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Fast and precise propagation of satellite orbits is required for mission design, orbit determination and payload data analysis. We present a method to improve the computational performance of numerical propagators and simultaneously maintain the accuracy level required by any particular application. This is achieved by determining the positional accuracy needed and the corresponding acceptable error in acceleration on the basis of the mission requirements, removing those perturbation forces whose effect is negligible compared to the accuracy requirement, implementing an efficient and precise algorithm for the harmonic synthesis of the geopotential gradient (i.e., the gravitational acceleration) and adjusting the tolerance of the numerical propagator to achieve the prescribed accuracy level with minimum cost. In particular, to achieve the optimum balance between accuracy and computational performance, the number of geopotential spherical harmonics to retain is adjusted during the integration on the basis of the accuracy requirement. The contribution of high-order harmonics decays rapidly with altitude, so the minimum expansion degree meeting the target accuracy decreases with height. The optimum degree for each altitude is determined by making the truncation error of the harmonic synthesis equal to the admissible acceleration error. This paper presents a detailed description of the technique and test cases highlighting its accuracy and efficiency.

We present the results of a comprehensive study in which the precision and efficiency of six numerical integration techniques, both implicit and explicit, are compared for solving the gravitationally perturbed two-body problem in astrodynamics. Solution of the perturbed two-body problem is fundamental for applications in space situational awareness, such as tracking orbit debris and maintaining a catalogue of over twenty thousand pieces of orbit debris greater than the size of a softball, as well as for prediction and prevention of future satellite collisions. The integrators used in the study are a 5th/4th and 8th/7th order Dormand-Prince, an 8th order Gauss-Jackson, a 12th/10th order Runga-Kutta-Nystrom, Variable-step Gauss Legendre Propagator and the Adaptive-Picard-Chebyshev methods. Four orbit test cases are considered, low Earth orbit, Sun-synchronous orbit, geosynchronous orbit, and a Molniya orbit. A set of tests are done using a high fidelity spherical-harmonic gravity (70 × 70) model with and without an exponential cannonball drag model. We present three metrics for quantifying the solution precision achieved by each integration method. These are conservation of the Hamiltonian for conservative systems, round-trip-closure, and the method of manufactured solutions. The efficiency of each integrator is determined by the number of function evaluations required for convergence to a solution with a prescribed accuracy. The present results show the region of applicability of the selected methods as well as their associated computational cost. Comparison results are concisely presented in several figures and are intended to provide the reader with useful information for selecting the best integrator for their purposes and problem specific requirements in astrodynamics.

We describe the phase space structures related to the semi-major axis of Molniya-like satellites subject to tesseral and lunisolar resonances. In particular, the questions answered in this contribution are: (i) we study the indirect interplay of the critical inclination resonance on the semi-geosynchronous resonance using a hierarchy of more realistic dynamical systems, thus discussing the dynamics beyond the integrable approximation. By introducing ad hoc tractable models averaged over fast angles, (ii) we numerically demarcate the hyperbolic structures organising the long-term dynamics via Fast Lyapunov Indicators cartography. Based on the publicly available two-line elements space orbital data, (iii) we identify two satellites, namely Molniya 1-69 and Molniya 1-87, displaying fingerprints consistent with the dynamics associated to the hyperbolic set. Finally, (iv) the computations of their associated dynamical maps highlight that the spacecraft are trapped within the hyperbolic tangle. This research therefore reports evidence of actual artificial satellites in the near-Earth environment whose dynamics are ruled by manifolds and resonant mechanisms. The tools, formalism and methodologies we present are exportable to other region of space subject to similar commensurabilities as the geosynchronous region., Comment: 26 pages, 9 figures. Comments and feedback appreciated

Satellite constellations are of utmost importance nowadays, since Earth is ‘inch-by-inch’ spanned in terms of communication. Depending on factors such as intended recipients of the service or capability and communication type required, satellite constellation deployment requirement varies. Satellite coverage and the resulting ground tracks are calculated using the type of the selected orbit while assessing conditions for deployment of the satellite constellation. For communication satellites, different types of primary orbits include Molniya orbit, low (Polar and Non-Polar) Earth orbit, geostationary Earth orbit (GEO), and the other elliptical orbits. This research assesses the benefits of every distinct satellite orbit, its overall area of coverage, and the correlated effects on satellite communication networks.

