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Code UG Weekly Notes 5-23-02

Status Report From: Microgravity Research Program Office
Posted: Thursday, May 23, 2002

Physical Sciences Division
Weekly Highlights for Week Ending 5/23/2002

*** Indicates item is appropriate for the HQ senior staff and may appear on the OBPR Web site: http://spaceresearch.nasa.gov

GENERAL

FLUID PHYSICS PI, ANDREAS ACRIVOS, RECEIVES NATIONAL MEDAL OF SCIENCE FROM PRESIDENT BUSH: President George W. Bush today announced the laureates of the 2001 National Medals of Science and National Medals of Technology, the nation's highest science and technology honors.

The National Medal of Science honors individuals in a variety of fields for pioneering scientific research that has enhanced our basic understanding of life and the world around us. The National Science Foundation administers the award established by Congress in 1959. Including this year's laureates, the honor has been conferred on 401 distinguished scientists and engineers. More information about the National Medal of Science is available at http://www.nsf.gov/nsb/awards/nms/.

The National Medal of Technology recognizes men and women who embody the spirit of American innovation and have advanced the nation's global competitiveness. Their groundbreaking contributions commercialize technologies, create jobs, improve productivity and stimulate the nation's growth and development. This award was established by Congress in 1980 and is administered by the Department of Commerce. Including this year's laureates, this honor has been bestowed on 120 individuals and 12 companies. More information about the National Medal of Technology can be found at http://www.ta.doc.gov/Medal/.

Andreas Acrivos, City College of the City University of New York, New York, N.Y. was also a member of the IMCE and REMAP task forces.

ISS FLIGHT PROGRAM

PAYLOAD RACK CHECKOUT UNIT (PRCU) (McIntosh/Johnson): The MSFC Microgravity Development Laboratory (MDL) PRCU is undergoing its first annual calibration and maintenance cycle since installation in January 2002 so that the system can continue to properly simulate International Space Station (ISS) interfaces for payload testing. The Boeing Co. is performing this work as part of their sustaining engineering contract to the Johnson Space Center. Work began on 5/13/02, and is scheduled for completion on 5/24/02. All measures are being taken, however, to be able to complete the work by 5/22/02 so that the Microgravity Science Glovebox (MSG) payloads can continue testing with the PRCU and remain on schedule.

PROPULSIVE SMALL EXPENDABLE DEPLOYER SYSTEM (ProSEDS) (Wallace/Johnson): The ProSEDS flight system, with a new EMI filter design, has successfully passed two thermal vacuum cycles. With this success, a new flight version of this unit can be installed into the test chamber on 5/22/02 for the remaining six thermal vacuum cycles. The Air Force has slipped the launch date for the DELTA launch vehicle and ProSEDS from mid-July to mid-September.

*THERMAL ENCLOSURE SYSTEM (TES) MODIFICATIONS AND VERIFICATION TESTS (Smith/King/Holloway): The TES, which provides a controlled thermal environment for Protein Crystal Growth (PCG) payloads, is being provided to the Observable Protein Crystal Growth Apparatus (OPCGA) project as Government Furnished Equipment (GFE). The TES, which was originally procured for use in the short duration missions of Spacelab and Spacehab, had to be modified to meet the long duration performance and environmental requirements of the International Space Station (ISS). These modifications have recently been completed and were verified last week by the successful completion of the TES functional and thermal performance tests. The TES is now being turned over to the OPCGA project and will immediately begin hardware integration with the OPCGA flight unit and integrated payload verification testing. The OPCGA is manifested to fly on ISS flight 12A.1 in May 2003.


SCIENCE HIGHLIGHTS

COMBUSTION SCIENCE:

QUANTITATIVE INTERPRETATION OF OPTICAL EMISSION SENSORS FOR MICROGRAVITY EXPERIMENTS: Dr. Greg Smith of the Molecular Physics Laboratory of SRI International leads this ground-based project to develop optical emission sensor strategies for microgravity combustion experiments. The specific goal of this project is to develop and demonstrate quantitative relationships between flame emission measurements and flame properties. Recently, LIF quenching measurements of Swan band C2(d-a) were made in the various low pressure flames to provide the decay information needed in the mechanism and to deduce excited state C2(d) production rate parameters from the emission data. Measurements were completed for eight flames, involving hydrogen, ethane, and ethylene fuels, and air and nitrous oxide oxidizers. Temperature data was taken by laser-induced fluorescence using 15 rotational lines in the R branch of the OH(A-X) 0-0 band near 307 nm. After careful corrections for the line strength, quenching, and absorption, rotational populations were obtained from which temperatures are determined. The final analysis, currently underway, will relate the emission data the excited state C2(d) production rate.

