The microscope for the Beagle 2 lander on Mars Express will provide 4 µm per pixel images of rock and soil samples. The instrument is described and test results are presented

Basilevsky, A. T.

Beauvivre, S.

Blümchen, T.

Hofmann, B.

Hviid, S. F.

Josset, J.-L.

Keller, H. U.

Markiewicz, W. J.

Oquest, C.

Pillinger, C. T.

Pullan, D.

Reynolds, R.

Rüffer, P.

Sims, M. R.

Smith, P. H.

Tanner, R.

Thomas, N.

Whitehead, S.

English

Open Research Online (The Open University)

Open Research OnlineThe Open University’s repository of research publicationsand other research outputsThe microscope for the Beagle 2 lander on ESA’s MarsExpressConference or Workshop ItemHow to cite:Thomas, N.; Hviid, S. F.; Keller, H. U.; Markiewicz, W. J.; Blu¨mchen, T.; Basilevsky, A. T.; Smith, P. H.;Tanner, R.; Oquest, C.; Reynolds, R.; Josset, J.-L.; Beauvivre, S.; Hofmann, B.; Ru¨ffer, P.; Pillinger, C. T.; Sims, M.R.; Pullan, D. and Whitehead, S. (2003). The microscope for the Beagle 2 lander on ESA’s Mars Express. In: SixthInternational Conference on Mars, 20-25 Jul 2003.For guidance on citations see FAQs.c© [not recorded]Version: Not SetLink(s) to article on publisher’s website:http://www.lpi.usra.edu/meetings/sixthmars2003/pdf/3015.pdfCopyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyrightowners. For more information on Open Research Online’s data policy on reuse of materials please consult the policiespage.oro.open.ac.ukTHE MICROSCOPE FOR THE BEAGLE 2 LANDER ON ESA’S MARS EXPRESS.  N. Thomas1,2, S.F. Hviid1,H.U. Keller1, W.J. Markiewicz1, T. Blümchen1, A.T. Basilevsky1,3, P.H. Smith4, R. Tanner4, C. Oquest4, R. Reynolds4,J.-L. Josset5, S. Beauvivre5, B.Hofmann6, P. Rüffer7,C.T. Pillinger8, M.R. Sims9, D. Pullan9, and S. Whitehead91Max-Planck-Institut für Aeronomie, Max-Planck-Str. 2, D-37191 Katlenburg-Lindau, Germany, 2PhysikalischesInstitut, University of Bern, Sidlerstr. 5, CH-3012 Bern, Switzerland, 3Vernadsky Institut, Moscow, Russia, 4Lunar andPlanetary Lab. University of Arizona Tucson, Arizona, U.S.A., 5Micro-Cameras & Space Exploration (SPACE-X),Neuchatel, Switzerland, 6Natural History Museum, Bern, Switzerland, 7Institut für Datentechnik undKommunikationsnetze der TU Braunschweig, Braunschweig, Germany, 8Dept. of Earth and Planetary Sciences, OpenUniversity, Milton Keynes, U.K., 9Dept. of Physics and Astronomy, University of Leicester, Leicester, UK.Introduction: The European Space Agency (ESA)will launch the Mars Express spacecraft in June 2003.The mission is intended to provide a flight opportunityfor re-builds of experiments lost as a result of theRussian Mars "96 launch failure and will reach Marsaround Christmas 2003. The re-build has allowed severalinstruments to be improved and upgraded. However, acompletely novel element of the Mars Express payloadis the Beagle 2 lander.Beagle 2 is designed to descend through the atmo-sphere of Mars to the surface using a combination ofaerobraking, parachutes, and airbags. After coming torest in the Isidis Planitia region of Mars, (260-270 W,5-10 N), the lander will deploy solar panels and beginscientific operations. The scientific payload comprises anX-ray fluorescence spectrometer, a Mössbauer spectrom-eter, a stereo camera system, a stepped combustion massspectrometer (GAP), a sampling device (``PLUTO''), aset of environmental sensors, and a microscope.Most of the experiments (the exceptions being theGAP and the environmental sensors) are mounted on arobotic arm referred to here as the ARM. The end of theARM has a flat experiment "platform", referred to as thePAW (position adjustable workbench), on which theexperiments are mounted.In addition to the experiments, a grinding and coringtool is also available on the PAW to scratch and flattenthe surfaces of rocks within reach of the ARM.This paper describes the aims and performance of themicroscope on the Beagle 2 PAW.Scientific Objectives: A microscope has fourdistinctly different tasks in a lander package. Firstly, theinstrument can be used to study the physical and struc-tural properties of a surface and hence make a geophysi-cal analysis and contribute to the overall geological andmineralogical interpretation of the landing site.Secondly, a microscope can contribute to studies ofthe atmosphere of Mars. Specifically, dust particles