This paper proposes the use of solar sail periodic orbits in the Earth-Moon system for ob-servation of the high-latitudes of the Earth and Moon. At the Earth, the high-latitudes will be crucial in answering questions concerning global climate change, monitoring space weather events and ensuring sustainable development of these fragile regions. The polar regions of the Moon, especially the South Pole, are of great scientific interest as well as a potential destination for a future permanent lunar base. The existence of families of solar sail periodic orbits in the Earth-Moon system has previously been demonstrated by the authors and is expanded in this paper by introducing additional orbit families. The paper focuses in particular on orbits that are achievable with near-term solar sail technology and that originate by maintaining the solar sail at a constant attitude with respect to the Sun such that mission operations are greatly simplified. The results provide a set of constellations for continuous observation of the high-latitudes. For example, a constellation of two solar sail L2-displaced vertical Lyapunov orbits can achieve con-tinuous observation of both the lunar South Pole and the center of the Aitken Basin at a mini-mum elevation of 15 deg, while at the Earth, a set of two, so-called ‘clover-shaped’ orbits can provide continuous coverage of one of the Earth’s Poles at 20 deg minimum elevation. Transfer-ring these orbits to a higher-fidelity model, taking among others the eccentricity of the Moon into account, shows that these orbits still exist without any significant impact on their perfor-mance for high-latitude observation of the Earth and Moon.

The decentralized consensus control of a formation of rigid-body spacecraft is studied in the framework of geometric mechanics while accounting for a constant communication time delay between spacecraft. The relative position and attitude (relative pose) are represented on the Lie group SE(3) and the communication topology is modeled as a digraph. The consensus problem is converted into a local stabilization problem of the error dynamics associated with the Lie algebra se(3) in the form of linear time-invariant delay differential equations with a single discrete delay in the case of a circular orbit, whereas it is in the form of linear time-periodic delay differential equations in the case of an elliptic orbit, in which the stability may be assessed using infinite-dimensional Floquet theory. The proposed technique is applied to the consensus control of four spacecraft in the vicinity of a Molniya orbit.

A novel type of multiple-apogee highly elliptical orbits termed as MAP HEO with a period of rotation between 14 h and 15 h is introduced. These orbits are designed to achieve continuous geostationary (GEO)-like imaging of the polar regions in an optimum way. The combination of GEO and HEO satellites would then offer continuous monitoring of weather from space at any point of the globe. This capacity would represent a breakthrough for short- and long-term weather forecasting and narrowing uncertainties in the knowledge of the Earth’s climate through better sampling and more accurate characterization of the diurnal cycle. MAP HEO systems can be launched at critical inclination and are characterized by a local minimum of ionizing radiation. These features simplify the process of orbit maintenance, reduce radiation shielding requirements, and favor a longer lifetime of the mission. Unlike previously considered HEO systems implemented for communications, such as 12-h Molniya and 24-h Sirius radio systems, a MAP HEO constellation achieves a uniform geometrical sampling, which reduces view angle dependent biases. These observational conditions with complete coverage of the diurnal cycle, diverse range of solar illumination, and viewing observational conditions are beneficial for high-latitude meteorological and climate applications, such as the retrieval of Essential Climate Variables (ECV).

