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Figure 1. Detailed measurements of how the elevation of the Greenland and Antarctic ice sheets have changed over a 16-year timeframe. | All images courtesy

NASA

ICESat-2 Spacecraft relies on negative-stiffness vibration isolation for testing

By Steve Varma • Operations Manager • Minus K Technology

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NASA’s Ice, Cloud and Land Elevation Satellite-2 (ICESat-2), which

lifted off three years ago, has generated a comprehensive portrait of the complexities of ice sheet change and insights into the future of Greenland and Antarctica. The ICESat-2 measurements, when compared to the measurements taken by the original ICESat from 2003 to 2009, showed that in Antarctica the ice sheet is getting thicker in parts of the continent’s interior, likely as a result of increased snowfall. But the massive loss of ice from the continent’s margins (due to ocean warming) far outweighs any small gains in the interior.

“The new analysis reveals the ice sheets’ response to changes in climate with unprecedented detail, revealing clues as to why and how the ice sheets are reacting the way they are,” said Alex Gardner, a glaciologist at NASA’s Jet Propulsion Laboratory.

This is one of the first times that researchers have used laser altimetry to measure loss of the floating ice shelves around Antarctica simultaneously with loss of the continent’s ice sheet. The researchers found ice shelves are losing mass in West Antarctica, where many of the continent’s fastest-moving glaciers are located. Patterns of thinning over the ice shelves in West Antarctica show that Thwaites and Crosson ice shelves have thinned the most, an average of about 16-ft and 10-ft of ice per year, respectively.

Measuring by space lasers ICESat-2 spacecraft serves as a power and pointing platform for the mission’s single instrument, the Advanced Topographic Laser Altimeter System, or ATLAS. It is a space-based LIDAR (Light Detection and Ranging), which measures

distances by illuminating a target with a laser and analyzing the reflected light. ATLAS measures the travel time of laser photons from the satellite to Earth and back; computer programs use the travel time from multiple pulses to determine elevation.

“ATLAS required us to develop new technologies to get the measurements needed by scientists to advance the research,” said Doug McLennan, ICESat-2 Project Manager.

“That meant we had to engineer a satellite instrument that not only will collect incredibly precise data, but also will collect more than 250 times as many height measurements as its predecessor.”

As it circles Earth from pole to pole, ICESat-2 will measure ice heights along the same path in the polar regions four times a year, providing seasonal and annual monitoring of ice elevation changes. Beyond the poles, ICESat-2 will also measure the height of ocean and land surfaces, including forests.

As ICESat-2 orbits, ATLAS generates six green laser beams arranged in three pairs to

Figure 2. Artist rendering of ICESat-2 in space.

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Figure 3. Isolation structure in the thermal vacuum chamber.

Figure 4. Diagram of ICESat-2 in the thermal vacuum chamber.

better determine the surface’s slope and provide more ground coverage. Each beam pair is 2.1 miles apart across the beam track, and each beam in a pair is separated by 1.6 miles along the beam track.

The laser array is rotated 2° from the satellite’s ground track so that a beam pair track is separated by about 300 ft. ATLAS emits visible laser pulses at 532 nm wavelength. Though powerful, the laser is not hot enough to melt ice from its vantage point some 300 miles above the Earth.

The laser pulse rate combined with satellite speed results in ATLAS taking an elevation measurement every 28-in., akin to taking 130 images of a single football field. Measurements are taken every 2.3-ft along the satellite’s ground path.

The laser fires at a rate of 10,000 times a second. Each pulse sends out about 200 trillion photons, almost all of which are dispersed or deflected as the pulse travels to Earth’s surface and bounces back to the satellite. About a dozen photons from each pulse return to the instrument and are collected with a 2.6-ft beryllium telescope.

The instrument’s filters ensure that only photons with a wavelength of 532 nm are counted, and computer programs further identify photons likely to have come from the laser.

Ensuring ATLAS can last ATLAS went through an initial round of testing in the spring and summer of 2016 at NASA’s Goddard Space Flight Center as it was being assembled. The testing team jolted it on a vibration table, blasted it with sound to simulate a noisy rocket launch, then put it in a vacuum chamber to test it in both extreme heat and extreme cold temperatures.

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While ICESat-2 is in orbit, it goes from basking in the heat of the sun to freezing in Earth’s shadow every 90 minutes. So before launching the satellite into the harsh environment of space, Goddard engineers wanted to make sure that the laser instrument worked consistently day and night, whatever the temperature.

