Space solar power vs space communications

To meet the future needs of energy on Earth, the transmission of solar power from space is being extensively studied. Since the power station will occupy a position in the geostationary orbit and will use radio frequency spectrum for transmission of energy to Earth, the relative benefits of space solar power and space communications should be considered. The resource allocation of orbit-spectrum to a power station requires a sacrifice from space communications as they both utilize similar limited resources. The power station is to energy what communication is to information. While the cost of energy is going up, the cost of information processing, storage, sharing and transmission is decreasing. Also, increased means of communication are used as a measure of energy conservation. With the advent of computer communication and the Large Scale Integrated (LSI) microprocessors, the technique of multiple access, message switching and satellite switching can be cost-effectively combined. The computer-satellite communication will allow information resource sharing among large numbers of users besides the conventional application of space communications. Since space communication means work effectively in many other areas where ultimate energy use and conservation is possible, the space solar power will not be able to compete or substitute on the basis of equality and social benefits. But, as the transmission technology is similar for both areas, the R & D effort for solar power will certainly increase efficiency and reduce cost for space communications.     

Assessment on the feasibility of future shepherding of asteroid resources

Most plausible futures for space exploration and exploitation require a large mass in Earth orbit. Delivering this mass requires overcoming the Earth's natural gravity well, which imposes a distinct obstacle to any future space venture. An alternative solution is to search for more accessible resources elsewhere. In particular, this paper examines the possibility of future utilisation of near Earth asteroid resources. The accessibility of asteroid material can be estimated by analysing the volume of Keplerian orbital element space from which Earth can be reached under a certain energy threshold and then by mapping this analysis onto an existing statistical near Earth objects (NEO) model. Earth is reached through orbital transfers defined by a series of impulsive manoeuvres and computed using the patched-conic approximation. The NEO model allows an estimation of the probability of finding an object that could be transferred with a given Δv budget. For the first time, a resource map provides a realistic assessment of the mass of material resources in near Earth space as a function of energy investment. The results show that there is a considerable mass of resources that can be accessed and exploited at relatively low levels of energy. More importantly, asteroid resources can be accessed with an entire spectrum of levels of energy, unlike other more massive bodies such as the Earth or Moon, which require a minimum energy threshold implicit in their gravity well. With this resource map, the total change of velocity required to capture an asteroid, or transfer its resources to Earth, can be estimated as a function of object size. Thus, realistic examples of asteroid resource utilisation can be provided.     

Space and the fate of humanity

Current growth and consumption rates on Earth cannot be sustained into the future. Space technology is already a vital tool in the management of the planet and we should look at it to mitigate some of the problems we face. However, this should not include colonization of interstellar space. Rather we should focus on using solar energy from space and on mining asteroids, both of which would be feasible if the Moon was developed as a space base and power station. The most difficult and expensive part of getting into space is escaping Earth's gravity - something that could be avoided once a presence was established on the Moon. A lunar base would also provide the obvious site from which to reach GEO, travel to Mars or back to Earth and, ultimately, to explore the further reaches of the Solar System.     

Evolution of the Orbit of an Earth Satellite with a Solar Sail

The efficiency of using the light pressure of solar radiation for increasing the semimajor axis of the orbit of an Earth Satellite carrying a solar sail is estimated. The orbit is nearly circular and has an altitude of about 900 km. The satellite is in the mode of single-axis solar orientation: it rotates at an angular velocity of 1 deg/s around the axis of symmetry, which traces the direction to the Sun. This mode is maintained by the solar sail, which serves in this case as a solar stabilizer. The following method of increasing the semimajor axis of the orbit (which is equivalent to increasing the total energy of the satellite's orbital motion) is considered. On those sections of the orbit, where the angle between the light pressure force acting upon the sail and the vector of geocentric velocity of the satellite does not exceed a specified limit, the sail is functioning as a solar stabilizer. On those sections of the orbit, where the above-indicated angle exceeds this limit, the sail is furled by way of turning the edges of the petals towards the Sun. Such a control increases the semimajor axis by more than 150 km for three months of flight. In this case, the accuracy of solar orientation decreases insignificantly.     

