Kenneth Hrovat

Interpreting the International Space Station Microgravity Environment

*† ‡ § The International Space Station (ISS) serves as a platform for microgravity research for the foreseeable future. A microgravity environment is one in which the effects of gravity are drastically reduced which then allows physical experiments to be conducted without the overpowering effects of gravity. A physical environment with very low-levels of acceleration and vibration has been accomplished by both the free fall associated with orbital flight and the design of the International Space Station. The International Space Station design has been driven by a long-standing, high-level requirement for a microgravity mode of operation. The Space Acceleration Measurement System has been in operation for nearly four years on the ISS measuring the microgravity environment in support of principal investigators and to characterize the ISS microgravity environment. The Principal Investigator Microgravity Services project functions as a detective to ascertain the source of disturbances seen in the ISS microgravity environment to allow correlation between that environment and experimental data. Payload developers need to predict the microgravity environment that will be imposed upon an experiment and ensure that the science and engineering requirements will be met. The Principal Investigator Microgravity Services project is developing an interactive tool to predict the microgravity environment at science payloads based on user defined operational scenarios. These operations (predictions and post-analyses) allow a researcher to examine the microgravity acceleration levels expected to exist when their experiment is operated and then receive an analysis of the environment which existed during their experiment operations. Presented in this paper will be descriptions of the environment predictive tool and an investigation into a previously unknown disturbance in the ISS microgravity environment.

Comparison tools for assessing the microgravity environment of space missions, carriers and conditions

The microgravity environment of the NASA Shuttles and Russias Mir space station have been measured by specially designed accelerometer systems. The need for comparisons between different missions, vehicles, conditions, etc. has been addressed by the two new processes described in this paper. The Principal Component Spectral Analysis (PCSA) and Quasi- steady Three-dimensional Histogram (QTH) techniques provide the means to describe the microgravity acceleration environment of a long time span of data on a single plot. As described in this paper, the PCSA and QTH techniques allow both the range and the median of the microgravity environment to be represented graphically on a single page. A variety of operating conditions may be made evident by using PCSA or QTH plots. The PCSA plot can help to distinguish between equipment operating full time or part time, as well as show the variability of the magnitude and/or frequency of an acceleration source. A QTH plot summarizes the magnitude and orientation of the low-frequency acceleration vector. This type of plot can show the microgravity effects of attitude, altitude, venting, etc.

Microgravity Environment on the International Space Station

ABSTRACT The International Space Station is being assembledon-orbit to serve as a research platform for the nexttwenty years. A primary feature of this research platformwill be its microgravity environment – an environment inwhich the effects of gravity are drastically reduced. Aphysical environment with very low-levels ofacceleration and vibration has been accomplished byboth the free fall associated with orbital flight and thedesign of the International Space Station. TheInternational Space Station design has been driven by along-standing, high-level requirement for a microgravitymode of operation. Various types of data are gathered when scienceexperiments are conducted, with common variablesbeing temperature, pressure, voltage, and power. Theacceleration levels experienced during operation shouldbe factored into the analysis of the experiment results ofmost microgravity experiments. To this end, the NASAFundamental Microgravity Research in the PhysicalSciences program has had the Space AccelerationMeasurement System recording the acceleration levelsto support microgravity researchers for over twelve yearsof Shuttle missions, three years on Mir, and now nearlythree years of International Space Station operations. The Fundamental Microgravity Research in thePhysical Sciences program also supports the PrincipalInvestigator Microgravity Services project to assist theprincipal investigators with their analysis of theacceleration (microgravity) environment. The PrincipalInvestigator Microgravity Services project providescataloged data, periodic analysis summary reports,specialized reports for experiment teams, and real-timedata in a variety of user-defined formats.Characterization of the various microgravity carriers(e.g. Shuttle and International Space Station) is alsoaccomplished for the experiment teams. In the future, the Principal Investigator MicrogravityServices project will provide a detailed predictiveanalysis of the microgravity environment for particularpayloads in specified locations. This will assist greatly inthe operational payload planning process. In addition, aneural-network-based system is planned which willautomatically interpret the environment in real-time andpresent the results to users in an easily understoodformat. Presented in this paper will be a short description ofhow microgravity disturbances may affect someexperiment classes, a snapshot of the microgravityenvironment, and a view into how well the space stationis expected to meet the user requirements. ABBREVIATIONS AND ACRONYMS

Motion of Air Bubbles in Water Subjected to Microgravity Accelerations

The International Space Station (ISS) serves as a platform for microgravity research for the foreseeable future. A microgravity environment is one in which the effects of gravity are drastically reduced which then allows physical experiments to be conducted without the over powering effects of gravity. During his 6-month stay on the ISS, astronaut Donald R. Pettit performed many informal/impromptu science experiments with available equipment. One such experiment focused on the motion of air bubbles in a rectangular container nearly filled with de-ionized water. Bubbles were introduced by shaking and then the container was secured in place for several hours while motion of the bubbles was recorded using time-lapse photography. This paper shows correlation between bubble motion and quasi-steady acceleration levels during one such experiment operation. The quasi-steady acceleration vectors were measured by the Microgravity Acceleration Measurement System (MAMS). Essentially linear motion was observed in the condition considered here. Dr. Pettit also created other conditions which produced linear and circulating motion, which are the subjects of further study. Initial observations of this bubble motion agree with calculations from many microgravity physical science experiments conducted on shuttle microgravity science missions. Many crystal-growth furnaces involve heavy metals and high temperatures in which undesired acceleration-driven convection during solidification can adversely affect the crystal. Presented in this paper will be results showing correlation between bubble motion and the quasi-steady acceleration vector.

Microgravity Acceleration Environment of the International Space Station (panel)

This paper examines the microgravity environment provided to the early science experiments by the International Space Station vehicle which is under construction. The microgravity environment will be compared with predicted levels for this stage of assembly. Included are initial analyses of the environment and preliminary identification of some sources of accelerations. Features of the operations of the accelerometer instruments, the data processing system, and data dissemination to users are also described.

Experiment-to-experiment disturbance of microgravity environment

The STS-87 Shuttle mission carried the Fourth United States MicroGravity Payload (USMP-4) as one of the primary payloads. Four USMP-4 science experiments were installed on two carriers in the cargo bay of the Shuttle. The Confined Helium Experiment (CHeX), located on the aft carrier, was particularly susceptible to vibrations in several frequency ranges due to structural resonances of the CHeX apparatus and the extreme sensitivity of the sample to vibrations. Shortly after activation of the USMP-4 payload, a strong, vibratory disturbance within the susceptibility region of the CHeX apparatus was detected. After investigating the characteristics of the disturbance and the time at which it first appeared, it was deduced that the vibration was generated by cooling fans in the Isothermal Dendritic Growth Experiment (IDGE). This paper will summarize the development of the conflict, briefly describe the disturbance source, and the susceptibility of the CHeX apparatus, and summarize the results of post-mission tests of IDGE.