Engineering News

By Design News Staff -- Design News, April 6, 1997

Saturn has rocket scientists thinking big again

Pasadena, CA--Cassini is a Cadillac among econo-box spacecraft designed for a smaller-is-better universe. It recalls the halcyon years of big science, big budgets, and big dreams for America's space program.

Now undergoing a final battery of testing at NASA's Jet Propulsion Lab in preparation for an October launch, Cassini will be the most complex, capable, and expensive object the U.S. has ever hurled into the nether regions of the solar system. Cassini's cargo of liquid-fuel propellant alone exceeds the combined mass of the Galileo and Voyager spacecraft.

A new generation of reliable components--such as solid-state data recorders, solid-state power switches, very-high-speed integrated circuits, and application-specific integrated circuits--replaces hundreds of traditional components. The Cassini mission also represents a vast international engineering effort, with credit going to Italy and France for design and inspiration.

Saturn is the prize. The spacecraft, like its namesake, Giovanni Domenico Cassini, a 17th century Genoese engineer and astronomer who became director of the Paris Observatory, owes its career to a widespread fascination with the ringed planet. Cassini will carry 12 sets of scientific instruments and subsystems for mapping, measuring, and analyzing Saturn and its environs upon its scheduled arrival in June, 2004.

In addition, Cassini carries the European Space Agency (ESA)-developed Huygens probe. The spacecraft will deposit the probe into the atmosphere of Titan, Saturn's largest moon, carrying six more experiment packages. The probe is named for Dutch astronomer and Cassini contemporary Christian Huygens, who discovered Titan and identified Saturn's ring system.

More ominously, the sixth planet is named for the titan of mythology who ate his children to avoid possible patricide. Engineers are keen to avoid offering up their addition to the Saturn system as a rich dessert.

Saturn family planning. "The most challenging aspect of the Cassini mission from a design standpoint is its trajectory," says Chris Jones, Cassini spacecraft development manager at JPL. It will require almost seven years for the spacecraft to reach Saturn by a route that will take it twice past Venus, back around Earth, then to Jupiter, accelerating at each encounter.

Cassini will keep its bearings with the help of an innovative wine-glass gyro from Litton that senses attitude using a permanent standing wave. The command and data subsystem, running on computers developed by Lockheed Martin Federal Systems, includes fault-protection software. In the event of an emergency, algorithms place the spacecraft in a neutral condition for up to two weeks at a time while a fix is engineered back on Earth. Two low-gain antennas back up the high-gain antenna, developed by the Italian Space Agency, ensuring command and control data transfer.

TRW designed the solid-state data recorders with no moving parts to jam: Galileo has been experiencing problems with its mechanical tape recorder. Cassini flies two recorders, each with 2-Gbyte capacity. Spacecraft reliability is also enhanced through the use of 192 solid-state switches supplied by Honeywell and CTS Corp. (West Lafayette, IN) that ramp up voltage for soft turn-ons. In the event of a failure, the afflicted switch will automatically shut off the system it serves, preventing a crippling power drain.

"Design requirements specify that no single point of failure can terminate the mission," Jones says. "Therefore, we designed Cassini with an architecture of redundancy and fault tolerance."

Finding out if components and subsystems will perform as advertised is the concern of Gary Parker, head of the test and integration portion of the program. "The fact we've been doing this for years allows us to proceed with some confidence," Parker says. "Our testing is designed to see whether new and proven technologies will function under conditions Cassini will experience."

A Cassini Developmental Test Model--identical to the flight version--was blasted with launch-level vibrations in an acoustic chamber at the JPL. The same model was alternately baked and cooled in a thermal/vacuum chamber.

After the Developmental Model checked out, the flight version was subjected to the same rigorous trials. According to development manager Jones, Cassini came through fine and is now ready to be fitted with its payload.

"We don't have enough money to include science instruments in the testbed," says Bill Fawcett, manager of instrumentation and payload for the project. Cassini is flying several unique and pricey items that nobody wants to break on the ground. Most of the equipment will be checked out rather gingerly in the lab before final assembly.