绳系空间太阳能电站动力学响应分析

利用绝对节点坐标方法研究绳系空间太阳能电站在轨飞行的太阳能电池板动力响应。通过勒让德变换引入广义动量,在约束哈密尔顿体系下建立轨道、姿态和弹性振动耦合的动力学方程。基于祖冲之类方法的思想,结合辛龙格-库塔方法对微分-代数方程进行数值求解。数值算例说明本文建模方法和数值算法都是有效的,能很好地保持系统约束和能量。最后分析了绳长、平台系统的质量、轨道高度对于梁中点挠度和轴向平均应变的影响。     

Orbit design for future SpaceChip swarm missions in a planetary atmosphere

The effect of solar radiation pressure and atmospheric drag on the orbital dynamics of satellites-on-a-chip (SpaceChips) is exploited to design equatorial long-lived orbits about the oblate Earth. The orbit energy gain due to asymmetric solar radiation pressure, considering the Earth's shadow, is used to balance the energy loss due to atmospheric drag. Future missions for a swarm of SpaceChips are proposed, where a number of small devices are released from a conventional spacecraft to perform spatially distributed measurements of the conditions in the ionosphere and exosphere. It is shown that the orbit lifetime can be extended and indeed selected through solar radiation pressure and the end-of-life re-entry of the swarm can be ensured, by exploiting atmospheric drag.     

Asteroidal resources for space manufacturing

Earth-approaching asteroids (Apollos and Amors) may be competitive candidates as raw materials for space manufacturing. The total energy per unit mass required to transfer material from some of these bodies to high Earth orbit is comparable to that for lunar material. Recent optical studies suggest ordinary and carbonaceous chondrite compositions for these asteroids, with some containing large quantities of metallic iron and nickel, and others, carbon, hydrogen and nitrogen. Discoveries of several new candidate asteroids over the next few years will allow for a better selection of materials and mission possibilities. Material from one of these asteroids, either in raw or manufactured form, could be returned to the vicinity of the Earth by a solar-powered mass-driver reaction engine. With a requirement of ～60 shuttle flights, and with minimal development costs, an automated mission to a 200-m dia. (10⁷ ton) metal-rich asteroid could be carried out by a mass-driver tug assembled in low Earth orbit using shuttle tankage as reaction mass. Such a tug could, within a few years, move the asteroid into high Earth orbit for the manufacturing of ～ 20 satellite power stations using a portion of the asteroid itself as reaction mass. In the next few years over 100 asteroids in this size range could be discovered, orbits determined and composition types classified using existing earthbased and spaceborne search techniques.     

On orbit control using gravity gradient effects

Possibility of orbit control using gravity gradient (GG) effects without any mass expulsion is discussed. For simplicity, a dumb-bell type satellite and circular orbits are mainly considered. It is shown that the GG effects can be applied to convert attitude torques into orbital torques and vice versa. In central gravitational force fields, maximum orbital torques or thrusts are available from the GG force when roll or pitch angle is $\text{±}\text{π}\text{4}$ provided that the attitude angle is null when the dumb-bell axis coincides with the local vertical. Such external torques as geomagnetic or solar wind pressure can be utilized to maintain the $\text{±}\text{π}\text{4}$ attitude, then the orbital torques are available forever. In non-central gravitational fields, without any external torque, the orbital radii of circular orbits can be increased by controlling the satellite attitude using electric energy. The use of the Earth's oblateness effects and the exterior Lunar potential is discussed.     

Space light: space industrial enhancement of the solar option

The solar option can be enhanced significantly by space light technology. Reflectors in suitable orbits beam to Earth measured amounts of sunlight, the most versatile and bio-compatible energy source. The multitude of space light functions ranges from night illumination of rural and urban areas (by Lunetta systems) to photosynthetic production enhancement for the growth of food and of biomass for conversion to chemical fuels, local agricultural irradiation for crop drying and weather stabilization and to electric power generation by irradiating suitable photovoltaic or thermal ground receivers at night or by adding to the natural solar energy input during daytime (Soletta systems).

