ems technologies space and electronics group in montreal use maya's tmg thermal analysis software to design innovative satellite antennas.
reliability in space
silently orbiting earth, transmitting telephone, broadcast and multimedia communications, mapping the earth's surface, watching weather patterns, and guiding international transportation, satellites have become critical to twentieth century life. we rely on satellite-based communications and remote sensing systems for many aspects of our daily lives. antennas are a satellite's eyes and ears - allowing it to communicate.
the satellite antenna systems built by ems technologies space and electronics group not only provide core communications but also satellite telemetry, telecommand and intersatellite links. they are critical to satellite operations and are required to work flawlessly in the harsh environment of space.
ems technologies space and electronics group has designed and manufactured advanced antennas for space-based and ground-based applications since the 1970's. their experience in antennas spans applications from mobile telephony, paging, fixed-base telephony, broadcast and multimedia to the most advanced ka-band applications for broadband communications. the engineering staff is world-class and acknowledged for its leading-edge work on high-power feed technologies. ems's antennas are in use today on satellites such as brasilsat, anik-c, anik-e, msat, radarsat and telecom2.
satellite engineering is an exacting discipline, with very little room for error or uncertainty. in an environment where the simplest component failure can cost millions of dollars to repair and minuscule alignment errors can degrade an antenna's performance, rigorous and precise engineering is more than a good idea, it's the rule. ems's challenge is to provide reliable, low mass, thermally stable and low cost solutions to their customers.
for over three decades ems technologies inc. has been leading the world in innovative satellite antenna solutions. ems has tremendous depth in antenna design and manufacturing and is a leader in the industry. over three locations bring together experts in various antenna specialties providing a forum for improving existing products and developing new ones. ems's antenna products are used in a variety of markets including broadcast, government, communications, multimedia and mobile satellite systems. ems also designs antennas for earth observation applications and airborne systems.
simulating thermal performance in space
before a satellite can be launched, every system needs to be tested under a myriad of launch and operational conditions. with the industry demanding ever shorter delivery schedules, it's becoming harder to find the time to perform the traditional "shake and bake" physical tests. engineers are turning to digital simulation to help speed up the process.
ems has been using maya's tmg thermal analysis software package since its first release in 1982. tmg has become an indispensable part of ems's arsenal of design and simulation regimen. they use it for complete spacecraft system thermal simulation as well as for the design and development of critical spacecraft antenna equipment.
dr. sylvain rheault, thermal skill manager at ems's montreal facility describes the formidable design challenges they face. "traditional schedules permitted 12 months or more for us to design, build and test one of our antennas. now, with ever increasing market demands, that time has been cut in half and is continuing to shrink. with tmg we can meet that demand."
temperature and thermal flux fluctuation in orbit can create significant dimensional distortion. since a fraction of a millimeter of undesirable distortion can result in unacceptable antenna performance, ems needs to accurately predict and control this behavior. they use tmg to evaluate the transient and steady state thermal behavior of their equipment.
an integrated approach to thermal modeling
ems performs thermal packaging analyses for a variety of products, from integrated controller units to beam forming networks for synthetic aperture radar (sar) payloads. the thermal design of compact electronic subassemblies is intimately related to their electrical design. although the physical form of an antenna controller or motor drive amplifier unit may appear straightforward to the electronics engineer, to a thermal designer the task is an exercise is subtlety. minor changes in the location, materials or component assembly can greatly affect functionality.
dr. sylvain rheault has come to rely on tmg's unique thermal couplings features. "we have found no other software in the space industry that can automatically calculate the couplings based on the material and geometrical information in the model." this advantage becomes clear when a late design change in an electronic unit is required and all the thermal conductances have to be re-evaluated. tmg's unique thermal coupling capability allows you to build thermal assemblies without aligning the element mesh between parts. the thermal conductances between parts are automatically calculated during solution based on the assembly geometry and properties.
dr rheault emphasizes that, "without tmg engineers would be encouraged to over-simplify the component layouts and due to time constraints simplify the element mesh, an approach that can produce inaccurate results that mask potential hot spots". pierre boisvert, thermal engineer, emphasizes that tmg's use of non-cartesian element meshes with automatic thermal couplings greatly assist with the packaging of the products as well as future design changes. "we couldn't model to the same degree of detail and fidelity with any other thermal analysis package."
the ability to mesh individual components and perform model simplification later is also a real advantage. ems often receives simplified thermal models from their suppliers of electronic units, usually the result of inferior analysis software. as a result the performance reported is usually marginal. "marginal performance sometimes means you restrict the amount of power you can have on an element such as a chip," comments dr. rheault. "luckily, with better tools such as tmg, these limitations are not present and often we can achieve better performance."
pierre boisvert summarizes, "one of the features we like the most about maya's tmg software is that it's an integrated package. it contains strong thermal modeling features such as thermal couplings, interfaces with other programs, varied element types, model validation and correlation as well as good simulation and radiation capabilities that we commonly use."