The vacuum chamber was configured with four vacuumcompatible 800CM-1CV negativestiffness vibration isolators to support the ATLAS instrument for the thermal vacuum testing. “The Minus K isolators’ primary use was inside the thermal chambers which did not have as stable of a mounting surface as we would have liked,” said Brian Simpson, mechanical lead for ATLAS testing. “The isolators were critical in cancelling out jitter introduced into our system by the facility.”

The ICESat-2 team worked around the clock to test ATLAS in a temperature-controlled vacuum chamber at Goddard, ensuring that its interconnected components worked together and functioned as expected.

“When we did these tests, we wanted to confirm that in the worst-case conditions on orbit, both hot and cold, with no air, you still get the expected performance that you want from the instrument,” said Melody Djam, system engineer at Goddard.

“It’s an extreme test.”

For the test, engineers calculated how hot the instrument will get on orbit either in full sun or in Earth’s shadow — then went 5° C beyond that to cover all bases in a “survival” test. With liquid nitrogen and heaters, the thermal vacuum then cycled four times between 55° C and -25° C. At each of those maximum or minimum temperatures, test engineers sent laser signals through a specially designed fiber optic cable that simulates laser light bouncing off Earth and returning to the spacecraft.

The science team had designed different scenarios that reflect light in different ways — a glacier in summer, DESIGN WORLD

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Aerospace/Defense for example, results in different photon returns than a forest in fall or an ocean under cloudy skies. And the instrument also must tell the difference between laser photons that it needs to count, and the static of background photons from natural sunlight. Plus, this must be done under the different temperatures that could cause materials to expand or contract.

Specifically-designed ground support equipment, or test fiber optics and lasers simulated all these scenarios, testing not only how the ATLAS detectors and electronics perform, but how the computer programs that will receive the data on Earth interpreted those returns.

“Because our integration and testing process is so long and involved, and because there are so many electronic interfaces, we really wanted to get most of those electronics together in the thermal vacuum tests to see how they all behaved,” said Cathy Richardson, ATLAS instrument project manager at Goddard.

“Problems that we might find during testing, we wouldn’t have otherwise found for another year. It’s a significant risk mitigator for us.”

“We really needed to see how everything plays off each other,” Richardson said. “What you care about is the flight hardware working together.”

And the avionics system performed well, she said, returning data that correlated with what the scientists expected to see.

Mapping subglacial lakes ICESat-2 has allowed scientists to precisely map subglacial lakes. The satellite measures the height of the ice surface, which, despite its enormous thickness, rises or falls as lakes fill or empty under the ice sheet.

Hydrology systems under the Antarctic ice sheet have been a mystery for decades. Scientists have hypothesized subglacial water exchange in Antarctica results from a combination of factors, including fluctuations in the pressure exerted by the massive weight of the ice above, the friction between the bed of the ice sheet and the rocks beneath, and heat coming up from the Earth below

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that is insulated by the thickness of the ice. That is a stark contrast from the Greenland ice sheet, where lakes at the bed of the ice fill with meltwater that has drained through cracks and holes on the surface.

Precise measurements of basal meltwater are crucial if scientists want to gain a better understanding of Antarctica’s subglacial plumbing system, and how all that freshwater might alter the speed of the ice sheet above or the circulation of the ocean into which it ultimately flows.

In 2007, Helen Amanda Fricker made a breakthrough that helped update classical understanding of subglacial lakes in Antarctica. Using data from the original ICESat, Fricker found for the first time that under Antarctica’s fast flowing ice streams, an entire network of lakes connect with one another, filling and draining actively over time. Before, these lakes were thought to hold meltwater statically, without filling and draining.

Recently, Fricker and another team of scientists explored this connection between freshwater and the Southern Ocean — but this time by looking at lakes near the surface of an ice shelf, a large slab of ice that floats on the ocean as an extension of the ice sheet. Their study reported that a large, ice-covered lake collapsed abruptly in 2019 after a crack or fracture opened from the lake floor to the base of Amery Ice Shelf in East Antarctica.

With data from ICESat-2, the team analyzed the rugged change on the landscape of the ice shelf. The event left a doline, or sinkhole, a dramatic depression of about four square miles (about 10 square kilometers), or more than three times the size of New York City’s Central Park. The crack funneled nearly 200 billion gallons of freshwater from the surface of the ice shelf into the ocean below within three days.

During the summer, thousands of turquoise meltwater lakes adorn the bright white surface of Antarctica’s ice

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shelves. But this abrupt event occurred in the middle of the winter, when scientists expect water on the surface of the ice shelf to be completely frozen. Because ICESat-2 orbits Earth with exactly repeating ground tracks, its laser beams can show the dramatic change in the terrain before and after the lake drained, even during the darkness of polar winter.