The Lunetta and Soletta concepts, developed by the author during the past ten years, building on the foundations laid by the great space pioneer Prof. H. Oberth (1928), are reviewed, along with their socio-economic merits. An assessment of terrestrial alternatives shows that many useful functions have no practical alternative, the major exception being electric power generation. Three systems are selected, bracketing the broad versatility of space light—Lunetta, Powersoletta and a large Biosoletta for large-scale seafood production in Antarctic and Artic waters. The systems, and several maintenance and supply requirements are described, sized and analyzed, along with suitable orbit selection for different applications. Models are developed for rural and urban area lighting, power generation at selected sites around the globe with photovoltaic and thermal ground stations and for the large-scale production of seafood at high southern and northern latitudes with ample nutrient upwell, but insufficient annual supply of solar energy. The economics of these systems is analyzed.     

On the possibility of long-time existence of submicron particles injected in elongated elliptical orbits with low perigee in the near-Earth space

On the basis of numerical experiments the theoretical possibility of long-time (longer than 1 month) and superlong-time (longer than 1 year) existence in orbit of technogenic microparticles (MPs) with radii of a few hundredths of a micrometer is demonstrated. MPs are injected into the near-Earth space (NES) in elongated elliptical low-perigee orbits with parameters, corresponding to Molniya satellite’s orbital parameters. Calculations were carried out taking into account disturbing effects on the MP orbital motion in NES of the following factors: the gravitational disturbance caused by polar oblateness of the Earth, the solar pressure force (calculated with using the techniques of the Mie theory), the drag force of a neutral component of background gas, as well as the electrodynamic forces caused by interaction of electric charge, induced on MPs, with the magnetic and electric fields of the NES.     

Manufacture in space: the MINOS system

The manufacture in Space of products for use on Earth is a possibility for the 1990s. The MINOS project is based on the idea of a free-flyer station for the current medium-level production of either unique products (which cannot be made on Earth), or of economic yields of products which cannot be obtained in sufficient quantities on Earth.At present, only the main system may be defined from general specifications: electrical power (10 kW), residual acceleration (10^?5 g), processing cycle duration (10 hr).The launch vehicle is Ariane I and its improved versions (models II, III and IV).The outer structure of the spececraft is described with solar panels, energy storage (battery and inertial storage) and control systems.The definition of orbital parameters capable of accommodating the basis specifications, especially the high energy level and the re-entry conditions on the Guiana base, is a major problem. The re-entry vehicle is studied from a pure ballistic trajectory point of view. From the results of orbital performance, the mass of the spacecraft and also the mass of the ascent vehicle are evaluated. For this latter value, its determination is directly related to the cost of space-processed materials.A general overview is given of the other spacecraft sub-systems such as satellite tracking, communications, ground stations, resources requirements, telemetry, onboard computing system etc.     

欧洲自动转移飞行器电源系统设计及启示

介绍了"自动转移飞行器"(ATV)电源系统采用的3项关键技术:太阳翼X构型设计,太阳电池电路交叉布阵,蓄电池组充电控制模式;探讨了这些技术对平衡不同光照条件输出功率、降低遮挡对每个太阳电池阵输出功率的影响,以及确保蓄电池性能安全可靠的优势;并讨论了ATV电源设计方案对我国货运飞船和空间站电源系统设计的借鉴意义。     

Design of optimal earth pole-sitter transfers using low-thrust propulsion

Recent studies have shown the feasibility of an Earth pole-sitter mission using low-thrust propulsion. This mission concept involves a spacecraft following the Earth's polar axis to have a continuous, hemispherical view of one of the Earth's poles. Such a view will enhance future Earth observation and telecommunications for high latitude and polar regions. To assess the accessibility of the pole-sitter orbit, this paper investigates optimum Earth pole-sitter transfers employing low-thrust propulsion. A launch from low Earth orbit (LEO) by a Soyuz Fregat upper stage is assumed after which solar electric propulsion is used to transfer the spacecraft to the pole-sitter orbit. The objective is to minimize the mass in LEO for a given spacecraft mass to be inserted into the pole-sitter orbit. The results are compared with a ballistic transfer that exploits manifold-like trajectories that wind onto the pole-sitter orbit. It is shown that, with respect to the ballistic case, low-thrust propulsion can achieve significant mass savings in excess of 200 kg for a pole-sitter spacecraft of 1000 kg upon insertion. To finally obtain a full low-thrust transfer from LEO up to the pole-sitter orbit, the Fregat launch is replaced by a low-thrust, minimum time spiral, which provides further mass savings, but at the cost of an increased time of flight.     

