CubeSats: good things come in small packages
Sen—For the vast majority of Earth’s history it had but one satellite—the Moon—but that all changed in 1957 when, on October 4, the Soviet Union launched the first artificial satellite into Earth’s orbit.
Sputnik-1 was a 58cm (23 inch) sphere that contained two 1-watt radio transmitters and three batteries (two for powering the radios and one to power a cooling fan). The 83kg aluminum sphere emitted radio signals that were transmitted back to Earth via four 2.4m-2.9m “whip” antenna.
Its radio did little more than beep at Earth, but its signal was picked up by amateur “ham radio” enthusiasts all over the world.
In many ways, Sputnik was not just the world’s first satellite, it was also the first “people’s satellite” – anyone with suitable radio equipment could listen to the plucky little satellite as, for 22 days, it whizzed around the globe at 29,000km/h (18,000mph).
Sputnik-1 kick-started the space race and the satellite industry, but was really little more than a transmitter that beeped. Image credit: NASA
America’s first satellite was even smaller. Launched on Jan. 31, 1958, and weighing in at just 14 kg, Explorer-1 boasted several scientific instruments including a cosmic ray detector, five temperature sensors and micrometeor detectors.
But satellites didn’t stay small, simple and accessible for very long.
As they increased in complexity, so they increased in size. From the size of a beach ball, satellites were soon the size of a family cars, then buses and (in the case of the International Space Station) the size of a football field.
With increased size and complexity came increased costs.
It can take a decade and hundreds of millions of pounds to develop an Earth observation satellite – but that is just the tip of the financial iceberg. Launching a satellite weighing several tonnes into orbit can cost between £30million and £250million ($50million to $400million) and just paying for the radio bandwidth needed to get your information back to Earth can cost up to £1million ($1.6million) a year. That’s not taking into account the cost of ground operations and maintenance of the satellite.
And then there is the chance that your shiny new satellite could be blown to smithereens if the launch fails, or that one of the thousands of bits of complex electronic kit could fail – meaning that, at best, you are left with a multi-million pound lump of space junk, or, at worst, you have to watch as your investment plummets back through Earth’s atmosphere as the world’s most expensive firework.
In short, you have to be a global company or government agency to get a satellite into space.
Rise of the citizen satellite
In recent years, improvements in electronics, communications, solar panel and battery technology have meant that the basic building blocks for a satellite are not only more compact and reliable but, more importantly, are drastically cheaper.
In 1999, two American scientists—Bob Twiggs at Stanford University and Jordi Puig-Suari at California Polytechnic State University—started developing a new sort of satellite that, rather than dwarfing your Ford Focus, would fit in palm of your hand; instead of tipping the scales at thousands of kilograms, would weigh the same as a bag of sugar; and, rather than costing hundreds of millions, would cost just tens of thousands to build. The CubeSat was born.
A CubeSat (unsurprisingly) is a cube that measures 10cmx10cmx10cm and weighs about 1kg. Small and cheap to build, their most important feature is that fact that they are standardised.
CubeSats give developers standard specifications for size, weight and basic construction, which enables parts to be built as a “one-size-fits-all” type of arrangement.
Inside a basic chassis, computer components, cameras, GPS and other components just slot in place. Power can be supplied by mobile phone batteries or by arrays of photovoltaic cells (solar cells) that either stick to the walls of the cube or can be built to pop up like tiny energy-converting wings.
A basic CubeSat. Image credit: Montana State University
This level of standardisation means that, for the most basic CubeSats, you no longer need a team of scientists and engineers to develop bespoke components. Basic components can be bought “off the shelf” – meaning that schools, universities and even individuals can develop their own satellites.
One UK company that specialises in “off the shelf” CubeSat parts is Glasgow-based company ClydeSpace who can boast that forty per cent of all the CubeSat missions ever launched contain their components. The company is also building Scotland’s first ever satellite a CubeSat called UKube-1.
Just as in the early days of home computing – when “homebrew” computer clubs started gathering in garages and basements – groups of CubeSat enthusiasts are popping up all over world. Like their computing forebearers, they share the designs and ideas they come up with, making CubeSat design a sort of “open-source” community endeavor.
In the 1970s, it was the “homebrew” clubs and the likes of Bill Gates and Steve Jobs that made computing affordable and opened it to the masses. The CubeSat community could be poised to do the same for satellites, turning expensive behemoths into something cheap and accessible.
But what about getting your satellite into space? It’s no good building a satellite for the price of family car if it costs Bugatti Veyron money to put it into orbit.
This is where CubeSats really come into their own.
Their tiny size and weight means that CubeSats can “piggyback” on the launch of bigger missions, which drastically reduces the cost of a launch – after all, that big mission was going up anyway.
