For the solar panels of the European Space Agency (ESA) satellites OTS/MAROTS and ECS/MARECS the thermal cycling tests were performed by using solar simulation methods. The performance data of two different solar simulators used and the thermal test results are described. The solar simulation thermal cycling tests for the ECS/MARECS solar panels were carried out with the aid of a rotatable multipanel test rig by which simultaneous testing of three solar panels was possible. As an alternative thermal test method, the capability of an infrared radiation method was studied and infrared simulation tests for the ultralight panel and the INTELSAT 5 solar panels were performed. The setup and the characteristics of the infrared radiation unit using a quartz lamp array of approx. 15 sq and LN2-cooled shutter and the thermal test results are presented. The irradiation uniformity, the solar panel temperature distribution, temperature changing rates for both test methods are compared. Results indicate the infrared simulation is an effective solar panel thermal testing method

Nuss, H. E.

English

NASA Technical Reports Server

..N81-14164
SOLAR PANEL THERMAL CYCLING TESTING
BY SOLAR SIMULATION AND INFRARED RADIATION METHODS
Hubert E. Nuss*
ABSTRACT
For the solar panels of the European Space Agency (ESA) sa-
tellites OTS/MAROTS and ECS/MARECS the thermal cycling tests
were performed by using solar simulation methods. The perform-
ance data of two different solar simulators used for these tests
and the thermal test results are described. The solar simul-
ation thermal cycling tests for the ECS/MARECS solar panels were
carried out with the aid of a rotatable multlpanel test rig by
which simultaneous testing of three solar panels was possible.
As an alternative thermal test method the capability of an in-
frared radiation method was studied and infrared simulation
tests for the ultralight panel (ULP) and the INTELSAT V solar
panels were performed. The setup and the characteristics of
the _nfrared radiation unit using a quartz lamp array of approx.
15 m_ and LN2-cooled shutter and the thermal test results are
presented. The irradiation uniformity, the solar panel temper-
ature distribution, temperature changing rates for both test
methods are compared. The results indicate the infrared simul-
ation is an effective solar panel thermal testing method.
INTRODUCTION
Thermal vacuum tests are required for qualification and ac-
ceptance of spacecraft subsystems. The purpose of qualification
tests is to prove the subsystem design by checking its perform-
ance capability under thermal vacuum conditivns more severe
than predicted for orbit. The aim of the more severe temper-
ature stress is to demonstrate design safety margin and to ac-
celerate failure in marginal design. The objective of the ac-
ceptance tests is to demonstrate the performance of the sub-
systems of proven design in the temperature range expected in
flight and to verify the workmanship according to flight stan-
dard quality. The cycling between temperature extremes is to
induce temperature gradients in the subsystem thereby permit-
tlng observation of operation at other than stabilized condit-
ions.
Thermal vacuum facilities are currently available with
four distinct types of energy control: temperature controlled
shrouds, solar simulators, infrared radiators, surface blanket
heaters.
*Industrieanlagen-Betr_ebsgesellschaft mbH (IABG), Space Divis-
ion, D 8012 0ttobrunn, West Germany.
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The development of infrared simulators with tungsten fila-
ment quartz lamps (refs. 1 to 4) and other methods for infrared
simulation (carbon cloth heat post, fluld controlled panels,
thermal canister, electrical heaters) were described in several
papers (refs. 5 to 8). The application of the different methods
for thermal balance testing was investigated in these studies
and the performance data, testing philosophy, and cost effect-
iveness were compared (refs. 9 to 14).
For satellite programmes thermal vacuum tests have to be
performed for a number of units according to the same specific-
ation. It is especially true for acceptance testin_ of the
different solar panels of communication satelllte's solar array.
The cost effectiveness of solar panel thermal testing can be im-
proved by testing simultaneously more than one panel. In this
paper the development of an infrared radiation unit for slmul-
taneous testing of three solar panels is described. The per-
formance data and operational conditions of the infrared radiat-
or setup were studied.
Thermal cycling test results and cost effectiveness for
infrared simulation, for solar simulation for one solar panel,
and for multl-panel solar simulation are compared in the follow-
ing.
1. TEST REQUIREMENTS AND FACILITIES
Thermal vacuum testing of solar panels can be performed
by irradiating the panel front side by a solar simulation or an
infrared simulation setup. By radiation to LN2-cooled shrouds
the temperature gradients through the panel and the temperature
changing rates during the transient phases are similar to the
expected orbit _ondltlons.