LOW STRETCH DIFFUSION FLAMES OVER A SOLID FUEL: This ground-based program, led by S. Olson of NASA Glenn, is geared toward experimentally demonstrating that microgravity flame characteristics can be generated in a normal gravity environment through proper scaling of the system. Such a demonstration will provide us with the information needed to develop a new Earthbound method of accurately evaluating materials flammability in various gravitational environments from normal gravity to microgravity, including the effects of partial gravity low stretch rates found on the Moon (1/6g) or Mars (1/3g). A series of 5.18-second Zero Gravity Facility tests was recently completed. A horizontal cylindrical polymethylmethacylate (PMMA) tube was ignited in normal gravity and a flame was allowed to stabilize. Upon release of the experiment in the drop tower, the buoyant force was abruptly eliminated, and the flow field transitioned from buoyancy-dominated to pure forced convection. Immediately after the experiment is released into microgravity, the flame is seen to overshoot the final purely forced standoff distance, as seen in the sample standoff time history. In the buoyant atmosphere, a sooty region is visible in the flame, with a thin, blue flame region on the outer edge (away from the fuel surface) of the soot zone. Once the experiment is dropped, the flame responds rapidly (e.g. standoff peaks in 0.2 s) and the soot zone becomes significantly brighter. The flame behaves violently during this period, most likely due to vapor jetting. After a relatively long period (from 1.5 s to 3 s), the soot zone almost entirely disappears, leaving only a blue flame region. In tests with a final forced stretch rate of 3 1/s, the blue flame is seen to extinguish after approximately 4 s. To assist in explaining the transient behavior of flames, a numerical model has been developed. Transient terms in both the gas- and solid-phases are included in the model. The model is able to reproduce most of the experimental observations. These include the transient overshoot of the flame standoff distance, the surface temperature drop and the transient time scales. Thus, the model provides a very useful tool to analyze the details of the flame behavior, especially at low-stretch rate.

FLUID PHYSICS:

SEGREGATION IN BINARY MIXTURES UNDER GRAVITY: Fluid Physics PI Prof. Jenkins (Cornell University) and his team employ kinetic theory for a binary mixture to study particle segregation in granular soilids by size and/or mass in a gravitational field. Simple segregation criteria are obtained for spheres and disks that are supported by numerical simulations. Particle segregation in agitated systems is still not well understood, although it is important in the manufacturing of pharmaceuticals, powder metallurgy, coal and mineral processing, solid state chemistry, and geophysics. [J. T. Jenkins and D. K. Yoon, "Segregation in Binary Mixtures under Gravity," Volume 88, Number 19 Physical Review Letters 13may 2002.]


ACTIVE ELECTROSTATIC STABILIZATION OF LIQUID BRIDGES IN LOW GRAVITY: Fluid Physics PI Prof. Marston (Washington State University and his team performed experiments aboard NASA's low-gravity KC-135 aircraft, it was found that rapid active control of radial electrostatic stresses can be used to suppress the growth of the (2,0) mode on capillary bridges in air. This mode naturally becomes unstable on a cylindrical bridge when the length exceeds the Rayleigh - Plateau (RP) limit. The RP instability of a liquid cylinder in the absence of gravity normally prevents the formation of cylindrical liquid bridges which have a length greater than their circumference. Capillary bridges having a small amount of electrical conductivity were deployed with a ring electrode concentric with each end of the bridge. A signal produced by optically sensing the shape of the bridge was used to control the electrode potentials so as to counteract the growth of the (2,0) mode. Occasionally the uncontrolled growth of the (3,0) mode was observed when the length far exceeded the RP limit. Rapid breakup from the growth of the (2,0) mode on long bridges was confirmed following deactivation of the control. [David B. Thiessen, Mark J. Marr-Lyon And Philip L. Marston, "Active electrostatic stabilization of liquid bridges in low gravity," J. Fluid Mech. (2002), vol. 457, pp. 285-294. 2002]

PHYSICAL OPTICS TREATMENT OF THE SHADOWGRAPH: Fluid Physics PI Prof. David Cannell (University of California, Santa Barbara) and his ream present an analysis of the shadowgraph method of visualizing convective flows based on physical optics, treating the refractive-index perturbation caused by the flow as a transmission grating. The shadowgraph method is very commonly used for visualizing convection patterns. It is used to study thermal convection of fluids and fluid mixtures, and to study electro-convection of nematic liquid crystals. It is simple to implement and provides a noninvasive measurement of the lateral index of refraction modulation of the convecting fluid. In the shadowgraph method, a parallel beam of light passes through the fluid layer, and the transmitted beam develops an intensity pattern some distance from the fluid layer. The spatial distribution of the intensity reveals the convection pattern directly. This phenomenon is easily understood qualitatively on the basis of geometrical optics. Rays of light deviate slightly in passing through the fluid, bending toward regions of higher refractive index and away from regions of lower index. Various patterns in thermal convection of an isotropic fluid as well as normal rolls in electroconvection of a nematic liquid crystal are considered. The results differ significantly from those of geometrical optics, showing that use of the shadowgraph as a quantitative tool for amplitude measurements should not, in general, be based on geometrical optics. [Steven P. Trainoff and David S. Cannell, "Physical optics treatment of the shadowgraph," Physics of Fluids Volume 14, Number 4 April 2002]

UPCOMING EVENTS

Additional meetings and symposia can be found at: http://microgravity.grc.nasa.gov/ugml/ugmltext.htm

The MRPO Program Calendar can be found at:
http://webcal.msfc.nasa.gov/webevent.cgi?cmd=opencal&cal=cal85&

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