1. Preliminary MAP - Sun On Secondary Reflector Analysis #3
David Neuberger
12/13/00

2. Overview Of Problem
Sun reflected off the primary reflector can overheat the secondary reflector.
Maximum temperature limit = 105°C
Overheating could occur during solar acquisition phase of the transfer orbit.

3. Assumptions - General Deployed solar array model
Starting temperatures are the final temperatures of the very long coast run. The very long coast has the highest final temperatures.
A worst case azumith angle is assumed. The sun is in the Y-Z plane such that it strikes the mirrors squarely. It is also assumed that the fluxes strike the secondary mirror with the higher a/e ratio and highest temperature.
Slew rate analyzed are 0° (no slew) per minute.
Starting sun angles = 70°
No aero heating is applied.

4. Assumptions - Specific
Flux Intensity
f(distance from center)
Chris Barns’s gif files “Rays Landing on the Secondary Mirror” 0° above the bore-sight
No scale factor
f(location on reflector) # suns
Chris Barns’s gif files
Flux Location
f(elevation angle)
Chris Barns’s

5. Assumptions - Method Superimpose node map on gif file
Estimate fraction of each flux band on node
Input elevation angle (actually 90 - elevation) as a function of time.
TMM works as follows:
It interpolates to find angle as a function of time
It interpolates to find flux as a function of angle
Solves for temperature at that time step.

6. Flux Location and Intensity

7. Flux Intensity

8. Assumptions - Orbital Environmental Properties
SC = 450 Btu/Hr/Ft2
Albedo = 0.4
Earth IR = 84 Btu/Hr/Ft2
Orbital Properties Sun Acq.
Altitude (km)
Beta (°)

9. Assumptions - Surface Properties

10. Secondary Reflector Node Map

11. TMM Input Info Nodes On Previous Page
= $ SLEW TIME
0.0, 60.0, 120.0, 180.0, 240.0, 300.0 C
= $ ANGLE ARRAY VS TIME
50.0, 60.0, 70.0, 80.0, 90.0, 100.0
= $ ANGLE ARRAY VS FLUX
0.0, 10.0, 20.0, 30.0, 40.0, 50.0, 60.0, 70.0, 80.0
90.0, 100.0, 110.0, 120.0, 130.0, 140.0, 150.0
C ANGLE ABOVE HORIZON
C , 35.0, 28.0, 25.0, 24.0, 22.0, 19.0, 16.0, 11.0
C , 8.0, 2.0, 0.0, -10.0
= $ ANGLE ARRAY
50.0, , , , ,
71.0, , , ,
88.0, ,
= $ REFLECTED PRIMARY FLUX FOR NODE: INSTR.46501
0.00, , , ,
0.00, , , ,
0.00, , ,
GSFC ACS Provides
Your elevation angle
Our sun angle =
90° - elevation angle
This is what we need.
This is one of 18 arrays of
Flux in W/in^2 at the above
sun angles

14. Summary
The secondary mirror will overheat in 90 seconds of continuous sun down the bore-sight at 1.6 hot suns.