Systems engineering of a satellite based data communication baseline concept is presented to achieve terabit per second throughput. It uses a constellation of five Molniya satellites and one dimension electronic scanning phased array ground terminals. The result is a baseline concept that meets customer needs for internet of things (IoT) data connectivity and for consumer high data rate internet access. Molniya orbit satellites provide the benefits of available bandwidth, lack of interference with other satellite links, and less crowded orbital paths. A drawback is that they are not geostationary since they have highly elliptical orbits. This requires ground station terminals with the ability track the satellites as they pass overhead during their orbit. However, since Molniya satellites with a properly selected eccentricity pass along the same path at nearly constant elevations relative to a fixed position on the Earth, simple and low-cost single axis scanning antennas can be used for the consumer ground terminal. This is a distinct advantage compared with competing low earth orbit constellations. The proposed solution leverages advances in semiconductor technology and low-cost antenna laminate substrate materials for an affordable phased array tracking ground terminal antenna. This paper presents link budget trade studies, system concept, orbital dynamics simulation results, and ground station component trade study.

This paper describes a new Solar Power Satellite (SPS) concept, based on the principle of wavelength-scale modular integration of all major functions, from solar collection through to beam-formation. Like the earlier HESPeruS [1] (Highly Elliptical Solar Power Satellite) concept, CASSIOPeiA (Constant Aperture, Solid-State, Integrated, Orbital Phased Array) has no rotating (or otherwise moving) parts, yet maintains a constant solar collecting area directly facing the Sun (no cosine losses), whilst its retrodirective microwave beam is steered to the terrestrial rectenna (rectifying antenna). The well-known beam steering limitations of planar phased arrays require other SPS concepts to have either physically rotating parts, redundant solar collector / RF transmitter area, or suffer cosine losses as the collector tilts away from the Sun. HESPeruS avoids this issue by operating from a highly-elliptical Molniya orbit. By contrast, the novel (patent pending) phased array of CASSIOPeiA permits beam steering through a full 360 degrees without degradation — allowing deployment along a multitude of orbits, including geosynchronous (GSO). The same ultralight physical substrate is re-used for efficient concentrated photovoltaics, power management / distribution, thermal dissipation and beam formation, with zero temporal redundancy of RF (Radio Frequency) elements. The structure exhibits sufficient self-rigidity to support itself in microgravity without additional trusses, yet is able to deploy from a highly compact stowed configuration — offering the enticing possibility of a fully functional SPS deployed as a single payload. The paper concludes with a roadmap for staged implementation, offering delivered power from 200 kW (near-space, daylight hours), through 90 MW (3 hour orbit, 23+ hours), to 430 MW of utility-scale baseload power (GSO, 24 hours).

The long-term galactic cosmic ray (GCR) environment response of the dosimeter and surface-charging monitors on two high-altitude satellites called F1 and F2 is analyzed. These satellites also host the National Aeronautics and Space Administration’s Two Wide-angle Imaging Neutral-atom Spectrometers. The trend of the GCR intensity with solar cycle from year 2006 through 2012 is estimated from in-situ Advanced Composition Explorer (ACE) and Ulysses data. The dosimeter average 25–45 MeV proton counts and the >2.4 MeV electron counts at apogee follow the expected GCR solar-cycle trend, but the best-fit variations are smaller than estimated from ACE heavy ion GCR data. The surface-charging monitor average minima ion counts at apogee on F1, one of the host spacecraft, are consistent with the solar-cycle variation of Ulysses proton GCR counts. Linear fits to the F1 surface-charging monitor response to the GCR environment that may be subtracted from the measured counts before conversion to particle fluxes are pro...

A double resonance model is applied to study the long term evolution of a Molniya orbit, which is highly elliptical (e >= 0.7), critically inclined (i approximate to 63.4 degrees), and in the state of the 2:1 mean motion resonance with the Earth rotation. The dynamics of a Molniya orbit can be divided into three kinds: short (12 h), intermediate (several years) and long (several centuries) period motions, with the latter two studied in this paper. The J(2) and J(12) (l = 2, 3,..., 8) harmonics are modelled, based on a careful selection. The analytic solution for the intermediate period motion is obtained, a first integral, (I) over bar (3), for the long period motion is derived analytically, and the phase structures are obtained by the level curves of (I) over bar (3). Three types of the phase structures, depending on the equilibria and stabilities, are observed when the Hamiltonian constant varies. Compared with the near circular 12-h satellite orbits and with the critically inclined orbits without mean motion resonance with the Earth rotation, the features of the Molniya orbits are discussed in detail. It is pointed out that (1) unlike the case of near circular orbits, the J(32) term does not dominate the 2:1 mean motion resonance problem (intermediate period motion), and that (2) instead of the J(2)(2) terms, the resonant tesseral harmonics dominate the critical inclination problem (long period motion). (C) 2014 COSPAR. Published by Elsevier Ltd. All rights reserved.

