An Asian perspective on the new US space policy: The emphasis on international cooperation and its relevance to Asia

This viewpoint examines the likely reasons behind the renewed focus on international cooperation in the new US National Space Policy, noting that the rise of various Asian space powers is one factor. It demonstrates the increase in US-Asian space cooperation that is already underway, arguing that such cooperation can only be to the good in providing Asian countries with a greater degree of cutting-edge technology and know-how, as well as contributing to the overall safety and security of outer space. Nevertheless, there will doubtless be problems such as cost overruns and delays and effort will have to be applied if cooperation is to work.     

A fast numerical approach for Whipple shield ballistic limit analysis

Whipple shield is widely used on manned spacecraft, numerical simulation is an important way for obtaining the ballistic limit. The large population of particles and the large space span of Whipple shield simulation model restrict the computational efficiency. A fast numerical approach is presented for Whipple shield ballistic limit analysis. First, the critical penetration analysis of the rear walls is converted into specific impulse analysis delivered by the secondary debris cloud, because the maximum of specific impulse is the main determinant of the penetration. The dual plate simulation model is then converted into single plate model and the population of particles is reduced. Second, based on the isotropic expansion theory of secondary debris cloud, the specific impulse analysis is further converted into particle position and velocity analysis when the stable secondary debris formed. The space span of the simulation model is reduced. An example of Whipple shield ballistic limit analysis is provided for the verification of the fast numerical approach, it shows that this approach can significantly increase the computation efficiency with acceptable accuracy.     

Nonlinear filtering methods for spacecraft navigation based on differential algebra

The paper investigates the problem of nonlinear filtering applied to spacecraft navigation. Differential algebraic (DA) techniques are proposed as a valuable tool to implement the higher-order numerical and analytic extended Kalman filters. Working in the DA framework allows us to consistently reduce the required computational effort without losing accuracy. The performance of the proposed filters is assessed on different orbit determination problems with realistic orbit uncertainties. The case of nonlinear measurements is also considered. Numerical simulations show the good performance of the filter in case of both complex dynamics and highly nonlinear measurement problems.     

Design concepts for the first 40 km a key step for the space elevator

The Marine Node for the Space Elevator Infrastructure is the base for all activities to load and unload the cargo and climbers. As the basic design of the space elevator power system is solar power only, the first 40 km is hazardous to operations and demands enclosed packaging of fragile tether climbers. A significant question is: how do we place a full-up tether climber, driven by solar power, above the atmosphere? Two approaches, starting at the Marine Node, allow the tether climber to initiate the climb with solar energy above the atmosphere. The third viable approach is to provide a platform at altitude for initiation of tether climb. These approaches would enable solar power to be the source of energy for climbing. The three approaches are:     

The new debate on the working methods of the UNCOPUOS Legal Subcommittee

The 2014 session of the Legal Subcommittee (LSC) of the United Nations Committee on the Peaceful Uses of Outer Space (UNCOPUOS) saw a particularly extensive and thorough debate on the working methods of this forum, which has the status of the highest body in space law making. By discussing the working methods it also became apparent how delegations actually regard the LSC and what expectations they have from it. In a time of considerable changes in space activities and space diplomacy alike, it was only a matter of time that such a comprehensive discussion arose. And while it did not immediately lead to decisions, it provided numerous signals for the future of the LSC.     

Analysis and experiments for delay compensation in attitude control of flexible spacecraft

Space vehicles are often characterized by highly flexible appendages, with low natural frequencies which can generate coupling phenomena during orbital maneuvering. The stability and delay margins of the controlled system are deeply affected by the presence of bodies with different elastic properties, assembled to form a complex multibody system. As a consequence, unstable behavior can arise. In this paper the problem is first faced from a numerical point of view, developing accurate multibody mathematical models, as well as relevant navigation and control algorithms. One of the main causes of instability is identified with the unavoidable presence of time delays in the GNC loop. A strategy to compensate for these delays is elaborated and tested using the simulation tool, and finally validated by means of a free floating platform, replicating the flexible spacecraft attitude dynamics (single axis rotation). The platform is equipped with thrusters commanded according to the on–off modulation of the Linear Quadratic Regulator (LQR) control law. The LQR is based on the estimate of the full state vector, i.e. including both rigid – attitude – and elastic variables, that is possible thanks to the on line measurement of the flexible displacements, realized by processing the images acquired by a dedicated camera. The accurate mathematical model of the system and the rigid and elastic measurements enable a prediction of the state, so that the control is evaluated taking the predicted state relevant to a delayed time into account. Both the simulations and the experimental campaign demonstrate that by compensating in this way the time delay, the instability is eliminated, and the maneuver is performed accurately.     

Reliability analysis and utilization of PEMs in space application

More and more plastic encapsulated microcircuits (PEMs) are used in space missions to achieve high performance. Since PEMs are designed for use in terrestrial operating conditions, the successful usage of PEMs in space harsh environment is closely related to reliability issues, which should be considered firstly. However, there is no ready-made methodology for PEMs in space applications. This paper discusses the reliability for the usage of PEMs in space. This reliability analysis can be divided into five categories: radiation test, radiation hardness, screening test, reliability calculation and reliability assessment. One case study is also presented to illuminate the details of the process, in which a PEM part is used in a joint space program Double-Star Project between the European Space Agency (ESA) and China. The influence of environmental constrains including radiation, humidity, temperature and mechanics on the PEM part has been considered. Both Double-Star Project satellites are still running well in space now.     

Analytical and semi-analytical investigations of geosynchronous space debris with high area-to-mass ratios

This paper provides a Hamiltonian formulation of the averaged equations of motion with respect to short periods (1 day) of a space debris subjected to direct solar radiation pressure and orbiting near the geostationary ring. This theory is based on a semi-analytical theory of order 1 regarding the averaging process, formulated using canonical and non-singular elements for eccentricity and inclination. The analysis is based on an expansion in powers of the eccentricity and of the inclination, truncated at an arbitrary high order.     

A ballistic limit equation for hypervelocity impacts on composite honeycomb sandwich panel satellite structures

During a recent experimental test campaign performed in the framework of ESA Contract 16721, the ballistic performance of multiple satellite-representative Carbon Fibre Reinforced Plastic (CFRP)/Aluminium honeycomb sandwich panel structural configurations (GOCE, Radarsat-2, Herschel/Planck, BeppoSax) was investigated using the two-stage light-gas guns at EMI. The experimental results were used to develop and validate a new empirical Ballistic Limit Equation (BLE), which was derived from an existing Whipple-shield BLE. This new BLE provided a good level of accuracy in predicting the ballistic performance of stand-alone sandwich panel structures. Additionally, the equation is capable of predicting the ballistic limit of a thin Al plate located at a standoff behind the sandwich panel structure. This thin plate is the representative of internal satellite systems, e.g. an Al electronic box cover, a wall of a metallic vessel, etc. Good agreement was achieved with both the experimental test campaign results and additional test data from the literature for the vast majority of set-ups investigated. For some experiments, the ballistic limit was conservatively predicted, a result attributed to shortcomings in correctly accounting for the presence of high surface density multi-layer insulation on the outer facesheet. Four existing BLEs commonly applied for application with stand-alone sandwich panels were reviewed using the new impact test data. It was found that a number of these common approaches provided non-conservative predictions for sandwich panels with CFRP facesheets.