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

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

Recent and current missions SMART-1 Clementine Lunar Prospector KAGUYA - SELENE Lunar Reconnaissance Orbiter Gruppo di Gravitazione Sperimentale 29/09/2009

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! Gruppo di Gravitazione Sperimentale 29/09/2009

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 Gruppo di Gravitazione Sperimentale 29/09/2009

Moon gravity field Spherical harmonics expansion: Resolution  5458 / l km Gruppo di Gravitazione Sperimentale 29/09/2009

Moon gravity field Mascons Konopliv et al. (2001) 29/09/2009 Gruppo di Gravitazione Sperimentale 29/09/2009

Moon gravity field Degree variance: Compare with Earth! 29/09/2009 Gruppo di Gravitazione Sperimentale 29/09/2009

Moon gravity field There is space for improvement! 29/09/2009 Gruppo di Gravitazione Sperimentale 29/09/2009

ISA: the accelerometer ISA sensing element ISA pick-up Gruppo di Gravitazione Sperimentale 29/09/2009

ISA: the accelerometer Gruppo di Gravitazione Sperimentale 29/09/2009

ISA: the accelerometer GReAT Gradiometer Geostar BepiColombo Gruppo di Gravitazione Sperimentale 29/09/2009

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 Gruppo di Gravitazione Sperimentale 29/09/2009

ISA: the accelerometer Gruppo di Gravitazione Sperimentale 29/09/2009

ISA: the accelerometer Gruppo di Gravitazione Sperimentale 29/09/2009

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 Gruppo di Gravitazione Sperimentale 29/09/2009

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) Gruppo di Gravitazione Sperimentale 29/09/2009

The mission MAGIA Gruppo di Gravitazione Sperimentale 29/09/2009

Seismic measurements Teleseismic (free oscillation of Earth) Seismic Noise Solid tide of Earth Gruppo di Gravitazione Sperimentale 29/09/2009

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

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

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

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 [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, 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 Gruppo di Gravitazione Sperimentale 29/09/2009

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 Gruppo di Gravitazione Sperimentale 29/09/2009

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! http://www.asi.org/adb/02/05/01/surface-temp-chart.html Gruppo di Gravitazione Sperimentale 29/09/2009

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 Gruppo di Gravitazione Sperimentale 29/09/2009

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 Gruppo di Gravitazione Sperimentale 29/09/2009

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