Post on 02-Aug-2020
Subsurface probing of planetary bodies
Marek BanaszkiewiczSpace Research Centre PAS
in cooperation with: B. Dabrowski, J. Grygorczuk, K. Seweryn, R. Wawrzaszek
Outline
Surface and subsurface thermal physicsMissions with subsurface scienceThermal sensors Models and measurementsHeat transport in granular media
Why to go under the surface
To take samples and analyse their chemical & mineralogical compositionTo perform measurements of physical properties (seismometry, thermal properties, mechanical properties, structure)To reach deep layers of the body (subsurface ocean on Europe)To collect minerals and precious materials (e.g. He3 on the Moon)
Techniques of surface and subsurface exploration
Taking samples
Drilling
Hammering
Penetrating mole
AnchoringMelting in
Thermal processes in planetary bodies
Heat sources- hot interior - surface irradiation
Thermal transport processes- heat conduction (in solid, liquid and gas phases)- radiative transfer - advection/convection (mass motion)
Quantities to be determined:
Temperature profile T(z)Heat flow K rTthermal conductivity K, thermal diffusivity, thermal inertia
Example: heat transport in comets
Heat transport equation (Prialnik & Podolak)
Koemle Conduction
Advection Amorph. ice <=> cryst. ice Sublimation
Missions with subsurface thermal experiments
Apollo 15 & 17Mars-Express: Beagle Rosetta: MUPUS (Philae)Phobos-GrundExo-Mars: HP3
Apollo: thermal probes inserted into boreholes 2m deep, but sensors not properly deployed, therefore heat flow values, 28-33 mW / m^2 questioned => the uncertainty in the lunar core temperature is 250 - 400º
Penetrators
Penetrators MUPUS on Philae (Rosetta Lander) PI – Tilman Spohn (DLR)
Penatrator designed & manufacturedin SRC, Warsaw
Penetrators: moles
HP3 (Exo-Mars) – Beagle heritage
SRCDesign
Thermal sensors
Resistance thermometers
Thermal sensors
Principle of operationHot rod method
MUPUS measurements on Earth
Potential problems
Conductivity of thin sensors (titanium, copper) is different than the conductivity of the bulk materialCalibration: precise K(T) dependence should be takenAging effects => recalibration 12 years after sensor manufacturing should be doneTwo wire method used => reference current should be measured before each measurementHeating and temperature measurements must be done sequentially
New sensors
SM
SL
SH
sample
(wires to measure- and-power-supply system)
a) b) c)
New sensors
15 mm
14 mm
10 mm
17,5 mm
173 473373273
99.6
99.4
99.8
100.2
100.0
T [K]
Resistance [Ω]
b)
ISOTAN
Resistance [Ω]
173 473373273
100
50
150
200
T [K]a)
PLATINUM
platinum sensor circuit
isotan heater circuit
Connection to datalogger using 4 wire resistance
measurement method
Electric power supplied andcontrolled by datalogger.
sensor
Copper wires
Thermal measurements
Cometary material & asteroid regolith analoguesTeflon and delrin as reference materials
Measurements in thermaland thermal-vacuum chambers
Models
Analytical: applicable for simple geometries and quite complicatedSemi analyical based
on Green functionsNumerical: FEM
Measurements: calibration
Measurements
Measurements
In thermal chamber => K in the narrow range0.2 -0.4 W/m/K
Granular media
Different transport processes (Slavin etal.)
Gs
GcGi
GrGo
Unit cell
R
Granular media (2)
When the parameters of cometary/asteroid analogues are used then K ≈ 0.2 W/m/K at atmospheric pressure
Slavin et al., 1 mm aluminum spheres
Future research
Different sensor designs should be testedModeling needs improvement => granularity of medium taken into accountThermal resistance between the sensors and the medium is the main experimental problem
Between not too frequent space missions most of the planetary research will be done in the lab
0 100 200 300 400 500 600 700 800 900 1000-40
-30
-20
-10
0
10
20
30
T ime [s]
Tem
per
atu
re [C
]S tanda rd diam ete rStandard diamete r+0.02 m m
S tanda rd d iame ter+0 .04 m m
Standa rd d iameter+0.0 6 mm
Thank you for your attention