Meltwater lakes and streams on Antarctica’s ice shelves are common during the warmer months. And because scientists expect these meltwater lakes to be more common as air temperatures warm, the risk of hydrofracturing could also increase in coming decades. Still, the team concluded it is too early to determine whether warming in Antarctica’s climate caused the demise of the observed lake on Amery Ice Shelf.

Witnessing the formation of a doline with altimetry data was a rare opportunity, but it is also the type of event glaciologists need to analyze in order to study all of the ice dynamics that are relevant in models of Antarctica.

“We have learned so much about ice sheet dynamic processes from satellite altimetry, it is vital that we plan for the next generation of altimeter satellites to continue this record,” Fricker said.

The new study provides critical insight for spotting new subglacial lakes from space, as well as for assessing how this hidden plumbing system influences the speed at which ice slips into the Southern Ocean, adding freshwater that may alter its circulation and ecosystems. This has allowed scientists to improve their maps of these hidden lake systems under the West Antarctic ice sheet, as well as discovering two more of these active subglacial lakes AD .

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Aerospace/Defense

TriStar,

a misunderstood failure of design

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By Charles Tschaggeny • Tschaggeny Design

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JET airplane and exited the world of commercial aircraft for good. For Lockheed, its latest passenger jet had been heralded as a technological marvel but was, in fact, a business disaster.

The TriStar is a fascinating story that clearly illustrates fundamental concepts about product development and the importance of focused innovation. It reveals how Lockheed lost sight of the principal objectives of an industrydefining tender and how leaders allowed their own goals to cloud the basic needs of their customer. Lockheed focused on impressing the entire aircraft industry with their technical wonder, but in doing so, its leaders failed to consider the market’s direction — ironically, the problem the tender was designed to address.

Until the early 1960s, Lockheed had been one of the world’s prominent passenger plane manufacturers. Aircraft such as the Constellation and the L-188 were well-liked by passengers and airlines. Technically, they were cutting-edge and led the aircraft industry into new directions. However, while Lockheed was seen to be successful in commercial aviation, it was the other side of the business — military projects — which provided its most reliable source of income.

The late 1950s witnessed Lockheed release a succession of pioneering military aircraft, including the C-130 and the Galaxy. Add to these secret projects such as the iconic Blackbird SR-71, the U2 spy plane, and the Starfighter, and it’s easy to understand why the military facet of Lockheed’s business demanded most of the company’s time, resources, and finances. So much so that, in fact, in 1961, Lockheed decided to withdraw from the commercial passenger market.

This decision, however, proved to be shortsighted.

Throughout the 1960s, the landscape of the commercial aviation industry had transformed entirely, and towards the end of the decade, enormous opportunities for aircraft manufacturers started to appear. The ongoing spacerace and the advent of the Jet Age in the late 1950s saw an emphasis on

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speed and technology. Initially, this was a glamourous period for aviation, and traveling by jet was the privilege of the few, but as costs began to lower, air travel became more mainstream. By the late 1960s, the whole industry had transformed.

Airlines now prioritized efficiency and cost over glamour. They had started to move more people on shorter routes.

The industry now desired an aircraft that could carry more passengers even further, and with less fuel. Airplane manufacturers were eager to meet this demand and vied to develop and supply such aircraft. Obligingly, Lockheed threw their hat back in the ring and announced a return to the commercial aviation business.

It was American Airlines (AA) in the mid-60s that had foreseen the future need for a wide-body, medium-to-long-range airplane that could transport large numbers of passengers. This would have to be an aircraft capable of flying internationally but still use AA’s existing airport infrastructure.

AA approached Boeing, Douglas, and Lockheed about designing a plane to meet their requirements.

Boeing was immediately out of the picture. AA needed an aircraft that could carry more passengers than the 737, but

April 2022

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In 1984, Lockheed ceased production of the L1011 TriStar

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which at that time, only permitted twin-engine aircraft to fly no further than 60 minutes from the nearest available airfield. These regulations made a twin-engine transatlantic route uneconomical and practically impossible. In addition, the threeengine design achieved a higher takeoff performance, which allowed the plane to use existing runways.

So, while the two aircraft concepts appeared similar at first sight, the truth was the opposite. The development paths of both manufacturers could not have been more different from one another.

Douglas was very constrained by budget and was highly costsensitive, and accordingly, its design approach was very conservative. The company simply leveraged the design of its existing DC-8 to save time and

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it needed to be smaller and more fuel-efficient than the 747. Boeing didn’t have a solution for this, and with resources focused on developing future variants of the 737 and 747, they turned down the opportunity.

