SAMPE Journal - March/April 2024 - 21

Run
1
2
3
4
5
6
heat flux qcw
configuration
Sideway
Sideway
Sideway
Stagnation
Stagnation
Stagnation
liner
Titanium
Graphite
Titanium
Titanium
Graphite
Titanium
Pel
kW
362.7
363.7
551.4
384.6
382.3
551
, stagnation pressure pstag
˙
qcw
kW/m2
3100
3100
5500
3500
3500
5500
, test time T.
pch
hPa
8.51
8.44
8.33
8.34
7.99
8.60
pstag
hPa
52.5
52.5
62.4
53.5
53.5
62.4
T
s
132.7
421.4
(demise)
174.1
96.2
290.7
(demise)
173.3
Table 5. Test conditions overview: test index, test configuration, sample liner at the stagnation point, electrical power Pel
˙ , chamber pressure pch
with the plasma stream. The Titanium liner did not
survive the harsh environment at the stagnation point
and through hole was observed. Surface and internal
temperature from various instruments were plotted
with respect to test duration Figure 10(b). Towards the
end of the test, at 150 sec, an interesting temperature
trend was captured, and a sharp increase in
temperature was observed. This behavior is due to
the carbon wrapping degrading all the way and a
hole opened in the material causing the specimen to
act as a cavity at high emissivity. This phenomenon
was only captured with the pyrometer, this could
be because the pyrometer was pointing at the
exact location where the small hole opened in
the center of the sample (Figure10(a)). Type-K
thermocouples are rated for temperatures below
1500 K, after reaching the maximum temperature,
the thermocouples were disconnected, noisy data
was obtained, and data collected past that point is
no longer reliable and shaded in gray on the graph.
Figure 10(c) shows a picture before and after
the experiment for test 6. Similar to test 3, it was
apparent that after 174 seconds of testing, most
of the frontal carbon wrapping had been removed
and the titanium liner did not survive leaving a
through hole in the specimen. Surface and internal
temperature are plotted vs time (Figure 10(d)).
, cold-wall
Figure 9. A picture of COPV test with the Plasmatron running.
The most remarkable observations from all the tests are supported in
Figure 11. They can be summarized as follows: for testing times leading to
the reproduction of the flight-integrated heat flux, mostly thermochemical
ablation of the fibers accompanied by intense pyrolysis could be observed but
the wrapping stayed almost intact. This suggests that under typical reentry
conditions, COPVs are expected to survive and reach the ground. It is only
for significantly longer runs that the ablation of the carbon fibers and the
char materials became important. After complete ablation of the protective
wrapping in the regions subjected to the highest heat flux, the melting of
the titanium liner accompanied by the injection of gaseous titanium species
could be observed, eventually leading to the creation of a hole in the liner. It is
(a)
(b)
(c)
(d)
Figure 10. (a) Test 3 pre- and post-test photographs, (b) Test 3 surface and internal temperatures, (c) Test 6 pre- and post-test photographs (d) Test
6 surface and internal temperatures.
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MARCH APRIL 2024
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