How satellites could 'sail' home

By Jonathan Amos
Science reporter, BBC News

Satellites and spent rocket stages could soon deploy "sails" to guide them back to Earth much faster than they would otherwise fall out of the sky.

With space becoming ever more crowded, there is a need to remove redundant objects that could pose a collision threat to operational missions.

Extending a sail on an old spacecraft would increase drag and pull it into the Earth's atmosphere to burn up.

Major European space firm EADS Astrium says the scheme has great potential.

"It is an interesting solution, especially for the satellite that has no propulsion system at the end of its life," Brice Santerre told BBC News.

Santerre and colleague Max Cerf have been working on what they call the Innovative DEorbiting Aerobrake System (IDEAS).

The concept involves extending booms and sheeting from spacecraft to increase the amount of drag they experience from the residual air molecules still present at altitudes up to even 750km (470 miles)

"The principle of aerobraking is to increase the surface over mass ratio of an orbital object, to accelerate the fall-out by increasing the drag on the system," Mr Santerre said.

"To do that, we need to deploy a very light structure. That's why we chose to use 'gossamer structures'. These are composed of booms and very thin membranes."

Microscope will investigate the behaviour of free-falling objects

Santerre and Serf have been developing an aerobraking sail concept for the forthcoming French Microscope satellite.

Microscope is a science mission that will investigate the force of gravity and the behaviour of free-falling objects in a test of what has become known as the equivalence principle.

The satellite will take about a year to make its measurements and will then have no further purpose.

Ideally, such a spacecraft would be removed from orbit, especially since it will be circling at an altitude where many important Earth observation satellites also operate.

"Microscope has no propulsion system so it cannot de-orbit by itself. If we were to do nothing, the fall-out duration would be between 50 and 100 years," said Mr Santerre.

By erecting their boom and membrane mechanism, Santerre and Serf believe Microscope could be brought out of the sky in less than 25 years, which meets international orbital junk mitigation guidelines.

Astrium is now investigating how the IDEAS concept could be applied to spent rocket stages.

The company leads the production of Europe's premier launcher, the Ariane 5.

The concept developed for Microscope would bring it back inside 25 years

Much of the Ariane's structure - its main core stage and solid boosters - fall rapidly out of the sky at the end of a flight; but the upper-stage is much longer lived in orbit.

Once it has ejected its satellite payload, the stage continues to circle the Earth in a large ellipse, running out to more than 35,000km from the Earth and coming as close as about 250km.

It may take 100 years before an upper-stage falls naturally from the sky.

"Our study shows that if we want to apply the aerobraking concept to an Ariane-class upper-stage then we need a system with booms, or masts, of about 12m and a deployed surface of about 250 sq m.

"This is possible with our current technologies. We need now to check that this is the best solution. We are also thinking whether this type of system can be applied to other launchers as well."

One alternative, of course, is to give the Ariane 5 upper-stage the capability to take a powered dive into the Earth's atmosphere.

The Ariane 5 upper-stage continues to circle the Earth for decades

This was done for the first time last year at the end of the launch of the Jules Verne space station freighter. This was considered essential because of the number of manned missions that routinely follow station's orbit.

Once Jules Verne was released from the rocket, the upper-stage reignited its engine to make a controlled burn-up over the Pacific.

The advantages of de-orbiting in this way are clear, but the extra fuel requirements and complexity of re-ignitable engines adds cost to what is already a very expensive endeavour.

Aerobraking sails, on the other hand, are lightweight and extremely simple. Their operation could even be controlled by a pre-set timer, fixed to deploy a certain number of minutes after the end of a flight.

This means that even an upper-stage that is out of control can still be guaranteed to return to Earth in a timely fashion.

Santerre and Serf presented their latest research at the recent European Conference on Space Debris in Darmstadt, Germany.

The meeting closed with a statement from its organisers saying that effective measures to clean up space debris needed to be devised and implemented.

The upper-stage that launched Jules Verne took itself into a controlled dive

Last-minute Conficker survival guide/Worm

April 1 -- is D-Day for Conficker, as whatever nasty payload it's packing is currently set to activate. What happens come midnight is a mystery: Will it turn the millions of infected computers into spam-sending zombie robots? Or will it start capturing everything you type -- passwords, credit card numbers, etc. -- and send that information back to its masters?

