MUPUS (MUlti-PUrpose Sensor) is designed to measure key material parameters at and near the surface of the cometary nucleus:
- thermal conductivity
- thermal diffusivity
- material strength
Together with the results of other instruments aboard the Rosetta lander probe Philae (SESAME, APX, COSAC, PTOLOMY, .....) the MUPUS sensor will contribute to characterize the material at and below the surface.
MUPUS consists of several components, regulated by a common electronics:
A hollow tube made of glass fiber, about 0.35 m long, which is driven into the ground by a recoilless hammering mechanism. At the inner mantle surface of the tube sensors for measuring the thermal conductivity and diffusivity as well as the temperature profile as a function of depth are attached.
An infrared sensor is positioned at the upper edge of the lander. It serves to measure the thermal radiation emitted from the cometary surface. If an ice-free, non-volatile dust mantle exists at the surface, model calculations predict a very steep temperature gradient at the surface, because such a porous dust mantle acts as a thermally isolating layer and thus woud hinder the evaporation of any underlying volatiles.
- Anchor Temperature Sensor
An additional temperature sensor is installed in the tips of the two anchoring harpoons. It will allow to record temperature variations over the whole lifetime of the lander. Since it may be expected that the anchors will penetrate deeper than the maximum penetration depth of the MUPUS penetrator, these measurements will be a valuable supplement to the temperature records obtained by the penetrator.
In each of the two anchoring harpoons identical accelerometer sensors are installed. They will measure the deceleration of the anchor projectiles during their penetration into the ground. These data will allow retrieving information on the material strength of the ground. In particular it will reveal whether or not any layers with different material strength exist near the surface, as theoretical models predict.
The instrument was developed in the frame of an international cooperation led by Prof. Tilman Spohn, presently head of the Institute of Planetary Research at DLR Berlin. Most of the hardware was built and tested at the Space Research Center of the Polish Academy of Sciences, Warsaw, under the guidance of its present director Dr. Marek Banaszkiewicz.
During the present cruise phase of Rosetta further laboratory work using the "Ground Reference Model" of the MUPUS penetrator as well as similar probes developed for terrestrial applications (EXTASE) are conducted both at DLR Berlin and at IWF Graz, in order to better understand the thermal behaviour of the penetrator when it will land on the comet. This includes both experimental work under controlled conditions and theoretical simulations of the thermal behaviour (Figure <MUPUS_simulation>).
These activities are important to ensure a successful evaluation of the MUPUS data after Philae will have landed at the surface of comet Churyumov-Gerasimenko in November 2014.