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Image: ESA/NASA Circling the earth at about 18,000 mph, the multinational crew of the International Space Station float high above the tensions that dominate the planet's international relations. And just as US and Russian crews leave behind any political antagonism, technologies that compete on the surface are also just part of the melting pot of different systems used on board. Since the first van-sized module blasted into orbit in 1998, the crew of the International Space Station (ISS) have relied on both Linux and Windows laptops to carry out their daily duties. For NASA, the spread of operating systems is a pragmatic choice. From the first days of the station, NASA astronauts have used Linux-based laptops to interact with the avionics, the critical systems that keep the station in orbit and the air breathable. Meanwhile Windows machines have always been used for general support, performing roles such as housing manuals and timelines for procedures, running office software, and providing that all important link with home, supporting communications by email and more recently by video chat.

Windows machines are also used for playing music, films and other entertainment. SEE: (TechRepublic). Laptops are also essential for managing and monitoring the many different scientific experiments run on board the ISS, as well as to control the several robotic arms that helped assemble the station and continue to play a vital role in maintenance and handling payloads. Stephen Hunter, manager for computer resources on board the ISS, explained why NASA initially chose Linux for the laptops that interact with the core systems on the station. 'It was just the applicational needs,' he said, describing how the laptop software that talked to the station's command and control systems in those early days was designed to run on a Linux-based OS. As for why NASA picked Windows for systems handling day-to-day office tasks and operations, it was mainly that the crew were familiar with the OS, he said.

'For the operations use and early payload items it was easier to migrate them to the more commercial platforms to make it easier for them to use.' Sticking with the same operating systems has allowed NASA to minimise the time and money spent on redesigning software during the almost 18-year lifespan of the ISS, said Hunter. Beyond NASA astronauts, each national space agency chooses the operating system and software they run - resulting in an array of OSes used on board. However, while the OS each laptop runs may differ, the hardware remains identical, with the same NASA-procured machines used throughout. So which laptops and operating systems have been used on the space station since construction began in 1998? The sidebar and shows the full list of the laptops and the operating systems used by the NASA crew. The laptops used on board the ISS 1998 launch of station - IBM ThinkPad 760XD.

Operating systems: Windows 95 and 'early Linux'. Windows 95 machines were later switched to Windows 2000. CPU: 166MHz Intel Pentium I MMX.

Display: 12.1' TFT (1024x768). Memory: 48MB EDO RAM. Storage: 3GB HDD 2003 - IBM ThinkPad A31p. Operating systems: Windows 2000, later switched to Windows XP alongside a 'variety of Linux distros'. CPU: 1.7GHz Intel Pentium 4-M. Display: 15.1' TFT (1600x1200). Buku pdf photography digital downloads.

Memory: 1GB DDR SDRAM. Storage: 60GB HDD. Battery: 3.6Ah rating. 2.6 hours recharge 2009 - Lenovo ThinkPad T61p Still the main laptop in use today.

Operating systems: Windows XP, later migrated to Windows 7. Scientific Linux for laptops that interface with command and control systems, and Debian Jessie 8.x.

CPU: Intel Core 2 Duo T7700 / 2.4GHz. Display: 15.4' WUXGA (1920x1200). Memory: 4GB DDR2 SDRAM. Storage: 100GB HDD. Battery: 7800mAh rating April 2016 - HP ZBook 15 NASA is in the process of transitioning the station to ZBooks, with the first batch of 30 mobile workstations sent to ISS in April.

Operating systems: Windows 10 Enterprise, with possibly odd Windows 7. Will have similar mix of Linux to A31p. Scientific Linux for laptops that interface with command and control systems, and Debian Jessie 8.x. CPU: Intel Core i7-4810MQ Quad Core. Display: 15.6 inch LED FHD (1920x1080). Memory: 32GB 1600MHz DDR3L RAM. Storage: 1TB 7200RPM, 256GB Z Turbo Drive PCIe Solid State Drive.

Battery: 8 Cell 75WHr NASA's choice of OS is also related to stability, with the agency going straight from XP to Windows 7, skipping the poorly-received Windows Vista. 'If you look at some of the Microsoft products, we tend to try to stay on the most stable of the operating systems. With XP, we stayed all the way through SP3. We did not make the leap to Vista, because of issues with it and waited until to Windows 7.' The agency also gave Windows 8 a miss, although Hunter said this was due to the timing of when it upgraded its laptops, rather than opposition to the operating system.

