The Cubesat standard: affordable satellite technology for all
A four-month delay of ESA’s MetOp added more than €10m to the bill: such high costs have limited access to space
MetOp is a ESA mission designed to provide weather data services to monitor the climate and improve weather forecasts
UKube-1 will use the properties of radiation strikes to create random numbers for cryptographic applicationsCredit: Clyde Space
Roland Coelho, Cal Poly: “The P-POD design is basically a glorified Jack-in-the box”
Solar radiation is a problem for smaller Earth-orbiting satellites
Norman Fitz-Coy, University of Florida: “We know we can get Cubesats to do something...”
The future of the satellite launch is cubed: meet the Jack-in-the-box that can carry your experiment into orbit on a realistic budget
When Sputnik was blasted into orbit and over the heads of the world in 1957, few back on Earth were aware of how little actual technology was inside the metal beachball-sized space probe. It was a product of sophisticated rocket design, much of it done without the aid of computers, and very simple electronics, but nervous observers in the West feared the instrumentation it carried and worried what the tiny ball's regular bleeps were telling its Soviet owners. In fact, very little was going on inside: a radio transmitter amplified the output of a basic electronic oscillator, its frequency controlled by simple temperature and pressure sensors.
Such simplicity did not last long. The military wanted high-powered cameras and instruments in the sky so far out of range of enemy guns that they could spy with impunity. Telephone companies quickly grasped the ease with which they could put people in touch, no matter where in the world they were, simply by passing calls through a sophisticated switchboard positioned hundreds of miles above the Earth – although the small matter of the speed of light meant pause-delays in conversations.
Satellite technology has, of course, progressed hugely over the last 50 years – as has its expense. It can take years to design and build a satellite these days, and can cost up to $1bn for a complex set-up – with around half of the funding going on the disposable rocket used to put the probe into orbit.
The three-satellite MetOp (Meteorological Operational satellite programme) project run by the European Space Agency (ESA) for weather monitoring is estimated to be costing a total of €3.2bn, including the expense of maintaining contact with Earth stations. A four-month delay to the launch added more than €10m to the bill. Such high costs have limited access to space to those with very deep pockets; now that situation is changing, due partly to the advent of the 'Cubesat'.
Enter the Cubesat
Cubesats are types of miniaturised satellite for space research that customarily have a volume of exactly one litre, have a mass of no more than 1.33kg, and typically use commercial off-the-shelf – rather than custom-designed – electronic components. Cubesats are now seen by many in the industry as the shape of satellite projects to come. Opening a US National Science Foundation (NSF) Cubesats workshop session in May 2012, its geosciences divisional director Michael Morgan declared that: "We need a lower-cost approach for access to space than we have with traditional methods."
Because the high cost of launches limits the number of satellites that make it into orbit, Morgan said that there are important fields in science that fail to get the data they need. Space weather research has suffered, according to Morgan: "The lack of essential observations from space: that has become a limiting factor. In situ space observations are critical to understanding phenomena, such as ionospheric irregularities, that can adversely impact the accuracy of satellite-based tracking systems."
The answer could come from a grass-roots effort among universities that the UK government has also embraced in an attempt to broaden its space industry in a way that costs comparatively little.
In the late 1990s, a group of scientists decided that they needed a way to get devices into space without diverting all their departments' funds into a single launch: essentially, it comes down to packing the electronics into boxes not much bigger than a milk carton. During that period Stanford University professor Bob Twiggs worked with colleagues at his institution and Cal Poly (California Polytechnic State University) to develop a concept for cheap satellites that turned into the Cubesat.
According to Cal Poly's Professor Jordi Puig-Suari, the overall design of the Cubesat came down to the availability of components at the end of the 1990s. They settled on a form factor of a cube measuring 10cm on a side as this could comfortably hold a limited stack of PC/104 embedded computer and peripheral boards.
