Louvers are active thermal control devices used on spacecraft. They are devices which mask a high-emissivity radiator with a low-emissivity surface. As the temperature of the radiator gets hotter, the mask is withdrawn, exposing the radiator. The drive mechanism is usually a bi-metallic actuator, but active control could be used. There are several styles of louvers. A bladed version is shown below.
A louver is modeled in TAK 2000 by specifying the node that represents the control temperature (usually the louver radiator node), an effective emissivity-versus-temperature array, an effective absorptivity-versus-temperature array, radiation conductors from the louver, I.R. flux tables, and solar flux tables. Multiple radiation conductors and flux tables can be entered by separating them with a slash "/". The format for a louver is shown below.
N#, A1, A2, G1/G2/...Gm, SA1/SA2/...SAn, IRA1/IRA2/...IRAnn $ (basic format)
HEADER LOUVER DATA
45, 101, 102, 3001/3002, 1056/1087, 2056/2087 $ louver above node 45
In the example, the radiator under the louver is represented by node 45. The doublet arrays 101 and 102 contain the temperature dependent surface finishes which are a characteristic of this particular louver assembly. Conductors 3001 and 3002 are adjusted continuously by multiplying the original value by the current emissivity (G= GORIGINAL x e* ). The "solar" heating arrays 1056 and 1087 are FLX arrays that were generated for the louver node as if it had a "black" surface. This heat is applied to node 45 as a function of time, as usual. However, it is multiplied by the solar absorptivity of the louver radiator (QABSORBED= QINCIDENT x a ). The"a" is obtained by interpolating array 102 using the temperature of node 45 as the independent variable. The I.R. heating arrays 2056 and 2087 were generated for node 45 as if it had an IR "black" surface. Again, these arrays are adjusted with the values obtained from the emissivity array (QABSORBED = QINCIDENT x e ). (NOTE: These heating arrays are in FLX format.)
If the user does not wish to model radiation conductors, or one type of flux tables, these fields should be left blank. However, as a general rule, if a non-empty data field follows an empty field then commas need to enclose the empty field. For example, if no radiation conductors are modeled, the following format should be used.
N#, A1, A2,     , SA1/SA2/...SAn, IRA1/IRA2/...IRAnn $ no radiation conductors
If no I.R. flux tables are modeled, then a comma after the solar flux tables need not be included .
N#, A1, A2, G1/G2/...Gm, SA1/SA2/...SAn $ no IR heating arrays
Remember, the louver node's surface is assumed to originally have an absorptivity and emissivity of 1.0 when the radiation and heat flux tables were generated.