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1.
The High Energy Transient Experiment (HETE), scheduled for launch this year, is a small satellite dedicated to multiwavelength observations of -ray and X-ray bursts. The HETE spacecraft will be equipped with gamma-ray detectors, X-ray detectors with a coded mask, and ultraviolet-sensitive CCD cameras. The UV cameras on HETE are wide-field imagers which will a) provide UV images of the regions in which -ray or X-ray bursts are detected, before, duringand after the burst, b) detect UV transients, whether associated with a high-energy transient or not, c) monitor the brightnesses of field stars for variability over a wide range of timescales, and d) serve as star trackers for HETE. In this poster, we describe the HETE UV instrumentation, control software, and data products.  相似文献   

2.
An analysis has been made of the narrow intensity spikes occurring in two cosmic gammaray bursts which were observed with a fast time resolution germanium spectrometer on board the low altitude polar orbiting satellite 1972-076B (Imhofet al., 1974a, 1975; Nakanoet al., 1974a). The bursts on 18 December, 1972 and 21 July, 1973, were also recorded on the Vela satellite system. The durations of three spikes were observed to be 0.06 s with the limits being 0.03 to 0.10 s. Four other narrow spikes were measured to have time width limits between 0.001 and 0.10 s. An additional eight spikes had widths less than 0.9 s. During the spikes, the gamma-ray intensities increased by factors of 2 to 10, with a median value of 3. These and other characteristics of the fast time structure are presented.Paper presented at the COSPAR Symposium on Fast Transients in X- and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975.  相似文献   

3.
We used theIRAS All Sky Maps in order to search for infrared emission in the direction of the Okroy Cloud (R.A.=12h50m, =22°). An enhancement of 100 m diffuse emission is evident in such a region, with an anomalous value of the ratioI v (100 m)/A v ; hydrogen 21 cm emission is also present with low radial speed, thus suggesting that the cloud could be a satellite of our Galaxy.  相似文献   

4.
This work contains a transformation of Hill-Brown differential equations for the coordinates of the satellite to a type which can be integrated in a literal form using an analytical programming language. The differential equation for the parallax of the satellite is also established. Its use facilitates the computation of Hill's periodic intermediary orbit of the satellite and provides a good check for the expansion of the coordinates and frequencies. The knowledge of the expansion of the parallax facilitates the formation of differential equations for terms with a given characteristic. These differential equations are put into a form which favors the solution by means of iteration on the computer. As in the classical theory we obtain the expansions of the coordinates and of the parallax in the form of trigonometric series in four arguments and in powers of the constants of integration. We expand the differential operators into series in squares of the constants of integration. Only the terms of order zero in these expansions are employed in the integration of the differential equations. The remaining terms are responsible for producing the cross-effects between the perturbations of different order. By applying the averaging operator to the right sides of the differential equations we deduce the expansion of the frequencies in powers of squares of the constants of integration.Basic Notations f the gravitational constant - E the mass of the planet - M the mass of the satellite - t dynamical time - x, y, z planetocentric coordinates of the satellite - u x+y–1 - s x–y–1 - the planetocentric distance of the satellite - w 1/ - 0 the variational part of - w 0 the variational part ofw, - n the mean daily sidereal motion of the satellite - a the mean semi-major axis of the satellite defined by means of the Kepler relation:a 3 n 2=f(E+M) - a the mean semi-major axis defined as the constant factor attached to the variational solution - e the constant of the eccentricity of the satellite - the sine of one half the orbital inclination of the satellite relative to the orbit of the sun - c(n–n) the anomalistic frequency of the satellite - c 0 the part ofc independent frome,e, and - g(n–n) the draconitic frequency of the satellite, - g 0 the part ofg independent frome,e, and - exp (n–n)t–1 - D d/d - e the eccentricity of the solar planetocentric orbit - a the semi-major axis of the solar orbit - n the mean daily motion of the sun in its orbit around the planet - m n/(n–n) - a/a-the parallactic factor - the disturbing function  相似文献   

