Michelson Interferometer for Global High-Resolution Thermospheric Imaging (MIGHTI): Monolithic Interferometer Design and Test

The design and laboratory tests of the interferometers for the Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) instrument which measures thermospheric wind and temperature for the NASA-sponsored Ionospheric Connection (ICON) Explorer mission are described. The monolithic interferometers use the Doppler Asymmetric Spatial Heterodyne (DASH) Spectroscopy technique for wind measurements and a multi-element photometer approach to measure thermospheric temperatures. The DASH technique and overall optical design of the MIGHTI instrument are described in an overview followed by details on the design, element fabrication, assembly, laboratory tests and thermal control of the interferometers that are the heart of MIGHTI.     

Michelson Interferometer for Global High-Resolution Thermospheric Imaging (MIGHTI): Instrument Design and Calibration

The Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) instrument was built for launch and operation on the NASA Ionospheric Connection Explorer (ICON) mission. The instrument was designed to measure thermospheric horizontal wind velocity profiles and thermospheric temperature in altitude regions between 90 km and 300 km, during day and night. For the wind measurements it uses two perpendicular fields of view pointed at the Earth’s limb, observing the Doppler shift of the atomic oxygen red and green lines at 630.0 nm and 557.7 nm wavelength. The wavelength shift is measured using field-widened, temperature compensated Doppler Asymmetric Spatial Heterodyne (DASH) spectrometers, employing low order échelle gratings operating at two different orders for the different atmospheric lines. The temperature measurement is accomplished by a multichannel photometric measurement of the spectral shape of the molecular oxygen A-band around 762 nm wavelength. For each field of view, the signals of the two oxygen lines and the A-band are detected on different regions of a single, cooled, frame transfer charge coupled device (CCD) detector. On-board calibration sources are used to periodically quantify thermal drifts, simultaneously with observing the atmosphere. The MIGHTI requirements, the resulting instrument design and the calibration are described.     

High-energy gamma radiation of solar flares as an indicator of acceleration of energetic protons

Using the SONG detector onboard the CORONAS-F satellite, gamma-ray emission of high energies (>100 MeV) was recorded during four solar flares. In the sequential spectra of gamma rays the peculiarity caused by generation and decay of neutral pions was isolated, which made it possible to determine with a high accuracy the moments of appearance in the solar atmosphere of protons accelerated up to energies above 300 MeV.     

Sesame – An Experiment of the Rosetta Lander Philae: Objectives and General Design

SESAME is an instrument complex built in international co-operation and carried by the Rosetta lander Philae intended to land on comet 67P/Churyumov-Gerasimenko in 2014. The main goals of this instrument suite are to measure mechanical and electrical properties of the cometary surface and the shallow subsurface as well as of the particles emitted from the cometary surface. Most of the sensors are mounted within the six soles of the landing gear feet in order to provide good contact with or proximity to the cometary surface. The measuring principles, instrument designs, technical layout, operational concepts and the results from the first in-flight measurements are described. We conclude with comments on the consequences of the last minute change of the target comet and how to improve and to preserve the knowledge during the long-duration Rosetta mission.     

The Rolis Experiment on the Rosetta Lander

ROLIS (Rosetta Lander Imaging System) is one of the two imaging systems carried by Rosetta’s Lander Philae, successfully launched to comet 67P/ Churyumov-Gerasimenko in March 2004. Consisting of a highly-miniaturized CCD camera, ROLIS will operate as a descent imager, acquiring imagery of the landing site with increasing spatial resolution. After touchdown ROLIS will focus at an object distance of 30 cm, taking pictures of the comet’s surface below the Lander. Multispectral imaging is achieved through an illumination device consisting of four arrays of monochromatic light emitting diodes working in the 470, 530, 640 and 870 nm spectral bands. The drill sample sites, as well as the Alpha X-Ray Spectrometer (APXS) target locations will be imaged to provide context for the measurements performed by the in situ analyzers. After the drilling operation, the borehole will be inspected to study its morphology and to search for stratification. Taking advantage of the Lander’s rotation capability, stereo image pairs will be acquired, which will facilitate the mapping and identification of surface structures.     

Theoretical studies of shock-initiated detonations

The dynamics of shock propagation have been studied theoretically for a variety of two-dimensional lattices. The approach used is based on molecular dynamics and hinges on the exact numerical solution by computer of the equations of motion for the individual atoms or molecules in each lattice. Shocks have been launched into the lattices under study by methods designed to simulate flyer-plate impact. Two different interatomic potentials have been used, one endothermic and one net-exothermic. For both types of potential, a shock launched at one side of the lattice will spall a group of atoms off the other side. However, the subsequent behavior of the two types of lattice is very different. For endothermic potentials, after the initial atomic spall, the residual lattice is quiescent with little further activity. For net-exothermic potentials, the initial atomic spall injects additional energy into the system in such a manner that subsequently further spall occurs at both sides. Once this new spall is initiated, it leads rapidly to further bond breaking and explosive disintegration of the system.     

