Mupus – A Thermal and Mechanical Properties Probe for the Rosetta Lander Philae

Advances in Space Research

Green

Ball

et al. 2015

The high inertia, i.e. high mass and low speed, of a landing spacecraft has the potential to drive a penetrometer into the subsurface without the need for a dedicated deployment mechanism, e.g., during Huygens landing on Titan. Such a method could complement focused subsurface exploration missions, particularly in the low gravity environments of comets and asteroids, as it is conducive to conducting surveys and to the deployment of sensor networks. We make full-scale laboratory simulations of a landing spacecraft with a penetrometer attached to its base plate. The tip design is based on that used in terrestrial Cone Penetration Testing (CPT) with a large enough shaft diameter to house instruments for analysing pristine subsurface material. Penetrometer measurements are made in a variety of regolith analogue materials and target compaction states. For comparison a copy of the ACC-E penetrometer used on the Huygens mission is used. A test rig at the Open * Corresponding author University is used and is operated over a range of speeds from 0.9 to 3 m sand under two gravitational accelerations. The penetrometer was found to be sensitive to the target's compaction state with a high degree of repeatability. The penetrometer measurements also produced unique pressure profile shapes for each material. Measurements in limestone powder produced an exponential increase in pressure with depth possibly due to increasing compaction with depth. Measurements in sand produced an almost linear increase in pressure with depth. Iron powder produced significantly higher pressures than sand presumably due to the rough surface of the grains increasing the grain-grain friction. Impacts into foamglas produced with both ACC-E and the large penetrometer produced an initial increase in pressure followed by a leveling off as expected in a consolidated material. Measurements in sand suggest that the pressure on the tip is not significantly dependent on speed over the range tested, which suggests bearing strength equations could be applied to impact penetrometry in sand-like regoliths.In terms of performance we find the inertia of a landing spacecraft, with a mass of 100 kg, is adequate to penetrate regoliths expected on the surface of Solar System bodies. Limestone powder, an analogue for a dusty surface, offered very little resistance allowing full penetration of the target container. Both iron powder, representing a stronger coarse grained regolith, and foamglas, representing a consolidated comet crust, could be penetrated to similar depths of around two to three tip diameters, probably more if impacting with a slightly higher speed.

Section: Subsurface Exploration Possibilities Using Penetrometers Andmentioning

confidence: 99%

Using the inertia of spacecraft during landing to penetrate regoliths of the Solar System

Advances in Space Research

Green

Ball

et al. 2015

“…In planetary exploration high-speed penetrators have been used as part of an anchoring system (Stöcker and Thiel, 1998) or ballistic delivery of science instruments into the subsurface or on the surface (Smrekar et al, 1999;Harri et al, 2003). Low-speed penetrators are normally deployed from a landed spacecraft as with the hammer-driven MUPUS probe (Spohn et al, 2007) or Beagle 2 mole (Pinna et al, 2001).…”

Section: D Paton Et Al: Investigating Thermal Properties Of Gas-mentioning

confidence: 99%

“…MU-PUS is part of the Rosetta lander, Philae's experiment suite to investigate the thermal and mechanical behaviour of the outer layers of a comet (Spohn et al, 2007). The thermal probe is a hammer driven penetrator that has temperature sensors mounted on the inside of its hollow shaft and may penetrate to a depth of 0.35 m. The resistance of the sensors are a function of temperature and is well known.…”

Section: D Paton Et Al: Investigating Thermal Properties Of Gas-mentioning

confidence: 99%

Investigating thermal properties of gas-filled planetary regoliths using a thermal probe

Geosci. Instrum. Method. Data Syst.

Harri

Mäkinen

et al. 2012

Abstract. We introduce a general purpose penetrator, fitted with a heater, for measuring temperature and thermal diffusivity. Due to its simplicity of deployment and operation the penetrator is well suited for remote deployment by spacecraft into a planetary regolith. Thermal measurements in planetary regoliths are required to determine the surface energy balance and to measure their thermal properties. If the regolith is on a planet with an atmosphere a good understanding of the role of convection is required to properly interpret the measurements. This could also help to identify the significant heat and mass exchange mechanisms between the regolith and the atmosphere. To understand the role of convection in our regolith analogues we use a network of temperature sensors placed in the target. In practical applications a penetrator will push material out of the way as it enters a target possible changing its thermal properties. To investigate this effect a custom built test rig, that precisely controls and monitors the motion of the penetrator, is used. The thermal diffusivity of limestone powder and sand is derived by fitting a numerical thermal model to the temperature measurements.Convection seems to play an important role in the transfer of heat in this case. Firstly a diffusion-convection model fits the laboratory data better than a diffusivity-only model. Also the diffusivity derived from a diffusivity-convection model was found to be in good agreement with diffusivity derived using other methods published in the literature. Thermal diffusivity measurements, inspection of the horizontal temperature profiles and visual observations suggests that limestone powder is compacted more readily than sand during entry of the penetrator into the target. For both regolith analogues the disturbance of material around the penetrator was determined to have an insignificant effect on the diffusivity measurements in this case.

“…Unfortunately the densitometer that was to be included on the MUPUS thermal probe was cancelled due to funding problems (Spohn et al, 2007). The temperature of the ice can be measured directly once the anchor has reached equilibrium with its surroundings.…”

Section: The Comet Ice Modelmentioning

confidence: 99%

“…Similar devices have been proposed or have been included on other space missions, although none have been successfully deployed, employing a variety of deployment techniques such as ballistic delivery (e.g. Urquhart et al, 2000, Tanaka et al, 2001 or hammering (Spohn et al, 2001, Spohn et al, 2007.…”

Section: Introductionmentioning

confidence: 99%

Computer modelling of a penetrator thermal sensor

Advances in Space Research

Kargl

Ball

et al. 2010

The Philae lander is part of the Rosetta mission to investigate comet 67P/Churyumov-Gerasimenko. It will use a harpoon like device to anchor itself onto the surface. The anchor will perhaps reach depths of 1-2 m. In the anchor is a temperature sensor that will measure the boundary temperature as part of the MUPUS experiment. As the anchor attains thermal equilibrium with the comet ice it may be possible to extract the thermal properties of the surrounding ice, such as the thermal diffusivity, by using the temperature sensor data. The anchor is not an optimal shape for a thermal probe and application of analytical solutions to the heat equation is inappropriate. We prepare a numerical model to fit temperature sensor data and extract the thermal diffusivity. Penetrator probes mechanically compact the material immediately surrounding them as they enter the target. If the thermal properties, composition and dimensions of the penetrator are known, then the thermal properties of this pristine material may be recovered although this will be a challenging measurement. We report on investigations, using a numerical thermal model, to simulate a variety of scenarios that the anchor may encounter and how they will affect the measurement.