Progress report three for the On-Planet team for Friday Feb., 25, 2000
For this week the On-Plane
team continued to focus on issues dealing with on-planet experimentations,
human physiological studies, and the required hardware:
1) Experiments
involving human physiology
An
Approach to Counteract Impairment of Musculoskeletal Function in Space
Goal:
·
To study the effects of
space flight on musculoskeletal functions by measuring maximal force and power
output during voluntary leg press exercise
·
To determine changes in
the cross-sectional area (CSA) of thigh muscles
·
To determine changes in
the muscle activation pattern of the quadriceps femoris
Approach:
An ergometer was specially
designed for measurement of muscle activity. The ergometer uses the inertia of
a fly-wheel to provide resistance during both shortening (concentric) and
lengthening (eccentric) muscle actions. The test protocol incorporated strength
measurements of isometric, concentric and eccentric muscle actions, assessing
strength and velocity of different types of muscle actions. In addition, EMG
activity from the knee extensor group was measured during maximal isometric
action. The EMG data will provide information on stimulation of the muscles by
the nervous system.
In a collaborative effort
with experiment E029, the CSA of the knee extensor muscle group was measured
before and after space flight by using Magnetic Resonance Imaging (MRI). All
measurements were taken before and after the 17-day space flight.
Hardware:
Electromyograph (EMG)
Ergometer III
Magnetic Resonance
Imaging (MRI) Device
Cardiovascular
Adaptation to Zero Gravity
Goal:
1. To investigate in detail
the cardiovascular adaptation to microgravity, including the overall
circulatory responses to the headward fluid shift and the impact on
cardiovascular control mechanisms.
2. To test the validity of
24-hour head-down tilt as a model of microgravity by comparing data obtained in
preflight simulation studies and during actual flight in the same group of
crewmembers.
Approach:
Data were collected in the
following sessions:
Preflight
Head-Down
Tilt Simulation Study, Autonomic Function Test, Lower Body Negative Pressure
(LBNP) Test, Supine-Standing Measurements, SVOP Flow and Compliance, SVOP Flow,
Compliance and Hyperemic Blood Flow, Resting CV with upright 30%, 60% and 100%
Maximal exercise
Inflight
CVP
Measurements, Leg Volume Measurement, Echocardiography, Resting CV, Resting CV
with upright 30% and 60% maximal exercise, Resting CV with upright 30%, 60% and
100% maximal exercise, SVOP flow and compliance, Descent/Reentry HR, BP and ECG
Postflight
Autonomic
Function Test, Lower Body Negative Pressure (LBNP) Test, Supine-Standing
Measurements, SVOP Flow and Compliance, SVOP Flow, Compliance and Hyperemic
Blood Flow, Resting CV with Upright 30%, 60% and 100% Maximal Exercise
Hardware:
Acetylene Rebreathing
Cardiac Output System
Analog Data Recorder
(RACAL)
Bicycle Ergometer
Biomedical
Instrumentation Port (BIP) - Launch
Biomedical
Instrumentation Port (BIP) - Reentry
Blood Pressure
Monitor, Continuous
Blood Pressure
Monitor, Intermittent
Cardiovascular /
Cardiopulmonary Interface Panel (CV/CP)
Cassette Data Tape
Recorder (CDTR)
Echocardiograph
Gas Analyzer/Mass
Spectrometer (GAMS)
Heart Rate Monitor
Infusion Pump
Life Sciences
Laboratory Equipment (LSLE) Microcomputer
Lower Body Negative
Pressure Device (LBNP)
Mercury-in-Silastic
"Whitney" Strain Gauge
Minioscilloscope
Physiological
Monitoring System (PMS)
Stocking
Plethysmograph
Strip Chart Recorder
System for
Measurement of Central Venous Pressure (SMCVP)
System for Venous
Occlusion Plethysmography (SVOP)
Tilt Frame
Venous Occlusion Cuff
Controller (VOCC)
Venous Occlusion
Plethysmography - Cuff Gauge
Clinical
Trial of Melatonin as Hypnotic for Neurolab Crew
Goal:
1)
Test the hypothesis that pre-sleep adminstration of melatonin during microgravity
exposure results in decreased sleep latency, reduced nocturnal sleep
disruption, and improved sleep efficiency, without significantly affecting the
spectral composition of the sleep-EEG, as compared to pre-sleep administration
of placebo during space flight.
2)
Test the hypothesis that the circadian rhythms of body temperature and
urinary melatonin will be appropriately synchronized to their required
sleep-wake schedule during the mission.
3)
Test the hypothesis that space flight results in substantial disruption of
sleep, even when sleep occurs at an appropriate circadian phase.
4)
Test the hypothesis that the improved sleep resulting from the pre-sleep
administration of melatonin as compared to placebo during spaceflight will
enhance next day alertness, vigilance, psychomotor performance and short term
memory. Subjects will undergo cognitive performance testing on the days
following polysomnography.