The main test requirements for solar panel thermal cycling
tests for different programmes are summarized in Table I. In
general the primary requirement for solar panel thermal testing
by solar simulation methods is the specification of the solar
irradlance to be simulated during test. For the ECS/MARECS
solar panel tests this Irradlance was defined equivalent to a
definite value of the open voltage readout during the sunphases
of the thermal cycling test. For the infrared radiation methods
the equilibrium temperatures were specified and therefore the
power of the infrared radiators had to be adjusted to values to
achieve the temperatures required.
i.i Solar Simulation Facility (Fig. 1 and 2)
The solar panel thermal cycling tests for the OTS/MA/%OTS
programme were performed in the 3m-space simulation facility of
IABG (ref. 16). The facillty Is equipped with an LN2-cooled
shroud of 3 m diameter and 7 m length. The solar simulator is
an off-axls system. The radiation is performed by four 25 kW
and five 6.5 kW Xenon Arc lamps. The light is collected in
elliptical mirrors, folded by a plane mirror system to a collim-
ation mirror dhlch directs the radiation into the reference
plane. By means of a light integrator the radiation of the dif-
ferent light sources is superimposed, hence Improving the unl-
formity in the reference plane.
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1981005626-328
_e collimation mirror consists of about I000 adjustable
mosaic elements anu was adjusted to irradiate a reference plane
of 1.9 m diameter, which was sufficient for the dimensions of
the solar panels with 1.31 m width and 1.45 m height. The uni-
formity measurements showed a maximum deviation from the mean
value of radiation intensity in the reference plane of _ 8 %.
For simulation of the cold phases an LN2-cooled shutter-between
collimation mirror and test article shielded the simulated solar
radiation.
The relatively low overall efficiency of the solar simulat-
or was due to the fact that the solar simulator was in a modif-
ication phase which was not completed when the tests had to be
performed.
The ECS/MARECS solar panel thermal cycling tests were car-
ried out in the 3m-space simulation facility with the complete
modified solar simulator implemented (Fig. 2). Compared to the
original design the folding mirror system for the modified sol-
ar simulator could be deleted. The solar simulator was equip-
ed with an integrator adjusted to the efficient operation of
five 25 kW Xenon Arc lamps. The mosaic mirror was exchanged
by a segment mirror consisting of 37 elements. Due to the optic-
al system modification a solar beam diameter of 2.4 m in the
reference plane and an overall efficiency of the solar simul-
ator of approximately I0 % could be achieved. For the ECS/
MARECS solar p_nel thermal cycling tests the facility was equip-
ed with a rotatable multipanel test rig of triangular shape
(ref. 2?.). By this additional device the cost effective simult-
aneouz testing of 3 solar panels was possible: one panel being
irradiatad by the solar simulator while for the other two a
coldphase was simulated.
1.2 Infrared Radiation Facility
(Fig. 3, 4, 5)
The thermal vacuum tests for the INTELSAT V solar panels
(dimensions 1.65 m width, 1.91 m height) were carried out in the
thermal vacuum facility 3.5 m-TVA of IABG (ref. 18). The facil-
ity is equipped with a GN2-cooled shroud of 3.5 m diameter and
6.3 m height. For the infrared simulation thermal cycling tests
the facility was furnished with an infrared radiation unit with
uartz-llne lamps and a liquid nitrogen-cooled, movable shutter
Fig. 3 and 4). The lamp array can be shielded during the cold-
phase by moving the LN2-cooled shutter in front of the lamp ra-
diators. The infrared radiation unit consists of three lam_
array modules with a total number of 300 quartz-line lamps (nom-
inal power 500 W each). Fig. 3 shows a schematic sketch of two
modules of the lamp array used for irradiating two solar panels.
For the third solar panel a third lamp array module on the rear
side of the two exhibited ones was used. In between the first
two and the third lamp array module an LN2-cooled shroud is
located to minimize the radiation of not LN2-cooled surfaces
to the panels during coldphase. By 150 electrical control units
and power supplies the 150 lamp pairs can be controlled sep-
arately.
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1981005626-329
For the thermal vacuum cycling tests of the ultrallght
panel (ULP, dimensions 1.1 m width and 3.22 m height) (ref. 19)
two lamp array modules as shown in Fig. 3 were used.
