Voyagers ride 'magnetic bubbles'

9 June 2011 Last updated at 22:11 GMT By Jonathan Amos Science correspondent, BBC News The domain of the Sun's influence is called the heliosphere: The Voyagers are approaching the edge of this enormous balloon of charged particles thrown out into space by our star Humankind's most distant emissaries are flying through a turbulent sea of magnetism as they seek to break free of our Solar System.

Nasa's Voyager probes, which were launched in 1977, are now approaching the very edge of our Sun's influence, more than 14 billion km from Earth; and they are still returning data.

That information has allowed scientists to build a better picture of what conditions are like in the zone where matter blown out from our star pushes up against interstellar space.

Computer modelling based on the Voyager insights suggests the edge of our Solar System is a froth of activity, like "an agitated jacuzzi", said Eugene Parker from the University of Chicago, US.

Magnetic field lines carried in the "wind" of material coming off our star are breaking and reconnecting.

This process is sculpting the wind into discrete bubbles that are many tens of millions of kilometres wide.

Researchers say this assessment has implications for our understanding of cosmic rays - the storm of high-energy particles that are accelerated in Earth's direction by exploded stars, black holes and other exotic locations in the galaxy.

Ray effects

It is highly likely the mass of individual magnetic structures actually makes the Solar System more porous to cosmic rays.

"It's more like a membrane that is permeable to the galactic cosmic rays, so we expect the galactic cosmic rays to enter and slowly wander through this sea of magnetic bubbles until they can access field lines that connect back to the Sun and quickly escape," explained Professor Parker.

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It takes 16 hours to get a message to Voyager 1. Read David Shukman's report from the Voyager control room at Nasa's Jet Propulsion Lab

The observation is of interest not just to physicists but also to astronauts, who must protect themselves from the damaging health effects of cosmic rays, and to spacecraft engineers who have to "harden" the electronic circuitry in satellites against the impacts from high-energy particles.

The modelling results will make no difference to their predicament; but it does say something about why the cosmic ray issue takes on such importance.

Researchers confess to being surprised; they thought the outskirts of our solar neighbourhood would be more sedate - that the Sun's field lines would simply turn around and reconnect with the Sun.

"The findings are significant as we will have to change our view on how the Sun interacts with particles, fields and gases from other stars, and this has consequences that reach down to Earth," commented Arik Posner, Nasa's Voyager programme scientist.

It is a demonstration once again of the extraordinary capabilities of the Voyagers, which continue to excite and intrigue more than three decades on from their launch.

Voyager 1 was put in space on 5 September 1977, and its sister spacecraft, Voyager 2, lifted off on 20 August 1977.

The Nasa probes' initial goal was to survey the outer planets Jupiter, Saturn, Uranus and Neptune, a task completed in 1989.

They were then despatched towards deep space, in the general direction of the centre of our Milky Way Galaxy.

David Shukman takes a close look at a replica of the Voyagers

Sustained by their radioactive power packs, the probes' instruments continue to function well and return data to Earth, although the vast distance between them and controllers in California means a radio message now has a travel time of about 16 hours (in the case of Voyager 1).

The primary task of the spacecraft currently is to define our Sun's limits - to map the extent of its heliosphere, as scientists call it.

Our star blows out huge volumes of excited particles. This wind, laced with a magnetic field, travels out at high speed until it crashes into the interstellar magnetic field, at which point the Sun's outpouring abruptly slows and begins to move sideways.

It is at this boundary - the heliopause - where the Voyagers find themselves today, and where the Sun's magnetic field lines are snapping and reconnecting to produce the structures reported by scientists.

No-one is quite sure where our Solar System ends and interstellar space begins, but the expectation is that the probes will break through soon - perhaps in the next three or four years.

Jonathan.Amos-INTERNET@bbc.co.uk

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Magnetic space future

17 May 2011 Last updated at 06:23 GMT UK engineers spent 12 years working on the device, only to see it dropped from the mission late on It's thought as many as half a million people crammed the roads and beaches outside the Kennedy Space Center to see Endeavour's final launch.

Thousands more had official guest status and got a slightly closer view from inside the spaceport itself. A magnificent morning ascent for the youngest of the Nasa spaceplanes as it began its final mission - the delivery of the $2bn Alpha Magnetic Spectrometer (AMS) instrument to the International Space Station.

There will, however, be a group of British engineers for whom Monday's lift-off was a bitter-sweet moment. These are the people whose technology got dropped from AMS in the year before launch.

For those not familiar with this story, let me back up and reprise events. They have some potentially fascinating implications for deep space travel.

AMS is one of the most expensive science experiments ever put in space - probably the most expensive.

