Dome seeing, one of the most important problems in LAMOST due to its special optical path, mainly depends on
thermal distribution and temperature gradients in the enclosure. It is necessary to compute and then control the thermal
distribution inside the enclosure. The paper puts up many thermal analysis models with Icepak software, calculates their
thermal distribution under different thermal cases, and analyzes the maximal temperature differences in different cross
sections along the optical path. We apply many cooling methods, which include adding openings, forming ventilation,
forcing convection and local cooling. We also take the maximal temperature difference as an optimization object to
control the thermal distribution and optimize the cooling structure. Computation results demonstrate that improving the
thermal distribution can greatly reduce the temperature gradient. Through analysis we have obtained one cooling method
that involves a specific ventilating duct forming local cooling and intake cooling air. Simulation shows the maximal
temperature difference has been decreased from 3.8°C to 0.8640°C and in every cross section the maximal temperature
gradient has reached 0.125°C/m, which is better than the project demand of 0.4°C/m. All results confirm the thermal
control system of this project.
Primary mirror with Φ 1m and f 3.5m is the most important optical part in the space Main Optical Telescope (MOT).
Since its required surface error is less than λ/40(rms.), where λ is about 0.6μm, the mirror deformation induced by space
heat and gravity must be within 0.015μm, it's necessary to make thermal calculation and structural analysis to improve
its structure. In this paper, the MOT structure and its finite element model is described. The mechanical properties are
then analyzed in order to verify whether this structure can meet the optical requirements of sufficient strength, stiffness,
and thermal stability. Mechanical analysis is carried out with MSC.Nastran software under 3 different load cases: gravity
influence on-ground, dynamic impact during launching, weightlessness and heat environment in-orbit. Space thermal
analyses are also done to simulate the space environment. The coupled deformation of heat and structure is finally
analyzed. Calculation results show that different support ways and support forces will be the keys to determine the
surface precision of primary mirror. The structure can meet the optical demands, but the thermal deformation can not,
especially in an asymmetric temperature distribution, which should be tested and controlled by some strict methods.
Primary mirror with Φ 1m and f 3.5m is the most important optical part in Space Solar Telescope (SST), which is
designed to make observations of transient and steady state solar hydrodynamic and magnetohydrodynamic processes
and is being researched and manufactured by National Astronomical Observatories. The primary mirror structure(PMS),
a crucial linker for the optical and other subsystems, includes primary mirror and its supporting frame. Therefore, this
part must satisfy the optical sufficient strength, stiffness, and thermal stability requirements under the space environment
and in the launching process. In this paper the primary mirror structure and its connection are described. The scheme of
modal analysis and experiment is built, according to the specific dynamic requirements of the primary mirror structure in
Space Solar Telescope. The dynamic response on the primary mirror structure is analyzed with MSC.NASTRAN
software. Comparing these results with mode parameters obtained from modal experiment analysis. Modal experiment
uses freely hanging primary mirror structure, simple input multi-output, and modal parameter identification through
CADA-X software. Both results provide evidences to develop this satellite design.
Space frame including satellite platform is the most important structure part in Space Solar Telescope (SST), which is designed to make observations of transient and steady state solar hydrodynamic and magnetohydrodynamic processes. This paper first introduces the space frame, which is not only a crucial linker between the optical and other subsystems but also a mechanical interface for the telescope and launching rocket. It must satisfy the optics with sufficient strength, stiffness, and thermal stability under the space environment and in the launching process. Then the author sets up finite element analysis model by MSC.Patran software and analyzes the mechanical quality under different load cases such as on-ground, during launching and in-orbit. In order to simulate the space environment and evaluate the influence of space heat to the whole space frame, the paper also presents space thermal calculation and analysis. Calculation results show that this space frame can meet the satellite’s requirements in space running. However, the thermal problem is still serious in primary mirror, which needs to be tested and controlled with strict way. Finally, the paper gives conclusions and forward suggestions, which will be applied to further research and fabrication in SST.
