# ENAE 483/788D Principles of Space Systems Design Fall, 2002

## Question 12:

For both ENAE 483 and ENAE 788D:

a) The front side of a photovoltaic array has an absorptivity of 0.7 and emissivity of 0.5, The back side of the panel has an absorptivity of 0.2 and emissivity of 0.85. Find the equilibrium temperature for this panel at the same distance from the sun as the Earth.

b) Find the equilibrium temperature for (a) when the array is shadowed (no solar illumination).

c) You are designing a solar sail for inner solar system exploration, The sunlit side of the sail has an absorptivity of 0.03. Find the required emissivity (assume front and back are the same) to keep the equilibrium temperature at 0.2 AU less than 400°K.

d) Assume the emissivity of the sail (front and back) is 0.85. You decide to accelerate the sail away from Earth by supplementing the solar flux with a high-powered laser, which reaches the sail at a power level of 10 kW/m2. What is the equilibrium temperature the sail must withstand for this case?

For ENAE 788D only:

You are responsible for the thermal analysis of a lunar landing vehicle. Assume the spacecraft is spherical with a diameter of 3 m. It has a constant internal power usage of 3 kW. The surface coatings have an absorptivity of 0.1 and emissivity of 0.9.

e) The spacecraft is in space on the way to the moon, and is illuminated by the sun. What is the equilibrium temperature?

f) It is lunar noon, and the spacecraft is sitting on the lunar surface on landing legs which do not affect the thermal equilibrium. Assume half the surface area of the ship radiates to deep space, and half radiates to the local ambient temperature on the lunar surface, which is 250°F. The spacecraft is fully illuminated by the sun. Find the equilibrium temperature for the spacecraft.

g) It is local midnight, and the surface ambient temperature is -250°F. Find the equilibrium temperature for the spacecraft.