Douglas and Lockheed accepted the tender, and in doing so, the DC-10 and the TriStar projects were born.

The DC-10 and the TriStar were configured similarly — not a surprise since they were responses to the same tender. They were both widebody aircraft that could hold more passengers than the 737 but fewer than the 747.

Interestingly, both companies submitted a three-engine design. AA would have ideally preferred a twinengine solution but understood the limitations of current-day jet-engines, in addition to the ETOPS regulations,

cost. In essence, the new DC-10, in many ways, was merely enlarged and modernized DC-8 technology.

Alternatively, Lockheed believed its competitive advantage lay in using the most advanced technology of the day. For many, the result was magnificent. The TriStar was undoubtedly the most advanced commercial airplane of its day. The seemingly endless list of advanced technology the TriStar employed is

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staggering. Innovations that would set the industry’s standard for many decades to come. Some cutting-edge technologies used on the TriStar such as autopilot, direct lift control, and the actual manufacturing processes were transformative. The aircraft was powered by three technically brilliant jet engines, developed from scratch

by Rolls-Royce to Lockheed’s lofty requirements.

Along with the advanced technology, the TriStar was a comfortable place for passengers, with its wide seats and large, tranquil open cabin. In addition, it featured new amenities such as an entertainment system, a portable water system, and even lounges.

However, developing these advanced technologies was highly complicated and time-consuming, significantly delaying the entire project. In particular, the development of the RB211 engines caused RollsRoyce such severe financial problems that it resulted in the re-structure and financing of the whole company.

Eventually, after Rolls-Royce had resolved these monumental issues, the entire TriStar project was certified 18 months behind schedule.

By this time, the DC-10 had already commenced service.

Development delays had stalled TriStar sales for almost two years, and unsurprisingly AA could wait no longer and went with the DC-10.

That wasn’t the end of the TriStar.

Although dogged with issues in the development and first production schedules, once finally launched, it went on to gain an excellent reputation for its reliability, the economy of operation, and low noise emissions and, in time, became a favorite for passengers.

However, it was expensive, and ultimately Lockheed struggled to sell the TriStar. In 1984, the company stopped production after only selling 249 planes; 500 had been needed to break even. The TriStar program had DESIGN WORLD

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almost bankrupted Lockheed and caused it to again exit the commercial aircraft business and focus solely on military aircraft.

An alternative perspective The TriStar’s development and ultimate demise are fascinating and have been retold many times since.

It’s a tale that can teach different things and act as a warning to be cautious in relationships with suppliers. Many others highlight the innovative advantage of taking the more straightforward route to the win. Most would agree there are undoubtedly aspects of truth in all of these and, indeed, lessons to be learned.

First is a typical view, and a common mistake in most industries — that there can only ever be one winner. The thought, in this case, is that the airline industry could not support two planes competing for the same market. The general conclusion is that the DC-10 killed off the TriStar.

The aircraft designed to meet the same tender simply beat Lockheed to the prize. One company beat another to win the tender.

However, there is a problem here: all these lessons stem draw their conclusions based on the same question. How did the DC-10 win the tender and kill off the TriStar? Is this even the right question? Possibly, it only represents a short-term view and doesn’t examine the broader picture.

Once production had begun, the life stories of the DC-10 and the TriStar were remarkably similar. Both aircraft were produced until the mid-80s.

The cheaper DC-10 sold 386 units, while the technically superior and more expensive Tristar sold 250. There was no outright winner when you compare it to other successful aircraft.

In contrast, the Boeing 747 and 737 have been in production for more than 50 years and have sold 1,600 and 11,000 units, respectively. That’s winning.

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Taking this into account, we can flip the perspective and ask a far more insightful question. What led to the failure of both the Tristar and the DC-10?

For the answer, we need not limit ourselves to the U.S. but look further afield to Europe. An innovative plane from a new manufacturer, Airbus, entered the market after these two planes and eventually killed them both off. This plane was the twin-engine A300.

Airbus was either lucky or very calculated, depending on whom you talk to. The company understood that the outdated ETOPS regulations were created for a previous generation of aircraft and predicted that the reliability and performance of modern jet engines had to be recognized and the regulations updated accordingly.

It gambled that ever-improving jetengine technology, together with an exemplary performance record for the A300 for non-transatlantic flights, would lead to ETOPS certification.

Airbus was right.

