Multi-objective planning of a multiple geostationary spacecraft refuelling mission

The multi-objective optimization of multiple geostationary spacecraft refuelling is investigated in this article. A servicing spacecraft (SSc) and a propellant depot (PD), both parked initially in geostationary Earth orbit (GEO), are utilized to refuel multiple GEO targets of known propellant demand. The capacitated SSc is expected to rendezvous with fuel-deficient GEO targets or the PD for the purpose of refuelling or getting refuelled. The multiple geostationary spacecraft refuelling problem is treated as a multi-variable combinatorial optimization problem with the principal objective of minimizing the propellant consumption and the mission duration. A two-level optimization model is built, and the design variables are the refuelling order X, the refuelling time T and the binary decision variable S. The non-dominated sorting genetic algorithm is employed to solve the up-level optimization problem. For the low-level optimization, an exact algorithm is proposed. Finally, numerical simulations are presented to illustrate the effectiveness and validity of the proposed approach.     

Proton and iron ion observations from a solid-state microdosimeter

The tissue equivalent proportional counter (TEPC) that utilises a gas cavity has been the standard to obtain microdosimetric observations. An alternative is the solid-state microdosimeter that replaces the gas with a solid-state detector with microscopic sensitive volumes. Here, we describe the development of two versions of a personal solid-state microdosimeter for space exploration applications and give test results for iron and proton beams with comparisons to TEPC measurements and Geant4 radiation transport code simulations. In addition, we describe and provide test results of an optical technique to carry out an end-to-end system test and calibration of a silicon solid-state microdosimeter. This technique eliminates the need for an ionising radiation source with its attendant issues on use and transportation and provides an advantage over the TEPC.     

A solid state microdosimeter based on a monolithic silicon telescope

A monolithic silicon telescope, consisting of a DeltaE and an E stage-detector ( approximately 1.9 microm and 500 microm thick, respectively), was coupled to a polyethylene converter in order to investigate the feasibility of a solid state microdosimeter with respect to the field-funnelling effect. This work discusses the preliminary results of an analytical approach for the correction of a spectrum measured with this silicon-based microdosimeter for tissue-equivalence and geometrical effects. The device was irradiated with 2.7 MeV monoenergetic neutrons at the INFN-Laboratori Nazionali di Legnaro (Legnaro, Italy). The non tissue-equivalence of silicon was corrected by exploiting the signals generated in the E-stage. The correction for the sensitive volume geometry was optimised by taking into account the track length distribution of the recoil-protons generated in the converter. The derived dose distribution of the energy imparted per event was compared to the one measured with a cylindrical tissue-equivalent proportional counter (TEPC). The agreement is satisfactory.     

Microdosemeter instrument (MIDN) for assessing risk in space

Radiation in space generally produces higher dose rates than that on the Earth's surface, and contributions from primary galactic and solar events increase with altitude within the magnetosphere. Presently, no personnel monitor is available to astronauts for real-time monitoring of dose, radiation quality and regulatory risk. This group is developing a prototypic instrument for use in an unknown, time-varying radiation field. This microdosemeter-dosemeter nucleon instrument is for use in a spacesuit, spacecraft, remote rover and other applications. It provides absorbed dose, dose rate and dose equivalent in real time so that action can be taken to reduce exposure. Such a system has applications in health physics, anti-terrorism and radiation-hardening of electronics as well. The space system is described and results of ground-based studies are presented and compared with predictions of transport codes. An early prototype in 2007 was successfully launched, the only solid-state microdosemeter to have flown in space.     

A method of calibrating magnetometers on a spinning spacecraft

This paper describes a procedure for quantifying and compensating for angular offsets and slow-varying drifts associated with a flux-gate magnetometer onboard a spinning spacecraft. Such magnetometers have been down on numerous spacecraft such as IMP-8, DE-1, and ISTP/GEOTAIL, and similar instruments are currently proposed to fly on the ISTP/WIND spacecraft. Consequently, slight geometric misalignment of the sensor from their chosen axes will create errors in the measured signal. These misalignments can be quantified using perturbation theory and compensated in the data analysis process. The technique is applicable to magnetometers on spinning spacecraft. Also, over long time periods, the magnetometer will develop slight drifts in the electronic components, and these too can be quantified in the data analysis process. A technique is discussed that quantifies and compensates for such perturbations from the measurements. The technique has been successfully applied for the last sixteen years to IMP-8 magnetometer data and more currently to the GEOTAIL magnetometer data, and can be applied in a general way to measurements from any magnetometer onboard a spinning spacecraft. Further improvements in the technique are also discussed     

Component testing of a series system in a random mission

Components of a series system are tested in order to assure desired levels of system reliability during the mission. The components are nonidentical but they all fail exponentially with failure rates that depend on the mission performed. There is a given set of missions that the device can be assigned randomly with respect to a given probability distribution. This directly implies that the failure rates of the components depend on the specific mission that the device performs. The objective is to find an optimal component test plan. We will show that, with some extra effort, this rather complicated but realistic model can be handled using available results in semi-infinite linear programming and d.c. (difference of convex functions) programming.     

