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Past Conference Papers:
Responsive Missions - Imagers
| Paper Number RS5-2007-2003: Spacecraft Slewing/Guidance Algorithm for Hyper Spectral Imagers | |
| Morris Frayman (Star Technologies Corporation), Robert R. Strunce Jr. (Star Technologies Corporation) | |
| View/Download:Presentation | Paper | |
| Abstract: Hyper Spectral Imagers (HSI) are planned as payloads on future Responsive Space missions. Typically, the mission requirements dictate a specific scanning rate that the spacecraft must support in order to body point the HSI such that a single pixel covers a specific Ground Sample Distance (GSD) size in one integration frame. The actual focal plane array is typically one pixel wide by several hundred pixels long. The frame rate (integration time) is the time to scan the length of the array in one GSD. All too often the requirements are stated as: a fixed GSD size (~3 meters); a fixed altitude (~400k); a fixed scanning rate which is usually constrained parallel to the spacecraft trajectory. Even for a nadir target, these specifications severely compromise the quality of the image and overly constrain the image swath which could lead to minimal utility to the war fighter on the ground. And in particular, following these requirements will produce increasingly poor image quality the more the target is off-nadir. While working on the Navy Research Laboratory’s (NRL) Naval Earth Mapping Observatory (NEMO), a generic guidance algorithm for body pointing its HSI was developed that overcomes these restrictions and provides a high level of image quality regardless of target location or swath direction with respect to the image swath orientation. This algorithm was implemented and simulated for a TacSat3 spacecraft. A unique spacecraft slewing algorithm was developed (including sun avoidance) that rapidly moves the spacecraft into the proper orientation and settles the HSI LOS jitter at the beginning of imaging swath. The guidance algorithm is based on a spacecraft line-of-sight (LOS) coordinate frame and a target coordinate frame at the target site. The target frame is defined as a function of the Image swath to be collected. The HSI telescope relationship with the spacecraft coordinate frame is defined with respect to the spacecraft LOS frame. The relationship between the LOS and target frames guarantees that the HSI scan line or focal plane remains perpendicular to the scan direction independent of the target swath orientation with respect to the spacecraft trajectory. The focal plane speed over the ground (SOG) is calculated based on the HSI parameters: output pixel angle; HSI camera frame rates; and the size of the GSD which is based on look angle to the target and the earth’s geoid. The slewing and guidance algorithms are developed in this paper and simulation results are presented. | |
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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 RS5-2007-3005: Future Radar Surveillance Using Small Satellites | |
| Stuart Eves (Surrey Satellite Technology) | |
| View/Download:Presentation | Paper | |
| Abstract: The paper will describe the AstroSAR-UK satellite, which is being developed by EADS-Astrium and SSTL for the UK Government. AstroSAR-UK is a multi-mode phased-array synthetic aperture radar satellite, capable of performing a variety of surveillance tasks. Details of these various collection modes will be provided, and it will be shown how the satellite can be rapidly switched between them to responsively support a crisis situation or a theatre commander’s needs. The mission will combine EADS-Astrium’s expertise in radar payloads, which, allied with SSTL’s low-cost platform technology, will allow the system to be launched and operated for a period of 5 years for a cost of less that $100M. | |
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| Paper Number RS6-2008-2006: CubeSat-Based Disaster Detection and Monitoring Systems | |
| Justin M. Akagi (University of Hawaii), Tyler N. Tamashiro (University of Hawaii), Reece T. Iwami (University of Hawaii), Jason T. Akagi (University of Hawaii), Wayne A. Shiroma (University of Hawaii), Joseph M. Cardenas (Oceanit Laboratories) | |
| View/Download:Presentation | Paper | |