In 1977, the Airbus A300 became the first twin-engine aircraft to be ETOPS-compliant and certified for transatlantic flights. And that was it really for both TriStar and the DC10. With three planes going after the same market segment, airlines went with the less expensive plane to operate and purchase. The TriStar was too expensive and the DC-10 had safety issues. Airbus may have been fortunate or remarkably smart to have the regulations to go their way. Still, the A300 was an innovative and compelling aircraft that could not be ignored — even by the Americancentric U.S. airlines of the time.

What can we learn from TriStar?

When we examine the troubled origins of TriStar and its development, there are three high-level takeaways that we can learn concerning product development and the innovation process. www.designworldonline.com

Designs are perishable.

Sooner or later, the job you are doing will be done better by someone else with a new perspective or approach. Even if these conflict with existing perceptions or taboos, a better methodology will always prevail.

1

Focus – don’t get distracted. At the time of AA’s tender, it and the other airlines were rapidly expanding. They needed an economical people-mover available in a reasonably short time frame.

Literally, they required the development of an off-the-shelf flying bus.

Lockheed took it on itself to undertake a research and development project and delivered a technological marvel that was neither cheaper (purchase price or operational price) nor available quicker than the competition. Specifically, AA had asked manufacturers to do a development project and quickly deliver a solution to fit their immediate requirements. It wasn’t looking for a R&D project.

This is an important distinction.

Since we commonly refer to R&D as the same activity, people tend to believe they are the same activity, but of course, they’re not — the output of research is knowledge. The output of development is a product. Research feeds into development, but research does not result in a product unless the development cycle is complete.

Lockheed simply viewed AA’s tender as a way to re-enter the commercial aircraft market, and they intended to make April 2022

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Aerospace/Defense a splash with the TriStar. Lockheed’s focus was not to provide an aircraft that would perform its job well. The company wanted to showcase its technical capabilities, and the best way to do this was to add every possible new technology to the plane. If that technology didn’t yet exist, Lockheed would invent it. And it did so at great cost, resulting in a TriStar only slightly cheaper than the much larger 747 and significantly more expensive than the DC-10.

The problem for Lockheed was that while all this technology packed into the TriStar was truly impressive, it didn’t help the TriStar differentiate itself from the competition. Range, passenger capacity, and fuel efficiency were practically the same as the DC-10.

Technology had added significant costs to the plane and delayed its release. While the aircraft was incredibly advanced, none of this technical brilliance made a substantial difference to an airline’s bottom line. The airline would have accepted and purchased a plane that was initially more expensive if it would have benefited from cheaper operating costs. However, since both aircraft were tri-engine designs, they had nearly identical operating expenses.

Lesson: Be sure to review the exact customer requirements — focus on getting your product to do the required job. Be careful to not get too creative and add features for the sake of features.

Focus on the target and don’t look beyond the mark. Remember, research and development are separate steps in the product development process. Don’t get caught up in making unnecessary research and development loops in your product development cycle, creating features that were never requested — and which your customer may not want to pay extra for.

2

Suppliers – you’re dependent on them. Lockheed’s desire to supply cutting-edge technology led them to choose Rolls Royce to develop a completely new motor for the

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TriStar. The RB211 engine Rolls Royce developed was indeed pioneering, producing more thrust and yet was smaller than other motors of the time.

However, the development needed to achieve such advanced innovation was extremely difficult, costly, and time-consuming. So much so, in fact, that the development of this motor forced Rolls Royce into receivership.

Already, it was too late for Lockheed to change motors or suppliers because the TriStar had been practically designed around these motors, and Lockheed was too advanced in development to contemplate a redesign. While Lockheed had faced other lesser problems during development, uncertainly, Rolls-Royce’s financial woes were a substantial factor in the two-year delay in bringing TriStar into production.

If Rolls-Royce couldn’t finish the development of the engine, then Lockheed wouldn’t have a plane. This implication for Lockheed was gigantic and, realistically, would have found itself in a similar financial position to Rolls-Royce. Fortunately, both the U.S. and British governments were able to step in provide the security, guarantees, and, in the case of RollsRoyce, the funding to keep the project rolling.

Highlighting Rolls-Royce’s developmental fails and misdirected focus, it was then discovered that the prototype engines were not as reliable as desired. It was so focused on meeting performance requirements and finishing the design that RollsRoyce had sacrificed reliability — which, in the aircraft industry, is paramount.

Furthermore, the ongoing issues had delayed the development of vital, more powerful engine variants required for heavy cargo transportation. Exasperating AA executives further, these were also necessary for some of their existing airports with stringent accessibility and take-off criteria. By this time,

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the DC-10, itself a year later than expected, had already been in service for seven months and given Douglas a considerable market advantage.