Approach:
During sleep, the subjects
were fully instrumented to record sleep stage, sleep latency, and related
parameters. Complete polysomnographic measurements included
electroencephalogram (EEG), electrocardiogram (ECG), electromyogram (EMG) and
electrooculogram (EOG), along with rib cage and abdominal motion measurements,
oxygen saturation, and heart rate. Polysomnographic data were recorded over
four separate nights, with two subjects studied per night. Drug administration
was such that one subject was medicated and the other was unmedicated on any
given night.
As a part of sleep
monitoring, the subjects participated in a double-blind study of the effects of
melatonin on sleep quality. On each of the 16 nights, subjects took a capsule
from a personal melatonin/placebo kit containing either melatonin or a
cellulose placebo 15 to 30 minutes prior to sleep. In this double-blind study,
four crew members were randomly assigned to two groups. Each group consisted of
two crew members. The subjects were unaware of the contents of the capsule, and
this information was available to those on the ground only if a medical problem
required breaking the code.
Subjects completed a short
oral sleep/wake log upon awakening every day. Activity levels were recorded
with the Life Sciences Laboratory Equipment Activity Monitor (Actigraph) placed
around the wrist. Two 24-hour periods of urine monitoring were performed to
allow determination of urinary melatonin excretion. In conjuction with the
periods of urine collection, two 32-hour periods of continuous body temperature
monitoring were done to document the circadian phase of the subjects. Core body
temperature was measured with an ingestible body temperature pill. A battery of
computer-based cognitive and subjective tests were performed during the days
following the four nights of full instrumentation sleep recording. The
cognitive tests were designed to assess alertness, vigilence, pyschometric
performance, and short-term memory. Cognitive testing was performed on the
following day after a sleep monitoring session so that the results could be
compared to the polysomnographic data.
Hardware:
Actillume
Digital Sleep
Recorder (DSR)
Electrode Impedance
Meter (EIM)
Electrode Kit
IBM ThinkPad
Computer
Ingestible
Temperature Monitoring System (ITMS)
Life Sciences
Laboratory Equipment (LSLE) Activity Monitor (Actigraph)
Life Sciences
Laboratory Equipment (LSLE) Microcomputer II
Life Sciences
Laboratory Equipment (LSLE) Refrigerator / Freezer
Modular Support
Structure (MOSO) with Automated Blood Pressure (ABP)
Personal Melatonin /
Placebo Kit
Personal Sleep Kit
Respiratory
Inductive Plethysmograph (RIP) Suit
Sleep Net
Thermoelectric
Freezing Module (TEFM)
Thermoelectric
Holding Module (TEHM)
Urine Collection
System (UCS)
Effects of Microgravity on the Biomechanical and
Bioenergetic Characteristics of Human Skeletal Muscle
Goal:
·
To determine the
force/length characteristics of the contractile component.
·
To determine the
force/length characteristics of the series elastic component.
·
To determine the
force/velocity characteristics of the contractile component
Approach:
The experiment protocol
consisted of a series of predetermined profiles, each lasting for several
seconds. Each profile was repeated twice, and 3 or 4 profiles were performed in
combined TVD modes, called experiment blocks. Throughout the experiment blocks
the muscle activity was recorded by electromyography (EMG). The same protocol
was performed preflight, during the space flight and postflight.
Initially, the subject had
to place the surface electrodes for EMG recording on the agonist and antagonist
muscle groups, then enter the TVD and perform the necessary strapping and
safety controls. The lever arm of the TVD was automatically positioned to the
appropriate angle and the subject was asked to exert either a maximal voluntary
contraction (MVC) or 50% thereof, and to maintain it for 7 seconds, the
duration of one profile. During each profile, a sequence of isometric and
isokinetic (concentric and eccentric) contractions were studied, automatically
imposed by the TVD. Between each profile the subject rested for 40 to 60
seconds. Overall, seven different profiles were used during the experiment.
The tests were performed
four times before the flight (at L-90, L-60, L-30 and L-15, days before
launch), three times in flight (Flight Day 2,3,4; FD 7,8,9; FD 13,14,15) and
four times after flight (R+1/2; R+4/5; R+8/9; R+15/16).
Hardware:
Electromyograph (EMG)
Electromyograph
(EMG)
Life Sciences
Laboratory Equipment (LSLE) Microcomputer II
Torque Velocity
Dynamometer (TVD)
Canal
and Otolith Integration Studies
Goal:
To study changes in the
coordination of head and eye movements associated with adaptation to
microgravity and to examine how vestibular and visual information are processed
in microgravity.
Approach:
Voluntary Head Movements (VHM) Experiment
The VHM investigation
allowed scientists to study the interaction of eye movement responses as
crewmembers voluntarily move their heads back and forth while staring at a
stationary wall target or while attempting to fixate the target after the eyes
have been blindfolded. In another part of the experiment, astronauts tracked a
target that was moving back and forth, first with their eyes only and then with
both the head and eyes together. Changes in canal-otolith interactions were
assumed by comparing responses during head movements in horizontal (yaw) and
vertical (pitch) planes. Greater changes were expected in the pitch plane
because these head movements stimulate both the canals and otoliths on Earth.