5.
This paper describes the detailed calibration at soft X-ray energies (0.1–2.0 keV; 125 Å-6 Å) of gold coated, paraboloidal X-ray mirrors, four of which were subsequently flow on the Ariel-6 satellite. Uncertainties in the attitude of the satellite together with an apparent reduction in sensitivity of the soft X-ray experiment necessitated observations using the Crab Nebula as a reference. These showed that a dramatic reduction in the reflection efficiencies of all four mirrors had occurred, almost certainly after or during launch. An initial recalibration of the mirrors using the Crab observation is described.  相似文献   

6.
A method of general perturbations, based on the use of Lie series to generate approximate canonical transformations, is applied to study the effects of gravity-gradient torque on the rotational motion of a triaxial, rigid satellite. The center of mass of the satellite is constrained to move in an elliptic orbit about an attracting point mass. The orbit, which has a constant inclination, is free to precess and spin. The method of general perturbations is used to obtain the Hamiltonian for the nonresonant secular and long-period rotational motion of the satellite to second order inn/0, wheren is the orbital mean motion of the center of mass and0 is a reference value of the magnitude of the satellite's rotational angular velocity. The differential equations derivable from the transformed Hamiltonian are integrable and the solution for the long-term motion may be expressed in terms of Jacobian elliptic functions and elliptic integrals. Geometrical aspects of the long-term rotational motion are discussed and a comparison of theoretical results with observations is made.  相似文献   

7.
This paper deals with a three-dimensional rotationally and dynamically symmetrical satellite. The centre of mass of the satellite moves in a circular orbit. The existence of two first integrals of motion enables one to transform the system of differential equations to a special form facilitating the choice of the zero-approximation solution. The angles of precession and nutation as well as the amplitude functionk 2(t) are taken as variables of the motion. The first approximation solution is constructed for the case of spatial libration of the satellite axis of dynamical symmetry about the position of stable equilibrium. The series representing the functionk 2(t) is fast convergent due to the fast convergence of the expansions for elliptic functions.  相似文献   

8.
The Solar X-ray Imager (SXI) was launched 23 July 2001 on NOAAs GOES-12 satellite and completed post-launch testing 20 December 2001. Beginning 22 January 2003 it has provided nearly uninterrupted, full-disk, soft X-ray solar images, with a continuous frame rate significantly exceeding that for previous similar instruments. The SXI provides images with a 1 min cadence and a single-image (adjustable) dynamic range near 100. A set of metallic thin-film filters provides temperature discrimination in the 0.6 – 6.0 nm bandpass. The spatial resolution of approximately 10 arcsec FWHM is sampled with 5 arcsec pixels. Three instrument degradations have occurred since launch, two affecting entrance filters and one affecting the detector high-voltage system. This work presents the SXI instrument, its operations, and its data processing, including the impacts of the instrument degradations. A companion paper (Pizzo et al., this issue) presents SXI performance prior to an instrument degradation that occurred on 5 November 2003 and thus applies to more than 420000 soft X-ray images of the Sun.  相似文献   

9.
A common mechanism for both X-ray and-ray bursters is proposed on the basis that a window can be created transiently in the polar cap of a degenerate star, a white dwarf for X-ray bursts and a neutron star for-ray bursts. The window exposes transiently a hot degenerate sub-layer of the star at shallow depth, from which escapes blackbody flux for a source at temperature 3 kev with window radius 10 km in the case of X-ray bursts and for a source at temperature 300 kev with window radius 0.5 km in the case of-ray bursts.  相似文献   

10.
Geocentric orbits of large eccentricity (e=0.9 to 0.95) are significantly perturbed in cislunar space by the Sun and Moon. The time-history of the height of perigee, subsequent to launch, is particularly critical. The determination of ‘launch windows’ is mostly concerned with preventing the height of perigee from falling below its low initial value before the mission lifetime has elapsed. Between the extremes of high accuracy digital integration of the equations of motion and of using an approximate, but very fast, stability criteria method, this paper is concerned with the development of a method of intermediate complexity using non-numeric computation. The computer is used as the theory generator to generalize Lidov's theory using six osculating elements. Symbolic integration is completely automatized and the output is a set of condensed formulae well suited for repeated applications in launch window analysis. Examples of applications are given.  相似文献   

11.
An improved X-ray polarimeter is briefly described and preliminary results of the measurements carried out on the satellite Intercosmos-7 are presented. One flare with considerable polarization (P 16%) was observed on 1972 August 4. Two other flares with rather low polarization (P 4%; P 2%) were observed on 1972 August 7 and 11.  相似文献   

