NASA's spare solar sail reaches orbit

[Shahid Shakoor]

For years, solar sail tests have met with nothing but stormy weather. But the path forward finally seems to be clearing up. More than two years after a rocket failure destroyed a new experimental solar sail, NASA has successfully launched a spare into orbit.

NanoSail-D launched on Friday from Alaska. If the sail unfurls as planned in about a week, it will be the first NASA sail to be opened in space.


Solar sails, which can harness the force of sunlight to propel themselves, have the potential to carry spacecraft vast distances without fuel. But attempts to the test the technology in Earth orbit have met with repeated setbacks. In 2001 and 2005, launch failures scuppered two solar sail missions spearheaded by the Planetary Society, a space advocacy group based in California. And NASA's original NanoSail-D, which was slated to launch in August 2008, was lost when its ride, a Falcon 1 rocket built by private firm SpaceX, failed to reach orbit.

Now the winds of fortune seem to be shifting. In May, Japan's space agency JAXA successfully launched an interplanetary solar sail called IKAROS, which piggybacked on a robotic mission to Venus. JAXA later announced that the sail had succeeded in using sunlight to propel and steer itself.

But the effect of sunlight may be hard to discern on the newly launched NanoSail-D. Even at its altitude of about 650 kilometres, NASA says the drag of Earth's atmosphere may overwhelm the push of solar radiation.


However, the atmospheric drag itself should help test whether solar sails could act as 'orbital brakes' to pull space debris out of orbit. The drag should pull the sail out of orbit within 70 to 120 days, Spaceflight Now reports.


A solar sail project called CubeSail, funded by aerospace company EADS Astrium, could launch in 2011 to demonstrate this same braking technology.


The Planetary Society is also working on a new sail. Dubbed LightSail-1, the sail will be larger than NanoSail-1 and will launch to a higher altitude. Increasing the distance from Earth's atmosphere and the size of the sail should make the effect of the sun's radiation on the spacecraft stronger and easier to discern.

[Shahid Shakoor]

Andre Geim and Konstantin Novoselov, winners of this year's physics Nobel, spoke to Michael Brooks about the enjoyment and frustrations of their work, and the prospects for graphene, the wonder material that brought them global fame

You included a hamster as co-author on one of your papers and made frogs levitate. You made graphene by playing with Scotch tape and pencil leads. It's not an approach that normally leads to a Nobel prize.

Andre Geim: A playful attitude has always been the hallmark of my research, but even the flying frog was a serious experiment at the start. Fun actually plays quite a minor part, but it certainly helps. Without it you would consider your job a burden. But you also have to do things no one else is doing. Unless you happen to be in the right place at the right time, or you have facilities that no one else has, the only way is to be more adventurous. There are some people around who specifically aim for a Nobel, but that's the hallmark of a megalomaniac.

Konstantin Novoselov: If you try to win the Nobel you won't. The only way is to enjoy doing your work. For a long time we didn't use any technology, just some pieces of graphite coated with silver paint. We started to get results that indicated graphite might operate as transistors and have other useful properties. But yes, the way we were working really was quite playful.
When did you realise you had done enough to win the Nobel prize?
AG: I guess I started thinking seriously about the Nobel prize in 2008, when the citations started piling up and people were patting me on the back and saying "you'll do it - just stay alive".

KN: There were rumours going round for a few years that a prize would be given for graphene. It was quite damaging, actually. I trained myself not to listen, otherwise you just keep thinking about it and it takes your mind away from what you're doing.

What makes graphene so special?

AG: It is a two-dimensional lattice of carbon atoms which is stronger and stiffer than diamond, yet can be stretched and is impermeable to gases and liquids. So many of those properties are things that no other material has. It is so remarkable and so amazing. Graphene is turning out to be a wonder material.

What made you leave Russia, the country where you were born and educated?