Development of a high pressure-differential turbine blade cooling system

A convective-film system of high pressure-differential turbine blade cooling is presented. The results of calculating the thermal-hydraulic blade state using the KW3D software are given.     

Single Degenerate Models for Type Ia Supernovae: Progenitor’s Evolution and Nucleosynthesis Yields

We review how the single degenerate models for Type Ia supernovae (SNe Ia) works. In the binary star system of a white dwarf (WD) and its non-degenerate companion star, the WD accretes either hydrogen-rich matter or helium and undergoes hydrogen and helium shell-burning. We summarize how the stability and non-linear behavior of such shell-burning depend on the accretion rate and the WD mass and how the WD blows strong wind. We identify the following evolutionary routes for the accreting WD to trigger a thermonuclear explosion. Typically, the accretion rate is quite high in the early stage and gradually decreases as a result of mass transfer. With decreasing rate, the WD evolves as follows: (1) At a rapid accretion phase, the WD increase its mass by stable H burning and blows a strong wind to keep its moderate radius. The wind is strong enough to strip a part of the companion star’s envelope to control the accretion rate and forms circumstellar matter (CSM). If the WD explodes within CSM, it is observed as an “SN Ia-CSM”. (X-rays emitted by the WD are absorbed by CSM.) (2) If the WD continues to accrete at a lower rate, the wind stops and an SN Ia is triggered under steady-stable H shell-burning, which is observed as a super-soft X-ray source: “SN Ia-SSXS”. (3) If the accretion continues at a still lower rate, H shell-burning becomes unstable and many flashes recur. The WD undergoes recurrent nova (RN) whose mass ejection is smaller than the accreted matter. Then the WD evolves to an “SN Ia-RN”. (4) If the companion is a He star (or a He WD), the accretion of He can trigger He and C double detonations at the sub-Chandrasekhar mass or the WD grows to the Chandrasekhar mass while producing a He-wind: “SN Ia-He CSM”. (5) If the accreting WD rotates quite rapidly, the WD mass can exceed the Chandrasekhar mass of the spherical WD, which delays the trigger of an SN Ia. After angular momentum is lost from the WD, the (super-Chandra) WD contracts to become a delayed SN Ia. The companion star has become a He WD and CSM has disappeared: “SN Ia-He WD”. We update nucleosynthesis yields of the carbon deflagration model W7, delayed detonation model WDD2, and the sub-Chandrasekhar mass model to provide some constraints on the yields (such as Mn) from the comparison with the observations. We note the important metallicity effects on ⁵⁸Ni and ⁵⁵Mn.     

Crustal S-Wave Velocity from Apparent Incidence Angles: A Case Study in Preparation for InSight

Retrieval of crustal structure and thickness of Mars is among the main goals of InSight. Here we investigate which constraints on the crust at the landing site can be provided by apparent P-wave incidence angles derived from P-receiver functions. We consider receiver functions for six different Mars models, calculated from synthetic seismograms generated via Instaseis from the Green’s function databases of the Marsquake Service, in detail. To allow for a larger range of crustal thicknesses and structures, we additionally analyze data from five broad-band stations across Central Europe. We find that the likely usable epicentral distance range for P-wave receiver functions on Mars lies between \(35^{\circ}\) and the core shadow, and can be extended to more than \(150^{\circ}\) by also using the PP-phase. Comparison to models for the spatial distribution of Martian seismicity indicates that sufficient seismicity should occur within the P-wave distance range around InSight within the nominal mission duration to allow for the application of our method. Apparent P-wave incidence angles are derived from the amplitudes of vertical and radial receiver functions at the P-wave onset within a range of period bands, up to 120 s. The apparent incidence angles are directly related to apparent S-wave velocities, which are inverted for the subsurface S-wave velocity structure via a grid search. The veracity of the forward calculated receiver functions and apparent S-wave velocities is ensured by benchmarking various algorithms against the Instaseis synthetics. Results indicate that apparent S-wave velocity curves provide valuable constraints on crustal thickness and structure, even without any additional constraints, and considering the location uncertainty and limited data quantity of InSight. S-wave velocities in the upper half of the crust are constrained best, but if reliable measurements at long periods are available, the curves also provide constraints down to the uppermost mantle. Besides, it is demonstrated that the apparent velocity curves can differentiate between crustal velocity models that are indistinguishable by other methods.