12.
In this paper the extended H filtering algorithms for the design of the GPS-based on-board autonomous navigation system for a low earth orbit (LEO) satellite are introduced. The dynamic process models for the estimation of position, velocity and acceleration from the GPS measurements are established. The nominal orbit of the small LEO satellite is determined by using the 7th–8th order Runge—Kutta algorithms. Three filtering approaches are applied to smooth the orbit solutions, respectively, based upon the simulated GPS pseudo range observables using the Satellite Navigation Tool Box. The simulation shows that the observed orbit errors obtained by using the extended H filtering algorithms can be reduced to a lower level than the observed orbit errors in the sense of RMS within 12 h of tracking time by using the H filtering algorithms and the extended Kalman filtering algorithms under the appropriately designed parameters. Based upon the position errors predicted by the three filtering algorithms after the last observation, we find that the extended H filtering algorithm provides the least position errors of the user satellite.This revised version was published online in October 2005 with corrections to the Cover Date.  相似文献   

13.
Résumé On donne une représentation possible de l'attitude d'un satellite aimanté dans le champ magnétique terrestre. Le moment magnétique du satellite est de l'ordre de 10 amp m2 et la rotation du satellite est voisine de 1 tour/mn. Dans ces conditions, le couple magnétique agissant sur le satellite ne peut plus être considéré comme un couple perturbateur.Dans la mesure où l'on peut admettre que l'axe de rotation du satellite, est fixe dans un repère lié au corps, on est conduit à résoudre un système d'équations différentielles linéaires à coefficients périodiques. Les coefficients contenant le temps ont en facteur une quantité 0<<1/3. On peut développer la solution suivant les puissances de les coefficients de ces développements sont donnés par des formules de récurrence. Les séries convergent en général; au voisinage des points singuliers le rayon de convergence peut être étudié.L'hypothése ci-dessus conduit à une représentation convenable de l'attitude du satellite lorsque la rotationr 0 n'est pas trop faible. Avec la valeur adoptée pour le moment magnétique, la valeur minimum de la rotationr 0 est de l'ordre de 0.8 t/mn.
A possible representation of the motion of a satellite about its centre of mass is investigated. The satellite's magnetic moment is of the order of 10 Amp m2 and its spin is about 1 rpm. Under these conditions, the magnetic torque acting on the, satellite can no longer be treated as simple perturbation.In the case where the axis of the satellite's rotation is assumed to be a constant in a system of axes fixed to the satellite, a system, of linear differential equations with periodic coefficients has to be solved. The time dependant coefficients have the small parameter 0<<1/3 as factor. The solution is expanded in power series of the parameter . The coefficients of these, series are given by recurrent formulas. The series generally do converge; in the vicinity of the singular points, the radius of convergence can be studied. The given hypothesis leads to a reasonable representation of the satellite's motion if its rotationr 0 is not too slow. With the adopted value for the magnetic moment, the minimum value ofr 0 is of the order of 0.8 rpm.
  相似文献   

14.
A problem of stability of odd 2-periodic oscillations of a satellite in the plane of an elliptic orbit of arbitrary eccentricity is considered. The motion is supposed to be only under the influence of gravitational torques.Stability of plane oscillations was investigated earlier (Zlatoustovet al., 1964) in linear approximation. In the present paper a problem of stability is solved in the non-linear mode. Terms up to the forth order inclusive are taken into consideration in expansion of Hamiltonian in a series.It is shown that necessary conditions of stability obtained in linear approximation coincide with sufficient conditions for almost all values of parameters ande (inertial characteristics of the satellite and eccentricity of the orbit). Exceptions represent either values of the parameters ,e when a problem of stability cannot be solved in a strict manner by non-linear approximation under consideration, or values of the parameters which correspond to resonances of the third and fourth orders. At the resonance of the third order oscillations are unstable, but at the resonance of the fourth order both unstability and stability of the satellite's oscillations take place depending on the values of the parameters ,e.  相似文献   

15.
The results of analysis of the trajectory parameters of the orbit of the CORONAS-F spacecraft since its launch (July 2001) and to the present time are reported. Two independent methods are used to compute a prediction for the active lifetime of the satellite in the near-Earth orbit for the period from 2005 through 2006.  相似文献   