Because NASA stuck with its Lenovo T61p laptops for so long, it ended upgrading directly from Windows 7 to 10. Within NASA, despite the headlines that the or vice-versa, the balance of operating systems the agency uses on board generally remains the same, said Hunter, who adds that such reports are sometimes taken out of context following small-scale shifts. Spaceman on a space LAN The guiding principle for NASA is how to make life as easy as possible for the ISS' crew when it comes to looking after the station's computer systems. 'One of the global strategies that we have for the ISS is, how we can both minimise and maximise crew time?' Expecting the crew to stay on top of laptop maintenance would be impractical, given the station is staffed by six people but runs about 100 laptops. In general, if there is a problem or a laptop needs updating, mission control will attempt to fix it from the ground. 'We'll use the flight controls on the ground to do the majority of the system upgrades so it doesn't take away from the crew's time and has minimal impact.

The ability to have remote administration has been a godsend for us, in terms of being able to deploy and help to manage our growing network node on board ISS,' said Hunter. The most difficult repairs that will be asked of the astronauts are slotting in a replacement battery or hard drive.

If fixing a laptop requires a more complicated adjustment, the computer will typically be replaced outright. NASA keeps 20 percent more laptops than needed on the station for use as spares. The crew will typically use each generation of laptops for about six years, although machines will begin to be replaced with a newer model after four years. That two year transition period between laptops means the station is 'never just absolutely on one platform', says Hunter.

The exception is the Lenovo T61p ThinkPad laptop that NASA still uses today, despite having been in use since 2009. Hunter said its longer than usual lifespan is due to the machine's low failure rate, which enabled the agency to skip a generation of laptops on board. Given the long lifecycle of the laptops, it's expected that some PCs will go wrong, as Hunter puts it: 'We use these platforms truly until failure.' The laptop part that fails most often is the screen, either the LCD display suffering a pressure crack or just outright failing after some 25,000 hours of being on 'pretty much on all the time'. Not wanting to waste a valuable resource, if NASA can establish the computer is still working, it will remotely repurpose the laptop to perform operations that don't require a screen. But why exactly does the station need so many laptops, more than 20 machines per person?

'People always ask 'You have six crew members and you have 100 laptops?' ,' said Hunter, explaining that the large computing infrastructure stems from the size and multi-faceted nature of the space station. 'It's the largest thing that's ever been made in space. It is a workspace away from home, it's where the crew live, it's where they work. It takes a lot of systems to not only control the vehicle but also the amount of science we're doing on board has really increased since our construction phase. Now we're in the complete utilisation phase, it's ever growing.' The laptop plays a 'very, very significant role' in the expansion of what work can be carried out on board the space station, says Hunter.

'We've been able to automate a number of things, so we actually say it's our electronic crew member.' Of the 100 laptops used by NASA and its fellow space agencies on board today, about 15 are used to interact with the avionics systems and about 30 are used for storing and retrieving manuals and other general office tasks. Those laptops are spread between NASA crew and their Canadian, European, Japanese and Russian counterparts. NASA provides the same laptops to everyone on the ISS in order to make them simpler to maintain. 'It makes maintenance and repair on board easy, since we only have to maintain one set of spares,' said Hunter.

Where the 1980s and 2010s collide NASA buys off-the-shelf laptops for the space station but given each machine will need to remain useful during their six year sortie, NASA chooses premium PCs aimed at businesses and specs them as high as they will go. 'We've always tried to target a high-end business class laptop, not a consumer-grade,' said Hunter. As the specs improve, so the laptops are tasked with doing more, with NASA able to use the latest HP ZBook laptops to render video related to crew eye exams, a task that previously required a dedicated workstation on board. There isn't just a gap between the computing power of the laptops and that of the station's onboard computers, there is a gulf. Unlike your average home PC, the station's systems are designed to run for between 20 to 30 years.

These are machines whose processors were already long in the tooth when they were rolled out, a result of extensive testing to ensure the electronics could survive the harsh and irradiated environment of space. Consequently the processors in these systems are almost as old as the astronauts, relying on a mix of chips based on Intel 386 and even 35-year-old 8086 designs.

While some of these systems have been upgraded to the 23-year-old Pentium processor, their computing power still pales compared to the laptops used on board. As time goes on, NASA is using the laptops to handle a growing number of non-critical, non-realtime tasks on the station. 'A lot of things have moved over to this platform because it's actually more economical to place that on a laptop and communicate it over our Ethernet network,' said Hunter, while adding that the decades-old station hardware is plenty powerful enough to carry out the ISS' core functions. For the the station's central systems, resilience to failure is more important than raw power, with the central command and control system that routes commands to the avionics, power, environmental control and other vital electronics, relying on three redundant computers. Reliability is also important for the laptops, although to a lesser degree.

