3.1 Major Mission Accomplishments

• Completed first dedicated United States Micro-gravity Laboratory flight laying the ground work for Space Station Freedom science operations.
• Completed 31 microgravity experiments in five basic areas: fluid dynamics, crystal growth, combustion science, biological science, and technology demonstration.
• Introduced several new microgravity experiment facilities for multiple users and multiple flights (including the Crystal Growth Furnace, Drop Physics Module, and the Surface Tension Driven Convection Experiment).
• Demonstrated the efficiency of interactive science operations between crewmembers and scientists on the ground for optimizing science return.
• Completed longest period of protein crystal growth in Space Shuttle program.
• Conducted iterative crystal growing experiments where chemical compositions were altered based upon microscopic observations of growth processes.
• Completed longest Space Shuttle mission (13 days 19 hours 30 minutes) and the first Extended Duration Orbiter (EDO) flight of the Space Shuttle Program.
• Demonstrated versatility of the new Glovebox facility for crewmember interaction with multiple experiments for maximum science.

The Space Shuttle Columbia rocketed to orbit for the longest Shuttle flight in history. Columbia touched down almost 14 days later returning with data and specimens amassed from an important suite of microgravity experiments. Shuttle mission STS-50 carried the first United States Microgravity Laboratory (USML-1) to space, conducting long-duration microgravity experiments. Microgravity is a term that refers to a gravitational acceleration that is small when compared to the gravitational attraction at Earth's surface. Through the action of free fall (e.g., Space Shuttle orbiting Earth), the local effects of gravity are greatly reduced, thus creating a microgravity environment.

During Columbia's extended mission, scientist crew members, working inside the Spacelab long module carried in Columbia's payload bay, conducted more than 30 microgravity investigations and tests. To maximize the scientific return from the mission, experiments took place around-the-clock. The investigations fell under five basic areas of microgravity science research: fluid dynamics (the study of how liquids and gases respond to the application or absence of differing forces), materials science (the study of materials solidification and crystal growth), combustion science (the study of the processes and phenomena of burning), biotechnology (the study of phenomena related to products derived from living organisms), and technology demonstrations that sought to prove experimental concepts for use in future Shuttle missions and on Space Station Freedom.

Three new major experiment facilities were flown on USML-1. They were the Crystal Growth Furnace, Surface Tension Driven Convection Experiment apparatus, and Drop Physics Module. An additional piece of new hardware on this flight was the versatile Glovebox, which permitted "hands-on" manipulation of small experiments while isolating the crew from the liquids, gases, or solids involved. Some of the USML-1 experiments are described below.

3.2 Spacelab Experiments

The Crystal Growth Furnace (CGF) is a reusable facility for investigating crystal growth in microgravity. It is capable of automatically processing up to six large samples at temperatures up to 1,600 degrees Celsius. Additional samples can be processed upon performing manual sample exchange. Two methods of crystal growth, directional solidification and vapor transport, were used on USML-1. By analyzing the composition and the atomic structure of crystals grown without the dominating influence of gravity, scientists will gain insight into correlations between fluid flows during solidification and the defects in a crystal. CGF operated for 286 hours and processed seven samples, three more than scheduled, including two gallium arsenide semiconductor crystals. Gallium arsenide crystals are used in high-speed digital integrated circuits, optoelectronic integrated circuits, and solid state lasers. Crew members were able to exchange samples, using a specially designed flexible Glovebox, to provide the additional experiment operations.

The Surface Tension Driven Convection Experiment (STDCE) was the first space experiment to use state- of-the-art instruments to obtain quantitative data on surface tension-driven flows on the surface of liquids over a wide range of variables in a microgravity environment. Very slight surface temperature differences are sufficient to generate subtle fluid flows on the surface of liquids. Such flows, referred to as "thermocapillary," exist on fluid surfaces on Earth. However, thermocapillary flows on Earth are very difficult to study because they are often masked by much stronger buoyancy-driven flows. In microgravity, buoyancy-driven flows are greatly reduced permitting the study of this phenomenon. STDCE provided the first observations of thermocapillary flow in a curved-surface fluid and demonstrated that surface tension is a powerful driving force for fluid motion.

The Drop Physics Module (DPM) permitted the study of liquids without the interference of a container. Liquids on Earth take the shape of the container that holds them. Furthermore, the materials that make up the container may chemically contaminate the liquids under study. The DPM uses acoustical (sound) waves to position a drop in the center of a chamber. By studying drops in this manner, scientists have the opportunity to test basic fluid physics theories in the areas of nonlinear dynamics, capillary waves, and surface rheology (changes in the form and flow of matter). Crew-members, through manipulation of the sound waves, were able to rotate, oscillate, merge, and even split drops. In another test, the crew members were able to create the first compound drop, a drop within a drop, to investigate a process that could eventually be employed to encapsulate living cells within a semi-permeable membrane for use in medical transplantation treatments.

