STS-75 Day 7 Highlights
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- On Wednesday, February 28, 1996, 7 a.m. CST, STS-75 MCC Status Report # 13
- With the focus of work aboard Columbia turning to weightless
investigations of the United States Microgravity Payload, flight
controllers in Houston and Huntsville continue to gather as much data
from the tethered satellite as possible before its batteries run out.
- USMP experiments are collecting data on various materials science
investigations including crystal growth, materials solidification and
- Half of the crew enjoyed a half day of free time as is customary on
two-week long shuttle flights. During the break, Pilot Scott
Horowitz, Mission Specialist Maurizio Cheli and Payload Specialist
Umberto Guidoni discussed the flight with the C-SPAN network and
answered questions from viewers.
- The ground commanding to the tethered satellite began yesterday and
is expected to continue today as it passes within range of the ground
station at the Johnson Space Center. Payload officials will again
take snapshots of data from the satellite to determine its health
before its batteries completely discharge; this is expected within the
next couple of days.
- On Wednesday, February 28, 1996, 6 a.m. CST, STS-75 Payload Status Report # 11
reports: (5/15:42 MET)
- As the third United States Microgravity Payload (USMP-3) performs
its early primary science operations aboard the STS-75 Shuttle
mission, the Tethered Satellite System (TSS) science teams at Spacelab
Mission Operations Control continue to receive data from the
free-flying tethered satellite.
- Overnight, Commander Andrew Allen maneuvered Columbia through a
series of orbiter calibrations for NASA Marshall Space Flight Center's
Advanced Automated Directional Solidification Furnace (AADSF) which
performed a "dress rehearsal" for their first experiment sample
processing, scheduled for early Thursday morning. The Shuttle's
on-board acceleration sensors made measurements that gave the AADSF
science team valuable information about how they will make adjustments
to enhance science collection during this first experiment run.
AADSF will grow three cylinder-shaped crystals using samples of
lead-tin-telluride, a material used to make infrared radiation
detectors and lasers. This process is expected to take a number of
days to complete. It is important to conduct this kind of experiment
in microgravity in order to provide insight into the influence of
gravity-driven fluid flows on crystal formation.
- Scientists hope that information gathered from this experiment will
lead to the production of better, faster semiconductors for components
used in products ranging from automobiles to computers. The speed and
amount of information that can be stored and sent by computers and
high-tech electronics, using sophisticated semiconductor materials,
may be increased by better control of how the semiconductors'
- AADSF findings will help researchers develop improved processes for
semiconductor materials that cost less to produce. "The ages of
humanity are known for the type of materials humans used, such as
'Stone Age,' 'Bronze Age,' etcetera," observed AADSF Principal
Investigator Dr. Archie Fripp of NASA's Langley Research Center. "If
we can contribute in any way to the development of the 'Semiconductor
Age,' then we have really achieved something."
- Rensselaer Polytechnic Institute's Isothermal Dendritic Growth
Experiment (IDGE), has completed its "science of opportunity" phase
and, now that USMP-3 is the primary mission payload, has entered its
main science gathering mode. The investigation team members are
studying the three-dimensional shape of their tiny "pine tree-shaped"
dendrite crystals. The device consists of a thermostat containing a
growth chamber filled with a transparent substance that imitates the
behavior of metals and solidifies as it cools to form these dendrites.
- IDGE scientists, led by Dr. Martin Glicksman, used the preliminary
acceleration data gathered by NASA Lewis Research Center's Space
Acceleration Measurement System (SAMS) and Orbiter Acceleration
Research Experiment (OARE) to evaluate their opportunity science data
and to relate the size and speed of the dendrite growths with
accelerations in the microgravity environment. Also, scientists
looked for relationships between the angle of the dendrites' direction
and the direction from which microgravity influences their growth.
The experiment's science team at Rensselaer will use their telescience
capabilities to remote-command and receive data from their IDGE
- Early in the evening, the Critical Fluid Light Scattering
Experiment, or ZENO, science team, led by Dr. Robert Gammon of the
University of Maryland, completed the collection of dynamic light
scattering data just above their xenon sample's "critical point." The
critical point is the exact temperature and pressure at which the
sample is simultaneously in both the liquid and vapor
phase. Understanding how matter behaves at the critical point can
provide insight into a variety of physics problems, ranging from state
changes in fluids to changes in the magnetic properties of solids.
This knowledge will prove valuable in a wide variety of applications,
including liquid crystals and superconductors.
- Meanwhile, science teams for the Tethered Satellite System
demonstrated their own brand of telescience throughout the night,
commanding and receiving data from their reactivated instruments on
the satellite. The Marshall Space Flight Center's Research on Orbital
Plasma Electrodynamics (ROPE), the Italian Space Agency's Research on
Electrodynamic Tether Effects (RETE) and the Second University of
Rome's Magnetic Field (TEMAG) experiments continue to collect what TSS
Mission Scientist Dr. Nobie Stone called "very good data" about the
satellite's interaction with its surrounding region of charged
particles and magnetic fields.
- Scientists report that they can measure a sunlight-induced
electrical charge on the satellite as it moves through the daylight
and night portions of its orbit around the Earth. Later today, the
satellite's ROPE and RETE instruments will measure the effects of
electron gun firings from the Shuttle Electrodynamic Tether System
(SETS) on the satellite and its environment.