Lesson: You go to suppliers for their expertise and capabilities, but their problems can quickly become your problems and affect your business. Even the best suppliers can and will have issues.

3

Innovation — keeping ahead of the curve. At the same time, AA identified the need for a wide-body, medium-to-long-range aircraft. On the other side of the Atlantic, Air France had arrived at the same conclusion. Air France’s tender led to the founding of a new airplane manufacturer, Airbus, and its twinengine A300. The concept would have the range and capacity of the TriStar and DC-10, but with only two engines, consuming 20-30% less fuel.

The two American airplane manufacturers probably didn’t feel overly threatened by this. The nonETOPS compliant A300 couldn’t operate the lucrative transatlantic flights with only two engines. And since Boeing had nothing similar in the pipeline, they only focused on each other as the competition. In addition, with the American-centric airlines and airplane manufacturers of the 1960s, the idea that a U.S. airline would buy anything but an American-made aircraft was unthinkable.

But Airbus had a plan; its management and strategists had studied the ETOPS regulations.

These regulations had been drawn up to govern aircraft from a different generation. Early jet engines and propeller aircraft from the 1960s didn’t have the reliability, durability, or power to cross the Atlantic confidently; Hence, the regulations limited the range of any two-engine aircraft to within an hour of the nearest airport.

They never conceived that a large airliner could maintain a safe altitude with only a single working engine.

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Airbus realized that it was only a matter of time before the reliability and performance of jet engines would get to a point where a twoengine passenger plane would force a change to the regulations and achieve ETOPS certification. Airbus also understood that in the short term, it would need to focus on shorter routes that did not need ETOPS. These were the less-lucrative markets that AA was not going after with its tender. Airbus could achieve sales and at the same time prove the airworthiness and reliability of the A300. Air France took delivery of the first A300 in May 1974.

Airbus had shrewdly calculated to intersect the trajectory of the regulations. The company was convinced that the combination of an impeccable safety record and reliable engines over the next few years would bring about a change to regulations by forcing ETOPS to recognize the safety and achievable range of twoengine jet aircraft. It took three years, but in 1977 the company succeeded in this.

Like Lockheed, Airbus viewed technology as the key differentiator.

However, Airbus did not incorporate technology for technologies’ sake.

It only included technologies that would increase the aircrafts’ safety, operational capacity, and profitability.

As a result of this approach, the A300 was reasonably priced, fuel-efficient, and adaptable. Unlike Lockheed, Airbus did not develop a new engine for the A300. It simply used an existing, proven engine.

When the A300 came on the market in 1974, it was a safe, versatile plane that was more efficient than any medium-to-long-range wide-body airplane. Innovative technologies were integral to the high performance and safety standards, making it the first ETOPS-compliant twin-engine aircraft. A safe and reliable aircraft with only two engines was something the airline industry had craved since AA first released their tender. With its ETOPS certification, the A300 could

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now directly compete against the TriStar and the DC-10 for transatlantic use.

Eastern Airlines, impressed with the A300’s fuel economy and adaptability, became its first U.S. customer, going on to order 34 aircraft in total. This was a double blow for both Lockheed and American aviation. Firstly, Eastern Airlines had previously ordered the TriStar. Now TriStar was losing orders. Secondly, before Eastern Airlines’ order, an American airline purchasing a foreignmade aircraft was unthinkable. Times had changed.

This purchase opened the door for the A300. Increasing amounts of orders from both U.S. and other global airlines heralded the beginning of the end for the TriStar and the DC-10, eventually pushing the triengine competition out of the market altogether.

Lesson: Designs are perishable.

Sooner or later, the job you are doing will be done better by someone else with a new perspective or approach.

Even if these conflict with existing perceptions or taboos, a better methodology will always prevail. AD

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Aerospace/Defense

Specifying MCUs

for satellites and spacecraft

By Jeff Shepard

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Figure 2: Space-qualified radiation-tolerant Ethernet transceivers and embedded MCUs are available based on widely deployed COTS and EP devices. | Microchip

There is not a single group of standards but a continuum of qualification criteria for the components and systems used in satellites and spacecraft (Figure 1). With the growth of low earth orbit (LEO) satellites where the environment is less demanding and where some satellites are expected to be replaced regularly with upgraded designs, the use of fully space-qualified components is often not necessary or cost-effective.

