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  • 1
    ISSN: 1572-8927
    Keywords: Freezing points ; enthalpies ; aqueous solutions ; Gibbs energy ; tetrahydropyran ; 1,3-dioxane and 1,4-dioxane ; 1,3,5-trioxane ; solute-solute interactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The enthalpies of dilute aqueous solutions of tetrahydropyran, 1,3-dioxane, 1,4-dioxane, 1,2,5-trioxane, and an equimolal mixture of tetrahydropyran and 1,3,5-trioxane were measured at 25°C and at molalities from about 0.1 to 1.0 mol kg1. The freezing points of the same aqueous solutions (except for 1,3-dioxane) were measured over a similar molality range. The results were used to calculate the enthalpies and Gibbs free energies of the pair-wise interactions of the above solutes in dilute aqueous solutions at 25°C. From these results, the additivity principle proposed by Savage and Wood was used to get the Gibbs free energy and enthalpies of interaction for the ether-ether and ether-methylene groups. Because of the limited number of measurements, the interaction parameters were not determined with great precision. Nevertheless, the standard errors for the predicted enthalpies and Gibbs free energies are quite reasonable. The signs and magnitudes are similiar to those determined for other polar groups.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2013-08-31
    Description: The peak deceleration load allowed for aerobraking of manned vehicles is a critical parameter in planning future excursions to Mars. However, considerable variation exists in the limits used by various investigators. The goal of this study was to determine the most appropriate level for this limit. Methods: Since previous U.S. space flights have been limited to 84 days duration, Soviet flight results were examined. Published details of Soviet entry trajectories were not available. However, personal communication with Soviet cosmonauts suggested that peak entry loads of 5-6 G had been encountered upon return from 8 months in orbit. Soyuz entry capsule's characteristics were established and the capsule's entry trajectory was numerically calculated. The results confirm a peak load of 5 to 6 G. Results: Although the Soviet flights were of shorter duration than expected Mars missions, evidence exists that the deceleration experience is applicable. G tolerance has been shown to stabilize after 1 to 3 months in space if adequate countermeasures are used. The calculated Soyuz deceleration histories are graphically compared with those expected for Mars aerobraking. Conclusions: Previous spaceflight experience supports the use of a 5 G limit for the aerocapture of a manned vehicle at Mars.
    Keywords: AEROSPACE MEDICINE
    Type: Aerospace Medical Association, Aerospace Medical Association 63rd Annual Scientific Meeting Program; 1 p
    Format: application/pdf
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