This paper demonstrates the use of polynomial chaos expansions for the nonlinear, non-Gaussian propagation of orbit state uncertainty. Using linear expansions in tensor products of univariate orthogonal polynomial bases, polynomial chaos expansions approximate the stochastic solution of the ordinary differential equation describing the propagated orbit, and include information on covariance, higher moments, and the spatial density of possible solutions. Results presented in this paper use non-intrusive, i.e., sampling-based, methods in combination with either least-squares regression or pseudospectral collocation to estimate the polynomial chaos expansion coefficients at any future point in time. Such methods allow for the usage of existing orbit propagators. Samples based on sun-synchronous and Molniya orbit scenarios are propagated for up to ten days using two-body and higher-fidelity force models. Tests demonstrate that the presented methods require the propagation of orders of magnitude fewer samples ...

Approximate numerical methods of optimization are presented for multi-orbit noncoplanar orbit transfers of low-thrust spacecraft. The linear representation of derivatives of boundary parameters is used in the vicinity of a reference trajectory with its discretization into small segments. For each segment a set of pseudo-impulses is introduced, representing possible directions of the thrust vector. In order to solve essentially nonlinear problems, the iterative process of upgrading the reference trajectory is used. At each iteration the linear programming problem of high dimensionality is solved, its boundary conditions being represented in the form of a linear matrix equation. Interval constraints are considered in the form of blocking the propulsion system operation on shadow segments of the orbit, as well as cycling constraints, and constraints on total duration of maneuvers at certain trajectory segments. The results of comparison with solutions obtained by other methods are presented together with examples illustrating the convergence of iterative processes. Optimizations of the trajectories for launching geosynchronous satellites to their orbits and of the trajectories of a noncoplanar transfer from low to high-elliptic Molniya orbit are considered under these constraints.

There has been a significant increase of interest in the building of a comprehensive Arctic observing system in recent years to properly and timely track the environmental and climate processes in this vast region. In this regard, a satellite observing system on highly elliptical orbit (HEO) with 12-h period (Molniya type) is of particular interest, because it enables continuous coverage of the entire Arctic region (58°–90°N) from a constellation of two satellites. Canada is currently proposing to operate such a constellation by 2017. Extending the pioneering study of S. Q. Kidder and T. H. Vonder Haar, this paper presents in-depth analysis of spatiotemporal sampling properties of the imagery from this system. This paper also discusses challenges and advantages of this orbit for various applications that require high temporal resolution and angular sampling.

The analysis of satellite solar power station (SSPS) is carried out for some specified locations (Delhi, Mumbai, Kolkata and Bengaluru) in India and consequently the performance of the system is evaluated for geostationary earth orbit (GEO) based SSPS, low earth orbit (LEO) based SSPS and Molniya (quasi geostationary) orbit based SSPS for sites located at different latitudes. The analysis of power; received energy over a year and weight of the rectenna array for the same beam intensity showed varied results for Molniya orbit based SSPS, LEO based SSPS and GEO based SSPS. The power delivered by the LEO SSPS was highest which indicated that this SSPS may be efficient for the short term power requirement. However, it is observed from the results of the energy received over a year that the GEO based system is suitable for base load power plant as it is capable of delivering constant energy through out a year. Further, the weight of the rectenna and hence the space required for ground station for same power output is smallest for Molniya orbit based system for a range of rectenna array radius considered. It is thus envisaged that the Molniya orbit based system would be a better choice for commercial use of SSPS. These findings may help for judicious selection of satellite orbit and ground station location for placing the satellite for SSPS for various applications.

