Solar Heating of the Secondary.
For about two minutes in flight, the spacecraft may be oriented so that the
sun is focussed on one of the secondary mirrors. A series of measurements
and predictions of solar secondary heating are underway.
Predictions
All predictions are made with this ray-tracing IDL code.
These predictions are based on a two parameter
BRDF, which has been tuned to match the Dec 27 Goddard Klieg light
measurements on the TRS. A description of the Dec 27 Goddard
measurents, and the process used to match the BRDF to them.
In addition, I used the measured alpha of 0.4 for the aluminum
surface.
These images are wide. Be sure to scroll right to see the secondary.
Numerical predictions for average and maximum intensities of sunlight
on the "nodes" of the secondary used
by the thermal group at Goddard are availible for best fit to current TRS data
predictions, as well as for a worst-case
fit BRDF coefficients. (In the worst-case scenario, I tuned BDRF
coefficients so the spot peak intensities to 10% above what was
measured, and the spot widths to 20% above what was measured; a 60%
increase in total flux). These predictions cover incoming sunlight
elevation angles from 25 degrees above to 17 degrees below the
boresight, for each of the 18 nodes used in the thermal model.
For comparison, the previous solar predictions (made before the Dec 27 Klieg light measurements) are availible. These
predictions should be considered out of date.
MAP Technical
Naming Conventions
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Instrument
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