In reality the size was not the obstacle to cheaper launches. The basic cube proved too restrictive; even the inaugural launch violated the original standard. One of the satellites was a double-height or 2U model; the other an even taller 3U design. The key to getting aboard launches in a cheap way lay in the cartridge the researchers designed.
Not everyone in the satellite industry welcomed the Cubesat innovation. Launch providers were wary of accepting even something as small as a Cubesat for fear of the probe going wrong and punching a hole in the multi-million dollar primary payload before it even got into orbit. Cal Poly research associate Roland Coelho recalls: "The priority was to protect the launch vehicle and primary payload in case something went wrong... We decided we could encapsulate it."
Cubesat carrier design
By adopting the same 10x10cm footprint, Cubesats can be loaded into a spring-loaded box: the Poly-PicoSatellite Orbital Deployer (P-POD). The design takes up to three Cubesats at once, or just one 3U package. "The design of the P-POD is really simple – we did not want to over-design it," says Roland Coelho. "It is basically a glorified Jack-in-the box."
The emphasis on protecting the expensive primary payload, together with the standardisation on footprint, makes booking a launch far less of an issue. Launch providers are happy to put one or more P-PODs onboard, whether they are filled or not. It is easy thereby to mix and match Cubesats and get a design on to a launch quite late in the day, as it were.
Missing a launch entirely is not a huge problem, as you can simply book the next available flight – a very different situation to the one that faces engineers working on the primary payload, where even delays of a few weeks cost into the millions. James Cutler of the University of Michigan says that simply by coming up with the design for the P-POD, the original team bought Cubesat designers two more months on their schedule.
By 2010, more than 30 Cubesats had made it into orbit. Nasa alone expects to launch 33 such satellites before the end of 2014. There are risks, of course. Not every launch is successful. Because so many can be packed into one rocket at once, if a launch vehicle fails, it can take down a lot of projects with it.
In July 2006, a Russian launcher carried the largest number of Cubesats so far assembled in history: rather than being propelled into orbit, they plunged back to Earth with their fragments spread across a 100m diameter crater. "For some of the universities this was their first and only shot," sighs Coelho. Though some were burnt by the crash badly enough to not have another go, the design philosophy behind most Cubesats embraces the idea that if a launch goes bad, it is reasonably easy to switch to a backup.
The ready availability of launch slots makes it easier for companies to get involved in space projects. This is one of the reasons why the high-profile UKube-1 project – developed, built and tested for the UK Space Agency by Clyde Space of Glasgow – is likely to serve as a demonstration how the UK, which already has an involvement in satellite technology through established players such as EADS Astrium and SST, can expand its space industry. Notionally, the satellite has already missed its first slot, having been scheduled to go into orbit in late 2012. The UKube-1 team is now aiming for a spring 2013 launch on a different rocket equipped with P-PODs.
UKube-1 widens access to space-based instruments right down to the level of schools. The five payloads represent a mix of commercial and academic projects. EADS Astrium wants to use one board inside the 3U (10x10x30) probe to work out whether cosmic radiation can lead to greater security for comms satellites: thus Cubesats can be used to gather data used to inform factors affecting much bigger, more expensive planned satellite projects.
Centimetres away from that board is MyPocketQub, a programmable host for experiments. During its first year of operation, a different user will be able to take over the board, upload software and run an experiment on MyPocketQub.
The constraints on Cubesats led engineers to take a very different approach to electronics design compared with their peers who work on larger satellites. Although there have been attempts to stretch the maximum height of conventional Cubesats to pack in more hardware, that demands a P-POD.
Coelho says one of the lessons learned over the past decade has been "to avoid just going down the easy path". It means using electronics to increase density rather than expanding the package to suit older but more robust hardware. "If you fit it into a 3U, that is how you get the launch opportunities," he suggests.
