In many cases, we have few optical observations over a short time span, and most of the information generated is too limited to compute a full orbit according to the angles-only method. This study aims to develop a mathematical model to determine the precise orbit from the optical observation data by the least squares method. We have used a set of the Global Navigational Satellite Systems, which are tracked by the Optical Satellite Tracking Station (OSTS) at the National Research Institute of Astronomy and Geophysics (NRIAG), Egypt, to access high-quality predictions for the orbits. We analyzed the orbit predictions from the observations of these satellites that are tracked from seven world stations using the laser ranging method, and the obtained results are compared with orbital elements produced using the Two-Line Element (TLE). The results showed that the orbital prediction accuracy differs for optical observations from laser observations because of the inaccuracy of the NORAD catalog information used; this is due to the difference between the time of observation and the epoch time of TLE.

In an effort to accomplish the real-time acquisition of the laser ranging results of space debris during the daylight and enhance the observation success rate, this paper establishes a joint distribution model of noise and echo signals grounded on the intensity distribution law of the daylight background noise. Through an in-depth analysis of the measurement characteristics of single-photon detectors, a real-time recognition algorithm based on the disparity in statistical distribution is put forward. This algorithm partitions the observation data into intervals of equal length. It then employs the goodness-of-fit test of the geometric distribution to ascertain the data distribution law. Subsequently, it locates the interval in which the echo signal resides by analyzing the contribution degree of the chi-square statistic. The experimental outcomes indicate that under the circumstances of a laser frequency of 400 Hz and a background noise photon rate of 2 × 10⁷ photons per second, the algorithm is capable of achieving real-time recognition of the echo interval for an intensity of 0.09 echo photons per single pulse within 1 s. This breakthrough resolves the critical challenge of daylight echo discrimination in high-noise environments. This method overcomes the constraints of the traditional signal intensity threshold and offers a novel technical approach for the tracking and precise orbit determination of space debris in a low signal-to-noise ratio environment.

In the presented paper, a model describing the range equation, the energy received, the number of returned photons, and photoelectrons as well as the Time-Of-Flight, has been analytically studied. The data concerning the Satellite Laser Ranging (SLR) observed from the Changchun Observatory are considered to evaluate some of the parameters such as the energy received to ground telescope E_recv, the number of returned photons N_p and photoelectrons N_pe. The SLR-data are taking into our consideration with the summarised results for the observations taken from the first quarter of 2018. The model is applied on a variety of satellites with different heights and configurations. The results have shown and confirmed the dependency of these parameters on the properties of the laser and detector systems and the used setup.

A low threshold current density of 2 μm InGaAsSb/AlGaAsSb muti-quantum well (MQW) laser diode with carrier blocking layer (CBL) is demonstrated by simulation and fabrication. The carrier leakage is found to be theoretically suppressed for the devices with CBL. All the laser wafers are grown with a solid source Molecular Beam Epitaxy(MBE) System. Experimental results reveal the samples with CBL exhibits ultra-low threshold current densities of 142 A/cm² and high slope efficiency of 0.158 W/A, which is better than 215 A/cm² and 0.122 W/A achieved in the conventional InGaAsSb/AlGaAsSb LDs at room temperature. This improvement in device performance comes from meticulously designing the carrier blocking layers to increase carrier confinement and injection efficiency.

Passive attitude estimation of spacecraft is both the focus and the difficulty in space situational awareness. Solutions based on photometry usually require complex scattering characteristics modeling, while solutions based on radar imaging have bottlenecks in feature extraction and association. In this article, a new attitude estimation scheme is described based on satellite laser ranging technology using corner-cube retroreflectors (CCRs) as beacons. The ground station simultaneously tracks multiple CCRs on the spacecraft and distinguishes the ranging signals to obtain high-precision range difference sequences containing complete attitude information. For this multi-CCR differential satellite laser ranging, we establish a complete set of methods for attitude inversion using range difference sequences. Firstly, geometric measurement models are established to determine the relationship between the range difference sequence, the line-of-sight (LOS) direction, and the 2-D projection distribution of CCRs. Secondly, assuming that the object rotates around a fixed axis, analytical methods for determining the initial value of the attitude based on the LOS direction are established. Finally, considering the dynamic model error in real spacecraft rotation, a minimum model error batch-estimation approach is adopted for initial value correction. The proposed methods determine the initial value for state estimation through analytical calculation, reduce the large number of iterations required for multi-parameter traversal in numerical calculation, and thus improve the computational efficiency. Based on the above methods, single short-arc ranging data of the defunct CZ-2C R/B with multi-CCRs were processed, and the rotation state trajectory satisfying the precession law was obtained.

With the increase in human space activities, there is a significant amount of space debris as well as defunct satellites that seriously threaten the safety of spacecraft in their orbits. The laser ranging technique is one of the most accurate methods of ground-based space target observation. Therefore, it is very meaningful to study efficient tracking and observation methods for defunct satellites and space debris. In this paper, time bias, which is in advance of the actual observation, was added by analyzing the deviation of the orbit prediction such as the time bias and range bias of the runaway space objects. A new method was used for the determination of the TB and RB in real-time tracking and in data processing. The data produced from the observation of the out-of-control targets, such as the Topex satellite and CZ-2C Long March Launch Vehicle, were presented and analyzed. Taking the laser ranging data of the Topex satellite obtained on 19 November 2019, as an example, the result of the first observation circle provided the initial time bias value for the second observation circle, proving that the laser ranging method for runaway space objects is effective. The results of this paper can effectively improve the acquisition efficiency of the defunct satellites.