28 July 2009

 MUPUS PEN (right, with golden hammering mechanism on top) and TM (left, small silver box) in their flight configuration on the Philae balcony.
zum Bild MUPUS PEN (right, with golden hammering mechanism on top) and TM (left, small silver box) in their flight configuration on the Philae balcony.
MUPUS (Multi purpose Sensors for Surface and Subsurface Science) is a scientific experiment onboard the Rosetta Lander Philae. The main science goals of MUPUS are:

  • to determine the thermal and mechanical properties of the outer layers of the comet's nucleus
  • to determine the energy balance at the comet’s surface and the adjacent boundary layers
  • to understand mechanisms of cometary activity
  • to derive the pristineness of the material in the outer layers, in support of cosmochemical observations

To achieve these goals the experiment consists of three different sensors which are controlled by a central electronics unit. The PEN (penetrator) is basically a hollow rod of 35 cm length which will be deployed at a distance of about 1.5 m from the landing module and inserted into the cometary soil by means of an electromagnetic hammering mechanism. During the insertion, progress per stroke is measured to provide data on the mechanical properties of the comet’s surface. Fixed to the inside of the rod are 16 temperature sensors made from Titanium and sputtered on a Kapton foil. These sensors provide a temperature depth profile of the comet’s surface layer as a function of local time and perihelion distance. Furthermore, the sensors can also be used in a heating mode which allows active measurement of the thermal conductivity depth profile. The PEN measurements are supplemented by surface-temperature measurements with the infrared sensor TM (Thermal Mapper) and measurements by temperature sensors inside the two anchoring harpoons of Philae which might penetrate to a depth of 1.5 m into the soil (depending on the soil properties). The TM sensor head is mounted on a strut of the Philae Lander at a height of about 1 m above the surface and measures the emitted thermal radiation from an area of ~1 m2 in 4 wavelength channels between 5 and 25 µm using thermopile detectors. Due to the nearly negligible gravitational force of the comet, anchoring harpoons are required to fix the Lander safely to the ground. Each of the harpoons contains a temperature sensor and an accelerometer, thus they also serve a scientific purpose as part of the MUPUS experiment. During the anchoring process, during which the harpoons are shot into the surface, the deceleration of the harpoons will be measured by the MUPUS accelerometers, providing additional data on the mechanical properties of the landing site down to the final depth of the anchors.

The MUPUS experiment was designed and built by an international consortium under the lead of the Principal Investigator (PI) T. Spohnfrom the Institute for Planetology (IfP) of the University of Münster, with major contributions from IfP (PI, science and management), SRC Warsaw (system and mechanical engineering, PEN hardware, electronics), DLR Berlin (DPU and TM), and IWF Graz (anchor sensors).

The Asteroids and Comets Department has been involved in MUPUS from the start of the project in 1994 with two scientific Co-I’s and the development of the IR sensor head TM. After the MUPUS-PI, T. Spohn, became Director of the DLR Institute for Planetary Research in Berlin in 2004 the project management and operations planning tasks for the whole experiment were transferred to the Asteroids and Comets Department.

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