The tracking performance of the Kalman filter (KF) for the downlink extra-fine synchronization sequence that supports high data rate (2.048 Mbps), transmitted by the Enhanced Polar System (EPS) in Molniya orbits, is investigated in the paper. At the receiver, a KF is used to track the range and range rate of the payload to estimate the payload clock and Doppler error. The tracking performance of the KF is characterized by the state error and measurement error. The state error is governed by the payload dynamics. The measurement error is governed by the signal-to-noise ratio (SNR), discrete time measurement, quantization error of the analog-to-digital converter (ADC), and the rate error. The rate error is governed by the oscillator frequency stability of the Rubidium or Cesium sources. Performance trade off between a 2nd and 3rd orders KF is investigated by computer simulation.

Real time optimal guidance is considered for a class of low thrust spacecraft. In particular, nonlinear model predictive control (NMPC) is utilized for computing the optimal control actions required to transfer a spacecraft from a low Earth orbit to a mission orbit. The NMPC methodology presented is able to cope with unmodeled disturbances. The dynamics of the transfer are modeled using a set of modified equinoctial elements because they do not exhibit singularities for zero inclination and zero eccentricity. The idea behind NMPC is the repeated solution of optimal control problems; at each time step, a new control action is computed. The optimal control problem is solved using a direct method-fully discretizing the equations of motion. The large scale nonlinear program resulting from the discretization procedure is solved using IPOPT--a primal-dual interior point algorithm. Stability and robustness characteristics of the NMPC algorithm are reviewed. A numerical example is presented that encourages further development of the proposed methodology: the transfer from low-Earth orbit to a molniya orbit.

An unclassified analytical trajectory design, performance, and mission study was done for the 1982-86 joint NASA-USAF Shuttle/Centaur G upper stage development program to send performance-demanding payloads to high orbits such as Molniya using an unconventional orbit transfer. This optimized three orbital burn transfer to Molniya orbit was compared to the then-baselined two burn transfer. The results of the three dimensional trajectory optimization performed include powered phase steering data and coast phase orbital element data. Time derivatives of the orbital elements as functions of thrust components were evaluated and used to explain the optimization's solution. Vehicle performance as a function of parking orbit inclination was given. Performance and orbital element data was provided for launch windows as functions of launch time. Ground track data was given for all burns and coasts including variation within the launch window. It was found that a Centaur with fully loaded propellant tanks could be flown from a 37deg inclination low Earth parking orbit and achieve Molniya orbit with comparable performance to the baselined transfer which started from a 57deg inclined orbit: 9,545 lb vs. 9,552 lb of separated spacecraft weight respectively. There was a significant reduction in the need for propellant launch time reserve for a one hour window: only 78 lb for the three burn transfer vs. 320 lb for the two burn transfer. Conversely, this also meant that longer launch windows over more orbital revolutions could be done for the same amount of propellant reserve. There was no practical difference in ground tracking station or airborne assets needed to secure telemetric data, even though the geometric locations of the burns varied considerably. There was a significant adverse increase in total mission elapsed time for the three vs. two burn transfer (12 vs. 11/4 hrs), but could be accommodated by modest modifications to Centaur systems. Future applications were discussed. The three burn transfer was found to be a viable, arguably preferable, alternative to the two burn transfer.

Optical systems havebeen an integral part of space technology since Lunik3 returned the Ž rst pictures from the far side of the moon in 1959.Meteoroids present an obvioushazard, and these natural projectiles have been joined by increasing numbers ofman-madedebris as space exploitationexpands.Although the probabilityof catastrophic impact caused by the micrometeoroid and orbital debris environment is still extremely small for any given lens or mirror, degradation caused by roughening of the optical surfaces by microimpacts is almost certain, especially in lower orbits. A straightforward algorithm is presented for analyzing this degradation, along with an example analysis for a spacecraft in a Molniya orbit.