No one knows, but we'll probably find out soon.

Or not. As Slate notes, Conficker is scheduled to go "live" on April 1, but whoever's controlling it could choose not to wreak havoc but instead do absolutely nothing, waiting for a time when there's less heat. They can do this because the way Conficker is designed is extremely clever: Rather than containing a list of specific, static instructions, Conficker reaches out to the web to receive updated marching orders via a huge list of websites it creates. Conficker.C -- the latest bad boy -- will start checking 50,000 different semi-randomly-generated sites a day looking for instructions, so there's no way to shut down all of them. If just one of those sites goes live with legitimate instructions, Conficker keeps on trucking.

Conficker's a nasty little worm that takes serious efforts to bypass your security defenses, but you aren't without some tools in your arsenal to protect yourself.

Your first step should be the tools you already have: Windows Update, to make sure your computer is fully patched, and your current antivirus software, to make sure anything that slips through the cracks is caught.

But if Conficker's already on your machine, it may bypass certain subsystems and updating Windows and your antivirus at this point may not work. If you are worried about anything being amiss -- try booting into Safe Mode, which Conficker prevents, to check -- you should run a specialized tool to get rid of Conficker.

Microsoft offers a web-based scanner (note that some users have reported it crashed their machines; I had no trouble with it), so you might try one of these downloadable options instead: Symantec's Conficker (aka Downadup) tool, Trend Micro's Cleanup Engine, or Malwarebytes. Conficker may prevent your machine from accessing any of these websites, so you may have to download these tools from a known non-infected computer if you need them. Follow the instructions given on each site to run them successfully. (Also note: None of these tools should harm your computer if you don't have Conficker.)

As a final safety note, all users -- whether they're worried about an infection or know for sure they're clean -- are also wise to make a full data backup today.

What won't work? Turning your PC off tonight and back on on April 2 will not protect you from the worm (sorry to the dozens of people who wrote me asking if this would do the trick). Temporarily disconnecting your computer from the web won't help if the malware is already on your machine -- it will simply activate once you connect again. Changing the date on your PC will likely have no helpful effect, either. And yes, Macs are immune this time out. Follow the above instructions to detect and remove the worm.

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A computer worm is a self-replicating computer program. It uses a network to send copies of itself to other nodes (computers on the network) and it may do so without any user intervention. Unlike a virus, it does not need to attach itself to an existing program. Worms almost always cause at least some harm to the network, if only by consuming bandwidth, whereas viruses almost always corrupt or modify files on a targeted computer.

Backdoors can be exploited by other malware, including worms. Examples include Doomjuice, which spreads better using the backdoor opened by Mydoom, and at least one instance of malware taking advantage of the rootkit and backdoor installed by the Sony/BMG DRM software utilized by millions of music CDs prior to late 2005.

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Reference :Yahoo!

Wikipedia

Microwaves 'improve fog landings'

Tom Symonds explains how the system works

By Daniel Emery
Technology reporter, BBC News

Passengers flying into Heathrow in fog or poor visibility will be guided in using a new microwave-based system.

The existing Instrument Landing System (ILS) is susceptible to interference, meaning aircraft had to be spaced further apart on their final approach.

The new Microwave Landing System (MLS) is less prone to interference, meaning aircraft can now land at a faster rate.

Initially, the system will be used by British Airways' Airbus 320s, although other airlines are expected to follow.

On a clear day, about 44 planes an hour land at Heathrow.

However, if the visibility drops and aircraft have to use the ILS system to land on full autopilot, that figure falls to 24 aircraft an hour.

This is because the radio transmitter at the end of the runway needs good line of sight to the approaching aircraft, but because it is at the far end of the runway, planes have to land and taxi clear before a full signal is restored.

BA's Airbus will be the first aircraft equipped with MIS

Not only does Heathrow's capacity fall significantly, but because long-haul international flights take priority, domestic and short haul passengers either find themselves circling London in a holding pattern, diverted to another airport, or find their flight has been cancelled altogether.

The new MLS allows an extra six aircraft an hour to land, meaning that while fog will still cause disruption, its effects will be less prominent.

In 2006, four days of heavy fog at Christmas stranded thousands of passengers and resulted in hundreds of cancelled flights to and from Heathrow.

