Mars as a Destination in a Capability-Driven Framework

This paper describes NASA s current plans for the exploration of Mars by human crews within NASA s Capability-Driven Framework (CDF). The CDF describes an approach for progressively extending human explorers farther into the Solar System for longer periods of time as allowed by developments in technology and spacecraft systems. Within this framework, Mars defines the most challenging objective currently envisioned for human spaceflight. The paper first describes the CDF and potential destinations being considered within this framework. For destinations relevant to the exploration of Mars, this includes both the Martian surface and the two moons of Mars. This is followed by a brief review of our evolving understanding of Mars to provide the context for the specific objectives set for human exploration crews. This includes results from robotic missions and goals set for future Martian exploration by NASA's community-based forum, the Mars Exploration Program Analysis Group (MEPAG) and the MEPAG-sponsored Human Exploration of Mars - Science Analysis Group (HEM-SAG). The paper then reviews options available for human crews to reach Mars and return to Earth. This includes a discussion of the rationale used to select from among these options for envisioned Mars exploration missions. The paper then concludes with a description of technological and operational challenges that still face NASA in order to be able to achieve the exploration goals for Mars within the CDF

Traverse Planning Experiments for Future Planetary Surface Exploration

This paper describes the results of a recent (July-August 2010 and July 2011) planetary surface traverse planning experiment. The purpose of this experiment was to gather data relevant to robotically repositioning surface assets used for planetary surface exploration. This is a scenario currently being considered for future human exploration missions to the Moon and Mars. The specific scenario selected was a robotic traverse on the lunar surface from an outpost at Shackleton Crater to the Malapert Massif. As these are exploration scenarios, the route will not have been previously traversed and the only pre-traverse data sets available will be remote (orbital) observations. Devon Island was selected as an analog location where a traverse route of significant length could be planned and then traveled. During the first half of 2010, a team of engineers and scientists who had never been to Devon Island used remote sensing data comparable to that which is likely to be available for the Malapert region (eg., 2-meter/pixel imagery, 10-meter interval topographic maps and associated digital elevation models, etc.) to plan a 17-kilometer (km) traverse. Surface-level imagery data was then gathered on-site that was provided to the planning team. This team then assessed whether the route was actually traversable or not. Lessons learned during the 2010 experiment were then used in a second experiment in 2011 for which a much longer traverse (85 km) was planned and additional surface-level imagery different from that gathered in 2010 was obtained for a comparative analysis. This paper will describe the route planning techniques used, the data sets available to the route planners and the lessons learned from the two traverses planned and carried out on Devon Island

The VLT-FLAMES survey of massive stars: Mass loss and rotation of early-type stars in the SMC

We have studied the optical spectra of a sample of 31 O- and early B-type stars in the Small Magellanic Cloud, 21 of which are associated with the young massive cluster NGC 346. Stellar parameters are determined using an automated fitting method. Comparison with predictions of stellar evolution that account for stellar rotation does not result in a unique age, though most stars are best represented by an age of 1-3 Myr. The present day v_sini distribution of the 21 dwarf stars in our sample is consistent with an underlying rotational velocity (v_r) distribution that can be characterised by a mean velocity of about 160-190 km/s and an effective half width of 100-150 km/s. The v_r distribution must include a small percentage of slowly rotating stars. If predictions of the time evolution of the equatorial velocity for massive stars within the environment of the SMC are correct, the young age of the cluster implies that this underlying distribution is representative for the initial rotational velocity distribution. The location in the Hertzsprung-Russell diagram of the stars showing helium enrichment is in qualitative agreement with evolutionary tracks accounting for rotation, but not for those ignoring v_r. The mass loss rates of the SMC objects having luminosities of log L/L_sun > 5.4 are in excellent agreement with predictions. However, for lower luminosity stars the winds are too weak to determine M_dot accurately from the optical spectrum. Two of three spectroscopically classified Vz stars from our sample are located close to the theoretical zero age main sequence, as expected.Comment: 35 pages, accepted for publication in A&

Chemical composition of Galactic OB stars I. CNO abundances in O9 stars

We present NLTE abundances of CNO for a sample of four O9 stars in the Galaxy, together with new determinations of their stellar parameters, $T_{\rm eff}$, $\log g$, $\epsilon$(He) and microturbulence. These new analyses take into account the effect of {\it line--blocking} in the spectral synthesis with our classical NLTE, plane--parallel and hydrostatic model atmospheres. The sample includes three O9 He normal stars: two dwarfs, HD 214680 and HD 34078, and one supergiant, HD 209975, and one fast rotating giant with a preliminary high He overabundance, HD 191423 with $\epsilon$(He)=0.20. We find first that the consideration of microturbulence in the spectral synthesis for the fast rotator leads to a considerably lower He abundance, $\epsilon$(He)=0.12. The CNO abundances of the three He normal stars are in good agreement with the values in the literature for Galactic B dwarfs with no evidence of mixing, and show that they all have the same chemical composition. We also discuss however the possible CNO contamination of the supergiant HD 209975. For the fast rotator we find that the abundances show the trend of the CNO contamination: a N overabundance together with C and O depletion. The N/C and N/O ratios of our stars as a function of their projected rotational velocities are consistent with the predictions of the recent evolutionary models of Meynet & Maeder [Mey&Mae00].Comment: 19 pages, 12 figures, 13 tables, accepted by A&

O-star mass-loss and wind momentum rates in the Galaxy and the Magellanic Clouds Observations and theoretical predictions

A new, very fast approximate method is presented to determine mass-loss rates of O-stars from H_#alpha# line profiles. The method uses H and HeII departure coefficients from unified model atmospheres parametrized in a simple way as function of wind velocity together with photospheric NLTE line profiles as the inner boundary condition for a numerically exact radiative transfer solution to derive a wind contaminated H_#alpha#-profile. The method is also applied to H_#gamma# to determine stellar gravities corrected for wind emission. A detailed analytical discussion of H_#alpha# line formation in O-star winds is given and it is demonstrated that former very simple approaches considering only optically thin wind emission lead to significant systematic errors. Scaling relations and generalized curves of growth are presented that connect mass-loss rate, terminal velocity, stellar parameters and H_#alpha# equivalent width. (orig.)Available from TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman