91̽»¨

Abstract:

Directional emissivity (DE) describes how the emissivity of an isothermal surface changes with viewing angle across thermal infrared wavelengths. The 91̽»¨ Space Environment Goniometer (OSEG) is a novel instrument that has been specifically designed to measure the DE of regolith materials derived from planetary surfaces. The DE of Nextel high emissivity black paint was previously measured by the OSEG and showed that the measured emissivity decreases with increasing emission angle, from an emissivity of 0.97 ± 0.01 at 0° emission angle to an emissivity of 0.89± 0.01 at 71° emission angle. The Nextel target measured was isothermal (<0.1 K surface temperature variation) and the observed change in emissivity was due to Fresnel related effects and was not due to non-isothermal effects. Here we apply several increasingly complex modelling techniques to model the measured DE of Nextel black paint. The modelling techniques used here include the Hapke DE model, the Fresnel equations, a multiple slope Fresnel model and a Monte Carlo ray-tracing model. It was found that only the Monte Carlo raytracing model could accurately fit the OSEG measured Nextel data. We show that this is because the Monte Carlo ray-tracing model is the only model that fully accounts for the surface roughness of the Nextel surface by including multiple scattering effects.

Abstract:

The InSight mission is due to launch in May 2018, carrying a payload of novel instruments designed and tested to probe the interior of Mars whilst deployed directly on the Martian regolith and partially isolated from the Martian environment by the Wind and Thermal Shield. Central to this payload is the seismometry package SEIS consisting of two seismometers, which is 91̽»¨ed by a suite of environmental/meteorological sensors (Temperature and Wind Sensor for InSight TWINS; and Auxiliary Payload Sensor Suite APSS). In this work, an optimal estimations inversion scheme which aims to decorrelate the short-period seismometer (SEIS-SP) signal due to seismic activity alone from the environmental signal and random noise is detailed, and tested on both simulated and Viking data. This scheme also applies a module to identify measurements contaminated by Single Event Phenomena (SEP). This scheme will be deployed as the pre-processing pipeline for all SEIS-SP data prior to release to the scientific community for analysis.

Abstract:

Measurements of the light scattering behaviour of the regoliths of airless bodies via remote sensing techniques in the Solar System, across wavelengths from the visible to the far infrared, are essential in understanding their surface properties. A key parameter is knowledge of the angular behaviour of scattered light, usually represented mathematically by a phase function. The phase function is believed to be dependent on many factors including the following: surface composition, surface roughness across all length scales, and the wavelength of radiation. Although there have been many phase function measurements of regolith analog materials across visible wavelengths, there have been no equivalent measurements made in the thermal infrared (TIR). This may have been due to a lack of TIR instruments as part of planetary remote sensing payloads. However, since the launch of Diviner to the Moon in 2009, OSIRIS-Rex to the asteroid Bennu in 2016, and the planned launch of BepiColombo to Mercury in 2018, there is now a large quantity of TIR remote sensing data that need to be interpreted. It is therefore important to extend laboratory phase function measurements to the TIR. This paper describes the design, build, calibration, and initial measurements from a new laboratory instrument that is able to make phase function measurements of analog planetary regoliths across wavelengths from the visible to the TIR.

Abstract:

CASTAway is a mission concept to explore our Solar System’s main asteroid belt. Asteroids and comets provide a window into the formation and evolution of our Solar System and the composition of these objects can be inferred from space-based remote sensing using spectroscopic techniques. Variations in composition across the asteroid populations provide a tracer for the dynamical evolution of the Solar System. The mission combines a long-range (point source) telescopic survey of over 10,000 objects, targeted close encounters with 10 – 20 asteroids and serendipitous searches to constrain the distribution of smaller (e.g. 10 m) size objects into a single concept. With a carefully targeted trajectory that loops through the asteroid belt, CASTAway would provide a comprehensive survey of the main belt at multiple scales. The scientific payload comprises a 50 cm diameter telescope that includes an integrated low-resolution (R = 30 – 100) spectrometer and visible context imager, a thermal (e.g. 6 – 16 μm) imager for use during the flybys, and modified star tracker cameras to detect small (~10 m) asteroids. The CASTAway spacecraft and payload have high levels of technology readiness and are designed to fit within the programmatic and cost caps for a European Space Agency medium class mission, whilst delivering a significant increase in knowledge of our Solar System.