The optical path of LAMOST is 60-meter long with its main optical axis fixed and lying in close to horizontal orientation, that causes much more serious dome seeing problem than the one in conventional 4-meter class telescopes. The temperature gradients generated by many thermal sources in the dome induce the seeing problem. It is necessary to control of thermal distribution inside the enclosure to keep a good dome seeing. In this paper we introduce our computation and experiments. Through analysis we have obtained a method dealing with design of the cooling system to remove the effect of local heat source and reduce temperature gradients. The methods are outlined as follows: Cool the main heat sources with the cooling air with a temperature of 5°C lower than the ambient temperature. Because of the temperature difference between summer and winter, we have developed two sets of cooling systems to deal with respectively, particularly to keep the system workable in wintertime. We have designed a special structure for removing heat resources inside the enclosure. There is enough ventilation to keep the wind velocity at 0.5~1m/s in the optical path, and special fans generating low velocity wind provide good ventilation and avoid vibration noises.
Temperature sensors feeding signals back to the computer, which adjusts the control loop to maintain a good thermal distribution in optical path and to minimize the dome seeing problem.
The Space Solar Telescope (SST), the first astronomical satellite proposal in China, is under researched, developed and manufactured. It is designed to make observations of transient and steady state solar hydrodynamic and magnetohydrodynamic processes. The space-frame of SST provides the mechanical interface between the telescope and instruments, and it is a crucial linker for all the optical, mechanical, and electronic subsystems. Therefore, the structural parts of SST must satisfy sufficient strength, stiffness, and thermal stability requirements of optical and other subsystems under the space environment and in the launching process. This paper first describes the static and dynamic analyses of the original structure by the Finite Element Analysis (FEA) tool. Then, it presents the structure optimization with the objective to enhance the natural frequency under the total weight unchanged. Finally, it verifies the optimized structure and analyzes the thermal influence of SST. The analysis results and structural responses with all the payloads being considered are discussed and illustrated in this paper. Now, SST is in the phase of test and key technology tackle, and some main parts have been finished. All analysis results shown in this paper will be applied to further research and fabrication.
LAMOST is a unique telescope, its optical axis is on the meridian plane with a 25 degree inclination to the horizontal, the optical path is 60 meters, much longer than that of traditional telescope, that causes much more serious dome seeing problems.
To improve the seeing around telescope, studies are carrying out on the enclosure thermal performance design, that include ventilation, air conditioning, cooling for heat sources, and calculation of thermal parameter of enclosure structure. Some experiments are taking for the remove the main heat from electronic.
This paper will concentrate on dome seeing improvement, related studies and experiments. The data obtained from calculation and experiments will be used for enclosure design to improve LAMOST dome seeing.
This paper presents a new optical transformer which can measure high voltage and large current simultaneously. The measurement of voltage is based on the Pockels effect. A novel structure is posed to realize an optical voltage sensor which has better stability. The measured high voltage is directly applied on the optical voltage sensor without using any capacitive voltage divider. The measurement of current is based on the Faraday effect. A bulk glass closed- loop structure for optical current sensor is used. The optical voltage sensor is in the middle of the HV polymeric insulator which is full of SF6 gas, and the otpical current as immunity of electromagnetic interference, no saturation, no oil inside, wide band range, excellent transient characteristics and light weight etc. The principles, structures and testing results of the combined optical voltage and current transformer are described in this article.
This paper presents a new practical optical fiber voltage transformer (OVT). It is different from the existing OVT. It has the high voltage directly applied across the electro- optical crystal of the OVT sensor and the other OVT uses capacitors to divide the high voltage. New types of silicon rubber insulators in which full SF6 gas is employed for HV insulation. It offers so many advantages like small volume, light weight, high accuracy, immunity form electromagnetic interference, no loss, wide bandwidth etc. The transformer could achieve +/- 0.2 percent accuracy. Compared with the conventional 110KV voltage transformer, its weight is only 1/3 of the former, and its cost is less than 1/2 of the conventional SF6 voltage transformer.
In this paper, a new type of optical fiber voltage transformer is introduced, which utilizes new porcelain capacitor divider. The optical; fiber voltage sensor is based on the BGO crystal Pockels effect modulated horizontally, sealed in a glass box with low expansion rate. Both the divider and the sensor are sealed in the compound silicon rubber insulator filled with SF6 gas. It has many advantages such as small volume, light weight, low price and high precision.
This paper deals with the design, testing results and practical application of a new type of optical voltage transformer (OVT) . It's different from the exist OVTs . The high voltage (beyond 110KV) is directly applied on the electrooptical crystal (Bi4Ge3012) sensor, without the divider. And a new type of the silicon rubber insulator, SF6 gas filled , is employed for high voltage insulation. Its precision is ±0.2% from 80% to 120% of the rating voltage, between -10°C and +40°C. All parts of the OVT are developed according to the requirement of products.