LISA — a study of the ESA cornerstone mission for observing gravitational waves

The primary objective of the Laser Interferometer Space Antenna (LISA) mission is to detect and observe gravitational waves from massive black holes and galactic binaries in the frequency range 10⁻⁴ to 10⁻¹ Hz. This low-frequency range is inaccessible to ground-based interferometers because of the unshieldable background of local gravitational noise and because ground-based interferometers are limited in length to a few km. LISA is an ESA cornerstone mission and recently had a system study (Ref. 1) carried out by a consortium led by Astrium, which confirmed the basic configuration for the payload with only minor changes, and provided detailed concepts for the spacecraft and mission design. The study confirmed the need for a drag-free technology demonstration mission to develop the inertial sensors for LISA, before embarking on the build of the flight sensors. With a technology demonstration flight in 2005, it would be possible to carry out LISA as a joint ESA-NASA mission with a launch by 2010 subject to the funding programmatics. The baseline for LISA is three disc-like spacecraft each of which consist of a science module which carries the laser interferometer payload (two in each science module) and a propulsion module containing an ion drive and the hydrazine thrusters of the AOCS. The propulsion module is used for the transfer from earth escape trajectory provided by the Delta II launch to the operational orbit. Once there the propulsion module is jettisoned to reduce disturbances on the payload. Detailed analysis of thermal and gravitational disturbances, a model of the drag-free control and of the interferometer operation confirm that the strain sensitivity of the interferometer will be achieved.     

Electrostatic Instability and Plasma Irregularities in the Topside Ionosphere above the South-Atlantic Geomagnetic Anomaly

The data of measuring the plasma density in the topside ionosphere for the South-Atlantic geomagnetic anomaly region are presented. It is shown that irregular plasma structures with a wide spectrum of irregularity scale (including large-scale structures with a dimension of order of some hundred kilometers) can be generated in the fields of electrostatic turbulence in inhomogeneous plasma.     

Convective Motions in Near-Critical Fluids under Real Zero-Gravity Conditions

The results of processing and interpreting the data of joint Russian–French experiments for studying the heat and mass transfer in near-critical fluids are presented. The experiments were carried out with the ALICE-1 instrument during an orbital flight of the Mirstation from September 30 to October 2, 1995 [1]. For such fluids with a point-like source of heat, when they are placed in the field of uncontrolled inertial accelerations of the spacecraft, the influence of thermovibrational and thermogravitational mechanisms of convection on the propagation of the region of optical irregularity is investigated. It is shown that, near the thermodynamic critical point, local heating of the medium leads to generation of either intense thermogravitational convection or averaged vibroconvective flow, depending on the frequency of variations of the microaccelerations. The structure and characteristics of discovered motions are studied. The results of numerical simulations are presented that confirm the conclusion about a possibility of generation of an averaged convective flow of a vibrational type by the high-frequency component of microaccelerations.     

The physics,biology, and environmental ethics of making mars habitable

The considerable evidence that Mars once had a wetter, more clement, environment motivates the search for past or present life on that planet. This evidence also suggests the possibility of restoring habitable conditions on Mars. While the total amounts of the key molecules--carbon dioxide, water, and nitrogen--needed for creating a biosphere on Mars are unknown, estimates suggest that there may be enough in the subsurface. Super greenhouse gases, in particular, perfluorocarbons, are currently the most effective and practical way to warm Mars and thicken its atmosphere so that liquid water is stable on the surface. This process could take approximately 100 years. If enough carbon dioxide is frozen in the South Polar Cap and absorbed in the regolith, the resulting thick and warm carbon dioxide atmosphere could support many types of microorganisms, plants, and invertebrates. If a planet-wide martian biosphere converted carbon dioxide into oxygen with an average efficiency equal to that for Earth's biosphere, it would take > 100,000 years to create Earth-like oxygen levels. Ethical issues associated with bringing life to Mars center on the possibility of indigenous martian life and the relative value of a planet with or without a global biosphere.     

Cave biosignature suites: microbes,minerals, and Mars

Earth's subsurface offers one of the best possible sites to search for microbial life and the characteristic lithologies that life leaves behind. The subterrain may be equally valuable for astrobiology. Where surface conditions are particularly hostile, like on Mars, the subsurface may offer the only habitat for extant lifeforms and access to recognizable biosignatures. We have identified numerous unequivocally biogenic macroscopic, microscopic, and chemical/geochemical cave biosignatures. However, to be especially useful for astrobiology, we are looking for suites of characteristics. Ideally, "biosignature suites" should be both macroscopically and microscopically detectable, independently verifiable by nonmorphological means, and as independent as possible of specific details of life chemistries--demanding (and sometimes conflicting) criteria. Working in fragile, legally protected environments, we developed noninvasive and minimal impact techniques for life and biosignature detection/characterization analogous to Planetary Protection Protocols. Our difficult field conditions have shared limitations common to extraterrestrial robotic and human missions. Thus, the cave/subsurface astrobiology model addresses the most important goals from both scientific and operational points of view. We present details of cave biosignature suites involving manganese and iron oxides, calcite, and sulfur minerals. Suites include morphological fossils, mineral-coated filaments, living microbial mats and preserved biofabrics, 13C and 34S values consistent with microbial metabolism, genetic data, unusual elemental abundances and ratios, and crystallographic mineral forms.     

