Kevin McPherson

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

Acceleration Environment of the International Space Station

Measurement of the microgravity acceleration environment on the International Space Station has been accomplished by two accelerometer systems since 2001. The Microgravity Acceleration Measurement System records the quasi-steady microgravity environment, including the influences of aerodynamic drag, vehicle rotation, and venting effects. Measurement of the vibratory/transient regime, comprised of vehicle, crew, and equipment disturbances, has been accomplished by the Space Acceleration Measurement System-II. Until the arrival of the Columbus Orbital Facility and the Japanese Experiment Module, the location of these sensors, and therefore, the measurement of the microgravity acceleration environment, has been limited to within the United States Laboratory.

A Summary of the Quasi-Steady Acceleration Environment on-Board STS-94 (MSL-1)

The continuous free-fall state of a low Earth orbit experienced by NASAs Orbiters results in a unique reduced gravity environment. While microgravity science experiments are conducted in this reduced gravity environment, various accelerometer systems measure and record the microgravity acceleration environment for real-time and post-flight correlation with microgravity science data. This overall microgravity acceleration environment is comprised of quasi-steady, oscillatory, and transient contributions. The First Microgravity Science Laboratory (MSL-1) payload was dedicated to experiments studying various microgravity science disciplines, including combustion, fluid physics, and materials processing. In support of the MSL-1 payload, two systems capable of measuring the quasi-steady acceleration environment were flown: the Orbital Acceleration Research Experiment (OARE) and the Microgravity Measurement Assembly (MMA) systems Accelerometre Spatiale Triaxiale most evident in the quasi-steady acceleration regime. Utilizing such quasi-steady events, a comparison and summary of the quasi-steady acceleration environment for STS-94 will be presented

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.

Effects of experiment location and orbiter attitude on the residual acceleration onboard STS-73 (USML-2)

A knowledge of the quasi-steady acceleration environment on the NASA Space Shuttle Orbiter is of particular importance for materials processing experiments which are limited by slow diffusive processes. The quasi-steady (less than 1 HZ) acceleration environment on STS-73 (USML-2) was measured using the orbital acceleration research experiment (OARE) accelerometer. One of the facilities flown on USML-2 was the crystal growth furnace (CGF), which was used by several principal investigators (PIs) to grow crystals. In this paper the OARE data mapped to the sample melt location within this furnace is presented. The ratio of the axial to radial components of the quasi-steady acceleration at the melt site is presented. Effects of orbiter attitude on the acceleration data is discussed.