AG: In the late 1980s it was very hard to do any research in the Soviet Union. Most of the research was military, and the facilities were not competitive compared with what you could get in the west. Then in the early 1990s, as the Soviet Union collapsed, everything went from bad to worse and it was impossible to do any work at all. I went for six months to the University of Nottingham in the UK. It was the first time I had spent any length of time abroad, and in that time I managed to do work that would have taken 20 to 30 years in Russia.

Is there any hope for Russian science?

AG: The country is rich in natural resources, including oil and gas, so there is a bit of investment in science. But the old gremlins - endemic corruption, for instance - are still hanging around. Education is probably the strongest part of the Russian system. That's because it was cheaper to sustain and a little bit harder to demolish. I noticed a dip in quality in the 1990s, but education is strong again now. That is the major source of hope for Russia.
Would you go back?

AG: Oh no. Firstly, I'm not a Russian citizen. I like Russia, I still miss the place where I was born, but for me work is part of life. If I went back I would spend my time fighting with bureaucracy, tilting at windmills.
KN: There are a few things about how science is organised there which makes it unattractive for science. Without change I don't think I'd be tempted to go back.

Is your work affected by the economic climate?

KN: As far as money goes, we're fine at the moment. There has been one upside to the economic crisis. Usually a huge fraction of our physics graduates go to work in banks and finance markets. This year we have had plenty come into the lab because the banks are not hiring.
AG: I told [UK science minister] David Willetts that I compare graphene's Nobel prize to the first glass of wine from a new vineyard. Thanks to the investment by [former UK science minister] Lord Sainsbury we have grown the vines, bringing UK science up to the same level as the rest of the world. But it took 10 to 15 years: for a man with a sharp axe it would take only an hour to destroy the whole vineyard. The damage done in a year would take several decades to recover from.
You didn't patent graphene, saying it would be indefensible and a waste of taxpayers' money. Do you still think you did the right thing?
KN: If we had tried to delay the paper [in order to apply for a patent] and hide some of the details of how to prepare it, it wouldn't have taken off like it did. The results were reproduced the very next day in labs across the world. In New York, Philip Kim of Columbia University read our paper, picked up some Scotch tape on the way into work the next day, and made graphene samples as soon as he got in.
AG: Very few people understand the problem with patents. If I was in government, I'd be asking not how many patents you've got, but how many you got any royalties from. It's so easy to file a patent, but it costs a lot, and it's hard to get any royalties out of them.
You are physicists, but you have started doing chemistry with graphene. Will the next graphene Nobel prize be for chemistry?
KN: We were extremely disappointed not to get the chemistry prize this year on top of the physics one. When the announcement was due I was already shaved and sitting next to the phone! Seriously, though, the chemists are teaching us a lot. I try to keep track, but I think I know about less than half of what is out there.
AG: It's hard to understand just how big graphene is. I usually move subject every five years. But graphene is such a huge area that I have already moved at least three times: from the electronics to chemistry to the structural properties.
What is the future for graphene?
AG: I've seen a huge industrial road map compiled by Samsung researchers which has something like 50 different applications. I'm optimistic that some of these - touchscreens, transistors and sensors - might come online in the next 10 years.
Samsung's industrial road map for graphene shows 50 different applications
KN: People are very optimistic. I've already underestimated the research several times: I've laughed at proposals pushed forward by industrial labs that went on to succeed. I think in terms of finding new physics we're only at the beginning. Every single property of graphene - optical, mechanical, electronic - is really unusual. Plus, you can combine them into electromechanical and electro-optical devices. The best experiments are only just starting now.
Will you be a part of this future, or will the Nobel prize sap your ambition?
AG: I'm a newly cooked winner so I can't judge what will happen in the long term. At the moment it's a nightmare - it's completely detrimental to my research. I have papers to write, there are people who depend on me for things no one else can do. But I'm not getting anything done. I try to pretend for a few hours that things are normal, but it's just a pretence.
KN: I sincerely hope I will carry on. But I can't predict the future, and I'm aware that many Nobel prizewinners didn't manage to carry on. It will be tough, but I hope I'll do active research for many years to come.

