GPS single-frequency orbit determination for low Earth orbiting satellites

The determination of high-precision orbits for Low Earth Orbiting (LEO) satellites (e.g., CHAMP, GRACE, MetOp-A) is based on dual-frequency tracking data from on-board GPS (Global Positioning System) receivers. The two frequencies allow it to eliminate the first order ionosphere effects. Data screening and precise orbit determination (POD) procedures are optimized under the assumption of the availability of two frequencies.     

Ultraviolet observations of Jupiter from Earth-orbiting satellites

The International Ultraviolet Explorer (IUE) has provided both improved spectral resolution and some spatial resolution for UV observations of Jupiter. Previous satellite observations have produced albedo curves for Jupiter showing the influence of Rayleigh scattering, and of some absorber(s) shortward of 2500Å on the UV spectrum. Constraints on the abundance of several minor constituents of the Jovian atmosphere were derived from the OAO-2 data. The IUE low dispersion data has a resolution of 8Å, making it possible to detect individual molecular features. A series of C₂H₂ absorptions in the 1750Å region have been identified, and indications of NH₃ absorptions are present in the 1950Å region.     

超低轨道卫星应用离子电推进技术方案

低地球轨道大气环境对诸如科学探测和对地观测卫星的阻尼作用十分明显,而且阻尼随太阳和地磁活动以及昼夜、季节交替变化范围宽.为了保证卫星轨道精度或飞行状态满足任务要求,需要利用推进系统对卫星受到的阻尼进行实时或间歇式补偿以实现轨道或飞行状态的保持.针对轨道高度220～268 km的无拖曳飞行和轨道维持应用,基于卫星轨道阻尼...     

Cratering records of the satellites of Jupiter and Saturn

The surfaces of most of the satellites of Jupiter and Saturn show marks of large-meteoroid impacts produced over much of solar system history and partly stemming from the early post-accretional heavy bombardment. An analysis of the crater size distributions shows that (i) crater densities on the most ancient terrains are comparable to those found on the lunar highlands, (ii) crater size distributions differ somewhat from those in the inner solar system but exhibit striking similarities in shape, (iii) the crater size distributions on all terrain types from oldest to youngest are very similar, i. e. the underlying impactor size distribution does not seem to have changed over time, (iv) there is no obvious difference in crater densities between apex and antapex parts of the satellites, (v) the cratering record can better be explained by impacts from bodies in planetocentric orbits rather than by bodies in heliocentric orbits.     

Auroral structures at Jupiter and Earth

This paper compares global structures of the aurora observed at Jupiter and Earth and our understanding of the mechanisms that produce these structures. Both planets have permanent, magnetically conjugate auroral ovals, although produced by quite different mechanisms. Both are multispectral, having been observed at X-ray, ultraviolet, visible, infrared, and radio wavelengths. The brightest structures are produced by downward accelerated electron fluxes associated with upward Birkeland (magnetic-field-aligned) currents. At both planets, the auroral forms are time variable, especially at highest latitudes. The main power source for auroral emissions is planetary rotation at Jupiter, and the solar wind interaction at Earth. Thus Jupiter's auroral structures tend to be fixed with respect to magnetic (System III) longitude while Earth's are fixed with respect to local time. Earth's auroral structure is strongly dependent on the direction of the interplanetary magnetic field (IMF). At Jupiter, no IMF dependence is known, but observations have not been sufficient to show such a dependence if it exists. A unique feature of Jupiter's auroral structure, with no counterpart at Earth, is the signature of the large (Galilean) satellites and, in the case of Io, even the corotational wake of the satellite.     

The LAGEOS satellites orbit and Yukawa-like interactions

LAGEOS II general relativity pericenter precession has been analysed in terms of the errors produced by the mismodelling of both the gravitational and non-gravitational perturbations acting on the satellite orbit. The accuracy in the pericenter determination may be considered as an upper-bound value for the estimate of the strength α of a possible new-long-range-interaction described by a Yukawa-like potential. In the present work we have focused on the constraints in α that can be obtained with the current best multi-satellites gravity field model EGM96 (α < 2.6 × 10⁻¹⁰) and also with the first promising models from the CHAMP (α < 1.8 × 10⁻¹⁰) and GRACE (α < 1.2 × 10⁻¹⁰) gravimetric missions. These results represent, potentially, an improvement of two or three orders-of-magnitude with respect to the best constraints obtained in the past with Earth–LAGEOS and Lunar–LAGEOS data (|α| < 10⁻⁵–10⁻⁸). The impact of the non-gravitational perturbations mismodelling in the final error budget has been determined together with the improvements obtainable in the constraint of the strength α with the proposed LARES satellite.     