Laptops destined for the ISS have to be able to withstand being bombarded by the higher levels of radiation that exists in low-earth orbit. Machines also have to survive the shakes, knocks and bumps of the journey to the station. NASA checks how the laptops perform while being irradiated, as well as carrying out thermal testing where it induces failures such as a fan stopping.

The agency also carries out extensive checks on battery safety, power demands and the ability of the laptops to interact with onboard systems. Many other tests - such as the ability to withstand vibrations - are already carried out by the laptop vendors, which in the past have also made small modifications for NASA. 'As laptops have been becoming more ruggedised we can minimise the amount of testing that we have to do on our back end,' said Hunter. The rise of phones and tablets The space station hasn't ignored the rise of mobile computing, with an increasing number of smartphones and tablets having found their way on board. Various iPhone and Android Nexus 5 handsets have made the trip.

Among the many uses for such devices, perhaps the most interesting is the SPHERES program. These are remote-controlled, floating drones built around smartphones that are being tested on their ability to perform simple tasks are often either too risky or too repetitive and mundane for the crew.

Think the practice droid used by Luke in the Millennium Falcon during Star Wars: Episode IV, only without the laser blasts. Image: NASA/ISS Several generations of iPad, as well as the iPad Air 2, have made it to the station, alongside three Microsoft Surface Pro 3 tablets. The Pros are being used in various experiments, most interestingly as a bio-DNA sequencer.

The iPads are used by both US and Russian crews, both for experiments as well as for keeping in touch with family and for entertainment. The crew are able to access the internet, for instance to access social media, albeit in a controlled fashion, with all traffic carefully managed by Houston, to minimise throughput and safeguard the security of onboard systems. It was an iPad app that recently allowed British astronaut Tim Peake to run the London Marathon — albeit a digital version — while pounding a space station treadmill 250 miles above earth. Augmented reality and the HoloLens As is befitting for a space station, the ISS is also home to kit designed to make good on the science-fiction promise of augmented reality (AR). The ISS recently tested out the Microsoft HoloLens, a headset that lays digital information into wearer's vision, for example, adding a virtual label to a real-world object in their view.

During tests in February this year, a NASA operator on the ground was able to provide remote assistance to a crew member wearing the HoloLens. Using the HoloLens cameras, the operator was able to see what the crew member saw and provide them with real-time guidance, annotating objects in that crew member's vision and talking them through tasks.

More about Innovation. 'We can save time when we have complex procedures where it would take two crew members.' Hunter was pleased with the HoloLens' performance. 'It performed well.

It performed in the way that we expected it to,' he said, saying that NASA was particularly happy about how robust the communications were, given the obvious constraints when relaying messages to and from the ground via satellite. Messages are passed between the ISS and NASA's Johnson Space Center in Houston via geosynchronous satellites - creating a round trip latency of about 600ms. As for the future plans for the HoloLens, NASA wants to make the device integral to its operations 'We have long-term plans to utilise it, to support operations, payload and experiment use, also repair and other procedures or complex tasks,' said Hunter, adding that NASA would wait until the commercial HoloLens headsets were available before expanding its use. NASA's forays into augmented reality, willingness to shift more work to powerful modern laptops and experiments with the diverse capabilities of smartphones reflect the agency's desire to continue finding new ways to exploit computers. Besides, if NASA were to stop sending new and more powerful kit to the station, Hunter jokes the trip into space might lose its lustre. 'If we didn't have the necessary computing power, then people wouldn't want to come.'

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Barring a catastrophic malfunction or damaging impacts from space debris, NASA should be able to keep the International Space Station (ISS) in operation at least through 2020 and, with steady funding, careful planning and a bit of luck, through 2028 - the 30th anniversary of the first module's launch - officials say. But reduced power from degraded solar arrays and other crippling consequences of decades spent in the extreme environment of space will slowly but surely take their toll and the cost-benefit ratio eventually will tilt in favor of abandonment and a fiery controlled re-entry. NASA While the engineering and management challenges associated with keeping the station operational are daunting, ISS program manager Michael Suffredini says they should be doable, as long as NASA has the resources to build spare parts, pay for cargo launches and provide transportation for U.S. Astronauts, either aboard U.S. Commercial spacecraft or Russian Soyuz capsules.

