The control device of the star simulator was designed using the international standard UBV magnitude system, including hardware and software design. The DSP emits three PWM pulses to control the brightness of the halogen tungsten lamp, and together with three sets of filters, forms the UBV system. Using DSP to control the rotation of the stepper motor, the motor drives the rotation control of the variable density disc, achieving automatic attenuation control. This device achieves photometric and spectral simulation of the star simulator. The experimental results indicate that it can meet the design requirements.
Star sensor is a high-precision attitude sensitive measurement instrument that determines satellite attitude by detecting stars at different positions on the celestial sphere, providing the three-axis attitude of spacecraft relative to the inertial coordinate system. A star simulator is a detection device that simulates the sky on the ground to perform functional testing on the star map recognition algorithm of the star sensor. The star simulator introduced here is designed and developed based on the UBV magnitude system. Mainly used for ground calibration of space optical measurement equipment such as star sensors.
The system composition is shown in Figure 1.
Figure 1 Schematic diagram of control system composition
The industrial control computer sends instructions to simulate star magnitude and sends them to the DSP control system through the RS232 serial port. The DSP sends instructions to control the driving circuit of the halogen tungsten lamp, thereby controlling the luminous status of the three halogen tungsten lamps. The light emitted by the halogen tungsten lamp converges through a condenser, filters through a narrowband filter group, attenuates through a variable density disk group, and then enters the integrating sphere through a fiber coupling system and atmospheric attenuation simulation system. There are four holes on the integrating sphere, one for entry and three for exit. The integrating sphere outputs two identical beams of light: one is used to illuminate the target, and finally the light emitted through the collimator system is simulated as infinite starlight; One line of photoelectric conversion device receives, forming a closed-loop control system. Leave a path of light for the low light level illuminometer to detect the illuminance value. The control system uses three light sources combined with three sets of narrowband filters for filtering, which is modeled after the UBV star system commonly used internationally. When simulating the stellar spectrum, a variable density disk group controlled by an electric motor adjusts the illuminance values of the three light sources separately. When the spectrum is constant, the DSP controls the optical power of the three light sources and works in conjunction with the attenuation plate group to attenuate the optical signal. Furthermore, it can simulate the luminosity and spectrum of spatial targets.
The system consists of an open-loop controlled stepper motor system and a closed-loop controlled light source system. The position command of the stepper motor rotation and the initial digital quantity of the driving light source of the closed-loop control system are sent by the industrial computer to the DSP through the serial port, and the closed-loop control system provides feedback
The signal is provided by the light source detection circuit. Selecting the TMS320LF2407A digital signal processor (DSP) from TI company in the United States as the core controller, coupled with a small amount of external interface chips, fully utilizes the role of event management (EV) in the microprocessor, completes the correction operation of the control circuit, generates PWM width modulation waves, and displays motor rotation position, voltage value of A/D conversion, and corresponding indication alarm information on the LCD module.
The entire experiment was conducted in a dark room at night, simulating stars of 0-6 magnitude. Each magnitude was measured 10 times, and the voltage values at the test points and readings from the low light level illuminometer were recorded. The results obtained from the mean square deviation calculation formula are shown in Table 1.
Table 1 Comparison Table of Illumination Mean Square Variance and Magnitude Mean Square Variance
Figure 2 Table of Illumination Mean Square Variance and Magnitude Mean Square Variance
From Table 1 and Figure 2, it can be seen that during the measurement process of simulating 0-6 magnitude stars, the mean square value of illumination measurement is
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