Larger, conventional satellites employ components that have gone through years of testing to determine their behaviour under the levels of intense radiation encountered while orbiting beyond the Earth's atmosphere. These parts are expensive and almost always built on much older process technologies than those used in contemporary consumer electronics. To cram as much as possible into the casing, Cubesat developers typically opt for these more advanced radiation-sensitive devices and then try to minimise the probability of a stray high-energy neutron or cosmic ray knocking out an entire subsystem.
The 30cm-long extended Strand-1 Cubesat, developed by volunteers from Surrey Satellite Technology Ltd in a joint mission with the University of Surrey's Space Centre, incorporates a standard Google Android smartphone. The team flew the satellite in a low orbit to reduce the overall radiation dosage the electronics received.
The Mission Interface Computer (MIC) developed by specialist Steepest Ascent for UKube-1, which coordinates all communications between the onboard experiments and the ground stations, will use several gigabytes of memory – all based on commercial devices. Rather than buy specific radiation-hardened devices, the MIC uses redundant memories that are powered down between uses to reduce the probability of damage to data. One approach adopted by the Cubesat fraternity is to use different makes of memory as redundant backups as they are unlikely to share identical failure modes.
In the US, meanwhile, Cubesats have become instrumental in delivering science programmes for the NSF. This, in turn, has helped accelerate the pace of development in this part of aerospace engineering. Cutler says: "If NSF had not come along I am willing to argue that our space programme would not be as far along as it is now."
The open question is whether Cubesats will become commercially important. This is an area that concerns Norman Fitz-Coy, assistant professor at the University of Florida, who is working with colleagues at North Carolina State University on the Astrec project to try to further expand the role of Cubesats.
"The question we always get from industrial partners is what can these Cubesats do beyond space weather? Where is the industry that comes out of this? But we have found that in collaborations with international partners there is an openness to think about what you can do," Fitz-Coy claims. "We know we can get Cubesats and small sats to do something; the question is, what?"
Fitz-Coy also says that there is an active interest in satellites coming from both developing and developed nations to track climate issues, such as the South Atlantic anomaly, water resources, and to capture imagery quickly after disaster: "The first images from Hurricane Katrina came from a developing country – Nigeria. We are trying to push the envelope of what comes out of the work on Cubesats. The primary utility we see is not Cubesats being used on their own but in constellations, and we are looking at using poco satellites and nanosatellites together," Fitz-Coy adds. "Existing US satellites are ageing. There is potential for 'gap fillers'."
Eloisa de Castro, chief mechanical engineer from a company that formed out of the university work, Princeton Satellite Systems, says Cubesats act as good prototyping platforms: "In industry we use Cubesats as testbeds for technology demonstration. You can make miniaturised prototypes of your instrumentation, and fly them on Cubesats."
The Earth's strong magnetic field and atmosphere protect us from most of the damaging radiation produced by the Sun, and even more energetic cosmic rays and particles scattered by exploding supernovas. Radiation is just as deadly to electronic hardware. Many of the circuits that function happily at ground level are much more likely to fail, sometimes irreversibly, when flung into orbit.
Specialised radiation-hardened components allow satellites to operate for years without problems; but they are expensive, which adds significantly to the overall cost of development. A further expense comes from the need to ensure that circuits have back-ups if one is unfortunate enough to be damaged by radiation. No wonder dealing with these damaging emanations have posed major challenges for satellite engineers.
One approach to ameliorating the effects of radiation is to use triple modular redundancy (TMR). Three sets of electronic circuits are used for each function, and vote on the output to weed out errors caused by stray alpha particles that may flip a control or memory bit. This is expensive to do across the board but Cubesats such as UKube-1 employ limited amounts of TMR to ensure critical subsystems, such as the Mission Interface Computer (MIC) can function after a failure.
Radiation may also have its practical uses up there. The EADS Astrium experiment to fly aboard UKube-1 will use the properties of radiation strikes to create random numbers for cryptographic applications. It is difficult to generate random numbers with sufficiently high entropy to defeat codebreakers. Spaceborne random number generators may provide an answer.
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