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Monday, July 7, 1997, 7 a.m. CDT
STS-94 Mission Science Report # 09s

After short breaks in their busy schedules, crew members of the Microgravity Science Laboratory mission are back to business, working around the clock to fulfill the objective of their mission -- fundamental scientific research in space. Most of the last 24 hours focused on combustion and materials science investigations in space.

Aboard Columbia Sunday, crew members completed three runs of the Laminar Soot Experiment -- a combustion investigation that could lead to a more environmentally friendly fuel burning engine. Using ethylene gas, Payload Specialist Dr. Greg Linteris completed one run in the morning, Payload Specialist Dr. Roger Crouch completed one in the afternoon and Payload Commander Dr. Janice Voss completed one late Sunday evening.

Lead scientist Dr. Gerard Faeth of the University of Michigan at Ann Arbor reported to the crew that the flames so far have been “super” and that the science team is very pleased with experiment data it has gathered. “We’ve learned that as we increase pressure, the amount of soot in the flame and the amount of soot it emits increases,” explained Faeth. “It’s probably one of the reasons that high pressure combustion processes -- such as what goes on in a bus engine -- tend to emit a lot of soot.”

Two samples of the experiment analyzing diffusion in liquid Lead-tin-telluride were processed in the Large Isothermal Furnace over the last 24 hours. Linteris initiated the first sample shortly before his shift ended at noon Sunday and Crouch initiated the experiment’s second run early Sunday evening. Early this morning, Mission Specialist Dr. Donald Thomas initiated a third run, and it is continuing to process in the facility.

The study, led by Ms. Misako Uchida of Ishikawajima-Harima Heavy Industries in Tokyo, Japan, is aimed at determining the diffusion coefficient -- a fundamental quantity which describes the diffusion process -- of liquid lead-tin-telluride. Diffusion is the process by which liquid metals mix without stirring -- similar to how food coloring disperses in a glass of water without stirring. Liquid lead-tin-telluride is a potential material for use in manufacturing infrared detectors and lasers. Uchida reported the completed runs were “very good.”

On Sunday, science teams determined that the Large Isothermal Furnace has been using more helium than expected. The furnace, a vacuum-heating facility that is designed to uniformly heat large samples, uses a helium purge to rapidly cool the samples. The science team is assessing the helium consumption rate, but estimates that it is not likely the facility will run out of helium before testing is completed.

In the German levitating furnace, known as TEMPUS, a sample of a glass-forming metallic liquid performed just as planned, according to principal investigator Dr. William Johnson of the California Institute of Technology in Pasadena. This experiment is measuring the thermophysical properties -- heat capacity, thermal conductivity, nucleation rates, surface tension, viscosity and thermal expansion -- of a complex alloy of titanium, zirconium, copper and nickel. “This is the first time that some of these fundamental measurements have been ever been taken,” said Johnson.

Early this morning, Thomas activated another experiment in the TEMPUS facility which studies how glass forms in zirconium-based alloys. Zirconium is an element found chiefly in ceramic and refractory compounds. This study is led by Dr. Hans Fecht of the Technical University Berlin in Germany. Results from TEMPUS investigations could lead to improved techniques for processing metallic alloys and in turn better products.

Voss completed another series of runs of the Droplet Combustion Experiment Sunday. That marked the beginning of the second of three phases of the study to map the burning characteristics of heptane fuel droplets over a range of atmospheric pressures. The first phase burned the fuel droplets at one atmospheric pressure, the same as on Earth. This phase is burning the droplets at one-half atmospheric pressure. “In each phase, we are keeping the pressure the same and slowly reducing the oxygen to see if the fuels can still burn and if so, how they burn,” said project scientist Dr. Vedha Nayagam of NASA’s Lewis Research Center in Cleveland, Ohio. “On Earth, we encounter low combustion scenarios -- for instance, in gas turbines -- so it’s important to know what happens when pressure is reduced.”

In one atmospheric pressure the flame burned out, leaving a residue of fuel. At the lower pressure, the flame is larger so the same results were expected, but the flame collapsed back on the droplet, completely consuming it. “It’s surprising to see the droplet burn out completely,” said Nayagam. “This tells us something about the extinction mechanisms.”

Linteris attempted to conduct another test this morning but the droplet did not ignite. The science team is reviewing data to understand why it didn’t. Also, the Droplet Imaging Camera, which records information about droplet size, is not working. The science team is proceeding with experiment runs while it assesses the problem.

Sunday, Crouch conducted an investigation that could result in an improved understanding of the mechanisms leading to the unstable operation and sometimes failure of specialized heat transfer devices in space operations. In space, capillary-pumped loops are used to transfer heat away from electrical devices to space radiators. These devices are not always reliable. However, they are very attractive because they require no power to operate, and are very economical in terms of weight, an important consideration in satellite design.

According to investigator Dr. Kevin Hallinan of the University of Dayton in Dayton, Ohio, the experiment is providing researchers with a better understanding of the mechanisms behind the unstable operation and occasional failure of these devices. “The experiment has shown us that the device is failing for reasons we didn’t expect, which provides new insight into potential failure mechanisms that may have not been considered before. We’re quite pleased with the results so far.”

Sunday evening, Voss successfully rebooted an electronics unit of the EXPRESS Rack -- powering it down then back up -- to restore the facility’s communication and telemetry capabilities. The EXPRESS Rack is designed for quick and easy installation of hardware and experiments on the International Space Station. Two experiments -- the Physics of Hard Spheres Experiment and the ASTRO/Plant Generic Bioprocessing Apparatus -- are being conducted in the EXPRESS Rack to test its design, development and adaptation.

The facility was experiencing problems relaying housekeeping information -- temperature, air pressure and water flow -- to the ground and receiving ground commands. The Physics of Hard Spheres science team is now able to send up commands, but the ASTRO/Plant Generic Bioprocessing Apparatus science team is still unable to command from the ground and is continuing to troubleshoot the problem. Crew members are able to command the experiment from the Spacelab, so there is no impact to science. Restoring housekeeping data functions would require rebooting the entire system which would interrupt science, so the EXPRESS Rack team is relying on other, indirect methods of gathering this information.

Ahead, Linteris will complete the series of runs under way in the Droplet Combustion Apparatus. Thomas will work in the Middeck Glovebox to conduct a study of techniques used to control the position and motion of free drops of liquid in low-gravity. Linteris will complete another test of the soot experiment, and Thomas will begin the first of six runs to study the diffusion process of tracers, or impurities, in melted germanium, an element widely used as a semiconductor and alloying agent.

The next scheduled Public Affairs status report will be issued at approximately 6 p.m., July 7.


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