It has taken a group of 600 or so researchers from 16 nations a total of 17 years to prepare it for flight. It promises some dramatic new insights into the origin and make-up of the cosmos.

AMS will do this by studying the storm of high-energy particles (cosmic rays) that are hurled at Earth from the deepest reaches of the Universe.

Critical to its operation is a very strong magnet. As the particles enter AMS, they will bend through this magnet. How they bend reveals their charge, a fundamental property that says a great deal about the nature of those particles and where they came from.

Endeavour climbs into the sky, the AMS packed in its payload bay

The UK at a programmatic level never got involved in AMS, presumably because it was a space station project (and the UK doesn't engage with human spaceflight), but one British company was contracted to build the all-important magnet.

Scientific Magnetics (formerly Space Cryomagnetics) of Culham, in Oxfordshire, spent 12 years developing this super-cooled beast, and it was - so the project leaders on AMS told me - a marvel.

It was incredibly powerful and directed its entire field inwards, like an enclosed bubble. From the outside, the magnet appeared as an inert beer can.

This was really important because if you put such a device on a shuttle or a space station and it hasn't been carefully designed, it will start to interact with its surrounding - even try to orientate itself with the Earth's magnetic field. Not what you want on a space vehicle.

But to cut a long story short, the British magnet's super-fluid-helium cooling mechanism meant that it was only ever going to be a short-lived device. And when the space station's life was extended last year to 2020, the AMS project leaders took the decision to remove the UK magnet and replace it with a less powerful, but much longer-lived, Chinese one.

Now, as I say, this is a story with some interesting outcomes.

The British magnet is currently sitting in store at the European Organization for Nuclear Research (Cern) where AMS was assembled and tested, and there's a lot of interest in seeing its technology put to other uses.

The first of these is astronaut protection. The cosmic rays that AMS is trying to characterise are particles that also represent a hazard to humans in space.

Ad Astra has been running a testbed incorporating British superconducting-magnet technology

When astronauts eventually go beyond the space station - back to the Moon, and on to asteroids and Mars - they will need to shield themselves from these high-energy particles. The idea of using a powerful magnetic field to do this job is being investigated Dr Roberto Battiston, the deputy principal investigator on AMS. He told me:

"We continue to work to understand how this technology could be used for future shielding of astronauts undergoing long exposure, for instance at a Moonbase or on a trip to Mars… because this is by far the most advanced super-conducting magnet-design ever built and completed for a space mission. It is not going to fly but it had everything that would allow it to fly.

"The European Space Agency asked me to submit a proposal for a feasibility study and [Scientific Magnetics] is part of it.

"We would design the magnet in a different way to the AMS one. AMS was designed to have a very strong magnetic field within an inner bore. By modifying the coils and the currents, we can design a magnetic field confined in an external ring surrounding an inner bore that is magnetic-field free. In this internal module will be the habitable part for the astronauts - where they will live. We are talking about something having a diameter of about five to six metres and the length of 10m - surrounded by this magnetic field that is intense enough to bend away cosmic rays coming from deep space."

The AMS (left) will sit on the station's truss, or backbone, slightly tilted to look past the giant solar wings

There are immense practicalities to overcome, of course. These special magnets get their strength because they are superconducting. This means running them at cryo-temperatures, which demands a lot of liquid helium.

This has a tendency to boil off over time, limiting the life of your device, which brings us back to AMS. All that said, Professor Battiston is encouraged by the research. He says it should be possible to limit radiation exposure on a Mars flight to something similar to that currently experienced by astronauts on a six-month stay at the space station.

The other big space application for which a magnet like the British device might be useful is in the plasma rockets that could one day propel all spacecraft.

These rely on the motion of highly excited gases, or plasmas, moulded by magnetic fields to provide thrust. Although they don't give the initial big kick you get from chemical combustion, their supreme efficiency means they can go on thrusting for extended periods, achieving far more acceleration per kilogram of fuel consumed. Proponents of plasma rockets say they could dramatically cut the journey time to Mars from months to weeks.

Scientific Magnetics has already produced a superconducting magnet for a testbed at Ad Astra in Texas, the company at the forefront of this propulsion technology.

Steve Harrison from Scientific Magnetics told me:

"These rockets use radio frequency heating to generate the plasma and then the magnets contain the plasma in the same way they do in a tokomak fusion reactor. The magnets are profiled such that they form a sort of nozzle out the back; and because the plasma is expanding and supersonic, it flies out and gives you thrust. For the system Ad Astra has been testing for the last two years, we designed and built the super-conducting magnet."

Similar obstacles to the magnetic shield prevent immediate adoption of the propulsion application as well, but both concepts are definitely worth watching for the future.

Magnet technology could provide both radiation shielding and propulsion on future deep-space vehicles

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