Combining solar science and asteroid science with the space weather observation network (SWON)

The peculiarity of space weather for Earth orbiting satellites, air traffic and power grids on Earth and especially the financial and operational risks posed by damage due to space weather, underline the necessity of space weather observation. The importance of such observations is even more increasing due to the impending solar maximum. In recognition of this importance we propose a mission architecture for solar observation as an alternative to already published mission plans like Solar Probe (NASA) or Solar Orbiter (ESA). Based upon a Concurrent Evaluation session in the Concurrent Engineering Facility of the German Aerospace Center, we suggest using several spacecraft in an observation network. Instead of placing such spacecraft in a solar orbit, we propose landing on several asteroids, which are in opposition to Earth during the course of the mission and thus allow observation of the Sun's far side. Observation of the far side is especially advantageous as it improves the warning time with regard to solar events by about 2 weeks. Landing on Inner Earth Object (IEO) asteroids for observation of the Sun has several benefits over traditional mission architectures. Exploiting shadowing effects of the asteroids reduces thermal stress on the spacecraft, while it is possible to approach the Sun closer than with an orbiter. The closeness to the Sun improves observation quality and solar power generation, which is intended to be achieved with a solar dynamic system. Furthermore landers can execute experiments and measurements with regard to asteroid science, further increasing the scientific output of such a mission. Placing the spacecraft in a network would also benefit the communication contact times of the network and Earth. Concluding we present a first draft of a spacecraft layout, mission objectives and requirements as well as an initial mission analysis calculation.     

Survival of plant seeds, their UV screens, and nptII DNA for 18 months outside the International Space Station

The plausibility that life was imported to Earth from elsewhere can be tested by subjecting life-forms to space travel. Ultraviolet light is the major liability in short-term exposures (Horneck et al., 2001 ), and plant seeds, tardigrades, and lichens-but not microorganisms and their spores-are candidates for long-term survival (Anikeeva et al., 1990 ; Sancho et al., 2007 ; J?nsson et al., 2008 ; de la Torre et al., 2010 ). In the present study, plant seeds germinated after 1.5 years of exposure to solar UV, solar and galactic cosmic radiation, temperature fluctuations, and space vacuum outside the International Space Station. Of the 2100 exposed wild-type Arabidopsis thaliana and Nicotiana tabacum (tobacco) seeds, 23% produced viable plants after return to Earth. Survival was lower in the Arabidopsis Wassilewskija ecotype and in mutants (tt4-8 and fah1-2) lacking UV screens. The highest survival occurred in tobacco (44%). Germination was delayed in seeds shielded from solar light, yet full survival was attained, which indicates that longer space travel would be possible for seeds embedded in an opaque matrix. We conclude that a naked, seed-like entity could have survived exposure to solar UV radiation during a hypothetical transfer from Mars to Earth. Chemical samples of seed flavonoid UV screens were degraded by UV, but their overall capacity to absorb UV was retained. Naked DNA encoding the nptII gene (kanamycin resistance) was also degraded by UV. A fragment, however, was detected by the polymerase chain reaction, and the gene survived in space when protected from UV. Even if seeds do not survive, components (e.g., their DNA) might survive transfer over cosmic distances.     

European Sail Tower SPS concept

Based on a DLR-study in 1998/99 on behalf of ESA/ESTEC called “System Concepts, Architectures and Technologies for Space Exploration and Utilization (SE&U)” a new design for an Earth-orbiting Solar Power Satellite (SPS) has been developed. The design is called “European Sail Tower SPS” and consists mainly of deployable sail-like structures derived from the ongoing DLR/ESA solar sail technology development activity. Such a SPS satellite features an extremely light-weight and large tower-like orbital system and could supply Europe with significant amounts of electrical power generated by photovoltaic cells and subsequently transmitted to Earth via microwaves. In order to build up the sail tower, 60 units - each consisting of a pair of square-shaped sails - are moved from LEO to GEO with electric propulsion and successively assembled in GEO robotically on a central strut. Each single sail has dimensions of 150m × 150 m and is automatically deployed, using four diagonal light-weight carbon fiber (CFRP) booms which are initially rolled up on a central hub. The electric thrusters for the transport to GEO could also be used for orbit and attitude control of the assembled tower which has a total length of about 15 km and would be mainly gravity gradient stabilized. Employing thin film solar cell technology, each sail is used as a solar array and produces an electric power in orbit of about 3.7 MW_e. A microwave antenna with a diameter of 1 km transmits the power to a 10 km rectenna on the ground. The total mass of this 450 MW SPS is about 2100 tons. First estimates indicate that the costs for one kWh delivered in this way could compete with present day energy costs, if launch costs would decrease by two orders of magnitude. Furthermore, mass production and large numbers of installed SPS systems must be assumed in order to lower significantly the production costs and to reduce the influence of the expensive technology development. The paper presents the technical concept and an economic assessment as well as results of a recent solar sail deployment ground demonstration at DLR's facilities in Cologne.     

