Proposed Space Station Research Articles

Instability of liquid flows investigated for a proposed space station cooling system

Standard techniques reveal two new instabilities that affect liquid sheets in vacuum, important insight for cooling mechanisms used in space.

Fluxes of galactic iron nuclei and associated HZE secondaries, and resulting radiation doses, in the brain of an astronaut

Although galactic iron nuclei constitute only a small percentage of the total flux of radiation in space, they are extremely significant from a biological standpoint, and represent a concern for long-term manned space missions of the future. Dosages resulting from iron nuclei, and the high-charge secondary nuclei subsequently produced in nuclear fragmentation reactions, have been calculated at the centre of a simple model of the human brain, shielded by various thicknesses of aluminium. Three mission scenarios are considered representing different geomagnetic shielding conditions at solar minimum. Without artificial shielding absorbed dose rates outside the magnetosphere, in polar orbit and in the proposed Space Station orbit, are approximately 0.3, 0.1 and 0.03 cGy/year respectively, corresponding to dose equivalent rates of 8.0, 2.5 and 0.8 cSv/year, and decreasing by roughly a factor of two behind 10 g/cm 2 of aluminium. In line with new approaches to risk estimation based on particle fluence and track structure, calculations of the number of cell nuclei likely to be struck by these HZE particles are also presented. Behind 10 g/cm 2 of aluminium, 3.4%, 1.3% and 0.5% of cell nuclei at the centre of the brain will be traversed at least once by such a particle within three years, for the three mission scenarios respectively.

An Analysis of Interplanetary Space Radiation Exposure for Various Solar Cycles

The radiation dose received by crew members in interplanetary space is influenced by the stage of the solar cycle. Using the recently developed models of the galactic cosmic radiation (GCR) environment and the energy-dependent radiation transport code, we have calculated the dose at 0 and 5 cm water depth; using a computerized anatomical man (CAM) model, we have calculated the skin, eye and blood-forming organ (BFO) doses as a function of aluminum shielding for various solar minima and maxima between 1954 and 1989. These results show that the equivalent dose is within about 15% of the mean for the various solar minima (maxima). The maximum variation between solar minimum and maximum equivalent dose is about a factor of three. We have extended these calculations for the 1976-1977 solar minimum to five practical shielding geometries: Apollo Command Module, the least and most heavily shielded locations in the U.S. space shuttle mid-deck, center of the proposed Space Station Freedom cluster and sleeping compartment of the Skylab. These calculations, using the quality factor of ICRP 60, show that the average CAM BFO equivalent dose is 0.46 Sv/year. Based on an approach that takes fragmentation into account, we estimate a calculation uncertainty of 15% if the uncertainty in the quality factor is neglected.

NASA BUDGET HEARING

The proposed space station came under vehement attack last week during a hearing on the National Aeronautics & Space Administration's (NASA) budget for fiscal 1995 held by the Subcommittee on Space of the House Committee on Science, Space & Technology. The hearing opened with a blistering statement from Rep. F. James Sensenbrenner Jr. (R.-Wis.), the ranking subcommittee Republican, assailing NASA's plans for joint space efforts with Russia that are to lead to an international space station (C&EN, Nov. 22, 1993, page 29). Citing the arrest last week of a Central Intelligence Agency official and his wife as alleged Russian spies, Sensenbrenner called the hearing's examination of space station plans involving Russia somewhat surreal, like measuring the size of the tea cups at the Mad Hatter's tea party. Sensenbrenner, who has long supported the space station, questions whether Russia is a trustworthy and reliable partner and whether the space station deal with Russia can be justified ...