Astrometric positioning and orbit determination of geostationary satellites

In the project titled “Astrometric Positioning of Geostationary Satellite” (PASAGE), carried out by the Real Instituto y Observatorio de la Armada (ROA), optical observation techniques were developed to allow satellites to be located in the geostationary ring with angular accuracies of up to a few tenths of an arcsec. These techniques do not necessarily require the use of large telescopes or especially dark areas, and furthermore, because optical observation is a passive method, they could be directly applicable to the detection and monitoring of passive objects such as space debris in the geostationary ring.     

Earth survey satellites and cooperative programmes

Earth Survey Satellite Systems are on the verge of becoming operational. It would require a sophisticated infrastructure, involving both men and machines, for a nation to set-up its own independent and comprehensive resources survey and management system using these space systems. Only nations having adequately trained scientific manpower can think of establishing such a system on their own. For the rest of the large part of the world, and specifically the developing nations, co-operative programmes are a must for their getting into and establishing a base for this new technology. Some examples of co-operative ventures in this field are presented. Possible co-operative programmes for varied situations are discussed.     

微小推力下小卫星的轨道递推与推力标定

针对采用微小推力进行轨道机动的小卫星,考虑复杂摄动力的基础设计了一种高精度轨道外推和推力在轨标定算法.首先,建立了考虑地球复杂摄动力和微小推力的小卫星轨道动力学模型;然后基于动力学模型,利用变步长龙格库塔算法,设计了对微小推力小卫星进行高精度轨道外推的方法.随后通过无迹卡尔曼滤波器(UKF),设计在轨标定算法,对存在误...     

The magnetospheres of Jupiter and Saturn and their lessons for the Earth

The study of planetary magnetospheres allows us to understand processes occurring in the Earth’s magnetosphere by showing us how these processes respond under different conditions. We illustrate lessons learned about the control of the size of the magnetosphere by the dynamic pressure of the solar wind; how cold plasma is lost from magnetospheres; how free energy is generated to produce ion cyclotron waves; the role of fast neutrals in a planetary magnetosphere; the interchange instability; and reconnection in a magnetodisk. Not all information flow is from Jupiter and Saturn to Earth; some flows the other way.     

New improved orbit solutions for the ERS-1 and ERS-2 satellites

Improved orbit solutions of the European Remote Sensing Satellites ERS-1 and ERS-2 have been computed in the ITRF2005 terrestrial reference frame using the recent models based mainly on IERS Conventions 2003. These solutions cover the periods 3 August 1991 to 8 July 1996 for ERS-1, and 3 May 1995 to 4 July 2003 for ERS-2. For each satellite, the final orbit solution is based on a combination of three separate orbit solutions independently computed at the Delft Institute of Earth Observation and Space Systems (DEOS) of the Delft University of Technology (The Netherlands), the Navigation Support Office of the European Space Operations Centre (ESOC, Germany) and the Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences (Germany) using three different software packages for precise orbit determination, but using the same models in the same terrestrial reference frame within the European Space Agency (ESA) project ‘Reprocessing of Altimeter Products for ERS (REAPER)’. Validation using radar altimeter data indicates that the new combined orbits of ERS-1 and ERS-2 computed by us are significantly more accurate, approaching the 2–3 cm level in radial direction, than previously available orbit solutions.     

Effects of orbit progression on the radiation exposures from solar proton fluxes in low Earth orbit under geomagnetic storm conditions.

