USAGE FOR THERMAL CONTROL: INSAT-1
DOMESTIC SATELLITE SYSTEM FOR INDIA
The Western Development Laboratories Division (WDL) of Ford
Aerospace Communications Corporation (FACC) was chosen by
the Government of India to design and build the first generation
spacecraft for the Indian National Satellite System …
INSAT-1. This spacecraft (shown in Figure 3-1) will introduce
sociological and economical advantages of modern communications
to India’s population which exceeds 613,000,000 and covers
a land area measuring 3,280,483 square kilometers. INSAT-1
will provide reliable communication capability to India’s
rugged terrain and inaccessible regions far more economically
than any alternative high quality terrestrial system.
To accomplish the satellite’s major communications,
direct broadcast satellite service, meteorology and data collection
missions, it will be placed in geostationary orbit 35,784
Km above India and will employ a single 445-newton (100 pound)
thruster for apogee boost. During design and development of
the thruster at WDL, protection of adjacent structure against
the plume was considered necessary. Titanium was the best
lightweight choice for a shield, provided the thermal absorptivity/emissivity
of less than 1.0 could be achieved. The TIODIZE Type I Process
has these characteristics, and samples of 6Al-4V titanium
were coated by TIODIZE Co., Inc. and evaluated by WDL utilizing
the Gier Dunkle Source Transfer Optical System. Subsequently,
preformed parts of the flight hardware were coated, and test
samples were processed with the parts to verify thermal characteristics.
Results of WDL tests on these test samples are presented below:
| |
Sample |
#1 |
#2 |
#3 |
#4 |
#5 |
| Absorptivity (as) |
|
.71 |
.70 |
.67 |
.63 |
.69 |
| Emissivity (en) |
|
.80 |
.81 |
.83 |
.85 |
.82 |
| as/en |
|
.89 |
.86 |
.81 |
.74 |
.84 |
| Absorptivity (as) |
.58 |
| Emissivity (en) |
.89 |
| as/en |
.65 |
Since the desired as/´n of less than 1.0 was achieved
by the single coating, the heavier coating used to achieve
the very low ratio was not used for production hardware. For
additional testing, see page 12 of the Tiodize Process Booklet.
ABSORPTANCE AND EMITTANCE TESTS
Another significant use for the TIODIZE PROCESS is the control
of thermal radiation. The solar absorptance (as) and normal
emittance (´n) for ULTRA V-E17 and bare Type I and II
TIODIZE PROCESS coatings were found to be as shown below:
| |
|
TYPE I |
|
TYPE II BARE |
| |
Bare |
|
Ultra V-EI7 |
|
| (as) |
0.62 |
|
0.89 |
0.82 |
| (en) |
0.89 |
|
0.91 |
0.51 |
| Sample |
Description |
Color |
Emittance |
Adhesion |
| A |
TIODIZE Type II all over
Ultra VE-17 one side
No Top Coat |
Black |
.928
.923 |
No Loss |
| B |
Same as A, except
with Top Coat |
Black |
.936
.934 |
No Loss |
| C |
TIODIZE Type I all over
Ultra VE-17 one side
No Top Coat |
Black |
.946
.947
|
No Loss |
| D |
Same as C, except with
Top Coat |
Black |
.950.951 |
No Loss |
| E |
TIODIZE Type I all over
+K-seal |
Tan |
.932.946
|
Some loss on side 1 of each panel; No loss on reverse
side of each panel. |
| Required Tests |
Test Method Used |
Test Results |
Requirements |
Pass/Fail |
| Outgassing |
ASTM E595 |
TML = 0.9100% VCM = 0.0000% |
TML Ë 1.0% VCM Ë 0.1%
|
PASS |
The specimens were made of Titanium 6Al-4V foil, .005 inches
in thickness, and TIODIZED with Type I and Type II. The ULTRA V-E17, when
used, was TIODIZE® black organic coating. The absorptance
was determined by the 19 point integration between 0.32 and
2.1 microns wavelength. The emittance was arrived at by a
25 point integration between 4.8 and 26.2 microns. Spectral
measurements were made in either a heated Hohlraum chamber
or a Gierdunkle integrating sphere with an incident angle
of 20 degrees on specimens water cooled to approximately room
temperature.
|
m
-s
)n.
