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Don’t have the money for blockbuster interplanetary missions? send a fleet of tiny cubes instead, says Maggie McKee

Space 3

I AM here to glimpse the future of spaceflight. I vaguely expect gleaming clean rooms and labs, and to be asked to don overalls – or at

the very least safety goggles – to view cutting-edge robotic probes destined to spy out Earth-like planets, or fan out across the solar system in search of life. This is the Massachusetts Institute of Technology, after all.

Instead, I’m ushered into a narrow, drab office whose main decoration is a signed photograph of astronomer and TV personality Neil deGrasse Tyson. My host, doctoral student Mary Knapp, points towards a table on which a model of her spacecraft is sitting. A metal box about the size of a loaf of bread, it has an 85-millimetre-wide Zeiss camera lens peeking from one end. “It’s a very nice lens, but it’s not exotic in any way,” she says.

I nod in what I hope is an enthusiastic manner, and mentally remove my safety goggles. But the more Knapp and her colleague Rebecca Jensen-Clem talk, the more I genuinely get excited. The past few years have been gloomy for space exploration, with

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missions seemingly more often in the news for having their funding cut than blasting off successfully.

But tiny modules of the kind I see before me are promising to change all that. Known as CubeSats, these standardised packages can be sent up into space individually or mixed and matched to make bigger missions. They might provide cheap tickets to the hotspots of Mars or the icy beltways of Saturn, and not just for the likes of NASA, but university research groups, poorer nations or even wealthy individuals. “It is levelling the playing field,” says Sara Seager, head of the MIT group. Are small satellites about to hit the big time?

In a way, CubeSats are about getting back to basics. The first ever satellite, Sputnik 1, beeped its way around Earth in 1957 heralding the dawn of the space age. It was the size of a beach ball. By contrast NASA’s recent flagship, the $2.5-billion Curiosity rover, which landed on Mars on 6 August, is the size of an SUV, and the $3.3-billion Cassini spacecraft, which went into orbit around Saturn in 2004, is bigger

still. You could park your car inside it.CubeSats were the brainchild in the mid

1990s of aerospace engineers Robert Twiggs, then at Stanford University in California, and Jordi Puig-Suari of the California Polytechnic State University in San Luis Obispo. They reasoned that advances in microelectronics meant that the minimum size of a satellite that could be shot into Earth orbit and do something useful there was actually quite small. Standardising dimensions and some components was a way to build orbiters quickly, cheaply and flexibly. “We were looking for a way to simplify the system so students could complete a spacecraft in a year or two,” says Puig-Suari.

In 2000, they published specifications for a cube satellite with sides just 10 centimetres long and a mass of no more than 1.33 kilograms. If the instrumentation for a particular mission did not fit into one cube, two or more could be slotted together to make something bigger, like the one I saw at MIT.

It was a midget compared with existing >

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Satellite liteCubeSats barely register in size compared with the European Space Agency’s Earth-observation satellite, ENVISAT

ENVISATDIMENSIONS: 26m × 10m × 5mMASS: 8210 kgLAUNCHED: March 2002STATUS: Still in Earth orbitthough contact lost,end of mission declared May 2012

DIMENSIONS: 10cm × 10cm × 10cmMASS: Approx 1 kgLAUNCHED: From 2003STATUS: 10 in low Earth orbit

CubeSats

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satellites (see diagram, right), and the reaction from research groups looking for a cheap entry into space was enthusiastic. Seager’s team at MIT is one of dozens dotted around the globe building probes according to the CubeSat specifications, enabling them to cooperate and share expertise on a common platform. Since the first CubeSat blasted off in 2003, around 100 have been launched, testing how components perform in space, assessing the survival of microbes or taking measurements in the upper atmosphere.

Initially, though, reactions from elsewhere were lukewarm. “Industry regarded CubeSats as little more than toys,” says Puig-Suari. But with every CubSat success, attitudes have begun to change. Private companies, the US air force, the US National Reconnaissance Office and even NASA have all recently announced funding for CubeSat programmes.

A mission the size of a tissue box is necessarily less ambitious than a Curiosity or a Cassini, with their panoply of heavy, complex instrumentation. But that does not have to be a problem, says Mason Peck, chief technologist at NASA: there is room for cheap spacecraft using off-the-peg components that concentrate on doing just one thing well. “It is not about replicating the kinds of science we can do with [flagships], but instead about doing new kinds of science,” he told a CubeSat conference held at MIT in May.