Control of vibrational systems

Vibrational systems, characterized by their second-order or "spring-mass" nature, occur throughout engineering. Examples range from lightly damped structures, such as the proposed space station, to regional power system models. While the study of such vibrational systems has a long and rich history, concern has traditionally focused on the properties of passive, uncontrolled systems. The growing need to actively control large, complex systems of this type leads us to the study of controlled vibrational systems. We provide stability assuring constraints for compensator design. These constraints directly use the initial system model, thus avoiding the need for order reduction techniques with the associated problems of "spill-over" from the full to the reduced system model.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A general formulation for the nonlinear dynamics and control of orbiting flexible structures

A relatively general Lagrangian formulation for studying the dynamics of a large class of spacecraft characterized by interconnected flexible members forming a tree topology, is presented. Methodology and development of the computer code suitable for parametric dynamical study and control are briefly outlined. Versatility of the general formulation is demonstrated through dynamics studies of the Permanently Manned Configuration (PMC) of the proposed Space Station Freedom and the slewing dynamics and control of the two-link Mobile Servicing System (MSS) aboard Freedom. The PMC study indicates the effect of flexibility cannot be overlooked. Even a small disturbance on the main or stinger can result in unacceptable magnitudes of velocity and acceleration. The MSS study compares the system response subjected to the InPlane (IP) and Out-of-Plane (OP) maneuvers. Results indicate that, without control, the OP maneuver excites large yaw motion of the Space Station. Consequently, the OP maneuver has a large pointing error. Nonlinear control, based on the Feedback Linearization Technique, appears promising. By controlling the librational motion of the station, the performance of the OP maneuver improves significantly.

Control-structure interaction study of the proposed space station freedom

A relatively general formulation for studying the dynamics and control of an arbitrary spacecraft with interconnected flexible bodies has been developed accounting for transient system properties, shift in the center of mass, shear deformations, rotary inertias and geometric nonlinearities. This self-contained, comprehensive, numerical algorithm using system modes is applicable to a large class of spacecraft configurations of contemporary and future interests. Here, versatility of the approach is demonstrated through the dynamics and control studies aimed at the evolving Space Station Freedom.

Vibration Isolation in a Microgravity Environment

Many in-space research experiments require the microgravity environment attainable near the center of mass of the proposed space station. Since dynamic disturbances to the surrounding structure may undermine an experiment’s validity, isolation of these experiments is imperative. This paper summarizes analytical and experimental work accomplished to develop an isolation system which allows the pay load to float freely within a prescribed boundary while being kept centered with forces generated by small jets of air. An experimental setup was designed and constructed to simulate the microgravity environment In the horizontal plane. Results demonstrate the air jet control system to be effective in managing payload oscillatory response. An analytical model was developed and verified by comparing predicted and measured payload response. The mathematical model is then used to investigate payload response to disturbances likely to be present in the space station.

Impact probabilities on artificial satellites for the 1993 Perseid meteoroid stream

It is argued that the new but short-lived maximum in the activity profile of the Perseid meteor shower may yield an enhanced meteoroid flux in 1993 August. An estimate of the impact probability of Perseid meteoroid stream particles with Earth-orbiting satellites is presented. The impact probability for objects comparable in size to the Hubble Space Telescope and the Space Shuttle is found to be small but non-negligible. The probability of meteoroid impacts on the proposed Space Station is also discussed

European space station: An affordable and incremental design approach

This paper discusses a design approach and phased assembly sequence for a proposed European Space Station. The configuration architecture is assembled from a series of building-block elements that are delivered to orbit in an established sequence over several years. The first building-block is derived from the Columbus Man-Tended Free Flyer. Elements are launched by Ariane 5 although other transportation vehicles may be feasible. By the end of the decade, Europe will have many of the ingredients for the delivery and construction of its own Station, with the Ariane 5 launcher, the Columbus man-rated elements and the Hermes spaceplane. However, any initiative for a European Station will need to secure the commitment and support of European Space Agency member nations to succeed. It is therefore essential that an affordable and incremental design approach is followed from the outset. The concept presented in this paper attempts to focus on such an approach with a design that includes some significant features. Results should begin to flow from the first mission onwards to obtain early and visible benefits. Established space hardware can be given priority to contain development costs. Mission operations objectives can be matched to the available transportation scenario. The development timetable should be cautiously paced to spread out the expenditure milestones. Additional factors are reviewed in a separate paper that describes the life support, habitability and laboratory facilities of the proposed Station (ref. 1). The paper concludes with a review of selected design issues and recommendations for further study to support the feasibility of the concept.