 The first time the full scientific package will operate together will be in space, where there's no second chance. Failure of a given piece of equipment will not affect other aspects of the mission, however. Assures Fawcett: "There are no show-stoppers."

Going down. Perhaps the most challenging integration problem was ensuring a perfect fit between the Cassini orbiter and the Huygens Titan probe, which is designed for a parachute descent through Titan's atmosphere lasting up to three hours.

The JPL's Don Kindt, manager of the Cassini/Huygens integration effort, says weekly teleconferences between the ESA and NASA teams help keep the effectively distinct projects in step. Although Cassini and Huygens have different missions, Cassini is responsible for delivering the latter on target, for supplying power on the way, and relaying Huygens telemetry back to Earth. Issues such as voltage and data-transfer standards had to be worked out.

More complex was the mechanism that attaches Huygens to Cassini, and enables separation at the proper time. Kindt points out that while Huygens appears similar to the Jovian atmosphere probe carried by Galileo, mission parameters imposed many design differences.

The Galileo probe was mounted at one end of the orbiter, blocking the main engines and facing Jupiter. (The orbiter's high-gain antenna, which never opened properly, is located on the other end, facing Earth.) The probe was released well before the main engines fired on approach to Jupiter orbit. This arrangement permitted a simple release mechanism.

The Cassini/Huygens separation subsystem (SEPS) is more elaborate. The main engines must fire before release to slow the probedown before it approaches the comparatively rarefied atmosphere of Titan. Therefore, Huygens is mounted on the side of the orbiter, clear of the engines. The SEPS provides the orbiter/probe structural load path and electrical attachment, and supports the separation device.

This device incorporates three stainless-steel springs that provide separation force; three guiding devices, each with two axial rollers that follow a T-shaped helical track for orienting the probe on release; a carbon fiber ring to compensate for dissymmetry in orbiter truss loads and to provide necessary stiffness; and three pyronuts to secure everything in place prior to separation. Extensive testing has verified the designs, says Kindt.

One final issue: As it stands, Cassini will be entrusted to only the second launch of a Titan IV with the new Solid Rocket Motor Upgrade. This puts the mission to Saturn near enough to the front of the queue to make some members of the Cassini team nervous. "Second is fine," asserts payload manager Fawcett. "We absolutely do not want to be first."

Michael Puttré, Associate Editor

Aircraft antenna 'fools' Mother Nature

Glendale, AZ--Federal aviation law requires that all U.S. commercial airlines install a Traffic Alert and Collision Avoidance System (TCAS) on all of their aircraft. In addition, although not legally required, many private corporate jets have a similar system.

These systems operate by sending out electronic signals to which other aircraft respond. The TCAS antenna, an integral part of the system, transmits and receives these electronic signals. If planes are on a potential collision course, on-board computers instruct one of the planes to climb and the other to descend. The antenna mounts on either the top or underbelly of the aircraft's exterior.

The Business and Commuter Aviation Systems Div. of Honeywell produces such a TCAS. The system's antenna, which resembles a Frisbee, measures about 1 inch thick and 10 inches in diameter. It features four active metal components that act as sensing elements.

Honeywell realized it needed to protect the antenna from wind, rain, snow, and any other elements that Mother Nature could throw at it. Lightning strikes, for example, posed a serious problem.

To make certain the antenna could survive these weather attacks, Honeywell sought the assistance of a company that could take the project from beginning to end. It found that company in McKechnie Plastic Components, Minneapolis. Not only did McKechnie help Honeywell incorporate a protective molded brass insert into the device for lighting protection and structural support, it assisted in the redesign of a plastic covering for the mounted antenna to eliminate stress cracks.

"Whether the plane was going to be cruising at a high altitude or just sitting on an open tarmac between flights, we had to anticipate potential problems and produce a covering that could withstand temperatures from -55C to 100C," says Bill Beningfield, Honeywell's director of radio-frequency products.

