Issues in deep space radiation protection.

The exposures in deep space are largely from the Galactic Cosmic Rays (GCR) for which there is as yet little biological experience. Mounting evidence indicates that conventional linear energy transfer (LET) defined protection quantities (quality factors) may not be appropriate for GCR ions. The available biological data indicates that aluminum alloy structures may generate inherently unhealthy internal spacecraft environments in the thickness range for space applications. Methods for optimization of spacecraft shielding and the associated role of materials selection are discussed. One material which may prove to be an important radiation protection material is hydrogenated carbon nanofibers.     

Got life? Hours of boredom followed by moments of sheer terror (and that''s just with the press)

It may be hoped that an initial discovery of extraterrestrial life and its disclosure will be done by accident. An event of that kind would have its own dynamic, and while communications about the discovery might be strained at times, there would be less likelihood that lines of inquiry and discourse would have already been taken by the participants and the press. In an ideal world (or worlds), the discovery would come ready-made with a picture or pictures that would be useful as an immediate verification of its reality. But such is not the way of the real world (or worlds, apparently). Lessons learned from the publication of the ALH84001 results in Science magazine are indicative of what may be a more likely scenario. Nonetheless, even that publication was held in confidence for much of the time leading up to NASA's press conference, and the science team doing the work was accordingly insulated from press inquiry while the work was underway. Envisioning a Mars sample return mission, or other, similar sort of endeavor that may involve a dedicated team of scientists—working under continual public scrutiny—it is clear that the circumstances that surround any fundamental discovery about life in the sample would be quite different. Planning for a communications strategy to support the operations of a Mars sample receiving facility (or facilities) must take those circumstances into account. An optimization of the time spent communicating the results of the facility's work should acknowledge the time and effort required, and make provisions for the work to proceed without extensive interruptions—and without being influenced by the expectations of the press or the public. This paper will discuss some of the initial planning associated with the communications strategy surrounding such a facility.     

Magnetic holes in the solar wind and their relation to mirror-mode structures

Data obtained by the Ulysses magnetometer and solar wind analyzer have been combined to study the properties of magnetic holes in the solar wind between 1 and 5.4 AU and to 23° south latitude. Although the plasma surrounding the holes was generally stable against the mirror instability, there are indications that the holes may have been remnants of mirror mode structures created upstream of the points of observation. Those indications include: (1) For the few holes for which proton or alpha-particle pressure could be measured inside the hole, the ion thermal pressure was always greater than in the plasma adjacent to the holes. (2) The plasma surrounding many of the holes was marginally stable for the mirror mode, while the plasma environment of all the holes was significantly closer to mirror instability than was the average solar wind. (3) The plasma containing trains of closely spaced holes was closer to mirror instability than was the plasma containing isolated holes. (4) The near-hole plasma had much higher ion (ratio of thermal to magnetic pressure) than did the average solar wind.     

Velocity Shear Induced Phenomena in Solar Atmosphere

We present a brief overview of the probable velocity-shear induced phenomena in solar plasma flows. Shear-driven MHD wave oscillations may be the needed mechanism for the generation of solar Alfvén waves, for the transmission of fast waves through the transition region, and for the acceleration of the solar wind. This revised version was published online in June 2006 with corrections to the Cover Date.     

MESSENGER and the Chemistry of Mercury’s Surface

The instrument suite on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft is well suited to address several of Mercury’s outstanding geochemical problems. A combination of data from the Gamma-Ray and Neutron Spectrometer (GRNS) and X-Ray Spectrometer (XRS) instruments will yield the surface abundances of both volatile (K) and refractory (Al, Ca, and Th) elements, which will test the three competing hypotheses for the origin of Mercury’s high bulk metal fraction: aerodynamic drag in the early solar nebula, preferential vaporization of silicates, or giant impact. These same elements, with the addition of Mg, Si, and Fe, will put significant constraints on geochemical processes that have formed the crust and produced any later volcanism. The Neutron Spectrometer sensor on the GRNS instrument will yield estimates of the amount of H in surface materials and may ascertain if the permanently shadowed polar craters have a significant excess of H due to water ice. A comparison of the FeO content of olivine and pyroxene determined by the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) instrument with the total Fe determined through both GRNS and XRS will permit an estimate of the amount of Fe present in other forms, including metal and sulfides.     

Rendezvous Navigation and Guidance Using a Hand-Held Self-Powered Digital Computer

This paper describes a simplified solution of the space rendezvous problem based on optical sightings taken with a hand-held sextant entered into and processed by a small digital computer. Compared to the manual method described in [1], this approach greatly reduces the astronaut's work load. Also, the computer can provide a more accurate solution, can present more flight plan options (allowing more tradeoffs between fuel usage and time), and can allow greater freedom in the sequencing of measurements and maneuvers. Physical characteristics, input-output parameters, and logic design of the computer are briefly described.     

Modeling of landing of a helicopter with skid undercarriage with regard for the second landing impact

A technique is suggested for calculating the helicopter spatial motion and the stress-strain state of a skid landing gear in the course of landing with regard for the second landing impact; geometric, material and design nonlinearity of undercarriage springs deformation is taken into account. The comparison between the analysis results and experimental data is presented.     

The high-LET radiation component measured during the EUROMIR-94 mission.

Stacks of CR-39 plastic nuclear track detectors were mounted inside the MIR-station during the EUROMIR-94-mission. We present LET-spectra determined separately for long range cosmic ray heavy ions and for short range target fragments produced in nuclear interactions of cosmic rays and measured charge distributions for relativistic and stopping particles.     

Ballistics of a nonfragmenting meteor body with allowance made for mass outflow in the non-isothermal atmosphere. I

The paper is devoted to studying the motion of meteor bodies with mass outflow in a planet’s atmosphere, taking into account the non-isothermal character of the latter. Analytical solutions are obtained at the constant parameter of mass outflow in the model of a nonfragmenting meteoroid. A theoretical analysis of the derived regularities of the ballistics of such bodies is presented.     

Gravisensitivity of cress roots.

The minimum dose (stimulus x time [gs]) eliciting a visible gravitropic response, has been determined using continuous and intermittent stimulation and two different accelerations at 1 g and 0.l g. The minimum dose of 20-30 gs estimated for microgravity roots and of 50-60 gs for roots grown on a 1 g-centrifuge indicated a higher sensitivity of microgravity roots. Applying intermittent stimuli to microgravity-grown roots, gravitropic responses were observed after two stimuli of 13.5 gs separated by a stimulus free interval of 118 s. The curvature of microgravity-grown roots to lateral stimulation by 0.1 g was remarkably smaller than by 1g in spite of the same doses which were applied to the seedlings. Microscopic investigations corresponding to stimulations in the range of the threshold values, demonstrated small displacement (< 2 micrometers) of statoliths in root statocytes. Accepting the statolith theory, one can conclude that stimulus transformation has to occur in the cytoplasm in close vicinity to the statoliths and that this transformation system was affected during seedling cultivation in microgravity.