Contributions of Italian Spring Accelerometer to Lunar exploration: gravimetry and seismology V....

Contributions of Italian Spring Accelerometer to Lunar

exploration: gravimetry and seismology

V. Iafolla, E. Fiorenza, C. Lefevre, S. Nozzoli,

R. Peron, M. Persichini, A. Reale, F. Santoli

Istituto di Fisica dello Spazio Interplanetario (IFSI/INAF), Roma, ItalyIstituto di Fisica dello Spazio Interplanetario (IFSI/INAF), Roma, Italy

IX CONGRESSO NAZIONALE DI PLANETOLOGIA

AMALFI

Renewed interest for the Moon

29/09/2009Gruppo di Gravitazione Sperimentale

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Nearest body outside Earth Solar System history Outpost for Solar System settlement Quiet place Fundamental physics

Photo Apollo 11

Recent and current missions


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Clementine

Lunar Prospector

SMART-1

KAGUYA - SELENE

Lunar Reconnaissance Orbiter

Lunar Laser Ranging (LLR)


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Three retroreflectors arrays were carried on The Moon by Apollo missions and two by Soviet missions

Probably the most important scientific contribution from Apollo missions!

SelenodesyLunar rotationGeneral relativity

Moon history


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Constraints on formation, evolution and present state of the Moon come from:Surface compositionMagnetic fieldGravitational fieldSelenoseismology

Picture NASAPicture ESA

Moon gravity field


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Spherical harmonics expansion:

1 0

sincoscos1)(l

l

mlmlmlm

l

mSmCPr

R

r

GMrU

Resolution 5458 / l km

Moon gravity field


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Konopliv et al. (2001)

Mascons

Moon gravity field


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Compare with Earth!

Degree variance:

l

mlmlml SC

lC

0

222

12

1

Moon gravity field


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There is space for improvement!

ISA: the accelerometer


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ISA sensing element

ISA pick-up



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Geostar

Gradiometer

GReAT

BepiColombo



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The use of an accelerometer in the lunar environment can be envisaged in at least three ways:

Support given to a Radio Science mission (removal of non gravitational perturbations)

Gradiometric measurementsSelenoseismology

Satellite

On-ground



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Scm

ACa SunRSun

ˆ



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The mission MAGIA


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MAGIAMAGIA (Missione Altimetrica Gravimetrica Missione Altimetrica Gravimetrica Geochimica lunAreGeochimica lunAre) is a Moon exploration mission, with Phase A funded by Agenzia Spaziale Italiana

Scientific objectivesScientific objectives

• Detailed study of the internal structureinternal structure of the Moon through its gravitygravity and figurefigure

• Study of the polar and subpolar regionspolar and subpolar regions in terms of their morphologymorphology and mineralogymineralogy

• Study of the lunar exosphere and radioactive lunar exosphere and radioactive environmentenvironment

• Improved measure of the gravitational redshiftgravitational redshift measurements from a circumlunar platform

• Determination of the position of the seleno-position of the seleno-centercenter

ISA contributio

n

The mission MAGIA


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The knowledge of the gravitational field of a celestial body is one of the few ways to constrain its interior structure and composition

An analysis of recent lunar gravity field models (from Clementine and Lunar Prospector) shows that their knowledge at high orders can be improved. This implies greater resolution, useful for accurate knowledge of mantle and crust structure and compositionThe proposed strategy for MAGIA implies use of a GRACE-like configuration with two satellites (the main spacecraft and a subsatellite) optimized for the sougth for spectral range (l ≤ 80)

Notice that this high resolution implies a rather low orbitrather low orbit for the satellites, thereby enhancing the strength of non-gravitational perturbations like albedo and infrared radiation pressure (and related thermal effects)

The mission MAGIA


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Seismic measurements


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12.74 12.75 12.76 12.77 12.78 12.79 12.8

-8.246

-8.244

-8.242

-8.24

-8.238

-8.236

x 10-3

Ac

ce

lera

zio

ne

[g

]

Tempo giorni dal 2001

Misure GEOSTAR

Earthquakes 13 gen 2001 17:33:29:22Off Coast of Central AmericaRegistrazione Gravimetro Geostar Ustica

Solid tide of Earth

Teleseismic (free oscillation of Earth)

Seismic Noise

ISA-S: the seismometer


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The accelerometer, placed on ground, is directly sensitive to seismic disturbances, and therefore acts as a seismometer acts as a seismometer without any changeswithout any changes

The three sensing elements are arranged with their centers of mass along the same axis (the local vertical)

tiltmeters

gravimeter

local vertical

ISA-S: the seismometer


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Parameter Value Remarks

Measurement Accuracy 10-9 m/s2 Accuracy required for the acceleration measurements