Enhanced Product (EP) devices can provide higher quality and reliability than standard commercial off-theshelf (COTS) components in those applications. These EP devices are typically plastic-encapsulated, compared with fully space-rated devices’ more rugged and more expensive hermetic packaging. Designers must understand the (physical and business) environment where the satellite will operate and specify components accordingly. Overspecification will be costly, but under specification can result in low reliability and shortened lifetimes.

EP devices can be certified to Government Electronics and Information Technology Association (GEIA)-STD-0002-1 for Aerospace Qualified Electronic Component (AQEC). They can also meet the qualification and processing requirements of MIL-PRF 38535 for QML Class N (non-hermetic) components.

Several things can be involved in converting a COTS device into an EP device: • COTS devices are often produced in multiple facilities; the related EP devices may all be produced in a single facility with a controlled process flow and the same test and material sets, reducing device variability.

• COTS devices typically are specified for operation from 0°C to 70°C or -40° to 85°C. EP devices operate from -55°C to 125°C. In addition, EP devices may experience temperature cycling from -65°C to 150°C for 500 cycles during qualification.

• EP devices typically use gold bond wires, while COTS devices have less expensive and less reliable copper bond wires.

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• Depending on the packaging design, EP devices use tin-silver-copper solder or nickel-palladium-gold for improved reliability compared with COTs and AEC Q100 components.

• Highly accelerated stress testing (HAST) to evaluate moisture sensitivity and capability for long-term storage for EP devices can last 250 hours compared with 196 hours for AEC Q100 and 96 hours for COTS devices.

Sometimes EP devices are not rugged enough for the needs of a specific application, and to use devices fully qualified to MIL-STD-883 is overkill. That’s when the use of EP+ (also called Space EP) devices can be beneficial. Moving from EP devices to EP+ devices incurs a significantly higher cost, but not as high as fully-space rated devices.

EP+ devices undergo more comprehensive parametric testing at temperature extremes, more comprehensive lot testing, including wafer lot acceptance using MIL-PRF-38535 QML when required, and various levels of radiation tolerance testing.

Rad tolerant vs. hard MCUs Radiation-tolerant (rad-tolerant) EP+ components are specified as reliable up to some limit below 100-kilo radiation (krad) absorbed doses, while radiation-hard (radhard) components are tested to much higher levels. One rad is defined as a dose of 100 ergs of energy per gram of the given material. Internationally, the rad has been replaced by the gray (Gy), equal to 100 rads, in the International System of Units (SI), only the U.S. still refers to rads of radiation.

Radiation tolerant components are appropriate for lower altitude systems that

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Figure 1: Over specifying MCUs and other components for satellites and spacecraft can be costly, underspecification can be tragic. | Analog Devices

will receive lower doses of radiation.

This also helps satisfy the drive for lower-cost military and aerospace systems. Rad-tolerant devices are used in cost-sensitive designs such as CubeSats and satellites that are expected to be replaced every five years with upgraded designs.

Like most semiconductor devices, MCUs are susceptible to radiation damage. Rad-tolerant and rad-hard MCUs are often based on their nonhardened counterparts, with design and manufacturing changes that reduce susceptibility to radiation damage (Figure 2). Rad-hard devices are tested to so-called resultanteffects tests such as total ionizing dose (TID), enhanced low dose rate

effects (ELDRS), neutron and proton displacement damage, and single event effects (SEEs).

There are a variety of forms of radiation, from fairly innocuous alpha particles to high-energy gamma rays and neutrons (Figure 3). Socalled galactic cosmic rays consist of electrons, protons, and neutrons that originate outside the solar system.

Solar radiation occurs in a broad spectrum from visible light to the ionizing radiation released during solar flares such as x-rays and gamma rays. The Van Allen radiation belt is a zone of energetic charged particles, most of which originate from the solar wind, captured by and held by the Earth’s magnetosphere. Rad-

Figure 3: types of radiation.

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hard MCUs and other electronics have extremely low failure rates even after years of operation in harsh radioactive environments.

Making chips rad-hard Rad-hard chips are often fabricated on insulating substrates such as siliconon-insulator (SOI) and silicon-onsapphire (SOS). Compared with COTS devices that can handle between 50 and 100 Gy (5 and 10 krad in the U.S.), SOI and SOS chips can survive 1000 to 3000 Gy (100 to 300 krad). SOI processes eliminate latch-up events but are not guaranteed to improve TID and SEE hardness. A shielding layer of depleted boron can be added to improve rad hardness. But that is usually not enough, and system design changes are needed.