Effect of weightlessness on posture and movement control during a whole body reaching task

Here are reported preliminary results of the “Synergy” experiment performed aboard the Russian orbital station “MIR” in July 1993 (Altaïr Mission). The experiment was carried out before, during, and after the space flight of two astronauts (S1 and S2). The duration of the flight was 21 days for S1 and 6 month for S2. The subjects were tested during preflight, inflight and postflight. The astronaut subjects were fixed on the ground by the feet. They were asked to pick up a box in front of them on the ground. Two velocities of movement and two distances of the target to be reached were tested. The movement of several small markers placed on the body was recorded on video tape.

Results show that the shape of head and hand trajectories in the sagittal plane remains roughly the same during the flight in spite of the modification of mechanical constraints. Trajectory invariance does not result in joint angular displacement invariance. These data indicate that the planning of the movement takes place in terms of head and hand trajectories rather than joint rotations as it was previously suggested for simple arm reaching movement.     

Orbital and relative motion of a tethered satellite system

A simplified model for the orbital and relative motion of a tethered satellite system is presented. The tether acts as a light elastic string with small structural damping but without bending stiffness. Its mass is taken into account in the calculation of the total kinetic and potential energies of the tethered system. This formulation allows the inclusion of the complete gravity gradient influence on the dynamics of the system. The resulting three-dimensional motion is separated in the centre of mass orbital motion on the one hand and the relative motion of the end-bodies on the other. No restrictions on length of the tether or on mass ratio of the end-masses are imposed. It is found that the frequencies and amplitudes of the longitudinal tether oscillations are realistic as long as the tether mass is less than that of the subsatellite.     

n-Body problem: Selective effects of triple close approaches

In Celestial Mechanics the triple close approach is a highly unstable phenomenon that leads very often to the formation of a very small binary escaping with a large velocity in the direction opposite to the escape of the third body.That third escaping body is generally either the smallest mass or the second smallest and it implies a very selective effect in star clusters: the lightest stars are statistically the first to be ejected.     

Exercise response to simulated weightlessness

Two bed rest analog studies of space flight were performed; one 14 d and the other 28 d in duration. Exercise response was studied in detail during the 28 d study and following both the 14 d and 28 d studies. This paper relates the results of these studies to physiologic changes noted during and following space flight. The most consistent change noted after both bed rest and space flight is an elevated heart rate during exercise. A second consistent finding is a postflight or postbed rest reduction in cardiac stroke volume. Cardiac output changes were variable. The inability to simulate inflight activity levels and personal exercise makes a direct comparison between bed rest and the results from specific space flights difficult.     

Skylab experiment M-092: results of the first manned mission

Blood pressure at 30-sec intervals, heart rate, and percentage increase in leg volume continuously were recorded during a 25-min protocol in the M092 Inflight Lower Body Negative Pressure (LBNP) experiment carried out in the first manned Skylab mission. These data were collected during six tests on each crewman over a 5-month preflight period. The protocol consisted of a 5-min resting control period, 1 min at -8, 1 min at -16, 3 min at -30, 5 min at -40, and 5 min at -50 mm Hg LBNP. A 5-min recovery period followed. Inflight tests were performed at approximately 3-day intervals through the 28-day mission. Individual variations in cardiovascular responses to LBNP during the preflight period continued to be demonstrated in the inflight tests. Measurements of the calf indicated that a large volume of fluid was shifted out of the legs early in the flight and that a slower decrease in leg volume, presumably due to loss of muscle tissue, continued throughout the flight. Resting heart rates tended to be low early in the flight and to increase slightly as the flight progressed. Resting blood pressure varied but usually was characterized by slightly elevated systolic blood pressure, lower diastolic pressure, and higher pulse pressures than during preflight examinations. During LBNP inflight a much greater increase in leg volume occurred than in preflight tests. Large increases occurred even at the smallest levels of negative pressure, suggesting that the veins of the legs were relatively empty at the beginning of the LBNP. The greater volume of blood pooled in the legs was associated with greater increases of heart rate and diastolic pressure and larger falls of systolic and pulse pressure than seen in preflight tests. The LBNP protocol represented a greater stress inflight, and on three occasions it was necessary to stop the test early because of impending syncopal reactions. LBNP responses inflight appeared to predict the degree of postflight orthostatic intolerance. Postflight responses to LBNP during the first 48 hours were characterized by marked elevations of heart rate and instability of blood pressure. In addition, systolic and diastolic pressures were typically elevated considerably both at rest and also during stress. The time required for cardiovascular responses to return to preflight levels was much slower than in the case of Apollo crewmen.