Preliminary geologic mapping near the Nilosyrtis Mensae, Mars

Virtually the entire map area is mantled by an irregular deposit of material that is apparently fine-grained and erodible. It is also extremely young, as there is not a single crater larger than 1 km in the map area that was emplaced atop the mantle. Knobs abound in the study area; many are presumably caused by the mantling of pre-existing topography. In many cases the older knob of the core is exposed. Many such knob cores are surrounded by small scarplets; it is not yet clear whether the scarplets are the eroded edges of mantle beds that at one time draped over the knob core and have been subsequently exposed by erosion, or whether they are eroded versions of lobate debris aprons. Many craters in the study area contain concentric crater fill, which may indicate downslope movement of volatile-rich materials or repeated cycles of aeolian gradation

Geologic mapping of MTM quads 40292 and 40297: In the Utopian lowlands north of the Nilosyrtis Mensae, Mars

Geologic mapping at 1:500,000 scale of the Mars transverse Mercator (MTM) quads 40292 and 40297 is being conducted under the auspices of the Mars Geologic Mapping Program. The study area is located in the southwestern portion of Utopia Planitia immediately north of the Nilosyrtis Mensae, between latitudes 37.5 and 42.5 degrees and longitudes 290 and 300 degrees. The goals of the mapping are to identify the major geologic features in the study area and to determine the sequence and scope of the geologic events that have modified the lowland side of the global dichotomy boundary in this region in order to at least partially constrain models of dichotomy boundary origin and evolution. The progress made towards achieving these goals is reported

Combined high and low thrust propulsion for fast piloted Mars missions

The mission benefits of using both high thrust nuclear thermal propulsion (NTP) and low acceleration, high specific impulse nuclear electric propulsion (NEP) to reduce piloted trip times to Mars with reasonable initial mass are assessed. Recent updates in mission design, such as the Earth fly-by return, are assessed for their impact on previous studies. In addition, the Synthesis Commission split mission to Mars in 2014 is also assessed using combined propulsion. Results show an 80 to 100 day reduction in trip time over the reference NTP or NEP systems and missions, with comparable or reduced vehicle initial masses. The impacts of the mission and system analyses upon technology planning and design are discussed

Photo-heating and the fate of hard photons during the reionisation of HeII by quasars

We use a combination of analytic and numerical arguments to consider the impact of quasar photo-heating during HeII reionisation on the thermal evolution of the intergalactic medium (IGM). We demonstrate that rapid (\Delta z 10^4 K) photo-heating is difficult to achieve across the entire IGM unless quasar spectra are significantly harder than implied by current observational constraints. Although filtering of intrinsic quasar radiation through dense regions in the IGM does increase the mean excess energy per HeII photo-ionisation, it also weakens the radiation intensity and lowers the photo-ionisation rate, preventing rapid heating over time intervals shorter than the local photo-ionisation timescale. Moreover, the hard photons responsible for the strongest heating are more likely to deposit their energy inside dense clumps. The abundance of such clumps is, however, uncertain and model-dependent, leading to a fairly large uncertainty in the photo-heating rates. Nevertheless, although some of the IGM may be exposed to a hardened and weakened ionising background for long periods, most of the IGM must instead be reionised by the more abundant, softer photons and with accordingly modest heating rates (\Delta T < 10^4 K). The repeated ionisation of fossil quasar HeIII regions does not increase the net heating because the recombination times in these regions typically exceed the IGM cooling times and the average time lag between successive rounds of quasar activity. Detailed line-of-sight radiative transfer simulations confirm these expectations and predict a rich thermal structure in the IGM during HeII reionisation. [Abridged]Comment: 20 pages, 6 figures, accepted by MNRA

Feasibility of intercalated graphite railgun armatures

Graphite intercalation compounds may provide an excellent material for the fabrication of electro-magnetic railgun armatures. As a pulse of power is fed into the armature the intercalate could be excited into the plasma state around the edges of the armature, while the bulk of the current would be carried through the graphite block. Such an armature would have the desirable characteristics of both diffuse plasma armatures and bulk conduction armatures. In addition, the highly anisotropic nature of these materials could enable the electrical and thermal conductivity to be tailored to meet the specific requirements of electromagnetic railgun armatures. Preliminary investigations were performed in an attempt to determine the feasibility of using graphite intercalation compounds as railgun armatures. Issues of fabrication, resistivity, stability, and electrical current spreading are addressed for the case of highly oriented pyrolytic graphite