| Abstract: The most critical element in the aftermath of a terrorist attack, natural disaster, or other large-scale emergency is for response teams to establish rapid, accurate, and consistent situational assessment. Terrestrial-based sensing and communication systems are infeasible in these situations, as they are often the target or are compromised in these attacks or disasters. An attractive solution is a small-satellite surveillance and tracking network that is autonomous, reconfigurable, redundant, and readily deployable. Due to their small size and weight, launching a network of these satellites is more cost-efficient than launching one large satellite. To provide image surveillance in the case of an emergency or crisis, the University of Hawaii Small Satellite Program developed a 1.5U CubeSat outfitted with a COTS camera, global positioning system (GPS) unit, and inertial measurement unit (IMU). The GPS unit and IMU tags the image acquired by the camera with its location and pointing coordinates. By utilizing a network of satellites, multiple images can then be stitched together to form a detailed view of the crisis area. In addition to the COTS-based imaging system, the satellite bus platform utilizes a number of COTS subassemblies (i.e., S-band transceiver and Linux-based microcontroller) and structure designed to fit the CalPoly San Luis Obispo P-POD form factor. This design approach enabled an 11-member student team (9 undergraduates, 2 graduates) to design, fabricate and demonstrate the satellite in a nine-month timeframe. Continued efforts of this program include developing standardized bus interfaces to allow independent development of subsystem modules. This approach will produce ready-made plug-and-play avionics modules that can be combined on a customizable bus platform, based on mission-dependent payload requirements. By focusing our efforts on this approach, we can expect a considerably shorter timeframe for demonstrating an integrated satellite system. | |
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| Paper Number RS6-2008-3001: Technology Development for Lightweight L-Band SAR | |
| Mark Webster (Ball Aerospace & Technologies Corp.), Dean Paschen (Ball Aerospace & Technologies Corp.), Mark Leifer (Ball Aerospace & Technologies Corp.), David Murphy (ATK Space Systems), Gary Heinemann (ATK Space Systems) | |
| View/Download:Presentation | Paper | |
| Abstract: The ORS Payload Development Initiative awarded 14 contracts to develop basic to complex technologies for potential TacSat missions. The largest of the complex awards, announced in February of 2007, went to Ball Aerospace and its partner ATK to perform development and risk reduction for a light-weight L-Band Synthetic Aperture Radar antenna. The program, started in April of 2007, has focused on determining the most practical and highest-performing configuration for the antenna and in reducing risk and increasing feasibility of the overall design. The motivation for this L-band SAR, which can provide worldwide coverage daily with only two satellites, is to enable perceptive monitoring of near-real-time changes over broad regions of interest. Where further investigation is required, this would be provided by tasking more focused sensors. In developing the L-Band SAR, Ball has focused on the distributed architecture design of the radiating aperture and ATK has focused on the lightweight backing structure and deployment systems. The optimized design consists of modular tiles of 2X2 radiating elements with transmit and receive functionality provided by local electronics. 416 of these “quad” module assemblies (QMAs) are mounted on stable lightweight composite panels to form a contiguous 28 m2 aperture, with linking deployment mechanization that is derivative of heritage solar array designs. The program is preparing a complete design review documentation package and building proof of concept models that will be used to validate the capabilities of the antenna in the relevant environment. The paper will review the system design and present the results of the engineering model tests. The antenna unfolds on orbit into a 2-m x 14-m array, an aperture size in line with heritage L-band SAR systems; however, operational concepts have been developed that achieve ambiguity to signal performance levels typical of a much larger system . Cost is further minimized through modularity and the extensive use of COTS components. Reliability is insured by designing for massive parallelism and graceful degradation with amplifiers, T/R switches, phase shifters, attenuators and combiner/splitters on the QMA behind the radiating elements. Use of lightweight bonded honeycomb structures for the QMAs and backing panels will keep the weight of the antenna, including cabling, and deployment structure, below 7.5 kg/m2. The approach promises high performance at low cost. A prototype T/R module has demonstrated power output of 2W/element at any selectable polarization angle from H through V, resulting in array transmit power in excess of 3 kW. | |
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| Paper Number RS6-2008-3005: WiSAR: A New Solution for High-Performance, Smallsat-Based Synthetic Aperture Radar Missions | |
