Thermal Subsystem PDR. Josh Stamps Nicole Demandante Robin Hegedus 12/8/2003. Mission Statement. To maintain temperature range of all hardware throughout the duration of flight.
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Knowing all sources of heat, as well as the geometry and thermal characteristics of all satellite components, we can predict the temperature at any point of interest.
- Specific Heat
Measure of how much heat energy per unit mass that an object gains or losses in a temperature change of one degree.
- Thermal Conductivity
Gives value to the heat flux that will travel through a material as a result of a temperature gradient.
- Absorptivity, Emissivity
Each is a percentage of how much incident radiation will be absorbed and emitted by an element. This is largely dependent on surface finish.Temperature Factors
- Sun (Direct Solar)
- Earth (IR)
- Earth Reflection (Albedo)
- Electrical Component
(Batteries, Solar Panels, etc.)
TAK III (Thermal Analysis Kit) – This software is what we utilize to obtain temperature predictions for any point in the satellite’s orbit.
The physical model is replaced by a collection of nodes linked together by conductors.
- conductivity in the case of conduction heat transfer
- emmissivity, absorptivity, and the incident radiation for the case of radiative conductors.
## - # - ### Each node is given a five digit ‘identifier.’
1 – Zenith (Boom) Panel
2 – Nadir (Camera) Panel
3,4,5,7,8,9 – Side Panels
6 – Internal Panels (example: Torque Rods)
10,11 – Aerofins
12 – FITS Panel
13,14,15,16,17,18,19,20,21 – Tip Mass
0 – Screws, Washers, etc.
1 – Most external components (Solar Panels)
2 – MLI nodes
3 – Frame Nodes (ISOGRID)
4 – Component Box Nodes
Letter Prefix is not part of the node index, but merely identifies the geometry of the node
A - .9855 x 8.255 x .5 (in)
B - .5 x .5 x .25 (in)
C - .12 x .25 x 1.9418 (in)
D - .656 x 11.781 x .25 (in)
NADIR ISOGRID (Side 2, Depth 3)
A - .25 x .3125 x 12 (in)
B - .25 x .3125 x 7.875 (in)
C - .25 x .5 x .8115 (in)
D - .25 x .5 x .5 (in)
E - .25 x .125 x 1.8832 (in)
F - .25 x .125 x 1.5 (in)
G - .25 x .125 x 1.75 (in)
H - .25 x .125 x 1.6819 (in)
SIDE Panel ISOGRID (Sides 3,4,5,7,8,9,10,11 Depth 3)
A – 10 x 10 x .3 (in)
B - .5 x .8492 x 8.25 (in)
C - .4822 x .4822 x .25 (in)
D - .12 x .25 x 1.697 (in)
E – 1.9418 x .12 x .25 (in)
F - .12 x .25 x 1.9423 (in)
G - .12 x .25 x 1.1709 (in)
H – 11.78 x 1.311 x .25 (in)
NADIR ISOGRID (Side 1, Depth 3)
- Nadir Frame (111 Nodes)
- Side Panels (462 Nodes)
- Zenith Panel (35 Nodes)
- MLI Nodes (56)
- Tip Mass (About 400 nodes)
- Components (About 75 nodes)
Percent Complete ~ 58%
There are two kinds of conductors, which connect nodes and explain heat transfer between them.
- Conduction based and Radiation based
The most basic conductor is the conduction based conductor. This represents heat that transfers between nodes via conduction.
The equation is C = k*A/L
k – material conductivity
A - is the interface area between nodes
L - length between the centers of each node
ERROR POTENTIAL – This assumes a tight interface between nodes, which becomes an issue in cases where nodes are connected by pressure (screws, MLI-side panels, etc.)
Radiation conductors are a bit more complex. Blame Ludwig Boltzmann for this. And for this reason, rather than hand calculating each conductor we use an algorithm developed by Bob Poley at Ball Aerospace.
The purpose of Supview is to input the orientation of all nodes modeled and to determine how much of one another they ‘see’. In this case, the nodes are treated as surfaces defined by Cartesian coordinates with respect to the exact center of DINO. The output is a collection of view factors to be taken as the interface area between the nodes.
Starting/Ending Days (3/21/6-3/22/7)
Universal Time (6AM or 3600 seconds)
Apogee/Perigee (6728 km)
Inclination (51.6 degrees)
Beta Angles (Hot-75.1 degrees, Cold-0 degrees)
Solar Flux (Hot-1428 w/m^2, Cold-1316 w/m^2)
Earthshine IR (Hot-227 w/m^2, Cold-175 w/m^2)
Albedo (Hot-56%, Cold-37%)
Enter Shadow (Hot-never, Cold-198.6 degrees)
Exit Shadow (Hot-always, Cold-61.4 degrees)
Purpose of Multi-Layer Insulation:
Mylar ‘Pillow case’
Dacron net spacers
It was hinted at recently that perhaps we could get pre-assembled MLI blankets from Ball. I have not been able to follow up on that at this time, but it is a possibility. Otherwise, we can simply purchase the materials and sow it together ourselves. We have met with an advisor at Ball, Leslie Buchanan, who is willing to aid us in the process.
- Materials. If we do end up purchasing the materials, we can select them based on which emmissivity and absorptivity values are required for our system to work. For example we can select other metallized finishes.
- Inner Layer Optimization. We need to optimize how many layers of Dacron netting are needed.
- Size Optimization. Currently we are assuming MLI’s will surround all surfaces with the exception of the zenith panel and aerofins. However, we must also determine if it’s possible to wedge MLI blankets between the frame and solar panels as well as between Lightband and the Nadir Plate.
The norm for testing the thermal model of a satellite is by placing it in a thermal vacuum, dropping the temperature to around 5 degrees Kelvin, and monitoring the temperature at several pre-selected locations using thermocouples.