arecontinuously precipitating out of the dusty atmosphereand hence a microscope can be used to constrain thesizes and shapes of particles for input into atmosphericscattering and radiative transfer models of the Martianatmosphere.Thirdly, the instrument can be used to characterizeand/or select a sample before it is passed to anotheranalytical instrument. It is used therefore to assist thechemical analysis.Finally, the instrument can be used to study themorphology of a potentially biological sample and henceidentify structures which are characteristic of past orpresent biological activity.Instrument Concept: The concept of the optics forthe microscope was based on a system originally de-signed for the Mars Environmental CompatibilityAssessment (MECA) experiment package which wasslated for launch on the cancelled Mars "01 mission.The detailed design of the microscope for Beagle 2was constrained by even more stringent mass andvolume limits. This suggested that we try to keep thefocal length of the experiment as short as possible. This,in turn, implied that we should select a relative shortworking distance (the distance between the objectposition and the first optical element) of the order of 12mm. This was considered a reasonable solution giventhat the ARM would be able to bring the microscope tothe sample. The optically active elements comprise aCook triplet. The optics provides a magnification of3.5:1.The sample is unlikely to be well illuminated bysunlight because the microscope itself shadows thesample. This implied that an illumination system wouldbe required. Microscopes in the laboratory use eithertransmissive illumination or confocal illumination.While a confocal system is desirable, at present thedevelopment of such a method of illumination forspaceflight is only at a preliminary stage. For Beagle 2,Sixth International Conference on Mars (2003) 3015.pdfFigure 1 The FM microscope views a target mountedon a translation stage during bench testing.Figure 2 Microscope image of yeast on agar. Thefield of view is 4 x 4 mm2. The brights dots on thesurface of the yeast come from specular reflectionsfrom the LEDs. Individual organisms are below theresolution limit. we have chosen to use light-emitting diodes (LEDs)mounted around the entrance aperture of the microscope.The system comprises 12 LEDs, 3 red, 3 green, 3 blueand 3 UV. The UV LEDs are designed to induce fluores-cence in rocks (or a biological sample). A filter has beenintroduced into the optics to eliminate reflected UV fromthe incoming beam.For mass reasons, it was decided to use a mi-cro-camera head including a CCD detector and itsassociated electronics (detector control electronics,analogue to digital converter, noise reduction filters,clock, memory buffer, serial digital interface drivers, and10 Mbit s-1 communication protocol) in a lightweight(ca. 80 g) highly integrated 3D module. This mi-cro-camera has benefited from developments bySPACE-X within a contract from the ESA TechnicalResearch Programme (TRP). The 14 micron pixel pitchleads to a pixel scale of 4 micron px-1. The CCD is a 1kx 1k device giving a field of view of just over 4 x 4 mm2.Even before detailed design commenced it was clearthat the depth of focus of the microscope would be under100 microns. It was also apparent that the accuracy withwhich the PAW could bring the microscope to thesample would be at least a factor of 20 larger than this.Thus, a focussing mechanism was necessary. Translationof the entire microscope at the interface to the PAW wasimplemented. The PAW provides a means of bringingthe microscope to within ±3 mm of its target. A "thumb"on the PAW prevents the microscope from impactingrocks unless their surface roughness is greater than ±12mm (the working distance). The full range of the steppermotor is  ±3 mm, matching the accuracy of the PAWmotion. The instrument is shown in Fig. 1.Test Results: An image scale of 4.075 micron px-1 atthe best focus position was derived in bench tests. Thevariation in the image scale across the field of view ofthe microscope corresponds to a 0.2% distortion. TheFWHM of a point source at the nominal focus positionis 4.50 microns (1.10 px) and is less than 6 microns (1.5px) within 50 microns of the nominal focus position.This result indicates that the accuracy of the steppermotor