An account is given of a simple program structure with low costs and short schedules for the space R&D community operating outside mission-oriented, government-funded programs. In addition to furnishing launch services into orbit, the program structure furnishes engineering services through its ground station, control room, and 3-year duration 'MMSB' platform. Flights may begin as little as a year after contract signature.
This paper presents the design for a low cost, light satellite used to aid in the control of vector-borne diseases like malaria. The 340 kg satellite contains both a synthetic aperture radar and a visual/infrared multispectral scanner for remotely sensing the region of interest. Most of the design incorporates well established technology, but innovative features indude the Pegasus launch vehicle, low mass and volume SAR and VISfR sensors, integrated design, low power SAR operation, microprocessor power system control, and advanced data compression and storage. This paper describes the main design considerations of the project which include the remote sensing task, implementation for malaria control, launch yehide, orbit, satellite bus, and satellite subsystems.
There is great and increasing interest within the scientific community to study and better understand the earth's climate and global climate changes. NASA plans to study these global changes via measurements of many aspects of the earth system. These measurements will be extensive, some being made simultaneously from many different locations. This paper examines the use of small satellites (less than 220 kg) as a potential option for providing necessary global change measurements. A survey of current and planned small satellite characteristics, including bus subsystems and science payloads, is provided. A brief survey of potential launch vehicles for small satellites is also described. Estimates of payload mass and power envelopes are made for representative small satellites in three size ranges.
For the first time, the Earth Imaging System (EIS) on the UoSAT-5 spacecraft has demonstrated the capability of remote sensing from microsatellites. In addition to the meteorological-scale CCD imager, the EIS incorporates a transputer-based processing unit that provides substantial processing power to the module. This transforms the EIS into a unique platform for research into sophisticated on-board image analysis, processing and compression. The use of these techniques is essential for full exploitation of sensing microsatellites, by maximizing the throughput and turnaround of image data on the narrow communications channels.
NASA's Office of Commercial Programs is funding a multispectral sensor system to be used in the development of remote sensing applications. The Airborne Terrestrial Applications Sensor (ATLAS) is designed to provide versatility in acquiring spectral and spatial information and will be a test bed for the development of specifications for airborne and spaceborne remote sensing instrumentation for dedicated applications. This objective requires spectral coverage from the visible through thermal IR wavelengths, variable spatial resolution form 2-25 meters; high geometric and geolocation accuracy; on-board radiometric calibration; digital recording; and optimized performance for minimized cost, size, and weight.
When private remote-sensing systems were first authorized in 1984, Congress imposed regulatory requirements intended to protect national security and international obligations. This article reviews the legal framework that now exists under the Land Remote-Sensing Commercialization Act of 1984, and discusses recent efforts to amend the Act in order to remove regulatory restrictions that inhibit development of private remote-sensing systems.
Portuguese technological and strategical objectives for space are described, in the context of drivers of general policy, defense, industry, education, science and industrial mterests In the field of small satellites -which has been given priority - cooperative actions between government and industry and international bilateral cooperation are easier to envisage and implement. The short and mid term programs that have been launched to setup a minimum level of human and technical infrastructures are described.
The Leostar spacecraft family is able to support data message communications, position-reporting, and voice communications for mobile users. The satellites are sufficiently small for launch by such systems as Pegasus and Scout, as well as by large launch vehicles, in either residual-space or multiple-launch configurations. Low costs are achieved through simple, standardized, off-the-shelf component-employing design practices.
DARPA's Advanced Space Technology Program (ASTP) encompasses the development and operation of the Pegasus (air-launched) and Taurus (standard small) launch vehicles and the 'lightsats' Microsat, Macsat, and Darpasat, as well as satellite subsystems, communications, optical-components, and submarine laser communication technology development programs. An assessment is made of the benefits derivable from these technologies by both the defense and civilian space communities.