Optokinetic Nystagmus Experiment
When we move our heads,
however, the visual background also moves relative to our eyes. This causes an
eye movement reflex called the optokinetic reflex. This reflex consists of slow
movements (following the visual background) alternating with corrective quick
movements (saccades), which prevent the eye from moving too far in its socket
and allow the subject to pick up new points of interest as the visual stimulus
moves.
These optokinetic responses
provide a visual input to the brain's simultaneous processing of visual and
vestibular information and function to orient our eye movement responses
gyroscopically in the proper plane relative to gravity. Normally, the axis
about which the eyes move is aligned with the direction of gravity. However, if
both head and visual stimuli are tilted so that the visual scene is no longer
aligned with gravity, the optokinetic response will be changed so that the
resulting eye movements continue to be aligned with gravity and not the visual
scene. This change in the axis of the eye movement to align with the
gravitational reference is called cross-coupling, and changes in this response
are the focus of the OKN experiments as the astronauts adapt to altered otolith
input in weightlessness.
Four crewmembers
participated as test subjects and operators for both experiments, obtaining
measurements early, midway, and late in the mission. Data were collected pre-,
in-, and postflight. Inflight data collection occurred four times for each
subject during the mission -- once each on Flight Days 1 and 2, once sometime
in mid-mission, and once within 48 hours after landing. Postflight data
collection occurred as soon as possible on the day of landing (R+0), and
continued on R+1, R+2, R+4 and R+8 days after landing.
Hardware:
Binocular Optokinetic
Stimulus Goggles (OKS)
Electronic Light
Occlusion Goggles (ELOG)
Instrumented Vest
Assembly (IVA)
Luminous Target
Display (LTD)
Superpocket Assembly
Target/Subject
Positioning Device
Human
Sleep, Circadian Rhythms and Performance in Space
Goal:
To study of sleep, circadian
rhythms, and mood in response to the microgravity environment to determine the
interrelationship between sleep, circadian rhythms and mood and task
performance.
Approach:
Sleep, Performance and Circadian Rhythms
Each
sleep session during the 72-hour measurement block was recorded using the
Medilog Sleep Research Recorder (MSRR) system. The subjects wore electroencephalograph
(EEG) electrodes to record brain wave patterns, which gave investigators an
idea of the type and depth of sleep. Electrooculograph (EOG) electrodes
recorded eye movements and electromyograph (EMG) electrodes recorded chin
muscle tone (a relaxed chin muscle is a second indication of REM sleep). The
electrodes recording EEG, EOG and EMG were positioned on the subjects' head
using a cap-based system. Signals were recorded on magnetic tape. After
recovery, the tapes were played back in order to
1) visually classify each minute of sleep into
conventionally defined sleep stages (0, 1, 2, 3, 4 and REM);
2) 2) run the signals through a computer-based analysis
system allowing the measurement of: a) EEG spectral density, b) a count of
delta waves, and c) a count of eye movements. The procedures allowed a detailed
characterization of the duration, depth and architecture of the entire sleep
episode.
After
each sleep period during the 72-hour measurement block, each subject completed
a modified computer-based version of the Pittsburgh Sleep Diary (PghSD). This
brief instrument assessed the estimated timings of sleep onset and offset,
recorded the number and nature of within-night awakenings, the use of
sleep-inducing medications, the use of medication to alleviate space adaptaion
syndrome (SAS), and concluded with visual analog scale ratings of 1) subjective
sleep quality, 2) mood upon awakening (tense vs. relaxed), and 3) alertness
upon awakening (sleepy vs. alert).
Five
times per day (within each measurement block) spread throughout the waking
interval, a very brief computer-based visual analog scale technique (Monk 1989)
was used to measure subjective alertness (global vigor) and overall mood
(global affect). These ratings will be used to create (1) "time of
day" functions in subjective alertness (yielding a further circadian
rhythm variable) and (2) daily mean levels of mood and alertness.
Three
times per day (within each measurement block), before breakfast, lunch and
dinner, each subject completed a 6-minute performance battery using the
computer. The two-component tests (the speed and accuracy of which are
evaluated) comprise 32 trials of a simple serial search task (searching for the
letter "E" in 30 random uppercase letters) and 32 trials of a modified
form of the Baddeley (1968) Reasoning Test (determining the truth or falsity of
statements such as "M is not before C - CM"). Results of these tests
will be used to create (1) "time of day" functions in performance and
(2) mean daily levels, for each of the two tasks.
At
the end of each work shift in the 72-hour measurement block, the subjects
completed a brief questionnaire regarding stresses such as fatigue, equipment
malfunction and changes in procedure, as well as ratings of how long the shift
lasted and how satisfied they were with their work during the shift.
Fluid and Electrolyte Balance
The
study of fluid and electrolyte balance had several steps, designed to determine
the following:
1)
Early (<24 hours) and delayed (>24 hours) hormonal and electrolyte
modifications and to demonstrate the correlation of these modifications with
space adaptation syndrome (SAS).
2)
Role of sympathetic nervous system transmitters (catecholamines, 3-methoxy
4-hydroxy phenyl glycol (MHPG)) and growth hormone (GH) with cortisol as
indicators of stress.
3)
the role of confinement and inactivity in the changes observed during flight.
