Therman Analysis of HP3, a Penetrometer to Measure the Planetary Surface Heat Flow

Paper number

IAC-06-A3.P.2.03

Author

Mr. Gabriele Messina, Deutsches Zentrum fur Luft und Raumfahrt e.V. (DLR), Germany

Coauthor

Mr. Riccardo Nadalini, Deutsches Zentrum fur Luft und Raumfahrt e.V. (DLR), Germany

Year

2006

Abstract

The Heat Flow and Physical Properties Package (HP3) is a set of sensors used to measure the planetary surface heat flow on Mercury or other terrestrial planets and developed by the institute of Planetary Research of the German Aerospace Center.

The system consists of two cylindrical units; one, the mole, to deploy the payload into the regolith, and the other, the payload compartment, to lodge the sensors and connect to the surface with an etched circuit flat tether.

The prime aim of the study was to find out and minimize the disturbances that the system produces on the measurement of the heat flow. Moreover, thermal analyses were performed to assist the design of a thermal control system able to warrant the instrument’s permanence within the operational temperature ranges.

The dedicated thermal model of the whole system is based on the thermal network analysis technique (Finite Difference Method); it includes detailed models of all the hardware components (Mole, payload compartment, tether and all sensors) and of the soil, with a complex dynamic connection to simulate the relative motion of the probe in the soil during the penetration. This allows to analyze the phase in which the system reaches its final depth of five meters and creates the biggest disturbances by injecting waste heat into the soil.

In the two-dimensional model of the soil (cylindrical symmetry around the borehole) thermal conductivity and capacity are function of temperature and bulk density, the latter further depending on depth.

In addition to modelling, different experiments were carried out, both to validate the model and to determine unknown parameters, among which, the determination of the thermal contact conductance between payload compartment and borehole surface.

Since the thermal interactions between a granular medium and solid materials in a vacuum environment (or in rarefied atmosphere) need to be analysed in detail, the first quantification given by these experiments is of certain interest.

The study used Mercury as baseline case but given the great similarity between all regolith rich inner system bodies, its results are easily applicable to other bodies (like the Mars, Moon or asteroids).

Abstract document

IAC-06-A3.P.2.03.pdf

Manuscript document

IAC-06-A3.P.2.03.pdf (🔒 authorized access only).

To get the manuscript, please contact IAF Secretariat.