Thermal Environment

Initial thermal calculations are based on a seven node blackbody analysis (six sides and the insides).

Thermal
The sun is modelled as a black body.
A node is a finite sub-division of the thermal system so that thermal balance and heat flow may be calculated in unsimilar components.

There are 2 elements to each node, and 3 types of node.
The elements are the Temperature T, which is analogous to potential.
and thermal mass C, or capacitance.

The 3 types are,
Diffusion
Arithmetic
Boundary

Errors that can occur are due to,
Material Thermal Properties
Boundary Conditions
Node Size (smaller the better)
Node Centre Placement
and Time Increment of Dynamic Calculations

Diffusion
-for normal materials
-heat flow in or out of materials
-involves potential, capacitance value, net heat flow, and time.

(1)
\begin{align} \Sigma { \delta Q \over \delta t } - {C \Delta T \over t} = 0 \end{align}

Arithmetic
-has zero capacitance
-useful for small components, such as bolts, thin films, gas contents of tubes and low-mass insulation
-but should only form a minority of the number of nodes

(2)
\begin{align} \Sigma {\delta Q \over \delta t } =0 \end{align}

Boundary
-has infinite capacitance
-for constant temperature boundaries or heat sinks (such as space)
-it can be used for nodes that have a large thermal capacitance (lots of mass) though this is not realistic for cubesat

(3)
$$T = constant$$

Nodes typically sub-divide the main structure into simple volumes that are easy to calculate.
In the case of a simple seven node model each of the solar panels, and the internal components are nodes.

The solar panels are modelled for 3 cases,
-in full sunlight, where the maximum number (3) of panels are illuminated
-in partial sunlight, where only 1 panel is illuminated
-and in shadow, where no panels are illuminated

page revision: 16, last edited: 08 Dec 2007 13:40