Honeywell had experienced resin quality problems in the early stages of the project. In response, McKechnie opted to use a polyethersulfone (PES) from LNP Engineering Plastics, Exton, PA, for the covering. The 15% glass-filled material, Thermocomp® JF-1003EM, possesses excellent mechanical properties, offers high-temperature and erosion resistance, is flame retardant, and is transparent to other radar frequencies. Moreover, McKechnie could process the material on a standard molding machine because of its rigid, tough, and stable formula and its low mold shrinkage during processing.

"It was a bit of a mystery as to why the cracking had occurred," recalls McKechnie Customer Account Specialist Keith Rhein. "We held a brainstorming session and brought in some of the suppliers of the parts and materials for their input."

The session resulted in McKechnie producing some new samples, inspecting them with Honeywell representatives, identifying which samples would achieve the best results, and, most importantly, pinpointing the best cycle run. As it turned out, the PES material contributed to the reduction of stress cracking. Only minor adjustments were needed on the tooling.

McKechnie also found that the PES had enough dielectric strength to withstand the high voltage of a lightning strike. Brass needed to be incorporated into the covering as a conductive element to protect the electronic components within the antenna. In addition, the brass insert provided added structural support for the antenna.

"A key issue that had to be addressed was making sure that the plastic wall was thick enough to handle the insert molding of the brass without causing cracking," notes Rhein. "We looked at the different options, completed some test runs, and achieved Honeywell's project objectives."

"The bottom line is that, regardless of the initial causes, we haven't had any stress cracking problems since the brainstorming session," says Sue Ohnstad, McKechnie quality team leader for commercial products.

CAD keeps play fun and safe

Charlotte, NC--We've all seen them strategically positioned in front of fast-food restaurants: the brightly colored playgrounds meant to keep kids occupied for harried parents. The engineers at Soft Play Inc. must develop and manufacture many of these recreation centers with both fun and safety in mind.

Each PLAYPARK facility produced by Soft Play is tailored to the architectural, engineering, and application constraints of its environment. "We modify nearly 100% of our standard components for every new installation," explains John Bernesser, Soft Play's senior design technician. This ensures that each job poses a fresh engineering challenge.

Bernesser uses Euclid 3 from Matra Datavision, Andover, MA, to create the framework for all the fun and games. "I've come to rely on CAD, especially Euclid 3, to do the job right in a timely way," he says.

A PLAYPARK installation might cover 4,000 sq ft, requiring a framework with a mile and a half of steel pipe. Such a framework requires about 40 different types of fittings and could have 1,200 fittings overall. Prior to using a CAD system, it took Bernesser six weeks to choose the correct fitting. Now the process takes five days.

The linchpin of Soft Play's Euclid 3 design software is a logic routine that automatically calculates the appropriate standard fitting for each junction in a framework. Bernesser then creates a 3-D schematic using Euclid 3's design tools. The software generates pipe designs from solid geometry, following its logic. Bernesser determines how the pipes should be secured to one another.

Soft Play's use of Euclid 3 has also improved customer service. Euclid 3 assists in preparing parts lists and assembly documentation for use by Soft Play's installation teams.

IR camera helps keep Apple cool

Cupertino, CA--An IR camera enables design engineers at Apple Computer's Newton Systems Group (N.S.G.) to identify sources of excessive heat in porta-ble computers.

In the setup used at Apple, a Thermovision® 900 from AGEMA Infrared Systems Inc., Secaucus, NJ, helps verify the design of new battery packs and power-supply units. Apple uses these subsystems in the new Newton® OS mobile computers.

"We must deal with heat generated by closely packed components without the benefit of air vents," says Conrad Rogers, manager, analog engineering for N.S.G. "The 900 lets us calculate junction temperature at critical terminal points to find any potentially troublesome hot spots."

The alternative to this approach--an electrical check--would require determining the voltage seen by each component. That value would allow engineers to discover, by extrapolation, the heat the component generates. Compared to this procedure, the IR scan significantly reduces the time needed to find junction temperatures. Technician Steve Kehres points out that the AGEMA camera also allows engineers to observe the power supply interacting with the Newton's CPU, LCD, logic, and memory boards.