For example, error correcting code (ECC) memory includes redundant bits to check for corrupted data. Radiation can damage memory content even when the memory is inactive. ECC memory designs include a circuit that continuously sweeps the RAM, reads out the data, checks the redundant bits for errors, and then writes back any corrections. Various forms of redundancy are common in rad-hard systems.

At the circuit level, a single bit DESIGN WORLD

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Aerospace/Defense can be replaced with three bits and “voting” logic for each bit to determine its result continuously.

This increases the size of the system but results in “fail-safe” operation.

Whether or not a single-bit failure is caused by radiation, the voting logic will continue to produce correct results.

At a higher level, voting can be extended to multiple MCUs. Redundant MCUs can be implemented with three separate circuit boards that independently compute a result and compare answers. Any board that does not produce a matching result will recalculate. If a specific board consistently has non-matching results, it will be shut down to save system resources.

General criteria for space qualification Space qualification extends beyond radiation hardening and includes extreme temperature operation.

Even getting into orbit is fraught with dangers in the form of very high levels of acoustic noise, vibrations, and acceleration forces during launch.

Some of the main space-grade certifications include: • MIL-STD-883 sets uniform methods, controls, and procedures for testing microelectronic devices • MIL-PRF-38534 for hybrid microcircuits Figure 4: It’s not just individual components such as MCUs subjected to stress testing. The fully assembled James Webb Space Telescope is being prepared for transport to nearby acoustic and sine-vibration testing facilities in this picture. | NASA

• MIL-PRF-38535 for single die microcircuits such as MCUs • AS9100 is the standardized quality management system for the aerospace industry.

• JESD22 establishes the physical, electrical, mechanical, and environmental conditions and a series of uniform methods and procedures for evaluating the reliability of packaged solid-state devices.

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Those are just the main certifications; there are many more, some regionally promogulated, including:

One thing all of these standards have in common is extensive testing requirements. Examples include:

• ESCC 9000 European standard for ceramic, hermetically sealed microcircuits for space applications.

• Burn-in is performed at the extreme thermal, electrical, and environmental operating specifications of components over a period of time.

• QML-V A quality standard for hermetically sealed microcircuits.

• QML-Q DLA class for hermetically sealed devices for military aeronautic applications.

• QML-Y DLA class for nonhermetic ceramic devices for space applications.

• NASA Levels A NASA quality standard for Plastic Encapsulated Microcircuits (PEM).

• ECSS Class A class standard from the European Cooperation for Space Standardization.

• Non-Destructive Bond Pull, for example, as defined in MIL-STD-883, is performed to identify faulty wire bonds without affecting any acceptable wire bonds.

• Temperature Cycling specifications include MIL-STD-202, Method 107, Thermal Shock; MIL-STD-810, Method 503, Temperature Shock; MILSTD-883, Method 1010, Temperature Cycling and; JESD22-A104D, Temperature Cycling.

• Mechanical Shock and Vibration tests simulate the application

of sudden force or abrupt change in motion, such as occur during a rocket launch.

Constant Acceleration testing can use a centrifuge to identity mechanical and structural weaknesses not necessarily detected in mechanical shock and vibration testing. MIL883 acceleration testing specifically applies to microelectronic devices.

Electrodynamic shakers can also be used for dynamic load testing and rocket launch simulations.

System Testing and James Webb – putting it all together The James Webb telescope is a recent example of the extended systems testing required to prove flight worthiness. NASA worked with its international partners to match Webb’s testing environment precisely

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to what would be experienced both on launch day and when operating in orbit. For example, the compete flight hardware had to pass a simulated launch environment performed in two stages for “acoustic” and “sine-vibration” testing (Figure 4).

In the first test, the flight hardware was exposed to sound pressure levels above 140 decibels, with a spectrum tuned to the specific signature of the Ariane 5 rocket it would ride to space. During the tests, nearly 600 individual channels of motion data were carefully observed and recorded. Typical acoustic and vibration tests measure about 100 channels of data, but the unusually complex size and shape of the observatory required more measurements.

Next, Webb was taken to a second facility where it was placed on a purpose-built shaker table capable of precise vertical and horizontal acceleration. The initial acoustic testing simulated the high-frequency launch dynamics, and the vibration testing on the shaker table covered the lower frequencies.

Summary Specifying MCUs for satellites and spacecraft is a complex process. There’s a continuum of qualification standards beyond COTS, including EP, EP+, and MIL-STD-883, before arriving at full space-rated MCUs. In addition, designers need to consider if radiation-tolerant performance is adequate or if a fully rad-hard device is required.

Depending on the necessary level of performance, there is a wide range of qualification testing for components and full systems before they can be launched into space. AD

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