Some 16 proposed new satellite systems operating at 36 to 46 GHz (Q-band) and 46 to 56 GHz (V-band) have been proposed to the U.S. Federal Communications Commission by U.S. companies. Of these. 14 are intended to provide global, or nearly global, service. One is intended for U.S. domestic service, and one is a package to provide additional store-and-forward capability on an earlier proposed “Little LEO” system. This paper provides a brief summary of the 14 global systems, which for the most part are designed to exploit the wide band of frequencies available for services such as multimedia distribution and Internet access. Systems are proposed that would use geostationary orbit, medium earth orbit, low earth orbit, and Molniya orbit satellites, and in some cases combinations of two of these orbits. Most of the new systems propose to employ new technologies such as multiple narrow spot-beam antennas, onboard demodulation and routing of traffic between beams, intersatellite links, and in some cases scanning beams to continuously illuminate the service area as the satellite flies by. Some of the difficulties involved in fielding systems at these high frequencies arise from the propagation impairments that can be expected and the high cost of solid-state power devices for user terminals, which will drive up costs. It is concluded that, while the large amount of bandwidth (3 GHz) proposed by the FCC for these systems is attractive, few if any are likely to be built while spectrum remains available at Ka-band.

SigniŽ cant discoveries about gas–surface interactions that havebeen made in 90 years of laboratory experiments and 30 years of orbital measurements are reviewed. This information is used to improve the calculation of drag coefŽ cients for satellites in low Earth orbit for several different satellite shapes and orientations by inserting the appropriate parameters in theoretical models of the drag coefŽ cient. The drag coefŽ cients so calculated provide increased consistency in orbital measurements of atmospheric density by satellites of different shapes near 200 km, where adsorbed atomic oxygen dominates the interaction and causes the energy accommodation coefŽ cient to approach unity. It is essential to improve the numerical value of the drag coefŽ cient so that the density of the neutral thermosphere can be inferred from satellite drag to better than the present 15% uncertainty. The key to this improvement is the calculationof drag coefŽ cients from parametersmeasured in space, rather than from those measured in the laboratory under conditions very different from the space environment.

In this paper, the individual relativistic perturbations are simulated and compared, for two orbit cases: (1) a medium altitude eccentric earth orbit (MEO), and (2) a Molniya orbit. The results of the simulations are presented in graphical and statistical form. The simulation data reveals that the specific forces that arise from the relativistic perturbations do manifest as variations in the classical orbital elements. It is also apparent from the simulated data that the specific forces exhibit similar effects that materialize from commonly considered perturbations that are used in orbit design and maintenance. ABSTRAK: Dalam kertaskerja ini, pengusikan relativistik disimulasi dan dibandingkan secara individu bagi dua kes orbit: (1) orbit eksentrik bumi ketinggian sederhana (MEO), dan (2) orbit Molniya. Hasil simulasi ini dibentangkan dalam bentuk grafik dan statistik. Data simulasi menunjukkan daya spesifik pengusikan relativistik timbul sebagai variasi bagi elemen orbit klasik. Data simulasi menunjukkan daya spesifik memberi kesan yang sama dengan pengusikan biasa yang digunakan dalam rekabentuk dan penyelenggaraan orbit.KEYWORDS: relatistic perturbations; orbit perturbations

The extension of highly elliptical orbits, with free selection of orbit period, using low thrust propulsion is investigated. These newly proposed orbits, termed Taranis orbits, are enabled by existing low-thrust propulsion technology, offering a radically new set of tools for mission design and facilitating new, novel Earth Observation science. One particular example considered herein, using general and special perturbation techniques, is the application of continuous low-thrust to alter the ‘critical inclination’ of an orbit from the natural values of 63.4deg or 116.6deg, to any inclination required to optimally fulfill the mission goals. This continuous acceleration is used to compensate for the drift in argument of perigee caused by Earth’s gravitational field. Pseudo-spectral optimization techniques are applied to the 90deg inclination Taranis orbit, generating fuel optimal low-thrust control profiles, with a fuel saving of ~ 4% from general perturbation results. This orbit provides an alternative solution for high latitude imaging from distances equivalent to geostationary orbits. Analysis shows that the orbit enables continuous, high elevation visibility of frigid and neighboring temperate regions using only three spacecraft, whereas a Molniya orbit would require in excess of fifteen spacecraft, thus enabling high quality imaging which would otherwise be prohibited using conventional orbits. Order of magnitude mission lifetimes for a range of mass fractions and specific impulses are also determined. Finally, a Strawman mass budget is developed, where the mission lifetimes for spacecraft with initial mass of 1000kg, 1500kg, and 2500kg, are found to be limited to 4.3 years, 6 years and 7.4 years respectively.