16.
The occurrence and uniqueness of the critical inclination in satellite theory is discussed.An infinite set of canonical transformations in Hill variables are shown to exist whereby the first order secular part of the disturbing function can be changed into an alternative form. As a result of such a transformation the critical inclination can become (a)any other real or complex inclination or a function independent of the satellite's orbital inclination and (b) a function dependent on the semi-major axis, eccentricity and inclination of the satellite's orbit. It is also shown that all transformations of types (a) and (b) are only valid for short intervals of time of the order of a few satellite revolutions. Furthermore if such transformations are modified so that they become valid for greater intervals of time, then the resulting solutions in all cases containno singular divisor other than the critical inclination.It is concluded that the singularity at the critical inclination is unique and that it represents an actual physical resonance rather than something resulting from the method of solution or the type of variable used in the analysis. This conclusion is supported by numerical evidence which shows that a satellite's perigee height does suffer resonant changes when the orbital inclination is equal to the critical inclination of 63.°4.  相似文献   

17.
An impulsive burst of 100–400 keV solar X-rays associated with a small solar flare was observed on October 10, 1970 with a large area scintillator aboard a balloon floating at an altitude of 4.2 g cm-2 above the Earth's surface. The X-ray burst was also observed simultaneously in 10–80 keV range by the OGO-5 satellite and in 8–20 Å range by the SOLRAD-9 satellite. The impulsive X-ray emission reached its maximum at 1643 UT at which time the differential photon spectrum in 20–80 keV range was of the form 2.3 × 104 E -3.2 photons cm-2 s-1 keV-1 at 1 AU. The event is attributed to a H-subflare located approximately at S13, E88 on the solar disc. The spectral characteristics of this event are examined in the light of the earlier X-ray observations of small solar flares.  相似文献   

18.
We consider the dynamics of a test particle co-orbital with a satellite of mass m s which revolves around a planet of mass M 0 m s with a mean motion n s and semi-major axis a s. We study the long term evolution of the particle motion under slow variations of (1) the mass of the primary, M 0, (2) the mass of the satellite, m s and (3) the specific angular momentum of the satellite J s. The particle is not restricted to small harmonic oscillations near L 4 or L 5, and may have any libration amplitude on tadpole or horseshoe orbits. In a first step, no torque is applied to the particle, so that its motion is described by a Hamiltonian with slowly varying parameters. We show that the torque applied to the satellite, as measured by s = js/(n s J s) induces an distortion of the phase space which is entirely described by an asymmetry coefficient = s/, where = m s/M. The adiabatic invariance of action implies furthermore that the long term evolution of the particle co-orbital motion depends only on the variation of m s a s with time. Applying a constant torque to the particle, as measured by s = js/(n s J p) is then merely equivalent to replacing = s/ by = (s – p)/. However, if the torque acting on the particle exhibits a radial gradient, then the action is no more conserved and the evolution of the particle orbit is no more controlled by m s a s only. We show that even mild torque gradients can dominate the orbital evolution of the particle, and eventually decide whether the latter will be pulled towards the stable equilibrium points L 4 or L 5, or driven away from them. Finally, we show that when the co-orbital bodies are two satellites with comparable masses m 1 and m 2, we can reduce the problem to that of a test particle co-orbital with a satellite of mass m 1 + m 2. This new problem has then parameters varying at rates which are combinations, with appropriate coefficients, of the changes suffered by each satellite.  相似文献   

19.
The paper introduces a new time element to be used with a general time transformation for satellite equations of motion. The purpose of this time element is to reduce the growth of the numerical errors with respect to the time integration. It is characteristic for the new time element , that the relation between the timet and the element does not depend on the independent variables.  相似文献   

20.
A semianalytical method has been developed to calculate the radiation-pressure perturbations of a close-Earth satellite due to sunlight reflected from the Earth. It is assumed that the satellite is spherically symmetric and that the solar radiation is reflected from the Earth according to Lambert's Law. To account for the increasing reflectivity of the Earth toward the poles, its albedo is assumed to have a latitudinal dependence given bya=a 0 +a 2 sin2. The effect of the terminator on the perturbations has been neglected. The perturbations within a particular revolution are given analytically, while the long-range perturbations are obtained by accumulation.  相似文献   

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