Spectrum-Roentgen-Gamma International Experiment
A Numerical Investigation
of Thermal Conditions and Deformations
of the Astronomical Roentgen Telescope
А. Ryabov, V. Spirin, S. Gulakov,
S. Garanin, S. Grigorovich
M.Pavlinskyi, N.Semena
Sarov Engineering Center
Institute of Laser Physics VNIIEF
Space Research Institute RAS
RUSSIA
STAR Global Conference 2012, March 19-21, Amsterdam
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International Spacecraft Platform
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Astronomical Roentgen Telescope-ART-XC
The main purpose of ART-XC telescope (Astronomical Roentgen
Telescope – X-ray Concentrator) with X-ray optical system is
searching of space under a hard X-ray range to solve scientific
problems in frame of “Spectrum-RG” international experiment.
One of the major requirements for the telescope is to ensure
restricted temperatures and minimal thermal deformations of the
construction from solar irradiation and heating effects of spacecraft
during orbital flight.
Therefore, a detailed computer simulation of temperature
conditions and thermal deformation of telescope parts in outer
space is carried out at a development stage using STAR-CCM+.
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ART-XC Orbital Motion and Solar Irradiation
Shadow and Sunlight interchange depending on a Spacecraft Orientation
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Operating Modes and Requirements
• The telescope is in orbit under solar irradiation that heats its different
construction zones depending on a spacecraft orientation. In addition,
some heaters of thermal control system may breakdown in flight.
• Separate parts of the telescope optical system are capable to run in
a certain temperature range that imposes stringent requirements for
the thermal control system during off-line operation in outer space.
• To meet these requirements 9 thermal modes are calculated:
minimal and maximal mode (depending on solar radiation presence),
7 scenarios of a survival mode (emergency modes – in case of some
heater or its circuit breakdown).
• Simulation of each mode adds up to finding the minimum required
power of heaters and their location that ensure an acceptable range of
construction temperatures.
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Methodology of Numerical Simulations
Meshing (pro-STAR)
Temperatures
(STAR-CCM+)
Thermal deformations
& Displacements
(Abaqus)
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Computer Models of Real Structure
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Description of Computer Models
Multi-band radiant heat exchange by Plank’s law for separate
simulation of the solar and heat radiation, temperature
dependence of material properties, an anisotropic solid model
causes extremely sophisticated and non-linear problem
formulation.
The solar and heat radiation are considered separately for
better accounting of the direct and reflected solar radiation
action.
512 rays (1024 by default) are assumed for the considering
construction that has about 700 thousand patches. This
combination is acceptable for the accuracy, computational time
and memory requirements.
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Description of Computer Models
The problem of heat conduction in anisotropic solids along with
multi-band radiative heat transfer was numerically implemented
in STAR-CCM+ using the fully implicit algorithm. AMG method
was used with an increased number of iterations at "coarse"
levels (W cycle) with the following parameters: maximum
number of cycles: n = 150, convergence rate: N = 0,001.
The selected solver parameters allow to obtain a converge
solution for about three thousand of iterations.
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Temperatures in a Tube
Research of Grid Solution Convergence. Temperatures correspond to Minimal Mode
1.2 million cells
9.7million cells
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X-Ray Mirror Spider and Detector Plate
Research of Grid Solution Convergence. Temperatures correspond to Minimal Mode
1.2 million cells
9.7million cells
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Temperatures of a Protective Unit
Minimal Mode Temperatures
Orbital Transfer Mode (Heaters turned off)
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Temperatures of Mirrors and Spider
Minimal Mode Temperatures
Orbital Transfer Mode (Heaters turned off)
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Thermal deformations
Maximal calculated thermal displacements of the optical channel
parts are almost the same for all considered temperature modes
and they are:
for X-ray mirrors – 0.25 mm, for block of X-ray detectors – 1.2 mm
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Conclusions
1.
Several computer models have been developed for
numerical simulations of ART-XC steady and unsteady
thermal states. The convergence of the solution and
adequacy of the numerical results were examined and
confirmed on the basis of these models.
2.
The anisotropic computer model of X-mirror heat equivalent
has been developed and numerically proved. This model
allows reflecting the actual construction adequately, without
significant distortion of the temperature field. Incorporating of
this heat equivalent to the telescope computer model
allowed significantly saving of the required computational
cost.
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Conclusions
3. Several thermal modes were analyzed: minimal and maximal
modes, seven scenarios of the survival mode. Minimum
required powers and location of 29 heat elements was defined
for each mode, providing the acceptable temperature range of
the construction.
4. The influence of surface emissivity variation (​​for a polished
surface of aluminum alloy=0.06…0.19, for carbon fiber=
0.74…0.92, for a polished surface of steel parts=0.1…0.47) on
the telescope thermal modes has been investigated by
numerical experiments, it causes temperature variation of the
main parts of about 2% or less than 5K.
5. Calculated maximal thermal deformations of X- mirror shells
and other telescope parts ensure the specified geometric
characteristics of the optical channels.
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Assembly of ART-XC Spacecraft Platform
With best wishes for
upcoming flight!
Sarov Engineering
Center
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