In cooperation with the German non-profit amateur satellite organisation (AMSAT-DL), the German Aerospace Center developed the idea of using AMSAT’s Earth satellite P3-D as a baseline for a Moon mission. For cost-effectiveness, P3-D was launched as an auxiliary payload on Ariane 5 into a geosynchronous transfer orbit (GTO) and used its on-board propulsion system to achieve a Molniya orbit. The present study describes how a similar satellite can reach a 100 × 100 km lunar orbit with the same launch strategy. A delta-v saving transfer scenario using the weak stability boundary transfer was found to be feasible taking a P3-D-like satellite bus into account. It contains phasing orbits as a solution for non-dedicated launch dates and deals with the constraints of Ariane’s GTO. This approach opens up the opportunity to accomplish a low-cost mission to the Moon with public and scientific value.

The Molniya orbit can be exploited for communications using laser technology. Since the Molniya orbit repeats, exactly, every 24 hours, such a system will allow high latitude and ground based lasers to use Molniya satellite links much the same way that equatorial located lasers can use geostationary satellites. Thus the benefits of a geostationary laser communications system can be employed worldwide.

The Space-Based Infrared Satellite System (SBIRS) is the follow-on to the Defense Support Program (DSP). DSP and SBIRS are military space programs. DSP provides a highly available, survivable, and reliable satellite-borne surveillance system which detects and reports missile launches, space launches, nuclear detonations, and other events in near-real-time during pre-, trans-, and post-attack operations. SBIRS will provide improved missile warning for attacks against North America and the rest of the world. SBIRS will also provide surveillance support to national and theater missile defense, technical intelligence, and battlespace characterization. The SBIRS system of systems is being implemented in a phased approach. The first phase, Increment 1, consolidates ground processing of DSP data in the U.S. Increment 2 launches the improved replacement satellites in geosynchronous and Molniya orbits. Increment 3, not yet on contract, adds a satellite constellation in low earth orbit.

Until the late 1980s, satellites in non-geostationary orbit had limited use for communication applications because, in general, these systems are more complex and, since geostationary satellites met most requirements anyway, not much effort was spent on their development. Molniya orbit was used in the former Soviet Union for providing services to very high-latitude regions where geostationary orbit (GSO) systems were not very reliable. However, since the beginning of the 1990s there has been considerable interest throughout the world in the use of various types of non-geostationary orbits. In this chapter, we will discuss the reasons behind the revival of this interest, considerations in design of a non-geostationary constellation with an example, and various types of network-related issues. We will then give examples of some of the more technically interesting emerging non-geostationary systems.

The Space-Based Infrared System (SBIRS) is the modern, cost effective follow-on to the Defense Support Program (DSP). SBIRS will support four broad mission areas: missile warning, missile defense, technical intelligence, and battlespace characterization. Like DSP, SBIRS will provide missile launch warning and attack assessment to the strategic and theater command centers. SBIRS additionally supports national and theater missile defense as well as technical intelligence and battlespace characterization. The SBIRS architecture includes constellation of satellites in high and low altitude orbits. Four satellites in geosynchronous (GEO) orbit and two sensors on multi-mission satellites in Molniya orbit (HEO, Highly Elliptical Orbit) comprise the high altitude component of the constellation. The Low Earth Orbit (LEO) configuration has not yet been selected, but it will likely include from eighteen to forty satellites. The SBIRS processing and reporting will be consolidated at a Mission Control Station (MCS) in the Continental United States (CONUS). The MCS will be developed first and go on-line in 1999 to support the DSP system; the high altitude satellites will be developed and launched next, starting in 2002; and the low altitude satellites will be launched last, starting in 2006. Lockheed-Martin will develop the SBIRS System of Systems and High Component. The SBIRS system Of systems architecture is referred to as "High now, Low later".