Shaun Kenyon, an engineer at Surrey Satellite Technology in Guildford, UK, agrees. “I don’t think CubeSats will usurp larger satellites, but they have their own niche,” he says. He is working on a CubeSat called Strand-1, which will test whether smartphone sensors and processors can be made to work in space. Taking advantage of the research that has made these components small and efficient, he hopes to use them as a cheap and cheerful data-acquisition system for future missions.

It won’t all be plain sailing for CubeSats, though. Projects so far have been restricted to putting the cubes into Earth orbit, often stowed in a package of three inside an aluminium box called a poly-picosatellite orbital deployer, or P-POD, and they have piggybacked on bigger missions that shoulder most of the launch costs. The hitchhikers don’t pose a risk to their rides. “Even if something goes wrong with your CubeSats, it is all contained in that box, which is not

opened until the main payload is clear of the rocket,” says Kenyon.

But depending on the kindness of strangers has its disadvantages. Propulsion systems for changing orbits generally involve highly combustible or toxic liquids or gases under high pressure, so most CubeSats don’t have them. For interplanetary missions, however, being able to move around in space, either to leave Earth orbit, explore a target or fly in formation, is crucial.

Kick into spaceThis year, NASA announced that it is sponsoring a $3 million prize, called the Nano-Satellite Launch Challenge, to develop dedicated systems capable of sending a small satellite beyond the grip of Earth’s gravity at least twice in one week using two different launchers. Meanwhile the United Launch Alliance, a private venture that operates the Atlas and Delta rockets used by NASA and others to send satellites into orbit, announced

it is working on a concept that would still see CubeSats piggybacking, but give them a bigger kick into space. The idea is that an Atlas rocket releases its main payload in Earth orbit and then boosts itself higher, when a ring-like structure called the Multi-payload Utility Lite Electric stage, or MULE, would detach. Studded with two dozen or more CubeSats and 800 kilograms of xenon propellant, the MULE would proceed to Mars, release the cubes and act as an orbiting relay station for them to communicate with Earth.

Vlad Hruby of the Massachusetts-based aerospace firm Busek, which is designing the MULE’s propulsion system, estimates it could be launched for $100 million, a cost that could be spread among the owners of the various CubeSats. Launching the rocket for a single conventional Mars mission, by comparison, would cost in excess of $250 million.

Once a CubeSat is safely launched, it must still propel itself to its destination (see “Up, up and away”, right ). Navigating through interplanetary space brings its own

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challenges. Beyond Earth’s protective magnetic shield, CubeSats will be exposed to more cosmic rays and charged solar-wind particles that can zap electronics. An extra 6 to 8 millimetres of shielding would act as protection from most of this extra radiation, says Robert Staehle of NASA’s Jet Propulsion Laboratory in Pasadena, California, but high-energy particles could still take out a CubeSat without backup systems in place. That raises the question of whether the cost of the extra space and mass required for redundant parts makes it worth the risk of flying without.

Austin Williams, co-founder of start-up CubeSat firm Tyvak Nano-Satellite Systems, suggests that could be a non-question: “On the big missions, you can say failure is not an option.” No one wants their CubeSat to fail but he says the lower costs associated with the failure of a smaller satellite means there is more scope to embrace risk and so make faster progress.

So where might CubeSats go? Seager’s top choice is Mars. The planet has a long history of tenuous and disputed lines of evidence for the presence of life there. Most recently, methane, a possible sign of life, has been detected in parts of the planet’s atmosphere, but we have been unable to follow up on that quickly. “In the regular NASA machinery, they can’t drop everything and go and land on the surface where there’s methane,” says Seager. She favours a fleet of cheap CubeSat landers that could be sent to different points on the surface, each equipped with a single experiment to detect whether there is any “handedness”, or chirality, in amino acids on Mars, as there is among amino acids

associated with life on Earth. That would not be cast-iron proof of life, as there are other conceivable ways to create molecular handedness, but it would be an intriguing hint, and give us a better idea of where on the planet to direct any more comprehensive follow-up mission.

