Week of November 14, 2005

Space tractor

More than a few Hollywood adventures have featured asteroids smashing into the earth and wiping out cities or generating monstrous tsunamis. The notion of taking defensive action against an earth-bound asteroid is starting to gain traction in the real world.

Two NASA astronauts have proposed a gravitational tractor spacecraft that could tow an asteroid to a safe trajectory. Existing asteroid rescue plans call for spacecraft to nudge asteroids aside, but have practical challenges: it would be difficult for a spacecraft to maintain both position and contact with an asteroid because most asteroids rotate and have unstable surfaces.

The NASA plan sidesteps contact by using gravity as an invisible tow line. This requires positioning a spacecraft of sufficient mass close to the asteroid's surface and angling its thrusters to just miss the asteroid. The plan also calls for patience and foresight. Given a lead time of 20 years, a 20-ton spacecraft would require a year to tow a a 200 meter asteroid to a safe trajectory.

The European Space Agency (ESA) is preparing to test another alternative asteroid deflection plan. The plan, dubbed the Don Quijote project, involves smashing a spacecraft into an asteroid in order to deflect it. The plan calls for two spacecraft -- one to smash into the asteroid and the other to record what happens. The agency recently narrowed the choice of asteroids for the initial test to two.

NASA tracks near earth objects and assesses the risks they pose. The site uses the Torino scale to indicate the chance of impact and the degree of damage.

(Gravitational Tractor for Towing Asteroids, Nature, November 10, 2005)

Chemical hubs

In recent years researchers have been teasing out the properties of all manner of networks as wide-ranging as the Web, social connections among people, and relationships among chemicals in the biochemical processes that support life.

Scientists from Northwestern University using this network analysis technique to probe relationships among organic chemicals showed that the collective endeavor of creating new molecules over the last century and a half can be modeled as a network with a scale-free structure similar to the Web.

Rather than being a random process of discovery and creation, chemistry turns out to have a structure that makes it possible to make predictions about it.

On the Web, nodes are Web pages and the links between them are hyperlinks. In an organic chemicals network, nodes are molecules and the links between them are chemical reactions. A link to a molecule at the start of a reaction is an outbound link, and a link to a molecule that results from a reaction is an inbound link.

Scale-free networks have a few heavily-linked nodes and many nodes with few links. Using a database of nearly 6 million molecules, the researchers found two types of hub molecules: commonly used ingredients, which have many outbound links, and highly desirable substances, which have many inbound links.

The information could be used to predict the ease of synthesizing a given molecule, the types of molecules that are likely to be created and the economic value of a molecule.

(Architecture and Evolution of Organic Chemistry, Angewandte Chemie International Edition, November 11, 2005)

Time simplifies quantum crypto

The field of quantum cryptography, which promises potentially perfectly secure communications, has matured rapidly. Current research is aimed at increasing data rates and improving reliability.

Researchers from the University of Geneva in Switzerland have developed a quantum cryptography scheme that encodes data in the time of arrival of laser pulses rather than the polarization or phase of photons. This promises to simplify and improve the reliability of quantum cryptography equipment.

The recipient occasionally tests the phase of some of the pulses using traditional quantum cryptography protocols to determine wether an eavesdropper has observed any of the transmission. Using time of arrival for data transmission makes for a faster and more reliable quantum cryptography system, according to the researchers.

The work shows that the bottleneck for quantum cryptography is the performance of photons detectors. Once those are improved, quantum cryptography could be used at the full data rates of today's communications networks.

(Fast and Simple One-way Quantum Key Distribution, Applied Physics Letters, November 7, 2005)

Spreadsheet drives sensor net

Networks of tiny, inexpensive sensors scattered throughout an environment could make it easier to monitor environmental conditions, collect scientific data and track people and vehicles for military and law enforcement purposes. Managing these sensor networks and analyzing the data they collect, however, promises to be challenging.

Researchers at Microsoft Research are using spreadsheets to organize and manage data collected by sensor networks. The researchers' system is a modified version of the company's Excel spreadsheet that allows users to analyze data from a network of sensors and program the sensors without special software.

The system allows individual sensors to be mapped to cells within the spreadsheet. Cell values are data from the sensors or variables that can be changed to reprogram the sensors.

The researchers set up prototype sensor networks to monitor vehicles in a parking lot and to monitor environmental conditions within a building.

The software should make it easier for scientists and others to deploy sensor networks for practical applications.

(A Spreadsheet Approach to Programming and Managing Sensor Networks, Microsoft Research Technical Reports, October 2005)

Bits and pieces

A solid acid made from sugars or starches is an efficient, recyclable catalyst for turning vegetable oil into biodiesel fuel; a carbon nanotube-polystyrene foam makes effective, lightweight electromagnetic radiation shielding; carbon nanostructures with wheels roll across surfaces, making steerable nanocars.