采用单轴双太阳帆板空间站的一种姿态定向模式

采用单轴双帆板供电和单框架控制力矩陀螺(SGCMG)作为执行机构的倾斜轨道空间站,当太阳方向与轨道面夹角较大时,帆板的光照条件不易保证,为此本文针对这种类型的空间站设计了一种姿态定向模式以保证帆板的光照条件,并通过在阴影区姿态机动,利用重力梯度力矩对SGCMG进行卸载。仿真结果表明,该姿态定向模式满足太阳帆板的光照条件,重力梯度力矩卸载方法保证了SGCMG中的角动量不超出给定的范围。     

Nonlinear Evolution of a Balloon Satellite Orbit

The motion of a spherically symmetric balloon satellite near the equatorial plane is considered. Taking the Earth's oblateness and solar light pressure into account, the integral of motion can be obtained under certain simplifications. The eccentricity is related to the solar angle which represents an angle between pericenter and the Sun. This analytical approximation describes a large and complicated evolution of the eccentricity in corresponding areas of the phase space and the space of parameters. Phase portraits contain fixed saddle points and separatrices that divide different types of oscillations of the eccentricity. In the unsimplified problem, separatrices break down, and specific stochastic motions arise. The aims of the present study are (1) evaluation of the accuracy of analytical approximation with the help of numerical integration using a sufficiently complete model of motion and (2) numerical investigation of stochastic motions and dimensions of stochastic zones in the region of broken separatrices for an adequate model of motion. For a balloon satellite with a semimajor axis of 2.15 Earth's radii and a windage of 30 cm²/g the dimensions of a stochastic zone in eccentricity and solar angle are 10^–5and 0.1°, respectively. The analytical approximation describes the orbit evolution in the right way, except for the cases of large eccentricities, e> 0.4, which corresponds to a pericenter height of less than 1400 km, where the atmospheric drag is already significant.     

等离子体接触器对空间站充放电的影响

针对采用100V高压电池阵的空间站结构体带电现象,提出采用等离子体接触器进行主动电位控制方案,根据此方案建立包含接触器的空间站充放电等效电路模型,研究等离子体接触器对空间站充放电过程的影响及空间站结构因素对接触器钳位效果的影响,从而了解等离子体接触器与空间站悬浮电位的耦合特性。结果表明,无论空间站处于“快速充电”还是“正常充电”情况,等离子体接触器均能有效将空间站悬浮电位钳制在合理范围内。空间站结构因素中,电池阵暴露导体面积对接触器钳位过程影响较大,结构体暴露导体面积和结构体等效电容的影响可忽略。     

Shuttle demonstration of large space structure fabrication and assembly

The purpose of this paper is to describe a program aimed at an early on orbit demonstration of a large space structure fabrication and assembly capability. Requirements for the demonstration concept have been formulated. The concept that has been selected to meet these requirements is a Large Space Structure Platform consisting of a triangular prism of 31.5 m length. Sensors can be mounted on this platform to perform Earth observation measurements from space. Structural elements of the platform are fabricated using an automated beam builder in the Shuttle Orbiter payload bay. Special fixtures are designed to assemble the structure with the aid of the Remote Manipulator System and two astroworkers in an EVA mode. Results are shown of the platform preliminary design in terms of a design layout with related structural, thermal, mass properties and control dynamics data. The assembly scenario is described. Estimates of the total construction time and Orbiter support requirements are also presented.