NASA/Spacelink File Name:6_6_9_3.TXT STS-48/UARS
HALOGEN OCCULTATION EXPERIMENT (HALOE)
FACT SHEET
Introduction
NASA'S Halogen Occultation Experiment (HALOE) is designed to
monitor the vertical distributions of ozone and key upper
atmosphere trace gases that affect the global ozone distribution by
measuring the attenuation (reduction in intensity) of the Sun's
energy in selected spectral bands as it passes through the Earth's
atmosphere.
One of the 10 highly-instrumented experiments on NASA's Upper
Atmosphere Research Satellite (UARS), HALOE is scheduled to be
launched in September aboard the Space Shuttle Discovery. The
instrument has a planned lifetime of at least 18 months.
UARS is the first comprehensive space experiment ever
mounted to study the chemistry, dynamics and energetics of the
Earth's upper atmosphere. It will provide valuable scientific
input to critical policy decisions aimed at protecting the thin,
fragile ozone layer which blocks harmful ultraviolet radiation from
reaching the Earth's surface.
The UARS spacecraft will be delivered into a 348-mile (560
km) circular Earth orbit. After deployment by the Shuttle remote
manipulator system, UARS will be boosted by a propulsion system on
the spacecraft to a 363-mile (600 km) circular orbit, inclined 57
degrees to the equator.
Goddard Space Flight Center manages and directs the UARS
mission for the Office of Space Sciences and Applications, NASA
Headquarters, Washington, D.C. The spacecraft was designed, built,
integrated and tested by GE Astrospace, Valley Forge, Pennsylvania,
and East Windsor, New Jersey.
HALOE Science Objectives
Scientific objectives of the HALOE mission are to:
% Improve understanding of stratospheric ozone depletion by
collecting and analyzing global vertical profiles of ozone and
gases important in its destruction: hydrogen chloride, methane,
water vapor, nitric oxide and nitrogen dioxide.
% Study the chlorofluoromethane impact on ozone by measuring
hydrogen chloride and hydrogen fluoride in addition to the other
key chemical species, and using data on Freon 11, Freon 12 and
chlorine nitrate obtained from other UARS experiments.
The science investigations will include studies of trace gas
sources and depositories, transport mechanisms, dynamics, and
validation of atmospheric and photochemical dynamics models.
The experiment uses gas filter correlation radiometry to
measure hydrogen chloride, hydrogen fluoride, methane and nitric
oxide, and broadband filter radiometry to measure water vapor,
nitrogen dioxide, ozone and carbon dioxide. The carbon dioxide
data will be used to obtain atmospheric temperature versus pressure
profiles.
HALOE Instrument Description
The HALOE instrument hardware is contained in two separate
packages, the Platform Electronics Assembly (PEA) and the Sensor
Assembly. The PEA links the instrument with the spacecraft. The
Sensor Assembly makes the science measurements and consists of
eight science detectors and radiometers, a Cassegrain telescope, a
two-axis gimbal assembly, a Sun sensor, the spacecraft adapter and
supporting electronics.
The operating principles of gas filter correlation
radiometry and conventional broadband filter radiometry are
described below:
Gas Filter Correlation Radiometry Principle - Solar energy
enters the gas correlation section of the instrument optics and is
divided for each channel (hydrogen chloride, hydrogen fluoride,
nitric oxide and methane) into two paths. Each channel has its own
broadband optical filter and detector. The first path contains a
cell filled with the gas to be measured; the second path is a
vacuum path without gas. By electronically comparing the outputs
of the gas and vacuum path detectors, scientists can derive
chemical measurements.
Broadband Filter Radiometry Principle - The water vapor,
nitrogen dioxide, ozone and carbon dioxide channels are
conventional broadband filter radiometers. In this case, energy
from the Sun comes in through only one path for each channel. After
passing through a broadband optical filter, the energy is focused
on a detector. By tracking the Sun, a signal is recorded outside
the atmosphere and during occultation after absorption by the
atmosphere. The ratio of the attenuated signal to the signal
outside the atmosphere can be used to measure the gas
concentration.
The Cassegrain telescope reflects solar energy through a
series of beamsplitters and spectral filters to the photovoltaic
detectors for the gas filter correlation channels and to the
broadband filter radiometer channels. The atmospheric target gases
are detected at specific wavelengths between 2.5 microns and 11
microns.
