Nadeem A. L. Ghafoor

A soft solid surface on Titan as revealed by the Huygens Surface Science Package

The surface of Saturns largest satellite—Titan—is largely obscured by an optically thick atmospheric haze, and so its nature has been the subject of considerable speculation and discussion. The Huygens probe entered Titans atmosphere on 14 January 2005 and descended to the surface using a parachute system. Here we report measurements made just above and on the surface of Titan by the Huygens Surface Science Package. Acoustic sounding over the last 90 m above the surface reveals a relatively smooth, but not completely flat, surface surrounding the landing site. Penetrometry and accelerometry measurements during the probe impact event reveal that the surface was neither hard (like solid ice) nor very compressible (like a blanket of fluffy aerosol); rather, the Huygens probe landed on a relatively soft solid surface whose properties are analogous to wet clay, lightly packed snow and wet or dry sand. The probe settled gradually by a few millimetres after landing.

Wind-driven surface waves on Titan

The surface of Titan represents the largest surface area in the solar system essentially unexplored, although recent observations from Hubble Space Telescope and ground-based telescopes using adaptive optics have given perhaps the first low-resolution indications of its nature. Whilst early models citing global oceans have been all but abandoned, substantial bodies of liquid up to several hundred kilometers in extent are not precluded. If such reservoirs do exist then in the presence of any surface winds it is expected that wind-driven surface waves will be generated. As on Earth, gravity remains the dominant controlling factor for such waves, with surface tension and viscous effects only becoming significant below wavelengths of several centimeters. Empirical models used for terrestrial wind-driven sea waves are adapted to investigate the properties of such waves on Titan using predicted parameters for Titans liquids. Significant wave height, peak period, wavelength, phase speed, and wave steepness are predicted as a function of wind speed and liquid body extent. It is found that waves will grow to a limiting height, limiting wavelength and limiting period which are all inversely proportional to gravity. The limiting significant wave height under the action of a 1 m s−1 Titan wind over 50 km, for example, is predicted to be 0.2 m compared to 0.02 m on Earth under similar circumstances. More interesting, however, is the wave growth prior to this limiting value. A useful visualization is that surface waves on a Titan sea arising from surface wind speeds of 0.3 and 1 m s−1 will resemble in scale waves on Earth generated by terrestrial winds of 1 and 3 m s−1 respectively. These particular Titan waves will have nearly 3 times the period and travel almost 3 times slower than the terrestrial waves, however. The wave parameters predicted in this work have potential surface mission implications for the European Space Agencys Huygens Probe which will land on Titan in 2004. Conversely, their measurement by instruments on board Huygens and NASAs Cassini spacecraft could yield important planetological information.

Field Testing of an Integrated Surface/Subsurface Modeling Technique for Planetary Exploration

While there has been much interest in developing ground-penetrating radar (GPR) technology for rover-based planetary exploration, relatively little work has been done on the data collection process. Starting from the manual method, we fully automate GPR data collection using only sensors typically found on a rover. Further, we produce two novel data products: (1) a three-dimensional, photorealistic surface model coupled with a ribbon of GPR data, and (2) a two-dimensional, topography-corrected GPR radargram with the surface topography plotted above. Each result is derived from only the onboard sensors of the rover, as would be required in a planetary exploration setting. These techniques were tested using data collected in a Mars analogue environment on Devon Island in the Canadian High Arctic. GPR transects were gathered over polygonal patterned ground similar to that seen on Mars by the Phoenix Lander. Using the techniques developed here, scientists may remotely explore the interaction of the surface topography and subsurface structure as if they were on site.

Field testing of a rover guidance, navigation, and control architecture to support a ground-ice prospecting mission to Mars

This paper provides an overview of a rover guidance, navigation, and control (GN&C) architecture being developed to support a ground-ice prospecting mission to Mars. The main contribution of this paper is to detail an integrated field campaign that demonstrates the viability of the key rover GN&C techniques needed to carry out this mission. Tests were conducted on Devon Island in the Canadian High Arctic during the summer of 2009, wherein a large field robot was driven on real polygonal terrain (a landform of interest on Mars). Lessons learned and recommendations for future work are provided.

Rover-Based Surface and Subsurface Modeling for Planetary Exploration

We develop and test a technique for the creation of coupled surface and subsurface models. Images from a stereo camera are used to estimate the motion of a rover that is collecting ground penetrating radar (GPR) data. The motion estimate and raw sensor data are used to build two novel data products: (1) A three-dimensional, photorealistic surface model coupled with a ribbon of GPR data, and (2) a two-dimensional, topography-corrected GPR radargram with the reconstructed surface topography plotted above. Each result is derived from only the onboard sensors of the rover, as would be required in a planetary exploration setting. These techniques were tested using data collected in a Mars analogue environment on Devon Island in the Canadian High Arctic. GPR transects were gathered over polygonal patterned ground similar to that seen by the Phoenix lander on Mars. Using the techniques developed here, scientists may remotely explore the interaction of the surface topography and subsurface structure as if they were on site.

Inukshuk Landed Robotic Canadian Mission to Mars using a Miniature Sample Analysis Lab for Planetary Mineralogy and Microbiology

This paper discusses the Inukshuk landed rover mission to Mars that is currently undergoing the Phase 0 mission study for the Canadian Space Agency. The Inukshuk landed rover mission addresses key science themes for planetary exploration; focusing on the search for hydrated mineralogy and subsurface water sites that can provide evidence of past or present life. New exploration and science will be accomplished using an innovative tethered combination of a small rover and a self-elevating sky-cam aerostat. The elevating visible (VIS) imager, at about 10 m altitude, will provide an informative high-resolution 2-D view of the rover below and surrounding terrain to greatly assist the semi-autonomous navigation of the rover around obstacles and selection of sites for detailed subsurface exploration. The solar-powered rover will employ MDA expertise in robotics and drilling with MPB’s expertise in miniature infrared (IR) spectrometers and fiber-optic sensors to provide subsurface analysis of mineralogy and temperature distributions at depths to about 1 m. Mission cost effectiveness is achieved through a synergistic instrument suite based on advanced but mature miniaturization technologies that enable high IR spectral measurement performance with minimal mass and power. Insitu systematic sample analysis at depths to about 1 m will be performed using a monolithic fiberoptic coupled probe integrated directly with the tethered mole driller.