Software supplied with the camera lets engineers calculate the temperatures of components hidden from the camera's direct view. Called COMPLETION, the package extrapolates the image of a component after removal from its normal environment. This backward extrapolation recreates the image that would have been produced if the camera had imaged the component directly.

Velcro-wrapped armor saves lives in Bosnia

Waltham, MA--In December 1995, a few dedicated workers at Foster-Miller Inc. toiled in their shop for 72 hours straight to meet a critical deadline. They weren't Santa's elves, but their achievement may be the stuff of legend. The customer: the U.S. Air Force. The product: special armor plating for air transport planes going to Bosnia.

The Air Force was sending units to supply the aid mission. Although it was a short mission, the Air Force needed to protect the C-130s, C-141s, and C-17s not pre-equipped with armor because of weight and payload considerations. The planes would be sitting ducks in volatile Bosnia.

Foster-Miller subsidiary LAST® Armor produced enough of the portable armor to protect the flight crews of 10 C-17s in just 10 days. Under normal circumstances, this would have taken six months. LAST doubled its staff by borrowing nine people from the headquarters office. Everyone pitched in, including Vice President Marty Smirlock, who worked on the sewing machines.

At first, the concept for this technology seemed comical. Using Velcro® to attach armor in the field? Crazy though it seemed, it worked. The armor, produced in kits, fits a specific armored vehicle, airplane, or helicopter. It takes about three hours to install the armor on a C-17 using no special tools.

Sheets of the ultra-strong hook material, made to LAST's specifications by Velcro, are layered with special ceramic or composite tiles, then literally stuck onto aircraft. The kits fit together like big jigsaw puzzles.

The tiles break the impact of incoming ordnance, acting like a catcher's mitt. They weigh less than half that of comparable steel armor. When tiles are damaged, they can be quickly and easily removed and replaced.

The Bosnia mission was not the first for the armor. It also saw duty in Saudi Arabia during Operation Desert Storm.

Thermal imaging system moves to PC

Portland, OR--Engineers who monitor thermal events that occur over time can record more than 20 minutes worth of real-time data using a new unit from Flir Systems Inc. Previously, real-time thermal imaging was limited to less than one minute.

Available as either a portable computer or in a minitower configuration, Tracer offers an open architecture, long-duration recording, and no data loss because it doesn't use data compression. Applications include process control, nondestructive testing, condition monitoring, preventative maintenance, and research and development. For example, the system could help determine how a piece of plastic cools after being removed from a mold.

Tracer combines a high-resolution thermal imaging camera with a Pentium-based PC, digital video recording system, and Windows 95-based analysis software. In the $69,000 base configuration, it can record five minutes of activity, capturing up to 9.3 Mbytes/sec of temperature data. Twenty minutes of data collected at 60 Hz requires expanding the Tracer's internal drive capacity to 18 Gbytes. (Capacity is externallyexpandable to any amount you can afford.) However, at less than 60 Hz, users can record thermal sequences for hours or days.

The system senses temperature differences of -0.1C at 30C, and can measure the temperature of objects from -10 to 2,000C with an accuracy of ±2%. Using a 12-bit dynamic range, Tracer digitizes temperature information across 4,096 thermal levels. The video camera measures temperature at 78,080 points via a 320×244 focal plane array.

Because the system is PC based, users can export data to popular spreadsheets or database programs for analysis, and upgrade the system as new PC technology emerges. Also, users can send video clips and text data to colleagues at remote sites or to another computer on a network

Analysis tools include user-definable recording rates, areas, record lengths, alarms, and trigger locations with pre- and post-trigger storage. Accessories include wide-angle and telephoto lenses, playback/analysis software for a secondary PC, internal and external disk drives, and 100-ft camera cables.

Flow detection drives tankless water heater

Conroe, TX--A new patented tankless water heater only heats water when someone turns on a faucet.

The Seisco^TM on-demand water heater's control system relies upon flow/no-flow detection to determine when it should energize each of the unit's heating elements. The temperature sensors used for flow/no-flow determination also compare water temperature to setpoint. During operation, the control system provides variable energization of each element so that during use, all elements are powered to the same energy level. The system requires 6 to 7 seconds to produce outlet water heated to the setpoint temperature.