ISRO spacecraft technology evolution

Evolutionary trends in the technologies related to Indian Space Research Organisation (ISRO) satellites, both past and present, are outlined. The issues related to the developmental complexities of different spacecraft subsystems are discussed in the context of the needs of the current generation operational spacecraft like the Indian Remote Sensing Satellite (IRS) and the Indian National Satellite (INSAT) II. Considerations pertinent to reliability and long-life requirements, crucial to operational satellites, are also highlighted.     

Dynamics of liquid-filled spacecraft

A method is presented for simulating coupled liquid-solid dynamics. An important example of a coupled liquid-solid system is a satellite carrying fuel. The dynamics of the satellite and the onboard fuel influence each other, which may lead to satellite motion that is uncontrollable. For better understanding of the complex dynamics of coupled systems, a numerical model is developed. The model consists of two parts. The first part that solves the liquid motion is only briefly discussed here. The focus in this paper is on the way in which the dynamics of the liquid and the solid body are coupled. For this, the governing equations are presented in which terms appear that represent the force and torque on the solid body due to the sloshing liquid. The governing equations are rewritten such that the discrete approximation of these equations can be integrated in a stable manner for arbitrary liquid/solid mass ratios. Results are presented demonstrating the stability of the present model. A grid-refinement study and a time-step analysis are performed. Finally, the flat-spin motion of a satellite, partially filled with liquid, that flew in 1992 as part of the Wet Satellite Model experiment is studied. Results from the simulation are compared with the actual flight data.     

The AGILE mission: The first 2 years

We summarize here the main highlights of the AGILE astrophysics mission. The satellite, launched in April 2007, is devoted to gamma-ray observations in the 30 MeV–30 GeV energy range, with simultaneous hard X-ray imaging in the 18–60 keV band, and optimal timing capabilities for the study of transient phenomena. The very large field of view (2.5 sr) of the gamma-ray imager coupled with the hard X-ray monitoring capability makes AGILE well suited to study Galactic and extragalactic sources, as well as GRBs and other fast transients. AGILE reaches its optimal performance near 100 MeV with good imaging and sensitivity. Gamma-ray and hard X-ray sources can be monitored 14 times a day, and an extensive database has been obtained for a variety of sources. We summarize here the breakthroughs and most important results obtained for several sources including microquasars and other Galactic compact objects (most notably, the discovery of gamma-ray emission above 100 MeV from Cygnus X-3), Supernova Remnants and pulsar wind nebulae, gamma-ray pulsars, a bright class of blazars (3C 454.3, TXS 0716+714, HB 1510-089, Mrk 421), short and long GRBs (including the remarkable short burst GRB 090510), and terrestrial gamma-ray flashes (TGFs).     

Solar sailing: mission applications and engineering challenges

Solar sailing is emerging as a promising form of advanced spacecraft propulsion, which can enable exciting new space-science mission concepts. By exploiting the momentum transported by solar photons, solar sails can perform high-energy orbit-transfer manoeuvres without the need for reaction mass. Missions such as planetary-sample return, multiple small-body rendezvous and fast missions to the outer Solar System can therefore be enabled with the use of only a modest launch vehicle. In addition, new families of highly non-Keplerian orbits have been identified that are unique to solar sails, and can enable new ways of performing space-science missions. While the opportunities presented by solar sailing are appealing, engineering challenges are still to be solved before the technology finally comes to fruition.     

Fault-tolerant spacecraft attitude control system

Spacecraft perform a variety of useful tasks in our day-to-day life. These are such that spacecraft need to function properly without interruptions for 7 to 15 years in space without any maintenance. Though most spacecraft have redundant systems to serve as back-ups in case of failures, they greatly depend on human assistance through ground stations for failure analysis, remedial actions and redundancy management, resulting in itnerruption in services rendered. There is, therefore, need for a fault-tolerant system that functions despite failures and takes remedial action, without human assistance/intervention, autonomously on board the spacecraft. Commonly used techniques for fault-tolerance in computers cannot be directly used for fault-tolerance in sensors and actuators of a closed loop control system. Further, for space applications fault-tolerance needs to be achieved without much penalty in weight and computational requirements. This paper describes briefly the attitude control system (acs) of a spacecraft and highlights the essential features of a fault-tolerant control system. Schemes for fault tolerance in sensors and actuators are presented with an analysis on various failure modes and their effects. Newly developed fault-detection, identification and reconfiguration (fdir) algorithms for various elements ofacs are described in detail. Also an optimum symmetrically skewed configuration for the attitude reference system using dynamically tuned gyros is developed. Some of the schemes have already been used in Indian Spacecraft. As future Indian space missions will directly cater to various applications on an operational basis, the ultimate objective is to have a totally fault-tolerant ‘intelligent’ autonomous spacecraft.     