'We have a space station that is designed in a modular fashion meant for repair,' Suffredini told CBS News. 'So as long as you have spares for all the things that can break, you can last as long as the structure will let you last. Within reason. 'The structure, it turns out, most of it was originally designed for 30 years. So all that margin has made it relatively easy for us to get to 2020. 2028 will be a little bit more challenging. We may have to sharpen our pencils to get to 2028.'

Boeing, NASA's space station prime contractor, is currently conducting a detailed engineering analysis to verify that the U.S. Segment of the complex can safely operate through the end of the decade. Russian engineers are assessing their own hardware, as are the other international partners.

The Boeing analysis is not yet complete and additional work will be needed to to show the lab can be safely operated beyond 2020. But Suffredini said no major surprises have cropped up so far and he's optimistic the station eventually can be cleared to fly through 2028 - in theory, at least. 'When we get to 2028, the solar arrays are going to be struggling, I'm probably going to have a handful of radiator lines that have been isolated,' he said. '2028 might be possible, but it also might be very challenging because then you're talking about the cost of replacing big things that may be prohibitive. 'All our analysis kind of says we think we can get to 2028 and that's the path we're headed on. As we start getting beyond 2028, if it makes sense, and things aren't failing at a rate that makes it difficult for us to keep up, and the country thinks it's the right thing to do, then we can look at going beyond that.

'But 2028's kind of where we're drawing our line today based on the original design of the structure.' An Engineering Marvel The first element of what would become the ISS was the NASA-financed, Russian-built Zarya propulsion and storage module, also known as the Functional Cargo Block, or FGB. It was launched 15 years ago this November by a Proton rocket. Two weeks later, a space shuttle carried the first NASA component into orbit, the Unity connecting node, and the two were 'mated' to form the core of the station. NASA NASA modified the assembly sequence in the wake of the 2003 Columbia disaster and a subsequent decision by the Bush administration to retire the shuttle by the end of the decade.

Segment of the outpost was declared complete after the final shuttle flight in July 2011. To understand the engineering challenge facing space station operators, it helps to visualize the 900,000-pound structure as it orbits the Earth, 260 miles up, streaking through space at 5 miles per second and enduring temperature swings of 500 degrees Fahrenheit as it moves from sunlight to shadow and back again. The long axis of the lab complex, normally oriented in the direction of travel, generally stretches out like a train, with pressurized modules connected fore and aft like passenger cars. At the front end of the complex - the locomotive in the train analogy - the U.S. Harmony module leads the way, with the European Space Agency's Columbus laboratory attached to a right-side port and Japan's Kibo lab extending to the left.

Harmony's aft port is connected to the U.S. Destiny laboratory module, which in turn is bolted to the central Unity connecting node. Quest airlock extends to the right and the Tranquility module extends to the left. A cargo storage compartment extends straight down and a set of four massive gyroscopes, used to re-orient the station and maintain its commanded position, or 'attitude,' is housed in a short truss that extends from Unity's top port.

Segment of the station, which includes ESA, Japan and the Canadian Space Agency, extends from Unity forward. The Russian segment begins just beyond Unity's aft port where the Zarya module is attached. The Russian Rassvet module extends down from Zarya and serves as a docking port for unmanned cargo ships and manned Soyuz spacecraft.

Bringing up the rear of the space station 'train' is the Russian Zvezda command module. The Poisk docking compartment extends upward from Zarya and the Pirs module, which serves as a docking port and an airlock, extends straight down.

An aft port is available for manned and unmanned vehicles. The Russians plan to replace Pirs next year with a large laboratory module. Later, they plan to attach a multi-port docking compartment to the new lab and then a solar array assembly that will extend from that module to the right. Mounted at right angles to the long axis of the station is its primary solar power truss, a huge assembly spanning the length of a football field that houses critical electrical components, ammonia coolant loops and steerable radiator panels. The Canadian robot arm can move from one side of the truss to the other atop a mobile platform. On each end of the truss, four huge sets of solar arrays rotate like giant paddle wheels to track the sun as the station orbits the Earth. The entire lab complex can be maneuvered, or re-oriented, by firing Russian rocket thrusters or by changing the speed of NASA's gyroscopes inside the Z1 truss atop the Unity module.

