An Analysis of the Low-Frequency Component in Measurements of Angular Velocity and Microacceleration onboard the Foton-12 Satellite

We compare the results of two methods used to determine the angular velocity of the Foton-12 satellite and the low-frequency component of microaccelerations onboard it. The first method is based on reconstruction of the satellite's rotational motion using the data of onboard measurements of the strength of the Earth's magnetic field. The motion (time dependence of the orientation parameters and angular velocity) was found from the condition of best approximation of the measurement data by the functions calculated along the solutions to equations of attitude motion of the satellite. The solutions found were used to calculate the quasistatic component of microaccelerations at certain points of the satellite, in particular, at the point of location of an accelerometer of the QSAM system. Filtration of the low-frequency component of the angular velocity and microacceleration from the data of measurements by a sensor of angular velocity and by the accelerometer of this system served as a second method. The filtration was made using the discrete Fourier series. A spectral analysis of the functions representing the results of determining the angular velocity and microacceleration by both methods is performed. Comparing the frequencies and amplitudes of the harmonic component of these functions allowed us to estimate the accuracy of measurements made by the QSAM system in the low-frequency range.     

Spore UV and acceleration resistance of endolithic Bacillus pumilus and Bacillus subtilis isolates obtained from Sonoran desert basalt: implications for lithopanspermia

Bacterial spores have been used as model systems for studying the theory of interplanetary transport of life by natural processes such as asteroidal or cometary impacts (i.e., lithopanspermia). Because current spallation theory predicts that near-surface rocks are ideal candidates for planetary ejection and surface basalts are widely distributed throughout the rocky planets, we isolated spore-forming bacteria from the interior of near-subsurface basalt rocks collected in the Sonoran desert near Tucson, Arizona. Spores were found to inhabit basalt at very low concentrations (相似文献   

Dynamics and control of variable-geometry truss structures

Variable-geometry truss structures are likely to be used extensively in the future for in-orbit space construction. This paper considers dynamics formulation and vibration control of such structures. The truss system is modelled as a collection of sub-structures consisting of truss booms, prismatic actuator elements, and in some cases a manipulator at the end. Each truss boom is treated as a separate ‘link’ and its flexibility is modelled using the finite element method. Equations of motion for individual sub-structures are obtained which are then assembled. The non-working constraint forces are eliminated to obtain the equations governing the constrained dynamics of the entire system. For vibration control, the singular perturbation method is employed to construct two reduced-order models, for quasi-static motion and for modal co-ordinates, respectively. Computed torque with PD control is applied to maintain the quasi-static motion, while an optimal LQR method is used for vibration control. Typical simulation results are presented for the planar case.     

微重力环境中重力梯度加速度引起的流体晃动力和力矩的模拟

本文研究了关于旋转轴在贮箱的非对称轴上且远离贮箱的几何中心情况下，流体在微重力环境中由重力梯度加速度诱发的晃动特性。我们以精密Ｘ光光谱天文物理实验卫星（简称ＡＸＡＦ－Ｓ）作为研究对象，获得了由于旋转运动引起的重力梯度加速度的数学表达式。关于晃动问题的数值计算是用与卫星固连的非惯性坐标系为基础，目的是寻求一种较为易处理且适合于流体力学方程的边界和初始条件。通过数值计算获得了流体作用于卫星贮箱上的力和力矩。     

Production of neutrons from interactions of GCR-like particles

In order to help assess the risk to astronauts due to the long-term exposure to the natural radiation environment in space, an understanding of how the primary radiation field is changed when passing through shielding and tissue materials must be obtained. One important aspect of the change in the primary radiation field after passing through shielding materials is the production of secondary particles from the breakup of the primary. Neutrons are an important component of the secondary particle field due to their relatively high biological weighting factors, and due to their relative abundance, especially behind thick shielding scenarios. Because of the complexity of the problem, the estimation of the risk from exposure to the secondary neutron field must be handled using calculational techniques. However, those calculations will need an extensive set of neutron cross section and thicktarget neutron yield data in order to make an accurate assessment of the risk. In this paper we briefly survey the existing neutron-production data sets that are applicable to the space radiation transport problem, and we point out how neutron production from protons is different than neutron production from heavy ions. We also make comparisons of one the heavy-ion data sets with Boltzmann-Uehling-Uhlenbeck (BUU) calculations.     

Future spacelift projections

In 1996 the NASA Advisory Council asked for a comprehensive look at future launch projections out to the year 2030 and beyond. In response to this request NASA sponsored a study at The Aerospace Corporation to develop long-range space transportation models for future commercial and government applications, and to analyze the design considerations and desired characteristics for future space transportation systems. Follow-ons to present space missions as well as a wide array of potential new space applications are considered in the study. This paper summarizes the space transportation system characteristics required to enable various classes of future missions. High reliability and the ability to achieve high flight rates per vehicle are shown to be key attributes for achieving more economical launch systems. Technical, economic and policy implications are also discussed.     

Evolution of Rotational Motion of a Symmetrical Satellite with Viscoelastic Rods

We study the motion of a symmetrical satellite with a pair of flexible viscoelastic rods in a central Newtonian gravitational field. A restricted problem formulation is considered, when the satellite's center of mass moves along a fixed circular orbit. A small parameter is introduced which is inversely proportional to the stiffness of flexible elements. Another small parameter is equal to the ratio of the squared orbital angular velocity and the squared magnitude of the initial angular velocity of the satellite. In order to describe the satellite rotational motion relative to the center of mass, we use the canonical Andoyer variables. In the undisturbed formulation of the problem, i.e., at = 0 and = 0, these variables are the action–angle variables. Equations describing the evolution of motion are derived by an asymptotic method which combines the method of separating motions for systems with an infinite number of degrees of freedom and the Krylov–Bogolyubov method for systems with fast and slow variables. The manifolds of stationary motions are found, and their stability is investigated on the basis of equations in variations. Phase portraits are constructed which describe the rotational motion of a satellite at the stage of slow dissipative evolution.     

One hundred US EVAs: a perspective on spacewalks

In the 36 years between June 1965 and February 2001, the US human space flight program has conducted 100 spacewalks, or extravehicular activities (EVAs), as NASA officially calls them. EVA occurs when astronauts wearing spacesuits travel outside their protective spacecraft to perform tasks in the space vacuum environment. US EVA started with pioneering feasibility tests during the Gemini Program. The Apollo Program required sending astronauts to the moon and performing EVA to explore the lunar surface. EVA supported scientific mission objectives of the Skylab program, but may be best remembered for repairing launch damage to the vehicle and thus saving the program. EVA capability on Shuttle was initially planned to be a kit that could be flown at will, and was primarily intended for coping with vehicle return emergencies. The Skylab emergency and the pivotal role of EVA in salvaging that program quickly promoted Shuttle EVA to an essential element for achieving mission objectives, including retrieving satellites and developing techniques to assemble and maintain the International Space Station (ISS). Now, EVA is supporting assembly of ISS. This paper highlights development of US EVA capability within the context of the overarching mission objectives of the US human space flight program.     

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.