[Shahid Shakoor]

ABSOLUTE zero sounds like an unbreachable limit beyond which it is impossible to explore. In fact there is a weird realm of negative temperatures that not only exists in theory, but has also proved accessible in practice. An improved way of getting there, outlined last week, could reveal new states of matter.

Temperature is defined by how the addition or removal of energy affects the amount of disorder, or entropy, in a system. For systems at familiar, positive temperatures, adding energy increases disorder: heating up an ice crystal makes it melt into a more disordered liquid, for example. Keep removing energy, and you will get closer and closer to zero on the absolute or kelvin scale (-273.15 °C), where the system's energy and entropy are at a minimum.

Negative-temperature systems have the opposite behaviour. Adding energy reduces their disorder. But they are not cold in the conventional sense that heat will flow into them from systems at positive temperatures. In fact, systems with negative absolute temperatures contain more atoms in high-energy states than is possible even at the hottest positive temperatures, so heat should always flow from them to systems above zero kelvin.

Creating negative-temperature systems to see what other "bizarro world" properties they might have is tricky. It is certainly not done by cooling an object down to absolute zero. It is, however, possible to leap straight from positive to negative absolute temperatures.

Objects can't be cooled to absolute zero, but you can leap straight to negative temperatures


This has already been done in experiments in which atomic nuclei were placed in a magnetic field, where they act like tiny bar magnets and line up with the field. The field was then suddenly reversed, leaving the nuclei briefly aligned opposite to the direction in which they would have the lowest energy. While they were in this state they fleetingly behaved in a way consistent with them having negative absolute temperatures, before they too flipped over to line up with the field.

Because the nuclei can only flip between two possible states - parallel to the field or opposite to it - this set-up offered only limited possibilities for investigation. In 2005 Allard Mosk, now at the University of Twente in the Netherlands, devised a scheme for an experiment that would offer more knobs to turn to explore the negative temperature regime.

First, lasers are used to herd the atoms into a tight ball, which is in a highly ordered or low-entropy state. Other lasers are then trained on them to create a matrix of light called an optical lattice, which surrounds the ball of atoms with a series of low-energy "wells".

The first set of lasers is then adjusted so that they try to push the ball of atoms apart. This leaves the atoms in an unstable state, as if they were balanced on a mountain peak, poised to roll downhill.

The optical lattice acts like a series of crevices along the mountainside, however, halting their progress. In this state, removing some of the atoms' potential energy, letting them roll away from each other, would lead to greater disorder - the very definition of a negative temperature system (see graph).

Mosk's ideas have now been refined by Achim Rosch of the University of Cologne, Germany, and colleagues. Their proposed experimental set-up is essentially the same, but Rosch and his team's calculations bolster the case that it is feasible.

Crucially, they also suggest a way to test that the experiment would create negative temperatures. Since the atoms in the negative-temperature state have relatively high energies, they should move faster when released from the lattice than would a cloud of atoms with a positive temperature

"The new work shows that achieving negative temperatures in this new way in the laboratory is realistic," says Mosk, who was not involved in the new study. "That is something I would be very excited to see."

Rosch and his colleagues are theorists, not geared up to perform the experiment, but they think a team of experimentalists could test their proposal within a year or so.

Using a combination of lasers and magnetic fields, the atoms in the set-up could be made to attract or repel one another at a range of different strengths. "One can use this to explore and create new states of matter and play with them in regimes we are not used to," says Rosch. This is uncharted territory, he says, and it may hold some surprises.

"The new work shows that achieving negative temperatures in this new way in the laboratory is realistic," says Mosk, who was not involved in the new study. "That is something I would be very excited to see."

Rosch and his colleagues are theorists, not geared up to perform the experiment, but they think a team of experimentalists could test their proposal within a year or so.

Using a combination of lasers and magnetic fields, the atoms in the set-up could be made to attract or repel one another at a range of different strengths. "One can use this to explore and create new states of matter and play with them in regimes we are not used to," says Rosch. This is uncharted territory, he says, and it may hold some surprises.