The residential version of the water heater employs four screw-type 7,000W heating elements in four chambers. "We control the power to each of four heating elements so that there's a balanced load, and all the elements are coming up at the same time, but not in series," says David Seitz of Microtherm Corp. "Because of the configuration, we're able to look throughout the entire four chambers along the flow path and know exactly what direction the temperature's moving and respond very rapidly. So the end result, when you use the heater, is that it's so responsive you don't recognize a difference between using it and a regular water heater."

Wattage delivered to each heating element normally amounts to less than 60% of the element's rating. When water flows through a chamber, its outlet temperature sensor sees a higher temperature than that at the inlet sensor. At shutdown, the inlet sensor sees a temperature that exceeds outlet temperature. This inversion indicates a no-flow condition and the controls, a mixture of analog and digital electronics, shut down the heating elements.

Microtherm injection-molds the water heater's seven-piece heating chambers from Dupont Zytel® nylon resin. Based on nylon 612 polymer with 33% glass-fiber reinforcement and a heat stabilization system, Zytel 77G33HS1L meets requirements for contact with potable water and provides long-term heat stability. A cover made from another DuPont plastic, Crastin® PBT thermoplastic polyester, protects the system.

Seisco water heaters come with power ratings from 10 to 28 kW. Seitz points out that Microtherm's on-demand water heaters can function either as standalone units, or as booster units in series with such hot-water sources as solar heating systems or small conventional water heaters. In such applications, the Seisco water heater won't operate unless water temperature is below the setpoint.

"It's a joy to the power companies," says Seitz. "When people are showering, your storage tank water heaters are on during operation and they're on during recovery. So the demand starts stacking." By comparison, the Seisco water heater must be either on or off. And, according to Seitz, modeling demonstrates that diversity of use by individuals ensures that peak demand remains lower than it would be were regular storage-tank water heaters used.

Supercomputer software goes PC

King of Prussia, PA--Formerly available only on UNIX platforms, Satellite Tool Kit Visualization Option (STK/VO^TM) software from Analytical Graphics Inc. can now run on Pentium-class PCs. The package gives users a true 3-D time-driven analysis environment, allowing realistic object animations. Further, the software can help in making mission-critical decisions based on data displayed both numerically and graphically.

When initially offered, STK/VO's graphics manipulation capability required that users have access to high-end workstations, such as those offered by Silicon Graphics. Graphics accelerators and Pentium processors now make the software available on PCs, including laptops. On a PC, STK/VO's performance remains essentially the same as on workstations. "With a 133-MHz Pentium PC and a $2,000 graphics card, STK/VO runs as fast as it does on a high-end UNIX workstation," says AGI CEO Paul Graziani.

During Hubble Space Telescope (HST) Service Mission II, launched early in February, NASA engineers used STK/VO software to help monitor the position of HST and Space Shuttle Discovery relative to the sun. At NASA's Space Telescope Operations Control Center at Goddard Space Flight Center, engineers use STK/VO to translate numerical data on the shuttle's angle to the sun into 3-D graphics. This visual correlation allows engineers to evaluate sun and Earth illumination on the spacecraft.

The software can provide an animated 3-D view of HST looking along the sun-spacecraft vector. This view enhances the engineering team's ability to decide when to make attitude corrections to avoid out-of-limit thermal conditions. Also, STK's sensor constrain capabilities let users define the minimum allowable angle between the HST's boresight and sun vectors (the solar exclusion angle). Doing so is vital to protecting the Hubble's sensitive optics from direct sunlight.

Analytical Graphics Inc. developed STK/VO using a card from 3Dlabs' GLINT® line of graphics processors, which are based on the OpenGL® software interface. Other cards can also be used.

For more information on AGI's satellite analysis software, visit the company's website at http://www.stk.com

Survey respondent wins $700

Southfield, MI--Kevin J. Breier, an application engineer with Federal-Mogul Corp., is the winner of a $700 Comp-USA merchandise certificate for participating in the Design News OEM Directory survey.

