1994 American crewed spaceflight
STS-62 was a Space Shuttle program mission flown aboard Space Shuttle "Columbia". The primary payloads were the USMP-02 microgravity experiments package and the OAST-2 engineering and technology payload, both in the orbiter's cargo bay. The two-week mission also featured a number of biomedical experiments focusing on the effects of long duration spaceflight. The landing was chronicled by the 1994 Discovery Channel special about the Space Shuttle program and served as the show's opening. A C.F. Martin backpacker guitar was also flown aboard "Columbia" during the mission.
Mission highlights.
Day 1.
Flight Day One (Friday, March 4) consisted of ascent operations and reconfiguration of the orbiter in order to support orbital operations, an OMS-2 burn to circularize "Columbia"'s orbit to a orbit, USMP-2 activation, PSE operations, APCG activation, CPCG operations, RMS checkout, DEE operations, CGBA activation. The payload bay doors were opened at 10:26 am EDT.
Day 2.
On Flight Day Two (Saturday, March 5), the astronauts took turns on the crew cabin exercise facility in an effort to slow down the effects of muscle atrophy. Pilot Andrew M. Allen and mission specialist Charles D. Gemar also spent time in the Lower Body Negative Pressure Container. Mission specialists Pierre J. Thuot and Marsha S. Ivins started the Protein Crystal Growth Experiment (PCGE) and the Physiological Systems Experiment (PSE), while scientists on the ground in the Payload Operations Control Center controlled eleven other experiments mounted in the orbiter's payload bay. Mission controllers in Houston also investigated a problem in a fuel line pressure sensor on one of "Columbia"'s three Auxiliary Power Units (APUs). Higher than normal pressures were detected and then returned to normal after engineers powered up heaters on the unit. The APUs provided hydraulic power to operate key landing systems and only one of the three was needed for a successful landing. However, flight rules called for a shortened mission in the event a single unit was lost.
Day 3.
On Flight Day Three (Sunday, March 6), following a morning of medical studies, the crew spent the last half of the day exercising and continuing to study the behavior of a space station truss model in weightlessness. Pilot Allen and mission specialists Ivins and Gemar each took a turn on a stationary bicycle mounted in "Columbia"'s middeck. The stationary bike had long been a staple of shuttle flights to allow exercise that countered the effect of weightlessness on the muscles. The bike aboard "Columbia", however, featured a new mounting system of shock-absorbing springs that was evaluated as a method of keeping vibrations from exercise, which could disturb sensitive experiments, to a minimum.
Also, Gemar set up a model of a scaffold-like truss structure that could be applied to a future space station design in the lower deck. The model, linked to sensitive recorders in a shuttle locker, was used to determine the characteristics of such structures in orbit. The model and its reactions were studied in several different configurations during the day.
Other activities for the crew included photography of the glow created as the orbiter's outer skin interacted with atomic oxygen in orbit, and continued monitoring of protein crystal growth experiments in the cabin.
Although not highly visible except to the Earth-bound scientists watching over them, "Columbia"'s wide assortment of external payloads continued their investigations throughout the day. The second United States Microgravity Payload (USMP-2) experiments continued to produce a wealth of data for scientists on the ground.
The Critical Fluid Light Scattering Experiment, or ZENO, science team reported that they expected to locate the critical temperature of xenon at "any time." Team members closely watched computer data traces which indicate their experiment was very near the critical temperature—the goal of a lengthy, methodical "sensitive" search process. This was a more precise search for the critical temperature after its location had been determined within a narrow band. Once the temperature was located, the team spent nearly 24 hours taking a good look at the phenomenon they waited years to see. They studied the properties of xenon at its critical point, taking subtle optical measurements in the region surrounding it. A fluid's "critical point" occurs at a condition of temperature and pressure where the fluid is simultaneously a gas and a liquid. By understanding how matter behaves at the critical point, scientists hope to gain a better insight into a variety of physics problems ranging from phase changes in fluids to changes in the composition and magnetic properties of solids.
The Space Acceleration Measurement System (SAMS) continued to measure the microgravity environment on the USMP-2 carrier in support of the four other experiments on board. The SAMS team began sending results of their data collection during various orbiter activities to the crew, as they were interested in how they could minimize their influence on the microgravity environment. Measurements were made with the system at specific times when microgravity disturbances were caused by events such as crew exercise and movement of the orbiter's Ku-band antenna. Such observations also collected "signatures" which the team were able to easily identify in future data.
A related system, the Orbital Acceleration Research Experiment (OARE), was managed by NASA's Johnson Space Center. It was useful on missions such as USMP-2 where it was important to accurately characterize a wide variety of disturbances in the microgravity environment. Working closely with SAMS, the OARE recorded any low-frequency activity such as the orbiter's friction with the rarefied upper atmosphere. SAMS was most suitable for recording higher-frequency activity such as crew exercise.
The Isothermal Dendritic Growth Experiment (IDGE) continued to assemble data to test theories concerning the effect of gravity-driven fluid flows on dendritic solidification of molten materials. Upon completion of its first phase of pre-programmed operations the previous night, the dendritic experiment entered its second phase of crystal growth when team members began sending commands to their experiment from the ground using a unique set of capabilities known as "telescience." This allowed them to get the best possible data from their investigation.