Communications links between Low Earth Orbit SATellites (LEOSATs) and mobile or portable terrestrial stations can be affected by several fading mechanisms. These mechanisms contribute to degradation of link performance in excess of those usually associated with radio wave communication links. A thorough understanding of these fading mechanisms and their effects on communications links is essential to the design of an effective communications system. In this paper we discuss a propagation model that includes the effects of multipath scattering and signal blockage. The signal behavior due to these effects is discussed along with its implications on communication system design and performance. The results presented are based on both theoretical modeling and measured propagation data.
The present analytical approach to the improvement of different encryption codes' effect on BPSK-modulated signals evaluated the upper bounds of soft-decision Viterbi decoding's BER, and is here applied to a CDMA-DS technique. A comparison is conducted with the sequential decoding process; the code is noted to decrease jammer effects.
Ni-H batteries have been developed for small satellites; these yield 2-20 A-hr capacities at competitive cost while retaining the long life/high reliability characteristics required for satellite applications. The RNHC-6-1 cell design presently discussed will be used by the USAF's experimental APEX small satellite and the Sea Star small satellite, where it will yield a 6 A-hr, 2.5 V capacity.
The PegaStar small satellite platform combines functions that are common to both satellites and launch vehicles (guidance and control, power, communications and data systems), thereby eliminating the cost and weight of duplicate systems and allowing users to launch heavier and more sophisticated platforms at lower cost. PegaStar's design is based on the satellite bus integrated into the Pegasus air-launched vehicle; the PegaStar for remote sensing missions aboard the Taurus booster will involve only modest modification of the current PegaStar design.
Sensing missions using small satellites impose thermal and power requirements upon the satellite which are difficult to meet due to the limited power available. Sensors such as short wavelength infrared detectors and gamma ray spectrometers require operating temperatures on the order of 100 to 200 Kelvin. A conventional thermal control system would use an active cooler or an active sun shade to meet the sensor temperature requirement. This solution requires significant power, increases the weight of the satellite, and reduces the reliability since active components are required. A completely passive design employing a radiator protected by a set of self actuating sun shade panels can alleviate the need for active cooling of the sensor, while reducing the weight of the satellite. A unique feature of this design is that it allows the radiator to continue to function while shading the radiator from the sun for low incident sun angles. In addition, this design can completely shield the sensor from direct overhead sunlight during non-operating modes. This protection is important in germanium crystal gamma ray spectrometers since cosmic rays can damage the crystal if the temperature rises above 110 Kelvin.
Preliminary results are presented from a multiple-node thermal analysis of the Sedsat satellite, using the 'THAWS' Thermal Analysis Workstation code to create the 48-node System Improved Numeric Difference Analyzer/Net Energy Verification And Determination Analyzer model. Attention is presently given to Sedsat's construction and temperature requirements; a 5-15 C temperature-control band is shown to be achievable.
The Dual Cone Scanner (DCS) a single-head earth horizon sensor which provides altitude and two-axis attitude information with minimal sun or moon error, will fly on the USAF Phillips Laboratory TAOS mission as part of an autonomous spacecraft navigation demonstration in 1993. These sensors also include an optional sun/moon visible light optical channel and employ a 1750 CPU-based signal processing electronics package. Barnes has since developed an analog processing technique which achieves a significant reduction in weight, power, and cost, making the DCSs available for small satellite applications. Optional features include a light emitting diode built into the detector that can be used for self testing or mission simulations and secondary radiance processing algorithm to reduce errors due to earth radiance variations. The sun/moon detectors used on the TAOS sensors may be incorporated in the new design in the future.
In order to capitalize on commercial advancements in GPS receiver technology that reduce size, weight, and power requirements while further enhancing capabilities, it is suggested that the next generation of GPS receivers should be based on commercial units. The SB-24 space-qualified GPS receiver presently discussed will be less expensive to develop than a dedicated, space-qualified unit and will be predicated on in-house-developed commercial technology.
A major diagnostic in understanding the response of the Earth's climate to natural or anthropogenic changes is the radiative balance at the top of the atmosphere. Two classes of measurements may be undertaken: (1) a monitoring of the radiation balance over decade-long long-time scales; and (2) measurements designed to provide a sufficiently complete data set to validate or improve models. This paper discusses some of the important ingredients in obtaining such data and presents a description of some candidate instrumentation for use on a small satellites.
