Analysis of the trajectory of spacecraft return from the lunar surface to a given region of the Earth

The paper describes a method developed for designing the trajectory of a spacecraft flight from the lunar surface to a given area of the Earth’s surface and analyzes a single-pulse flight scheme, in which the trajectory of a take-off lunar rocket is approximated by a single velocity pulse. The characteristics of the spacecraft entry into the Earth’s atmosphere are chosen so as to ensure that the conditions along the entry corridor during the ballistic entry are met and to ensure the landing of the reentry vehicle at a given point on the Earth’s surface. The criterion for optimizing the trajectory of the spacecraft return to the Earth is considered to be the value of the impulse that provides the spacecraft launch from the lunar surface. The method relies on the analysis of an auxiliary problem, the solution of which makes it possible to estimate the main properties of the investigated maneuver and find an initial approximation for the selected characteristics of the optimized trajectory.

High-precision prescribed-time path following for quadrotor

A high-precision prescribed-time guidance law is developed for a quadrotor to accomplish precise path following at predesigned time T. Firstly, a new control structure is proposed for a quadrotor to perform fixed-velocity back-to-turn flying mode by introducing four controllers, which can realize a non-sideslip and bank-to-turn flight scheme just like a fixed-wing unmanned aerial vehicle. Then, prescribed-time guidance law is presented based on fixed-velocity back-to-turn flying mode via combining sliding mode control with a compensation function [Formula: see text] to improve tracking precision of conventional methods. Compensation function [Formula: see text] is designed to make state error achieve convergence at prescribed time exactly. Meanwhile, global sliding mode is established to enhance robustness of the system. Then, the stability and characteristic of prescribed-time convergence are proved strictly. Finally, simulations with a 6-degree-of-freedom quadrotor model are carried out to demonstrate the effectiveness and superiority of prescribed-time guidance law by comparing with traditional guidance law.

Method of graphoanalytical finding borders space-time areas of reachability service spacecraft man-made space objects in geostationary orbit

At the present time at various stages of creation and development there are several projects of service spacecraft. One of the tasks of which is to service orbital objects as soon as possible. During the planning maintenance is needed to perform a large amount of calculations associated with the choice of a rational flight scheme. To reduce the amount of computation, an approach is needed that provides a search for the set of realized flight paths. One of such approaches is the method for determining the boundaries of the spatiotemporal reachability regions, which allows one to evaluate the a priori capabilities of service spacecraft for servicing orbital objects located in circular orbits. To construct spatiotemporal reachable regions, the mathematical apparatus of the hodograph theory is used, which allows, sequentially, based on the analytical solution of the optimization problem of a two-pulse flight, to determine the minimum and maximum duration of the spacecraft’s movement, which is understood as the time required for the flight from the point of maneuvering to the meeting point with the serviced an orbital object under the condition of the application of one velocity impulse. A graphical comparison of the trajectories of the serviced orbital objects and spatiotemporal reachable areas of the service spacecraft makes it possible to determine the potential for service, as well as the time intervals and phase angles at which such service is possible. The proposed methodological apparatus can be used to find a solution providing an initial approximation for the subsequent accurate calculation of the trajectory of motion by numerical methods, as constructing a control program for the spacecraft.

Analysis of the features of the implementation of the launch unit flight scheme for micro spacecraft injections in an intermediate orbit with synchronous precession

The article considers features of the implementation of the launching scheme for a group of small spacecraft at the stage of the Volga type launch unit operation during the transition from the reference orbit formed by the “Soyuz 2.1 v” launch vehicle to the intermediate orbit, where the small spacecraft separate. The orbit with synchronous precession velocity of the ascending node longitude with respect to the working orbit is chosen as an intermediate orbit, to which the small spacecraft transfer independently, using their propulsion system, after separation from the launch unit. The article solves the problem of choosing the rational orientation of the launch unit during the release of pulses, in the passive flight segments, as well as for the safe separation of the small spacecraft in an intermediate orbit with synchronous precession. Parameters of maneuvers to flood launch unit after separation of small spacecraft are calculated. Numerical results of fuel consumption for direct deorbiting and selection of maneuvering intervals for launch unit submersion in a given area of the world ocean are obtained. The calculations of the Earth shadow- and semishadow-sunlight time for small spacecraft are performed.

Distributed reactive collision avoidance for a swarm of quadrotors

The large-scale of unmanned aerial vehicle applications has escalated significantly within the last few years, and the current research is slowly hinting at a move from single vehicle applications to multivehicle systems. As the number of agents operating in the same environment grows, conflict detection and resolution becomes one of the most important factors of the autonomous system to ensure the vehicles’ safety throughout the completion of their missions. The work presented in this paper describes the implementation of the novel distributed reactive collision avoidance algorithm proposed in the literature, improved to fit a swarm of quadrotor helicopters. The original method has been extended to function in dense and crowded environments with relevant spatial obstacle constraints and deconfliction manoeuvres for high number of vehicles. Additionally, the collision avoidance is modified to work in conjunction with a dynamic close formation flight scheme. The solution presented to the conflict detection and Resolution problem is reactive and distributed, making it well suited for real-time applications. The final avoidance algorithm is tested on a series of crowded scenarios to test its performances in close quarters.

A Fast Inverse Algorithm Based on the Multigrid Technique for Cloud Tomography

A fast inverse algorithm based on the half-V cycle scheme (HV) of the multigrid technique is developed for cloud tomography. Fourier analysis shows that the slow convergence problem caused by the smoothing property of the iterative algorithm can be effectively alleviated in HV by performing iterations from the coarsest to the finest grid. In this way, the resolvable scales of information contained in observations can be retrieved efficiently on the coarser grid level and the unresolvable scales are left as errors on the finer grid level. Numerical simulations indicate that, compared with the previous algorithm without HV (NHV), HV can significantly reduce the runtime by 89%–96.9% while retaining a similar level of retrieval accuracy. For the currently feasible two-level flight scheme for a 20-km-wide target area, convergence can be accelerated from 407 s in NHV to 13 s in HV. This reduction in time would be multiplied several times if the target area were much wider; but then segmental retrieval would be required to avoid exceeding the time limit of cloud tomography. This improvement represents an important saving in terms of computing resources and ensures the real-time application of cloud tomography in a much wider range of fields.