The comparison of flight data with a 17-day bed-rest study and a postflight
ground-based study will be of great importance in determining these.
Hardware:
Actillume
Bar Code Reader
(BCR)
Blood Collection
Belt (BCB)
Electrode Impedance
Meter (EIM)
Inflight Blood
Collection System (IBCS)
Ingestible
Temperature Monitoring System (ITMS)
Life Sciences
Laboratory Equipment (LSLE) Refrigerator / Freezer
Medilog Sleep
Research Recorder (MSRR)
Oral Thermometer
Payload General
Support Computer (PGSC)
Rack Mounted
Centrifuge
Saliva Collection
Kit
Spacelab
Thermoelectric Freezer (STEF)
Temperature
Monitoring System
Thermistor Recorder
Temperature Monitoring System
Thermoelectric
Freezing Module (TEFM)
Thermoelectric
Holding Module (TEHM)
Urine Monitoring
System (UMS)
Measurement of Energy Expenditure During Spaceflight with
the Doubly Labeled Water (DLW) Method
Goal:
To measure the relationship
between energy needs and dietary intake during space flight.
Approach:
Water labeled with the
nonradioactive, stable isotopes deuterium (2H) and oxygen (18O) was ingested by
the subjects in known levels. The two isotopes leave the body at different
rates. Deuterium leaves primarily in urine, while 18O leaves in both urine and
exhaled carbon dioxide (CO2). The amount of difference between the two isotopes
in urine samples is equal to the rate of CO2 production - and the CO2 rate
indicates the rate of energy expenditure.
During flight, the subjects
used the Urine Monitoring System (UMS) for urine sampling. This device, which
is incorporated into the Shuttle's toilet, takes accurate measurements of urine
volume and collects a 2 ml sample of each urine void. The subjects also
collected saliva samples. The urine and saliva samples were stored at -20°
Celsius and analyzed after landing.
To support the findings from
the urine and saliva samples, three additional measures were taken:
(1)
During flight, the astronauts kept a log book, monitoring their dietary and
drug intake, as well as their activities.
(2)
The subjects measure their mass in the beginning and towards the end of the
mission.
(3)
It was necessary to check the background levels of the isotopes 2H and 18O in
the galley water supply of the Shuttle, because this water was used for
rehydrating all food items and drinks consumed by the astronauts.
The experiment was divided
into ground-based data collections, which took place before and after the
mission, and the inflight segment. While in orbit, the experiment was repeated
three times by the participating astronauts: in the beginning, mid-mission and
toward the end of the 17-day mission. Each repetition was conducted over 3
days: on day 1 the background samples were collected, on day 2 the astronauts
collected saliva and urine before and after drinking the doubly-labeled water,
and over the next 1.5 days they continued to sample saliva and urine.
Hardware:
Bar Code Reader (BCR)
Blood Collection
Belt (BCB)
Inflight Blood
Collection System (IBCS)
Life Sciences
Laboratory Equipment (LSLE) Refrigerator / Freezer
Rack Mounted
Centrifuge
Saliva Collection
Kit
Spacelab
Thermoelectric Freezer (STEF)
Thermoelectric
Freezing Module (TEFM)
Thermoelectric
Holding Module (TEHM)
Urine Monitoring
System (UMS)
Pulmonary
Function During Weightlessness
Goal:
The primary experimental
objectives were to determine the following parameters before, during and after
spaceflight:
a.
distribution of ventilation/gas mixing in the lung
b.
distribution of perfusion
c.
distribution of ventilation/perfusion ratios
d.
pulmonary diffusing capacity
e.
pulmonary capillary blood volume
f.
overall lung mechanics
g.
overall pulmonary gas exchange
h.
total pulmonary blood flow
Approach:
Data were acquired in the
following sessions:
Preflight
Pulmonary
Function Test, Extended Pulmonary Function Test, Head-Down Tilt Simulation
Study
Inflight
Pulmonary
Function Test
Postflight
Pulmonary
Function Test
Hardware:
Bag Dryer Assembly
Bag-in-Box (BIB)
Assembly
Cardiovascular /
Cardiopulmonary Interface Panel (CV/CP)
Electronics Control
Assembly (ECA)
Gas Analyzer/Mass
Spectrometer (GAMS)
Gas Cylinder Assembly
(GCA)
Life Sciences
Laboratory Equipment (LSLE) Microcomputer
Physiological
Monitoring System (PMS)
Rebreathing Assembly
(RBA)
Spirometry Assembly
Strip Chart Recorder
Vacuum Interface
Assembly (VIA)
Pulmonary
Function in Weightlessness
Goal:
This investigation extended
studies of the human lung in four major areas:
·
To study lung function
after the stress imposed by heavy exercise in the microgravity environment.
·
To monitor motion in
the rib cage and abdomen.
·
To study the effects of
microgravity on the musculoskeletal aspects of breathing during rest, during
heavy exercising, and during deep breathing.
·
To measure the body's
response to inhaled carbon dioxide, which may be altered by space flight.
·
To determine how gas is
distributed within the lung.
Approach:
Each subject performed a
battery of pulmonary function tests before and immediately after exercise.