The primary requirements for an infrared radiator setup to
be applied for thermal cycling tests are optimum uniformity of
irradience in the test plane and minimum blockage of cold shroud
during the coldphases. The blockage of the shroud was reduced
by the LN2-cooled shutter as shown in Fig. 4. By measuring the
irradiance distribution before the test and adjusting tho dif-
ferent control units the irradiance uniformity was optimized.
To monitor the irradiance distribution ofg_he infrared
lamp array modules a solarcell sensor of 16 cm_ surface area
was moved vertically and horizontally in the testplane. A typ-
ical readout of the sensor measured by scanning along a distan-
ce of approximately 5000 mm is shown in Fig. 5. The result of
the evaluation of a total number of 765 measured extreme values
for the three infrared lamp array modules is given _n Table II.
This Table indicates that for the testplane of 15 m an irradi-
ance uniformity of & + i0 % could be achieved with approx. 75 %
of the measuring points within the range of _ + 5 %.
2. TEST RESULTS
The temperature Tp of a solar panel in a space simulation
facility is described _y the following equation:
mc =_FI - _ e_F (T - Tsh) (I)
mc : Thermal capacity of lest article
: Temperature change of test articlewith time
I, F : Irradiance and surface area, respectively
: Stefan-Boltzmann-Constant
e, Tsh : Viewfactor to shroud and shroud temperature,resp.
6, _ : Emissivity and absorptivity, respectively
The solar panel thermal equilibrium temperature TE can be
derived from equation i:
TE = + T4 (2)sh
From equation 2 the relative temperature change ATE/T E
due to a relative intensity variation aI/I can be
calculated (ref. 20):
ATE 1 AI
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1981005626-330
Taking into account the irradiation uniformity and the
neat conductivity in the panel surface (characterized by the
expression AFt2) the following expression for the temperature
change ATE1 i_ found from equation l:
TEl = - _,,, , AI (4)
8 G £ TEl3 + AFI2
For the transition from warmphase to coldphase from equat-
ion 1 the ratio f of the slopes of the temperature - time -
plotts for solar simulation and infrared simulation can be de-
rived:
dT/atlsol ,"_%hI4
= 4 P .... (5)f
_Tp/dtllR'- Tp - Tsh24 - 21Fle I 4
T1
For the infrared radiation method surface parts of the
lamp array which are not completely covered by the LN2-cooled
shutter are taken into account by including an irradiance of an
emissivity E1 , of a viewing factor el, of an area F 1 and of s
temperature T1 .
2.1 Solar Panel equilibrium Temperature Distribution
In Fig. 6 a typical transient phase for solar simulation
thermal cycling is exhibited. The tempel _tures o_ the solar
panel frontside were measured in the range 61 + 4 CA According
to equation 2 an equilibrium temperature of T_-= 60vC can be
calculated. By using equation 3 and a value _f + 8 % for th_
irradlance uniformity a maximum temperature variitlon of + 7vC
is estimated. The measured temperature uniformity of + 4OC can
be interpreted by the effect of heat conductance in the panel
surface as described by equation 4.
A typical transient phase for infrared simulation cycling
tests with three solar panels is plotted in Fig. 7. The temper-
atures_on the three solar panels were measured in the range
85 + 5°C. The lamp array modules with 300 radiators were _per-
atea with a total power of 39 kW on a surface area of 15 m .
Using the given reflectivity of the lamp reflector and the view-
ing factor determined2bY geometry of the test setup an Irradi-
ance of I - 1.83 kW/m is calculated. From equation 2 an equll-
ibrlum temperature of T_ - 83oc is determined in good agreement
with the experimental r_sults.
The panel temperature distribution at the end of the cold
phases is measured in the range -158 + 5°C for solar simulation
cycling tests with one and with three'panels and for infrared
simulation tests with one and with three panels.
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1981005626-331
2.2 Temperature Changing Rates
During transition from warmphase to coldphase the temper-
ature changing rates AT./At for solar simulation and for in-
frared simulation were Vmeasured as indicated in Table III.
There is no essential difference in the temperature chm.glng
rates of solar simulation and infrared simulation in the temper-
ature range T _ 50°C to T - -50°C. For a panel temperature
of T_ - -150oPc the tempe_ture changing rate for infrared slm-
ulaulon is by a factor of 2 lower than the rate for solar sim-
ulation. In this temperature range the influence of structure
parts of the lamp array modules which are not completely cover-
ed by the shutter has to be considered.
