By the end of 2018, 42 years after the landing of the two Viking seismometers on Mars, InSight will deploy onto Mars’ surface the SEIS ( S eismic E xperiment for I nternal S tructure) instrument; a six-axes seismometer equipped with both a long-period three-axes Very Broad Band (VBB) instrument and a three-axes short-period (SP) instrument. These six sensors will cover a broad range of the seismic bandwidth, from 0.01 Hz to 50 Hz, with possible extension to longer periods. Data will be transmitted in the form of three continuous VBB components at 2 sample per second (sps), an estimation of the short period energy content from the SP at 1 sps and a continuous compound VBB/SP vertical axis at 10 sps. The continuous streams will be augmented by requested event data with sample rates from 20 to 100 sps. SEIS will improve upon the existing resolution of Viking’s Mars seismic monitoring by a factor of at 1 Hz and at 0.1 Hz. An additional major improvement is that, contrary to Viking, the seismometers will be deployed via a robotic arm directly onto Mars’ surface and will be protected against temperature and wind by highly efficient thermal and wind shielding. Based on existing knowledge of Mars, it is reasonable to infer a moment magnitude detection threshold of at epicentral distance and a potential to detect several tens of quakes and about five impacts per year. In this paper, we first describe the science goals of the experiment and the rationale used to define its requirements. We then provide a detailed description of the hardware, from the sensors to the deployment system and associated performance, including transfer functions of the seismic sensors and temperature sensors. We conclude by describing the experiment ground segment, including data processing services, outreach and education networks and provide a description of the format to be used for future data distribution. Electronic Supplementary Material The online version of this article (10.1007/s11214-018-0574-6) contains supplementary material, which is available to authorized users.

Two formulations for calculating the total acoustic power radiated by a structure are compared; in terms of the amplitudes of the structural modes and in terms of the velocities of an array of elemental radiators on the surface of the structure. In both cases, the sound radiation due to the vibration of one structural mode or element is dependent on the vibration of other structural modes or elements. Either of these formulations can be used to describe the sound power radiation in terms of a set of velocity distributions on the structure whose sound power radiation is independent of the amplitudes of the other velocity distributions. These velocity distributions are termed "radiation modes." Examples of the shapes and radiation efficiencies of these radiation modes are discussed in the cases of a baffled beam and a baffled panel. The implications of this formulation for the active control of sound radiation from structures are discussed. In particular, the radiation mode formulation can be used to provide an estimate of the number of independent parameters of the structural response which need to be measured and controlled to give a required attenuation of the radiated sound power.

The active control of sound transmission through a panel has been formulated using a near-field approach. The effects of minimizing the sound power radiated by the panel and of canceling the net volume velocity of the panel are compared not only in terms of the reduction in sound radiation but also in terms of the change in the space average mean-squared velocity of the panel and the space average mean-squared pressure at its surface. Simulations of a thin panel excited by an incident acoustic plane wave and a piezoelectric control actuator show that volume velocity cancellation gives similar reductions in the transmitted sound power to the minimization of sound power radiation up to frequencies at which the size of the plate is about half an acoustic wavelength. The acoustic radiation is analyzed in terms of the radiation modes of the panel which are also used to explain spillover effects. Spillover, which leads to increases in the mean-squared velocity of the panel and to increases in near-field pressure levels when using a piezoelectric patch as a secondary actuator can be removed by using an actuator which generates a uniform force over the surface of the panel. Such an actuator is the reciprocal of the volume velocity sensor and could be fabricated in the same way. The transfer function between such a matched actuator/sensor pair is shown to be minimum phase, so that the performance of a feedback control system should be as good as a feedforward one, which would allow control of arbitrary broadband excitation of the panel.

Active minimization of total power output and active absorption of sound power are analyzed, using a general impedance-based approach, for an array of controllable secondary sources and an array of original primary sources. When the total power output of the two arrays is minimized, and the primary source array is all in phase, the power output of each of the secondary sources is found to be exactly zero. When the power absorption of the secondary source array is maximized, the net power output of the primary source array can be either reduced or increased, compared to that in the absence of control, depending on the properties of the transfer impedances. If the primary and secondary sources are well coupled (as is the case when they are spaced less than a quarter wavelength apart in free-space or when they are in an enclosure excited near the natural frequency of a lightly damped mode) minimizing the total power output gives worthwhile reductions in the radiated power of the primary source. Maximizing the power absorption of the secondary source under these conditions, however, can considerably increase the power output of the primary source. If the sources are well separated, compared with the wavelength, in the free-field, or are placed in a diffuse sound field in an enclosure, the coupling between the sources is weak. Under these conditions the secondary source can effect little reduction in the power output of the primary source. Although acoustic power can still be absorbed by the secondary source under such circumstances, the amount of absorbed power will always be small compared with the power output of the primary source.

The equivalent source method has previously been used to calculate the exterior sound field radiated or scattered from bodies in the free-field. In this paper the method is used to calculate the internal pressure field for an enclosure which can have arbitrary boundary conditions and may include internal objects which scatter the sound. Some of the equivalent source positions are chosen to be the same as the first order images of the source inside the enclosure, some are positioned within the scattering objects, and the remainder are positioned on a spherical surface some distance outside the enclosure. The normal velocity on the surfaces of the scattering objects and the enclosure walls is evaluated at a larger number of positions than there are equivalent sources. The sum of the squared difference between this velocity and that expected because of the admittance of the boundary, is minimized by adjusting the strengths of the equivalent sources. The convergence of the method is checked by evaluating the velocity at a larger number of monitoring positions. Example results are presented for the sound field and frequency response inside a damped rectangular enclosure, which compare very well with the conventional modal model. The effect of having rigid spheres inside the enclosure are then investigated, and it is found that the effect is significant even some distance from the spheres and at frequencies for which the size of the sphere is small compared to a wavelength. Finally the effect of a nonlocally reacting boundary condition is illustrated by assuming that one of the walls of the enclosure is an elastic plate.