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Past Conference Papers:
Orbits
| Paper Number RS5-2007-1002: Clustered Architecture for Responsive Space | |
| Gregory A. Orndorff (Johns Hopkins University Applied Physics Laboratory), Buruce F. Zink (Johns Hopkins University Applied Physics Laboratory), John D. Cosby (Science Applications International) | |
| View/Download:Presentation | Paper | |
| Abstract: The tenets of operationally responsive space need to be addressed and implemented systematically, in a supportive and enabling framework. We discuss a proposed satellite architecture consisting of multiple clusters of satellites in geosynchronous orbit, providing standard communications and propulsion services to client satellites flying within the clusters. This allows the offloading of propellant and mission communications and the use of the cluster’s services as a utility, enabling smaller, lighter, cheaper mission satellites. We show how offloading mission communications from satellites in favor of a high-speed wireless local area network in space enables efficient use of both space and ground communications capabilities. We show how enabling operators to utilize communications and delta-V as commodities enables highly responsive operations, on the order of days for major satellite constellation reconfigurations, and how these services themselves form the foundation of truly responsive space operations. | |
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| Paper Number RS5-2007-2001: Partially Continuous Earth Coverage from a Responsive Space Constellation | |
| Scott C. Larrimore (USAF Institute for Defense Analyses) | |
| View/Download:Presentation | Paper | |
| Abstract: Over the past half century of spaceflight, national security space systems have evolved from principally serving strategic decision makers in national capitals to providing near real time information to tactical combat commanders. United States military leaders are searching for means to provide persistent coverage and sensor access to crisis locations. Small, responsive space platforms in low Earth orbit (LEO) may offer one answer to this persistency problem. Traditional constellations of small satellites have focused on providing continuous global or near-global coverage. These large, robust, and expensive constellations are deployed over many months or years. This paradigm is not suitable for providing responsive, tailored combat support to military theater forces. Alternatively, a small number of current LEO spacecraft provide short, fleeting accesses to a geographic region of interest, denying fielded forces the persistency they desire. These short, sporadic accesses are better suited for strategically oriented missions rather than tactical ones. One can, however, design a relatively small constellation of spacecraft to provide optimized, partially-continuous coverage for a given local geographic region or latitude band. Although this configuration will not provide continual coverage throughout the entire day, several hours of contiguous access is possible. The method consists of first analytically determining the inclination yielding the maximum access to a surface target location based upon a satellite’s altitude and sensor limitations. This inclination will normally be a little greater than the target’s latitude. Next, the orbital plane at this inclination is populated with spacecraft in a modified “streets of coverage” chain. The number of satellites in the chain depends upon the size of the area to be observed, satellite sensor constraints, and launch considerations. Continuous access times over several hours long are possible along with cumulative dwell times of 50% or more. Near continuous access of a local region is possible by populating a complementary second chain. Tailored constellations of this manner may provide the contextual structure tomorrow’s responsive spacecraft need to provide persistent overhead access deployed forces desire. This is just one of several new acquisition and operational paradigms needed to turn responsive space forces technologies into true tactical combat support enhancement capabilities. | |
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| Paper Number RS5-2007-2004: ORS HEO Constellations for Continuous Availability | |
| Brian L. Kantsiper (Johns Hopkins University Applied Physics Laboratory), Patrick A. Stadter (Johns Hopkins University Applied Physics Laboratory), John H. Benson (Johns Hopkins University Applied Physics Laboratory), Pamela L. Stewart (Johns Hopkins University Applied Physics Laboratory) | |
| View/Download:Presentation | Paper | |
| Abstract: Since 2005, the Integrated Systems Engineering Team (ISET), a working group drawn from industry, academia, and the national laboratories, has been developing standards for a standard spacecraft bus for Operationally Responsive Space (ORS) missions. As part of this effort, two highly elliptical orbits (HEO), with three and four hour periods, have been identified as options for missions which require long dwell-time over a particular region. Tacsat-4 will demonstrate the utility of one of these orbits to provide persistent communications. This analysis addresses the design of the constellation of the objective system. Walker-like constellations from three to eight satellites as well as the full range of arguments of perigee are considered for the critically inclined orbits. In addition, an alternate configuration using equatorial orbits is also examined. The impact of different approaches to handling times when multiple spacecraft are in view is discussed. For high latitudes, there is typically a one satellite penalty for using the lower orbit. This penalty becomes slightly more severe for lower latitudes, unless the equatorial configuration proves feasible, in which case five spacecraft in either orbit can provide continuous availability to low latitudes. | |
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| Paper Number RS5-2007-2005: Circular vs. Elliptical Orbits for Persistent Communications | |
| James R. Wertz (Microcosm) | |
| View/Download:Presentation | Paper | |
