Number Of Spacecraft Research Articles

Automatic Orbit Selection for a Radio Interferometric Spacecraft Constellation

A constellation of radio telescope spacecraft can leverage interferometry to accurately image distant objects throughout the universe, but mission design must balance among many interrelated constraints. In particular, the number of spacecraft and their time-varying orbital parameters determine what interferometric baselines are feasible for each target, which in turn drives the imaging capabilities of the constellation. The large combinatorics of dynamic constellation configuration and the numerous competing engineering concerns present a challenge that is not well addressed by labor-intensive manual mission design processes. This paper describes search-based optimization methods that direct mission design effort toward promising constellation geometries: those that achieve broad interferometric coverage but remain cost-effective and resilient to failures. Six families of automatic optimization algorithms with complementary search strategies were created to explore among explicit constellation configuration plans. Evaluation of each candidate constellation plan was accelerated by efficiently combining precomputed caches of orbital and interferometric data. Comparative results indicate that leveraging automated optimization for constellation mission design is practical and useful. Optimized constellations demonstrated target image reconstruction errors 10% better than a manually designed constellation and up to 35% better than random solutions.

Multi-asset System Design Methodology for Earth Observation

To better understand the Earth environment and climate change, to mitigate its effects and to provide emergency services, ensuring civil security, future European Earth observation (EO) infrastructures will heavily rely on operational satellite missions. To ensure continuous and timely provision of spaceborne Earth-observation data, these missions will be characterized by high temporal resolution, high availability, low latency and enhanced synergies between different observation products. These goals will likely be achieved by deploying multi-asset satellite systems, such as constellations. In order to design robustly the architecture of these EO systems, given a certain set of observational requirements, OHB System AG has developed a methodology and the associated tools, to optimize the multi-asset system, taking into account physical and technical constraints. In general, for a specific repeating ground track Sun-synchronous orbit and a given number of spacecraft, one (or more) optimal orbital configuration(s) (i.e. anomaly separation on the same orbit) exists that allows achieving full global coverage in a prescribed number of days and minimizes the required swath size. The objective of this paper is to define the optimization model associated to this problem: the swath size is a key design parameter, most of the time constrained by mission requirements and/or technology readiness. Both Non Linear Programming and Mixed Integer Linear Programming are proposed to solve the optimization problem and are investigated in the paper: the formulation is derived and advantages and drawbacks of each are detailed. Finally, the two formulations are tested with different software and on multiple study cases: the effectiveness of the developed methodology is supported by application and validation examples.

Modeling of the zones of the Earth surface illuminated by the directional patterns of active multibeam antenna arrays

A kinematic model of the motion of a spacecraft (SC) constellation along circular orbits and an expression for calculation of the number of SCs required to completely illuminate the entire Earth surface with the visibility cones of the directional patterns (DPs) of onboard antennas are presented. A simplified procedure for construction of multiple footprints of partial DPs formed by multibeam phased-array antennas on the Earth surface has been developed. Expressions for calculation of the slant distance, the grazing angle, and zones of visibility of the Earth surface from the SCs at the normal and oblique incidence of the antenna beam have been obtained. Numerical examples and the respective graphic illustrations are given.

The space-based high-precision time transfer method based on navigation constellation inter-satellite link

With the development of space technology with increasing number of spacecraft and its expanding orbit, a uniform and high performance timing method is urgently required to guarantee the efficient cooperation among spacecrafts. Inter-satellite link (ISL) of navigation constellation is widely used for precise orbit determination and time synchronization. Because the coverage of ISL extends to medium Earth orbits (MEO) and high Earth orbits (HEO) users, it can be used as an ideal space-based high-precision time transfer method. Highly depending on ephemeris parameters, current ISL based time synchronization method is inappliable to spacecraft with low-precision and incomplete space position information. A new dynamic delay correction method is proposed on the basis of dual-way ranging. Assume the Doppler or pseudo-range can be measured by the ISL terminal in users, the method can achieve high-precision time synchronization with middle-precision position information which is easily calculated and realized. Theoretic analysis shows that the timing accuracy is prior to 0.1 ns. Finally, experiments on time synchronization between BeiDou satellite and ground station which is used to simulate a spacecraft are conducted. The test results verify the validity of the method.

