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Embargoed for 12pm, Thursday 4th October 2007

Mirror “bees” swarm to save Earth from asteroid impacts

The most effective way of saving the Earth from a catastrophic collision with a Near Earth Object (NEO) could be to focus a beam of sunlight onto the surface of an asteroid using a swarm of mirrors.

Researchers at the University of Glasgow have compared nine methods of asteroid deflection for a variety of NEO’s. The results of the studies were unveiled today at the University of Manchester’s Jodrell Bank Observatory, as part of celebrations to mark the 50th anniversary of the launch of Sputnik.

The team found that a technique using mirrors, known as a solar concentrator, has clear advantages and that the technology could be implemented within two decades. Rapid developments in swarm intelligence mean that a formation of mirrored satellites would be capable of concentrating sunlight to heat a spot on the surface of the asteroid to the rock’s melting point. Evaporated material would create a rocket thrust, nudging the asteroid into a new orbital path.

Dr Massimiliano Vasile said: “Asteroid impacts are a real threat. The Tunguska explosion in 1908 devastated an area bigger than Greater London. With only 10 spacecraft flying in formation, each with a 20 metre mirror, we could deflect a similar-sized asteroid into a safe orbit in about six months”

In a series of ongoing feasibility studies for the solar concentrator mirror technique, the Glasgow team have looked at configurations ranging from a single flat mirror to parabolic reflectors accompanied by a focusing lens and directional mirror mounted on upwards of a thousand small satellites. Although single or flat mirror configurations proved unworkable, the team found that the orbit of an asteroid 150 metres across could be sufficiently modified by a swarm of 100 mirrors in few days. For an asteroid on the scale that caused the Chicxulub crater, which is believed to have wiped out the dinosaurs, a 5000-strong fleet of spacecraft would need to focus a beam on the surface for three or more years.

Dr Vasile said: “As many other deviation techniques, the solar concentrator one works best when the deviating action is applied well in advance before the impact. However, our studies show that this technology is genuinely feasible and, unlike methods where an explosion or impactor is used to divert the asteroid, there is no further risk from fragments. We have estimated, for the ten satellite formation, a launch mass for each individual spacecraft of around 500 kilograms. This is a smaller and lighter satellite constellation than, say, the Galileo positioning system, so is well within our launch capabilities.”

The melting point of rocks in a typical NEO is around 2100 degrees Celsius. To achieve these temperatures, the beam must be focused on an area of the asteroid 0.5 – 1.5 metres, which requires careful orbital control. The team at Glasgow have carried out extensive modelling of the gravitational environment around the asteroid, taking into account perturbations from asteroid, radiation pressure and the gravitational pull of the Sun. They found that to ensure a stable orbit, a solar concentrator must be placed outside the asteroid’s gravitational sphere of influence which is typically less than 1 km.

The initial comparison of deflection techniques included a nuclear explosion, an electric propulsion system fixed to the asteroid, a mass-driver system where material is excavated and catapulted away from the asteroid, a kinetic impactor which would knock the asteroid out of its orbit, as well as the solar concentrators. The study investigated in each case the mass of spacecraft needed, the warning time required, the orbital deflection achieved and the current readiness of technology. For each strategy, simulations were run with six different target asteroids ranging in size from 0.2 to 1.2 km across with a warning time ranging from 2.5-13 years. For every factor, the dominance of each method over the other techniques was assessed. The solar concentrator and nuclear impactor clearly dominated the other methods. However, a possible fragmentation of the asteroid due to a too aggressive action, as well as issues relating to the launch of nuclear weapons into space, made the solar concentrator the preferred option.

Further studies will investigate the dynamics, navigation and control of the mirror-bee formation. In particular sophisticated mathematical techniques will be used to evolve the swarm behaviour making it capable of adapting to any change or failure during the deflection operations. The control of each mirror-bee will take into account the dynamic effects due to the solar pressure and the overall system design of the spacecraft.

IMAGES

Artist's impression of the mirror bee swarm deflecting an asteroid (JPEG)

Artist's impression of mirror bee swarm deflecting an asteroid (PNG file)

Artist's impression of single mirror bee deflecting an asteroid

NOTES FOR EDITORS

Near Earth Objects
Near Earth Objects (NEOs) are asteroids and comets whose orbits bring them into the Earth’s neighbourhood. Pieces of rock and ice impact the Earth every day, however, most of these are so small that they go largely unnoticed. On average, every 26-30 million years, a 10-km sized asteroid (the size of impactor believed to have wiped out the dinosaurs) strikes the Earth, while every 100 years there is a Tunguska class (100m in size) asteroid impact. Each of these impacts permanently alters the characteristics of the planet to varying degrees.
For further information see: http://www.nearearthobjects.co.uk/

The Space Advanced Research Team (Space Art), University of Glasgow
SpaceART in the Aerospace Engineering Department of the University of Glasgow is a group of young scientists actively working on many research topics in the space field.

The team is presently made up of two senior staff members, one research fellow and nine PhD students covering the following general areas: spacecraft formation flying, Near Earth Objects (NEOs), global optimisation for space applications, concurrent engineering, multidisciplinary design, attitude control, autonomous space robotics, preliminary mission design, low-thrust trajectories and moon exploration. The team is constantly involved in several studies, mainly supported by the European Space Agency (ESA), ranging from the automated design and planning of space trajectories to the development of control systems for space webs (in close collaboration with the Mechanical Department). In the past two years a particular effort has been put into the analysis and development of techniques to intercept and deviate potentially dangerous asteroids.

The team gives technical support to ESA for missions like Bepicolombo and to many UK companies like QinetiQ for missions such as Don Quijote. More recently, SpaceART has been chosen as prime team for the analysis and design of transfers to the Moon for the ESA mission ESMO (European Student Moon Orbiter).
For further details, see: http://www.aero.gla.ac.uk/Research/SpaceArt/index.html

CONTACT

Dr Massimiliano Vasile
Space Advanced Research Team
Department of Aerospace Engineering
University of Glasgow
Tel: 0141 330 6465
Fax: 0141 330 5560
E-mail: m.vasile@aero.gla.ac.uk
Web : http://www.aero.gla.ac.uk/Research/SpaceArt

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