motion (20 microns) should be more than suffi-cient.The flat-field shows some slight evidence of vignett-ing at the corners of the FOV. This is partly due to aslight misalignment of the detector in its housing andpartly due to the baffling system. The red LEDs are slightly susceptible to temperatureand their central wavelength decreases from nominal(642 nm) at room temperature to 625 nm at 183 K. Thewavelengths of the other LEDs vary by less than 2 nmover this temperature range. The output of the UV LEDsis strongly temperature dependent below 220 K and theybecome very faint below 200 K.Sixth International Conference on Mars (2003) 3015.pdfThe illumination field has been calibrated for all LEDcombinations and the system absolute response com-puted. (Care needs to be taken here because, unlike mostimagers, the microscope also provides the irradiance ofthe target.)For amusement we show in Figure 2 an image ofsome yeast grown on agar. This shows that the micro-scope still does not have high enough resolution toresolve individual organisms.Flight Software: The microscope can generate ahuge volume of data. In particular, because we have noa priori knowledge of the focus position and becausedifferent parts of the field will have different focuspositions as a result of surface roughness, many imagesat different positions need to be acquired to ensure thatall parts of the field are in focus at some point. Poten-tially, 60 or more images may be required to guaranteethat we obtain all parts of the field in focus at somestage.Two approaches to solving the problem of datavolume have been implemented on Beagle 2. Firstly, awavelet compression algorithm has been incorporatedinto the lander software to reduce the total data volumefrom the experiment. The algorithm will also be used tosupport the other imaging experiment (the stereo pan-oramic camera) onboard Beagle 2. Wavelet compressorsresolve the image into a series of coefficients which arerelated to spatial frequencies. The more detail one wishesto see in an image, the more coefficients one has toreturn. For the microscope this scheme is extremelyeffective. The reason is because an out of focus imagedoes not require many coefficients. It is smooth. There-fore, unfocussed frames compress extremely well withratios in excess of 40:1 often achievable with almost noloss. Hence, one possibility is to transmit all 60 framescompressed according to a quality criterion.The second approach is to analyse the data onboard.Here we acquire all 60 frames but investigate the entropyat each position in each image to determine which imagehas the best focus for that position. We then downlink acompletely focussed composite image.In both cases, an important result from the analysisis that the image in which focus has been achieved for aposition allows us to define unambigiously its depth.Hence, not merely does the microscope gives us a 2-Dpicture of the surface, it also gives us a depth mapallowing complete 3-D reconstruction of the surface.Summary: The microscope for Beagle 2 is a highlycompacted (160 g) device which will provide 6 micronresolution images of surface material in Isidis Planitia.The elegant design of the system makes it ideal forfuture landed missions where microscopic imagingmight be required. Adaption of the system to supportother experiments (e.g. Raman spectrometer or lasermass spectrometer) should be relatively straightforward.This abstract is a summary of a more detailed instru-ment paper submitted to Planetary and Space Science.Acknowledgments: The development of the micro-scope optics was funded by the University of Arizona'sspecial fund. The micro-camera head was sponsored bySPACE-X. The Max-Planck-Gesellschaft supportedintegration and test. Software development was partlysponsored by DLR. The Beagle 2 PAW microscopefocussing mechanism was funded by the Particle Physicsand Astronomy Research Council of the UK. M.R. Simsacknowledges funding from the University of Leicesterand via the Royal Society Industry Fellow scheme. Sixth International Conference on Mars (2003) 3015.pdf

The microscope for the Beagle 2 lander on ESA's Mars Express

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The microscope for the Beagle 2 lander on ESA's Mars Express

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