Their standardised dimensions means that a launch carrier already knows exactly what they have to find room for within their payload. Furthermore, because they are cubes, multiple CubeSats can be stacked up like Lego bricks.
The basics – cubed
At its most basic level, a CubeSat is a transmitter with a power source – just as Sputnik-1 was all those years ago – but their modular design means they can be so much more than that.
At one of the UK’s biggest satellite manufacturers, Surrey Satellite Technology Ltd (SSTL), a small team of scientists are building their own CubeSat called STRaND-1.
Built with the support of SSTL and Surrey Space Centre, but undertaken in the volunteers' own free time, STRaND-1 is a CubeSat, cubed – three CubeSat units bolted together to act as one.
When it launches sometime in the next year, STRaND-1 (which stands for Surrey Training, Research and Nanosatellite Demonstration) will be one of the most sophisticated CubeSats yet launched.
Measuring 30cmx10cmx10cm, the satellite will have at its heart an Android smartphone. The phone (a Google Nexus 1 model), which is completely intact and untampered with, contains many components that make it an ideal piece of satellite hardware, such as orientation and acceleration detectors (to determine the satellite’s angle and motion), integrated computing and memory, and open source software (making it easy for designers to write specific software).
STRaND will make use of the phone’s camera, which peeks out of the Earth-facing side of the satellite. To enable people back on Earth to see what the phone is doing, a second camera has been rigged to view the phone’s screen.
But STRaND will be so much more than just a fancy, orbiting mobile phone case. Despite its size, it will actually have control of its movements in space itself (just like a proper grown-up satellite).
Obviously, given its size, conventional thrusters were out of the question, so the SSTL engineers have come up with an ingenious solution. The craft will be fitted with eight micro-thrusters, called Pulsed Plasma Thrusters (PPT).
The craft’s eight thrusters work a little like a car’s spark plugs. A spark of electricity is made to jump between two electrodes but, instead of igniting fuel, the spark erodes particles of metal from the electrodes. The particles are accelerated by a magnetic field and vented from a tiny nozzle (like the gas from a rocket engine), which creates thrust.
STRaND-1’s plasma thrusters in action. Image credit: SSTL, SSC
To adjust the craft’s “attitude” (the direction the satellite is pointing, not its emotional outlook) it is equipped with a series of “reaction wheels” – small, precisely balanced metal wheels that, when spun at high speed, cause the spacecraft to spin on its axis.
STRaND even has a tiny butane gas thruster.
If the propulsion and attitude control system work, STRaND will be able to precisely control, not just the direction it is pointing, but also its orbit – meaning it will be able to stay in space longer (rather than just falling out of the sky after a few trips around the Earth).
Despite its complexity, STRaND-1 will only cost £80,000 ($130,000) to build (thanks, in part, to the unpaid volunteers that are building it).
But it’s not all hi-tech. One particularly endearing feature is the satellite’s data-transmitting antenna, which is made of a teeny tape measure (of the kind you get inside a Christmas cracker).
To paraphrase Spider-Man’s uncle: “with great manoeuvrability, comes great reconfigurability”.
Once CubeSats have the ability to move about with precision in space, all sorts of exciting possibilities open up.
One almost science-fiction-like idea being considered by SSTL and the California Institute of Technology (CalTech) is the Autonomous Assembly of a Reconfigurable Space Telescope (AAReST). This would use several CubeSats as a sort of miniature space telescope but, instead of being locked together in a rigid shape, these satellites would have the ability to detach from each other, manoeuvre into new positions and magnetically re-attach to create a completely different configuration (like pulling apart Lego bricks and building something new).
CubeSats might be tiny, but their minimal costs make them a very attractive alternative to “traditional” large satellites, and scientists all over the world are finding ways to make them punch beyond their weight – turning them from a novelty to viable space missions in their own right.
Playing with the big boys
Despite an initial belief that CubeSats would never be sophisticated or powerful for complex operations, large space agencies, the military and the intelligence community are now looking seriously at CubeSats.
NASA’s future technologies division, the Defense Advanced Research Projects Agency (DARPA) is funding a $75 million CubeSat research project. They are looking at ways that stable constellations of CubeSats could replace traditional satellites – imagine, instead of one Hubble Space Telescope, a constellation of hundreds, or even thousands, of tiny CubeSats working as one.
In medicine, CubeSats are being used to test the feasibility of “lab on a chip” pharmaceutical research in microgravity. Researchers at NASA’s Ames Research Center have used CubeSats to test the effectiveness of anti-bacterial drugs in space – the first step towards developing space-specific drugs for lengthy manned missions.
In 2010, a Houston-based company, NanoRacks, installed a CubeSat rack on the International Space Station and leases the space to pharmaceutical companies, research institutions and the education community.
