Theamal Analysis

FUNCTION

It assumes that CUTE encounter hard thermal environment in the space.Therefore demands arise as follows.

    · Grasp the range of operating temperature in the space
    · Aarrange environment for CUTE to operate surely
    · Improve the arrangement of each board

That is why we have got to thermal analysis

Thermistor

For future satellite development, it is important to know real thermal environment of the satellite on the orbit.
Especially students have little information about the environment of the satellite on the orbit.
So we put thermistors on CUTE to determine the heat environment for future.
This thermistors will let us know the heat environment of CUTE on the orbit.

We adopt PT5-51F as thermistor.

And refer to here to get where the thermal measurement points are in CUTE.

We conducted calibration for the thermistors which are used in CUTE.
The range of temperature is -25〜30℃.As an example, we show the calibration curve of one attached to battery.

THERMAL ANALYSIS

We have done thermal analysis by a package software of finite element method.
To grasp the flow of heat,we simplified the model of BBM. And we did thermal analysis with that.
The condition of that is as follows.

We adopt the model for thermal analysis as follows.

Also we define the name of each part of the model.

We conduct thermal analysis with the heat input is 13W in a wall1. This condition is a part of heat vacuum examination.

Foremore we defined that space temperature is 3K. And we used the values of these materials for CUTE as showed bellow.

	Al6061	PBTResin	Iron(SUS304)	SunCell	Li-ionBattery
Heat conduction　[W/m²]	180	0.2326	499	962	886.07
Specific heat　[J/kg/K]	896	2093.5	16	0.265	35
Density　[kg/m³]	2700	1310	7920	1811	2746.5

In addition we define other conditions as follows

    · Emmisivity is equal reflectivity because of restriction of package software which we use
    · All emmisivity of each material toward outside of CUTE is 0.9 for black paint,
      the emmisivity of each material toward inside of CUTE is 0.3.
      And the emmisivity of resin is 0.06.
    · Regard the generation of heat of each element as the generation of itself
    · All surface that is regarded to have small area doesn't have emmisivity
    · All initial temperature is 273K.
    · The end time of analysis is 80000 second.

Then we'll show a part of the result of the heat vacuum examination.

Wall0	Wall1	Wall2	Wall3	Wall4	Wall5
-30.8	180	0.2326	499	962	886.07
DJC1	DJC4	CommBox	Battery	CommBoard	OBCBoard
-20.3	-21.6	-23.6	-20.4	-24	-11.4
SensorBoard1	SensorBoard2	PowerBoard	DCDCConvertor	InterfaceBoard	UnderPaddle(Wall6)
-16.7	-26.2	-13.1	-9.7	-21.4	-80.5
UnderWall5(外)	Pillow1	Pillow2	Pillow3	Pillow4
-52.7	-25.8	-51.6	-45.2	-44.7

And we'll show the result of thermal analysis.

RESULT

Comparing the result of heat vacuum experiment and thermal analysis, the result of analysis donot correspond to the one of vacuum experiment completely. We could say that one of the reason is to hang our CUTE by strings and wiring for thermistor which are not taken into account in thermal analysis. We will store the skill of thermal analysis with monitering temperature of CUTE on the orbit in future.

RESULT

Considering the circumstances we can estimate the max temperature is about 80 Celsius degree, and the mininum temperature is -40 Celsius degree.
Actually this range of temperature will make for CUTE difficult to survive. Especially power system will be severe.
Because allowance of range of operating temparature is extremely narrow. But some error must be included to some extent because of assumption we difined.Error evaluation will be neccesary.
Anyway severe thermal condition will be expected from this analysis.