航天器制冷机的发展概况

随着空间技术的发展，使得各种遥感仪广泛用于航天器上。如红外探测器、Ｘ射线、γ射线和亚毫米波探测器等须在低温下工作才能提高灵敏度，降低热噪声。因此，制冷系统是空间技术不可缺少的重要组成部分。目前采用的制冷系统有：被动制冷包括辐射制冷和低温制冷剂贮存系统；机械制冷机。主要介绍了空间制冷机分类、特点，在航天器上已经和即将使用的制冷机。     

Modelling radiation loads to detectors in a SNAP mission

In order to investigate the degradation of optical detectors of the Supernova Acceleration Project (SNAP) space mission because of irradiation, a three-dimensional model of the satellite has been developed. A realistic radiation environment at the satellite orbit, including both galactic cosmic rays and cosmic ray trapped in radiation belts, has been taken into account. The modelling has been performed with the MARS14 Monte Carlo code. In a current design, the main contribution to dose accumulated in the photo-detectors is shown to be due to trapped protons. The contribution of primary alpha particles is estimated. Predicted performance degradation for the photodetector for a four-year space mission is 40% and this can be reduced further by means of shielding optimisation.     

新型双向缓冲飞船座椅方案设计

由于地面通过座椅传递过来的多向冲击过载存在超过航天员头盆向过载耐受极限的可能性,提出了一种吸收垂直和水平两个方向着陆冲击能量的新型双向缓冲杆座椅方案.利用Lagrange方程建立了座椅系统动力学模型,并在Adams软件中进行了验证.通过数值算例,比较了竖直缓冲座椅和双向缓冲座椅的缓冲效果,讨论了座椅头部点和转动中心点的响应规律.研究结果表明,双向缓冲座椅能够明显降低头盆向加速度峰值,而对原有竖直缓冲杆的工作特性和胸背向加速度影响很小,实现了胸背向和头盆向加速度峰值降低至航天医学要求范围内的目标.     

Mathematical simulation of heat exchange in a nonhermetic instrumental compartment of a spacecraft

We present physical and dynamic thermal mathematical models in distributed and lumped parameters, calculation algorithms, software, and some results of numerical calculations of radiative-conductive heat exchange in blocks and modules carrying thermally loaded on-board equipment in a nonhermetic instrumental compartment of a proposed durable communication spacecraft with improved mass, size, and energy characteristics improved in comparison with traditional hermetic compartments. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 73, No. 1, pp. 113–124, January–February, 2000.     

Risk-based spacecraft fire safety experiments

This paper utilizes the scenario approach of risk assessment to identify modeling needs and, in turn, experiments that would aid in the development of models that would meet these needs. Due to the closed environment of a spacecraft and the lack of egress, fire on-board may pose a severe problem. There are many differences between a fire on-board the spacecraft and one in a terrestrial facility and they must be accounted for in the assessment of risk. Both the risk assessment methodology and the phenomena-based models must be modified. This paper discusses some of the methodology modifications, as well as special experimental results. Multiple experiments have been conducted in terrestrial and microgravity environments in order to construct and validate models required for the assessment and management of risk on-board spacecraft. A logic diagram analyzing the ways in which the crew may be injured and/or the spacecraft may be damaged, as well as operating experience, have identified wire overheating events as being potentially significant accident initiators. As a result, the experiments have concentrated on quantifying the pyrolysis event of a wire being overheated with excessive current. A preliminary set of experiments at the 2·2-second NASA Lewis Drop Tower has led to several observations. The event is violent due to the high heating rates. At these high heating rates, a jet of hot gases and smoke was observed. Frequently the conductor would melt down, sometimes ejecting molten pieces of the copper conductor. The event poses a threat to targets in the near vicinity and further away. Also, the smoke particle size distribution is shifted towards larger sizes in a microgravity environment. This may prove very important in designing a smoke detector. While significant results were obtained from these tests, longer durations of microgravity are required for further quantification to be possible.     

Digital Doppler measurement with spacecraft

Digital and analog phase-locked loop (PLL) receivers were operated in parallel, each tracking the residual carrier from a spacecraft. The PLL tracked the downlink carrier and measured its instantaneous phase. This information, combined with a knowledge of the uplink carrier and the transponder ratio, permitted the computation of a Doppler observable. In this way, two separate Doppler measurements were obtained for one observation window. The two receivers agreed on the magnitude of the Doppler effect to within 1 mHz. There was less jitter on the data from the digital receiver. This was due to its smaller noise bandwidth. The demonstration and its results are described     

Hybrid CFRP/titanium bolted joints: Performance assessment and application to a spacecraft payload adaptor

This paper presents an experimental investigation of the mechanical response and the industrial manufacturability of CFRP–titanium hybrid laminates using the example of a spacecraft payload adaptor. The local hybridization with metal within a bolted joint region of composite laminates is proven to be an effective method of increasing the mechanical joint efficiency of highly loaded bolted joints. High-strength titanium foils are locally embedded into the composite laminate by means of ply substitution techniques, thus avoiding any local laminate thickening and providing for a local laminate with high bearing and shear capabilities. An extensive sample and component test program has been performed evaluating the impact of different design parameters and load conditions. The verification of the hybrid technique’s processability, inspectability and compatibility with a standard industrial fibre placement process has been successfully demonstrated through the manufacturing of a spacecraft payload adaptor featuring diverse applications of the hybridization technique.