CubeSats are also finding a role in environmental science. NASA’s CloudSat, launched in 2006, was designed to study the formation and structure of vertical clouds, something meteorologists have been unable to do from aircraft. There also been CubeSat launches designed to improve earthquake prediction, study the Earth’s magnetic field and monitor space weather.
CloudSat was designed to study cloud formation. Image credit: NASA
In the Army now
CubeSats could even find military applications. The US military are looking into the possibility of deploying CubeSats around sensitive military or communications satellites. These tiny guardian CubeSats would detect (and possibly attack) any spacecraft that attempt to spy on the sensitive hardware.
On the flip side, swarms of CubeSat spies could be deployed to snoop on, or sabotage, the satellites of other countries (or rival companies), summoning images of CubeSat dogfights, rather like fighter planes defending and attacking bomber aircraft during WW2.
The US military are also thinking of enlisting CubeSats in the “war against terror” by developing miniaturised technology that would allow them to find and track terrorists on the ground.
After more than 50 years of space vehicle and satellite launches, the once pristine environment around Earth is now littered with thousands of pieces of space junk, some of which has been in orbit since the dawn of the space age.
With a new frontier of private space enterprise on the immediate horizon, reducing the amount of hazardous debris in Earth orbit is a pressing international concern.
Some people believe that CubeSats will be perfect suited for an orbital janitorial role.
Scientists at the Swiss Federal Institute for Technology (EPFL) are developing CleanSpace One – a CubeSat designed to remove space junk from orbit. Using the same three-cube configuration as STRaND-1, the Swiss satellite will be armed with a retractable claw to grab space junk (no easy task when it is traveling at 28,000km/h).
CleanSpace One intercepts a piece of space debris (in this case another CubeSat). Image credit: EPFL
Once the target is grabbed and stabilised (if it is spinning), CleanSpace One will “de-orbit” the offending article by heading back into the Earth’s atmosphere, where it (and CleanSpace One) will burn up.
Back in the UK, engineers at the Surrey Space Centre are planning a space janitor that will use a seemingly old-fashioned propulsion method – a sail.
CubeSail (also made up of three CubeSat units) will house a thin, 25-square-metre plastic sheet, which will be unfurled when the craft is in orbit. The sail will be pushed along by the tiny amount of residual air molecules that still cling on in low-Earth orbit.
Sails could also be used to carry CubeSats as far as Mars, but instead of using air molecules to push them along, they will use the photons found in sunlight. Even though the amount “push” provided by a light photon is incredibly small, the CubeSat’s tiny mass coupled with the sail’s large surface area (relative to the satellite), means that, in the vacuum of space, all those tiny pushes add up.
Thanks to their low mass, CubeSats (like NanoSail-D, pictured) make perfect craft to test solar sail technology. Image credit: NASA
Space agencies in Europe and the US are considering solar sails for a CubeSat missions to Mars. NASA has ambitious plans for a sample-return mission to the Martian moon, Phobos.
The mission would consist of two CubeSat units, a drive vehicle and a lander. Equipped with a solar sail, the drive vehicle would propel the craft to Phobos. Once at the moon, the lander would separate, touch down on its surface and collect a sample.
The ingenious part is that the lander would remain attached to the drive vehicle with a tether. As the drive cube moved away from Phobos, it would take up the tether’s slack and yank the lander off the moon’s surface. The two cubes would then re-attach and start sailing back to Earth.
Another option for interplanetary CubeSat propulsion would be a small, solar-powered ion engine. Researchers at the École Polytechnique Fédérale de Lausanne (EPFL) in France have created a prototype ion engine that gets its thrust from tiny particles extracted by electrodes from an “ionic” liquid.
Nor are CubeSat ambitions limited to our Solar System.
NASA’s ExoPlanetSat will search for exoplanets, but instead of studying entire star-fields, it will focus its gaze on a single star. It will look for the tiny (but measurable) drop in brightness that occurs when a planet passes across (transits) the face of its parent star. If next year’s test is successful, then a fleet of planet-hunting CubeSats could be launched, each one dedicated to watching a different star.
ExoPlanetSat: Searching for alien Earths. Image credit: MIT
CubeSats might be small and cheap, but they have the potential to do for space science what the PC did for computing, or what the mobile phone did for communications – making it cheap and accessible to all.
“CubeSats are here to stay, and I doubt anyone in the space industry would deny that.” Shaun Kenyon, STRaND-1 Lead System Engineer, told sen. “Where there is still debate however is where they fit and how capable they will become.”
“They have their advantages and disadvantages just like any class of satellite. I like to think of it as an ecosystem – you need all of different sizes of animal for the ecosystem to work as a whole”.