Near-space Platform Research Articles

Terahertz-Band Near-Space Communications: From a Physical-Layer Perspective

Facilitated by the rapid technological development of the near-space platform stations (NSPS), near-space communication (NS-COM) is envisioned to play a pivotal role in the space-air-ground integrated network (SAGIN) for the sixth generation (6G) communications and beyond. In NS-COM, ultrabroadband wireless connectivities between NSPSs and various airborne/spaceborne platforms are required for a plethora of bandwidth-consuming applications, such as NSPS-based ad hoc networking, the in-flight Internet and the relaying technology. However, such requirement seem to contradict the scarcity of spectrum resources at conventional microwave frequencies, which motivates the exploitation of terahertz (THz) band ranging from 0.1 to 10 THz. Due to huge available bandwidth, THz signals are capable of supporting ultra-high-rate data transmission for NS-COM over 100 Gb/s, which are naturally suitable for the near-space environment with marginal path loss. Against this background, this article provides an extensive investigation on THz-band NS-COM (THz-NS-COM) from a physical-layer perspective. Firstly, we summarize the potential applications of THz communications in the near-space environment, where the corresponding technical barriers are analyzed. Secondly, the channel characteristics of THz-NS-COM and the corresponding modeling strategies are discussed. Thirdly, three essential research directions are investigated to surpass the technical challenges of THz-NS-COM, i.e., robust beamforming for ultramassive antenna array, signal processing algorithms against hybrid distortions, and integrated sensing and communications. Several open problems are also provided to unleash the full potential of THz-NS-COM.

Ground-Based Near-Space-Oriented Spray Cooling: Temperature Uniformity Analysis and Performance Prediction

Thermal control systems in near-space-oriented vehicles are bound to be different from those on either traditional airplanes or typical space shuttles owing to the extremely thin atmosphere caused by the high altitude and awfully hot air produced by the aerodynamic heat. The tough thermal environment encountered by the vehicle will pose great challenges for the thermal control system deployed in the near-space platform, which is hazardous for the onboard electrodriven equipment. Therefore, it is imperative to invent a novel cooling scheme for the reliable operation of the device. For thermally protecting the onboard permanent magnet synchronous motor in a rudder cabin, a novel large-space spray cooling system was proposed in a previous study by Wang, J. X., Li, Y. Z., Yu, X. K., Li G. C., and Ji, X. Y. ("Investigation of Heat Transfer Mechanism of Low Environmental Pressure Large-Space Spray Cooling for Near-space Flight System," International Journal of Heat and Mass Transfer, Vol. 119, April 2018, pp. 496–507); based on which, a further study of the experimental data is conducted in this paper. Temperature uniformities within the small-scaled motor and among different motors are studied, and strategies for enhancing the temperature uniformity among motors are proposed. In addition, thermal predictions of the small-scaled permanent magnet synchronous motor for both of the flash-boiling subcooled regimes using the backpropagation neural network are developed. A maximum relative error of is observed, which illustrates the superiority of the current model as compared with the fitting correlation developed in the previous study.

Near-Space TOPSAR Large-Scene Full-Aperture Imaging Scheme Based on Two-Step Processing.

Free of the constraints of orbit mechanisms, weather conditions and minimum antenna area, synthetic aperture radar (SAR) equipped on near-space platform is more suitable for sustained large-scene imaging compared with the spaceborne and airborne counterparts. Terrain observation by progressive scans (TOPS), which is a novel wide-swath imaging mode and allows the beam of SAR to scan along the azimuth, can reduce the time of echo acquisition for large scene. Thus, near-space TOPS-mode SAR (NS-TOPSAR) provides a new opportunity for sustained large-scene imaging. An efficient full-aperture imaging scheme for NS-TOPSAR is proposed in this paper. In this scheme, firstly, two-step processing (TSP) is adopted to eliminate the Doppler aliasing of the echo. Then, the data is focused in two-dimensional frequency domain (FD) based on Stolt interpolation. Finally, a modified TSP (MTSP) is performed to remove the azimuth aliasing. Simulations are presented to demonstrate the validity of the proposed imaging scheme for near-space large-scene imaging application.

Integrated Wireless Sensor Systems via Near-Space and Satellite Platforms: A Review

Due to extreme conditions, the near-space region is vastly underused and can be utilized for various scientific uses. The unconstrained orbital mechanism and low fuel consumption advantages for using synthetic aperture radar over the satellites and airplanes navigation systems make these conditions superior for a wide range of services, monitoring, earth observation, and sensing applications. The augmented integration within the existing global navigation system can help in measuring the direction-of-arrival, as well as collecting and distributing accurate location information. For wireless sensing applications, it can enable a new range of opportunities, a wide range of smart sensor applications as experimental platforms for deployment of new technologies. Here, we also examine the implementation of near-space platform (NSP) coverage and associated technologies. Then, a brief integration of communication and navigation services using NSP from a top-level system description of how to relay, associated complementary systems, including radar sensor systems, satellite systems, and terrestrial networks can be used.

