NEOShield to assess Earth defence

NEOShield is a new international project that will assess the threat posed by Near Earth Objects (NEO) and look at the best possible solutions for dealing with a big asteroid or comet on a collision path with our planet.

The effort is being led from the German space agency's (DLR) Institute of Planetary Research in Berlin, and had its kick-off meeting this week.

It will draw on expertise from across Europe, Russia and the US.

It's a major EU-funded initiative that will pull together all the latest science, initiate a fair few laboratory experiments and new modelling work, and then try to come to some definitive positions.

Industrial partners, which include the German, British and French divisions of the big Astrium space company, will consider the engineering architecture required to deflect one of these bodies out of our path.

Should we kick it, try to tug it, or even blast it off its trajectory?

"We're going to collate all the scientific information with a view to mitigation," explains project leader Prof Alan Harris at DLR.

"What do you need to know about an asteroid in order to be able to change its course - to deflect it from a catastrophic course with the Earth?"

It's likely that NEOShield will, at the end of its three-and-a-half-year study period, propose to the politicians that they launch a mission to demonstrate the necessary technology.

The NEO threat may seem rather distant, but the geological and observational records tell us it is real.

The European Space Agency designed - but never launched - the Don Quijote mission

On average, an object about the size of car will enter the Earth's atmosphere once a year, producing a spectacular fireball in the sky.

About every 2,000 years or so, an object the size of a football field will impact the Earth, causing significant local damage.

And then, every few million years, a rock turns up that has a girth measured in kilometres. An impact from one of these will produce global effects.

The latest estimates indicate that we've probably found a little over 90% of the true monsters out there and none look like they'll hit us.

It is that second category that merits further investigation.

Data from Nasa's Wise telescope suggests there are likely to be about 19,500 NEOs in the 100-1,000m size range, and the vast majority of these have yet to be identified and tracked.

New telescopes are coming that will significantly improve detection success. In the meantime, the prudent course would be to develop a strategy for the inevitable.

The strongest mitigation candidates currently would appear to be:

Kinetic impactor: This mission might look like Nasa's Deep Impact mission of 2005, or the Don Quijote mission that Europe designed but never launched. It involves perhaps a shepherding spacecraft releasing an impactor to strike the big rock or comet. This gentle nudge, depending when and how it's done, could change the velocity of the rock ever so slightly to make it arrive "at the crossroads" sufficiently early or late to miss Earth.

"The amount of debris, or ejecta, produced in the impact would affect the momentum of the NEO," says Prof Harris.

"Of course, that will depend on what sort of asteroid it is - its physical characteristics. What's its surface like; how porous or dense it is? This is really something you would want to test with a demonstration mission."

Can a gravity tractor be relied upon to work for as long as its effort is needed?

"Gravity tractor": This involves positioning a spacecraft close to a target object and using long-lived ion thrusters to maintain the separation between the two. Because of gravitational attraction between the spacecraft and the NEO, it is possible to pull the asteroid or comet off its trajectory. "It's like using gravity as a tow-rope," says Prof Harris. "It's not straightforward of course. Can you be sure those thrusters will keep working for the time they're needed - a decade or more? Do you have confidence that the spacecraft can look after itself autonomously all that time? These are the sorts of technical problems we will look at."

In both scenarios, the effects are small, but if initiated years - even decades - in advance should prove effective enough.

What we've learnt about asteroids, however, is that they are not all the same. Different rocks are likely to need different approaches.

One method often discussed but about which there is great uncertainty is "blast deflection" - the idea that you would detonate a nuclear device close to, or on the surface of (even buried under the surface), an incoming rock.

The Russian members of the NEOShield consortium will take a close look at the option.

At present, I detect a lot of scepticism out there about this approach. Delivering the device to just the right place would prove very difficult, and the outcomes, depending on the composition and construction of the NEO, would be very hard to predict. But some better numbers than we have currently are required and TsNIIMash, the engineering arm of the Russian space agency (Roscosmos), will gather all the available data.

"What we want to do is take a comprehensive view, to try to draw everything we know together, with the right expertise so that this thing has momentum," commented Dr Ralph Cordey, from Astrium UK.

"We will look at the spectrum of techniques, trying to see which ones might be applicable in different cases. And then taking it to a level where we do some detailed design work on a possible mission to demonstrate one or more of these techniques."

And Prof Harris added: "At the end of this, we want to be able to say to the space agencies 'if you're interested in asteroid mitigation, this is what we think. We have six countries represented in our consortium and we're all agreed this is the way to go'.

"The politicians would then have everything on a plate. All they have to do is decide whether or not to execute the mission."