An approach to dynamics of flexible orbiting systems with application to the proposed space station

Space Station Freedom will be a gigantic flexible structure, extending over 100 m, with the Habitation, Laboratory and Logistics modules located near its geometric center. The Mobile Servicing System, itself a highly elastic two-arm manipulator, will be responsible for integration, operation, maintenance and future evolution of the Space Station. The paper presents a relatively general approach for studying dynamics of such complex multibody time varying systems, characterized by interconnected beam and plate type members, forming the open tree topology. The formulation accounts for transient system inertias, shift in the center of mass, shear deformations, rotary inertias and geometric nonlinearities. The Lagrangian approach employs symbolic manipulation in conjunction with an efficient algorithm that identifies the system character under study for optimum allocation of computational resources. Versatility of the formulation is demonstrated through a dynamical study pertaining to several stages of the evolving Space Station.

ACS, others fail to stem space station

Despite a last-minute appeal by an unusual coalition of scientific societies, a Senate panel has voted to give the Bush Administration all the funds it requested for space station Freedom —thereby limiting money available for other scientific The day before the panel made its decision last week, a group of 14 scientific society presidents—including the American Chemical Society's S. Allen Heininger—sent a letter to every Senator. We are particularly concerned that the excessive cost of the proposed space station . . . threatens the vitality not only of the National Aeronautics & Space Administration's science and technology programs, but those of other independent agencies as well, the letter read. We are especially disturbed by the possibility of a reduction in funds for the National Science Foundation, the principal source of funding for the nation's fundamental science and engineering research. But their efforts had no effect on the Senate Committee on Appropriations' Subcommittee on VA, ...

Dynamics and control of an orbiting flexible mobile manipulator

This paper presents a Lagrangian formulation for studying the dynamics and control of the proposed Space Station based Mobile Servicing System (MSS) for a particular case of inplane libration and maneuvers. The simplified case is purposely considered to help focus on the effects of structural and joint flexibility parameters of the MSS on the complex interactions between the station and manipulator dynamics during slewing and translational maneuvers. The response results suggest that under critical combinations of parameters, the system can become unstable. During maneuvers, the deflection of the MSS can become excessive, leading to positioning error of the payload. At the same time the libration error can also be significant. A linear quadratic regulator is designed to control the deflection of the manipulator and maintain the station at its operating configuration.

System modes and dynamics of the proposed space station type configurations

The paper studies libration/vibration interaction dynamics of the space station Freedom during its evolutionary phases. To that end, a relatively general nonlinear formulation, applicable to a system of interconnected plate and beam-type structural members forming a tree topology is developed. System modes, obtained through a finite element analysis, are employed in the discretization process and the response study is purposely confined to the orbital plane to emphasize interactions between librational dynamics and flexibility. Finally, an approximate closed-form nonlinear solution of the problem is attempted using the variation of parameters method. Its validity is assessed through comparison with the numerically obtained results over a range of system parameters and initial conditions. Results provide information pertaining to the levels of librational and vibrational response and the associated acceleration tield, which may prove helpful in appropriately locating experiments and monitoring instruments. It may also aid in the planning of the control system. The analytical approach provides surprisingly close correlation with the more elaborate numerical procedure, thus promising better physical appreciation of the complex interactions as well as a considerable saving in the computational cost.

Nondestructive construction error detection in large space structures

Continuum modeling of large space structures is extended to the problem of detecting construction errors in large space structures such as the proposed space station. First-order dynamic sensitivity equations for structures involving eigenfrequencies, modal masses, modal stiffnesses, and modal damping are presented. Matrix equations relating changes in element parameters to dynamic sensitivities are summarized. The sensitivity equations for the entire dynamical system are rearranged as a system of algebraic equations with unknowns of stiffness losses at selected locations. The feasibility of the formulation is numerically demonstrated on a simply-supported Euler-Bernouilli beam with simulated construction defects. The method is next extended to large space structures modelled as equivalent continua with simulated construction defects.