This paper studies the feasibility of using a new implementation of electrodynamic propulsion to change the inclination, right ascension of the ascending node, and argument of perigee for a spacecraft. Thrust in electrodynamic propulsion is the Lorentz force which results when electric current flows in a conductor segment placed in the Earth's magnetic field. Field directed propulsion is an implementation which uses multi-turn conductor loops onboard the spaceraft that are partially shielded to produce a net force. It offers the advantage of no propellant requirement on a relatively compact vehicle. Instantaneous and orbit average power demands are the primary considerations in sizing a field directed propulsion unit and the associated power supply and power processing units. An expression for the specific power is derived that is vehicle independent and is applicable to any maneuver. Acceleration profile and the associated current vector required t o accomplish an orbit element change are developed based on examination of force requirements in Lagrange's planetary equations. Results show field directed propulsion can be used to change either inclination or right ascension of the ascending node of a low-Earth polar orbit at a rate of approximately 0.4 degrees/day using an average specific power of 4 Watts/kilogram (W/kg). Field directed propulsion can also be used to offset the effects of the Earth's oblateness on the argument of perigee. For a 24-hour Molniya orbit at 90' inclination, the average specific power requirement is 3.4 W/kg. These average power levels are within the range of specific power which can be produced with current power technology.

Measurements have been made of the dose received by silicon components under 100 mils of aluminum aboard satellites in a Molniya orbit. Nearly continuous data are presented for the time period from August 1983 until March 1990. It is concluded that the observations are consonant with the predictions of the NASA AP-8 model but not with those of the AE-8 model. Molniya Orbit, NASA AP-8 Model, NASA AE-8 Model, Space Radiation Environment.

This paper compares three possible orbit options for satellite mobile systems for Europe: (1) a geostationary system, (2) a 24 h Tundra orbit system and (3) a 12 h Molniya orbit system. A comparison of the traffic capacities and overall systems costs which would be applicable in a first and second generation land mobile system has been made. The estimated traffic capacity of these systems, which depend critically on both the propagation margin and the type of mobile antenna, indicate a clear advantage for inclined orbit systems over the geostationary approach. The CCIR prediction technique was used as the basis for establishing the system margins as a function of elevation angle. The orbit optimization for the elliptical orbit systems requires detailed consideration, as the satellite range, elevation angle and antenna beam patterns alter throughout the “useful part of the orbit” between hand-over points. Both the Molniya and Tundra situations require slightly different considerations. In the Molniya based system the particular case of the Loopus orbit was chosen, i.e. where the Earth tracks nearly touch at the hand-over point. The equivalent Tundra situation gives an impractical solution to coverage areas. Other considerations such as orbit life time, operational problems and radiation environment are also discussed. Comparative cost estimates were deduced for two satellite options.

The SAGACE experiment consists of a mm/sub-mm telescope with a 3-m diameter primary mirror, coupled to a cryogenic multi-beam differential spectrometer. SAGACE explores the sky in the 100-760 GHz frequency range, using four diffraction-limited bolometer arrays. The instrument is designed to perform spectroscopic surveys of the Sunyaev-Zeldovich effects of thousands of galaxy clusters, of the spectral energy distribution of active galactic nuclei, and of the [CII] line of a thousand galaxies in the redshift desert. In 2008 a full phase-A study for a national small mission was completed and delivered to the Italian Space Agency (ASI). We have shown that taking advantage of the differential operation of the Fourier Transform Spectrometer, this ambitious instrument can operate from a Molniya orbit, and can be built and operated within the tight budget of a small mission., Proceedings of the 12th Marcel Grossman Meeting