Design News conducted the survey to discover how to improve the directory, which lists 6,500 suppliers of components, systems, materials, and engineering tools, and includes more than 2,600 product categories.

The information in the directory is also available on the Supply Chain Link Web site () and the Supply Chain Link CD-ROM. Look for the directory's 1998 edition this October.

To get your own copy of the Design News 1997 OEM Directory, phone (303) 470-4445

Polyimide pad propels printer

Irvine, CA--When you're up against a tight deadline, the last thing you want is to have the printer producing that essential report break down. That's what prompted Printronix Inc. to settle on a thermoplastic polyimide material for the anti-rotation pads in its line of matrix printers.

The anti-rotation pad provides a non-wearing surface that keeps the printing mechanism in an exact angular position for the lifetime of the printer. After exhibiting outstanding wear resistance in a 3,000-hour test, Printronix selected AURUM® JRF 3025 polyimide supplied by Mitsui Toastsu Chemicals Inc., Purchase, NY, for the injection-molded pads.

The tests involved about 20 graphite and PTFE lubricated pads machined from an AURUM stock shape. The tests were conducted at a temperature of 240F under a 10-lb load at 190 ft/min. The lubrication was a general-purpose M-3 grease; the mating material 410 stainless steel/R40.

The preliminary tests were followed by life tests in printers that accumulated more than 5,000 hours of operation. Only after passing these tests did Printronix give the go ahead to Putnam Precision Molding, Putnam, CT, to begin injection molding the pads on a commercial basis. The injection-molded components not only met Printronix's exacting performance standards, but were produced at a cost of about 50% less than conventional, non-injection-moldable polyimide.

Engineering systems to reduce global product lead times

Rochester, NY--To remain competitive, Xerox is synchronizing its design and manufacturing teams in North America, Brazil, Europe, and Japan. The company is currently implementing tools that improve engineering analysis, data access, and the ability to manage product development across the global enterprise. The driver? The need to reduce lead times and improve time to market (TTM) for new products.

The result of this initiative was a dual-pronged effort. To resolve system-integration hurdles and provide designers with the necessary computing power to solve complex engineering problems, Xerox first standardized engineering systems on a client/server architecture featuring Sun SPARC (and recently, UltraSPARC) servers and desktop workstations. It then developed a comprehensive CAD/CAE architecture encompassing design, analysis, simulation, and mathematical tools.

"When we put this architecture together, the main purpose was to standardize on a common set of best-in-class tools so we could take better advantage of our CAD/CAE resources," says Ravi Tulsyan, CAE leader of the engineering systems group at Xerox.

Docuplex, Xerox's document-management system, automates access to authorized engineering drawings, replacing the handling of hard copy, microfiche, tapes, and other forms of storage. Docuplex has been implemented as the worldwide image-management system at the company's engineering and production sites, linking those in New York, California, the UK, the Netherlands, France, Brazil, and Mexico.

With Docuplex, an engineer can consult a master index of drawings numbered according to part type and maintained on a local SPARCserver. Consequently, engineers can quickly retrieve electronic drawings in vector format, preserving the original detail and specifications.

Xerox is also seeking to master the storage process for its CAD designs by migrating to Structural Dynamics Research Corp.'s (SDRC) Metaphase product data-management (PDM) software.

The system runs under Solaris 2.0 and the Oracle 7 database, and includes a central metadata server and distributed servers at each site that contain the data files. Today, the system serves more than 300 users at Xerox's eastern U.S. and Canadian sites, with further rollout to more than 500 users outside North America planned by the end of 1997. The goal is to improve performance by tuning the Oracle database and to implement a new upgrade of Metaphase.

With the basic building blocks established, Xerox is looking to expand the functionality and the use of the engineering systems environment. "We must continue benchmarking the best hardware and software systems that we can provide to our users," says Korhan Sevenler, manager of engineering systems at Xerox. He adds, "Xerox has also been developing a benchmark time-to-market process and training our staff to use this environment. After all, these are only computer systems. The real benefit is achieved by a disciplined workforce using these applications smartly to their fullest extent."

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