Rocket thrusters are typically used for major maneuvers while the gyros are primarily used for more minor attitude changes. The power truss is anchored to the long axis of the station by 10 massive struts that connect the central S0 truss segment to the top of the Destiny laboratory. Those struts, like all of the station structure, expand and contract as the lab moves into and out of sunlight.

NASA They also have to handle the stresses generated when the station is maneuvered, when visiting vehicles dock at the outpost and when Russian thrusters are fired to boost its altitude. Those same forces also act on module ports and attachment fittings. While the station might appear to be a rigid structure, it actually bends and flexes under a wide variety of loads.

And that flexing, repeated year in and year out, poses a threat to the lab's structural integrity. To assess the long-term structural health of the station, Boeing engineers developed detailed computer models based on NASA's projected use - the expected stresses caused by future dockings, reboosts, crew activity and thermal cycles - and combined that with actual data from on-board accelerometers and strain gauges. The idea was to characterize the stresses acting across the station to identify areas of particular concern and to find out how they will fare over an extended mission. 'What we're looking at is theoretical crack growth,' Pamela McVeigh, the engineer in charge of the Boeing structural analysis in Houston, told CBS News.

'So the failure mode would be you'd have a crack beginning, probably (at) a bolt hole, and the crack would grow to another edge. So you'd lose like a flange on a C-beam, or an I-beam. The stiffness of your structure would then change, the bolt hole you that you were growing the crack out of, now that bolt wouldn't be effective.' McVeigh's boss, Boeing space station vehicle director Brad Cothran, said the stress comes from a combination of mechanical loads and temperature.

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'It doesn't really care which one broke it,' he said. 'If the loads get high enough in a piece of structure, it will cause it to either yield or hit ultimate, which means crack in half.' And once a crack starts, it can propagate and eventually weaken the affected component. McVeigh said the phenomenon is similar to bending a paperclip. 'If you bend that paperclip back and forth, back and forth, back and forth, eventually it snaps,' she said. 'That's essentially what we're trying to prevent from happening.

Repetitive stress, thermal and mechanical, is one area of concern. Another is making sure periodic rocket firings or other activities don't overly 'excite' the station structure, setting up some sort of harmonic oscillation. 'That's what we want to avoid,' Cothran said, 'anything that hits a mode of the structure that would cause an interaction. Think about the Tacoma bridge. It starts rocking and it just violently comes apart, right? So those are the kinds of things we want to avoid.' NASA He was referring to the ill-fated Tacoma Narrows Bridge, a one-mile-long suspension bridge in Washington state that collapsed in 1940, four months after its dedication, when 40-mph winds coupled with the bridge's natural vibration mode to set up a catastrophic 'torsional flutter.'

'We have seen some of those kind of interactions,' Cothran said. 'Nothing like the bridge, it didn't keep going, but we've seen some things interact up there.' He recalled a yaw maneuver about a year ago, when the station was rotated 180 degrees so Zvezda was in front and Harmony was at the rear. 'A lot of times, we flip the station around and fly backwards when people come to dock and just in that simple yaw. 180 degrees, that was one that really sent us into a tizzy,' he said.

'What happened was, as the control system saw us spinning, there was flex in the structure, it appeared the structure wasn't moving. Then it would cut off and the structure would move ahead. Then it would fire on again. So we got into this oscillation setting up in the structure, that we were like whoa, time out. Don't do that again, right?'

Such oscillations can be corrected by updating the station's control software to change the timing of rocket firings and other activities. Even so, the station endures constant stress and strain from normal, day-to-day operations.

As it turns out, the struts connecting the power truss to the Destiny module are not the area of highest concern. 'The 10 struts that connect the S0 to the lab are definitely one of the areas we wanted to look very closely at,' McVeigh said. 'The lab side of that interface didn't turn out to be too much of a concern. The struts themselves are very beefy. It's the connections at the two ends. The S0 side is a little more challenging, but the teams were able to show the connections are good to 2020.' Interestingly, one of the areas of highest stress on the station is the integrated electronics assembly at the base of the far left P6 solar array.

The P6 truss segment was launched early in the assembly sequence and because the solar panels turn to track the sun, the P6 IEA has experienced higher heating than other components. But McVeigh said the hardware should be good through the end of the decade and while the Boeing analysis is not yet complete, 'I'm feeling fairly confident in reaching 2020,' she said. 'I have not seen anything that rules it out. I've seen a few things that will be challenges.'