The instrument size is approximately 36 in. (spacecraft
adapter to frame radiometer) by 24 in. (elevation gimbal to
telescope) by 32 in. (telescope to Gimbal Electronics Sssembly) or
(92 x 62 x 81 cm). The Platform Electronics Assembly is
approximately 9 x 10 x 6.6 inches (23.5 x 24.3 x 22.1 cm). The
total mass of the instrument (Sensor Assembly and PEA) is 222
pounds (101 kg).
The initial design phase for HALOE was conducted by TRW
Defense and Space Systems Group in Redondo Beach, California. The
final design, fabrication, assembly and testing was completed
in-house at Langley Research Center.
Instrument Operation
The HALOE instrument operates autonomously once powered and
initialized. Commands are sent to the spacecraft computer to
operate the instrument for one day to perform the sunrise and
sunset data observations. When the spacecraft sends a command to
perform a sunrise or sunset sequence, the instrument automatically
performs a solar acquisition, a balance of all gas filter
correlation radiometer channels, limb to limb scans of the solar
disk, a calibration activity, the science data measurement during
occultation and then slews back to the stow position.
The Sun pointer/tracker subsystem consists of two coarse and
one fine Sun sensors, a two-axis gimbal assembly, a microprocessor
and drive electronics for gimbal motor control. Its function is to
acquire the Sun, scan the solar disk and track a specified location
on the solar disk during balance, calibration, and science data
measurement activities for orbital sunrise or sunset events.
Acquisition and tracking control signals for the gimbals are
derived from the Sun sensors.
During a typical event, measurements will begin at a tangent
height of 93 miles (150 km), where there is no atmospheric
interference, down to the Earth's surface or until the Sun is
obscured by clouds. HALOE will view approximately 15 sunrises and
sunsets each day collecting data on vertical trace gas
concentrations. Each event will occur at a different latitude and
longitude, and global coverage is repeated every 3 to 4 weeks.
Data Processing
Data from the HALOE instrument will be stored in one of two
tape recorders aboard the UARS observatory. The data will be
transmitted to the White Sands receiving system through the
Tracking Data Relay Satellite System (TDRSS). Routine processing
of the data will occur at the Central Data Handling Facility (CDHF)
at the Goddard Space Flight Center with software provided by the
Langley science team. Interaction with the CDHF will be through a
direct data link between the HALOE Remote Analysis Computer at
Langley Research Center and the CDHF.
Processed data will contain species concentration profiles
as a function of global location and time. The profiles will be
mapped out on a global and seasonal basis as the data accumulates
during the mission.
All UARS data will be archived at the Goddard Space Flight
Center.
Scientific Value
Ozone in the Earth's atmosphere reaches concentrations of
only about 12 parts ozone to one million air molecules, yet it has
profound effects on Earth life. If the ozone level is changed, the
solar ultraviolet level at the Earth's surface is altered. Serious
biological and economical impacts can occur in areas such as human
health, crop and plant growth, perturbations to micro-organisms in
the soil and oceans, weathering of materials, and possible climate
and weather alterations. A 1 percent decline in ozone levels, for
example, can lead to a 2 percent rise in human skin cancer. Also,
if ozone is depleted, the stratospheric temperature rise will be
altered leading to changes in atmospheric stability due to the
weakened temperature inversion.
A growing body of evidence has led to a consensus in the
scientific community that man-made activities are perturbing the
ozone layer. The recent Antarctic ozone "hole" finding, for
example, can only be explained by considering reactions involving
aerosol particles and chlorine compounds formed after dissociation
of the man-made chlorofluoromethanes (CFM's). These CFM's are used
as refrigerants and in various industrial applications. The
extent to which such effects occur outside the Antarctic region is
unknown. Consequently, it is very important that the ozone layer be
monitored globally and over a long time period.
The overall goal of HALOE is to provide global-scale data on
temperature, ozone and other key trace gases needed to study and
to better understand the chemistry, dynamics and radiative
processes of the middle atmosphere (6-74 miles or 10-120 km) and to
study the impact of CFM's on ozone using hydrogen fluoride
observations, in combination with other HALOE data. The figure
shows the major chlorine source species entering the middle
atmosphere.
