Small Body Seismology

J. Plescia H. Yu, K. Strohbehn, N. Schmerr, J. Leary, J. Atchison, C. Apland, O.

Barnouin June 29, 2015

SBAG

Small Body Seismology

• Basic Objectives • Energy Analysis • Instrument Concept • Spacecraft

Internal Structure

Lunar Thumper

1-D Wave Propagation in Asteroids We can answer these questions with wave propagation in a spherical asteroid GEMINI (Green’s Functions by Minor Integration) by Friederich and Dalkolmo (1995)

Spherically symmetric body by a numerical computation of the Green's function in the frequency domain Different models of attenuation, velocity, source types, including impulse functions

Accurate out to ~300 Hz for small bodies (exploration seismic range), but cannot account for 3-D structure and scattering (model with diffusion theory?)

GEMINI Seismograms Range of Impact Sizes:

Assume mass and velocity 1 Ns to 107 Ns (~Mw -7.0 to 1.0)

Allow for attenuation (Q=1000) Asteroid Structure (250 m radius)

10 m regolith 140 m megaregolith 100 m rocky core

Solution valid out to 300 Hz, full waveforms

Detectability of Seismic Waves

Measure the peak amplitude of the surface wave and P-waves radiated from the impact source to estimate of the detectability of the seismic energy Amplitude of propagated seismic energy as a function of angular distance across body at different energies. M -1.1 is an energy of 1.4x108 J, -3.1 = 1.4x105 J and -7.1 = 1.4x10-1 J. Red line: surface (Rayleigh) wave; blue lines: propagated (P waves). 0° is source, 180° at antipode.

Sensitivity of Apollo PSE Instrument ~0.2 nm (Latham, 1969)

MET Based Seismic Sensor

Molecular Electric Transducers work as a novel motion sensing mechanism by integrating Mass-Spring system and electro-chemical reaction.

Molecular electronic transducer 4 electrodes (Pt) Inter-electrode spacers Channels Iodine ion solution Flexible diaphragm

Sensor Configuration

Manufacture sensor cell an package with 3D printing technology for uniformity of materials and compact design. 3-axes sensor package has dimensions of 10 cm by 10 cm by 10 cm with temperature and tilting sensors together.

Spacecraft Configuration

Spacecraft Configuration

Surface Package

Deployment Concept

Deployment

Deployment

Flight System Mass Summary Subsystem CBE (kg) Cont. (%) MERV (kg)

Structures 52 10 57

Integrated Propulsion 16 3 17

Avionics 11 4 11

Electrical Power 27 7 29

Attitude Determination Control 12 7 12

Thermal Control 4 15 4

RF Communications 4 6 4

Harness 11 10 12

Spacecraft Bus 136 8 146

Instrument packages 42 15 49

Total Dry Mass 174 10 195

Usable Hydrazine Propellant* 109

Propellant Residual & Pressurant 5

Total Mass* 309

Launch Capability* 358 * These values are for target 1991VG. Maximum expected resource value: MERV Contingency = Maximum expected resource value - current estimate of resource value % Contingency = [Contingency / (MERV-Contingency)] *100

NEO Targets

Athena II Launch Vehicle

Target ID Number Absolute Magnitude

Launch Year Spacecraft ΔV (km s-1)

Dry Mass (kg)

Wet Mass (kg)

1991VG 3005816 28.5 2020 0.8 249 358

2007UN12 3390109 28.7 2020 1.0 235 369

2006RH120 3403148 29.5 2024 1.1 216 350

2008HU4 3409707 28.2 2024 1.3 206 268