The JUSTSAP experiment on STS-95 |
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Authors: | Robert J Naumann Glen Haulenbeek Hiroshi Kawamura and Keisuke Matsunaga |
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Affiliation: | (1) University of Alabama in Huntsville, Room M-43, von Braun Research Hall, 35899 Huntsville, AL, USA |
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Abstract: | An instrumented flow cell in the form of a cylinder with differentially heated end walls and adiabatic sidewalls was flown
on STS-95 as the Japan-US Thermal Science Accelerometer Project (JUSTSAP). The purpose of the experiment was to map disturbances
in the thermal field during the course of a Shuttle mission in order to correlated them with various mission events and to
determine if any global transport could be detected from second order, non-zero time average flows resulting from periodic
accelerations (g-jitter).
Significant disturbances in the thermal field were noted each time the Shuttle changed attitude, such as the maneuver to -Z
solar inertial, which is done periodically for thermal conditioning. Burns from the main thrusters associated with the launch
and retrieval of the Spartan satellite produced overturning flows, as might be expected. During extended periods in which
the attitude was held constant, the perturbations to the thermal field correlate extremely well with calculated accelerations
from gravity gradient and drag. Fair agreement was found between the observed temperature perturbations and those predicted
from a modification of the analytical model developed by Bejan and Tien (B&T) for the flow and heat transfer in an infinite
cylinder with a constant axial thermal gradient. A full three-dimensional computational fluid dynamic analysis with more realistic
thermal boundary conditions provided better agreement after adjustments were made to account for the heat flow away from the
measuring thermistors.
Once calibrated with a reliable thermal model, the flow cell was found to serve as a high-precision accelerometer, capable
of measuring the quasi-steady acceleration with a sensitivity of better than 0.1 micro-g in the presence of the higher amplitude
g-jitter typical of Shuttle operations. Further, it was found that the gravity gradient acceleration accounted for virtually
all of the observed quasi-steady accelerations during such extended periods. The thermal response time of the JUSTSAP was
too slow to expect to see the effects of fluctuating first order flows resulting from the vibrational environment of the Shuttle.
However, an indication of a change in the thermal field near the ends of the flow cell was seen during periods of crew exercise
that may possibly be attributed to circulating eddies resulting from the higher order terms in the momentum equation. At higher
amplitudes, these second order effects can produce non-zero time average flows of a global nature, as can the start-up transients
in first-order periodic flows. No such effects were observed, thus it is possible to place an upper limit on the integrated
power spectral density of the vibrational environment experienced as well as the nature of the start-up transients of the
periodic flows. |
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