Prolonged weightlessness and calcium loss in man

Data have been accumulated from a series of studies in which men have been subjected to weightlessness in orbital space flight for periods of up to 12 weeks. These data are used to predict the long term consequences of weightlessness upon the skeletal system. Space flight induced a loss of calcium which accelerated exponentially from about 50 mg/d at the end of 1 week to approx. 300 mg/d at the end of 12 weeks. The hypercalciuria reached a constant level within 4 weeks while fecal calcium losses continued to increase throughout the period of exposure. This apparent diminution of gastrointestinal absorptive efficiency was accompanied by a slight decline in the plasma level of parathyroid hormone and a slight elevation in the plasma level of calcium and phosphorus. Although losses in mineral from the calcaneus were closely correlated with the calcium imbalance, no changes were detected in the mineral mass of the ulna and radius. From the data presented it is concluded that the process of demineralization observed in space flight is more severe than would be predicted on the basis of observations in immobilized, bed rested, or paralyzed subjects. It is, moreover, suggested that the process may not be totally reversible.     

Postmission plasma volume and red-cell mass changes in the crews of the first two Skylab missions

Red-cell mass determinations were performed before and after the first two Skylab missions. The data showed a 14% mean decrease in red-cell mass after the 28-day mission and a 12% mean decrease after the 59-day mission. The red-cell mass returned to premission levels more slowly after the shorter (28-day) than after the longer mission. Plasma volume decreases were found after each mission. with the crew from the longer mission showing the greater change (13% vs. 8.4%). Postmission decreases in red-cell mass and plasma volume have been a general finding in crewmen who return from short or long spaceflight.     

Performance Degradation Due to Specular Multipath Intersymbol Interference

Plots of performance degradation are used to compare the effects of fading and intersymbol interference in a two- component specular multipath digital communications channel. Similar plots are then used to compare two practical receivers designed to combat the interference. Degradation plots are shown to allow easy identification of each receiver's range of usefulness, as well as identification of variance bounds demanded of channel parameter estimates which the receivers require.     

Origin of planetary atmospheres

The near absence of noble gases on earth, other than those of radioactive origin, indicates that the earth was formed by the accumulation of planetesimals; this process systematically excluded all constituents that did not enter into the solid phase. The atmosphere and the ocean with many of its dissolved salts have arisen from gases emitted from the earth's interior, a process that continues today. The oxygen in the earth's atmosphere plus a greater quantity that has been removed from the atmosphere to oxidize geologic materials, has arisen mainly from a small excess of photosynthesis over decay of organic material. The atmospheres of Mars and Venus have probably arisen in a manner similar to the atmosphere on earth, by emission from the planetary interiors. However, they have not received any oxygen from photosynthesis and so are nearly oxygen free. Mars has very little water in its atmosphere, and this can be explained by its lower than freezing average surface temperature. Venus also has very little water, and this requires an ad hoc explanation; one possibility is that Venus was formed from much drier planetesimals than was the earth. Mercury and the moon are virtually without atmospheres. Although some gases may be emitted from their interiors, they are presumably rapidly lost by escape. Whatever atmosphere they possess is probably due to the neutralized solar wind that impinges upon them. The outer planets retained volatiles, including hydrogen and helium, to a much greater extent than did the terrestrial planets.     

Leveling of Analytic Platforms

Use of an analytic platform or strapdown system requires that the system em be initially leveled just as a conventional multigimbaled platform must be leveled. The process of leveling involves the determination of the orientation between the local vertical and an instrumented reference nce frame. With a conventional platform it is quite common to use a pair of servo loops to precess the inner gimbal until gravity signals are nulled on two orthogonally mounted accelerometers. The input axes of these two accelerometers thus define the horizontal plane and the platform is said to be leveled. A strapdown system, however, lacks the physical entity of the inner gimbal and consequently cannot be physically precessed into verticality. The method of leveling is nonetheless analogous if we consider the computational reference frame of the analytic platform to be the "alter ego" or counterpart of a physical inner gimbal. In general, strapdown leveling techniques can be divided into two categories: closed-loop leveling and open-loop leveling. These two techniques are quantitatively developed and discussed in this paper.     

Attitude Determination Via Nonlinear Filtering

The theory of nonlinear filtering has been applied to the problem of the attitude determination of a satellite. Two approximation methods have been studied with a view to practical implementation. Computer simulation results are included.     

Logistics Transportation for Space Station Support

Logistics support of a long duration space station will dictate a high degree of space flight activity to rotate personnel and transport supplies and equipment. Systems characteristics and mission requirements for space station logistics have been analyzed within the context of a broad spectrum of space missions. Preliminary concepts for a space shuttle system (space transportation) have been developed. This system can support not only a space station program, but a wide variety of space missions for both NASA and the DOD.     

Effects of gravity perturbation on developing animal systems

Developing systems provide unique opportunities for analyzing the effects of microgravity on animals. Several unusual types of cells as well as various extraordinary cellular behavior patterns characterize the embryos of most animals. Those features have been exploited as test systems for space flight. The data from previous experiments are reviewed, and considerations for the design of future experiments are presented.     

The optical parameters of the atmosphere of Venus

This work is devoted to the derivation of the optical properties of the Venus atmosphere from “Venera-10” optical measurements. Within the framework of a two-layer model of Venus atmosphere it is found that in the spectral interval 0.52 – 0.85 μm the optical thickness of the upper cloud layer is ≈ 50 and the optical parameters of the lower layer are similar to the Rayleigh ones. Comparison is made between the measurements of radiation field within the atmosphere and the results of strict calculations. A preliminary conclusion is suggested that there are considerable numbers of aerosol particles with a radius ? 0.03 μm in the lower layer. The results of the upper boundary of the cloud layer is estimated to be ≈ 70 km.