These included measurements of cardiac output, lung water, pulmonary diffusing
capacity, pulmonary ventilation, perfusion, and ventilation-perfusion ratio.
Also, the metabolic rate was measured via resting oxygen consumption and carbon
dioxide production.
Further, the alterations in
intra-acinar gas mixing in microgravity were investigated by measuring
inspiratory flow rates as subjects inhaled and exhaled. In parallel, the pattern
of chest wall and abdominal movements during normal ventilation, exercise
ventilation, and induced hyperventilation was observed. While performing these
studies, the subjects were instrumented with a respiratory inductance
plethysmograph (RIP), a noninvasive device that allows continuous monitoring of
the motion and expansion of the rib cage and abdomen. While the subject was not
breathing through the mouthpiece, simple measurements of inspiratory and
expiratory times were made.
To determine the ventilatory
response to carbon dioxide during microgravity, as well as during the preflight
and postflight periods, the test subjects performed a hypercapnic response test
in which they rebreathed from a bag containing some CO2 in a hyperoxic gas
mixture.
The ventilatory response to
acute hypoxia was determined only before and after flight by a protocol that
required the subjects to rebreathe a low oxygen gas mixture from a bag in which
the CO2 was actively removed to maintain isocapnia in the face of increased
ventilation and decreasing O2.
Hardware:
Bag Dryer Assembly
Bag-in-Box (BIB)
Assembly
Calibration Syringe
Electronics Control
Assembly (ECA)
Gas Analyzer System
for Metabolic Analysis Physiology (GASMAP)
Gas Cylinder Assembly
(GCA)
Life Sciences
Laboratory Equipment (LSLE) Microcomputer II
Physiological Signal
Conditioner (PSC)
Pulmonary Function
Facility (PFF)
Respiratory
Inductive Plethysmograph (RIP) Suit
Respitrace
Electronics Module (REM)
Temperature and
Humidity Monitoring System (THMS)
Vacuum Interface
Assembly (VIA)
Plants
Response
of Crown Gall Tissue to the Space Environment: Glutamine Synthetase Activity
Goal:
In plants, glutamine
synthetase (GS) is the enzyme associated with seeds and relatively
undifferentiated embryonic activity. It was of interest, therefore, to
determine if the specific activity of this enzyme would be affected by gravity
compensation or weightlessness in crown gall tumor tissue.
Approach:
Upper sections of carrots
were cross-sectioned and inoculated with bacterial suspensions (1 x 10-8
cells/µl) of Agrobacterium tumefaciens.
Upon arrival, flight, and similarly treated control material, were weighed,
frozen, lyophilized, and stored at -20 degrees C until assayed. Assays for GS
specific activity depended on the gamma- glutamyl-transferase properties of the
enzyme and were performed by a sodium arsenate modification of the D. Rudnick
et al. method. The specific activity was calculated as the number of micromoles
of gamma-glutamyl-hydroxymate produced per hour, per mg protein.
Hardware:
Carrot Tumor Growth
Container I
Cosmos Centrifuge
Source:
http://lsda.jsc.nasa.gov/
2) Experiments
involving on-planet experimentation
Visual Imagery at Micro-Scales Visual examination as a mineral identification tool relies on the optical reflection properties of mineral surfaces. These properties are observed and then compared to a database of similar observations on all known minerals. This examination is usually performed with some sort of magnification instrument; in this case the preferred tool would be a hand lens of 5X-15X. The properties that are observed usually are color, cleavage, fracture, luster and habit. Fracture characterizes the morphology of broken mineral surfaces (smooth, irregular, conchoidal, etc.). Cleavage refers to how the species breaks apart (straight, jagged). Luster describes the reflective properties of the surface (dull, glassy, resinous, etc.). Lastly, habit refers to the shape of a mineral grain. Visual Imagery will not answer all questions, but will provide rapid identification of common minerals and guidance in what minerals will need to be tested more.NEEDED INSTRUMENT: 5X-15X hand lens X-ray Diffraction Analysis This analytical technique utilizes two unique properties of X-rays: first, that they interact with atomic nuclei, and second, that their wavelengths are of the same order of magnitude as the distances between atoms and crystalline solids. The best diffraction technique would probably be powder X-ray diffraction because it can be used to characterize the complex mixtures found in the natural environment. After completing the process of powder X-ray diffraction the experimenter can compare the data of the interplanar spacing within the crystal and the diffracted intensities to equivalent listings in data bases (ICDD powder diffraction file). The only stipulation for powder X-ray diffraction is that the material should be fine grained (wind-blown dust, soil). This way the material may be analyzed without preparation. Therefore, if the material is coarse-grained (>50 micrometers) its grainsize must be reduced by a drill or grinder. NEEDED INSTRUMENTS: powder X-ray diffraction instrument, grinder Mössbauer Spectroscopy This technique makes use of the resonance absorption of recoil-free emitted gamma-rays by certain nuclei in a solid to investigate the splitting of nuclear levels that is produced by interaction with its surrounding electronic environment. To achieve resonance conditions, the energy of the emitted amma-quanta has to be modulated, which is done by using the Doppler effect by mounting the source on a velocity transducer and moving it with respect to the absorber. Therefore, a Mössbauer spectrum is the measurement of the rate of resonance absorption as a function of the relative velocity between source and