The Advanced Automated Directional Solidification Furnace (AADSF) studied the directional solidification of semiconductor materials in microgravity. Downlinked experiment data from the third day of the mission indicated that solidification of a crystal of mercury cadmium telluride took place, and the AADSF science team constantly monitored this slow but steady progress. Testing the AADSF in microgravity was beneficial because on Earth, gravity causes fluids to rise or fall within the melted portion; a warm liquid is less dense than a cool one and will rise to the top of the melt. These convective movements of molten material contribute to physical flaws in the internal structure of the growing crystal. Such flaws affect a crystal's overall electrical characteristics, and consequently, its usefulness in electronic devices.
The MEPHISTO team reported that they had gathered good data with their directional solidification furnace. During the day, the team troubleshooted a problem discovered on the previous night with a troublesome "Seebeck measurement." This electronic signal measured changes in the microstructure of a solidifying metal, and was conducted on one of three experiment samples of bismuth-tin. Other measurement techniques were used on the two remaining samples later in the mission; both these samples operated nominally.
Flight controllers had a quiet Sunday in Mission Control with no significant troubles seen aboard the spacecraft. A reading of high pressure that was seen in a fuel line to one of the shuttle's three auxiliary power units earlier in the flight had dissipated, and controllers became confident the APU would operate well if needed. However, they continued to closely watch the readings from that area. The crew began eight hours of sleep at 4:53 pm.
Day 4.
Flight Day 4 began on Monday, March 7 at 12:53 am. The crew started its day with a medley of armed forces anthems sung by the U.S. Military Academy Glee Club. The medley honored all four branches of the service which were represented by the STS-62 crew. During the time of the mission, Commander Casper was a colonel in the U.S. Air Force, Pilot Allen a major in the U.S. Marine Corps, mission specialist Gemar a lieutenant colonel in the U.S. Army, and mission specialist Thuot was a commander in the U.S. Navy.
After completing their post-sleep activities, the crew started the payload work for the day. The crew performed checks of the Protein Crystal Growth Experiment and the rodents that were housed in the middeck as part of the Physiological Systems Experiment. Gemar also continued his work with the Middeck 0-Gravity Dynamics Experiment, designed to study the fundamental, non-linear, gravity-dependent behavior of hybrid scaled structures. Understanding these structures became important for designers of large space structures such as the International Space Station.
Casper conducted a special presentation about the Space Acceleration Measurement System. A frequent flyer on the shuttle, SAMS used accelerometers to take measurements of on-board vibrations and accelerations. Such disturbances, though slight, could have affected the sensitive microgravity experiments. SAMS measurements allowed scientists to adjust their experiments to improve their scientific results.
Allen and Gemar got a half-day off from their busy schedule operating the many microgravity experiments on the mission. Due to the long duration of the mission, each crew member received two half-days off during the 14-day mission.
The other astronauts spent the first half of the day working with the Middeck 0-Gravity Dynamics Experiment, or MODE, and a model of a truss structure which was under consideration for use on a future space station. The truss model, set up to float free in the middeck, was analyzed to determine its behavior in weightlessness.
Around the clock, experiments with the U.S. Microgravity Payload-2, the Office of Aeronautics and Space Technology-2, the Space Shuttle Backscatter Ultraviolet instrument and the Limited Candidate Duration Materials Exposure experiments continued to operate, many of them being controlled by scientists on the ground. The SSBUV instrument operated since the first day of the flight, and plans were made by its ground controllers on Flight Day 4 to attempt to detect sulfur dioxide emissions from volcanoes in Central America. The objective of the observations by SSBUV were to investigate whether such emissions low in the atmosphere were detectable from orbit. SSBUV's measurements in general were used to fine-tune satellites that monitored the ozone and other gases in the Earth's atmosphere. The crew began its eight-hour sleep period at 4:53 pm EST.
During USMP-2 operations on Flight Day 4, the Critical Fluid Light Scattering Experiment, or ZENO, team reported overnight that they started seeing behavior in the fluid xenon unlike any they had seen on Earth. They believed this meant the experiment had passed through the xenon sample's critical point. Meanwhile, the team continued their delicate temperature manipulations in order to verify what they had seen. Once the team was certain they had located the critical point, they planned to conduct a series of precise measurements in the area surrounding it using laser light scattering. When xenon is at or extremely near its critical point—the point where it is simultaneously a liquid and a gas—patches of the otherwise clear substance briefly take on a "milky" iridescence. Closer to the critical point, the milky-white areas are larger and exist for longer periods. When a laser light is passed through the sample in these areas, fluctuations in the sample's density cause the light to be scattered.
Team members for the MEPHISTO furnace began running a series of metal solidification studies and received analyzable data. On Monday, the team made much progress in overcoming some difficulty they had been experiencing with one of the experiment's electronic measurements and successfully completed a Seebeck run. The Seebeck measurement is an electrical signal which measures temperature variations during crystal growth at the boundary where liquid becomes solid—the solidification front. MEPHISTO was used to conduct a series of melting and solidification cycles on three identical rod-shaped samples of a bismuth-tin alloy. During these runs, temperature, velocity and shape of the solidification front were measured in order to study the behavior of metals and semiconductors as they solidified.
Team members of the Isothermal Dendritic Growth Experiment (IDGE), said they were pleased with the performance of their apparatus and the data they acquired during USMP-2. While dendrite growth was taking place, two 35 mm cameras took photographs for post-mission analysis. When a dendrite growth cycle was completed, the small crystalline structure was re-melted and another grown at a different "supercooling" temperature. Dendrites were grown at 20 different levels of supercooling ranging up to approximately 1.3 degrees Celsius. Supercooling is the