a numerical investigation of thermal conditions and...

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Spectrum-Roentgen-Gamma International Experiment

STAR Global Conference 2012, March 19-21, Amsterdam

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

2 STAR Global Conference 2012, March 19-21, Amsterdam

International Spacecraft Platform

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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+.


Astronomical Roentgen Telescope-ART-XC

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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


Temperatures (STAR-CCM+)

Thermal deformations & Displacements (Abaqus)

Meshing (pro-STAR)

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Computer Models of Real Structure


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.

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.


Description of Computer Models

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1.2 million cells 9.7million cells

Temperatures in a Tube


Research of Grid Solution Convergence. Temperatures correspond to Minimal Mode

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X-Ray Mirror Spider and Detector Plate

1.2 million cells 9.7million cells


Research of Grid Solution Convergence. Temperatures correspond to Minimal Mode

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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

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.

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.

Conclusions


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Assembly of ART-XC Spacecraft Platform


With best wishes for

upcoming flight!

Sarov Engineering

Center

a numerical investigation of thermal conditions and...

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