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SD2

SD2

Among the specific subsystems and instruments carried on board of PHILAE (the comet lander of the ROSETTA mission), the Drill, Sample and Distribution (SD2) subsystem plays a key role for the success of the in-situ part of its scientific mission. This system is in charge to take comet's soil samples at different depths and to distribute them to different instruments for analysis [1].

During comet surface operations, SD2 shall interface with three scientific instruments [2] devoted to samples analysis:

  • COSAC (COmetary Sampling And Composition experiment) [3], one of the two evolved gas analysers designed to detect and identify complex organic molecules from their elemental and molecular composition;
  • PTOLEMY [4], the other evolved gas analyser designed to perform accurate measurements of the isotopic ratios of light elements;
  • CIVA [5], composed of seven micro-cameras, six mono and one stereo pair, that take panoramic pictures of the surface. A visible light microscope coupled to an infrared spectrometer will provide data on the composition, texture and albedo of the samples collected.

SD2

Fig.1 - SD2 - Drill, Sample & Distribution


The project has to cope with strong requirements in terms of low mass, low power consumption, wide operative range and very stringent environmental conditions (thermo-vacuum). The primary characteristics of SD2 are here below summarised [5]:

  • capable to drill the surface and to collect samples (tens of mm3) at different controllable depth up to 230 mm (assuming a clearance between the lander Balcony and comet surface of 300 mm)
  • capable to move and distribute the collected samples to the different scientific instruments (visible and I/R microscope, gas volatile analysers)
  • capable to cope with the expected comet material properties (e.g. hardness in the range from fluffy snow to some MPa)
  • compatibility with the extreme temperature environmental condition (for the electromecanics down to -160°C for storage and -140°C operative)
  • compatibility with vacuum environment
  • compatibility with the long inactivity time at extreme environmental condition (more than 9 years during cruise)
  • no thermal and chemical contamination are allowed to the sample material
  • challenging mass and power budgets: ~5 Kg and 10 W average including mechanics and electronics.
The SD2 system has been conceived as a four degrees of freedom robotic system. Particular importance has been given to the tribological and to the reliability aspects. Indeed all materials, processes and technological solutions have been carefully selected in order to cope with the given conditions, specifically [5]:
  • solid and self lubrication
  • brushless actuation and sensors
  • low friction/ antijamming approaches
  • cutting technology (for all range of materials)
  • low power consumption and radiation resistant electronics
  • special composite material approach.
[1] A. Ercoli Finzi, F. Bernelli Zazzera, C. Dainese, F. Malnati, P.G. Magnani, E. Re, P. Bologna, S. Espinasse and A. Olivieri, "SD2 - How to Sample a Comet", Space Science Reviews (2007) 128: 281-299.

[2] Berner, C., Bourillet, L., Ellwood, J., Kasper, M., Kletzkine, P., Schulz, R., et al.: 2002, ESA Bull. (112), 10.

[3] F. Goesmann, H. Rosenbauer, R. Roll, C. Szopa, F. Raulin, R. Sternberg, G. Israel, U. Meierhenrich, W. Thiemann and G. Munoz-Caro, "Cosac, The Cometary Sampling and Composition Experiment on Philae", Space Science Reviews, (2007) 128: 257-280.

[4] I. P. Wright, S. J. Barber, G. H. Morgan, A. D. Morse, S. Sheridan, D. J. Andrews, J. Maynard, D. Yau, S. T. Evans, M. R. Leese, J. C. Zarnecki, B. J. Kent, N. R. Waltham, M. S. Whalley, S Heys, D. L. Drummond, R. L. Edeson, E. C. Sawyer, R. F. Turner and C. T. Pillinger, "Ptolemy - an Instrument to Measure Stable Isotopic Ratios of Key Volatiles on a Cometary Nucleus", Space Science Reviews (2007) 128: 363-381.

[5] J.-P. Bibring, P. Lamy, Y. Langevin, A. Soufflot, M. Berthé, J. Borg, F. Poulet and S. Mottola, "CIVA", Space Science Reviews (2007) 128: 397-412.

[6] P.G. Magnani, E. Re, A. Ercoli Finzi, R. Mugnuolo and A. Olivieri, "ROSETTA lander - SD2 subsystem"


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Copyright 2007 SD2 Team - Politecnico di Milano - Dipartimento di Scienze e Tecnologie Aerospaziali