Atmospheric densities and temperatures from the drag analysis of the San Marco Satellite

Atmospheric densities and temperatures from drag analysis of San Marco satellit

Meteor masses and luminosity

Analysis of meteor luminous efficiency based on photographic data, taking into account fragmentation effect

Automated Individually-Adaptive Astronaut Training Algorithms in Virtual Reality for Deep Space Missions

Long-duration exploration missions (LDEM) pose a unique challenge for astronaut training. Astronauts may experience a degraded capcity to perform complex tasks due both to the time elapsed from initial ground training and to the neural decrements associated with spaceflight. This effect may be particularly pronounced for complex, mission-critical tasks such as maneuvering spacecraft during entry, descent, and landing (EDL). Since the time delays and crew constraints on deep space missions preclude facilitated, operator-mediated training, mitigating this risk requires a cost-effective, lightweight, and automated system for recurrent training. Virtual reality (VR), long-used as an immersive, easily-programmable, dynamic environment for training, is an ideal medium for training during LDEM. To date, there is no literature investigating the effect of responsiveness, integration, and personalization on the efficacy of automated training algorithms. This study used a virtual simulator to train subjects to pilot and land a spacecraft on the surface of Mars and a physical mock-up of a spacecraft cockpit to put skills acquired during training to the test. The study assessed the effect of multiple training algorithms on skill acquisition, learning retention, progression of training difficulty, subtask performance, and skill transfer between the virtual and physical environments. The training algorithms varied the threshold for difficulty progression (sensitivity), the effect of subtask performance on the difficulty progression of other subtasks (lockstep), and the use of fixed rather than adaptive difficulty progression. The study found that highly responsive training algorithms leads to faster difficulty progressions and higher achieved difficulty in training but lower skill and performance in the cockpit environment. It also found that low levels of subtask integration which allow for discrete rather than unified subtask progressions leads to higher performance and achieved difficulty in training, and slightly better performance outcomes in the cockpit. Finally, the study found that personalized training leads to higher levels of skill and performance in both training and the cockpit compared to non-adaptive, fixed progression training. Future work can build upon these results by analyzing the effect of responsiveness on the duration of the familiarization phase during training as a function of task complexity and expanding analysis on personalization to investigate the limiting effect of fixed training progression on top performing subjects. Future studies should investigate run-dependent shifts in PEST staircases, dynamic variable response paradigms which scale difficulty increments to subject performance, Bayesian methods to predict optimal challenge given both individual and aggregate data, subject-selected difficulty, and the incorporation of unobtrisvely-gathered psychophysiological data to estimate workload and challenge, closing the loop on characterizing and optimizing human performance in space.</p

Mass Loss Due to Sputtering and Thermal Processes in Meteoroid Ablation

Conventional meteoroid theory assumes that the dominant mode of ablation is by evaporation following intense heating during atmospheric flight. In this paper we consider the question of whether sputtering may provide an alternative disintegration process of some importance.For meteoroids in the mass range from 10^-3 to 10^-13 kg and covering a meteor velocity range from 11 to 71 km/s, we numerically modeled both thermal ablation and sputtering ablation during atmospheric flight. We considered three meteoroid models believed to be representative of asteroidal (3300 kg m^-3 mass density), cometary (1000 kg m^-3) and porous cometary (300 kg m^-3) meteoroid structures. Atmospheric profiles which considered the molecular compositions at different heights were used in the sputtering calculations. We find that while in many cases (particularly at low velocities and for relatively large meteoroid masses) sputtering contributes only a small amount of mass loss during atmospheric flight, in some cases sputtering is very important. For example, a 10^-10 kg porous meteoroid at 40 km/s will lose nearly 51% of its mass by sputtering, while a 10^-13 kg asteroidal meteoroid at 60 km/s will lose nearly 83% of its mass by sputtering. We argue that sputtering may explain the light production observed at very great heights in some Leonid meteors. The impact of this work will be most dramatic for very small meteoroids such as those observed with large aperture radars.Comment: in pdf form, 48 pgs incl figures and table

Observations of 1999 YC and the Breakup of the Geminid Stream Parent

Apollo asteroid 1999 YC may share a dynamical association with the Phaethon-Geminid stream complex (Ohtsuka et al. 2008). Here, we present photometric observations taken to determine the physical properties of 1999 YC. The object shows a nearly neutral reflection spectrum, similar to but slightly redder than related objects 3200 Phaethon and 2005 UD. Assuming an albedo equal to 3200 Phaethon's we find that the diameter is 1.4+/-0.1 km. Time-resolved broad-band photometry yields a double-peaked rotational period of 4.4950+/-0.0010 hr while the range of the lightcurve indicates an elongated shape having a projected axis ratio near 1.9:1. Surface brightness models provide no evidence of lasting mass loss of the kind seen in active short period cometary nuclei. An upper limit to the mass loss is set at about 0.001 kg/s, corresponding to an upper limit on the fraction of the surface that could be sublimating water ice of 0.001. If sustained over the 1000 yr age of the Geminid stream, the total mass loss from 1999 YC (3e7 kg) would be small compared to the reported stream mass (1e12 - 1e13 kg), suggesting that the stream is the product of catastrophic, rather than steady-state, breakup of the parent object.Comment: 36 pages, 8 figures, in press at Astronomical Journa

The comet Halley dust and gas environment

Quantitative descriptions of environments near the nucleus of comet P /Halley have been developed to support spacecraft and mission design for the flyby encounters in March, 1986. To summarize these models as they exist just before the encounters, we review the relevant data from prior Halley apparitions and from recent cometary research. Orbital elements, visual magnitudes, and parameter values and analysis for the nucleus, gas and dust are combined to predict Halley's position, production rates, gas and dust distributions, and electromagnetic radiation field for the current perihelion passage. The predicted numerical results have been useful for estimating likely spacecraft effects, such as impact damage and attitude perturbation. Sample applications are cited, including design of a dust shield for spacecraft structure, and threshold and dynamic range selection for flight experiments. We expect that the comet's activity may be more irregular than these smoothly varying models predict, and that comparison with the flyby data will be instructive.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43774/1/11214_2004_Article_BF00175326.pd

ALCUNI RISULTATI DI UNA RICERCA SULLA DENSITA DEI CORPI METEORICI

Dopo una breve discussione delle cause dell'incertezzaattualmente esistente al riguardo della densita e della struttura dei corpimeteorici, viene presentato un inetodo per calcolare la densita delle meteoreutilizzando dati fotograflci. Inflne vengono esposti i risultati ottenuti dall'autoreanalizzando dati pubblicati ad Harvard. Tali risultati mostranochiaramente clie quasi t u t t e le meteore hanno una densita minore di 1 g cm-3e quindi una struttura porosa in accordo con il modello cometario di Whipple

Meteor masses and luminosity /

Includes bibliographical references (page 195)