The presently discussed triaxial fluxgate magnetometer calibration and alignment facility was developed for the magnetometers aboard the Indian Remote Sensing Satellite and the Stretched Rohini Satellite Series missions. Magnetometer alignment is accomplished by optical methods; the coil axis is transformed into the optical axis by both an autocollimator and an optical cube mounted on the coil platform.
A standard NTSC television video raster image digitized with a 10 MHz sample clock, results in 333, 375 pixels per frame (one frame = two interleaved fields). To send this amount of digital data, uncompressed, over a KHz bandwidth telephone line at a 2400 BAUD rate using ASCII data format requires over 25 minutes of time. The same uncompressed video image can be transmitted over the same 4 Khz bandwidth channel using video signal signature synthesis in a little more than a minute with virtually no loss of image quality.
Proc. SPIE 1691, Spacecraft fabrication and test manufacturing operations and development integration laboratory: establishing a spacecraft fabrication culture, 0000 (10 August 1992); doi: 10.1117/12.138037
MODILs (Manufacturing Operations and Development Integration Laboratory) were established to mitigate risk and cost escalation of producing SDI systems. The Spacecraft Fabrication and Test MODIL has been established to impact spacecraft producibility and create a spacecraft industry quantity production culture. We describe the background of MODILs, objectives and scope, current organization (including cooperating government agencies), and the current thrusts of Materials and Structures. Test and Assembly, Spacecraft Integration Technology, and Precision Technologies. The current plan is to initiate selected productivity demonstration projects with industry to show benefits of the MODIL approach and prepare comprehensive plans for follow-up activities.
Cryocoolers are a key component for many spacecraft. We summarize some spacecraft cryocooler requirements and discuss our observations regarding the current production capabilities of cryocoolers. The MODIL's interaction with industry, especially throught the Producible Technology Working Groups is also summarized. The current Spacecraft Fabrication and Test MODIL's plans to improve producibility include working closely with industry, executing a demonstration project, and holding a workshop to bring key members of the current cryocooler development network together.
The Automated Spacecraft Assembly Project is studying the potential for leveraging 'soft' (computer-based) technologies in spacecraft manufacturing, because above-the-shop-floor costs typically account for 40 to 70 percent of the total costs of manufacturing. Our preliminary survey of soft technologies of above-the-shop-floor operations identified the areas which show the greatest potential benefit in cost and time savings for SDIO spacecraft fabrication and test. The preliminary survey reviewed initiatives from DARPA, and SDIO, among others.
Composite materials have demonstrated performance benefits for a variety of satellite applications. Now, an emphasis on smaller, more specialized satellites produced in higher quantities than before is emerging. Due to the competitive economic environment, realization of cost reduction potential by the use of composite materials is critical. Productivity techniques, long employed by other areospace segments, offer an approach to cost reduction while retaining improved performance. One cost reduction approach is to reduce the number of piece parts and assembly operations by converting from a metal-based design to one based on composite technology. Alternate composite fabrication approaches can then be compared for thermoplastic and thermoset matrices for additional producibility benefits based on properties and comparative costs. Previously developed representative data are presented for this transition from a metallic component to composite and for alternate fabrication approaches. The next step in cost reduction would appear to be the introduction of automation techniques and minimizing post fabrication operations while maintaining performance properties. The program described in section 3 is structured to provide a key confirming experiment to demonstrate that such a goal can be realized.
The Amsat Phase 3D (P3D) Satellite is now in the construction phase at Weber State University's undergraduate manufacturing and mechanical engineering technology program. The first year of a three-year manufacturing project has brought the students many interesting and challenging tasks. This paper discusses some of the unique manufacturing aspects of the P3D satellite by focusing on a satellite component fabricated from honeycomb panel and an assembly fixture designed and built by the students.
The tendency toward smaller satellites that is imparted by growing budget constraints suggests an intrinsic applicability of fiber-optic and photonic devices to small satellites in virtue of these technologies' compactness. Attention is presently given to the results of the first operation in space of four active fiber-optic data links, which proceeded over a period of 69 months.