| Peter Fox (MDA Corporation), Kenneth James (MDA Corporation), Alan Thompson (MDA Corporation) | |
| View/Download:Presentation | Paper | |
| Abstract: Cost effective, responsive Synthetic Aperture Radar (SAR) missions will only be possible when technology-enabled breakthroughs and efficiencies in manufacturing allow SAR satellites to be rapidly deployed on low-cost launch vehicles. This will be achievable when SAR satellites can be built at substantially lower mass and for significantly lower cost than current technologies allow. The key challenge to date has been in developing low cost, low mass phased array antenna technology without compromising resolution and performance. MDA’s Wireless Synthetic Aperture Radar (WiSAR™) is a new SAR antenna technology that offers leading-edge performance in both X- and C-band at significant reductions in cost and mass over the conventional state of the art. The WiSAR solution uses proven off-the-shelf technologies from the automotive and terrestrial wireless communication industries to enable an innovative space-fed active lens architecture that replaces the heavier and bulkier traditional constrained feed design. Key elements of the WiSAR payload include: self-contained active antenna nodes; low cost RF radiators; thin, lightweight, easily deployed antenna panels; and RF ranging for dynamic antenna distortion compensation. This paper will describe the WiSAR payload technology and the results of a project to build, test and operate a fully functioning C-band prototype WiSAR phased array antenna. | |
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| Paper Number RS6-2008-4007: Very High Resolution Imaging Using Small Satellites | |
| Stuart Eves (Surrey Satellite Technology) | |
| View/Download:Presentation | Paper | |
| Abstract: The paper will discuss the techniques required to deliver sub metre imaging from a small satellite, (with a total mass of less than 500 kg), commencing with an analysis of the trade-off between orbit height, image resolution and the lifetime of the system. This initial trade-off is required to identify the most appropriate operational altitudes associated with different orbit maintenance strategies. Also included in the discussion will be the high-level optical system design, showing how simpler, on-axis optical designs can achieve the required performance without involving the complexities, time constraints, and associated higher costs, of aspherical, off-axis mirror designs. Some of the trade-offs associated with detector design will also be addressed, including the potential need for active attitude control during imaging to control the read-out rate required from the sensor. The paper will cover the mechanical engineering challenges of flying a sophisticated optical bench into orbit, and the modes of operation that can be supported using such a concept. The paper will also indicate the sort of performance that could be derived from a similar satellite designed to operate in the IR rather than the optical spectrum. | |
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| Paper Number RS6-2008-6003: TopSat- Assessing the Military Utility of a Tactical ISTAR Demonstrator | |
| H.S. Jolly (Defence Science and Technology Laboratory), D. Beard (Defence Science and Technology Laboratory), T. Burt (Royal Air Force) | |
| View/Download:Presentation | Paper | |
| Abstract: Launched on 25 October 2005, TopSat is a small (<110kg) low-cost (~ $28M), electro-optical (EO) imaging satellite demonstrator designed, built and operated by a British consortium led by QinetiQ under contract to the UK Ministry of Defence (MOD) and the British National Space Centre. Despite early technical difficulties, the programme demonstrated that the UK could successfully build and operate a small, low cost, satellite that could be tasked quickly and provide very fresh imagery. It also provided potential users with insights into how a future system might be employed and also clarified potential user requirements. The military utility of TopSat was assessed by the UK MOD TopSat Users Group (TUG) through an evaluation of the performance of the satellite system during a series of experiments, trials and exercises through 2006-2007. The TUG comprised participants from Front Line Commands and other MOD organisations, and was assembled to undertake the assessment of the military utility of TopSat. This paper presents the joint assessment made by the TUG participants and includes the conclusions and lessons drawn from the programme relevant to the implementation of responsive space. | |
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