2.5 Cost effectiveness
Th_ primary test cost saving effect can be achieved by
simultaneous testing of three instead of one solar panel. Using
a solar simulation facility and a multipanel test rig for three
solar panels the operational test costs per panel amount to ap-
proximately 40 % of the costs for single pane], testing. With a
setup of infrared lamp array modules for three panels the oper-
ational test costs per panel are about 38 % of the operational
costs for single panel solar simulation testing.
5. CONCLUSIONS
The comparison of multipanel thermal testing data for sol-
ar simulation and infrared simulation with single panel test-
ing data indicate that the essential thermal cycling test re-
quirements can be fulfilled for the two multlpanel testing me-
thods.
During an operational tame of approximately !000 hours for
the infrared lamp array modules including an LN2-cooled shutter
no essential operationa] problems occurred and, therefore, the
reliability of the system is promising.
In cases where no spectral match and no low collimation
angle of the radiation are required infrared simulation thermal
cycling of solar panels is advantageous because of cost effect-
iveness of multiple panel testing, high efficiency of infrared
radiation setups and high llfe time of radiators.
REFERENCES
i. Skinner,D.J.; Wallin,S.P.; Wolff,C.M.: The Design and Ap-
plication of an Infrared Simulator for Thermal Vacuum Test-
ing, NASA SP-298, 1972, p. 197.
2. Dewey,R.L.: Control of an Artificial Infrared Environment
to Simulate Complex, Time-Varying Orbital Conditions, NASA
SP-298, 1972, p. 217.
3. Nelson,L.A.; Levine,M.B.: Development of a Heater Post and
Spotlight Array for Thermal Vacuum Testing of the INTELSAT
V Communication Satellite, NASA SP-556, 1975, p. 665.
4. Williams,F.U.: Analysis of Radiative Sources with Both
Specular and Diffuse Characteristics in the Visible and
Infrared Spectrum, NASA SP-379, 1975, p. 355.
323
I I
1981005626-332
5. Levine,M.B.; Nelson,L.A.: DeveloFment of a Carbon Cloth
Heat Post Module for Thermal Vacuum Testing of a Spinning
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Infrared Simulator for Testing of the Shuttle Radiator Sys-
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7. GUlpen,J.; Lorenz,W.: Infrared Test Techniques Developed
for the Helios Spacecraft, ESA SP-95, 1973, p. 301.
8. Esposti,P.L.D.; Strom,B.: Experimental Comparison between
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9. Arnoult,J.F.; Rollier,P.: Thermal Design Verification,
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12. Schmidt,W.F.: A Comparison of Test Philosophies for S_ace-
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13. Weydandt,J.; Schwarz,B: Study of Thermal Design Verificat-
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14. Brinkmann,P.W.; Shickle,W.A.| Walker,J.B.: Economic Use of
Facilities for Thermal Testing of Large Satellites _nd Sub-
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16. Nuss,H.: Calibration and Characteristic Reasurements of a
Solar Simulator Facility for Thermal Balance Tests, ESA SP-
95, 1973, p. 137. ,.
17. Brodersen,H.; Rlzos,I.: INTELSAT V Solar Array, ESA SP-140,
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18. Relmann,J.: Facility for High Intensity, Thermal Balance
Testing Using the Infrared Cs.nlster Method, ESA SP-95, 1973,
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19. Schneider,K.: Development and Testing of ULP Solar Array,
ESA SP-140, 1978, p. 231.
20. Nuss, H.: Thermal Vacuum Testing of Solar Panels by Solar
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25th Technical Annual Meeting, Seattle, 1979, p. 188.
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Solar Panels in Solar Simulation Facilitios with a Multi-
Panel Test Rig, ESA/DFVLR, Second Europes _ Symposium on
Photovoltalc Generators in Space, 15-17 April 1980•
• Division,22 Fokker-VFW, Space Document ECS/O57/PRO/OO28/FOK
324 and ECS/O57/PRO/OO3_/FOK.
,!
1981005626-333
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1981005626-334
\ I
\
I IL..... 1
_z
4
? 4 Referenceplane
2 Collimatin9mirror
8 _ r_ld shroud
4 _uartz window
5 Integrator
6 Collectorwithhighpressure
Fig, 1; _pace SimulationFacility Xenonlamp
withSolarSimulator ? Foldingmirrors
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Fig.2: _pace SimulationFacilitywith
ModifiedSolarSimulator
326
1981005626-335
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Solar panel thermal cycling testing by solar simulation and infrared radiation methods

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