absorber. The shape of this spectrum is determined by hyperfine interaction of the Fe nucleus with its electronic environment. The three hyperfine parameters, which can be determined by this technique, are isomer shift, quadrupole splitting, and magnetic hyperfine field. These parameters are different for different materials. These parameters are also dependent on temperature, thus, the measurements can be made during the day and night would supply additional information. When on Mars the Mössbauer spectroscopy would be performed with backscatter geometry. This means that the source and radiation detector are on the same side of the sample. Backscatter geometry has no restrictions on sample shape and thickness. Also no preparation of the sample is required.NEEDED INSTRUMENTS: miniaturized Mossbauer instrument---->6 detector-channel versionMass < 500 g; Dimensions @ 600 cm^3; Power @ 4 watt Visible and Near IR Spectroscopies These two spectrometers are used for their remote determination of mineralogy. This occurs by having the spectral properties of light reflected from a surface and it is measured through a large number of contiguous spectral channels. This radiation has interacted with the surface, has been transmitted through several grains, and has obtained an imprint of absorption bands and other spectral features, which are evidence of the minerals present.INSTRUMENTS NEEDED: visible and near IR spectrometers Imaging Spectrometers This instrument produces "image cubes" of data: three dimensions of 10-14 bit data numbers, each with several hundred elements. Two of the dimensions contain spatial elements and the third contains spectral elements or channels. The application of this instrument would be the ability to evaluate spectral properties of individual surface elements in a geologic context.INSTRUMENT NEEDED: image spectrometer Mid-/Thermal IR These two IR techniques are employed because many geologically important elements (Si, Al, O) do not absorb directly in the visible or near infrared spectrum. Strong spectral activity in the mid-IR results from structural, chemical, and physical properties of silicate rocks and minerals. The other technique, thermal emission spectra, is used for natural surfaces. It scatters the outgoing energy within the ground surface. Therefore, physical properties such as particle size and packing can affect emission spectra. The effects become significant when the particle size is too small (< 100 micrometer) and are important when the size approaches the wavelength that is being observed.INSTRUMENTS NEEDED: mid-IR and a thermal emission spectrometer (TES) ---Mass = 14.4 kg ---Power = 14.5 watt Electron Paramagnetic Resonance (EPR) This technique studies atoms, ions or molecules with unpaired electrons in an applied magnetic field by irradiation of microwaves to induce transitions between electronic spin states. The electronic states and their energy levels are modified through various interactions; for example, interaction with nuclear spin (within same atom or neighboring one), molecular environment, or crystalline matrix. The magnitudes of these interactions can be found through EPR spectra and used to find information about the molecular structures of radicals, oxidation states of ions, electronic structures, symmetry of ionic sites and the surroundings. Solids, liquids, and gasses can be studied by EPR. Some specific ways EPR can be used for Mars exploration are the following: nature of oxidant (radicals ) in Martian soil; oxidation state of paramagnetic ions in the soil; characterization of volatiles (carbonates, sulfates, nitrates); color centers in icy samples (impurity level chemicals in ice, inorganics, organics, cabonates); and detection of possible organic from the subsoil.INSTRUMENT NEEDED: EPR spectrometer Ferromagnetic Resonance (FMR) Ferromagnetic samples include metals of iron, cobalt, nickel and some rare earth elements. The FMR spectrometer detects these samples because they are strongly coupled and possess a spontaneous magnetic moment even in the absence of an applied magnetic field.INSTRUMENT NEEDED: FMR spectrometer
3) More hard
requirements
Mars Array Technology Experiment (MATE):
ABSTRACT:
Future missions to Mars will rely heavily on solar power. Different solar cell
types and structures must be evaluated to find the optimum. Sunlight on the
surface of Mars is altered by airborne dust and fluctuates from day to day. The
dust affects both the intensity and spectral content of the sunlight. The MATE
flight experiment was designed for this purpose and will fly on the mission as
part of the Mars In-Situ Propellant Production Precursor (MIP) package. MATE
will measure the performance of several solar cell technologies and
characterize the Martian environment in terms of solar power. This will be done
by measuring full IV curves on solar cells, direct and global insolation,
temperature, and spectral content. Our mission is to be launched soonbut the
site location has not been identified. The mission is expected to last from
300- to 500 days. The intent of this paper is to provide a brief overview of
the MATE experiment.
INTRODUCTION
This
flight experiment is one of five experiments that make up the MIP package. MIP
is designed to demonstrate the conversion of atmospheric CO2 into propellant
which can be used to return to earth. One of the most important resources
required to produce propellant on Mars is energy. Power is required for all
phases of propellant production, from the initial collection and compression of
atmospheric carbon dioxide to the liquification and storage of the cryogenic
propellants produced. In many propellant production systems, the power system
is the single largest and most massive component. This power will be solar
power.