They interact with ozone, the nitrogen and hydrogen oxides, and
with solar radiation to form the reservoir molecules hydrogen
chloride and hydrogen fluoride. For every chlorine atom formed in
the middle atmosphere by dissociation of the CFM molecules,
approximately 1,000 ozone molecules are destroyed. HALOE studies
will be aimed at evaluating the relative importance of man-made and
natural chlorine sources in ozone destruction. Since the primary
man-made chlorine sources (i.e., the CFM's) contain both chlorine
and fluorine in the molecule, while natural sources (e.g. methyl
chloride and carbon tetrachloride) contain only chlorine, hydrogen
fluoride becomes an indicator of man-made chlorine input to the
middle atmosphere. Hydrogen chloride is an indicator of the total
chlorine input. The relative importance of these two sources can
be inferred by studying changes in hydrogen chloride and hydrogen
fluoride with time.
HALOE Implementation
The Langley Research Center is responsible for providing the
scientific instrument for the HALOE investigation, the instrument
flight operations, the science data products through HALOE data
processing and data management systems, and managing the Science
Team and its investigations.
HALOE Science Team
Dr. James M. Russell III, HALOE Principal Investigator, Langley Research
Center
Dr. Ralph J. Cicerone, University of California/Irvine
Prof. S. Roland Drayson, University of Michigan
Prof. John E. Frederick, University of Chicago
Dr. Adrian F. Tuck, Aeronomy Lab/NOAA/ERL, Boulder, Colorado
Prof. Dr. Paul J. Crutzen, Max Planck Institute for Chemistry, Federal
Republic of Germany
Dr. John E. Harries, Rutherford Appleton Laboratory, United Kingdom
Dr. Jae H. Park, NASA Langley Research Center
Larry L. Gordley, Gats Inc., Hampton,Va.
W. Donald Hesketh, SpaceTec Ventures Inc., Hampton, Va.
HALOE Project Management
Dewey M. Smith, Project Manager
Thomas C. Jones, Deputy Project Manager
Dr. James M. Russell III, Principal Investigator
John G. Wells, Flight Operations and Science Manager
Kenneth V. Haggard, Science Software and Data Processing Manager
9/6/91
NASA/Spacelink File Name:6_2_2_32_9.TXT STS-48
MIDDECK 0-GRAVITY DYNAMICS EXPERIMENT
FACT SHEET
In 1987, the National Aeronautics and Space Administration
(NASA) initiated an outreach program, called In-Space Technology
Experiment Program (IN-STEP), which allows universities, industry
and the government to develop small, inexpensive technology flight
experiments. Five flight experiments have been selected for
IN-STEP, which is funded by NASA's Office of Aeronautics,
Exploration and Technology, NASA Headquarters, Washington, D.C.
The first university experiment to fly in the program is
called MODE- -for Middeck 0-gravity Dynamics Experiment--developed
by Massachusetts Institute of Technology (MIT). The MODE
experiment will study mechanical and fluid behavior of components
for Space Station Freedom and other future spacecraft.
Testing space structures in the normal 1-g environment of
Earth poses problems because gravity significantly influences
their dynamic response. Also, the suspension systems needed for
tests in 1-g further complicate the gravity effects. Models of
space structures intended for use in microgravity can be tested
more realistically in the weightlessness of space.
The MODE experiment consists of electronically-instrumented
hardware that Shuttle astronauts will test in the craft's
pressurized middeck section. MODE will study the sloshing of fluids
in partially-filled containers and the vibration characteristics of
jointed truss structures.
MODE occupies 3 1/2 standard Shuttle middeck lockers. One
locker contains the experiment support module (ESM) that controls
the experiment. The other middeck lockers accommodate the fluid
test articles (FTAs), a partially-assembled structural test article
(STA), optical data storage disks and shakers needed for the
experiment. The FTAs and shaker attach to the support module for
testing; the STA floats free in the weightlessness of the middeck,
but connects to the support module with an umbilical through which
excitation and sensor signals travel.
EXPERIMENT SUPPORT MODULE
The experiment support module contains a special purpose
computer, high speed input/output data and control lines to the
test articles, a power conditioning system, signal generator,
signal conditioning amplifiers, and a high-capacity optical disk
data recording system.
Experiment Support Module.
In orbit, the astronauts command the computer via a keypad
to execute test routines stored on the optical recorder before
launch. Once a test routine begins, the computer and associated
control circuits excite the containers or the truss with precisely
controlled forces and then measure the response. The Shuttle crew
members use an alpha-numeric display to monitor the status and
progress of each test.
