Wednesday, April 18, 2007

Ashes to ashes, dust to dust.

RE: Exploring Space: 'smart dust' & 'Deflector' shields

----------------- Bulletin Message -----------------
From: Planet Pride
Date: Apr 18, 2007 12:27 AM

Exploring Space

from: New Scientist Space

Shape-shifting 'smart dust' may explore alien worlds

00:01 18 April 2007 news service
Will Knight

Thousands of miniscule wireless sensors, or "smart dust," could one-day be used to explore other planets, swirling across the landscape by subtly altering their shape. At least, that's the exotic vision put forward in new computer simulations.

Several different research groups are developing tiny smart dust devices. Each is a few cubic millimetres in volume and can perform simple sensing tasks and relay messages to other such devices over distances of less than a metre. Together, they can be sprinkled across an area or throughout a building, and used to sense chemicals or vibrations, and relay messages from one another back to a central control.

John Barker, an electronics researcher at the University of Glasgow in the UK decided to investigate whether a cloud of similar smart dust "motes" could navigate across the surface of Mars from one point to another, simply by modifying their shape.

In his experiment, 30,000 motes were released on a simulated Martian surface. Each device in the simulation could sense its position and switch between two shapes – smooth or dimpled (rough). While the smooth motes were carried easily on the Martian wind, the rough ones experienced enough drag to cause them to fall back to the surface.

This allowed the motes to navigate by shape-shifting. By programming the virtual motes with a simple set of rules, Barker found that most could be made to follow a predefined course. In his simulations, about 70% were able to successfully navigate a 20-kilometre track.

Acceptable losses

Barker employed a technique known as a Monte Carlo simulation to develop his computer model. It used random numbers to reproduce the erratic behaviour of the Martin wind. "If you've got a steady wind, it's a waste of time," he says. "But, if you've got a lot of turbulence – as you have on Mars – it works."

Barker hopes to interest astronomers in his idea, pointing out that expendability would be a key advantage. "You'd actually lose a hell of a lot," he told New Scientist. "But that's the point."

Barker stresses that his research is purely speculative at this stage, since no devices can yet perform like those in his simulation. But he adds that, in theory, the same trick could work in other turbulent environments – like in a liquid or in deep space – with the motes riding solar wind.

And Barker is confident that suitable motes will be developed before long. For example, progress in electronic manufacturing should help miniaturise smart dust while electro-active polymers could be used to change their shape, for a very small amount of power. Furthermore, he says, larger landing modules on the surface of a planet could transmit signals that tell a cloud of motes exactly where they are.

Synchronised messages

Having a cloud of smart dust relay messages over long distances would be a serious challenge. But Barker suggests that their radio signals could be synchronised, possibly allowing messages to be transmitted over many kilometres.

Other smart dust experts also see promise in the area. "I do think that smart dust will be used for planetary exploration," says Kris Pister an expert at the University of California at Berkeley in the US, who is also investigating the possibility.

"It is a serious possibility," adds Michael Sailor, who works on smart dust at the University of California, San Diego, US. "The distributed networked approach means that individual devices don't have to be that reliable – if one mote goes down, another fills its place."

However, Sailor points out that there would also be drawbacks to using smart dust for inter-planetary missions. "The smaller you make it, the harder it becomes to place high-fidelity, high-sensitivity sensors in the device," he says. "This is the promise and the challenge of nanotechnology."

Barker's work will be presented at the at the Royal Astronomical Society's Annual Meeting, at the University of Central Lancashire in the UK, on 18 April.

from: New Scientist Space

'Deflector' shields could protect future astronauts

01:23 18 April 2007 news service
David Shiga

Magnetic "deflector shields" could one day guard astronauts against dangerous space radiation, if experiments now underway pay off.

Exposure to energetic charged particles could put astronauts on lengthy missions at increased risk of cancer and even cognitive problems (see Future Mars astronauts have radiation on their minds). The particles come from the solar wind and also from supernovae and still-unidentified sources outside the solar system.

The Earth's magnetic field protects spacecraft in low-Earth orbits, such as the space shuttle and International Space Station, from such particles. But astronauts journeying to Mars or living on the Moon would benefit from no such protection.

A radiation shield that mimics the deflection properties of the Earth's magnetic field could one day protect astronauts on long missions. An imaginative view – not to scale – shows a spacecraft protected from solar activity by such a shield (Illustration Ruth Bamford et al/Rutherford Appleton Laboratory)

Now, US and European plans for long-term missions to the Moon and Mars have sparked renewed interest in the problem of radiation shielding.

One group at the University of Washington in Seattle, US, has just completed a round of experiments investigating one possible approach, using a bubble of charged particles, or plasma, as a deflector shield (see Plasma bubble could protect astronauts on Mars trip).

Now, a second team has begun deflector shield experiments of their own. The team, led by Ruth Bamford of the Rutherford Appleton Laboratory in the UK, hopes to eventually fly a test satellite surrounded by a cloud of plasma in space.

Test mission

The concept is based on the fact that plasma clouds have strong magnetic and electric fields that can in principle deflect charged particles.

The group has begun testing a simple magnetic field generator that consists of loops of wire with electric current running through them.

Within a few months, they plan to use it to trap a cloud of plasma and test its ability to deflect particles inside a vacuum chamber about 2 metres long. By the end of 2007, they hope to test it in a chamber about twice as large, using higher speed particles.

Eventually they hope to attract funding for a demonstrator mission that uses wires around a spacecraft to generate a magnetic field that can contain a plasma cloud. "Hopefully we'll be able to fly a test mission in the next, say, 10 to 15 years," says team member Robert Bingham of Rutherford Appleton Lab.

Early promise

It would not be the first time a satellite had released a plasma cloud in space. In 1984, one of three satellites in a mission called the Active Magnetospheric Particle Tracer Explorer (AMPTE), which was designed to study the basic physics of plasmas, produced a plasma cloud thousands of kilometres across.

The cloud protected the satellites from the solar wind, but the mission had no way of containing the plasma, so it simply drifted away after a while, leaving the satellites unprotected.

Some researchers say the deflector shield concept shows early promise. John Slough, who leads the University of Washington group, says its NASA-funded feasibility study showed they were able to deflect charged particles with a plasma bubble and a wire mesh measuring a few centimetres across. "The question is, can you do it on a larger scale," Slough says.

Disappearing shield

But Frank Cucinotta, NASA's chief radiation health officer at the agency's Johnson Space Center in Houston, Texas, US, says there are drawbacks to such 'active shielding' methods compared to simply using extra layers of material to block out the dangerous particles.

For example, if something breaks in the device generating a plasma shield, the whole shield could disappear, whereas material shielding has no moving parts to break down.

He says materials like polyethylene could provide effective shielding, at least against particles from the Sun. As for cosmic rays from outside the solar system, he says there is a lot of uncertainty in how big the health risk really is. "We will not be able to understand how poorly or efficiently shielding works until more biological knowledge is obtained," he told New Scientist.

Bamford is presenting the work this week at the Royal Astronomical Society's National Astronomy Meeting in Preston, UK.

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