- Also today, science data collection by the USMP-3 experiments will
continue, and the crew will perform a Forced Flow Flamespreading Test
(FFFT), an investigation led by Dr. Kurt Sacksteder of NASA's Lewis
Research Center, the first in a series of hands-on combustion
experiments conducted in the Middeck Glovebox.
- On Wednesday, February 28, 1996, 5 p.m. CST, STS-75 MCC Status Report # 14
- NASA managers decided today not to return Columbia to the Tethered
Satellite for either a close inspection or a possible retrieval after
concluding that propellant margins would not be adequate to support
- Officials were asked to investigate the possibility of a rendezvous
with TSS. After reviewing propellant margins, spacewalking
considerations, and radar requirements, a decision was made not to
fire Columbia's engines to begin what would have been a six-day
phased approach to meet up with the satellite.
- The Tethered Satellite is currently 7,100 nautical miles ahead of
Columbia with the distance between the two spacecraft closing at the
rate of 340 nm with every revolution of the Earth. The two spacecraft
will pass within 50 nm of one another about 11:48 p.m. Thursday, at a
Mission Elapsed Time of 7/09:30.
- Earlier today, Mission Specialist Jeff Hoffman set a record for the
most hours flown on a Space Shuttle, breaking the previous record of
975 hours 18 minutes held by Kathy Thornton. Hoffman will break the
1,000 hour mark aboard the Shuttle on Thursday.
- Work with the United States Microgravity Payload experiments continues
with the astronauts supporting a variety of investigations including
crystal growth, materials solidification and fluid dynamics.
- Columbia is functioning normally, with no problems being tracked by
the flight control team as the Shuttle orbits the Earth every 90
minutes at an altitude of 180 statute miles.
- On Wednesday, February 28, 1996, 6 p.m. CST, STS-75 Payload Status Report # 12
reports: (06/3:42 MET)
- With the shift to the third United States Microgravity Payload
(USMP-3) as the primary science on STS-75, the Tethered Satellite
System (TSS) is in a "science of opportunity" mode. The spirit of
cooperation was evident at Spacelab Mission Operations Control as the
USMP-3 team worked with their TSS colleagues to accommodate
post-tether-break science plans.
- After ground controllers successfully commanded the free-flying
satellite's on-board instruments to turn on yesterday, data began to
flow to TSS science teams in Huntsville. TSS Mission Manager Robert
McBrayer emphasized that "a tremendous amount of cooperation" has made
this possible. The satellite is now operating on battery power, with
enough energy to last another day, depending on how commanding and
data resources are handled.
- TSS Mission Scientist Dr. Nobie Stone confirmed that "we have a very
interesting and high-quality data set. We are still taking data and
already are seeing evidence that some very significant things will
come out of this mission." The science of opportunity being
formulated by the entire TSS Investigators Working Group involves
firing electron accelerators, known as "electron guns," located in
Columbia's cargo bay, to see if the satellite's instruments detect
plasma disturbances as they spread out through the ionosphere. This
experiment has been executed once, and there are opportunities to
repeat it several times as the Shuttle and satellite move toward a
closer approach of about 56 nautical miles.
- One of the TSS primary mission objective may be met in spite of the
overall situation. Dr. Marino Dobrowolny, the Italian Space Agency
TSS mission scientist, noted that a main goal was to characterize the
relationship between current collected and voltage across the tether.
During tether deployment, current and voltage levels were observed
under conditions that cannot be duplicated in the laboratory. He said
"we have shed light on plasma physics questions raised in the 1920s
that have never before been understood and are too difficult to
duplicate in the laboratories or model with computers."
- Data gathered while the satellite was deployed is better than
scientists anticipated. There are cases where twice as much current
was collected than was predicted by the best computer models
available. This may indicate some degree of ionization around the
satellite even during the period when the satellite thrusters were not
on when no enhanced gas cloud was present. In fact, when satellite
thruster operations were performed, the current went even higher, up
to 580 milliamps, compared to the 270 milliamps predicted by the
- In addition, after commanding current to flow in the tether,
energetic electrons were observed on the satellite with energies
ranging up to 10 kiloelectronvolts -- ten times the energy of the
electron beams that were emitted. This provides valuable clues into
the physical processes by which electrons become energized.
- The acceleration that should be seen with a 12.2 mile (19.7
kilometer) tether hanging below the satellite was predicted
theoretically to be 0.9 milli-g's, or less than one-thousandth of
Earth's gravity. The satellite's linear accelerometer data measured
accelerations within this range, indicating the tether to be intact.
Based on this, it may be possible to tell if the tether length changes
by more than 4 kilometers due to orbital debris or micro-meteoroid
hits over the next day or so. Dr. Stone noted that "this would be an
interesting and useful data point for future applications. If it
doesn't sever, that's even better information." The accelerometer
also is providing tether dynamics data that indicates a possible
swinging back and forth motion known as libration.
- During the post-break, free-flight phase, the Research on Orbital
Plasma Electrodynamics (ROPE) equipment, located on one of the
satellite's booms, is collecting information about the plasma sheath
created by applying a voltage to the boom tip. Understanding this
effect that may be significant to geosynchronous satellites, such as
those that transmit television and telephone signals, where
differential charging occurs on the order of kilovolts.
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