The present study examines the effects of orbit progression on the exposures within a Space Station Freedom module in a 51.6-degree inclined orbit at 450 km. The storm evolution is modeled after the November 1960 event, and the solar proton flux evolution is taken from the August 1972 solar proton event. The effects of a strong magnetic shock, such as was observed during the October 1989 event, is also modeled. The statistics on hourly average storm fields for the last forty years reveal that the largest geomagnetic storms approach a Dst value of -500 nanotesla at the storm peak. Similarly, one of the largest satellite-measured proton flux (> 10 MeV) for space exposures is the event of August 1972. The effects of orbit progression (advance of the line of nodes) is examined for the above conditions to study the variation of exposures under differing times of occurrence of the solar proton peak intensity, attainment of geomagnetic storm maximum, and the location of the line of nodes of the last geomagnetically protected orbit. The impact of the inherent inhomogeneity of the space station module is examined as a limiting factor on exposure with regard to the need of additional parasitic shielding.     

基于自适应滤波的编队卫星实时相对定轨

提出基于自适应滤波的编队卫星实时相对定轨算法,利用2005-12-09—10两颗GRACE（Gravity Recovery and Climate Experiment）卫星的GPS（Global Positioning System）实测数据进行实时相对定轨试验计算,采用JPL（Jet Propulsion Laboratory）轨道对试验结果外部检核,结果表明:①自适应滤波相对定轨通过自适应因子,可以较好地平衡编队卫星的观测信息和相对动力学信息,其相对定轨结果精度优于Kalman滤波相对定轨结果;②自适应滤波相对定轨结果随着星间基线缩短而精度提高;③两颗GRACE卫星采用单频伪距和广播星历进行自适应滤波相对定轨,可以得到精度优于6cm的星间基线。     

The use of Earth resources satellites in the development of Latin America

Remote Sensing Technology has been used since 1972 by the governments of Latin America to promote national and regional development activities. Dedicated centers totally involved in remote sensing research and development were created. Major investment programs were also promoted by the Latin American countries to include satellite remote sensing technology in their national projects.     

Very low thrust station-keeping for low Earth orbiting satellites

Traditional station-keeping for Earth observation satellites with chemical thrusters generally involves maneuvers every couple months that are able to change significantly the semi-major axis and the inclination. These strategies do not scale down to very low thrust level (a few hundreds of μN) electrical thrusters. This paper presents both in-plane and out-of-plane strategies that spread corrections over very long arcs and discretize them to tiny maneuvers every couple orbits, taking into account mission-constraints on maneuvers locations. These strategies scale up to medium thrust strategies, filling the gap between propulsion technologies. The out-of-plane strategy although features a new no-deadband property and controls the full orbital momentum. All strategies allow control very close to the reference (a few hundreds meters in osculating parameters) and very low cost.     

基于广义相对论的轨道摄动下星间激光相位比对

针对纳米到皮米量级星间激光测距,在地心非旋转坐标系(GCRS)下,考虑卫星轨道摄动引起的广义相对论效应,建立了星间单向以及双向星间激光相位比对模型.通过仿真研究了地球主引力场范围内轨道摄动引起的广义相对论效应对星间激光相位比对误差的影响,并通过星间激光相位比对误差计算星间激光测距误差.不同轨道高度的卫星仿真结果表明,对...     

The classical Laplace plane as a stable disposal orbit for geostationary satellites

The classical Laplace plane is a frozen orbit, or equilibrium solution for the averaged dynamics arising from Earth oblateness and lunisolar gravitational perturbations. The pole of the orbital plane of uncontrolled GEO satellites regress around the pole of the Laplace plane at nearly constant inclination and rate. In accordance with Friesen et al. (1993), we show how this stable plane can be used as a robust long-term disposal orbit. The current graveyard regions for end-of-life retirement of GEO payloads, which is several hundred kilometers above GEO depending on the spacecraft characteristics, cannot contain the newly discovered high area-to-mass ratio debris population. Such objects are highly susceptible to the effects of solar radiation pressure exhibiting dramatic variations in eccentricity and inclination over short periods of time. The Laplace plane graveyard, on the contrary, would trap this debris and would not allow these objects to rain down through GEO. Since placing a satellite in this inclined orbit can be expensive, we discuss some alternative disposal schemes that have acceptable cost-to-benefit ratios.