Research of Characteristic Extraction and Matching Algorithm of Ballistic Missile Hyperspectral Data Based on Quantization Coding Method

A characteristic extraction algorithm of the ballistic missile hyperspectral data based on the quantization coding method is studied. The ballistic missile hyperspectral data of imaging spectrometer based on near-space platform is generated by numerical method. The characteristic of the ballistic missile hyperspectral data is extracted and matched using the characteristic extraction algorithm based on the quantization coding method. The simulation result show that the characteristic extraction algorithm is easy to implement and low complexity. The characteristic, which extracted by this algorithm, is enough to represent the speciality of the ballistic missile hyperspectral data. The matching algorithm has high accuracy.

Research of Characteristic Extraction Algorithm of Ballistic Missile Hyperspectral Databased on Horizontal Traversing Time

A characteristic extraction algorithm of the ballistic missile hyperspectral data based on the horizontal traversing time is studied. The ballistic missile hyperspectral data of imaging spectrometer based on near-space platform is generated by numerical method. The characteristic of the ballistic missile hyperspectral data is extracted using the characteristic extraction algorithm based on the horizontal traversing time. The simulation result show that the characteristic extraction algorithm is easy to implement and low complexity. The characteristic, which extracted by this algorithm, is enough to represent the speciality of the ballistic missile hyperspectral data. The characteristic is not sensitive to disturbed signal and improve the timeliness of the following object matching and recognition.

Dynamic Modeling and Dynamic Characteristic Analysis of a New Concept Stratospheric V-Shaped Airship

It has important scientific and engineering applications for near-space platform to design the buoyancy-lifting aircraft with both bigger volume and higher aerodynamic efficiency. This paper provided a design of a new concept V-shaped airship which has a capacity of buoyancy-lifting configuration than the same-weight class conventional airship. In addition, two engines could provide rolling, yawing and pitching moments for the V-shaped airship by changing directions and creating different thrust. Based on the thick aerofoil, the geometry of this V-shaped configuration was then used to develop an aerodynamic estimating model for the V-shaped airship. It renewed estimating methods for the added mass, inertia, the forces and the moments including aerodynamic and engine thrust of the V-shaped airship. Then this paper described a 6 Degree of Freedom (DOF) dynamic model for the V-shaped airship. The open-loop disturbance characteristic of the dynamic model was analyzed across a range of flight conditions and the added mass of the V-shaped airship were compared with the same weight-class teardrop-shaped dull-hull airship. Finally, the characteristics of buoyancy and lift between V-shaped airship and dull-hull airship were compared at different velocity. The results show that the aerodynamic efficiency of the V-shaped airship is improved obviously from the same-weight class dull-hull airship across a range of flight velocity.

Multimode Heat Transfer in a Near-Space Environment

A thermal circuit model has been used to examine the heat transfer characteristics of an idealized station-keeping near-space platform. Forced convection, natural convection, and thermal radiation heat transfer mechanisms have been included in the model. The contributions of forced and natural convection were incorporated using previously published correlations. Thermal radiation heat transfer was assumed to be the result of direct solar flux, planetary infrared, and planetary albedo thermal radiation contributions. Model closure was obtained by using data from the 1976 standard atmosphere model, an empirical model for wind speed and models for variable thermophysical properties. The results of the scaling analysis indicate that, as expected, natural convection may be neglected above certain altitudes. The results also show the relative importance of thermal radiation and forced convection as the dominant heat transfer mechanisms with respect to altitude. Results from parametric studies of albedo and surface material effects are also included.

Application of Near-Space Passive Radar for Homeland Security

To protect the homeland from terrorist attacks employing explosive devices, revolutionary advances across a wide range of technologies are required. Inspired by recent advances in near-space (defined as the region between 20 km and 100 km), this paper proposes a new passive radar system using opportunistic transmitter as an illuminator and near-space platform as a receiver. This concept differs substantially from current radars. This system can be operated as a passive bistatic or multistatic radar and hence largely immune to jamming. By placing the receiver in near-space platforms, many functions that are currently performed with satellites or airplanes could be performed much more cheaply and with much greater operational utility. These advantages make near-space passive attractive for a variety of applications, many of which fit well with the needs of homeland security. This paper details the role of near-space passive radar as sensor system that can support homeland security applications. The strengths and weakness of near-space passive radar, compared to current spaceborne and airborne radars, are detailed. The signal models and processing algorithms for near-space passive radar are provided. It is shown that the use of cost effective near-space platforms can provide the solutions that were previously thought to be out of reach to remote sensing and government customers.