STS-94 Mission Science Report # 24s
Wednesday, July 16, 1997 6 p.m. CDT
As researchers aboard the first Microgravity Science Laboratory mission prepared for Columbia’s return to Earth Thursday, their counterparts at Spacelab Mission Operations Control Center in Huntsville, Ala., began tallying the mission’s research accomplishments -- which often surpassed expectations.
"We've done better than anybody expected,” said Mission Scientist Dr. Michael Robinson, looking back at the wealth of science information collected during the course of this 16-day mission, set to end Thursday at 5:47 a.m. CDT when the Space Shuttle lands at Kennedy Space Center in Florida.
“A highlight of the mission is that everything worked so well,” said Robinson, of the Marshall Space Flight Center in Huntsville, where the microgravity science mission is managed. “All orbiter, Spacelab and payload systems have performed superbly. We are very pleased to have been able to take full advantage of this reflight opportunity,” added Mission Manager Teresa Vanhooser, also of Marshall:
This record-setting mission provided fundamental new knowledge in the principal scientific fields of combustion, biotechnology and materials processing.
More than 200 fires, or combustion experiment runs were conducted on MSL-1. Only 144 had been scheduled for the mission.
A study of the phenomena of soot resulted in discovery of a new mechanism of flame extinction caused by radiation of soot. Scientists found that the flames emit soot sooner than expected. These findings have direct impact on spacecraft fire safety, as well as the theories predicting the formation of soot -- which is a major factor as a pollutant and in the spread of unwanted fires.
Seventeen tests were completed in the soot study -- three more than originally scheduled -- on this mission and the shortened April Shuttle flight. “Every one worked and yielded good data,” said lead scientist Dr. Gerard Faeth of the University of Michigan at Ann Arbor. “That’s beyond my wildest dreams.”
Another combustion study -- this one on spherical flame structures, or flameballs -- resulted in the MSL-1 crew igniting the weakest flames ever burned either in space or on Earth. Flameball powers are as low as one watt -- or 1/50th the power of a birthday candle. The study also resulted in the longest burning flames ever ignited in space, burning for the entire 500-second duration of the experiment run. These tests provide new information for models of weak combustion processes needed to develop cleaner, more fuel- efficient internal combustion engines.
From the experiment, said lead investigator Dr. Paul Ronney of the University of Southern California in Los Angeles, “we can learn the burning limits of fuel mixtures. It gives us an idea of just how lean a fuel can be -- and still burn. It may lead to better gas mileage and less auto emissions.” Other benefits include improved fire safety for future spacecraft.
Experiments processed in MSL-1’s unique, levitating furnace facility known as TEMPUS yielded the first measurements of specific heat and thermal expansion of glass-forming metallic alloys. These measurements -- never taken before on Earth -- are fundamental measurements necessary for modeling industrial materials systems needed to manufacture new and better products.
The study has resulted in more than 120 melting cycles with zirconium, with a maximum temperature of 2,000 degrees Centigrade and was able to undercool to 340 degrees -- the highest temperature and largest undercooling ever achieved in space. The TEMPUS investigators also have provided the first measurements of viscosity of palladium-silicon alloys in the undercooled liquid alloy which are not possible on Earth. One TEMPUS lead investigator, Robert J. Bayuzick of Vanderbilt University in Nashville, said, “I’ll go out on a limb and say this is the most successful mission in microgravity research that’s ever been flown. It went perfectly.” His study focused on the changes that certain metals undergo as they are cooled from a liquid to a solid state in a containerless environment. “What we showed,” he said, “in this particular regime is that relative to one another, there’s no difference in the effect on nucleation between the moderate flow and the turbulent flow conditions. That’s a unique result. This kind of experiment has never been performed before, ever, in history.”
Studies conducted in the multipurpose Middeck Glovebox have demonstrated its value in supporting a variety of experiments in microgravity -- including those on this mission in the areas of liquid and bubble behavior, fluids-based heat transfer devices, and solid-liquid mixtures. In a testimony to the glovebox’s usefulness, the crew has performed well over 100 test runs in the facility -- more than double the number planned.
Real progress has been made during this mission in learning how to control and position liquid drops, according to Mission Scientist Robinson. Experiments on this mission have demonstrated that quiescent positioning and control of the rotation of a liquid drop can be achieved using acoustic levitation in the microgravity of space. The investigation of internal flows in a free drop has provided information on the dependence of acoustic torque on acoustic pressure and the internal flows in a liquid drop. This study is allowing researchers to assess a potential method of mixing which could lead to improvements in chemical manufacturing, petroleum technology, and the cosmetics and food industries.
In another glovebox study on MSL-1, researchers have obtained the first data for the nonlinear free decay frequency for a totally free drop, and the first accurate data for drop deformation as a function of acoustic pressure. This has lead to discovery of an effective method for bubble positioning and manipulation in microgravity. These findings could lead to techniques that eliminate or counteract the complications that bubbles cause during materials processing.
Large droplets of fuel were ignited and information collected on the burn rates, flame shape and radiation emitted in another glovebox experiment. This study resulted in the first microgravity experiment in which droplet arrays were burned.
In a novel and unplanned twist to this experiment, scientists -- pleased with the single-droplet tests -- decided to expand the study to run tests using two droplets. The pairs of drops were positioned on a fiber and ignited simultaneously. This provided a bonus to researchers as they observed the interaction of the droplets. The experiment’s lead investigator, Dr. Forman Williams of the University of California at San Diego, called the view of the two droplets “the most beautiful set of twins I’ve ever seen.” Only 52 test runs were planned on MSL-1. Yet 125 runs were completed -- a 240 percent science return. Information from the study is expected to improve theoretical models of combustion.
