The
ISS microgravity acceleration environment
consists of two regimes: the quasi-steady
environment and the vibratory/transient
environment; therefore, the measurement
of the microgravity acceleration environment
is best accomplished by two accelerometer
systems. In the United States Laboratory
Module, the measurement of these two regimes
is accomplished by the Space Acceleration
Measurement System-II (SAMS-II) and the
Microgravity Acceleration Measurement System
(MAMS). The vibratory/transient environment,
consisting of vehicle, crew, and equipment
disturbances and covering the frequency
range 0.01 300 Hz, will be measured
by the SAMS-II. Due to the localized nature
of these vibrations, this frequency range
requires measurement of the environment
near the experiment hardware of interest.
SAMS-II provides this distributed measurement
system through the use of Remote Triaxial
Sensor systems (RTS). An individual RTS
consists of an Electronics Enclosure (EE)
and two Sensor Enclosures (SE). A SAMS-II
Control Unit housed in an International
Subrack Interface Standard (ISIS) drawer
collects data from all active EE's and prepares
the data for downlink.
The
MAMS will record the quasi-steady microgravity
environment (f < 0.01 Hz), including
the influences of aerodynamic drag, vehicle
rotation, and venting effects. The MAMS
unit will be located in the United States
Laboratory Module in a double middeck locker
enclosure. PIMS will utilize MAMS for its
ability to sense the quasi-steady regime.
The MAMS Miniature Electrostatic Accelerometer
(MESA) sensor is a flight spare from the
Orbital Acceleration Research Experiment
(OARE) program that was used to characterize
the quasi-steady acceleration environment
of the Space Shuttle Columbia. Like the
OARE data recorded during eleven STS missions,
utilizing rigid body assumptions at these
low frequencies will allow MAMS MESA data
to be mapped to alternate locations within
the ISS using ISS body rates and body angles
data.
Due
to the dynamic nature of the
microgravity environment and
its potential to influence sensitive
experiments, the Principal Investigator
Microgravity Services project
has initiated a plan through
which the data from these instruments
will be distributed to researchers
in a timely and meaningful fashion.
Beyond the obvious benefit of
correlation between accelerations
and the scientific phenomena
being studied, such information
is also useful for hardware
developers who can gain qualitative
and quantitative feedback about
their facility acceleration
output to the ISS. Further,
a general characterization of
the ISS microgravity environment
will be obtained that affords
scientists and hardware developers
the pre-flight ability to anticipate
the acceleration environment
available for experimentation.
Similar to STS operations, a
handbook of acceleration disturbance
sources for the ISS will be
developed and maintained to
provide a concise visualization
of the ISS disturbance database.
PIMS
ground support equipment located
at the NASA Glenn Telescience
Support Center will be capable
of generating a standard suite
of acceleration data displays,
including the various time domain
and frequency domain options
described in Table 3. These
data displays will be updated
in real-time and will periodically
update images available via
the PIMS WWW page. The planned
update rate is every two minutes.
Future plans involve routing
the measured ISS acceleration
data directly to a PI's operations
facilities.
To
supplement the near real-time
displays, planned information
resources will also be provided
throughout the tenure of the
systems on the ISS. General
characterizations of the environment
as it evolves will be made available
on a regular basis so that investigators
are aware of the overall environment
in which their experiments were
conducted. Accelerometer data
archives and automated data
analysis servers will allow
investigators the ability to
request customized data analysis
support. Additionally, a catalog
of characterized disturbance
sources will be available in
the form of an ISS MEDH.