The Glovebox facility perhaps proved to be the most versatile new space laboratory equipment introduced in the last few years. The Glovebox offers crew members the opportunity to manipulate many different kinds of test activities and demonstrations and materials (even toxic, irritating, or potentially infectious ones) without making direct contact with them. The Glovebox has a viewport (window) into a clean workspace, built-in gloves for manipulation of samples and equipment, a negative air pressure system, a filter system, and an entry door for passing materials and experiments into and out of the work area. The primary use of the Glovebox was to selectively mix protein crystals and monitor their growth. The Glovebox allowed crew members to periodically change compositions to optimize the growth, a first for space. Other tests conducted inside the Glovebox included studies on candle flames, fiber pulling, particle dispersion, surface convection in liquids, and liquid/container interfaces. Sixteen tests and demonstrations in all were conducted inside the Glovebox. The Glovebox also provided crew members the opportunity to perform backup operations on the Generic Bioprocessing Apparatus which were not planned.

Another of the Spacelab experiments was the Generic Bioprocessing Apparatus (GBA), a device for processing biological materials. The GBA processed 132 individual experiments with volumes of several milliliters. The apparatus studied living cells, microorganisms used in ecological waste treatment, and the development of brine shrimp and wasp eggs, and other biomedical test models which are used in cancer research. One sample studied, Liposomes, consist of spherical structures that could be used to encapsulate pharmaceuticals. If this biological product can be formed properly, it could be used to deliver a drug to a specific tissue in the body, such as a tumor.

3.3 Middeck Microgravity Experiments

While most STS-50 experiments were conducted in the U.S. Microgravity Laboratory, others were operating in Columbia's mid-deck. Included in the mid-deck experiments were studies of Protein Crystal Growth, Astroculture, and Zeolite Crystal Growth.

The Protein Crystal Growth experiment made its fourteenth shuttle flight, but USML-1 represented the first time crew members were able to optimize growth conditions using the Glovebox facility. About 300 samples were seeded from 34 protein types including HIV Reverse Transcriptase Complex (an enzyme that is a chemical key to the replication of the AIDS virus) and Factor D (an important enzyme in human immune systems). About 40 percent of the proteins flown will be used for X-ray diffraction studies. The increased size and yield can be attributed to the extended crystal growth time provided by this mission. Scientists on the ground will use X-ray crystallography to study each protein's three-dimensional structure which, when determined, may aid in controlling each protein's activity through rational drug design.

The Astroculture™ experiment evaluated a water delivery system to be used for supporting the growth of plants in microgravity. Plant growth in space is looked at as a possible method of providing food, oxygen, purified water, and carbon dioxide removal for long-term human habitation in space. Since fluids behave differently in microgravity than they do on Earth, plant watering systems used on Earth do not adapt well to microgravity use.

The Zeolite Crystal Growth experiment processed 38 separate samples which were mixed in the Glovebox. Zeolite crystals are used to purify biological fluids, as additives in laundry detergents, and in waste clean-up applications.

3.4 Extended Duration Orbiter (EDO)

STS-50 not only marked the first U.S. Microgravity Laboratory flight, but also the first Extended Duration Orbiter flight. To prepare for long-term (months) microgravity research aboard Space Station Freedom, scientists and NASA need practical experience in managing progressively longer times for their experiments. The Space Shuttle usually provides a week to ten days of microgravity. Thanks to the Extended Duration Orbiter kit, the Space Shuttle orbiter Columbia remained in orbit for almost 14 days and future missions with Columbia could last as long as a month. The kit consists of extra hydrogen and oxygen tanks for power production, extra nitrogen tanks for the cabin atmosphere, and an improved regeneration system for removing carbon dioxide from the cabin air.

One of the practical aspects of remaining in space longer will be the requirement to maintain crew member health and performance. During STS-50, crew members conducted biological tests as part of the EDO Medical Project. Crew members monitored their blood pressure and heart rate and took samples of the cabin atmosphere during the flight. They also evaluated the Lower Body Negative Pressure (LBNP) device as a countermeasure to the normal reduction of body fluids that takes place in space. If the beneficial effects of the LBNP could last for 24 hours, it would improve crew member performance on reentry and landing.

3.5 Other Payloads

The STS-50 crew members also operated the Shuttle Amateur Radio Experiment (SAREX). Through the experiment, crew members were able to contact short wave radio operators, a Polynesian sailing vessel replica out in the Pacific Ocean, and selected schools around the world.

The Investigations into Polymer Membrane Processing (IPMP) experiment has flown previously on six Shuttle missions. It is used to study the formation of polymer membranes in microgravity with the aim of improving their quality and use as filters in biomedical and industrial processes.

4 Mission insignia

The mission insignia shows the space shuttle in the typical flying position for microgravity. The USML banner extends from the payload bay, in which the spacelab module with the text μg—the symbol for microgravity. Both the stars and stripes on the USML letters as well as the highlighted United States on the earth below the shuttle depict the fact that it was an all-american science mission.

5 Related articles

• Space science
• Space shuttle
• List of space shuttle missions
• List of human spaceflights chronologically

6 External links

• NASA PAO page about STS-50

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