The
four other experiments on MIP are: Mars Atmosphere Acquisition and Compression
(MAAC), Oxygen Generating System (OGS), Mars Thermal Environment Radiator Characterization
(MTERC), and Dust Accumulation and Removal Technology (DART). The MIP
experiment control and main structure is being built and operated by NASA
Johnson Space Center, as is OGS. MAAC and MTERC are being built at the NASA Jet
Propulsion Laboratory, and DART is being built at NASA Lewis [now NASA Glenn]
Research Center as well. The MATE and DART experiments share a 34 cm. x 24 cm.
honeycomb substrate.
2. MATE DESCRIPTION
MATE
is the Mars Array Technology Experiment, and its primary goal is to determine
the optimum solar cell type for future missions. To do this it will measure the
performance of solar cells, the solar spectrum, the solar intensity, and
temperature. The flight experiment has several components, which cover a range
of functions. These components are divided into several basic areas. It
includes the following components:
·
10 solar cells (5
pairs)
·
2 solar cell strings
·
2 radiometers, direct
and global
·
8 temperature sensors
·
1 dual spectrometer,
300 1700 nm
·
Components in warm electronics
box (WEB)
2.1
Component Description
Each component is described briefly. Figure 1 below
shows a diagram of the MATE experiment, the empty spaces are for the DART
experiment and a dust cover.
Figure 1: MATE experiment plate
Figure 2: MATE schematic
The MATE experiment also includes the electronics.
The schematic in figure 2 above shows the major parts of the experiment as
related to the spacecraft and MIP. The experiment has a dedicated 4" x
6" circuit board in the warm electronics box. This board, when energized,
is told what tests to perform, runs IV curves, senses temperature, reads
insolation, runs the spectrometers, sorts the data, repeats any measurements,
and then sends the data back to MIP, which it sends to the Lander. The Lander
stores the data until it is ready to be transmitted. This experiment has no
moving parts.
Solar Cells
(10): The solar cells will be made
from a variety of materials and sizes. There will be 5 pairs of different cell
types. The space available, 100 mA maximum current and 10 V maximum voltage
limit the sizes of the cells. The cell types currently selected include; high
efficiency Si (figure 3), Amorphous Si (figure 4), two types of GaInP/GaAs/Ge
triple junction space cells, and GaAs/Ge. The solar cell selection is an
ongoing process of evaluations [1,2]. Cells must perform well at lower
temperature and lower intensity then is common to most space cells [3]. The
solar intensity on Mars is approximately one third of the AM0 intensity at
Earth orbit, or 45 mW/cm2. Preliminary spectral data from Mars Pathfinder and
Viking have shown that the sunlight on Mars varies with dust content and tends
to lose the blue part of the spectrum.
Figure 3: High Efficiency Si Solar Cell (Sharp)
Other factors that affect solar cell selection
include weight and cost. As power requirements grow, the size of the array must
also grow; weight and cost naturally become a major concern. Thin film cells
offer both weight and cost savings. Studied show that large area roll out thin
film arrays prove very useful for many Mars missions. Thin films include CIS
and Amorphous Si, both of which are making inroads in the space community.
Figure 4: Amorphous Si Solar Cell (United Solar Systems)
Solar Cell
Strings (2): The strings will have
the same limitations as the solar cells. These will be cells in series and
therefore will not have higher currents but will have higher voltages (voltages
add). Plans are to connect five cells in series for a string. One string will
be standard solar cells; the other will be a thin film. These strings are
intended to test new technology as well as identify any problems with array
designs. A string of Si cells and a CIS array are tentatively planned.
Figure 5: Global and Direct Radiometer (Dexter Research)
Radiometers
(2): The radiometers are
thermocouple type devices that measure radiation based on thermal techniques.
These are small devices that consist of multiple thermocouple junctions using
thin film technology. They are very small and unlike traditional radiometers,
require temperature correction. These devices generate a voltage proportional
to the solar intensity. The voltages from these devices are in the 10s of mV.
There are two radiometers, one measuring global and
the other measuring direct radiation or solar insolation. The global
measurement is done with a radiometer that has approximately 130 field of
view. This field of view is considered adequate based on the limitations of the
device and the expected amount of scattered light. A second radiometer will
have a conical shell placed over it with a slit; this will measure direct
radiation with the sun overhead. The direct radiometer can only be read once
per day.
Temperature
Sensors (8): Eight temperature
sensors will be scattered around the MATE experiment, two will be attached to
the radiometers, two will be on the photodiode arrays of the spectrometers, and
the rest will be under solar cells. The temperature sensors are platinum
devices known as RTD (resistance temperature dependence). They have a well-characterized
linear change in resistance with temperature (.385 %/°C). They can be selected
with a variety of resistances from 100 ohm and up. The device selected will
have a 0° C resistance of 1000 ohm and be in a small ceramic case with two
wires. Measurement accuracy will be 1 degree C.
Dual Spectrometer (2): The dual spectrometer consists of an input optic and
two spectrometers, both having optical fiber inputs. This will span the solar
spectrum from .3µm to 1.7 µm with a nominal resolution of 10 nm. This range was
selected based on the bandwidth of solar cells and the AM0 spectrum, covering
86% of the total energy. The input optic converts incident radiation into a
diffuse light source. It consists of a tube, thin diffusing element made of
Spectralon, a folding prism, and a fiber output. Light enters this diffusing
element and is scattered uniformly and therefore each fiber will see the same
amount of light. This diffuser extends the capability to look at the sky at any
time of the day. Figure 6 shows a sketch of the input optics and figure 7 shows
the individual components.
