocks to the device using a wrench. later experiments, was that the rotation speed of the dosing device The final experiment was used to confirm the findings of the was up to ten times slower in the lower temperatures. This was previous test. Once again, the dosing worked after the pressure probably caused by increased friction due to thermal effects, and was reduced to 6 – 8mbar, but failed after cooling for several is another point that needs to be taken into consideration in the hours, with the sample here reaching a temperature of -20 °C. PSDDS’s development. Once again the dosing mechanism was able to rotate, but this time The dosed material was collected and compared with the orig- the material could be seen to be gradually disappearing from the inal dry material prepared before the water content was added, as entrance funnel, until it was emptied. After this, the PSDDS was seen in Fig. 11 . Visually there is little difference, with both having removed from the chamber and shocks were applied to the exit round coagulated particles of a few millimetres; however there is funnel, causing the material to pour out. a significant mechanical difference. While the dry clumped parti- These tests have shown that the performance of the PSDDS cles are very soft, with little resistance to destruction, the dosed could be seriously compromised when handling samples contain- particles are clearly cemented and mechanically cohesive. ing a high percentage of clay-like material such as the S8 simu- The second experiment’s sample had a darker appearance with lant. A dry S8 sample will tend to coagulate, forming globules up larger and more frequent clumps of material, due to its higher wa- to several millimetres or even half a centimetre in size. When wet- ter content. The experiment was cut short due to a failure of the ted to have even a small water mass content of 5%, these clumps cooling system; however some observations could still be made. develop an internal strength under Mars conditions. When one or While the first dosing test, performed after Mars pressure had more of these comes close to the exit of the entrance funnel, this been achieved, was successful, those performed after several hours can result in either a blockage of the funnel or the dosing rota- of cooling were not, with no material coming out and the dosing tion being stopped. The risk of blockages occurring is even greater mechanism not moving. The material remaining in the funnel was in the exit funnel, as the hole in the exit funnel is even smaller manually removed, until only the material close to the base of the than that of the entrance funnel. This resulted in material piling funnel remained. It can be seen in Fig. 12 that several large parti- up that was unable to be removed by the action of the piezo vi- cles, including one piece with an area of 5 ×3 mm, which were ce- brator, and required significant shocks to be removed. Given that mented and had internal cohesion, were blocking the funnel’s exit, this blocking occurred both in cold and warm conditions, the co- preventing material entering the dosing device. hesion the clumps gained from the initial cooling is maintained. The third experiment, using the 5% sample, had dosing tests This may cause a real single point of failure that would very likely similar to the second, in that they were successful before cooling occur if the system in its current design were to be operated on and unsuccessful after. Afterwards the sample was allowed to Mars. The easiest way to reduce this risk would be to increase the warm up to around + 10 °C and further dosing tests were per- diameter of the opening of the dosing device and the funnel holes, formed. These were also unsuccessful, with no material being in particular the exit funnel. The piezo system could also be im- removed from the entrance funnel. However this time the dosing proved by applying stronger vibrations and by letting it act closer mechanism did not appear to be blocked, as it was still able to to the funnel exits. rotate. The experiment was left to run overnight, allowing the sample to warm up to ∼ 20 °C, yet the tests performed after were 5. Conclusions still unsuccessful. Hereafter the PSDDS was removed from the vacuum chamber and placed on a table. The dosing was performed This paper has presented a study of cementation in Mars again, and this time the test was successful. It is assumed that due regolith simulants, in particular the formation of duricrusts on to the slight mechanical shocks created by moving the device and the surface, and the effect this has on the operation of sampling N. Kömle et al. / Icarus 281 (2017) 220–227 227 devices that will be handling such material, as part of the qual- References ification testing for the PSDDS subsystem of the ExoMars rover. 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