Search Results (11)

This study investigates the basic characteristics of force transmissibility for a passive launch and on-orbit vibration isolation system (PLOVIS-II), which was developed to examine the microvibration attenuation of a spaceborne cryogenic cooler. The design, based on a coil spring-type passive vibration isolation system without an additional launch-lock device, demonstrated an effective vibration attenuation performance in both launch and on-orbit vibration isolation. In this study, a test setup and method were developed to measure the force transmissibility of an isolator along each axis using a voice-coil-type non-contact vibration excitation instrument. In addition, the test results included the position sensitivity of PLOVIS-II, considering the worst misalignment of the isolation system, and its performance was compared with that of PLOVIS-I proposed in a previous study. Full article

The high-precision gravitational reference sensor, which hosts a heavy test mass (TM) surrounded by electrodes with a relatively large gap, is crucial in all high-sensitivity drag-free sensors. Consequently, a dedicated locking mechanism is needed to securely hold the TM during the launch phase. After reaching the intended orbit, the TM is released to a free-falling state and subsequently captured by electrostatic actuation, which demands that the transferred momentum and angular momentum to the TM do not exceed ${10}^{-5}\mathrm{kgm}/\mathrm{s}$ and ${10}^{-7}{\mathrm{kgm}}^2/\mathrm{s}$, respectively. This paper introduces a three-level structural design of the locking-and-release mechanism. In order to investigate the release requirement, a pendulum system has been developed for on-ground testing. The mock-up of the TM is entirely consistent with the size and mass of TianQin TM, and the dual-sided release tips constrain the TM and then rapidly retract simultaneously, after which the transferred momentum and angular momentum are estimated from the free oscillations as $0.38\left(21\right)\times {10}^{-5}\mathrm{kgm}/\mathrm{s}$ and $0.15\left(14\right)\times {10}^{-7}{\mathrm{kgm}}^2/\mathrm{s}$ with a preload force of 0.3 N. This proposes a feasible scheme for validating the release mechanism conducting impulse testing for the TianQin project. Full article

Continuously rotating gimbals for scanning purposes are widely used in space applications. For high-precision gimbals, it is essential to lock the gimbal before launch and unlock it on orbit. This kind of gimbal puts forward the need for hold down release mechanisms that are able to clear the gap between the rotating and fixed parts at release. Existing technologies either lack the function of gap avoidance after separation or rely more or less on the elastic deformation of the structure or limited spring forces for unlocking, which are either unreliable or complicated. To address this problem, this paper presents the design of a novel non-pyrotechnic heavy-load hold down release mechanism (HDRM) based on shape memory alloy actuator. The proposed HDRM is shock-free and capable of clearing an axial gap of 8 mm for safe rotating at release. The structure and operational principle of the proposed design are straightforward. Detailed tests show the proposed HDRM may withstand a maximum external force of 50 KN with relatively high stiffness under 15 KN of preload, indicating a better performance than existing products. The HDRM demonstrates its promising usage as an alternative to traditional pyrotechnic and non-pyrotechnic HDRMs. Full article

In recent years, low-Earth-orbit (LEO) constellations have been proposed for Positioning, Navigation and Timing (PNT) applications. Moreover, a couple of test satellites have already been launched and many more are scheduled in the near future. LEO constellations are characterised by their rapid change in geometry in comparison to the current medium-Earth-orbit (MEO) Global Navigation Satellite Systems (GNSSs). In this study, we analyse the impact of this high geometry change rate on the code-range error induced by multipaths. We develop a simulation environment with a static receiver and a nearby large building. We track the multipath signal using classical delay- and phase-locked loops (DLL and PLL). Multiple scenarios are simulated and analysed, comparing different orbit heights, MEO and LEO, and carrier frequencies (L-, S- and C-band). The LEO scenarios show up to 96% less code-range error for fast-changing multipath components. We show that this phenomenon is linked to the large phase delay rate between the direct signal and the multipath components, which is up to 75 times higher for LEO satellites when compared to MEO satellites. The phase delay rate reaches values higher than the DLL bandwidth. As a result, the DLL filters out the errors induced by fast-changing reflected signals, partially eliminating the multipath-induced code-range errors. The presented effect is coupled to the wavelength of the used carrier frequency. Our simulations show a reduction in multipath-induced code-range error for S- and C-band LEO-PNT signals in comparison to L-band signals. Full article

We have studied the ultrafast saturation behavior of a high-density well-aligned single-walled carbon nanotubes saturable absorber (HDWA-SWCNT SA), obtained by a high-pressure and high-temperature treatment of commercially available single-wall carbon nanotubes (SWCNTs) and related it to femtosecond erbium-doped fiber laser performance. We have observed the polarization dependence of a nonlinear optical saturation, along with a low saturation energy level of <1 fJ, limited to the detector threshold used, and the ultrafast response time of <250 fs, while the modulation depth was approximately 12%. We have obtained the generation of ultrashort stretched pulses with a low mode-locking launching threshold of ~100 mW and an average output power of 12.5 mW in an erbium-doped ring laser with the hybrid mode-locking of a VDVA-SWNT SA in combination with the effects of nonlinear polarization evolution. Dechirped pulses with a duration of 180 fs were generated, with a repetition rate of about 42.22 MHz. The average output power standard deviation was about 0.06% RMS during 3 h of measurement. Full article