Figure 6: Input Optic Assembly
The spectrometers are two separate devices with the
same basic design except for the wavelength range they are designed for.
Traditional spectrometers have used a rotating grating with a single detector,
measurements for each wavelength range had to be made sequentially by turning
the grating and reading the detector. These spectrometers have a fixed grating
with multiple detectors where the entire spectral range is read simultaneously
(figure 8). The multiple detectors are a photodiode array (PDA), each of these
spectrometers has a PDA with 256 elements or detectors. These are very compact
devices, but must be designed for a specific resolution.
Figure 7: Input Optics Components
Each spectrometer has the following parts: 1) fiber
optic feeds, 2) Optical Boxes: light tight boxes with fiber optic input and/or
slit, 3) Optical Grating, spread light into spectrum, 4) filters: as necessary
to block first order light across array, 5) PDA, linear array of photodetectors
(figure 8), and 6) driving electronics and digital data readout.
Figure 8: Spectrometer Conceptual Design
The spectrometer concept is that light is spread out
spectrally across photodiode array so that each diode sees and responds to a
different part of the spectrum, no moving parts.
One spectrometer operates from 300-1100 nm and uses a
Si PDA with 256 elements (figure 9). This is made by Zeiss and Hamamatsu makes
the PDA. The second spectrometer operates from 900-1700 nm and uses an InGaAs
PDA with 256 elements. Control Development Inc. makes this and the PDA is made
by Sensors Unlimited. Both are modified off-the-shelf spectrometers, all of the
electronics will be designed by NASA Lewis engineers as part of the electronics
board in the WEB.
The sensitivity of the spectrometers is adjusted by
one of two ways, by a gain adjustment or a change in the integration time.
These spectrometers will have a fixed gain amplifier with a variable integration
time to optimize the signal for the A/D. With the gain fixed, the integration
time is proportional to the signal level and can be divided out to compare
readings over different days. The resolution of the spectrometers is fixed in
the design and limited by technology and packaging. It is much higher then any
current or planned measurements and should be able to resolve many narrow
absorption bands over a wide range of environmental conditions [4,5].
Figure 9: 300-1100 nm spectrometer (Zeiss)
2.2 MATE specifications
The exact power and specifications for the MIP
experiment are still not finalized. The MATE/DART plate is tentatively 34 cm. x
24 cm., MATE has been allocated a surface area of 500 cm2, parts are allowed to
protrude above the top plate by as much as 3 cm. The total mass including the
electronics is 960 kg.
3. MATE Operation
The MATE operation has five different measurement
scenarios. Three of the measurement scenarios are identical and only vary by
the time(s) of day, a fourth scenario is for the direct radiometer, and the
fifth is a health check during cruise and prior to landing. MATE is scheduled
to run once per day at solar noon, once per hour throughout the day one day per
week, and once per week at night. MATE is operated 19 times per week unless
power limitations or mission priorities prevent it.
The three operation scenarios will measure full IV
curves on all cells and strings, the radiometers, temperatures, and
spectrometer. This sequence will run about 5 minutes, use 750 mW nominally, and
take about 10 Kbits of data. All of the data will be in 8-bit format with the
A/D scaled to optimize resolution. An IV curve will have >40 points and
clearly identify open circuit voltage, short circuit current, and maximum
power. The temperature will be within 1 degree C. Solar Insolation will be a
converted voltage and temperature measurement The spectrometers will first be
reset, read once to adjust the integration time, and then read and averaged if
necessary.
The direct radiometer measurement can only be done
when the sun is passing over the slit. The radiometer will be measured every 20
seconds over a 15 minute interval centered around solar noon. A plot of this
data will result in a peak measurement under direct illumination. Comparison of
the other data is necessary to interpolate the direct insolation.
4. CONCLUSIONS
The
mission is baselined for between 300 and 500 days depending on site location
and power. MATE main objectives are to:
·
Measure solar cell
performance in-situ
·
Evaluate different
types of solar cells
·
Study long term effects
of the Martian environment, particularly dust, on solar cells [6].
·
Characterize the
Martian environment by measuring the spectral content, solar insolation, and
cell temperature
The
MATE experiment is teamed up with the DART experiment [7]. With these two
experiments, many of the concerns related to providing solar power on Mars will
be studied.
Successful
operation of the MATE experiment is dependent on several factors. The most
important test condition is a dust free baseline measurement on the surface of
Mars. A second issue is the field of view of the solar cells and sensors; the
IIT mission equipment may shadow some of the experiment. The orientation and
location of the IIT mission must be known; the site and the location of the sun
must be identified. These are critical elements in interpreting the data. The
IIT mossion to Mars is expected to have a precision landing and the orientation
should be known, the DART experiment contains a sun sensor which will locate
the sun. These two elements will aid in data analysis and measurement timing.