STATION'S COMPLEXITY, SPACE ENVIRONMENT ADD TO MANAGEMENT CHALLENGE Along with structural integrity, the Boeing study is focussed on three other areas: systems that could suffer catastrophic failures unrelated to fatigue; the availability of critical spares; and the expected lifetime of key components. NASA Even with a sound structure, the station still faces the possibility of catastrophic failures resulting from micrometeoroid impacts or collisions with space debris.

The station was designed to withstand the sorts of impacts expected over its lifetime and flight controllers are always on guard for possible 'conjunctions' that might require the station to maneuver out of the way. Boeing engineers are focusing on systems like the station's high-pressure oxygen tanks and 3,000-psi lines attached to the Quest airlock that are used to repressurize the compartment and service spacesuits. 'We wanted to make sure those kind of things weren't going to fail that could result in a catastrophic hazard,' Cothran said. 'We've been through all that analysis now and we've cleared all those systems.

Our oxygen high-pressure system. Turned out to be very robust.' Other equally important systems include the station's ammonia coolant loops and radiators, which are used to get rid of the heat generated by the lab's electronics. But in that case, a failure would impact the operation of the station, not threaten its survival.

'If I ever get a hole in an ammonia line, it will be a challenge for us to find it and repair it,' Suffredini said. 'The only way to ID (a leak) is to actually see the ammonia coming out and the conditions usually don't stay right to see ammonia coming out very long once you start to lose pressure.' As a result, NASA has ordered a high-tech sensor that the station's robot arm can move about to sniff out low-level traces of ammonia. The sensor should be ready for launch in about a year and a half. The availability of critical spares is another area of focus for the Boeing engineers, making sure the components currently in orbit have backups available or in the pipeline for launch before a failure might occur. New lithium-ion batteries, which feed stored solar array power to the station when the lab is in Earth's shadow, are scheduled for launch in 2017 that will keep that system healthy through 2020. More than a ton of spare parts are being readied for launch to upgrade the Zarya module, and a steady stream of components is in production for launches downstream, including high-pressure oxygen and nitrogen tanks and ammonia coolant pumps.

NASA The solar arrays themselves are degrading over time as a natural consequence of flying in space, but Cothran they will continue to supply the station's electrical needs through 2020. Getting to 2028 will require increased efficiency and at some point, the Russians, who currently get about 8 kilowatts of power from NASA's arrays, will have to rely on their own solar panels.

'We can be more efficient in our distribution system. So the power to the end user, even though you've lost it at the transmission station, your end user will get some more power,' Cothran said. 'We're even thinking out of the box. Ten years from now, if you just wanted to go throw some dumb blankets out there, if you will, and just wrap them around the truss (you would) get something out of them. There are all sorts of things the team is looking at that we could do.'

Shelf life is another challenge facing station operators. Electrical components might be used, or stored, for many years and Boeing is doing a top-to-bottom analysis to identify internal systems that might be susceptible to failure after extended periods in storage, either in space or on the ground. One problem already identified: programmable computer chips that somehow lose their internal charge over time. 'We've got a lot of data points that say that those (chips), once they start getting into double-digit years, they lose their internal charge and can't necessarily retain their memory,' Cothran said.

'It's not something you find in the commercial industry because cell phones, laptops, anything we use down here on the ground has only got a useful life of three to five years, right? 'But since a lot of our parts were built back in the 90s and we've got spare units, it's something we're having to worry about. It's not that it totally fails, what we have to do is we have to go back in and refresh it. So it's not something that's a show stopper, it's just something we learned and as long as we're proactive, we're fine.'

Assuming the primary structure passes muster and no show stoppers turn up in the areas of shelf life or catastrophic failure scenarios, ensuring a steady supply of spare parts will remain NASA's major technical challenge through 2020 and beyond. 'It's a whole integrated process to make sure every one of the (replaceable components) will last to 2020, and you've got the right sparing,' Suffredini said.

'And then every year, we redo our analysis to see is this better or worse? You can imagine that for everything that's failed, that's a new data point. 'If I do my job right, we really could go to 2028 if I don't have. To buy a whole bunch of new hardware, I just keep going and just let the analysis year to year tell me what I have to do.'

William Harwood Bill Harwood has been covering the U.S. Space program full-time since 1984, first as Cape Canaveral bureau chief for United Press International and now as a consultant for CBS News. He covered 129 space shuttle missions, every interplanetary flight since Voyager 2's flyby of Neptune and scores of commercial and military launches. Based at the Kennedy Space Center in Florida, Harwood is a devoted amateur astronomer and co-author of 'Comm Check: The Final Flight of Shuttle Columbia.'