Spaced‐based search coil magnetometers

AbstractSearch coil magnetometers are one of the primary tools used to study the magnetic component of low‐frequency electromagnetic waves in space. Their relatively small size, mass, and power consumption, coupled with a good frequency range and sensitivity, make them ideal for spaceflight applications. The basic design of a search coil magnetometer consists of many thousands of turns of wire wound on a high permeability core. When a time‐varying magnetic field passes through the coil, a time‐varying voltage is induced due to Faraday's law of magnetic induction. The output of the coil is usually attached to a preamplifier, which amplifies the induced voltage and conditions the signal for transmission to the main electronics (usually a low‐frequency radio receiver). Search coil magnetometers are usually used in conjunction with electric field antenna to measure electromagnetic plasma waves in the frequency range of a few hertz to a few tens of kilohertzs. Search coil magnetometers are used to determine the properties of waves, such as comparing the relative electric and magnetic field amplitudes of the waves, or to investigate wave propagation parameters, such as Poynting flux and wave normal vectors. On a spinning spacecraft, they are also sometimes used to determine the background magnetic field. This paper presents some of the basic design criteria of search coil magnetometers and discusses design characteristics of sensors flown on a number of spacecraft.

Designing nonuniform satellite systems for continuous global coverage using equatorial and polar circular orbits

We present a method for designing nonuniform satellite systems for continuous global coverage using a combination of equatorial and near-polar satellite segments in circular orbits. Equations are derived to determine the basic design parameters of the satellite system itself and the conditions of its closure at the joint of near-polar and equatorial segments. We analyze specific features of near-polar and equatorial satellite systems and their advantages and disadvantages compared with existing classes of near-polar phased and kinematically correct satellite systems. We estimate the minimum required number of spacecrafts in satellite systems for a given fold of coverage and present calculated dependences for classes of near-polar phased and equatorial satellite systems with different types of closure. For the class of kinematically correct satellite systems, we analyze the characteristics of systems with a minimum spacecraft flight height and reveal that the number of satellites in the orbital plane depends on the flight height for different folds of coverage. We bring examples of the best near-polar equatorial satellite systems of global coverage for different folds and a class of satellite systems with a fixed number of spacecrafts and orbital planes in them.

Forecast analysis on satellites that need de-orbit technologies: future scenarios for passive de-orbit devices

Propulsion-based de-orbit is a space-proven technology; however, this strategy can strongly limit operational lifetime, as fuel mass is dedicated to the de-orbiting. In addition previous reliability studies have identified the propulsion subsystem as one of the major contributors driving satellite failures. This issue brings the need to develop affordable de-orbit technologies with a limited reliance on the system level performance of the host satellite, ideally largely passive methods. Passive disposal strategies which take advantage of aerodynamic drag as the de-orbit force are particularly attractive because they are independent of spacecraft propulsion capabilities. This paper investigates the future market for passive de-orbit devices in LEO to aid in defining top-level requirements for the design of such devices. This is performed by considering the compliances of projected future satellites with the Inter Agency Space Debris Coordination Committee de-orbit time, to quantify the number of spacecraft that are compliant or non-compliant with the guidelines and, in this way, determine their need for the previously discussed devices. The study is performed by using the SpaceTrak™ database which provides future launch schedules, and spacecraft information; the de-orbit analysis is carried out by means of simulations with STELA. A case study of a passive strategy is given by the de-orbit mechanism technological demonstrator, which is currently under development at Cranfield University and designed to deploy a drag sail at the end of the ESEO satellite mission.

Revisiting the Single-Fluid Modeling of the Solar Wind–Comet Interaction: Closer Look at the Cometosheath

Earlier developed single fluid gas-dynamic model of solar wind–comet ionosphere interaction is applied to reveal some specifics in the morphology of the shocked “contaminated” solar wind region (cometosheath). The model is based on the Euler equations with added mass-loading, mass-loss and frictional force terms. Numerous reactions are taken into account in these terms including photoionization, charge transfer, dissociative recombination and ion-neutral frictional force. The electromagnetic terms are omitted, thus reducing the MHD single-fluid system of equations to gas-dynamic one. The used shock-fitting numerical scheme allows the separation of distinct areas formed by the considered interaction and exploration of their properties in detail. Attention is focused on the region between the shock wave and the contact surface as well as on the positions of these boundaries. Accurate examination of the distribution of density, temperature and velocity reveals spatial variations that resemble the variations registered by a number of spacecraft in the vicinity of comets. No specific comparisons with data are made at this stage. Two very first events of the Rosetta spacecraft’s crossing of the magnetic cavity boundary around Comet 67P/Churyumov–Gerasimenko are discussed using a “faux-transient” application of our steady-state model.

Combined satellite systems for continuous global coverage in equatorial and polar circular orbits

A method is presented to design nonuniform satellite systems for global coverage using a combination of the equatorial and polar satellite groupings. Equations are derived for determining the basic design parameters of the entire satellite system and the conditions of its closure at the joint of the polar and equatorial segments. We analyze the constitutive features of such systems and their advantages and disadvantages in comparison with the most famous types of the polar phased and kinematically correct satellite systems. We consider versions of the nonuniform satellite systems with different flight altitude and the number of spacecraft in the equatorial and polar planes, as well as we present numerical examples.

