1. IX Congresso Nazionale di Planetologia Amalfi
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, Italy

2. Renewed interest for the Moon
Nearest body outside Earth
Solar System history
Outpost for Solar System settlement
Quiet place
Fundamental physics
Photo Apollo 11
Gruppo di Gravitazione Sperimentale
29/09/2009

3. Recent and current missions
SMART-1
Clementine
Lunar Prospector
KAGUYA - SELENE
Lunar Reconnaissance Orbiter
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29/09/2009

4. Lunar Laser Ranging (LLR)
Three retroreflectors arrays were carried on The Moon by Apollo missions and two by Soviet missions
Selenodesy
Lunar rotation
General relativity
Probably the most important scientific contribution from Apollo missions!
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29/09/2009

5. Moon history
Constraints on formation, evolution and present state of the Moon come from:
Surface composition
Magnetic field
Gravitational field
Selenoseismology
Picture ESA
Picture NASA
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29/09/2009

6. Moon gravity field Spherical harmonics expansion:
Resolution  5458 / l km
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29/09/2009

7. Moon gravity field Mascons Konopliv et al. (2001) 29/09/2009
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8. Moon gravity field Degree variance: Compare with Earth! 29/09/2009
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9. Moon gravity field There is space for improvement! 29/09/2009
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10. ISA: the accelerometer
ISA sensing element
ISA pick-up
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29/09/2009

11. ISA: the accelerometer
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12. ISA: the accelerometer
GReAT
Gradiometer
Geostar
BepiColombo
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29/09/2009

13. ISA: the accelerometer
Satellite
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 measurements
Selenoseismology
On-ground
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29/09/2009

14. ISA: the accelerometer
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15. ISA: the accelerometer
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16. The mission MAGIA ISA contribution
MAGIA (Missione Altimetrica Gravimetrica Geochimica lunAre) is a Moon exploration mission, with Phase A funded by Agenzia Spaziale Italiana
Scientific objectives
Detailed study of the internal structure of the Moon through its gravity and figure
Study of the polar and subpolar regions in terms of their morphology and mineralogy
Study of the lunar exosphere and radioactive environment
Improved measure of the gravitational redshift measurements from a circumlunar platform
Determination of the position of the seleno-center
ISA contribution
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29/09/2009

17. The mission MAGIA
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 composition
The 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 orbit for the satellites, thereby enhancing the strength of non-gravitational perturbations like albedo and infrared radiation pressure (and related thermal effects)
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29/09/2009

18. The mission MAGIA
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29/09/2009

19. Seismic measurements Teleseismic (free oscillation of Earth)
Seismic Noise
Solid tide of Earth
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29/09/2009

20. ISA-S: the seismometer
The accelerometer, placed on ground, is directly sensitive to seismic disturbances, and therefore acts as a seismometer without any changes
local vertical
The three sensing elements are arranged with their centers of mass along the same axis (the local vertical)
tiltmeters
gravimeter
Gruppo di Gravitazione Sperimentale
29/09/2009

21. ISA-S: the seismometer
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 Hz
The 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 s
The 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
Gruppo di Gravitazione Sperimentale
29/09/2009

22. Requirements ILN Core Instrument Working group Seismometry
Science Goal
Understand 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 Requirement
Multiple, simultaneously operating sites about the Moon are required to interpret seismic events
2) Multiple, simultaneously operating sites about the Moon are required to interpret seismic events.
Science Rationale
Seismic 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 Requirements
Measure 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
Gruppo di Gravitazione Sperimentale
29/09/2009

23. Requirements ILN Core Instrument Working group Seismometry
Mission Requirements
At 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 Requirements
Three axis Very Broad Band (VBB) seismometers with: Dynamic Range >24 bits; High Frequency Cutoff about 20 Hz Sensitivity [ 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, Thermal
Mass 6 kg: Power 2 W(peak), and 1 W(cont.), and 0.2 W (low power). May need additional power for instrument heating.
Data
100 Mbits per Earth day; no down link drivers.
Seismometry
New fundamental physics
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29/09/2009

24. Site selection
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
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
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25. Thermal issues More than 200 °C range during lunar day
 104 m/s2 for the most sensitive (gravimetric) component
Need for an adequate thermal control system!
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29/09/2009

26. Thermal issues ISA thermal control system performance
Passive Seismic Experiment on Apollo 16
T. A. Sullivan, Catalog of Apollo Experiment Operations, NASA Reference Publication 1317
ISA thermal control system performance
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29/09/2009

27. Proposals Response to REQUEST FOR INFORMATION (RFI)
Instruments for U.S. ILN Lunar Missions
19 December 2008
Response to
ESA First Lunar Lander: Request for Information
8 April 2009
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29/09/2009

28. Conclusions
We are seeing a renewal of interest and studies on lunar environment
Gravitational physics will play an important role
Fundamental physics is always here!
ISA accelerometer can support lunar science in many ways
Gruppo di Gravitazione Sperimentale
29/09/2009