big antennas in small packages
tmg was a valuable asset for ems when they assisted the european space agency and matra marconi space (mms) in the design of the envisat advanced synthetic aperture array radar (asar) antenna. among their tasks was the design and analysis of the asar structure and feed network for the 10m by 1.2m large deployable antenna.
the large active array antenna, with stringent dimensional requirements, was subject to the effects of different operational modes as well as shadowing and varying albedo and sun conditions. the antenna contained several active elements on the radiating tiles that demanded minimal temperature variations to ensure unit reliability. of course minimizing mass was critical so the thermal control hardware had to be kept to a minimum. among other things, this meant that no deployable stiffening structure could be used to control distortion -- a formidable challenge for this type of array.
ems used maya's tmg to analyze the antenna. the modeling included active and passive mechanisms for hold down, release and deployment, power supply units, feed networks, t/r modules, and support structure. ems's team evaluated both stowed and deployed configurations and incorporated thermal design options that helped ensure the antenna could function reliably in the harsh environment. tmg was able to simulate the operation of thermostats and the system as a whole during all stages of operation. models pinpointed critical temperature limits in the bearings, motors and other sensitive equipment.
ems has met the challenge for canada's advanced 5.3 ghz space-based synthetic aperture radar.
the radarsat imaging system is unique in that it provides full global coverage,
brought about by arctic and antarctic alternative satellite bus orientations. ems designed and built
the deployable 15m x 1.5m radiating panel structure for the sar antenna. the antenna provides
for reconfigurable beam-shaping in the elevation plane in order to allow advanced sar imaging
modes such as scansar. its all-aluminum construction and special temperature-compensated design
features enable the electrical performance of the antenna to be maintained over the wide
temperature ranges implied by the arctic/antarctic requirement.
tmg's direct solver access was also very popular. "it is another attractive feature that allows us to verify how the analysis is being performed while permitting us to incorporate custom subroutines to support our activities," explains pierre boisvert. over 900 simulations and sensitivity analyses were run to validate all the possible operational scenarios. "when running several simulations," says boisvert, "it's a lot easier to use an integrated package like tmg and combine external thermal models and custom sub-routines." as a result, the entire antenna supporting structure was optimized to achieve maximum stability and acceptable operating/storage temperature performance.
tmg's solver interface features also eased the exchange of thermal analysis data between ems and its european customers. tmg provides input files for trasys, esatan or sinda applications while accepting output files from both sinda and esatan.
ems telemetry and telecommand (tt&c) antennas have been used on many satellites
including msat (pictured here). ems tt&c antennas reflect a simple, low-cost, high-performance design.
depending upon the coverage requirements, designs include bicone antennas, global horns,
right loaded open ended waveguides and dielectric loaded horns.
just-in-time and innovative broadband reflector antenna design
ems must meet just-in-time delivery schedules, leaner budgets, and stringent requirements imposed on mass, volume and power that continue to challenge established designs. all spacecraft reflector antennas possess design challenges but large broadband reflector antennas face unique challenges. these antennas often must be highly coupled to the satellite's thermal control systems. component temperatures may vary quickly between 60°c and -160°c.
innovative thermal design and control systems are required to dissipate the high heat load on the antenna and feed systems. tmg has been key to meeting these challenges for the antenna and feed system design on matra marconi's st-1 spacecraft and alcatel's thaicom ill satellite.
pierre boisvert notes, "no matter what design changes occur, material changes, modifications to the antenna shape or control systems, tmg can perform the modifications quickly, providing us with new simulation results. tmg's ability to perform coupled conduction and radiation analysis is a big plus and provides ems with a competitive advantage. typically our competitors require much more time to perform their analyses or must use established models and designs. ems can meet schedule deadlines and design optimal solutions for their customer. tmg is able to accommodate our changing needs in meeting shorter and shorter delivery schedules."
sylvain rheault agrees, "when it comes to incorporating design changes, tmg produces results a lot faster than any other package we have seen."
features that don't come in a box
tmg will continue to meet ems's simulation and thermal design requirements for years to come. features such as tmg's open architecture, its external solver interface, its ability to calculate thermal couplings using dissimilar meshes, and its powerful orbital and environmental heating capabilities all contribute to an integrated time saving approach to spacecraft analysis.
but one of its best features, according to pierre boisvert, is the one that doesn't come in the box. "one of the nicest things about working with maya is that when we have a question we just get on the phone and call. maya's engineers are knowledgeable and we get our questions addressed quickly - that's a big plus."
maya heat transfer technologies ltd.
4999 st. catherine st. west, suite 400
montreal, quebec, h3z 1t3
visit maya at www.mayahtt.com
©1999, maya heat transfer technologies ltd.
i-deas and i-deas master series are trademarks of structural dynamics research corporation.
images courtesy of ems technologies inc.