ISA-S intrinsic random noise S0(f) = 10-9 m/s2/Hz1/2 Level of the total random noise in the ISA measurements process

Frequency Range 10-5 – 1 HzThe max resolution is obtained inside the frequency band, but ISA-S can works quite well also at frequency out of the indicated band, increasing the bit rate and taking into account the mechanical transfer function

Dynamic range 106 Set by the acquisition system and converter

Frequency readout interval 1 sThe required data rate is 1 sample/s for the three acceleration components and the three sensing temperatures

Resonance frequency 3.5 Hz Frequency of the mechanical oscillator

Quality factor Q 10 Quality factor of the oscillator

Thermal stability x,y 5∙10-7 m/s2/°C ISA-S thermal stability for the two tiltmetric components

Thermal stability z 1.6∙10-6 m/s2/°C ISA-S thermal stability for the gravimetric component

Mass, total 5.5 kg ISA-S Total mass

Dimension 300 x 300 x 300 mm

Electronic power dissipation 6 W ISA-S Total power dissipation

Data rate (nominal) 15 kbit/s

Capability of ISA-S /Capability to recover the local vertical autonomously, in order to operate with two of its elements like tiltmeters and one like gravimeter

Requirements


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Science GoalScience GoalUnderstand the current seismic state of the Moon, and determine the internal structure of the Moon.2) Detection of new aggregate states of matter (e.g., strange quark nuggets)

Network RequirementNetwork RequirementMultiple, simultaneously operating sites about the Moon are required to interpret seismic events2) Multiple, simultaneously operating sites about the Moon are required to interpret seismic events.

Science RationaleScience RationaleSeismic waves from lunar tectonic events can be used to determine the structure and composition of the crust, mantle and core.2) The existence of strange quark nuggets is an important prediction which could also provide a candidate for Dark Matter.

Measurement RequirementsMeasurement RequirementsMeasure lunar seismicity using broad-band seismometry at multiple, geographically dispersed, locations.2) Measure lunar seismic events using broad-band seismometry at no fewer than 5 geographically dispersed locations.

Seismometry New fundamental physics

ILN Core Instrument Working group

Requirements


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Mission RequirementsMission RequirementsAt least 4 sites simultaneously operating for 6 years. Inter-station timing accuracy: 5ms. Instrument attached to ground and vibrationally isolated from the spacecraft.2) Detection of strange quark nuggets via epilinear seismic source identification requires at least 5 sites simultaneously operating for as many years as possible.

Instrument RequirementsInstrument RequirementsThree axis Very Broad Band (VBB) seismometers with: Dynamic Range >24 bits; High Frequency Cutoff about 20 Hz. Sensitivity [0.001-0.1 Hz] 10-11m/s [0.1-1 Hz] 2x 10-11m/s [1-20Hz] 10-9m/s. Thermal stability +/_ 5deg with need to thermal blanket ground within 1m if surface deployed. Altitude knowledge.Same.

Mass, Power, ThermalMass, Power, ThermalMass 6 kg: Power 2 W(peak), and 1 W(cont.), and 0.2 W (low power). May need additional power for instrument heating.Same.

DataData100 Mbits per Earth day; no down link drivers.Same.

ILN Core Instrument Working group

Seismometry New fundamental physics

Site selection


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Barbara Cohen (SDT Co-chair), The International Lunar Network (ILN) and the US Anchor Nodes mission, Update to the LEAG/ILWEG/SRR, 10/30/08

• Strong science desire for farside placement. Due to dependency upon communications satellite, SDT also identified suitable nearside sites.

• Node 1 must be placed antipodal to a moonquake epicenter known by the Apollo network: -5°S, 75°W is only nearside site

• Node 2 must be placed within ~30° of the same epicenter, so could also be nearside 2: 30°N, 75°E

• Nodes 3 and 4 should form a triangle with western node, preferably on the farside

• Site selection criteria will also involve desires from engineering for DV and comm

Thermal issues


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http://www.asi.org/adb/02/05/01/surface-temp-chart.html

More than 200 °C range during lunar day

104 m/s2 for the most sensitive (gravimetric)

component

Need for an adequate thermal control system!

Thermal issues


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Passive Seismic ExperimentPassive Seismic Experiment on Apollo 16

T. A. Sullivan, Catalog of Apollo Experiment Operations, NASA Reference Publication 1317

ISA thermal control system performance

Proposals


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Response toREQUEST FOR INFORMATION (RFI)Instruments for U.S. ILN Lunar Missions

19 December 2008

Response toESA First Lunar Lander: Request for Information

8 April 2009

Conclusions


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We are seeing a renewal of interest and studies on lunar environment

Gravitational physics will play an important roleFundamental physics is always here! ISA accelerometer can support lunar science in many ways

Contributions of Italian Spring Accelerometer to Lunar exploration: gravimetry and seismology V....

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