| Abstract: Responsive Communications missions typically require “persistent communications,” i.e., repeat coverage that lasts for an extended period or the entire day. LEO orbits cannot provide this coverage without a large number of satellites. The solution has traditionally been thought of as moderate altitude elliptical orbits, such as Magic or Cobra orbits. However, recent IR&D work by Microcosm suggests that this may be the wrong answer. This paper compares moderate altitude elliptical and circular orbits in terms of coverage, accessibility, flexibility, robustness, the environment, and impact on spacecraft design. The conclusion reached is that circular MEO orbits are a better choice than elliptical MEO orbits for supplementary or persistent communications. Broad rules for selecting the best orbit for specific communications applications are given. | |
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| Paper Number RS6-2008-2001: Semi-Analytical Approach to Target Access in the Responsive Space Problem | |
| Prasenjit Sengupta (Texas A&M University), Srinivas R. Vadali (Texas A&M University), Kyle T. Alfried (Texas A&M University) | |
| View/Download:Presentation | Paper | |
| Abstract: The problem of orbit design for Responsive Space has received renewed interest due to several geopolitical and environmental reasons. Whereas low-cost satellites can easily be launched to cover regions on the Earth, their effectiveness can be maximized via optimization of their orbital parameters, resulting in reduction in the costs of launch, orbital maintenance, and orbital transfer. Satellite orbit design involves the study of several performance metrics. For example, time of coverage, percentage daylight coverage, and area of coverage due to successive passes over a target region, while accounting for sensor attributes, have been identified as metrics for several missions. This paper presents semi-analytical techniques that are useful for the evaluation of these metrics, with a reduction in computation time without compromising on the accuracy of the results. Algorithms are also presented for optimal impulsive maneuvers for station-keeping in the presence of environmental effects such as drag and terrestrial oblateness. | |
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| Paper Number RS6-2008-2002: Responsive Coverage Using Propellantless Satellites | |
| George E. Pollock (Purdue University), Joseph W. Gangestad (Purdue University), James M. Longuski (Purdue University) | |
| View/Download:Presentation | Paper | |
| Abstract: Traditional reconnaissance satellites, which are fixed in their orbits, are limited in responding to rapidly-evolving conditions on the battlefield. For example, typical satellites cannot alter their time of arrival over a current region of interest. Further, as one conflict subsides and another emerges, these satellites cannot change their inclination to cover different latitudes. Thus, to support the warfighter in dynamic battlespaces, significant on-orbit maneuvering capability may be highly desirable. In this paper, we introduce the Lorentz spacecraft, a near-term propellantless vehicle, which can change orbit inclination, arrival time, altitude, and other orbit characteristics. The spacecraft modulates an electrostatic charge that interacts with Earth’s magnetic field to induce a propulsive Lorentz force. Assuming a conventional satellite power system (e.g. solar panels or RTGs), this spacecraft has inexhaustible maneuvering capability. In a matter of days a satellite’s orbit can be reconfigured to provide coverage of new theaters, perform flyby inspection of foreign space assets, and evade foreign tracking. We demonstrate the feasibility of Lorentz spacecraft by 1) characterizing the orbit dynamics of a charged spacecraft in Earth’s magnetic field, 2) deriving control laws for a variety of responsive space applications, and 3) providing an overview of hardware considerations and development efforts. | |
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| Paper Number RS6-2008-2003: Angels and Demons – Cooperative and Non-Cooperative Formation Flying with Small Satellites | |
| Stuart Eves (Surrey Satellite Technology) | |
| View/Download:Presentation | Paper | |
| Abstract: The paper will discuss the challenges of both cooperative and non-cooperative formation flying using small satellites; operating either as guardians of larger satellites, or as space situation awareness collection assets. It is axiomatic that Angels or Demons will have different ballistic coefficients to the larger assets with which they are associated, and this leads to specific challenges for the small satellites in order to maintain station. The paper will discuss these challenges, and the potential propulsion system designs that would be appropriate in order to meet them; recognising that in different operational modes, the ideal inter-satellite separation distance could also be different. The paper will also address some specific design requirements that arise for these classes of formation flying systems. For example, in order to maintain their relative positions, both Angels and Demons will require collision avoidance systems to ensure that they do not inadvertently compromise the operation of the primary satellite asset. In the case of an Angel, where cooperative behaviour by the primary asset can probably be assumed, this is a somewhat more tractable problem than for a Demon. This is especially true if the concept of operations for a Demon requires not just a one-time rendezvous with a target, but also a period of continuous station maintenance with a manoeuvring target, and the situation is more complicated still if the Demon is also required to be stealthy. For some surveillance concepts, the relative position of the primary and secondary satellites will be important, (possibly to ensure appropriate lighting conditions for imaging systems, or to provide a line of sight between particular antennas), and clearly the laws of orbital dynamics will influence this over time. This introduces additional design constraints for the Angel or Demon, either of which will presumably wish to retain the option of communication to the Earth whilst performing its mission. The paper will thus conclude with recommendations concerning both the technical design and the concept of operations for these co-orbiting systems. | |
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