FLUID TEST ARTICLES
The study of fluid dynamics and spacecraft interaction in
microgravity is an integral part of NASA's research and technology
base. It is a research area that has influenced space vehicle
design since the Apollo program of the 1960s. A detailed
understanding of such fluid/spacecraft interactions is needed to
design a broad spectrum of future spacecraft that will carry
liquids for fuel and life support, including an Earth-orbiting fuel
depot for Mars missions.
The behavior of fluids depends on the gravity level present.
In addition to experiments in normal gravity, researchers obtained
a large database on fluid dynamics in microgravity by flying the
MODE-type hardware on NASA's KC-135 aircraft.
The aircraft repeatedly flew a special parabolic flight path
that produced short periods of weightlessness. Although the KC-135
studies provided useful data, they were too brief to understand the
behavior of fluids in space. The MODE flight experiment aboard
STS-48 gives researchers access to a much longer duration micro-
gravity environment.
The four fluid test articles are Lexan cylinders --two
containing silicon oil and two containing water. Silicon oil has
dynamic properties that approximate those of typical spacecraft
fluid propellants. Water is more likely than the silicon oil to
stay together at one end of the cylinder--an important test
condition. The same basic dynamic information will be obtained for
both fluids.
The cylinders mount one at a time to a force balance that
connects to a shaker on the support module. The balance will
measure the forces arising from the motion of the fluid inside the
tanks. These forces, with other data such as the test article
acceleration and the ambient acceleration levels of the entire
assembly, will be recorded in digital form on an optical disk.
STRUCTURAL TEST ARTICLE
The structural test article is a truss model of part of a
large space structure. It includes 4 strain gauges and 11
accelerometers and is vibrated by an actuator. When deployed in
the Shuttle orbiter's middeck, the test device is about 72 inches
long with an 8-inch square cross section.
There are two types of trusses: deployable and erectable.
The deployable structures are stored folded and are unhinged and
snapped into place for the tests. The erectable structure is a
collection of individual truss elements that screw into round
joints or "nodes."
Four different truss configurations are slated for testing.
First, the basic truss will be evaluated. It is an in-line
combination of truss sections, with an erectable module flanked by
deployable modules mounted on either end. Next, a rotary joint,
similar to the Space Station Freedom "alpha joint" that will govern
the orientation fo the station's solar arrays, will replace the
erectable section.
The third configuration will be L-shaped combination of a
deployable truss, rotary joint and erectable module (all mounted
in-line) and another deployable section mounted at a 90-degree
angle to the end of the erectable truss. The final arrangement
will mount a flexible appendage simulating a solar panel or a solar
dynamic module to the elbow of the L- shaped third configuration.
Both test articles will be tested using vibrations over a
specified frequency range. On-orbit experiment operations with
both devices will include assembly, calibration, performance of
test routines and stowage.
MODE requires two eight-hour test periods in orbit.
Researchers expect to obtain more than four million bits of digital
data, about 4 hours of video tape, and more than 100 photographs.
The space-based data will be analyzed and detailed comparisons made
with pre- and post-flight measurements done on the flight hardware
using laboratory suspension systems. The results also will refine
numerical models used to predict the dynamic behavior of the test
articles.
This low-cost experiment will provide better understanding
of the capabilities and limitations of ground-based suspension
systems used to measure the dynamic response of complex structures.
It should lead to more sophisticated computer models that more
accurately predict the performance of future large space structures
and the impact of moving liquids in future spacecraft.
In response to the 1987 IN-STEP program solicitation, the
Massachusetts Institute of Technology Space Engineering Research
Center developed MODE and received a NASA contract that same year.
MIT selected Payload Systems Inc., Cambridge, Mass., as the prime
subcontractor responsible for hardware fabrication, certification
and mission support. McDonnell Douglas Space Systems Company,
Huntington Beach, Calif., joined the program in 1989 using its own
funds to support design and construction of the structural test
article.
NASA's Langley Research Center, Hampton, Va., manages the
contract. With NASA Headquarters, Langley also provides technical
and administrative assistance to integrate the payload into the
Space Shuttle.
Sherwin M. Beck is the NASA MODE project manager and Robert
N. Buchan is the NASA MODE experiment manager, both at Langley. MIT
Professor Edward F. Crawley is the experiment's principal
investigator. Edward Bokhour is hardware development manager and
Dr. Javier de Luis is experiment support scientist, both at Payload
Systems, Inc. Dr. Andrew S. Bicos is the project scientist at
McDonnell Douglas Space Systems Company.