In the coarsening in solid-liquid mixtures experiment -- also in the glovebox -- researchers studied a process that can cause metals to weaken or fail in alloy products, such as turbine blades in aircraft engines. By examining this process in space, the design and control of metals processing on Earth may be improved.
In another experiment, researchers were able to take a very pure look at the combustion process without the effects of gravity. The Droplet Combustion Experiment has provided scientists with fundamental knowledge of the burning process -- and may provide a method for verifying which complex, chemical model accurately describes the process. It may also lead to cleaner and safer ways to burn fuels.
In this experiment, researchers pushed the envelope of knowledge of combustion by setting a fire at the lowest atmospheric pressure yet during a mission. The study’s lead investigator, Dr. Forman Williams of the University of California at San Diego, said, “On the ground, there have been a lot of studies on heptane. But all have been less than 2 millimeters in diameter. This is the first complete burn of a 3-millimeter diameter heptane droplet.” Williams said that “because in the atmosphere of normal air, we were able to observe a fuel droplet that burns for a longer period of time.” Additionally, as a fuel droplet burned in a spherical shape, the heat dissipated outward, and actually extinguished the flame before all the fuel vapor was completely burned away. This gave researchers that very pure look at the combustion process.
During MSL-1, samples were processed in the Large Isothermal Furnace to study the diffusion of tracers, or impurities, in melted germanium -- an element widely used as a semiconductor and alloying agent. This mission marks the first time diffusion in semiconductors has been studied in space. Findings may have applications for improving the performance of electronic components made from semiconductor materials, such transistors and integrated circuits.
The Physics of Hard Sphere experiment, which examined changes that occur during transition of a substance from liquid to solid and solid to liquid, could improve the design of metallic alloys and processing techniques. Initial findings from this mission show model crystals in this experiment grew faster in space than on Earth. Also, the time scale for particle movement or diffusion is considerably different than in low-gravity.
Researchers have gained yet a better understanding through MSL-1 of what makes certain types of heat transfer devices fail in space. In a study involving the Capillary-driven Heat Transfer Device, scientists have examined the device’s ability to transfer heat away from a particular location. In the future, these devices may be used to transfer heat from electrical equipment to radiators on spacecraft.
The benefits of these systems are that they weigh less than conventional units because they operate on evaporation and condensation, and are more economical because they do not require power. The experiment’s lead investigator, Dr. Kevin Hallinan of the University of Dayton, Ohio, said, “With the science learned on this mission, we’ve been able to characterize boundaries of what we call unstable operations which accelerates this transition to this failed -- or disrupted state. We are closer to our goal of understanding why the Capillary-driven Heat Transfer devices have failed in space -- yet succeed in 1-G (on the ground). We are confident new designs can be rendered that will work.”
A plant growth experiment on MSL-1 is examining the effect of space on certain types of plants. Scientists hope the study reveals how to manipulate processes to improve plant growth on Earth. Findings may also verify evidence that plants grown in microgravity require less metabolic energy to produce lignin, permitting greater production of secondary metabolites -- a source of many medicinal drugs. Secondary metabolites also may be used to attract, repel or poison insects. Plants being studied aboard MSL-1 include a source of the antimalarial drug artemisinin; a plant used in chemotherapy treatment of cancer; and a species widely used in the paper and lumber industries.
More than 700 crystals of various proteins were grown on MSL-1 during its 16-day mission. Knowledge of protein structures is very important to our everyday lives, as many diseases involve proteins, either directly or indirectly. The microgravity environment of space allows researchers to grow larger and higher quality crystal specimens. Back on Earth, scientists will perform X-ray diffraction studies on the specimens to determine their structures. Better understanding of a protein’s structure could allow scientists to design more effective drugs to treat diseases such as cancer, diabetes, alcoholism, chagus, AIDS and Alzheimer’s
In addition to contributing new scientific knowledge, the first Microgravity Science Laboratory has served as a bridge to America’s future in space, spanning the gap between today’s Spacelab and tomorrow’s International Space Station. It has used Spacelab as a transition vehicle -- testing hardware, facilities and procedures that will be used on Space Station.
Flying for the first time on MSL-1, the EXPRESS Rack, designed and developed at Marshall, demonstrated quick and easy installation of experiment and facility hardware in orbit. The rack will be used on Space Station.
Two payloads -- the Physics of Hard Spheres experiment and the Astro/Plant Generic Bioprocessing Apparatus experiment -- were flown on MSL-1 to check the design, development and adaptation of EXPRESS hardware. During this mission, the two experiments were transferred from the Shuttle middeck to the EXPRESS Rack, operated, and then returned to the middeck. “The procedure went beautifully with no problems,” said Cindy Sanderson, EXPRESS Operations Controller at Marshall. “We're very satisfied with our demonstration of the EXPRESS rack,” said Mission Manager Vanhooser: “The goals we set were accomplished.”
In all, 25 primary experiments, four glovebox investigations and four accelerometer studies flew on this mission of Columbia. The experiments were contributed by scientists from four international space agencies -- NASA, the European Space Agency, the German Space Agency and the National Space Development Agency of Japan.
A gauge to the amount of science research conducted aboard this mission is the record number of commands sent from Spacelab Mission Operations Control Center at Marshall to experiments aboard Columbia. The more than 35,000 commands sent broke the previous record of 25,837 set in 1994.
Now, said Mission Scientist Robinson, “as Columbia prepares to return to Earth -- its mission accomplished -- it is time for researchers to get down to the task of analyzing the data. That’s going to keep everybody very busy for quite a while."
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