Cheap and cheerfulAnother intriguing possibility is to send a fleet of CubeSats fitted with seismometers to land on an asteroid. By measuring seismic waves created either by a man-made impactor or by the deforming gravity of a passing body such as Earth, this kind of network would give clues to whether asteroids are solid bodies or just agglomerations of rubble left over from the solar system’s early days. That would help to determine both how larger bodies accreted from smaller ones in the solar system and how best to deflect or destroy one should it stray too close to Earth.

Sending a similar fleet of seismometers to Jupiter’s icy moon Europa, which is deformed by tugs from the giant planet and its other moons, could reveal whether it harbours a subsurface ocean, another potential home to

life. NASA and the European Space Agency had planned a flagship mission to Europa to launch in 2020, but funding constraints have put it under threat.

Even further out, we might send CubeSats as probes into Saturn’s rings, says Matt Hedman of Cornell University in Ithaca, New York. “They would basically be instrumented ring particles,” he says. Using radio beacons and accelerometers, the probes would reveal the distribution and motion of the icy ring particles and how they collide and rebound from each other. That again could shed light on how rocky objects in the early solar system coalesced into planets.

Doing any of these things will be extremely difficult, in part because the size restrictions limit the room for scientific instruments and communications systems. Lasers or inflatable antennas are being developed to transmit information more efficiently than the coaster-shaped antennas used on many CubeSats so far, but Staehle points out that good science can be done even without high transmission rates. A powerful antenna on NASA’s Galileo spacecraft failed to deploy after its launch in 1989, so the Jupiter-bound probe sent back data at just a few per cent of the anticipated rate – yet this trickle revolutionised our understanding of the solar system. “We don’t necessarily need the palatial data rates we’ve come to expect out of planetary missions today,” says Staehle.

Knapp, Jensen-Clem and their colleagues have certainly taken this can-do spirit to heart. The model in their office is of a $5-million prototype made from three CubeSats called ExoPlanetSat that should blast into Earth orbit in 2014 to observe the dip in starlight as specific extrasolar planets pass in front of their host stars. Their first target is a known planet 41 light years away from Earth called 55 Cancri e, but ultimately they hope to launch a fleet of similar or larger probes that each could be built for $750,000 or so, in the hope of discovering new Earth-like planets.

In the current economic climate it is easy to argue that small is beautiful. Big science is always going to need big probes and big budgets. Yet while miniature CubeSats may not dazzle at first glance, they could do more than a little to make the future of space exploration bright. n

Maggie McKee is a freelance writer based in Boston

How might a CubeSat be propelled through space? One possibility is to adapt systems first devised for larger spacecraft. Pulsed plasma thrusters vaporise and ionise a dense, chemically inert solid fuel such as Teflon, and accelerate the ions through an electromagnetic field to provide thrust. Or perhaps we might use electrospray thrusters, which do something similar with salty liquids pushed through tiny capillaries. Both systems were originally introduced for precise thrust delivery, for example, to keep a large spacecraft pointed continuously towards a small patch in the sky, says aerospace engineer Paulo Lozano of the Massachusetts Institute of Technology.

There are other, more daring proposals. One, from a company called Tethers Unlimited based in Bothell, Washington, is to fling a CubeSat outwards using a spinning tether that itself hitchhiked a ride to space with a geostationary satellite. “It’s a lot like a

hammer toss,” the company’s Jeff Slostad told an MIT conference on CubeSats in May. “It’s a really simple approach.”

Another concept to be tested from next year by two groups, from Finland and Estonia, is called the Electric Solar Wind Sail, or E-sail. It would attach a spider-web-like network of positively charged tethers to the probe that would repel positive ions in the solar wind, providing a propulsive force that could be controlled by the amount of positive charge applied to the tethers.

Meanwhile, California-based space advocacy group the Planetary Society is spearheading investigations into the possibility of using a regular solar sail. They and their collaborators should soon be testing this technology, which uses the gentle pressure of photons of sunlight pinging off a reflective surface to produce a propulsive force, on a CubeSat mission called LightSail-1.

UP, UP And AWAy

” CubeSats promise cheap tickets to the methane hotspots of Mars or the icy beltways of Saturn, not just for NASA but for individuals too”

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