Keyless systems have replaced the old-fashioned methods of inserting physical keys into keyholes to unlock the door, which are inconvenient and easily exploited by threat actors. Keyless systems use the technology of radio frequency (RF) as an interface to transmit signals from the key fob to the vehicle. However, keyless systems are also susceptible to being compromised by a threat actor who intercepts the transmitted signal and performs a replay attack. In this paper, we propose a transfer learning-based model to identify the replay attacks launched against remote keyless controlled vehicles. Specifically, the system makes use of a pre-trained ResNet50 deep neural network to predict the wireless remote signals used to lock or unlock doors of a remote-controlled vehicle system. The signals are finally classified into three classes: real signal, fake signal high gain, and fake signal low gain. We have trained our model with 100 epochs (3800 iterations) on a KeFRA 2022 dataset, a modern dataset. The model has recorded a final validation accuracy of 99.71% and a final validation loss of 0.29% at a low inferencing time of 50 ms for the model-based SGD solver. The experimental evaluation revealed the supremacy of the proposed model. Full article

The deployment performance of the unfolded wing determines whether the winged missiles can fly normally after being launched, infecting the attack performance of the winged missiles. The paper proposes a new deployment mechanism with clearance eliminator. Based on the slider-crank principle, the proposed deployment mechanism achieves fast and low-impact deployment of the wings. The proposed clearance eliminator with shape memory alloy (SMA) effectively eliminates the clearance of the sliding pair and improves the support stiffness and stability of the deployed wing. The collision characteristics and the clearance elimination are studied for the deployment mechanism. The influence of the collision force on the motion state of the wing during the deployment is analyzed. The static stiffness of the wing under the clearance state and the deformation is analyzed. The dynamic stiffness under the catapult clearance elimination state is modeled based on the fractal geometry and contact stress theory. The relationship between the locking force and the support stiffness is revealed. The kinetic simulation is used to analyze the motion response during the action of the deployment mechanism. Modal analysis, harmonic response analysis, and random vibration analysis were conducted for the whole wings. A prototype was developed to verify the ejection performance of the wing according to the input load characteristics. The dynamic stiffness of the unfolded wings is tested by the fundamental frequency experiments to verify the performance of the clearance elimination assembly. The experimental results show that the designed deployment mechanism with clearance compensation achieves fast ejection and high stiffness retention of the missile wing. Full article

The launch method of one arrow with multiple satellites can greatly shorten the time for constellation networking and improve the deployment efficiency. A new compression and separation device with a four-bar perimeter arrangement is proposed for multi-satellite compaction and in-orbit release. A compression device with gap elimination is designed to implement the reliable compaction of stacked flat satellites. An electromagnetic separation device is proposed to achieve the fast, low-interference release of multi-satellites. The dynamic model with flexible guide bars is established. The separation characteristics of multiple satellites are analyzed by the kinematic simulation. The prototype is developed, and the related experiment is implemented. The results show that the four-guide-bar-edge arrangement scheme with a gap elimination device achieves reliable locking and fast separation under a vibration environment. The dynamic separation characteristics of satellites are investigated by the air floatation experiments. The results show that a stable separation speed and low disturbance angular velocity are achieved under 10% spring error. Full article

The separation mechanism is a critical device that transports and releases satellites during launch and on-orbit. However, as satellites become smaller and more compact, the traditional belt-locking device or pyrotechnic release and separation device cannot meet the micro-nano satellite’s separation requirements. A novel separation mechanism kinematic system was designed, analyzed, and experimentally verified to achieve non-interference and non-pyrotechnic separation of the satellites from the launch vehicle while maintaining the initial separation attitude. First, an overall structural strategy for the kinematics system was proposed based on the MF (product code of the satellite) satellite’s structural properties. The structural characteristics of the separation mechanism were also confirmed by the principle of energy conservation. Then, a finite element model and a dynamic model of the kinematic coupling system between the MF satellite and the separation mechanism during launch and deployment were constructed, along with an analysis of the mechanical characteristics and a kinematic simulation. Finally, the mechanical characteristics and dependability of the separation mechanism were verified using a ground vibration test and a separation test. The prototype test results demonstrate that the separation process is essentially identical to the numerical simulation results and that the MF satellite can be deployed successfully without interference, with the MF satellite’s initial separation attitude fully satisfying the designed technical indexes. Full article

The Microgravity Platform (MP) of the Chinese Space Station is locked and released by Lock-or-Release (L/R) mechanism on both sides. In order to ensure the safety and reliability of the MP under the vibration environment during the rocket launch, the L/R mechanism must output the appropriate locking torque value. Based on the structural characteristics of the Scientific Experiment Cabinet (SEC), this paper proposes a method of evaluating locking torque by combining theory with experiment, and the relationship between locking force and locking torque of L/R mechanism is proved that the locking force on both sides can reach 2000 N at 25 Nm driving torque. Finally, it is verified by vibration test that the locking torque obtained by this method can effectively guarantee the safety and reliability of the MP under vibration environment. Full article

The Chang’e-4 (CE-4) lunar rover, equipped with a visible and near-IR imaging spectrometer (VNIS) based on acousto-optic tunable filter spectroscopy, was launched to the far side of the moon on December 8, 2018. The detection band of the VNIS ranges from 0.45 to 2.4 μm. Because of the weak reflection of infrared radiation from the lunar surface, a static electronic phase-locked acquisition method is adopted in the infrared channel for signal amplification. In this paper, full-link simulations and modeling are conducted on the infrared channel information flow of the instrument. The signal characteristics of the VNIS are analyzed in depth, and the signal to noise ratio (SNR) prediction and laboratory verification are presented. On 4 January 2019, the VNIS started working successfully and acquired high-resolution spectrum data of the far side of the moon for the first time. Through analysis we have found that the SNR ratio is in line with our predictions, and the data obtained by VNIS in orbit are consistent with the information model proposed in this paper. Full article