It is thought the cumulative costs of the Christmas fog ran into the tens of millions.

Speaking to the BBC, British Airways' flight operations manager, Captain Tim Price, said that the financial argument in favour of MLS stacks up.

"If we had had this system in December 2006, then the system would have paid for itself within four days," he said.

'Great reputation'

Designed in the 1940s, the ILS system uses two radio signals - one transmitted at the far end of the runway and the other at the side on two separate frequencies - to guide the aircraft down on an approach making a horizontal angle of three degrees with the runway.

MLS, on the other hand, uses a single frequency in a band far removed from that of the ILS system to broadcast the azimuth and elevation (horizontal and vertical angle) data to the aircraft.

The National Air Traffic Service (NATS) says that the new MLS system will guide planes down along the same flight path, so as to not interfere with ILS landings.

Heathrow can be prone to fog, especially early in the morning

As such, it will not be implementing so-called curved approaches. Rather than the three degree approach in line with the runway, aircraft could - in theory - approach the airport from up to 40-degrees off the end of the runway, lining up with it a mile or so before touchdown.

Even without this feature in the short term, the space between aircraft will be reduced, resulting in more planes landing per hour.

For pilots, the display for the MLS and the ILS is identical, meaning that there is very little training to get air crew up to speed.

Professor Graham Braithwaite, director of the Safety and Accident Investigation Centre at Cranfield University, said that anything that reduced delays at Heathrow had to be welcome.

"This is a precision-approach tool and is something that the International Air Aviation Organisation endorses.

"The challenge for air traffic controllers (ATC), now that distance between planes is reduced, is ensuring you get a good mix of aircraft. The last thing you want is a Fokker 50 flying into the turbulence generated by a 747 flying ahead of it.

"Some aircraft are worse for feeling the effects [of turbulence] than others, but Heathrow ATC would know this better than anyone else and they have a great reputation."

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Note:

Microwaves are electromagnetic waves with wavelengths ranging from 1 mm to 1 m, or frequencies between 0.3 GHz and 300 GHz.

Apparatus and techniques may be described qualitatively as "microwave" when the wavelengths of signals are roughly the same as the dimensions of the equipment, so that lumped-element circuit theory is inaccurate. As a consequence, practical microwave technique tends to move away from the discrete resistors, capacitors, and inductors used with lower frequency radio waves. Instead, distributed circuit elements and transmission-line theory are more useful methods for design and analysis. Open-wire and coaxial transmission lines give way to waveguides, and lumped-element tuned circuits are replaced by cavity resonators or resonant lines. Effects of reflection, polarization, scattering, diffraction and atmospheric absorption usually associated with visible light are of practical significance in the study of microwave propagation. The same equations of electromagnetic theory apply at all frequencies.

While the name may suggest a micrometer wavelength, it is better understood as indicating wavelengths very much smaller than those used in radio broadcasting. The boundaries between far infrared light, terahertz radiation, microwaves, and ultra-high-frequency radio waves are fairly arbitrary and are used variously between different fields of study. The term microwave generally refers to "alternating current signals with frequencies between 0.3 GHz (3×10⁸ Hz) and 300 GHz (3×10¹¹ Hz)."^[1] Both IEC standard 60050 and IEEE standard 100 define "microwave" frequencies starting at 1 GHz (30 cm wavelength).

Electromagnetic waves longer (lower frequency) than microwaves are called "radio waves". Electromagnetic radiation with shorter wavelengths may be called "millimeter waves", terahertz radiation or even T-rays. Definitions differ for millimeter wave band, which the IEEE defines as 110 GHz to 300 GHz.

Electromagnetic spectrum with visible light highlighted

Microwave frequency bands

Letter Designation	Frequency range
L band	1 to 2 GHz
S band	2 to 4 GHz
C band	4 to 8 GHz
X band	8 to 12 GHz
Ku band	12 to 18 GHz
K band	18 to 26.5 GHz
Ka band	26.5 to 40 GHz
Q band	30 to 50 GHz
U band	40 to 60 GHz
V band	50 to 75 GHz
E band	60 to 90 GHz
W band	75 to 110 GHz
F band	90 to 140 GHz
D band	110 to 170 GHz

Reference: http://en.wikipedia.org/wiki/Microwave
http://news.bbc.co.uk/2/hi/technology/7961501.stm