The physics and detection of nanodust in the solar system

The mass distribution of small bodies in the solar system extends over more than 35 orders of magnitude, from asteroids to nanodust, which bridge the gap between molecules and macroscopic submicron grains. The small size of nanograins compared to the relevant basic scales gives them peculiar properties. Some of these properties affect their electric charging and their large charge-to-mass ratio drives their acceleration to very high speeds in moving magnetised plasmas, as the solar wind and rotating planetary magnetospheres. The electric charge and/or high speed of nanograins have enabled them to be detected serendipitously in various parts of the solar system by several instruments designed to study larger dust, plasma particles, or waves, on a number of spacecraft. These discoveries have opened an emerging field of research, in which many open questions remain, in particular concerning the lower size limit of the particles.

Dynamics of Robotic GEostationary orbit Restorer system during deorbiting

With the development of human space activities, the number of spacecraft in geostationary orbit (GEO) has increased dramatically. According to the European Space Agency (ESA), by the end of 2008, there were 1186 objects in GEO of which only 32% were controlled operational satellites [1]. In the GEO, there are also many malfunctioning or abandoned spacecraft and lots of space debris that need to be deorbited [2] orbiting alongside functioning spacecraft. It has become necessary to monitor and deorbit these uncontrolled spacecraft and space debris to afford a safe environment for operational spacecraft so that collisions can be avoided. To do this, several alternatives have been proposed by scholars and aerospace research institutions all over the world. Among the suggestions are the RObotic GEostationary orbit Restorer (ROGER) for orbital monitoring and deorbiting [3, 4], an ion beam shepherd for contactless space debris removal [5], electrodynamic tether deorbiting [6-8], deorbiting using solar radiation force [9-11], and space robots. [12, 13]

Statistical characteristics of the coordinates of a point on the Earth's surface, when applied the combination of differential-ranging and dynamical methods on spacecraft

The paper shows the analytical relations for calculation in the linear approximation by measurement errors assessment of geographical coordinates and correlation matrix of points on the Earth's surface when using a combination of differential-ranging and dynamical methods. There is said that the use of dynamical and differential-ranging methods reduces the number of spacecraft to 2 when implementing high positioning accuracy inherent to RDM and simplifies the maintenance of configuration groups.

A Hierarchical Evolutionary Trajectory Planner for Spacecraft Formation Reconfiguration

A hierarchical evolutionary trajectory planner (HETP) for spacecraft formation reconfiguration is presented. Two levels are included in HETP. The high-level planner performs global planning which includes configuration optimization and collision avoidance between spacecraft. The low-level planners design multiple optimal or near optimal trajectories which are separated one from another for each spacecraft by parameterizing the controls in terms of Chebyshev polynomials. Based on the attributes of the system dynamics, a flexible scheme is used to select final trajectories and to avoid collisions. Our approach scales well with the number of spacecraft by planning trajectories for each spacecraft in parallel. The high level and the low level can coevolve, and multiple trajectories can be generated simultaneously as alternatives. The control precision constraints which could reduce control errors are also taken into account. The experiments described here demonstrate the efficiency of the proposed algorithm.

Transmission Power Control and Routing Strategy Based on Differential Games in Deep Space Exploration

The spectrum resource is a kind of scarce resource in the deep space exploration, the total bandwidth need for deep space communication is related to the required data rates, the number of spacecrafts, and the extent of spectrum frequency sharing. Future requirements of deep space communication may need to accommodate more spacecrafts within a particular band allocation, so the spread spectrum and multiple access techniques are widely used in deep space communications. And for the purpose of save power and reduce mutual interference, transmission power control may be introduced in the communication process. In this paper, a noncooperative differential game is proposed, and a power control algorithm is get from the equilibrium of the game, the results show that the algorithm can effectively reduce mutual interference, and also provide a way of route setup through relay nodes selection.

Stigmergy based behavioural coordination for satellite clusters

Multi-platform swarm/cluster missions are an attractive prospect for improved science return as they provide a natural capability for temporal, spatial and signal separation with further engineering and economic advantages. As spacecraft numbers increase and/or the round-trip communications delay from Earth lengthens, the traditional “remote-control” approach begins to break down. It is therefore essential to push control into space; to make spacecraft more autonomous. An autonomous group of spacecraft requires coordination, but standard terrestrial paradigms such as negotiation, require high levels of inter-spacecraft communication, which is nontrivial in space. This article therefore introduces the principals of stigmergy as a novel method for coordinating a cluster. Stigmergy is an agent-based, behavioural approach that allows for infrequent communication with decisions based on local information. Behaviours are selected dynamically using a genetic algorithm onboard. supervisors/ground stations occasionally adjust parameters and disseminate a “common environment” that is used for local decisions. After outlining the system, an analysis of some crucial parameters such as communications overhead and number of spacecraft is presented to demonstrate scalability. Further scenarios are considered to demonstrate the natural ability to deal with dynamic situations such as the failure of spacecraft, changing mission objectives and responding to sudden bursts of high priority tasks.