Crew Quarters for Space Station

The only long-term United States manned space mission completed has been Skylab, which has similarities as well as differences to the proposed Space Station. With the exception of Skylab missions, there has been a dearth of experience on which to base the design of the individual Space Station Freedom crew quarters. Shuttle missions commonly do not have sleep compartments, only “sleeping arrangements”. There are provisions made for each crewmember to have a sleep restraint and a sleep liner, which are attached to a bulkhead or a locker. When the Shuttle flights began to have more than one working shift, crew quarters became necessary due to noise and other disturbances caused by crew task-related activities. Shuttle missions that have planned work shifts have incorporated sleep compartments. To assist in gaining more information and insight for the design of the crew quarters for the Space Station Freedom, a survey was given to current crewmembers with flight experience. The results from this survey were compiled and integrated with information from the literature covering space experience, privacy, and human factors issues.

Dynamics of interconnected flexible members in the presence of environmental forces: A formulation with applications

A relatively general formulation for studying the dynamics of spacecraft with interconnected flexible bodies is presented accounting for thermal deformations and transverse vibrations of the structural members. In addition, the shift in the center of mass of the system and the slewing maneuvers of the members are incorporated. The formulation can be applied to study the U.S. proposed Space Station as well as a large class of present and future spacecraft. An example illustrates application of the formulation. The model under study is a satellite with a central rigid body and a pair of appendages. The satellite response is investigated numerically over a range of system parameters and effect of the thermal deformations assessed. An approximate closed-form (analytical) solution of the problem is also obtained to quickly assess trends and gain better physical appreciation of response characteristics.

A dynamical study of the proposed Space Station type configuration

The planar libration-vibration interaction dynamics of the proposed Space Station is studied using a simplified model where the keel and solar panels are represented as beams and the central pressurized modules as a rigid body. In the beginning, the governing nonlinear, nonautonomous and coupled equations of motion are derived using the classical Lagrangian procedure. This is followed by a relatively general finite element analysis of the structure to arrive at the first seven system modes and associated frequencies. Next, a parametric analysis is undertaken, through numerical integration of the equations of motion in conjunction with the modal discretization, to assess the librational and vibrational response of the system. Finally, a closed form-solution of the simplified nonlinear problem is attempted using the variation of parameters (Butenin) method. Its validity is assessed through comparison with the numerical results over a range of system parameters and initial conditions. Results provide information pertaining to the levels of librational and vibrational response and associated acceleration fields, which may prove helpful in appropriately locating experiments and monitoring instruments. It may also aid in the planning of the control system. The analytical approach provides surprisingly close correlation with the more elaborate numerical procedure, thus promising a better physical appreciation of the complex interactions as well as a considerable saving in the computational cost.

Dynamics and control during slewing maneuvers

The paper presents a relatively general formulation for studying librational dynamics of a flexible platform supporting a mobile base connected to a series of slewing, flexible appendages. It is applicable to missions requiring slew maneuvers of antennas, telescopes, scientific instruments and, in particular, the U.S. proposed Space Station's Mobile Remote Manipulator System (MRMS). Application of the formulation is illustrated through three simple examples: (i) a satellite consisting of a rigid platform with a slewing, rigid appendage; (ii) a flexible beam-type platform representing the Space Station with a mobile, flexible, slewing arm; (iii) the SCOLE configuration representing the Space Shuttle-based flexible beam supporting a rigid reflector at its end. The analysis provides a useful insight into interactions between inertia parameters, orbit geometry, translational and slewing time histories, flexibility and initial conditions. Results suggest that under critical combinations of the parameters the system may become unstable. Application of the infinite time linear regulator is demonstrated to regain stability.

New group advices on Space Station

Scientific uses o f the proposed space station will be reviewed periodically by a new committee appointed by the National Aeronautics and Space Administration (NASA) in February. The Space Station Science and Applications Advisory Subcommittee will channel to NASA's Office of Space Science and Applications (OSSA) views of the scientific community on how the station can be used for scientific research and applications. The focus is equipment development, as well as operational procedures and capabilities.