# 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/m^{2}. 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.