The Puzzle of the Flyby Anomaly

Close planetary flybys are frequently employed as a technique to place spacecraft on extreme solar system trajectories that would otherwise require much larger booster vehicles or may not even be feasible when relying solely on chemical propulsion. The theoretical description of the flybys, referred to as gravity assists, is well established. However, there seems to be a lack of understanding of the physical processes occurring during these dynamical events. Radio-metric tracking data received from a number of spacecraft that experienced an Earth gravity assist indicate the presence of an unexpected energy change that happened during the flyby and cannot be explained by the standard methods of modern astrodynamics. This puzzling behavior of several spacecraft has become known as the flyby anomaly. We present the summary of the recent anomalous observations and discuss possible ways to resolve this puzzle.

Magnetic Fields of the Satellites of Jupiter and Saturn

This paper reviews the present state of knowledge about the magnetic fields and the plasma interactions associated with the major satellites of Jupiter and Saturn. As revealed by the data from a number of spacecraft in the two planetary systems, the magnetic properties of the Jovian and Saturnian satellites are extremely diverse. As the only case of a strongly magnetized moon, Ganymede possesses an intrinsic magnetic field that forms a mini-magnetosphere surrounding the moon. Moons that contain interior regions of high electrical conductivity, such as Europa and Callisto, generate induced magnetic fields through electromagnetic induction in response to time-varying external fields. Moons that are non-magnetized also can generate magnetic field perturbations through plasma interactions if they possess substantial neutral sources. Unmagnetized moons that lack significant sources of neutrals act as absorbing obstacles to the ambient plasma flow and appear to generate field perturbations mainly in their wake regions. Because the magnetic field in the vicinity of the moons contains contributions from the inevitable electromagnetic interactions between these satellites and the ubiquitous plasma that flows onto them, our knowledge of the magnetic fields intrinsic to these satellites relies heavily on our understanding of the plasma interactions with them.

New results on radiation effects on human health

Humans are exposed to ionizing radiation all the time, and it is known that it can induce a variety of harmful biological effects. Consequently, it is necessary to quantitatively assess the level of exposure to this radiation as the basis for estimating risks due to ionization radiation. During the Work Package 2400 of the COST-724/WG-2 action, a number of spacecraft and aircraft experiments have been performed with both active and passive detectors. A large data base has been created.

Interplanetary Periodic Trajectories in Two-Planet Systems

A new technique is proposed to identify infinite families of candidate periodic trajectories (cyclers) in any restricted,coplanar,circular,two-planetsystem.Inthesimplestcaseinwhichonlyoneoftheplanetsenablesgravityassisted maneuvers, a method based on Henon’s diagram is used instead of solving Lambert’s multiple-revolution problem.Itprovidesthesolutionsinacomprehensiblegraphicalformandsuggeststheirnaturalclassification.Inthe particular Earth–Mars case, it is shown that all previously found solutions for cyclers are present in Henon’s diagram. For the more general case in which both planets enable gravity-assisted maneuvers, Henon’s diagram is extended to present the trajectories that start and end near the same planet with the same relative velocity. This new extended diagram can be also used to predict periodic trajectories in this more general system. A discussion of all classes of periodic trajectories is presented. Nomenclature a = semimajor axis e = eccentricity F, G = Lagrange/Gibbs functions h = angular momentum vector h = angular momentum magnitude hp = height of the hyperbola’s pericenter i = inclination angle M1, M2, M3 = bodies in the three-body problem: central (sun), primary (planet), and spacecraft m1, m2, m3 = masses of M1, M2, and M3 m = number of spacecraft’s semirevolutions n = number of primary’s semirevolutions P1, P2 = primary bodies (planets) in the four-body problem p = semilatus rectum

Ground truth from the Opportunity Rover for Mars thermal inertia data

[1] The temperature of the Martian surface has been measured by a number of spacecraft and numerical models of the surface thermal response constrain the near-surface physical properties. The results allow inferences regarding the surface layer and help determine potential hazards for landed spacecraft. However, thermal models generally do not incorporate the degree of surface complexity that is seen from landers. Here we examine potential contributions to the thermal response along the Opportunity Rover's traverse by using ground truth in conjunction with orbiter data from the THEMIS instrument on Mars Odyssey. We show that the size distribution of the ubiquitous hematite spherules varies in a way that is consistent with expectations from orbiter data. Secondly, exposures of bedrock along Opportunity's traverse have no observable effect on the bulk thermal response seen from orbit. These field observations are an important step toward improving understanding of the physical composition of the Martian surface.